Exam 2

Migration: Difference b/w migration and dispersal

*Migration* - mass directional movement of a species from one location to another -Ex: butterfly migrations, locust swarms, African herbivore herds moving across the savanna, migratory birds and whales, the trek of lemmings across the tundra *Dispersal* - movement of individuals from one another (especially from siblings or parents)

The Demographic Transition: 3 Stages

*Stage 1*: high birth and death rates *Stage 2*: lowered death rates but birth rates stay high *Stage 3*: low birth and death rates ^this occurs in developing nations as they become industrialized and have better living conditions

Population Growth: Exponential Growth Populations increase and decrease in size over time

*linear* or *arithmetic growth* -one potential population growth pattern -the #s of individuals increases at a linear rate over time: 1, 2, 3, 4, 5, and so on -however, linear growth often is not observed *exponential growth* -during the early phase of the successful colonization of a new optimal habitat (ex: imagine that a group of rats that 'jumped ship' onto a lush tropical island, w/ lots of food and no natural predators), the population can initially grow at a rapid pace -this nonlinear type of population growth, when the population is increasing rapidly and exhibiting a J-shaped curve, is called *exponential growth* (our hypothetical rat population [in the absence of competitors, disease, weather, predators and in the presence of lots of food] may increase in #s in an exponential fashion) -a population that is growing exponentially adds a # of individuals over time in proportion to the population size N (ex: if a population grows at 200% per unit time, a population of size N = 10 individuals would add 20 organisms, but if the population size was 10,000, then 20,000 additional individuals would be added w/ 200% growth) -*Charles Darwin*, a famous biologist of the 19th century, appreciated this type of population growth -he stated if one started with 1 pair of elephants, and the elephant population increased at its maximal rate, then over the course of 750 years, 19 million elephants would be born as descendants from that original pair -exponential growth can occur in all living organisms, including those with long life spans and low birth rates (elephants live to 100 and have only about 6 offspring during their life, but even elephant populations can grow exponentially) (ex: population growth in a protozoan that splits by binary fission -each protozoan divides into 2 daughter cells after 1 hour -if we were to plot population #s [on the y-axis - dependent variable] as a function of time [x-axis - independent variable], we would see a J-shaped or exponential curve)

Population Regulation: Allee Effects

-*Allee Effects* -- a decline in birth rates or survival at low population size (named after W. C. [Warder Clyde] Allee, American) -low population sizes may mean that the population is so sparse that individuals do not find each other for mating and for reasons that promote survival, such as foraging or predator defense -in the 3 scenarios depicted in Figure 11, if death rates (situation 1), or birth rates (situation 2), or both birth and death rates (situation 3) are affected by small N, then the population will decline to extinction if N is less than A

Metapopulations: the Spatial Structure of a Population Levins model

-*Richard Levins* developed a deterministic model where there are extinctions of local populations, but the entire metapopulation does not go extinct bc of the migration of individuals from one patch to another -the metapopulation lives in multiple patches - its subpopulations are linked by dispersal, w/ extinction and recolonization continuously occurring over time -the Levins' model focuses on patch occupancy as dictated by the balance b/w local extinctions and recolonization -Levins' model is analogous to individuals that interact and form a population: a metapopulation is a population of interacting subpopulations -Levins' model assumes that the local subpopulations were either at K or extinct, and thus only extinction and colonization via dispersal occur -in Levins' model, the spatial arrangement of the patches also wasn't important, in that any individual from a patch can be equally likely to migrate to another patch -the Levins model doesn't care about the size of the population, but about its persistence -the model doesn't care about the fate of an individual subpopulation, but about the fraction of all patches that are occupied 1) First consider the *probability of local extinction* (e) -- the probability that a subpopulation goes extinct -e = 0 means that the persistence is certain -e = 1 means the probability of extinction is certain for that particular time scale -e = 0.3 -- then the subpopulation has a probability of 30% of going extinct in a year, and a 70% chance (1 - e = 0.7) of persisting -the chances that the population could persist for 2 years is (1 - e )(1 - e ) = (0.7)^2 =0.49 = 49%, or roughly a 50:50 chance it will persist for 2 years -the probability for any *one subpopulation (Pn)* to persist after n years is thus shown as, Pn = (1-e)^n 2) Now assume that we have two subpopulations, each with e = 0.7 -assume that the subpopulations are independent of each other, and that they have the same probability of extinction (e) -the probability of *regional persistence (Px)* is the probability that at least 1 of the subpopulations (and thus the species) persists after 1 year ^shown as, Px = 1 - (e)^x -x is the # of subpopulations -in ex above, Px = 0.51 -so even though each population has a 70% probability of going extinct, the metapopulation has a 51% chance of persisting -if there were 3 subpopulations, then the probability of at least 1 subpopulation persisting is 65.7% (0.657 = 1 - [0.7]^3) 3) Let's now build the basic Levins model -assume a set of homogeneous patches exist, and each patch can hold 1 subpopulation -*the fraction Po is the fraction of those patches that are occupied* (if Po = 1, all patches are occupied, if Po = 0, no patches are occupied and the entire metapopulation is extinct) -this fraction Po can increase w/ time (more patches filled) only if there is an *immigration* (= *colonization*) rate, C -the fraction Po also can decrease with time if there is an *extinction rate*, E dPo/dt = C - E -the fraction Po will reach equilibrium when C = E, and the metapopulation will persist if C > E -the *immigration rate* depends on two factors: a) the *probability of local immigration* (m) -if the patches are linked by migration, then immigration rate C depends upon the fraction Po of sites already colonized, so C depends on Po and m in this model b) the # of sites not currently occupied, or (1- Po) C = m Po (1-Po) -the *extinction rate* is equal to the probability of local extinction e times the fraction of sites occupied (Po): E = (e)(Po) -substituting for C and E back into the equation above gives the basic model shown, dPo/dt = mPo(1-Po) - ePo -when dPo/dt > or = 0, then the metapopulation population persists w/ Po sites occupied at any one time -the fraction of patches occupied is always > 1 -the # of occupied patches at *equilibrium* (Peq, when Po does not change) is Peq = 1 - (e/m), and e can't be > m

Habitat Selection: Habitats should be selected in order to maximize fitness

-*Steve Fretwell* (1972) developed a simple model on habitat selection, based on the *ideal free distribution* (IFD) -this model has been confirmed and used as the null hypothesis in many studies, but there are studies that either don't support the IFD, or suggest additional constraints or modifications 1) If the quality of the various habitats (patches) in an environment varies, individuals should distribute themselves in such a way as to maximize their own fitness -the suitability of a patch depends on both the intrinsic value of the patch (amount and quality of food, shelter, and nest sites) but also on the density of the conspecifics -a patch that is perfectly fine in terms of resources, but is already occupied, may be of less value than a lesser quality, unoccupied (or less occupied) patch 2) *There are several important assumptions to the basic IFD model*: a) the individuals are 'ideal', in that they have complete knowledge of the quality of the patches that could be inhabited, including knowledge of how many other organisms using the patch in the same way are present b) individuals are 'free', in that they have complete freedom of choice c) all individuals occupying a patch have equal fitness (they share the patch evenly and equally) d) each individual selects a patch in such as way as to maximize its fitness e) there is no territoriality or aggression amongst the individuals f) patch quality declines with increasing density 3) If the assumptions listed above are met, then: a) the # of individuals per patch is proportional to the fraction of resources that are in the patch b) the intake of resources per individual is equal across all patches 4) In situations conforming to the ideal-free distribution (IFD) model, animals can freely move among habitats and sort themselves in proportion to resource availability -however, once a critical density is attained in preferred habitats, individual fitness is depressed (Fretwell and Lucas 1970) -at that point, individuals may colonize less preferred habitats where competition is less -in figure 4, at density x, some animals will select habitat B because habitat A is crowded and the fitness has dropped to the point where it makes sense to select habitat B -at density y, individuals will start to colonize habitat C -even though C is a poorer quality patch, the animals all have similar fitness at density y to select C (ex: perhaps the overall amount or quality of food is less per unit area of C, but the animal may possess a larger area to compensate) -the end result is that fitness is equal over a range of habitats, resources, or other conditions for all individuals -a # of alternative models predict that subordinate individuals are constrained in their choice of area by dominant individuals -in these models, territoriality or dominance would occur and fitness would vary among patches

Demography: Survivorship

-*Survivorship* l(x) -- probability of surviving to age x -3 *survivorship curves* can be described -*Raymond Pearl* (American, 1928) first described these 3 curves 1) *Type I* -- survivorship (indicative of many mammals) most mortality occurs late in life -mammals invest a lot of energy into fewer individual offspring, offspring survival increases 2) *Type II* -- mortality - mortality rates are *constant* with age (many birds, a few mammals) -w/ a log transformation, the type II survivorship curve becomes a straight line 3) *Type III* -- most mortality occurs w/ juveniles (as in most invertebrates) where out of 100s of eggs only 1 or 2 survive to adulthood -many plants and invertebrate animals fall into this category -the strategy is to invest little energy into each offspring, and make more offspring

Human Populations: Birth Rates and Death Rates Age-dependency ratio

-*age-dependency ratio* -- ratio of dependent age people (0-15 years and over 65 years) to working age people (15-65 years) 1) In 1976, for the USA, 52.5 million people were under 15 and 22.9 million people above 65 for a total of 75.4 million dependent people -there were 139.7 million working age people -thus the ratio was 0.54 (54 dependents for every 100 working age people) -however, this ratio will approach 1:1 in your lifetime -in 1980 there were three workers paying into Social Security for every one of the 25 million retirees -by 2030 two workers will be supporting one of the estimated 60 million retirees -this shows the big disadvantage of populations that have unstable age distributions -the Boomers are beginning to retire, w/in a few decades, there will be fewer workers present to support them 2) *One estimate is that the 7.3 billion people alive today represents more than 10% of all of the humans that have ever lived on the planet* -the current human population growth rate assures us of expanding our population size out to perhaps *10 to 20 billion people* -where these people are located is important as well -*developed nations represent about 20% of the world's population, yet they use 80% or more of many of the Earth's resources* -imagine what the effect would be if all people lived as Americans do -clearly, the max population size depends also on the quality of life attained by all people on Earth, not just for Americans

Population Growth: Exponential Growth Biotic Potential

-*biotic potential* - power of a population to increase in #s under optimal conditions -ecologists also call the biotic potential the *intrinsic rate of increase*, which occurs when the population has a stable age distribution (a stable age distribution means that the relative proportions of children, young adults, adults, and older adults stays constant through time) and the population is in an optimal habitat -*the maximum r (r[max] or r[m]) is the biotic potential for a species* -the r(max) for humans is about 0.0003 additional offspring per person per day (3 x 10^-4) -it looks like a small #, however, it is a big #! -it means that if all of the progeny of one couple live and reproduce, the descendants would weigh as much as the earth in less than 500 years! -r(m) of other species: rats r(m) = 0.015 insects r(m) ranges from 0.001 to 0.1 ciliates r(m) = 1.0 bacteria r(m) = ~60.

Population Regulation: Density Independence

-*density Independence* -- these factors are usually considered *abiotic factors* (nonliving forces including weather, fire, rainfall, floods and drought) -the factor's effect doesn't depend on population size N (ex: a fire in the woods doesn't matter if 10 or 10,000 deer are present, the fire kills 90% of them anyway) -thus density-independent factors alter birth and death rates w/out regard to population size -density-independent factors may influence the exponential growth rate of a population, but they don't regulate its size

Population Regulation: Density Dependence

-*density dependence* -- *biotic factors* (factors exerted by living organisms, such as competition, predation, parasitism, aggression, disease, food limitations, and migrations) are very important factors thought to work more in a density-dependent fashion -if population growth rates are affected by population size, either by affecting birth rates or death rates, then the population is regulated by density-dependent forces -density-dependent factors are thought to stabilize population size NOTES: Examine the five possibilities shown in Figure 10 (situations 1 through 5). In the first three cases, either birth rates, death rates, or both, are acting in a density-dependent fashion. The b and d lines cross, indicating that there is some equilibrium population size (at K) where the population stabilizes. However, in situations 4 and 5, the b and d lines do not cross, suggesting that the population increases exponentially in a J shaped curve (situation 4) or declines exponentially in a backwards J shaped curve (situation 5).

Dispersion and Ranges: Density

-*density* - # of individuals of a species per unit area or volume -the # of individuals of a species found per unit area is important bc it affects the reproductive characteristics of that population and it affects how we protect that species -if the population is sparsely distributed, individuals may only infrequently meet and produce offspring

Estimation of Density: Two methods

-*density* of species - # of organisms per unit area or volume Densities or population sizes can be estimated in 2 ways: 1) Total counts or absolute counts or *census* (direct count) -a census is often impractical to do in many populations 2) *Sampling* -the ecologist takes samples and produce a generalization about the population size from the samples -there are 2 main types of sampling techniques: *mark recapture* (mobile animals) and *quadrat sampling* (immobile animals and plants)

Desertification and Salinization: Desertification

-*desertification* occurs due to bad farming practices -poor plowing practices (allows for wind or water runoff to carry topsoil away), overgrazing (the loss of plants and their roots, along heavy animals compacting the soil structure), poor forestry practices (deforestation for fuel and building materials), or growing inappropriate crops on the land causes the land to become desert-like -the land is denuded, and the soils are degraded, so much so that a 'desert' is produced -this cycle of desert-like conditions maintains itself and causes a permanent change in the soils and biota of a region -the land essentially becomes desert-like, and crops cannot be easily grown

Dispersal: Dispersal

-*dispersal* - the movement or transport of organisms across space -dispersal can be passive (the organism is carried by the medium - air or water), or active (the organism crawls, walks flies or swims into other habitats) -the simplest reason a plant or animal is not at a given site (that is suitable for the species to live) may be because they simply have not dispersed to it yet from some other site -dispersal is important bc the movement of individuals also represent movement of genes, and the change in the genes affects the genetic structure of the populations

Dispersion and Ranges: Dispersion

-*dispersion* - the spatial distribution in which the individuals are spaced out in the habitat 3 types of dispersion patterns: 1. *random dispersion* -organisms are randomly scattered in space -this pattern is seen often in absence of territoriality or the lack of an important site that could attract animals -this pattern is relatively rare in nature (ex: a watering hole) 2. *uniform dispersion* (or *spaced dispersion*) -somewhat rare, seen in territorial animals that set up individual territories (ex: seagulls and seagull nests) -in addition, uniform dispersions are typically seen in habitats altered by or created by humans (ex: apple orchards) -sometimes competition plays a role in uniform dispersion (ex: in the southwest US, creosote bushes are spaced uniformly, due to water competition) 3. *clumped dispersion* -pattern usually seen in nature -social animals form breeding groups or herds -animals also tend to clump around sites of water, food, nest sites -clumping often is an adaptation to a stressful factor of the environment (ex: many animals will huddle in response to cold, or clump in response to the presence of predators) -clumping occurs bc young tend to stay with parents -in plants w/ vegetative reproduction, many shoots come from one root or rhizome, but above ground, the plant may appear as many different plants that are highly clumped -there is a predation cost to clumped dispersions -often, if a predator discovers and consumes one prey item, and it then inspects the area where it last found prey, clumped prey are thus at high risk, particularly if they have no group defense tactics, or the prey are totally defenseless eggs or young -all 3 types of dispersion may change over time -in addition, the dispersion pattern changes w/ a change in *spatial scale* bc of mating patterns (clumping occurs during mating season, males w/ females, or young w/ parents), or bc of seasonal changes in the habitat (ex: individuals may be in small groups [clumped] at the local scale, but the groups in turn may be randomly distributed over a larger geographic scale) -*territoriality*... territorial behavior involves costs (ex: territorial animals announce their territories and defend them against intrusion) -many animals are not territorial -benefits include attracting females and thus higher fitness -territoriality may also be advantageous if one is protecting a valuable foraging area from others -however, if prey items don't stay in place and unpredictably move around, then territorial behavior is not an advantage -instead of territories common in many birds (who can quickly survey their territories from above), large mammals generally have *home ranges* in which they roam but not defend, in part bc a very large territory is indefensible -*home range* - area in which an animal lives and generally spends most of its time moving through, the area is generally is too large to defend against others -the home ranges of different individuals thus may actually overlap to some extent, although the animals that use the same space may not necessarily be present at one location at the same time -a *territory* generally is a smaller, defended area in which the animal lives, forages, and reproduces -the animal (or mated pair, or group) actively defends the territory against intrusion by conspecifics and sometimes other organisms that may be competitors or potential predators of their eggs or young

Dispersion and Ranges: Geographic range

-*geographic range* of a species - the total observed geographical area in which the species currently exists -individuals may be wide ranging or sessile, spending their entire lives at one spot -populations come in a variety of sizes -a species' distribution is often described by presence/absence of the appropriate habitat -the potential range for a species may not be known until the organism gets there (ex: zebra mussels colonizing the USA)

Human Populations: Birth Rates and Death Rates Life expectancy and life span

-*life expectancy* is the estimated # of years that a person of a given age can expect to live -*life span* is the max possible age an individual could reach -life span is probably controlled by heredity: for humans, it is considered by many (but not all) experts to be around 120 years (however, the vast majority of people don't live this long) -at birth, the average life expectancy varies by sex, age, location, nationality, stress, diet, alcohol, smoking and drug abuse, exposure to pollution, and other factors -in Roman times, once a person reached age 75, they had a better chance to reach 90 than does a person now living in the USA!

Life Tables: Definition

-*life table* -- incorporates both age specific survival and fecundity rates to predict population growth -a life table can be made in 2 different ways

Metapopulations: the Spatial Structure of a Population Metapopulations and subpopulations

-*metapopulations* occur when populations are divided into discrete subpopulations with partially independent local population dynamics -each subpopulation is found in a more or less suitable homogeneous habitat called a *patch* -some patches are occupied and others are not -immigration and emigration (into and out of) subpopulations, colonization of new patches and extinction of small subpopulations are important for understanding metapopulations -most populations are actually made up of several *subpopulations* (= *local populations* = *demes*) -a subpopulation consists of individuals in one patch that have a high potential to interbreed amongst themselves -the term *metapopulation* is used to describe a series of local populations (which have a high probability of local extinction) that are linked by dispersal -migrating individuals dispersing to other patches reestablish extinct demes and rescues declining populations

Population Growth: Exponential Growth Natality and Mortality

-*natality* = birth rate -the birth rate is defined as the # of new individuals produced per unit time, per individual alive in the population -the *maximum birth rate* is the largest # of individuals that could be produced per unit time under ideal conditions, when there are no limiting factors ^this maximum birth rate is constant for a species and is determined by physiological factors, such as # of eggs produced per female per unit time, the proportion of females in the species, an optimum amount of food is present, environmental conditions are optimal, and so on -the *actual birth rate* (b) is almost always less than the maximum -*mortality* = death rate -the death rate is defined as the # of individuals dying per unit time, per individual in the population -there is a theoretical *minimum death rate*, somewhat analogous to maximum birth rate, where very few deaths occur under ideal conditions, when old age is the only cause of death -the *actual death rate* (d) is higher than the minimum death rate in most cases r = b - d + i - e ^the *reproductive rate per individual*, or *growth rate of population* -r = 0, no growth (b = d) -r < 0, negative growth (d > b) -r > 0, positive growth (b > d) -b = # of births / time interval per individual -d = # of deaths / time interval per individual -the rate of increase in #s varies in direct proportion with N -the complete equation for r also includes population *immigration rates* (i) and population *emigration rates* (outmigration, e) as well -if i = e, then the migration rates cancel each other out Bacteria: -under optimal conditions, bacteria can divide about every 30 minutes -a single bacterium could create a colony of 1.4 x 10^14 bacteria [140 quadrillion] after 24 hours! -this is why health experts tell you to put away any food that can spoil as soon as possible in the refrigerator, to allow frozen meats to thaw in the refrigerator, to cook your food thoroughly, and to wash and clean cutting boards and other utensils with soap and hot water -these precautions slow down bacterial growth and makes it less likely for you to get sick from eating food containing large #s of bacteria

Dispersal: Neighborhood size

-*neighborhood size* of a population - the # of conspecifics that an organism (primarily referring to animals) could meet throughout its life and with whom the individual potentially can mate -it is the # of conspecifics that live in a circle whose radius is twice the potential distance an individual could travel over its lifespan (a radius = 2St) -the value St is the dispersal distance of the average individual over its life span (Why is the neighborhood size equal to a circle of radius 2St? Two individuals meet at the edge of their maximum ranges) -once you have the dispersal distance and the species density (# of individuals per unit area), you can calculate the neighborhood size (ex: -dispersal distance is 100 meters -there are 0.002 starlings / m^2 -then there are pi r^2 = 3.14 * 200m^2 * 0.002 starlings/m^2 = 251.3 starlings (recall that the area of a circle = pi r^2)

Ways to increase the food supply: Grow more crops locally and reduce the energy costs associated with transporting food

-*note that the # of miles those meats and vegetables you have on tonight's dinner table have traveled, on average, is 1300 miles, according to the USDA* -in a year, 4.25 million trucks travel 50 million miles and burn $6 billion in fuel, and add 4 million tons of pollutants to our air, and cause $100s of millions of dollars damage to our roads (a fully loaded truck, weighing 40 tons, causes much more damage than a single passenger car) -farmers generally make less money on food that is in the packages as those who package the food

Human Populations: Birth Rates and Death Rates Replacement-level fertility rate (RLFR)

-*replacement-level fertility rate (RLFR)* -- the average # of children each couple must have to replace themselves -*world population size can level off only when the average # of children of all women on the planet have (during their reproductive years of age 15 to 44) stays at or below a replacement level (RLFR) of about 2.1 children/woman for a considerable length of time* -Why is the RLFR not equal to 2.0 (analogous to twice the net replacement rate, if males are included)? -there are several assumptions to this metric -not all people survive to adulthood, and not all people have children -in addition, it assumes a 1:1 sex-ratio exists (1:1 male:female) -it also assumes that the actual population size of a given population in question is known - many population sizes are not accurately known

Desertification and Salinization: Salinization

-*salinization* of cropland is a real problem in California and elsewhere -salinization occurs when long-term use of irrigating the land w/ water increases the amounts of salts in the soils (this happens bc water evaporates, leaving salty deposits behind) -salty soils have salty water, which may impede the ability of the plant to take up water by *osmosis* (the diffusion of water across cell membranes) -therefore, the plants wilt in salty soils, and the fields have to be abandoned or cleaned at great expense -desertification and salinization prevention depends on monitoring the aquifers and soils for symptoms of desertification

Population Regulation: Lifespan and Factors

-*the length of the organism's life span (life cycle) may account for the importance of either density dependent or density independent factors* -if the organism's life span is short (< 1 year), then the annual change in weather may be quite important -if the life span is longer (> several years), the organism lives through the seasons, and other factors (such as predation and competition) may be important

Life Tables: The net replacement rate, R(0)

-R(0) = the average # of female offspring produced by each female of the population R(0) = sum(l(x)m(x)) -R(0) can be considered an estimate of population growth: ^if Ro > 1, then the population increases ^if Ro = 1, then the population remains constant or stable ^if Ro < 1, the population declines -if survivorship and fecundities stay the same, the population's future can roughly be predicted by R(0) -over the long run, stable populations have a mean R(0) equal to 1

Demographic Transition: Postindustrial Stage

-a fourth stage in the demographic transition, the *Postindustrial stage*, is sometimes described in some texts -this is where the birth rates decline further, and the population declines towards a more manageable size, and a shift from unsustainable to sustainable economic development occurs -only a few countries in western Europe have entered stage 4

population

-a group of interbreeding individuals of one species that live in a defined area -may be naturally described by geographical area, or the area may be arbitrarily defined by the investigator

Pesticides (biocides): Types

-a pesticide is any chemical manufactured to kill organisms considered undesirable -they include *herbicides* (plants), *rodenticides* (rodents), *molluscicides* (snails and clams), *insecticides* (insects), *fungicides* (fungi), *nematocides* (roundworms) -*herbicides are the most used type of pesticide, followed by insecticides* -billions of pounds of pesticides are applied to our fields and lawns annually -although only few people are known to die each year from accidental poisonings from a large dose of pesticide, perhaps several thousand additional people (particularly farm workers) die of cancers from pesticides (and perhaps one million people suffer injuries)

Metapopulations: the Spatial Structure of a Population Potential distribution

-a population's potential distribution is described by presence/absence of suitable habitats -the potential distribution for a species may not be known until the organism gets there (ex: zebra mussels colonizing the USA)

Food: The average-sized human adult requires ~2000-25000 calories/day

-adult males need about 2500 calories, while adult females need around 2000 calories (-the typical lunchtime meal of a large burger, large fries, and a milkshake is approximately 1500 calories -you would have to walk about 5 hours, or 15 miles, at a moderate pace, in order to burn that much off via exercise) 1) *Undernourishment* - the lack of sufficient calories in available food, so that the person is unable to work 2) *Malnourishment* - the lack of specific components of food, such as vitamins or minerals (needed for proper functioning of metabolic enzymes), or proteins and essential amino acids and fatty acids (enzymes, muscles, bone, cell membranes) -a person may be consuming sufficient calories, but is still suffering from malnourishment

Human Populations: Birth Rates and Death Rates Human population birth rates and death rates

-as long as the birth rate is greater than the death rate, the global human population will grow at a rate that depends on the difference between birth rate and death rate -if there is almost no migration of people into and out of a country, changes in population size are determined by the difference b/w the # born (birth rate) and the # that die (death rate) each year, or *net population change* -the net population change is calculated by subtracting the # of people leaving a population (through death and emigration) from the # entering the population (by birth and *immigration*) during some time period (usually a year) 1)The annual rate at which the size of a population changes is called the *annual rate of population change* (also called *rate of natural increase* or r) or percentage annual growth rate -it indicates how fast the population size of the world (or region) is growing or decreasing -when the crude death rate = the crude birth rate, the population size remains stable (assuming no migration) -this condition of stable population size is known as *zero population growth (ZPG)* -*net population change* = growth rate = (# of live births) - (# of deaths) -*crude birth rate, b* = # of live births per 100 people/year -*crude death rate, d* = # of deaths per 100 people/year -*annual rate of population change, r* = [crude birth rate - crude death rate] -the annual rate is thus a percentage, or the rate of change per 100 people 2) Note that the population growth rate is > 1% or more in the Lesser Developed Countries (LDCs: the listing is not a fixed one, but the LDCs are generally thought to be many of the countries in Asia, South America and Africa), and is < 1% in the *Mostly Developed Countries* (MDCs: the listings are not definitive, but the MDCs generally are thought to be the USA, Canada, Australia and New Zealand, the countries of western Europe and Scandinavia, Japan and Taiwan) -*the US is currently the third largest country, yet many LDCs will approach us in size in the next century* -China is the largest country, followed by India 3) Another way to indicate the rate at which a population is growing is called *doubling time*: the time it takes for a population to double in size -although doubling time gives a picture of *present* growth rates, it is only an estimate of *future* population size -this is bc doubling times assume a constant growth rate over decades, however, growth rates normally change over time D.T. = ln(2)/r -it is calculated by using the integral form of the exponential growth equation, where N(t) = 2 * N(0) 4) We can approximate doubling time in years by using the following *Rule of 70: Doubling time (in years) = 70/r* (Where the growth rate, r, is in %) 5) Doubling times can also be used to illustrate the dramatic increase in the rate of population growth on earth during the past 300,000 years -for 290,000 years the human population grew at an annual rate of only about 0.002%, doubling every 35,000 years -since the development of agriculture about 10,000 years ago, human population growth began to mushroom, especially during the past 100 years, and now grows at 1.7% a year w/ a doubling time of 41 years 6) The exponential growth equation states that the change in population size (it could be (+) or (-)) is equal to the intrinsic rate of increase r multiplied by the # of individuals alive (N) at time t

Human Populations: Birth Rates and Death Rates Iteroparity and semelparity

-big bang reproduction, *semelparous* -- where individuals have many small offspring at one time -this strategy occurs in r-selected individuals which we will cover later where individuals spend little investment in protecting and nourishing young -*iteroparous* -- where individuals have many small offspring repeatedly over time -this strategy is K-selection, where larger, longer lived animals usually have fewer, larger young with lots of parental care

Food: The differences between domesticated plants and their wild ancestors

-domesticated plants, like corn, are a far cry from their ancestral plants -over the last several thousand years, humans have domesticated many varieties of crop plants -differences b/w domesticated plants and their wild ancestors: 1) Domesticated plants are cultivated (protected from herbivores and competition with other plants) 2) Domesticated plants have been bred for a variety of selected traits through artificial selection experiments (increased yields, resistance to drought, thus they are more suitable for growing on given soils, etc.) 3) Domesticated plants may not be able to survive in the wild -some have limited tolerances to temperature or water extremes, and many can't reproduce w/out our help 4) Domesticated plants have little genetic diversity relative to wild plants, and thus may be more likely to be wiped out by a new pathogen than wild plants 5) Domesticated plants don't look like their ancestral wild plants -we have selected plants that increase the amount of energy they put into certain edible parts (like the seed heads, or roots) 6) Domesticated plants depend on lots of water and fertilizers for proper growth and maximum yields, compared to their wild ancestors

Ways to increase the food supply: Eating lower on the food chain

-eating lower on the food chain eliminates the need for large #s of rangelands and domestic animals for food (recall the laws of thermodynamics)

Ways to increase the food supply: Improved irrigation

-especially the use of drip irrigation (application of water slowly from tubes next to the soil) -less water is lost in this way from evaporation, but it is expensive and labor-intensive

Population Regulation: J. B. S. Haldane

-evolutionary biologist *J. B. S. Haldane* (John Burdon Sanderson, British-Indian, 1953) pointed out that there must be some regulating or limiting factors that explain how many individuals are present -imagine an insect that lives one year -the population size N(1) and the population size the next year as N(2) -N(2) = R(1)N(1) where R is the net rate of increase or decrease [can be larger or smaller than 1 -- this is the net replacement rate] -but N(3) = R(2)R(1)N(1), and so on, the product of R(n) has to be very close to 1 -if R(n) = 1.01 over 1000 years [a short time evolutionarily], the population would increase by 21,000 times -similarly, if R = 0.99, the N would be 0.000043 of its original # -bc no population grows w/out limit, and whole species only occasionally go extinct naturally, there must be some density-dependent effect that cause the densities as a whole to go up when the effect is small, and densities to go down when the effect is large

Agriculture and Food Supply:

-food is a problem for growing populations -*the World Health Organization estimates that over one billion people are underfed and undernourished because they are too poor to buy adequate food supplies* -another estimate is that 20-40 million children die each year from hunger and diseases worsened by malnutrition

Habitat Selection: Why are populations of one species found at one place and not at other places?

-for small organisms, if they are present in an unsuitable microhabitat (ex: pillbugs on a dry, hot sidewalk), they move around, stopping once they enter a more congenial habitat (ex: humid microhabitats underneath leaves or rotten logs, where the humidity is higher) -for large, mobile animals, dispersal barriers, the presence of conspecifics and other organisms (including food), and physical / chemical features about the environment all can be important factors affecting the choice of habitat 1) *Some species simply haven't had enough time or opportunity to disperse into an area* -in other cases, species have had the opportunity and ability to disperse, but for some other reason, they didn't choose to be at one location -the behavioral mechanisms that an organism uses to pick a site to live (habitat selection) thus become important -for plants and fungi, they don't 'choose' a site to move to (thus habitat selection is not as important in the same sense as the mobile animals), bc the adults don't move -however, seeds and spores arrive through dispersal, and then either the individuals survive and the population may persist, or the population dies out, based on biotic and physical factors 2) *Dispersal Barriers*: first, there may be barriers to the migration or dispersal of the species to a given area -even though the Ohio River was a perfect habitat for zebra mussels, they didn't arrive until the early 1990s -zebra mussels were probably introduced into the USA many times over the last 100 years, but it wasn't until the late 1980s that they successfully established themselves in North America -there were probably many reasons why zebra mussels didn't make it here earlier, but the Atlantic Ocean acts as a large geographic barrier to their dispersal -one important project to determine if the absence of a species is simply due to dispersal barriers is to do a *transplant experiment* -if the transplanted population is established, then some dispersal barrier may be in place (it is also possible that chance factors have not provided an opportunity for colonization) 3) *Behavioral interactions and the presence of conspecifics*: habitat selection may have a genetic basis, but observation, learning, and experience can come into play -one important cue is the presence of conspecifics and other organisms in an area -songbirds migrate away from their natal areas, and return to those same areas to breed -many songbirds learn the local 'dialect' from their fathers, and come back to that area 4) *Interactions with other species*: if barriers can be overcome and organisms could choose to live in a certain habitat, they may not bc of the presence of other species -predators, disease agents, and competitors may negatively affect a species and preclude them from living in certain habitats (ex: cattle populations from North America cannot survive long in Africa, due to diseases vectored from biting flies) 5) *Physical / chemical cues*: for mobile organisms, specific cues about the habitat can be examined while they move -mobile flying insects may seek out the source of chemical odors emanating from food plants -for a # of animals, perch or oviposition sites are reliable cues of suitable habitat -in a few cases, some species' distributions can be correlated to gradients or limits of physical/chemical factors at various spatial scales -some insects are known to 'sample' the environment (ex: aphids land on host and nonhost plants equally - they taste the plant, and if it is not suitable, the aphids simply fly away) (ex: migrating fish return to their natal streams by recognizing the 'odors' from those streams, and they consequently ignore the mouths of other streams) 6) Finally, traits for habitat preference can be genetic and thus inheritable: they are passed to offspring

Human Populations: Birth Rates and Death Rates Net migration rate

-if more people *immigrate* (enter) than *emigrate* (leave) a particular country, city, or area during a given period, the population of that area will grow at a rate that depends on the difference b/w the immigration rate and the emigration rate -this factor doesn't affect world population, but it does affect the size and rate of growth in various countries, cities, and areas as people move from one place to another -*in addition to birth and death rates, the annual rate of population change for a particular country, city, or other area is also affected by the movement of people into (immigration, i) and out of (emigration, e) that area* 1) net migration rate = [# of immigrants (i) - # of emigrants (e)] per 100 people per year -thus r = growth rate = [(b + i) - (d + e)] 2) Some countries control their rates of population growth to some extent by restricting immigration -only a few countries in the world annually accept a large # of immigrants or refugees -however, migration w/in countries, especially from rural to urban areas, play an important role in the population dynamics of cities, towns, and rural areas 3) The US has not reached *zero population growth (ZPG)* (where dN/dt = 0) in spite of the dramatic drop in average total fertility rate -the major reasons for this lack of attaining ZPG are: a) the large # of women still moving through their childbearing years b) high levels of annual legal and illegal immigration c) an increase in the # of unmarried young women (including teenagers) having children

Dispersion and Ranges: The importance of spatial scale on dispersion

-if you look at a different spatial scale, you could see a different pattern of dispersion -the individuals may be clumped at a small spatial scale (multiple plant stems coming off one common root, or a # of related animals w/ their parents/mother, for example, a troop of monkeys or a pride of lions), but the family clumps are evenly spaced (uniform) at a larger scale -this event may be due to a scarcity of needed resource (ex: herds gathering around watering holes) or due to territoriality, where a group defends an area against intrusion by other groups

Dispersal: Factors that favor not dispersing

-if you were successfully reared in one habitat, why disperse? -in many situations, most of the dispersing organisms die in the process of dispersing -there are several reasons to stay in place (often in clumped dispersion) and not disperse 1) *Kin selection* and helpers -by staying w/ relatives, you may increase your chance of survival and increase your inclusive fitness (by helping relatives rear additional kin) -in turn, you may become the dominant individual and have your relatives aid you in rearing offspring -this situation is observed in bees and other social insects, as well as in mammals and birds, such as the Florida scrub jay -young adult jays that are closely related to the dominant birds do not breed themselves (at least not initially), but they help their kin (parents or older siblings) raise additional offspring -one potential benefit is that older helpers in turn are helping rear their own helpers, if and when the older helpers become the breeding birds 2) *Protection against predators* -as part of a herd or flock, a group may successfully thwart any predator 3) *Facilitation of finding food* -ex: mixed flocks of birds forage together in winter 4) *Overwhelming predators* -one hypothesis for clumping is to overwhelm and satiate predators -ex: the emergence of periodic cicadas and 'masting' performed by oaks and other trees (a mast year is one where trees produce such a huge crop of seeds that the seed predators cannot eat all of them) 5) In many animal species, parents force grown offspring to leave

The human carrying capacity of the planet: Disease

-in developing countries, acute diseases (from infectious organisms) are responsible for most mortality -in the developed world, chronic diseases (heart disease and cancer) are the predominant mortality factors 1) If we examine the causes of mortality in industrialized and developing nations, we will see the prevalence of cancer and circulatory diseases (stroke and heart disease) - the 'diseases of the old' - are the main causes of mortality in MDCs -however, in the LDCs, respiratory and gastrointestinal diseases, childhood diseases, and parasites are important causes of mortality instead -gastrointestinal diseases were more important in the past than now 2) Historically, disease was an important biotic factor controlling human populations -as long as we existed as small, dispersed, and largely isolated groups, there was no potential for the rapid spread of disease -however, with the advent of agriculture, followed by commerce and urbanization, the potential for disease increased dramatically (disease is considered a density-dependent factor) -tuberculosis, leprosy, malaria, smallpox and bubonic plague were partially effective in reducing population sizes in isolated countries and villages over the centuries -AIDS had become an important disease of the late 20th century, especially in Africa, and it has some dire regional consequences 3) Our knowledge of infectious disease agents and basic sanitation has changed the potential of disease to regulate human populations, both initially in the MDCs, and more recently (as we exported our medical technology) to the rest of the world -sewage is no longer dumped into the streets -surgical instruments are sterilized between operations -food workers and health workers are required to wash their hands at regular intervals -as commonplace as these practices now seem, they were not routinely done as recently as a century ago and are not faithfully done in many parts of the world even today 4) *In short, current diseases by themselves will not prevent our reaching and maintaining a global population of a given size* -new diseases continue to evolve, and the larger and denser the population, the more the opportunity exists for a devastating population crash caused by disease -such a crash could dramatically disrupt our social structure

Metapopulations: the Spatial Structure of a Population Fragmentation

-in many cases, due to the increased fragmentation of the landscape by the growing human population (ex: suburban sprawl's impact of new subdivisions, new roads and new shopping centers, and the larger # of roads and highways cutting through natural, relatively untouched wildlife areas), many populations now are fragmented and essentially function as fragmented metapopulations -if each small subpopulation has a high probability of extinction, relative to one large, contiguous population, the species may quickly go extinct as all subpopulations go extinct over a short period of time, with no new subpopulations established

Population Regulation: Boom and Bust Cycle

-in reality, there is a complex interaction among many factors (both density-dependent and density-independent) that affect the population size via changing the birth rate, death rate, and migration rates of a population -many populations may exhibit a *boom and bust cycle* to population size (ex: hares and lynx -these cycles appear to be the result of predators and winter food shortages interacting to cause the cyclic nature of the hare population)

Population Growth: Logistic Growth Logistic Differential Equation

-integral form of logistic growth is: N(t) = K / (1 + [(K-N(0))/N(0)]e^-rt) -logistic differential equation is: dN/dt = rN(K-N/K) -the differential equation states that the change in the # of individuals added or removed from the population over time (dN/dt, which could be negative) is a function of: 1) the rate of per capita growth, r 2) the population density at the time before, N 3) the proportion of unutilized resources still left to support growth, [(K-N)/K] -the (K-N)/K term in the logistic equation reduces the rate of unrestricted growth (in other words, it represents the unutilized capacity for population growth) -initially, N is small and not near K, so the population at first grows exponentially -as population size (N) approaches the carrying capacity (K), the population growth rate (dN/dt) slows down -when N = K, dN/dt = 0 -the growth rate r at that time also equals 0, bc and b and d are then equal -let's observe what happens when N is a very small # (the population is at low densities) -- as N is near 0 -[(K-N)/K] = (K/K) = 1, therefore dN/dt = rN(1) = rN -at small population size, the population can grow exponentially -as the population increases, it begins to use up the resources (food, nest sites, and so on), and food limitations or other factors (such as pollution, disease, predators) begin to limit the population -as the population size N reaches K, growth is slowed considerably -as N nears K, then the [(K-N)/K] = [(K-K)/K] = 0, the change in the population size (dN/dt) thus approaches 0, and the population size stabilizes at N = K -populations may overshoot K, in this case, the [(K-N)/K] becomes negative, and the population declines (dN/dt is negative) -some populations have shown explosive exponential growth -a population can rapidly overshoot the carrying capacity, and damage the resources to an extent that the carrying capacity is drastically lowered in the local environment, and the population rapidly declines, sometimes to extinction (ex: if there are too many deer in a forest, they strip all of the twigs and branches on all of the vegetation, as far as they can reach -this severely cuts back on plant growth, and the deer all starve that winter -the vegetation takes time [perhaps several years] to recover from the heavy browsing, thus the # of deer that can be supported is dramatically lower the next year [K is lower]) -the point at which dN/dt is greatest (in other words, when the change in the population is greatest), occurs when *N = K/2* -note that at K/2, the ability for the population to rebound is hypothetically maximal -*the carrying capacity is not a fixed #* -it can vary from season to season, and from place to place -the carrying capacity is actually difficult to quantitatively measure in nature -note that these models are *deterministic*, in that there is not variation or uncertainty -each time you run the equations, you get the same results -in reality, chance factors and disturbance of the environment may slow or increase reproduction and survival -however, we can mimic reality using a couple of modifying factors 1. one factor is called a *lag time* -females don't instantaneously give birth (ex: human females give birth to offspring nine months after conception) -the introduction of a lag time causes populations to show oscillations or even chaotic behavior 2. we can also add *stochasticity* to our models -a stochastic model allows for changes in r due to predators, extreme storms, uneven sex ratios, and other disturbances -small populations may behave randomly as a result of the variability in r -however, over the course of many runs, the average response of stochastic populations can mimic the deterministic model -large populations in stable environments may behave much more in a deterministic fashion

The human carrying capacity of the planet: Q's

-let's assume that current projections for the world's population are accurate, and that, by the year 2030, we will number some 9 billion as a minimum estimate -estimates vary, but various groups and international agencies have projections from 9 to 12 billion for our eventual stable population size -is that # above or below the carrying capacity of the earth? -right now (2016) there are an estimated 7.3 billion people on the Earth, and over 324 million Americans -as we address the question of population growth, we must pay attention to ecological principles -remember that ecosystems import energy but recycle matter -can we generate enough energy to sustain a population of 9-10 billion affluent people? -can we recycle matter with enough efficiency so as to avoid exhausting some vital resource, thereby imperiling our ability to sustain a population of 9 billion or more?

Food: Note

-note that although there has been a large increase in the use of fertilizers (whose raw ingredients [nitrates and phosphates] may become scarcer and thus more expensive w/in the next century), *there has been no increase in the per capita yields, due to increases in human population growth*

Habitat Selection: Range

-obviously, organisms are distributed in different ways at a global scale -some organisms are widely distributed, whereas others exhibit very small geographic ranges

Pesticides (biocides): Earlier (elemental) versions of pesticides

-one of the first chemicals used as a biocide was the element *arsenic* -it is toxic to all life, including people -it was indiscriminate, killing pests and beneficial insects and species as well -*arsenic, lead, sulfur* and *copper* were earlier versions of pesticides which are still used today in a few places, like they were used centuries ago (ex: molluscs are controlled by copper-containing compounds -by the 1920s, these were abandoned primarily because of their toxicity to humans) -*nicotine* (from tobacco) was also used as a pesticide (think about this if you smoke!) -oils, soaps, and naturally derived chemicals from plants have been sprayed on crops (these pesticides are called *botanicals*) -various plants have been planted with crop plants to protect them from insect pests -basically, inorganic pesticides were very long lived, or could be considered permanent (they persisted in the environment over the course of many decades, until they were diluted and flushed out of the system)

The Tragedy of the Commons

-our modern livestock industry relies on *feedlot production*, which concentrates animals and increases the overgrazing effects -as demand for meat increases worldwide, a major challenge will be to meet the demand while protecting the sustainability of the local ecosystem -*Garrett Hardin* wrote an influential article called *'The Tragedy of the Commons'* -a *commons* is a central rangeland where everyone raises their livestock on common ground -if everyone is moderate in their herd size, then all people are able to raise their cows on the commons -however, bc no one owns the commons, each person could think they can get additional money or food by adding more cows to their herds -if everyone does this selfish act, then the commons can be destroyed -many environmentalists warn that this could occur on government lands in the West, where people raise cattle -serious depletion of some commons occurs at taxpayer expense -one solution is the privatization of the land, and relying on the landowners to take care of their property -some people don't like the idea of selling off commonly owned public property to wealthy landowners who could abuse the land anyway for short-term profit Hypothetical scenario of 'tragedy of the commons': -initially, each of 5 families next to a common pasture have 2 cows (year 1) -even if everyone agrees to limit their herd to 2 cows, each rancher may look out their window and see unutilized land (let's say that the carrying of the commons is actually 10 cows) -one year, a single rancher adds a third cow and greatly benefits -if only one rancher does this selfish act, the overall negative effect could be minor, and the negative effect is shared by all ranchers (the negative impact is spread over all 11 cows, so that any potential loss in weight is minor) -however, suppose each rancher looks outside and see that there is potential for more cows to be placed on the pasture, and each selfishly goes out and buys 4 more cows (year 2) -the greatly increased grazing pressure caused by the extra cattle reduced the carrying capacity to the point that each family can only keep 1 cow (year 3) on the land -the overuse of the commons was unsustainable -this is an example where selfish behavior may be favored, but at a tremendous cost to all people concerned

Population Growth: Exponential Growth Limiting factors

-populations can't grow exponentially forever -there is usually a resource in short supply that eventually limits growth -this factor is called a *limiting factor* (or factors, if 2 work together in concert) (ex: phosphorus P, nitrogen N, and potassium K are all nutrients needed for plant growth -the plants take up these important nutrients from the soil -we can add the following nutrient treatments to different plants in pots, and observe the effects the addition of extra P, N and K have on plant growth)

Population Growth: Logistic Growth Environmental Resistance

-populations don't grow exponentially indefinitely -eventually environmental resistance slows down the rapid growth, and a population either stays relatively stable around some constant value (the carrying capacity - see below), fluctuates or oscillates through time, or the population declines and goes locally *extinct* -factors that slow population growth are called *environmental resistance* -the difference b/w the potential ability of a population to increase and the actual change in the size of the population is a measure of environmental resistance -*environmental resistance is the sum of the physical and biological factors preventing a species from reproducing at its maximum rate* (ex: environmental resistance includes food limitations, disease, predators, limited nest sites, and other such factors) -3 possible types of population growth: exponential, linear, and logistic -note that exponential growth rapidly increases in a geometric or exponential fashion, whereas linear growth refers to the simple addition of individuals over time -note that the logistic growth is sigmoidal or S-shaped, where the max population size seems to level off at a particular size (the carrying capacity K) -populations can decline as well: a population could grow in a *negative exponential* fashion (a backwards J-shaped curve) or a *negative logistic* (backwards S-shaped curve) way

Pesticides (biocides): Characteristics of desirable pesticide

-regardless of whether or not the pesticide used is a naturally derived chemical from plants or it is a human made chemical, pesticides eliminate a pest by killing the pest outright, or by interfering with the pest's life cycles -*the most desirable pesticide should have all of the following characteristics*: 1) narrow spectrum of organisms harmed by the chemical 2) high rate of effectiveness 3) be cost effective 4) possess a short life span in the environment, where it is soon degraded into harmless byproducts 5) doesn't concentrate in other organisms by the process of *bioaccumulation* and *biomagnification*

Dispersal: Factors that favor dispersing

-several hypotheses explain why migration/dispersal is needed -these reasons are not mutually exclusive - they can cooccur 1) *Food limitations* -many migratory birds have nonmigratory populations -thus, it is not temperature directly, but food limitations, that cause insectivorous songbirds (like the robin) to migrate -ex: seasonal variations in the insect abundance in deciduous forests overlap with the greatest proportion of migratory bird species in the Northeastern United States 2) *Reduce competition with others* -dispersal may occur bc of other individuals (of the same or other species) all using a limited resource -dispersal then occurs to reduce crowding, and should occur in a density-dependent fashion 3) *Competition with kin* -by migrating away, you may find new or open habitats -in addition, by dispersing away from parents and siblings, you may reduce competition amongst close relatives and increase your fitness -in many mammal and bird species, parents aggressively chase away their grown young, so that they do not become future competitors 4) *Competition for mates and sex-biased dispersal* -one sex may be under intense competition for mating opportunities, so that sex disperses -although it is not universal, sex-biased dispersal has been observed in many species, w/ interesting differences among taxa, especially b/w birds and mammals -among birds, the predominant dispersing sex is female, while among mammals the predominant dispersing sex is male *Why is there apparently a difference between mammals and birds in sex-biased dispersal?* MAMMALS: -reasons why dispersal may be more costly to female mammals: female reproductive success is limited primarily by nutritional constraints, while males are limited by # of females they can inseminate -so, females may benefit more than males from familiarity with food resources, den sites and their neighbors -in contrast, male mammal reproductive success depends more on access to mates, they may benefit by moving to areas or groups where there are larger #s of mates (ex: lions and primates) -male mammals are often more polygamous than male birds -bc intrasexual competition for mates is likely to be more intense among males in polygynous species, many males are more likely to be evicted and consequently have to disperse to find mates BIRDS: -for birds, it can be a different story -there is an asymmetry in costs and benefits for males or females to disperse -avian mating systems are largely based on resource defense (males generally compete for and defend resources needed for successful reproduction) -so, males might be more successful in establishing territories in their natal area bc familiarity may permit higher feeding rates of young and reduced predation rates -it may also be easier to set up territories in the vicinity of relatives -once this happens, female birds might benefit from the potential to choose b/w the resources of different mates and if inbreeding is costly, female birds rather than males should disperse 5) *Avoidance of inbreeding* -having one sex migrate instead of both reduces the probability of inbreeding in populations -if only one sex migrates, this maximizes the degree of outcrossing (mating with unrelated individuals) 6) *Fugitive species and dispersal* -many weedy, r-selected species, such as dandelions, live in highly disturbed, relatively ephemeral habitats that vary across time and space -these species often are not strong competitors -thus, they rely on colonizing patches that open up due to disturbance, in areas consisting of relatively ephemeral habitats -those ephemeral sites eventually are colonized by stronger competitors that outcompete the fugitive species -in order to persist in the area, the fugitive species thus must use their high dispersal powers to recolonize new ephemeral sites

Soils: Soil erosion has caused much of the topsoil to be washed or blown away

-since World War II, about 1 billion hectares (2.5 billion acres) of land has been damaged (about 10.5% of our best soils) -erosion is considered to be higher now than in the past -*plowing disturbs the soil in ways unlike natural disturbances, bc it greatly increases erosion (by wind and water), and loss of soil organic content* -soil erosion also leads to sedimentation of inorganic material into lakes and streams, affecting aquatic life (this can eventually affect marine life in coral reefs and estuaries)

Soils: Making soils *sustainable* involves a series of changes to traditional farming practices

-soil can be regenerated (it can be sustainable), if it is not used up and eroded at a faster rate than it is created -sustainable practices include the following: 1) *Contour plowing*: plowing parallel to the slope of the land (reducing erosion) 2) *No-till* or *low till agriculture* (stems and roots of the previous crops allowed to stay in place and rot, thus adding nutrients, and holding the soils) 3) *Strip farming* and *terracing* (level strips of crops at right angles to the slopes, reducing erosion) 4) *Crop rotation* and *polyculture* (several crops grown at once), and leaving in fence rows of trees and hay/grassy strips around the fields -crop rotation also helps to not deplete the soil of micronutrients 5) *Green manure*: plowing under a nitrogen rich crop, such as clover -as it decomposes, it adds nutrients back to the soil

Soils: Soil particles

-soil particles - the types and amounts of mineral grain particle sizes are important -*sands* are particles from 2-0.5mm -they feel gritty and you can see them -silt particles are from 0.002-0.05 mm -silt feels like flour -clay particles are the finest, <0.002 mm -they feel slick -soils that are good for plants contain a mixture of all 3 particle types: *loams* contain similar amounts of all 3 particles and are good for many plants -the amount of clay and sand determines the water holding capacity of the soil (how much and how long)

Soils: Soil Horizons are layers of soil

-soils develop a vertical structure, often with distinct *horizons* -not all horizons are present in a given soil, depending on type and location -different books and authorities label soil horizons differently - we will use the following classification: Oranges And Everything But Cherry Reds 1) O -the O horizon is the topmost layer -consists of an upper layer of loose *plant litter* (heterogeneous, undecomposed leaves and stems) and fairly homologous decomposed dead organic matter called *humus* underneath the litter -depending on the soil type, litter takes about a year or more to decompose to humus -the O horizon can be thick (in temperate forests), or almost absent (in deserts) 2) A -this zone is dark from the humus produced in the O horizon mixing in w/ some mineral grains -earthworms and other decomposers are very important in producing and maintaining this horizon -earthworms and other burrowers help aerate the soil as well (roots need oxygen for metabolism), and many microbes interact w/ roots in this region -*leaching* by rainfall percolating downward through the O horizon dissolves many minerals out of the A horizon -this horizon is what is typically referred to as the *topsoil* -we actually are farming on land in many areas with a depleted topsoil layer, and thus mix in part of the subsoils in with the remains of the topsoil -the soils underlying temperate zone grasslands are considered best for most crops, and crops can be raised on cleared deciduous forest lands and on desert soils, if enough moisture is available 3) E -this horizon is sometimes found b/w the A and B horizons -when present, this zone typically is light in color, compared to the A and B horizons -it is the zone of maximum *leaching* (E for eluviated) of ions -the minerals are dissolved in water -little humus is present 4) B -the B horizon is the zone of deposition, or zone of *accumulation* -there is little humus in the B horizon -you observe deposits of clays and the Ca, Al and Fe oxides that have leached out of the horizons above and from below -the B horizon is usually dark or red -the B horizon is sometimes referred to as the *subsoil* 5) C -the C horizon is very similar to bedrock -only slight weathering has taken place to the rocky materials of the C horizon -the C horizon tends to be hard and impermeable, w/ many rock fragments -little biological activity occurs in this horizon 6) R -the R horizon is the bottommost layer, consisting of unweathered bedrock -bedrock weathers by the actions of wind and rain, breaking apart the solid rock into smaller mineral grains, which mix w/ living and dead organic matter to form soils

Soils: Soils form a symbiotic relationship with plants

-soils provide plants w/ water and mineral nutrients, and oxygen for the roots -plants produce soils, reduce the rate of soil erosion and reduce the effects of runoff -soil microbes and fungi decompose plant remains, and help improve soils -soil microbes also assist plants in taking up nutrients -earthworms and other soil organisms help to aerate the soils, benefitting both soils and plants -thus, plants and soils form a mutualistic association: each maintains the other -plants help create the soil, and the soils help to provide nutrients to the plants

Ways to increase the food supply: Genetic engineering, seed banks, and increased shelf life

-some methods are examined now to increase food production and to maintain or increase shelf life of food 1) *Irradiation* -is one method of killing bacteria in meats and other foods (some worry about possible radiated foods being radioactive - this however does not occur) 2) *Genetic engineering* -is the process where special genes that increase yields, or increase resistance to heat, cold, wet or dry conditions, etc., are inserted into the genome of the crop plant or the livestock animal 3) *Seed* or *germ banks* -are located over the world, holding seeds and genetic material for our crops -these seed repositories are valuable, bc we are losing most of the ancestral species of our domesticated crops -many crops are *polyploids* or *hybrids* of native plants, selected for high yields -a polyploid plant means that the # of chromosomes, or copies of the chromosomes in the cells, have been doubled, tripled or quadrupled -in plants, this can lead to hardier, more productive plants -however, in animals, polyploidy almost never occurs - increasing chromosome #s appears to be harmful -most animals are diploid (2 sets of chromosomes) -however, monoculture practice could lead to the loss of an entire crop due to an insect or disease outbreak -we are losing the genetic variability of the ancestral populations, bc the ancestral plants are endangered by agriculture and urbanization 4) The *Green Revolution* of the 1970s -by increasing the yields of certain crops (by advances in genetic technology and breeding techniques), it was thought that this would help take care of our food shortage problem -the first 'Green Revolution' occurred in the MDCs of western Europe and North America in the 1950s-1970s, when farmers used pesticides, fertilizers and water irrigation, as well as improved genetic varieties of corn and wheat and rice in monoculture, as well as using large machines and lots of fossil fuel energy to dramatically increase the yields of crops -the introduction of new high yield varieties of rice and wheat indeed increased yields dramatically in many parts of the world in the 1960s and 70s, primarily in the LDCS, creating a second Green Revolution -however, the hopes for the Green revolution in solving the hunger crisis were somewhat overly optimistic -*2 problems exist with the Green Revolution*, however - it takes a lot of energy, and it causes some damage to the environment -large amounts of energy, and in some cases, fertilizer, were needed to make it work -plants have been less responsive to genetic engineering than animals, and it takes about as long (5-15 years) to produce by genetic engineering new varieties, as it does to generate new varieties via conventional crossbreeding -in addition, the economics of buying expensive engineered strains prevents its use in many areas -areas w/out adequate rainfall or w/ poor soils cannot benefit from new varieties as well in most cases -finally, water supplies are increasingly being depleted and degraded in parts of the world, and many pesticide-resistant strains of pests are beginning to be seen -farming has become big business - in 1880, 44% of America lived on farms -now, only 2% of Americans are farmers, and big companies are running very large farms 5) *Food storage* -most of the food we eat isn't harvested and then immediately eaten, but it is stored and processed -there are 2 parts to food processing: drying, canning, freezing, pasteurizing and irradiating food to prevent bacterial spoilage & the second part involves *food additives* (chemicals that enhance the taste, nutritional value, color or texture of food) and *preservatives* (retard spoilage) -however, some of the earlier chemicals were found to be potentially toxic or carcinogenic (the preservative BHA, BHT, various red dyes [for example, red dye #2], and nitrates and nitrites) -the earliest food additives were salt and sugar, which in the ancient times were quite valuable commodities for their preservative powers, when used in high amounts -*the Food and Drug Administration (FDA)* is in charge of monitoring food additives -2 viewpoints exist on food additives: either that they should not be added at all (because of the risks), or that the risks are so exaggerated and the hazards are quite minimal, and thus the hazards of such chemicals should be put in perspective (ex: many plant foods have natural carcinogens that are found in higher amounts than the preservatives used in the food)

The human carrying capacity of the planet: Limiting factors for humans

-some people argue that signs point to the fact that we have reached the upper limits of some limiting factors -if you look at *per capita availability (production)*, per capita production of wool peaked in 1960, wood peaked in 1967, fish production peaked in 1970, mutton production peaked in 1970, beef production peaked in 1977 -world grain per capita production of rice, wheat and corn leveled off in the 1980s -part of the decline in the availability of these resources is possible due to economic forces, however, the decline probably is due to the fact that we are near the limit -most of the arable lands on Earth (about 1.5 billion hectares or 3.7 billion acres) are now being used for growing crops -we may be able to use more land, but it will be very costly -a population of 9 billion people will be on the planet soon and even if most of these people are on a meatless subsistence diet, we will need to double the total global food production and distribution, if we want to avoid sharply rising death rates in some countries -obviously other forces may come into play before certain limiting factors such as food ultimately limit our growth (ex: wars for resources)

Population Growth: Logistic Growth Carrying Capacity

-the *carrying capacity* (symbolized by K) is the maximal, sustainable population size (the N that the habitat can support indefinitely) -in all populations, there is some max limit to the size that population can attain in any habitat -ecologists use the following logistic growth equations as a model for describing how populations act when they are faced with limited resources: N(t) = K / (1 + [(K-N(0))/N(0)]e^-rt) dN/dt = rN(K-N/K) -this doesn't mean that all organisms are doing calculus in their heads as the population grows, but the logistic model has been successful in describing this type of growth -w/ the logistic equation, you get a S-shaped curve called the *logistic curve*, which is symmetrical around a population size of K/2 (note that dN/dt is highest at K/2)

Population Growth: Exponential Growth Integral vs. differential form of the exponential growth equation

-the *integral form of the exponential growth equation* will tell us the expected population size at some time t in the future -if we wish to examine the *change* in the population's size from one time period to the next, we would use the *differential form of the exponential growth equation* dN/dt = rN -it states that over the change in time t (the 'dt' in the equation), the change in the population size ('dN') is equal to the difference in birth and death rates ('r'), times the initial population size at time t ('N') (ex: suppose that r = 0.5 and N is 100 -let's suppose that the growth rate r is the # of organisms added or subtracted per individual per year [in this case, 0.5 organisms per individual per year] -that means that for the time period t [suppose it is 1 year long], 0.5(100), or 50 individuals were added to the population that year -so at the end of the year, there are now 150 organisms)

Life Tables: The intrinsic rate of increase, r

-the *intrinsic rate of increase*, r -- intrinsic capacity for increase (discussed by *A. J. Lotka* in 1925) -the intrinsic rate of increase can give an estimate of the growth rate of a population -it can be estimated: r = ln(R(0)) / G -this is only an approximation bc generation time is also an estimate -the maximal intrinsic rate of increase, r(max), is the max r under optimal conditions -the population can grow faster as r approaches r(max) -the rate of increase r can be: ^r < 0, d > b, population is declining ^r = 0, b = d, population is stable ^r > 0, b > d, population is growing through time

Population Regulation: Negative Feedback

-the change in birth rates or death rates by density-dependent factors are an example of negative feedback working at the population level -w/ density-independent factors, there is no negative feedback to slow down a population's growth (or collapse) -bc we almost never see this type of response (a total collapse, or sustained exponential growth) for long periods of time in any population, density-dependent factors do come into play, eventually stabilizing the population's size

Habitat Selection: When examining the entire geographic range of a species, is the density relatively constant across the entire range, or are there centers (hot spots) where the species is of high density, surrounded by areas of low density?

-the densities of many bird species across the USA have been estimated from data from Christmas bird counts (one of the largest data sets on many different species, due to the thousands of people who have participated since 1900). -at the continental scale, birds were clumped -for many species, there are *hot spots*: areas of high densities that are surrounded by lower densities

Human Populations: Birth Rates and Death Rates Age structure

-the length of time it takes for world population to stabilize after average total fertility rates reach or remain below the replacement level depends on the # or % of persons at each age level in the population -a major factor in population dynamics is the *age structure* (or *age distribution*) of a population -- the # or % of persons at each age level in a population -the larger the # and % of women in their reproductive years (15 to 44) and in their prereproductive years (under age 15), the longer it will take for population size to stabilize 1) *Age Structure Diagrams* (or *population pyramids*) -we can obtain an age structure diagram for the world, or a given region or country, by plotting the percentages of males and females in the total population in 3 age categories: 1. *prereproductive* (ages 0 to 14) 2. *reproductive* (ages 15 to 44) 3. *postreproductive* (ages 45 to 85+) -an important factor is the # or % of women of childbearing age (especially the # in the prime reproductive years of ages 20 to 29) and the # or % of people below age 15 (who will soon be moving into their prime child-bearing years) -if a large # of women are of or near childbearing age, births can rise even when each woman, on average, has fewer children 2) *The general shape of the age structure diagram is a key to whether a population might expand, decline, or stay the same* -a rapidly expanding population has a broad base with a large # already in the 15-44 age group and an even larger # of individuals aged 0-14 -this is the general shape of LDC age structure diagrams 3) Age structure diagrams for nations w/ relatively slow growth (ex: USA) have a smaller base than those populations that are growing rapidly -those nations exhibiting ZPG rates have a shape with almost vertical sides rather than pyramidal sides -in such a stabilized age structure, all generations and age groups are about the same in size, and the population stays in this stable age distribution -a population that will decline in the future (not taking immigration into account) will have more individuals in older age classes than younger age classes 4) *Demographic inertia* -in 1994, about 33% of the people on this planet were under 15 years of age -this explains why population will continue to grow (especially in LDCs) years *after* replacement level TFRs are reached, unless death rates rise sharply -the # of individuals entering the reproductive years is increasing -in the USA, population age structure partly explains why it will probably take at least 50 years for us to reach ZPG, even if we maintain a low TFR of 2.1 or less -the population will grow simply bc we will have relatively more women in their childbearing years during the next few decades -this type of demographic inertia also applies if there is a relatively small pre-reproductive age class -- the population will continue its downward slide until m(x) rates rise sharply

Population Regulation: Relation of population dynamics and size

-the logistic equation has been used to successfully describe growth of populations -this suggests that factors limiting growth exert stronger effects on survivorship and fecundity as the population grows -population dynamics can be related to population size in 2 different ways: 1) *density dependence* 2) *density independence*

Metapopulations: the Spatial Structure of a Population Importance

-the metapopulation concept is very important in conservation biology -when trying to conserve a species, does the population behave as one metapopulation, or a series of small populations? -does a housing development or dam or golf course prevent migration to and from smaller subpopulations? -would development wipe out important subpopulations?

Desertification and Salinization: Poisoning soils can cause desertification

-the overuse of pesticides, pollution by toxic chemicals, excessive manure inputs from feedlots - all of these phenomena can all poison soils and lead to desertification and farm abandonment

The Demographic Transition: How?

-the rapid growth of the world's human population over the past 100 years was not the result of a rise in birth rates but largely due to a decline in death rates - especially in the LDCs -the demographic transition occurs as a country develops from LDC to MDC -the increase in the standard of living affects birth and death rates, but changes in both don't typically occur at the same time

Pesticides (biocides): A third step in the evolution of pesticides is the use of chemicals found in nature and thus are more biodegradable

-the toxins produced by the bacterium Bacillus thuringiensis is toxic to many pest insects -the naturally occurring biochemicals have several advantages: they are less persistent in the environment (they are broken down by bacterial activity and other processes) and they tend to not be toxic to mammals and birds (ex: synthetic molting hormones could be applied, thus affecting the ability of the insect to molt and complete development - this hormone has no effect on birds and mammals)

Soils: Plant water relationships

-the various sizes of mineral particles are important -various-sized particles make up the *soil skeleton*, which influences the water holding capacity and the amount of drainage from the soils -coarse sand soils holds more water (larger *pore spaces*, or the spaces b/w mineral grains) but it drains more quickly -if soils are made of clays, water is held longer (smaller pore spaces) -if there is more water than can be held in the pore spaces in the soil, the soil is said to be *saturated* -excess water then would stay above ground and/or run off towards nearby water bodies

Population Growth: Exponential Growth Discrete generations vs. continuous generations

-there are 2 types of population growth - *discrete* and *continuous (overlapping) generations* 1) *Discrete model*: -the population reproduces, and then dies before the next generation reaches maturity - leaving only 1 generation alive at one time (this is called a *discrete population*) -if we look only at the females of the population, the mother dies, and a # of female offspring are left behind -at any one time, the size of the next population can be predicted from the discrete population growth model N(t+1) = R(0)N(t) -N(t+1) = population size at time t+1 -R(0) = *net replacement rate* (NRR - the average # of female offspring left behind by each female of the generation before) -N(t) = population at time t earlier -w/ higher R(0), you see more rapid population growth -if R(0) = 1, then the population size stays the same from generation to generation -if R(0) < 1, then the population will decline -if R(0) > 1, the population will increase during the next generation -if male offspring are to be included in NRR, in order for the population to remain stable in size, R(0) should equal 2 (but only if the sex ratio is 1:1) -if the sex ratio is not 1:1, then the # of males and females have to be estimated -many populations cannot grow exponentially for very long -the net replacement rate drops with higher density -at some equilibrium point, R(0) = 1 and the population would be stable at that size, N(eq) -this is what we would call a *density-dependent* effect 2) *Overlapping* or *continuous model* -many populations have overlapping generations or a continuous breeding season, thus we can't use the equation above (which is useful for discrete generations only) -the population grows following the *integral form of exponential growth* N(t) = N(0)e^rt -N(0) = initial population size -r = *intrinsic rate of increase* (r = b - d + i - e) -e = base of natural logarithms = 2.718 -time t is measured in days, years, or some set value (ex: if N(0) = 10 and r = 0.1, then what would the population size be after 5 and 10 years, if the population is growing exponentially? N(5) = 10^e(0.1)(5) = 10(2.718)^(0.5) = 16.5 N(100) = 10^e(0.1)(100) = 220,036)

Metapopulations: the Spatial Structure of a Population Immigration rate effects

-w/ a low rate of migration and high chance of local extinctions, the entire metapopulation behaves erratically and may go extinct -w/ low immigration rates, the metapopulation acts more like a group of disconnected and smaller subpopulations, each w/ a high probability of going extinct -w/ a high rate of migration, however, the flux of individuals into each subpopulation dampens drastic changes among the subpopulations, and the metapopulation behaves as a large single population -if the colonizing source is a large, relatively permanent population (ex: a population of birds on a *mainland*), small demes on oceanic islands may go extinct and recolonized by the mainland population -if the sources of colonists are other oceanic islands, then there can be no 'rescue effect' by a large permanent mainland source population -there are different models that incorporate mainland populations

The human carrying capacity of the planet: Future?

-we began this section by asking if a human population of 9-10 billion sometime in the 21st century reaches the carrying capacity of the planet for our species -we have examined some of the essential factors underlying this question, and it seems clear that 10 billion may be beyond the carrying capacity of the planet, at least in terms all of these people making the types of demands the developed countries presently place on the environment -we must either settle for a population well below 9 billion, or change many aspects of how we live, or do both! -the question is whether we can do so voluntarily, or whether we are destined to reproduce rapidly, reach large population sizes, outstrip our resources and suffer a dramatic population decline, w/ our standards of living drastically lowered -*the carrying capacity for humans must take into account the desired standard of living, a matter of human values*

Agriculture and Food Supply: Differences between manmade agroecosystems and natural ecosystems

-when we farm we create an abnormal and novel ecosystem -these *agroecosystems*, as well as other human use areas (everything from parks to golf courses and playing fields), differ from natural ecosystems in *seven major ways* 1) *We stop/slow down ecological succession on farm fields and park areas* -succession is the somewhat predictable change in the community of plants in the ecosystem over time -stopping succession requires lots of time and effort, in terms of materials (fertilizers, pesticides and herbicides) and labor (and back-breaking work of plowing, planting, mowing, removing weeds) -farming actually encourages early successional weeds and pest insects, which become competitors and predators on the crops 2) *Large areas are planted with one genetic strain of one crop (monoculture)* -most crops are early successional species -monoculture allows us to maximize yields, yet endangers the entire crop to disease and pest outbreaks -repeated use of one crop drains the soils of certain micronutrients (trace elements), thus the soil is 'worn out' -*crop rotation* is one solution to this impact -by rotating crops w/ different requirements, and allowing the fields to go fallow (unused) for a year occasionally, crop rotation allows the soils to recover -some crops, such as the legumes (beans and clovers), have mutualistic bacteria (nitrogen fixers) that assist the crop plants in taking up nitrogen from the atmosphere, and building up soil 3) *Uniform dispersion of individual plants* -in agriculture, crops are planted in neat rows, allowing for maximal use of space and ease of harvesting and planting (we create artificial uniform distributions) -natural ecosystems never form neat rows of one plant species -natural ecosystems usually don't allow a large increase of a given pest insect or disease to occur, like crop fields consisting of one species often can do -we thus use pesticides and herbicides against the early successional weeds (ex: lambsquarters) and against the insect pests and diseases that rapidly build up in farm fields 4) The *food chains are simpler and shorter in farm fields and human recreation areas* (1-2 additional trophic levels above the crop plant) -we wipe out the other species, especially herbivores and plant parasites, making the community less diverse, and less resilient to change 5) *Plowing is unlike any natural disturbance of the soil* -repeated plowing exposes the soils to erosion and can damage the soils, leading to a decline in the organic matter and nutrient levels -sedimentation of local streams and the accumulation of pesticides and fertilizers in streams are a major problem in rural areas 6) *Large amounts of inorganic fertilizers must be added to farm fields in order to support the high yields* -we interfere w/ the normal cycling of nutrients in farm fields -ball parks, golf courses, farm fields and other manmade ecosystems lose nutrients (bc they are carried away as produce, or they wash away by erosion) -the flux rate into and out of natural ecosystems is relatively lower, bc nutrients are recycled more w/in the systems -bc the mineral nutrients are harvested in human altered ecosystems, they are not recycled back into the soils, and mineral fertilizers must be repeatedly added (at high costs) 7) We have *sped up pest species evolution in our human-made environments, compared to natural environments* -we use large doses of pesticides to eradicate insect pests -pesticide use exerts a large selective force against the pest insect species, and most of the population dies -however, a few resistant individuals may be present, and the resistant organisms rapidly increase because intraspecific and interspecific competition are reduced -this result often leads to farmers using larger doses of pesticides and further acceleration of the evolution of pest species resistance

Pesticides (biocides): Manmade pesticides

1) *Chlorinated hydrocarbons* -the earliest organic (carbon containing, human made) pesticides were broad-spectrum and long-lived, such as *dichloro-diphenyl-trichloroethane (DDT)* -it is a member of a class of chemicals called the *chlorinated hydrocarbons* -these chlorinated hydrocarbons (including *DDT, DDD, aldrin, dieldrin, lindane* and others) were found to be very effective in controlling crop pests, as well as mosquitoes, in some areas -DDT was used widely in the 1950s until 1971, when it was banned for use in the USA (it is used elsewhere however) -these pesticides were not as long lived as inorganic pesticides (such as arsenic), but they could last 10 years or more unaltered in the soil -*2,4,5-T* and *2,4-D* are two common herbicides that are chlorinated hydrocarbons -most of these have been banned for use in the USA, in part bc of their long lifetime and great potential to undergo *biological magnification* (DDT has one of the highest fat solubilities measured for any compound) -chlorinated hydrocarbons are the worst pesticides in terms of biomagnification -inorganic compounds (such as arsenic and lead) also biomagnify 2) *Organophosphates* -a second class of manmade chemicals, the organophosphates, was produced for pest control -these affect the nervous systems of insects, and humans if we are overexposed! -*these chemicals break down in the soils more rapidly than do the chlorinated hydrocarbons or the inorganic pesticides, however, they are extremely toxic to people* -they contain phosphorus and sulfur as a central part of the molecule -*parathion, malathion, diazinon* are some of the common organophosphates 3) *Carbamate pesticides* -a third class of organic manmade pesticides is the carbamate pesticides -*Sevin* is a common carbamate pesticide -carbamates are also short-lived, present in the environment for a week or two -chlorinated hydrocarbons are generally far less expensive, yet longer lasting, than the more expensive organophosphates and carbamates -all 3 groups work in the same general fashion: they attack the nervous systems of insects (and other organisms) -in the USA and MDCs, the chlorinated hydrocarbons have been replaced by the carbamates and organophosphates, which break down more readily -however, chlorinated hydrocarbons are more toxic to birds, people and other organisms, and they are more water-soluble, meaning they can more easily become groundwater and surface water pollutants -farmers have tended to apply them often, thus they are as continuously present in the soils and water as much as the slowly degradable pesticides they replaced

Dispersal: Three modes of dispersal

1) *Diffusion* -is the gradual movement of population across hospitable terrain -occurs over many generations -most common form of dispersal (ex: the spread of the gypsy moth) -over the course of thousands to millions of years, even slow-moving species can travel a great distance 2) *Jump dispersal* -is the rapid movement of individual organisms across a large distance, followed by the successful establishment of a new population -the intervening areas in between the old and new habitats can be unsuitable for the species to live (ex: the spread of the zebra mussel) -island colonization is another form, particularly from intentional or unintentional introduction by humans (ex: the initial introduction of the African killer bee into South America) -many organisms use a blend of diffusion and jump dispersal 3) *Secular dispersal* -gradually occurs over evolutionary time (thousands of years) -the population can evolve over time in place, eventually becoming another species in the same physical area -another possibility for secular dispersal occurs when the species slowly disperses over a larger area over geologic time, and through natural selection and other selective forces, the local populations become new species

Migration: Migration patterns

1) *Diurnal and tidal patterns* are instances where organisms move on a short-term or daily basis from one microhabitat to another 2) *Seasonal migration* is due to seasonal influences -types of seasonal migration patterns: a) *Multiple-return migration* -the animal migrates and returns several times during its life to a given location -Ex: bats, birds, frogs, whales, caribou b) *One-return-only migration* -example of this type is the migration of salmon -a fish starts out hatching in the headwaters of a freshwater stream -the young fish then migrates downstream to the sea -after growing and maturing in the open ocean, it migrates once back to the freshwater river of its birth to spawn and die c) *One-way-only migration* -several generations may pass before the offspring of one individual that started the migration makes it back -Ex: Monarch butterfly as it migrates to Mexico and overwinters ^they then begin to migrate back, stop, breed, and die along the way ^their offspring mature, fly north, and breed and die in the northern USA ^thus, once the return trip is complete, several generations may have been born before the Monarch population makes it back to the northern USA 3) *Long distance migration* - arctic terns and other seabirds migrate continuously from one pole to the other throughout their lifetime

Demography: Fecundity, m(x)

1) *Fecundity*, or m(x), is the # of female offspring produced per female at age x -Why are only females generally included in this analysis? ^it is easier to measure m(x) for females, bc paternity is hard to confirm -in most m(x) curves, after puberty occurs (the ability to reproduce), there is a peak or optimum age for reproducing -in a few species, the ability to reproduce stops completely (menopause in human females, where m(x) = 0), but different m(x) curves exist for different taxa -many species show a curve where the m(x) values peak and then levels off or declines with further age 2) Why is the # of offspring produced per year greatest at intermediate age? -if the mother is too young, she may not have enough energy reserves -if the mother is too old, she also may not have enough energy reserves for reproduction, or she may be too weak or physiologically unable to breed, feed, and/or protect young

Life Tables: Two types of life tables

1) *Horizontal life table* -a group of individuals born in a given year (or some other short time interval) -- a *cohort* is followed through time, until the last member dies (could take 100+ years) -this is a *cohort* or *horizontal life table* where you record survival and fecundity directly -this method works better than the second 2) *Vertical* or *static life table* -you look at the age structure at an entire population (all cohorts) at one date -one records the distribution of fecundity with age, and uses the relative abundance of age classes as an estimate of survivorship -this method is easier to do and takes less time, but it assumes l(X) and m(X) don't vary over time among cohorts

Estimation of Density: Quadrat sampling

1) *This method works well for sessile animals and for plants* (ex: snails, trees) -suppose you want to know the # of oaks in forest that is 10,000 acres in size -divide forest into # of sections (quadrats) -randomly choose a # of quadrats -count the # of oaks in each quadrat (which will give a density estimate) -then multiply the mean # of oaks/quadrat (H) by the total # of quadrats (T) to get N N = Tx (x = avg) -you can also calculate the # of organisms per square meter (m^2) and then multiply that # by the total area in m^2 2) *Assumptions for quadrat sampling*: a) Appropriate quadrat size is chosen b) Quadrats to be sampled are chosen randomly c) Enough quadrats are chosen to provide an accurate estimate d) Organisms are randomly distributed among the quadrats of the area e) There is only 1 habitat type examined, not 2 or more distinct habitats f) All sampling is done at about the same time 3) *Example*: -suppose you wanted to determine the # of white oaks in a 100-acre forest -you chose ten 1- acre quadrats randomly, and counted the following # of white oaks in each: 0, 2, 1, 6, 0, 5, 2, 2, 4, and 10 trees -mean = 3.2 -standard deviation = 3.12 -variance = 9.73 -thus: 3.2 trees/acre x 100 acres = 320 white oaks in forest -you can determine the # of trees / m^2 by the following: -3.2 trees / acre divided by 4046.68 m^2 /acre = 0.0007865 trees / m^2 -another way to estimate the # of trees in the forest: 0.0007865 white oaks / m^2 times 4046.86 m^2 / acre times 100 acres / forest = 320 white oaks in the forest

Ways to increase the food supply: Increasing the amount of land used for agriculture

1) -the possibility of increasing the amount of agricultural land is very limited -most of the available land is in use today -about 1/2 of the Earth's land surface is 'suitable' for cropland and grazing land, and we are currently growing crops on about 1/2 of that -the other 1/2 not currently in use is found in deserts, tropical and temperate forests, and wetland areas 2) -*we may have to rely on mariculture (culturing marine fish and other animals and plants), aquaculture (culturing freshwater fish and animals and plants) and hydroponics (growing plants in fertilized water solutions in greenhouses (this process is extremely expensive)* -however, these methods may actually be of limited use 3) -we can increase more arable land by wetland drainage and irrigation and deforestation, but these practices damage important ecosystems, losing valuable forest resources and biodiversity of plants and animals -we also would affect the earth's ability to clean air and water by destroying most of our natural ecosystems and replacing them w/ agriculture -we lose more and more land every year to highways, urbanization (ex: strip malls) and erosion, along with desertification 4) -some desert soils can grow crops, if given enough water -however, the problems w/ desertification and salination and water limitation make desert soils less likely to be extensively developed 5) -*some places just can't be used for crops or as rangelands, because of*: a) poor soils (little available nutrients available for plant growth, or high levels of toxic compounds) b) high potential for erosion c) the presence of insect pests (ex: the tsetse fly, the carrier of sleeping sickness, prevents many domesticated cattle varieties from being used in central Africa) 6) -*carrying capacity of range lands* -some lands can't be used for crops, but they can be used for grazing domesticated animals (ex: cattle, sheep, horses) -however, we often put too many grazing animals in one area, exceeding the carrying capacity of the land -this excess in grazers can cause loss of species diversity, soil erosion (plants are cropped off and killed in an area, leading to erosion), wetland degradation, and eutrophication of streams and ponds -*eutrophication* is an increase in nutrients by runoff from eroded soils, as well as the nutrients in feces and urine of livestock, which causes increases algal growth in streams -the algal populations grow and then die, lowering oxygen levels and affecting other organisms -however, we can't use the rangeland crops for food directly -animals provide the most easily assimilated protein and minerals for humans -domestic animals are also used for other purposes: carting goods, transportation, plowing and sources of income from wool and hides -forest lands typically have poor soils, making them unfit for crops w/out using high amounts of fertilizers (which are becoming scarcer and more expensive) -converting these other lands into crops causes the loss of biodiversity, an important hidden cost

The Demographic Transition: Trends in the demographic transition

1) An increase in food supplies bc of improved agricultural production 2) Better food distribution due to improved transportation 3) Better nutrition 4) Reduction of diseases associated with crowding, such as tuberculosis, bc of better housing 5) Improved personal hygiene, including the use of soap, which reduced the spread of disease 6) Improved sanitation and water supplies, which reduced death rates from plague, cholera, typhus, dysentery, diphtheria, and other fatal epidemic diseases 7) Improvements in medical and public health technology through the use of antibiotics, immunization, and insecticides (DDT), which was used against malaria-carrying mosquitoes -all of the above factors lead to higher birth rates, along with decreased death rates -developed nations have low death rates due to these diseases, but developing nations continue to have epidemics -as growth rates rise, educated and more affluent populations tend to have decreased birth rates until the growth rate r is 0 or near 0

Human Populations: Birth Rates and Death Rates Increasing the generation time decreases the times a female is fertile, thus fewer offspring can be produced during the female's lifetime

1) As the average age of marriage increases, the lower the average # of children born to women b/w ages 15 and 44 (total fertility rate) and the sooner the world population size will stabilize (increasing the generation time G) 2) Recent studies have shown that a) the average age of marriage was rising in MDCs and in Asia, but not in Africa and Latin America b) the average marriage age would have to rise to at least 25 in order to lower fertility -birth rates tend to be much lower in countries where the average marriage age of women is at least 25 years -putting off marriage to age 25 reduces the typical childbearing years (ages 15 to 44) by ten years and cuts the prime reproductive period (ages 20 to 29, when most women have children) in half

Food: There are approximately 250,000 species of plants, yet the human species depends only really about 300

1) Categories of plants include: cereal grains (wheat, rice, corn, barley, oats, sorghum, millet, rye), legumes (soybeans, peas, green beans, chickpeas, pigeon peas and peanuts), starchy roots (including potatoes, sweet potatoes and yams, cassavas [tapioca]), grapes and other berries, sugarcane, sugar beets, apples, tomatoes and peppers, oranges and other citrus fruits, bananas and plantains, coconuts, watermelons and other melons, cabbages and other brassicas, including rapeseed [canola], onions, sunflowers, and mangos 2) Forage crops, especially alfalfa and other grasses grown for hay, are other important sources -the land we use to raise corn, wheat, beans, cotton, and land for hay/dairy/cattle is most of the agricultural lands in use here in the USA

Life Tables: Calculations of a life table

1) For both sexes first calculate: -x: age at beginning of interval -n(x): # alive at beginning of interval x (n(x)-d(x) = n(x+1)) -d(x): # that die during interval x -l(x): proportion of cohort still alive at the start of interval x (survivorship) (l(x) = n(x)/n(0)) Ex: Suppose we have 100 individuals in a cohort. The life table for this cohort is in the box above. (NOTES) 2) In addition, for females (usually) we also record fecundity -recall from above that m(x) is the *age specific fecundity rate* = # of female offspring / female during time interval x -let's go back to the previous hypothetical population and say 3 female offspring are produced per year once they become 1 year old -2 more statistics can thus be generated: 1. l(x)m(x) = *the age class contribution to next generation* 2. xl(x)m(x) = *the time weighted contribution to next generation*

Metapopulations: the Spatial Structure of a Population Assumptions of Levin metapopulation model

1) Local subpopulations were either at K (carrying capacity) or are extinct, and thus only extinction and colonization (via some form of dispersal) occur 2) Only homogeneous patches are present (in terms of size and quality), and only 1 subpopulation is found in each patch 3) There is no spatial structure (the spatial arrangement of patches doesn't matter) 4) All individuals from all patches are equally likely to disperse to a given patch 5) The total population size, as well as the subpopulation population sizes, don't matter 6) The subpopulations are independent of each other, w/ respect to extinction 7) No time lags exist (dPo/dt responds instantly to changes in m, Po or e) 8) The variables m and e are constant through time 9) There are a large # of patches or sites that could be colonized present

Life Tables: The generation time, G

1) The *generation time*, G, is a statistic that is the average # of years b/w the birth of a mother and the birth of all of her offspring G = sum(xl(x)m(x)) / sum(l(x)m(x)) 2) The concept of generation time is important -short generation times can cause faster population growth (more females alive per longer time interval, thus more births per century, bc there are more generations per century)

Soils: Water and soil

1) The water in soils comes in 3 categories: *gravitational water, capillary water* and *hygroscopic water* a) *Gravitational water* -is held by only temporarily - it fills the large spaces b/w soil grains -over time, however, the pull of gravity is stronger than the attractive pull from the mineral grains of the soil, so the water leaves and joins the groundwater below -the amount of water left in the soil after several days is called the *field capacity* of the soil -this water is held in place by capillary attraction b/w the soil grains and the water -the best soils have a variety of particle sizes, which helps increase the water-holding capacity of the soil b) *Capillary water* -is the main source of water for plants (they can also use some of the gravitational water, but it typically drains away rapidly and thus is often not available) c) *Hygroscopic water* -is much more tightly bound (absorbed) to the soil particles and is unavailable to most plants (this water cannot be 'pulled away' by the plants' roots) -when the only available water left in soil is the hygroscopic water, the plants lose turgor pressure and then they *wilt* 2) Plants draw water from soil by *osmotic potential* in roots and by the *water potential* for evaporation at the leaves -the osmotic potential is due to increased amounts of sugars and organic acids in root cells - this increase in solutes increases the osmotic pressure inside cells, which then attracts water into the root from the soil -the 'pull' occurs bc water molecules are transpiring from the leaves (evapotranspiration)

Soils: Soil forms from 4 basic mechanisms

4 ways soil forms: 1) Weathering of bedrock (*residual soils*) a) rain and ice crack up rock over time -soils form primarily from physical weathering, but biological activities also contribute b) water dissolves some ions (such as K, Cl, Mg, Na and Ca), leaving H+ ions behind -the lowered pH causes remaining oxides (of Fe, Al, Si) to form new minerals -the hydrogen ions are from rainfall (a normal pH of 5.6) and from the decomposition of dead organic matter c) biological activity is also important -plant roots can exert pressure due to water and can split rocks -the activities of animals, such as burrowing animals and grazing snails, help to weather rock as well d) different residual soils form depending on rainfall, evaporation, if all of the cations are washed away or if certain salts accumulate w/in some horizon, the accumulation of organic material, if the soils are poorly drained and can become anoxic, and the mineral composition of the parent bedrock 2) Soil blown in from other areas (*loess*) 3) Soil brought in by rivers (*alluvial soils*) 4) Soil brought in by glaciers (*glacial till*)

Dispersion and Ranges: Coefficient of Dispersion

How can we tell if the observed distribution is random, or significantly different from random (ex: it is clumped or uniform)? -one way to test for significance is to use a statistic called the *Coefficient of Dispersion* (*C.D.*) -if the dispersion pattern is uniform, almost all quadrats will have the same # of individuals, and the sample variance will be less than the mean (average) # of individuals per sample -if the population is clumped, the sample variance will be higher than the mean (due to a # of zeroes and a preponderance of higher values) -if the variance and the mean follow the Poisson distribution (the mean and variance are roughly equal), then the population is randomly dispersed -we call this the ratio of the variance to mean (s^2/x) the Coefficient of Dispersion (C.D.) 1) -if C.D. < 1, (x > s^2), then dispersion is uniform -if C.D. ~ or = 1, (x = s^2), then dispersion is random -if C.D. > 1 (x < s^2), then dispersion is clumped 2) Example: -mean = 1.11 insects/leaf -variance = 2.04 -then, C.D. = 1.84 -so, the insects tend to be clumped - most leaves either have no insects or have several insects 3) How significantly different does the variance to mean ratio have to be from 1 in order to say a population dispersion is clumped or uniform? -we can us inferential statistics (using a Chi-square test) to tell us if the C.D. significantly differs from 1.0 (but for this class, if you are told that the C.D. significantly differs from 1.0, then the dispersion is either clumped or uniform) -you have to then state whether or not it is clumped (C.D. > 1) or uniform (C.D. < 1) by looking at the C.D. -the 3 dispersion patterns can be distinguished by comparing the results (observed) w/ the values expected of a random dispersion (a Poisson distribution)

Estimation of Density: Mark-recapture techniques

N/F = S/R or N = FS/R 1) *This method is good for mobile animals* -there are unknown N individuals in the area -first, at time T1, capture F individuals, mark them, release them back into area -then, come back at time T2 and capture S individuals, a fraction of which are marked (and thus recaptured, R) -the unmarked individuals are U ^thus, S = U + R 2) *Assumptions for mark recapture* -- the method works well if: a) A large fraction of population can be collected at random for marking b) All individuals of population have equal probability of capture: age, sex, and health, can't affect probability of capture c) No change in N by births, deaths, immigration, or emigration between T1 or T2 d) No change in habitat has occurred b/w sampling periods e) Rates of survival not affected by marking - the mortality rates of marked and unmarked animals are the same f) Marks are not lost or overlooked g) Marked individuals are given enough time to disperse randomly through population 3) *Example*: estimate the # of dragonfly larvae in a hypothetical pond, using the following data: -at T1, F= 75 -at T2, S=50, R=25 N = ((75)(50))/(25) = 150 4) In order to improve accuracy of your estimate, you should: -maximize the # caught at T1 and T2 -increase time b/w the two sampling periods ^but you can't wait too long a time in between the sampling dates, bc N changes over time, which then dilutes the # of marked individuals (due to the deaths of both marked and unmarked individuals, and the births of new individuals, which of course will be unmarked)

Agriculture and Food Supply: The negative effects of agriculture are numerous

Negative effects include: 1) The buildup of pest weeds and insects, some of which may become resistant to pesticides 2) Erosion and loss of soils, and a drop in soil fertility 3) Soil erosion causes an increase in sedimentation of streams next to the fields, affecting aquatic life (many aquatic animals don't do well in turbid waters) 4) An increase in pesticides, herbicides and fertilizers in soils, streams, and rivers, affecting aquatic life and human health (through our drinking water and crops) 5) Water runoff of manure and urine from feedlots drains into streams and lakes, affecting productivity in aquatic areas 6) Desertification, salination and waterlogged fields, which lower crop productivity 7) Depression of water tables: aquifer depletion, thus affecting water availability 8) Groundwater pollution, air pollution (use of fossil fuels), affecting productivity 9) Deforestation for new fields endangers wildlife, thus increased loss of biodiversity 10) Depression in the genetic variety of crops and livestock, making the entire population susceptible to disease 11) Runoff affects the marine fisheries and the coral reefs of the oceans -in the Gulf Coast, a '*Dead Zone*' has been found, where little or no life occurs in the areas, off the Gulf Coast away from the Mississippi River, which drains the middle 2/3 of the USA and is heavily laden with silts and chemicals of various kinds (pesticides and fertilizers)

Soils: The type of soil in a region is affected by many processes and factors

Processes/factors affecting type of soil in a region: 1) The local climate, especially rainfall and the presence of rivers and streams 2) The underlying bedrock 3) The overlying vegetation (which breaks up rocks and soils, adds and removes materials from soils) 4) Topography of area (flatland, hilly) 5) Time since the bedrock was exposed at the surface

Ways to increase the food supply: Simultaneously or sequentially growing several crops or several strains of a crop on the same plot of land is one important technique to improve yields

Several types of sequential crop use include: 1) *Polyvarietal variation* -growing several genetic varieties of a crop at the same time (lessens the chance of a total loss due to disease) 2) *Intercropping* -2 or more crops grown simultaneously (like a carbohydrate-rich grain that depletes the soil of a nutrient, like nitrogen, and a protein-rich legume that adds nitrogen back to the soil) -the combination of beans w/ corn or rice provides a complete protein for humans (each crop may lack one or more essential amino acids, but together they provide all of the essential amino acids) 3) *Agroforestry* -growing forest trees w/ crops simultaneously on one field -the trees can be harvested, and growing shade tolerant crop plants allows them to grow under the trees 4) *Advanced polyculture* -growing different crops w/ different harvest dates 5) *Crop rotation* -growing different crops in successive years

Soils: Composition

Soils are composed of: 1) *weathered rock* (from underlying bedrock) 2) *humus* (dead organic matter) 3) *organisms* in the soil 4) *air, nutrients,* and *water*