Population Ecology

quadrats

when researchers sample habitats of sedentary organisms, they count the individuals that occur inside rectangular plots set up at random locations in the habitat. these rectangular plots are called quadrats

Two fundamental concepts in ecology - population ecology to be specific

Distribution and abundance "Where do they live, and how many are there?"

Which processes increase a population's size? a. Deaths and emigration. b. Deaths and immigration. c. Births and immigration. d. Births and deaths.

c. Births and immigration.

What can we not determine from examining age pyramids of human populations? a. the future population size b. the fecundity of a future population c. the age structure of the population d. the success of future generations e. how populations reproduce

d. the success of future generations

Which of the following statements are true of logistic growth? a. The population grows at a steady rate. b. As the population approaches carrying capacity, it grows more slowly. c. As the population approaches carrying capacity, it grows more rapidly. d. When the population reaches carrying capacity, it stops growing.

b. As the population approaches carrying capacity, it grows more slowly. d. When the population reaches carrying capacity, it stops growing.

Under which of the following conditions would a population most likely experience exponential growth? a. Habitat with limited resources. b. Young populations with few individuals. c. Environment with a low carrying capacity. d. Large number of individuals in the starting population.

b. Young populations with few individuals. Young populations with few individuals are more likely to experience exponential growth because they have not used up the supply of resources.

Which trait would you expect to see in a species with high survivorship? a. growth b. increased seed size c. increased seed abundance d. sexual maturity at a young age

b. increased seed size This life history tends to invest more in quality rather than quantity.

The number of individuals present in a population depends on four processes:

birth, death, immigration, and emigration Populations grow as a result of births and immigration Populations decline due to deaths and emigration

carrying capacity is not ____

fixed K varies among species and populations. K varies because for any particular species, some habitats are better than other habitats due to differences in food availability, space, and other density-dependent factors. - K varies in space It also varies with time, because conditions are better in some years than in others. The same habitat may have very different carrying capacity for different species. The same area will tend to support many more individuals of a small-bodied species than of a large-bodied species, for example, simply because large individuals demand more space and resources.

carrying capacity

maximum number of individuals in a population that can be supported in a particular habitat over a sustained period of time. The carrying capacity of a habitat depends on many factors: food, space, water, soil quality, and resting or nesting sites. Carrying capacity can change from year to year, depeneding on conditions Carrying capacity reflects resource limitation. - Assumption: Individuals affect each other and each inhibits the others' growth and reproduction equally.

life table

summarizes the probability that an individual will survive and reproduce in any given time interval over the course of its lifetime.

replacement rate

the average fertility required for each woman to produce exactly enough offspring to replace herself and her offspring's father. (slightly above 2)

fertility rates

the average number of surviving children that each woman has during her lifetime

age-specific fecundity

the average offspring produced by a female in each age class.

generation

the average time between a mother's first offspring and her daughter's first offspring.

fecundity

the number of female offspring produced by each female in the population

population density

the number of individuals per unit area.

survivorship

the proportion of offspring produced that survive, on average, to a particular age. lx = Nx/No lx = survivorship Nx = Number of females in age class x No = Number of original females

population ecology

the study of how and why the number of individuals in a population changes over time and space.

zero population growth

when fertility rate is sustained for a generation, r = o

intrinsic rate of increase

when r, the per capita rate of increase, is at its max.

transects

when researchers sample habitats of sedentary organisms, they count the individuals that occur along lines of known position set up at random locations in the habitat. these lines of know position are transects

age class

A group of individuals of a specific age

emigration

occurs when individuals leave a population to join another population

Analyses allow biologists to determine which aspects of survivorship and fecundity are especially sensitive for particular species:

- Whooping cranes, sea turtles, spotted owls, and many there endangered species have high juvenile mortality, low adult mortality, and low fecundity. In these species, the fate of a population is extremely sensitive to increases in adult mortality - Climate change has enormous implications for the life-history traits of populations. For example, the sex of many reptiles is determined by the temperature of the eggs in the nest. Researchers have observed a change in sex ratio of some reptile species due to warmer climate, and this finding has significant implications for the growth rates of these populations.

Lecture: Life history stages

- time to reproduce - offspring produced - specialized stages - reproductive value

Population sizes change as a result of two general type of factors

1. Density-independent factors - alter birth rates and death rates irrespective of the number of individuals in the population, and they usually involve changes in the abiotic environment - variation in weather patterns, or catastrophic events such as cold snaps, hurricanes, volcanic eruptions, or droughts 2. Density-dependent factors - change in intensity as a function of population size, and they are usually biotic. When trees crowd each other, they have less water, nutrients, and sunlight at their disposal and make fewer seeds.

population growth

A populations growth rate is the change in the number of individuals in the population (ΔN) per unit time (Δt). If no immigration or emigration is occurring, then a population's growth rate is equal to the number of individuals (N) in the population times the difference between the birth rate per individual (b) and the death rate per individual (d). The difference between the birth rate and death rate per individual is called the per capita rate of increase (r). Per capita means for each individual. ΔN/Δt = N*(b-d) or ΔN/Δt = N*r when there is no emigration or immigration If the per capita birth rate is greater than the per capita death rate, then r is positive and the population is growing. But if the per capita death rate is greater than the per capita birth rate, then r is negative and the population is decreasing. If r is zero then the population is stable When conditions are optimal for a particular species - meaning birth rates per individual are as low as possible - then r reaches a maximal value called the intrinsic rate on increase, rmax. When this happens, growth rate is expressed as ΔN/Δt = rmax*N Examples of rmax in populations: - In fruit flies, which breed at a young age and produce many offspring each year, rmax is high. - rmax is low in species such as giant pandas and coconut palms, which take years to mature and produce few offspring each year. Each species has a characteristic rmax that does not change. But at any specific time, a population has an instantaneous growth rate, or per capita rate of increase, symbolized by r. Whereas rmax tells you what the max growth rate is, r tells you what it is at a particular time. So r is always less than or equal to rmax. A population's r is likely to be different from r values of other populations of the same species (such as upland and lowland populations of L. vivipara), and to change over time (such as in wet years versus dry years). The instantaneous growth rate is dynamic.

Lecture: Density-Dependent/Independent Regulation

Density-Dependent Factors - Competition for limiting resources (food, space) - Predation: predators may key in on abundant prey species. - Disease may be spread more easily when population density is high. - Most biological factors act in a density-dependent manner. Density-Independent Factors - Environmental factors (storms, desiccation, extreme temperature) may affect mortality independently of population density.

life history

An organism's life history describes how an individual allocates resources to growth, reproduction, and activities or structures that are related to survival. Traits such as survivorship, age-specific fecundity, age at first reproduction, and growth rate are all aspects of an organism's life history. Life history is shaped by natural selection in a way that maximizes an individual's fitness in its environment. Ex: In L. vivipara populations, biologists contend that females who live a long time but mature late and have few offspring each year have high fitness in cold, high-elevation habitats, such as Austria. In these habitats, females have to reduce their reproductive output and put more energy into traits that increase survival in a harsh environment. In contrast, females who have short lives but mature early and have large numbers of offspring each year do better in warm, low-elevation habitats, such as France.

demography

Analyzing birth rates, death rates, immigration rates, and emigration rates is fundamental to demography: the study of factors that determine the size and structure of populations through time. To predict the future of a population, biologists have to know the population's age structure. They need to know how likely individuals of different ages are to survive to the following year, how many offspring are produced by females of different ages, and how many individuals of different ages immigrate and emigrate each generation.

Human Population Growth: Population Momentum/Inertia

Combined with high survivorship, age structures with make continues increases in the total human population inevitable

Populations can be _____ dependent or ______ dependent

Density Independent - in population ecology, referring to any characteristic that does not depending on population density. when r is constant. exponential growth. Density Dependent - in population ecology, referring to any characteristic that varies depending on population density. when r is constant and then becomes not constant. logistic growth

Lacerta vivipara: A Case Study

European biologists Henk Strijosch and Raymond Creemers set out to construct a life table of a low-elevation population of L. vivipara in the Netherlands, with the goal of comparing the results to data that other researchers had collected from L. vivipara populations in the mountains of Austria and France. They only focused on females. In most cases, biologists focus on females when calculation life-table data, because the number of males present rarely affects population growth. There are almost always enough males present to fertilize all of the females in breeding condition, so growth rates depend entirely on females. LOOK AT STUDY SHEET FOR LIFE TABLE SPECIFICS Results - In the Netherlands, almost no 1-year0old L. vivipara reproduce - In Brittany, France, 50% of 1-year old females reproduce - In the mountains of Austria, females don't begin breeding until they are 4 years old. - In the Austrian population the females live much longer than do individuals in either lowland population - in the Netherlands or France. - In France, fecundity is high but survivorship is low; in Austria, fecundity is low but survivorship is high. The population in the Netherlands is intermediate. In this species, key aspects of the life table vary dramatically among populations

Limits to Growth

Exponential growth - May occur only under nonlimiting conditions. N(t) = No*e^(rt) Carrying capacity - K = the maximum population that can be supported by an environment. - Growth rate = r(K-N)/K - When N << K, growth rate ≈ r - As N --> K, growth rate --> 0

Why isn't it possible for L. vivipara females to have both high fecundity and high survival?

Fitness trade-offs Fitness-trade offs occur because every individual has a restricted amount of time and energy at its disposal - meaning that its resources are limited. If a female lizard devotes a great deal of energy to producing a large number of offspring, she is not able to devote that same energy to her immune system, growth, nutrition stores, or other traits that increase survival. That is, a female can maximize fecundity, maximize survival, or strike a balance between the two.

Dynamics of Metapopulations

Given enough time, each population within the larger metapopulation is expected to go extinct. The cause could be a catastrophe, such as a storm; it could also be a disease outbreak or a sudden influx of predators. Migration from nearby populations can reestablish populations in empty habitat fragments In this way, the balance between extinction and recolonization exists within a meta population. Even though populations blink on and off over time, the overall metapopulation is maintained at a stable number of individuals The history and future of a metapopulation is driven by the birth and death of populations, just as the dynamics of a single population are driven by the birth and death of individuals. Further, migration is an important source of individuals to recolonize patches of vacated habitats.

Preserving Metapopulations

Habitat destruction caused by suburbanization and other human activities leaves small populations isolated in pockets of intact habitat. Metapopulations that are most likely to persist have the following four attributes: 1. They have larger population sizes 2. They occupy larger geographical ranges 3. They are closer to neighboring populations (and hence more likely to be colonized) 4. The have higher genetic diversity Results like these have important messages for conservation biologists: - Areas that are being protected for threatened species should be substantial enough in area to maintain large populations that are unlikely to go extinct in the near future - When it is not possible to preserve large tracts of land, an alternative is to establish systems of smaller tracts that are connected by corridors of habitat, so that migration between patches is possible - If the species that is threatened exists as a metapopulation, it is crucial to preserve at least some patches of unoccupied habitat to provide future homes for immigrants. These results are made much more complex by climate change. Data on existing populations show that changes in temperature and precipitation are already changing the ranges of species.

Lecture: Life history questions?

How long should I live? When should I reproduce? How often should I reproduce? How many kids should I have?

Human Population Growth

Human population size is becoming a critical ecological, economic, and political problem. - Social factors play a critical role in regulating human population size and growth rate. - Resources and population are both unevenly distributed. - Local resource consumption doesn't necessarily match either population density or resource availability!

How to count population size for mobile organisms

If individuals can be captured and then tagged in some way, the total population size of a mobile species can be estimated by using a research approach called mark-recapture mark-recapture: researchers must catch and mark individuals with leg bands, ear tags, or some other method of identification. They then release the marked individuals and allow them to mix with the unmarked animals in the population for a period of time.

What is rmax in a species like the giant panda?

It is low. Giant pandas have a low rate of increase for the population.

Factors the affect K: For a hypothetical mouse population, determine whether the actions described will increase K, decrease K, or not affect K. - a main competitor for food is eliminated, increasing food availability - offspring live longer - wetlands are drained, decreasing the amount of water available - a parking lot is built,shrinking the habitat - an abandon building created more nesting areas - a species with the same food requirements is introduced

K increases: - a main competitor for food is eliminated, increasing food availability - an abandon building created more nesting areas K decreases: - wetlands are drained, decreasing the amount of water available - a parking lot is built,shrinking the habitat - a species with the same food requirements is introduced K is not affected - offspring live longer

Lecture: Life histories

Life histories - Phenotypic traits that tend to emerge after reproduction ceases are not acted upon by natural selection - Senescence - the increased probability of dying per unit time as the organism ages reflects expression of increasing numbers of deleterious alleles

Lecture: Population Management

Many species are exploited as resources. - Fisheries provide a good example of attempts to exploit and manage natural populations. - The general idea is to harvest just enough to reduce intraspecific competition and increase growth rates. - In principle, the fishery yield can be maximized by fine-tuning the catch rate. - In practice, it's extremely difficult to really fine-tune the catch and many species have been harvested to commercial extinction.

exponential population growth

N =Noe^(rt) occurs when r does not change over time The key point about exponential growth is that the growth rate does not depend on the number of individuals in the population. This type of growth is density independent. In nature, exponential growth is common in two circumstances: (1) a few individuals found a new population in a new habitat, or (2) a population has been devastated by a storm or some other type of catastrophe and then begins to recover, starting with a few surviving individuals. It is not possible for exponential growth to continue indefinitely. If it did, then the population would eventually fill all available habitat. When population density gets very high, the population per capita birth rate will decrease and the per capita death rate will increase, causing r to decline. ALL populations have the innate capacity to grow exponentially!

Lecture: Reproductive Costs

Plants and animals have to budget their investments of biomass and energy - Growth/maintenance and reproduction compete for an organism's resources. - In general, reproduction and survival are inversely related; larger investments in reproduction lead to a reduced life span. - Some organisms reproduce once and die, having invested all their resources in that one event.

Assume there are 200 MendAliens living on an island in my back yard. If my island has an area of 20 hectares, what is the population density of MendAliens in terms of MendAliens per hectare?

Population density is calculated as population size divided by area: 200 MendAliens / 20 hectares = 10 MendAliens per hectare.

Lecture: Number of Offspring Produced

Some animals produce enormous numbers (millions) of eggs/young with each reproductive event (e.g. cod or urchins), others produce very few offspring each time. - In general, # of eggs/offspring produce is inversely correlated with the parental investment in each offspring - Some organisms have such high larval mortality that even high output rates don't always result in successful recruitment to the population (e.g. cod) - Greater parental investment in "rare" offspring may lead to high survivorship - Both general strategies may be successful

age of maturity

age where they can begin to reproduce

survivorship curve

Survivorship curves are plot using a logarithmic scale while plotting number of survivors vs. age Three types of survivorship curves: 1. Humans have a type 1 survivorship curve. Survivorship throughout life is high - most individuals approach the species' maximum lifespan 2. Type II survivorship occur in species where individuals have about the same probability of dying each year of life. Blackbirds and other songbirds have this type of curve 3. Many plants have Type III curves - a pattern defined by extremely high death rates for seeds and seedlings but high survival rates later in life.

Lecture: Reproductive Value

The average number of offspring that will be produced by an individual of a given age - Reproductive value is influenced by the probability of survival as well as the probability of successful reproduction. - Reproductive value increases through the onset of sexual maturity then declines with age - Selection acts most efficiently on age classes and life cycle stages with high reproductive value.

The UN's projections make what important point?

The future of the human population hinges on fertility rates - on how many children each woman living today decides to have. Those decisions, in turn, depend on a wide array of factors, including how free women are to choose their family size and how much access women have to education (more educated a woman is, she'll put off having children until school is over typically and only have time to have a small amount of offspring). Access to education and reliable birth control methods, in addition to overall economic development and access to quality health care, will play a large role in determining how world population changes over your lifetime.

Maximum sustainable yield (MSY)

The largest harvest that can be removed repeatedly from a population without driving it towards extinction.

logistic population growth

The logistic growth equation, ΔN/Δt = rmax*N*[(K-N)/K)], describes logistic population growth, or change in growth rate that occurs as a function of population size.

What did studies of the bridled goby, a coral-reef fish, and song sparrows of Mandarte island demonstrate?

There is a strong density-dependent relationship in survivorship. When population density is high, mortality rates are also high relative to fecundity.

Lecture: Reproductive Maturation

Time to reproductive maturity is quite variable - May be short as a few days in some insects - Humans have an unusually long time to reproductive maturity o ca. 13 years. - Animals with a long developmental time often have extensive parental investment in care of offspring

You are doing a mark-recapture experiment to determine the population size of the MendAliens living on an island in my back yard. Initially, you catch and mark 130 MendAliens, which you then release. Next, you capture 90 MendAliens, of which 20 are marked. What is your estimate of the population size of MendAliens living on the island in my back yard?

To get the population size N, multiply the number marked in the first catch, M1, by the total number caught in the second catch, C, and divide that by the number of marked recaptures in the second catch, M2: N = (M1 x C) / M2 Or: (130 x 90) / 20 = 585.

True or false? Factors that determine the per capita rate of increase of a population include the age of breeding and the number of offspring produced each year.

True The per capita rate of increase of a population is the difference between the per capita birth rate and the per capita death rate, and is determined by factors that include the age of breeding and the number of offspring produced each year.

Continuous growth

Under nonlimiting conditions, b = intrinsic birth rate d = intrinsic death rate r = (b - d) = intrinsic rate of net growth

metapopulation

When individuals from a species occupy many small patches of habitat, is that they form independent populations. a population of populations connected by migration. Because humans are reducing large, contiguous ares of forest and grasslands to isolated patches or reserves, more and more species are being forced into metapopulation structure. example - Glanville fritillaries

Why is population ecology a vital field in biological science?

With the explosion of human populations across the globe, the massive destruction of natural habitats, changes in climate, and the resulting threats to species throughout the tree of life, population ecology has become a vital field in biological science. Specific mathematical and analytical tools predict changes in population size and design management strategies to save threatened species

population

a group of individuals of the same species that live in the same area at the same time populations are often defined operationally (functionally)

cohort

a group of the same age that can be followed through time

Which of the following statements about density-independent growth is true? a. Density-independent growth is also known as exponential growth. b. The per-capita rate of increase may exceed rmax during density-independent growth. c. Density-independent growth can continue indefinitely in nature. d. A population that is experiencing density-independent growth levels off at the environment's carrying capacity.

a. Density-independent growth is also known as exponential growth.

You observe two female fish of the same species breeding. One female lays 100 eggs and the other female lays 1000 eggs. Which one of the following statements does not agree with the concept of fitness trade-offs? a. The eggs from the female laying 1000 eggs should have larger yolks compared to the yolks of the eggs from the female laying 100 eggs. b. The female laying 1000 eggs should be larger than the female laying 100 eggs. c. The female laying 100 eggs should live longer than the female laying 1000 eggs. d. The female laying 100 eggs should be able to breed more often compared to the female laying 1000 eggs.

a. The eggs from the female laying 1000 eggs should have larger yolks compared to the yolks of the eggs from the female laying 100 eggs.

Which of the following statements are true of a population at carrying capacity? a. The rate at which resources are used is equal to the rate at which they are supplied. b. The population growth rate equals zero. c. The birth rate equals the death rate. d. The population continues to grow at a constant rate.

a. The rate at which resources are used is equal to the rate at which they are supplied. b. The population growth rate equals zero. c. The birth rate equals the death rate.

What is the primary limiting factor that determines why no female animal can produce a very large number of very large eggs? a. There are energy constraints. b. Temperature constraints will prevent females from carrying too many eggs. c. Time is limited. d. There will be an increase in predation pressure if the females carry too many large eggs. e. Male availability is limited.

a. There are energy constraints.

The mark-recapture method would be best for sampling a population of _____. a. sharks b. oysters c. wheat d. rose bushes e. maple trees

a. sharks

Which of the following statements about a population experiencing logistic growth is true? a. If N is less than K, the population will not grow. b. If the K and N values are far apart, the population will grow very slowly. c. If N is greater than K, the population will shrink. d. If the K and N values are similar, the amount of available resources is high.

c. If N is greater than K, the population will shrink. This statement is true, since K is the maximum number of individuals that can be supported in a particular habitat over a sustained period of time.

Which factor does not affect a habitat's carrying capacity? a. Number of nesting sites. b. Availability of food. c. Maximum number of individuals in a population. d. Intensity of predation.

c. Maximum number of individuals in a population. The maximum number of individuals in a population that can be sustained in a habitat over a period of time is the carrying capacity of a habitat.

What is the defining feature of exponential growth? a. The growth rate increases rapidly over time. b. The population is growing very quickly. c. The growth rate is constant. d. The growth rate is very high.

c. The growth rate is constant. r is not dependent on the population so it is constant

If food were the limiting factor in reproduction, how would the line change if unlimited food were available? a. The line would slope up rather than down. b. The line would not change. c. The line would be horizontal. d. The line would not change direction, but the clutch size values would significantly increase at each density.

c. The line would be horizontal. Removing the limiting factor would remove the relationship (assuming no other limiting factor took its place).

In what populations does exponential growth tend to occur? a. populations that experience high rates of predation b. populations that have surpassed their carrying capacity c. populations that colonize new habitats d. populations that experience intense competition

c. populations that colonize new habitats

K-selection predominates where on the logistic graph?

carrying capacity

population dynamics

changes in populations through time and space uses spatial distribution of populations, demography, and population growth rates, along with immigration and emigration. General demographic equation. N(t+1) = N(t) + B(t) - D(t) + I(t) - E(t) B = birth rate D = death rate I = immigration rate E = emigration rate Population growth rate depends on the number of individuals present and is therefore inherently exponential.

Which of the following factors does not contribute to environmental resistance? a. weather conditions b. competition for space c. environmental toxins d. competition for food e. birth rate

e. birth rate

range

geographic distribution of different species two factors that determine range are: (1) Abiotic factors - temperature, rainfall, the presence of geographical structures like mountains and oceans, and large scale ongoing and historical process such as continental drift (2) Biotic factors - past and current presence of other species that provide habitat, food, or competition Ranges are dynamic - in constant flux as abiotic and biotic factors change overtime

Individuals from species with high fecundity tend to

grow quickly, reach sexual maturity at a young age, produce many small eggs or seeds, and have low survivorship

Individuals from species with high survivorship tend to

grow slowly and invest resources in traits that reduce damage from enemies and increase their own ability to compete for water, sunlight, or food. Have low fecundity.

r-selection predominates where on the logistic graph?

half way in between 0 and K

peak of reproductive age

highest survivorship x fecundity(average number of offspring produced per female of age x

age structure

how many individuals of different ages are alive

The population size should increase...

if the population consists primarily of young individuals with a high survival rate and reproductive rate

The population size should decrease...

if the populations comprises chiefly old individuals with low reproductive rates and low survival rates.

As a population approaches carrying capacity, environmental resistance __________.

increases

net reproductive rate

indicates whether the population is increasing or decreasing (as long as immigration and emigration are insignificant) - Stable reproductive rate is 1 - If the rate was larger than 1, then the population would be increasing. - If the rate was less than 1, then the population would be decreasing. R0 = sum of all (lx*mx) lx = survivorship rate at age x mx = fecundity at age x

Density-dependent factors can be based on ______ interactions or _____ interactions

intraspecific - "within species" - competition among members of a cohort for food interspecific - "between-species" - predation, parasitism, or competition among species for food. Analyzing population cycles has been a particularly productive way to understand how intraspecific and interspecific interactions interact.

***The tragedy of the commons...

is a term, originally used by Garrett Hardin, to denote a situation where individuals acting independently and rationally according to each's self-interest behave contrary to the best interests of the whole group by depleting some common resource.

logistic growth

occurs when growth is density dependent. ΔN/Δt = rmax * N * [(K-N)/K)] where K is carrying capacity (K-N) defines the number of additional individuals that can be accommodated in a habitat with carrying capacity K; dividing K-N by K turns this number of individuals into a portion. Thus (K-N)/K describes the number of individuals of "unused resources and space" in the habitat. it can be thought of as the environment's resistance to growth. - When N gets small, then (K-N)/K gets close to 1, and the growth rate should be high. - When N gets larger, (K-N)/K gets smaller, and the growth rate should be low. - When N is a t carrying capacity (meaning that K-N), then (K-N)/K is equal to 0 and growth stops.

immigration

occurs when individuals leave a population to join another population.

Logistic growth is ____ vs _____

population size vs generation/time

Individual organisms can be arranges in different patterns within populations. Those patterns are...

random - if the position of each individual is independent of the others, as may occur when seeds are dispersed by the wind. clumped - if the quality of the habitat is patch or the organisms associate in social groups (such as schools of fish) uniform - if negative interactions occur among individuals, such as competition for space, water, or other resources.