Chapter 52 - Population Characteristics
survivorship curve
Displays the rate of survival for individuals over the species' average lifespan.
What are the two assumptions of the Logistic Model that are unrealistic? - Time lag - N increase -->
For example, the model predicts that survivorship and fecundity respond immediately to changes in a population's density. But many organisms exhibit a delayed response, called a *time lag*. Some time lags occur because fecundity is usually determined by the availability of resources at some time in the past, when individuals were adding yolk to eggs or endosperm to seeds. Moreover, when food resources become scarce, individuals may use stored energy reserves to survive and reproduce, and the effects of crowding may not be felt until those reserves are depleted. The addition of new individuals to a population doesn't always decreases survivorship and fecundity. In small populations, modest population growth probably doesn't have much effect on these processes and some organisms may require a minimum population density to survive and reproduce.
random dispersion
For some populations, environmental conditions don't vary much within a habitat, and individuals are neither attracted to nor repelled by others of their species. These populations exhibit random dispersion, which has a formal statistical definition that serves as a theoretical baseline for assessing whether organisms are clumped or uniformly distributed. In cases of random dispersion, individuals are distributed unpredictably.
Models of Population Growth Which models are for unlimited growth vs finite
Geometric and exponential models apply when populations experience unlimited growth. The logistic model applies when population growth is limited, often because available resources are finite.
What are the 3 factors that contribute to fitness
Health and survivorship Size Number and quality of eggs
Mark-Release-Recapture Method of Estimating Population Size Imagine that you capture 120 butterflies, mark each with a black spot on its wing, and release them. A week later, you capture a second sample of 150 butterflies, and find that 30 of them have the black mark. How many of the total population was that? And how many butterflies are in the total population?
How many of the originally captured 120, were captured the second week? 30. 30 is 20% of 120. Thus, we assume that just like the newly captured percent is only 20%, we originally only captured 20% of the total population. So 120*5 = 600 in total
Age-Structure Diagrams - How to read this diagram - young vs mature popn
Hypothetical age-structure diagrams differ for countries with zero, negative, and rapid population growth rates. The width of each bar represents the proportion of the population in each age class
How does an animal determine how to use it's energy?
If the animal is likely to survive, then it won't put all of its energy into reproduction. If it isn't likely to survive to the next reproduction cycle, then it will put all of its energy into reproduction.
Early Reproduction versus Late Reproduction
Individuals that first reproduce at the earliest possible age may stand a good chance of leaving some surviving offspring. But the energy devoted to reproduction is no longer available for maintenance and growth. Thus, early reproducers may be smaller and less healthy than individuals that delay reproduction in favor of these other functions. Conversely, an individual that delays reproduction may increase its chance of survival and its future fecundity by becoming larger or more experienced. But there is always some chance that it will die before the next breeding season, leaving no offspring at all. Thus, a finite energy budget and the risk of mortality establish a trade-off in the timing of first reproduction.
Pests - 3 Main Examples - Population Consequence of pesticide use (related to r)
Kudzu, Opuntia, Rabbits Pests don't just eat what we don't want them too, they also reproduce much faster. Meaning that they have a higher r and recover fast. They develop resistances to pesticides faster and are more likely to develop a resistance
Sequential incubation
Lay their eggs every couple of days but start incubating immediately. So the first egg out is the first egg to hatch. Will always be the biggest is fed first
Density-independent factors
limiting factor that affects all populations in similar ways, regardless of population size Fires, earthquakes, storms, and other natural disturbances
active parental care
parents' investment of time and energy in caring for offspring after they are born or hatched
age-specific fecundity
the average number of female offspring produced by a female in each age class
generation time
the period between the birth of one generation and the birth of the next generation Generation time is usually short in species that reach sexual maturity at a small body size, increases with size
Logistic Model - Graphical Representation How does N effect r? - As N increases --> R? - In a small population (N<<K), what is r and what is N-K/K? - In a large population (N≈K), what is r and what is N-K/K? - When N=K, what is r and what is N-K/K? - When N>K, what is r and what does this mean?
- As the value of N increases the value of R decreases - In a small population (N<<K) there are plenty of resources still available; the value of (K − N)/K is close to 1 because there is a high % of the carrying capacity still available. And the r is near rmax as there are no crowding organisms so fast reproduction. - In a large population (N≈K) there are few additional resources available, the value of (K − N)/K is very small, and the per capita growth rate r is very low. - When the population reaches the carrying capacity and N==K; the value of r is 0 and the value of K-N/K is also 0. Called ZPG - When the population goes beyond the carrying the capacity, the value value of r is negative meaning the death rate rate is greater than the birth birthrate and the population will start to decline in size.
Explanation of the Inverse Relationship between Passive and Active Parental Care If you have 100 units of Energy 1 huge egg = _____ units energy 10 medium eggs = ____ units energy 100 medium eggs = ____ units energy
1 huge egg = 100 units energy 10 medium eggs = 10 units energy 100 medium eggs = 1 units energy
2 Factors controlling Fecundity
1. Energy to make eggs, embryos 2. Energy to take care for young after they hatch
What are the two limitations of the geometric model?
1. Some animals die 2. Some populations have overlapping generations
Simultaneous incubation
A female will wait until all the eggs have been produced and then start to incubate them. The eggs and the chicks are the same size. So they all get food if they're the same size
metapopulation
A group of spatially separated populations of one species that interact through immigration and emigration.
Fitness
Ability of an organism to survive and reproduce in its environment Can be measured as the number of surviving offspring an individual produces
Age-specific mortality and age-specific survivorship
Age-specific mortality is the proportion of individuals alive at the start of an age interval that died during that age interval, whereas survivorship is those the proportion of individuals that died during that interval If you add them together they should be equal to 1.
Exponential Population Growth: Mathematical Representation Define the following - B - D - Δt - ΔN - Population growth equation (when we know numbers not rates)
B = absolute number of births D = absolute number of deaths Δt = time period this change occurs ΔN = Population size ΔN/ Δt = B - D The change in population size over time = number of births - number of deaths
Life Histories: birds/mammals What's its growth and reproduction cycle?
Birds, mammals - they have repeated reproduction but NO growth. When birds leave the nest they are pretty much full size (they get fatter). They don't reproduce until they're reproductively mature. Delay reproduction for several years
determinate growth vs indeterminate growth - what is - what type of animals
Determinate growth - growth stops at a certain point in an animal's life (mammals) Indeterminate growth - keep growing (trees, fishes, snake). No final adult size, so they start reproducing when they reach sexual maturity. Have to make decision every year to grow and reproduce based on evolution. Continue growing through their life. Once their able to reproduce these animals have to make a choice if they're gonna grow, reproduce or both
Factors Affecting Survivorship What are the biotic/living factors? What are the abiotic/nonliving factors?
Living factors: 1. Food, predators, parasites, disease Non-living factors 1. Weather/physical environment 2. Accidents and natural diseases 3. Availability of water and nutrients
Allocation of Resources Energy is allocated for three reasons, what are they?
Maintenance, growth and reproduction
Exponential Population Growth: What is rmax, the intrinsic rate of increase? - What conditions - What's the new population growth equation
Maximum population growth rate A hypothetical population living in an ideal environment—one with unlimited food and shelter, no predators, parasites, or disease, and a comfortable abiotic environment. Under such circumstances, which are admittedly unrealistic, the per capita birth rate is very high, the per capita death rate is very low, and the per capita growth rate, r, is as high as it can possibly be. Under these ideal conditions, the exponential growth equation is dN/dt = rmax * N
Altricial Birds
Offspring that are completely dependent on parental care Everyday birds: when the babies hatch they are hopeless. Huge investment of active parent care
Geometric Population Growth (Discrete) - Simple Definition - Overlapping or Non-overlapping - Simplest case - Assumption
Population growth in which generations do not overlap (Non-Overlapping generations) and in which successive generations differ in size by a constant ratio. Growth in populations that produce a single batch of offspring in a year (Discrete) Simplest case is bacterial division, called binary fission At t=0, N=1 At t=1, N=2 At t=2, N=4 This pattern of population growth is described as "geometric," because the population is doubling after the passage of each time interval. With a hidden assumption that no bacteria are dying
sex ratio
Populations also vary in their sex ratio, the relative proportions of males and females. In general, the number of females in a population has a bigger impact on population growth than the number of males because only females actually produce offspring. Moreover, in many species, one male can mate with several females, and the number of males may have little effect on the population's reproductive output.
Source vs. sink populations
Populations that are either stable or increasing in size are described as *source* populations because they are a possible source of immigrants to other populations Those that decline in size are called *sink* populations because they receive available immigrants. Individuals usually move from source populations to sink populations, and sink populations persist because they receive immigrants from source populations in the metapopulation.
Life Histories:Salmon What's its growth and reproduction cycle?
Provide an example of delayed single reproduction. Salmon produce many offspring in a single reproductive episode. They hatch out in the headwaters of the stream, spending a year getting a little bigger. And then when they're mature (at max size and reproductively mature), they swim back to the point of the river where they were produced and reproduce and then die.
Geometric Population Growth: Mathematical Representation - Equation
R0= replacement rate = 2 Discrete model Nt = N0(R0^t)
iteroparity
Reproduction in which adults produce offspring over many years; also known as repeated reproduction.(iterum = again) Ex: Deers/mammals and trees. Devote only some of their energy budget to reproduction at any time, with the balance allocated to maintenance and growth.
semelparity
Reproduction in which an organism produces all of its offspring in a single event; also known as big-bang reproduction. (semel=once;parus = giving birth) This is what happens with salmon
K-selected species - life span - reproduction traits - environmental traits - parental care - growth rate
Species that produce a few, often fairly large offspring but invest a great deal of time and energy to ensure that most of those offspring reach reproductive age. By contrast, K-selected species thrive in more stable environments. They are generally large, have long generation times, and produce offspring repeatedly during their lifetimes. Their offspring receive substantial parental care, either as energy reserves in an egg or seed or as active care, ensuring that most survive the early stages of life (Type I or Type II survivorship). Because K-selected species typically have a low rmax, their populations often grow slowly.
r-selected species - life span - reproduction traits - environmental traits - parental care - growth rate
Species that reproduce early in their life span and produce large numbers of usually small and short-lived offspring in a short period (Type 3 survivorship) Function well in rapidly changing environments The offspring receive little or no parental care of any kind have high rmax, their populations grow exponentially when environmental conditions are favorable—hence the name r-selected.
demographic transition model - define
The demographic transition model describes changes in the birth and death rates and relative population size as a country passes through four stages of economic development. The bottom bar describes the net population growth rate, r.
per capita growth rate
The difference between the per capita birth rate and the per capita death rate, b − d, is the per capita growth rate of the population, symbolized by *r*.
How can you tell whether an environmental factor causes density-dependent or density-independent effects on a population?
The effects of density-dependent factors get stronger (that is, they affect a larger percentage of the individuals in the population) as the population's density increases. The effects of density-independent factors do not change (that is, they affect the same percentage of the individuals in a population) as the population's density changes.
Are the effects of infectious diseases on populations more likely to be density-dependent or density-independent?
The effects of infectious diseases are usually density dependent effects because disease-causing pathogens spread more quickly through dense populations of the organisms they infect.
Exponential Population Growth - Definition - Overlapping or Non-overlapping?
The geometric increase of a population as it grows in an ideal, unlimited environment. No limitation to population size Represents overlapping generations. they can live side by side and even be reproducing at the same time.
life histories
The lifetime patterns of growth, maturation, and reproduction—that maximize the number of surviving offspring an individual produces.
How does Intraspecific Competition come into play with the Logistic Model?
The logistic model assumes that vital resources become increasingly limited as a population grows larger. Thus, the model is a mathematical portrait of intraspecific (within species) competition, the dependence of two or more individuals in a population on the same limiting resource.
Logistic Model - What does K-N mean? - What does K-N/K mean?
The mathematical expression (K − N) tells us how many individuals can be added to a population before it reaches carrying capacity. And the expression (K − N)/K indicates what percentage of the carrying capacity is still available
How does the prediction of the exponential model of population growth differ from that of the logistic model?
The model of exponential population growth predicts unlimited population growth over time, generating a J-shaped curve of population size versus time. The logistic model predicts that population growth slows down as the population approaches its carrying capacity, generating an S-shaped curve of population size versus time.
Clumped dispersion - Why is this so common?
The most common pattern of dispersion; individuals aggregated in patches. This is common because plants are often in patches. Animals live in social groups. Some reproductive patterns require this.
Exponential Population Growth: Mathematical Representation Ecologists usually express births and deaths as per capita (per individual) rates, allowing them to apply the model to a population of any size. Define the following - b - d - Population growth equation (incorporating per capita birth rates)
The per capita birth rate, symbolized b, is simply the number of births in the population during the specified time period divided by the population size b =B/N Similarly, the per capita death rate, d, is the number of deaths divided by the population size d=D/N The change in a population's size during a given time period (ΔN/Δt) depends on the per capita birth and death rates, as well as on the number of individuals in the population. ΔN/Δt = B-D = bN - dN = (b-d)N Or dn/dt =(b-d)N
Male Guppies from Streams Where Pike-Cichlids Live (Top) Are Smaller, More Streamlined, and Have Duller Colors than Those from Streams Where Killifish Live (bottom). Why?
The pike-cichlid prefers to eat large guppies, and the killifish feeds on small guppies. Thus they changed size to avoid being eaten. Either getting smaller and less noticeable or larger and more noticeable to fend off. The female guppies with pikechilds reproduce often and produced more small young (avoid predators), and the opposite with the killfish which need time to get large
Examples of Life Histories: Annuals (Plants/insects)
They complete their entire lifecycle in one year, produce seeds and then the cycle starts over in the spring
Life Histories: Trees What's its growth and reproduction cycle?
Trees - repeated reproduction and long term growth. Most trees will reach a minimum size at which they can reproduce. A couple of years later it will flower. After it first reproduces it will continue to grow and reproduce every year
Type 1 Curve - What is - What kinda animals/care
Type I curves reflect high survivorship until late in life, when mortality takes a great toll. Type I curves are typical of large animals that produce few young and provide them with extended care, which reduces juvenile mortality (less babies dying).
Type 2 Curve
Type II curves reflect a relatively constant rate of mortality in all age classes, a pattern that produces steadily declining survivorship.
Type 3 Curve
Type III curves reflect high juvenile mortality, followed by a period of low mortality once the offspring reach a critical age and size.
Exponential Population Growth: Mathematical Representation (with r) - Define equation (incorporate r) - What does the value of r mean (pos, neg, 0)
Using the per capita growth rate, r, in place of (b − d), the exponential growth equation is written: dN/dt = rN If the birth rate exceeds the death rate, r has a positive value (r > 0), and the population (N) increases. If the birth rate is lower than the death rate, however, r has a negative value (r < 0), and the population (N) decreases. In populations where the birth rate equals the death rate, r=0, and the population's size is not changing—a situation known as zero population growth, or ZPG. Even under conditions of ZPG, births and deaths still occur, but the numbers of births and deaths cancel each other out.
Logistic Model: Mathematical Representation - What is r? - What is the logistic growth equation
We regulate r because it gets smaller as it approaches its max size r = rmax(K-N/K) dN/dt= rmax(K-N/K) * N
brood parasitism - what is - example
When a bird of one species lays its eggs in the nest of a bird of another species. Usually produce an egg that looks similar to the host eggs. Sometimes she'll sneak in and eliminate the host eggs and replace with her own. example: Cuckoos and cowbirds
uniform dispersion
When the individuals in a population repel each other because resources are in short supply, they tend to be evenly spaced in their habitat, a pattern called uniform dispersion.
The Logistic Model - Definition - Carrying capacity - Key Assumption
a model of population growth that assumes that finite resource levels limit population growth The maximum number of individuals that an environment can support indefinitely is termed its carrying capacity, symbolized K Assumes that a population's per capita growth rate, r, decreases as the population gets larger. In other words, population growth slows as the population size approaches the carrying capacity
passive parental care
amount of energy invested in each offspring before it is born yolk, size of eggs etc
life table
an age-specific summary of the survival pattern of a population To collect life-table data for short-lived organisms, demographers typically mark a cohort, a group of individuals of similar age, at birth and monitor their survival until all members of the cohort die
Precocial Birds
chickens and turkeys covered with down Long incubation time, young birds active as soon as they hatch