Chapter 53 Population Ecology Population Ecology u Study
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Chapter 53 Population Ecology
Population Ecology u. Study of the factors that affect population size and composition.
Population u. Individuals of a single species that occupy the same area.
Population Dynamics
Important Characteristics 1. Density 2. Dispersion
Density u. Number of individuals per unit area or volume. u. Ex: u. Diatoms - 5 million/m 3 u. Trees - 5, 000/km 2 u. Deer - 4/km 2
Dispersion u. Pattern of spacing among individuals. u. Types: 1. Clumped 2. Uniform 3. Random
Clumped Dispersion u. May result form a patchy environment. u. May increase chances for survival. u. Ex: u. Schooling behavior u. Flocks of birds
Uniform Dispersion u. Often the result of antagonistic interactions between individuals. u. Ex: u. Territories u. Spacing between desert plants
Random Dispersion u. Often the result of the absence of strong attractions or repulsions between individuals. u. Not a common pattern.
Demography u. The study of the vital statistics that affect population size. u. Ex: Birth and Death rates
Demographic Factors u. Age structure of the population. u. Birth and Death rates. u. Generation time. u. Sex ratio and reproductive behavior.
Life Tables u. Mortality summary for a cohort of individuals. u. First developed from life insurance studies.
Life Tables Show u. Mortality rate per year. u. Life span of the organism. u. Fecundity (birth rate).
Survivorship Curve u. Plot of the numbers of a cohort still alive over time. u. Curve Types: u. Type III
Type I u. Low early deaths. u. High late deaths. u. Ex: u. Humans u. Other large mammals
Type II u. Constant death rate. u. Ex: u. Annual plants u. Many invertebrates
Type III u. High early deaths. u. Low late deaths. u. Ex: u. Trees u. Oysters
Comment u. Curve type may change between young and adults. u. Ex: Nestlings - Type III Adult Birds- Type II
Life History Strategies u. Are the product of natural selection. u. Can favor Maximize survival u Maximize reproduction u
Examples u. Semelparity – one shot reproduction with many offspring. u. Ex. – Salmon, Agave u. Iteroparity – repeated reproduction events with a few offspring each time.
Life History Strategies 1. "r" or Opportunistic species 2. "k" or Equilibrial species
"r" Species u. Increase fitness by producing as many offspring as possible. u. Do this by: u. Early maturation u. Many reproductive events u. Many offspring
Result u. Maximize reproduction so that at least a few offspring survive to the next generation. u. Most offspring die (Type III curve).
"k" Species u. Increase fitness by having most offspring survive. u. Do this by: u. High parental care u. Late maturation u. Few reproduction events u. Few offspring.
Result u. Maximize survivorship of each offspring. u. Few offspring, but most survive (Type I curve).
What is the strategy u. For a weed? u. For an endangered species? u. For Garden Pests?
Population Growth u. DN/Dt =b-d u. Where: u. N= population size ut = time ub = birth rate ud = death rate
Rate of Increase ur = difference between birth rate and death rate. ur = b - d
Equation: u. DN/Dt = r. N u. N = population size ut = time ur = rate of increase
From Calculus u. The equation DN/Dt = r. N becomes: ud. N/dt = rmax N urmax = intrinsic rate of increase
Exponential Growth ud. N/dt = rmax N u. Characteristic of "r" species. u. Produces a “J-shaped” growth curve. u. Only holds for ideal conditions and unlimited resources.
Logistic Growth ud. N/dt = rmax N K-N K u. K = carrying capacity
Result u“S-shaped” growth curve. u. Characteristic of “k" species. u. Common when resources are limited.
Comment u. K is not a constant value. u. Populations often oscillate around “K” as the environment changes.
Additional Comments u. Populations often overshoot “K”, then drop back to or below “K”. u. AP Exam rarely asks you to work the equations, but you should be able to give them.
Regulation of Population Size 1. Density- Dependent Factors 2. Density- Independent Factors
Density-Dependent u. Affect is related to N. u. As N increases, mortality increases. u. Ex: Food, nesting space, disease
Density-Independent u. Affect is not related to N. u. Mortality not related to population size. u. Ex: Weather and climate
Population Cycles u. Cyclic changes in N over time. u. Often seen in predator/prey cycles. u. Ex: Snowshoe Hare - Lynx
Causes u. Density dependent factors. u. Chemical cycles. u. Saturation strategy to confuse predators.
Age Structure Diagrams u. Show the percent of a population in different age categories. u. Method to get data similar to a Life Table, but at one point in time.
Importances u. Can be used to predict future population growth trends, especially for long lived species.
Exponential Growth u. Produces age structures that are a triangle or pyramid shape.
Logistic Growth u. Produces age structures that have even sizes between most age categories.
Declining Populations u. Produce age structures with a narrow base and wider middles.
Summary u. Know density and dispersion patterns. u. Know Life Tables and survivorship curves. u. Be able to contrast and compare “r” and “k” strategies.
Summary u. Know exponential and logistic growth curves and equations. u. Know density and densityindependent growth factors.
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