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.

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 I u Type II 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 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   N/  t = b - d u Where: u N= population size u t = time u b = birth rate u d = death rate

Rate of Increase u r = difference between birth rate and death rate. u r = b - d

Equation:   N/  t = rN u N = population size u t = time u r = rate of increase

From Calculus  The equation  N/  t = rN becomes: u dN/dt = r max N u r max = intrinsic rate of increase

Exponential Growth u dN/dt = r max N u Characteristic of "r" species. u Produces a “J-shaped” growth curve. u Only holds for ideal conditions and unlimited resources.

Logistic Growth u dN/dt = r max 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 density- independent growth factors.