population ecology u study of the factors that affect population size and composition
TRANSCRIPT
Density
Number of individuals per unit area or volume.
Ex: Diatoms - 5 million/m3
Trees - 5,000/km2
Deer - 4/km2
Clumped Dispersion May result form a patchy
environment. May increase chances for
survival. Ex:
Schooling behavior Flocks of birds
Uniform Dispersion
Often the result of antagonistic interactions between individuals.
Ex: Territories Spacing between desert plants
Random Dispersion
Often the result of the absence of strong attractions or repulsions between individuals.
Not a common pattern.
Demographic Factors
Age structure of the population.
Birth and Death rates. Generation time. Sex ratio and reproductive
behavior.
Life Tables
Mortality summary for a cohort of individuals.
First developed from life insurance studies.
Survivorship Curve
Plot of the numbers of a cohort still alive over time.
Curve Types: Type I Type II Type III
Comment
Curve type may change between young and adults.
Ex: Nestlings - Type III Adult Birds- Type II
"r" Species
Increase fitness by producing as many offspring as possible.
Do this by: Early maturation Many reproductive events Many offspring
Result
Maximize reproduction so that at least a few offspring survive to the next generation.
Most offspring die (Type III curve).
"k" Species
Increase fitness by having most offspring survive.
Do this by: High parental care Late maturation Few reproduction events Few offspring.
Exponential Growth
dN/dt = rmax N Characteristic of "r" species. Produces a “J-shaped”
growth curve. Only holds for ideal
conditions and unlimited resources.
Comment
K is not a constant value. Populations often oscillate
around “K” as the environment changes.
Additional Comments
Populations often overshoot “K”, then drop back to or below “K”.
AP Exam rarely asks you to work the equations, but you should be able to give them.
Density-Dependent
Affect is related to N. As N increases, mortality
increases. Ex: Food, nesting space,
disease
Density-Independent
Affect is not related to N. Mortality not related to
population size. Ex: Weather and climate
Population Cycles
Cyclic changes in N over time.
Often seen in predator/prey cycles.
Ex: Snowshoe Hare - Lynx
Age Structure Diagrams
Show the percent of a population in different age categories .
Method to get data similar to a Life Table, but at one point in time.
Importances
Can be used to predict future population growth trends, especially for long lived species.
Summary
Know density and dispersion patterns.
Know Life Tables and survivorship curves.
Be able to contrast and compare “r” and “k” strategies.