Populations

Goals

1. To understand how and why populations are structured in space (dispersion)

2. To understand how life histories come about

3. To understand how the environment can control how a population grows, and how life history characteristics contribute to patterns of population growth

4. To understand how ecologists use models

Outline

Introduction: what is Ecology?

Levels of ecology:

• organisms
• populations
• communities
• ecosystems
• the biosphere

How are populations dispersed (distributed geographically)?

Patterns of dispersion (clumped, uniform, random) are caused by interactions within a population, with other populations, or with the abiotic environment.

e.g. Warblers, humans

Life history strategies

Life history = the traits that affect an organism's schedule of reproduction and death

a. reproduction

the principle of allocation

tradeoffs between surviving and reproducing

• # of reproductive episodes
• # of offspring/episode
• amount of parental investment

Two basic patterns of life history traits

• r stratetegists -- many offspring, little investment in each
• K strategists -- few offspring, much investment in each

b. death

3 types of survivorship curves: determined by the chance of dying (or surviving) during a particular phase of life (infancy, old age etc.)

Population growth

Intro -- how is ecology done?

1. observation (Natural history)
2. experimentation
3. modeling (conceptual, computer, and mathematical models)

1. Density-independent growth

In our model population:

• no migration
• ideal conditions (unlimited resources, etc.)

population size will change according to this model:

since b-d = r, where r = per capita population growth rate, then:

and since conditions are ideal, r here = r_max or the intrinsic rate of increase -- the fastest a pop can grow, based on its life history

the result is exponential growth, where pop density doubles over a regular time interval (2-4-8-16-32-...)

2. Density-dependent growth

since this is unrealistic, how does a pop grow when resources become limited?

K = carrying capacity, the limit on N imposed by crowding, limited resources, etc.

which results in logistic growth

r-strategist populations are controlled by density-independent factors in the environment, e.g., storms, flood, seasonal change

K-strategist populations are controlled by density-dependent factors (e.g., intra- and interspecific competition, predation, disease)

Vocabulary

click here to go to population ecology vocabulary