4-Population Ecology 1

Study Notes

Population ecology is the study of births, deaths, and the factors affecting population size and dynamics within a specific area.
A population is a group of interbreeding individuals of a single species living in the same general area.
Key characteristics of describing populations include:

Density: The number of individuals per unit area or volume.
Dispersion: The pattern of spacing among individuals within the population's boundaries. Common patterns are clumped, random, and spaced (also known as over-dispersed).
- Spaced dispersion relates to competition or territoriality
- Clumped dispersion may indicate social patterns or resource distribution
- Random dispersion patterns are less common.

Birth rates: Patterns and factors influencing birth rates.
Death rates: Patterns and factors influencing death rates.
Life history traits: Characteristics like age at first reproduction, reproduction frequency/duration, total offspring number, and life expectancy. These are products of natural selection.
- Semelparous species: Organisms that reproduce only once in their lifetime (e.g., Pacific salmon, agave)
- Iteroparous species: Organisms that reproduce multiple times throughout their life (e.g., most vertebrates, shrubs, and trees)
Survivorship curves: Illustrate patterns of survival across the lifespan. Include Type I, II, and III patterns.
- Type I: High survival early and middle, and death rates increase in old age.
- Type II: Uniform death rate across the lifespan
- Type III: High mortality early in life, with survival rates improving later in life.

Mark-recapture techniques: Used to estimate population size, especially for mobile organisms
- Capture, tag, release animals
- Recapture animals, record number of marked and unmarked animals in the second capture
- Calculate population estimate: (Number marked × total of capture 2) / number of marked found in the second capture
Other methods: Counting individuals outright, or counting signs of an individual (foot prints etc) to get relative density estimates. Remote sensing technology has improved counting of individuals.

Exponential growth: Describes population growth in ideal (unlimited resource) environments.
- Growth rate is constant (rmax).
  - The growth rate stays the same, but the numbers of individuals change.
Per capita birth rate: Number of births per individual
Per capita death rate: Number of deaths per individual
Per capita rate of increase: Per capita birth rate minus per capita death rate. A positive value indicates population growth, and a negative value indicates population decline.
Formula for population growth (change in population size / given time): change in N / change in T = rN (r = per capita rate of increase, N = pop. size)
Important Note: The exponential growth model assumes unlimited resources. In reality, populations rarely undergo exponential growth for long stretches of time. Environmental limitations such as resources and competition eventually influence population growth.