Chapter 6: Population and Community Ecology

Key Ideas There are clear patterns in the distribution and abundance of species across the globe. Understanding the factors that generate these patterns can help us preserve global biodiversity. These factors include the ways in which populations increase and decrease in size and the ways in which species interact with one another in their communities

Population Characteristics population size (N) population density population distribution population sex ratio population age structure

Population Dispersal Patterns Random Clumped Uniform

Factors that Influence Population Size Density-dependent factors- the size of the population will influence an individual ’ s probability of survival. Density-independent factors- the size of the population has no effect on the individual ’ s probability of survival. Carrying capacity (K)

population growth birth immigration

population decline death emigration

carrying capacity environmental resistance exponential growth logistic growth population time population growth biotic potential

Fig. 6-12, p. 121 Logistic Growth of Sheep Population Overshoot Carrying Capacity Year Number of sheep (millions) dieback

Variations of the Logistic Model If food becomes scarce, the population will experience an overshoot by becoming larger than the spring carrying capacity and will result in a die-off, or population crash.

Estimating Population in the Wild sampling- mark and recapture-

Assumptions for validity of mark and recapture techniques tagging does not change the behavior of the animal tagged animals must have time to freely mix with the rest of the population animals must be captured randomly

Species Interactions

Keystone Species play critical ecological roles top predators pollinators engineers

Competition interspecific intraspecific resource partitioning reduces competition

Mutualism Mutualism- A type of interspecific interaction where both species benefit.

Ecological Succession Change Over Time

primary succession

secondary succession

Aquatic Succession