Interactions and population dynamics What drives evolution? All competition driven by limited resources • Intraspecific competition: same species • Interspecific competition: different species What resources are competed over? Anything an organism consumes or uses that increases population growth rate when more available Renewable resources Nonrenewable resources Competitive exclusion principal: two species cannot coexist if they use the same resource Competition generates niches Competitive coexistence: resource partitioning Consequence of resource partitioning: Character displacement Socrative question 1 Predation Keystone species Evolutionary response to predation • Behavioral • Crypsis • Structural • Chemical • Mimicry Behavioral defense Crypsis Structural defense Chemical defense Mimicry Batesian mimicry: harmless species evolves look of poisonous/distasteful species to fool predator Mimicry Mullerian mimicry: well defended species evolve to look similar, so that predators will better learn to avoid them All defenses have a cost What is the evolutionary tradeoff exhibited by these snail species Evolutionary arms race Beneficial species interactions Commensalism Animal-animal mutualists https://www.youtube.com/watch?reload=9&v=8YFKdjtLozc Plant-fungi mutualists: mycorrhizal fungi Ectomycorrhizal fungi Endomycorrhizal fungi Termite-protist mutualists Pollination Seed dispersal Mutualism improves community diversity Socrative question Population dynamics • Study of the size and growth factors of populations • When would this be important? Characteristics of population distributions • Range • Abundance • Density • Dispersion • Dispersal Geographic range All areas that members of a species inhabit during their life (through all stages of life) Endemic species are only found in one area Having a small range in a single area makes species more vulnerable to extinction Abundance Number of individuals that exist within a defined area (doesn’t have to be entire geographic range) Density Number of individuals per unit area Highest density often indicates ideal environment Dispersion Why would a species have a regular dispersion pattern? Why would a species have a clumped dispersion pattern? Dispersal Dispersal Population growth What influences how a population increases/decreases in size? Formula for population growth • • • • dN=change in number of individuals dt=change in time r=growth rate N=starting number of individuals If r is positive? • • • • dN=change in number of individuals dt=change in time r=growth rate N=starting number of individuals Would you expect to find persistent exponential population growth in nature? Renewable resources Nonrenewable resources Carrying capacity (K) Competition Disease Environment Water supply Space Etc. Logistic growth model: includes constraints on growth Fast versus slow reproduction and growth High parental care k-selected Rapid growth r-selected Prey r-selected Long lifespan k-selected Survivorship Curves reflect life history strategies Socrative question
