Predation – what is it? One animal kills another for food ( + - interaction ) One animal kills another for food ( + - interaction ) Parasitism / Parasitoidism Herbivory

Any ecological process in which energy and matter flow from one species to another. Any ecological process in which energy and matter flow from one species to another. Predation One organism consumes another in the classic “+ -” interaction: carnivore herbivore parasite / parasitoid (virus, bacteria, etc) ‘cannibalism’ One organism consumes another in the classic “+ -” interaction: carnivore herbivore parasite / parasitoid (virus, bacteria, etc) ‘cannibalism’

Why do we care? 1. Predation can act as a force to structure communities. 2. Predation can act as a mechanism for natural selection. 3. Predation can control species distribution or density. Keystone predator Regulation Trophic cascades

Lotka-Volterra: classic 2-species model Primary Assumptions ● all individuals represented by the average ● linear relationship between predator and prey ● no time lag in response ● exponential growth, no K

(Begon et al p. 118) Reality

Gause 1934 – rotifer vs. protist unmanipulated prey refuge added “immigration”

Huffaker 1958 – mites and oranges Initial results – similar to Gause, simple systems were incapable of sustaining coexistence Initial results – similar to Gause, simple systems were incapable of sustaining coexistence Coexistence was only possible with extreme environmental heterogeneity “hide and seek” Coexistence was only possible with extreme environmental heterogeneity “hide and seek” Eotetranychus sexmaculatus vs. Typhlodromus occidentalis

Adding reality to model predictions: C.S. Holling 1959 Adding reality to model predictions: C.S. Holling 1959 II III IV I Individual predation rate Prey density

2 types of predator response: 2. Numerical: Increase in the total number of predators - reproduction - aggregation 2. Numerical: Increase in the total number of predators - reproduction - aggregation 1. Functional: Change in the rate of predation by an individual predator - ‘search image’ - ‘prey switching’ 1. Functional: Change in the rate of predation by an individual predator - ‘search image’ - ‘prey switching’ Holling 1959

2 types of predators: Generalists Specialists

Krebs et al Specialist numerical response:

Quick review Simple dynamics (L-V) predicts a steady cycle This cannot be re-created empirically without interference by the investigator In reality, we observe a wide variety of dynamics - cycles- stability - extinction- chaos - periodic fluctuations Simple dynamics (L-V) predicts a steady cycle This cannot be re-created empirically without interference by the investigator In reality, we observe a wide variety of dynamics - cycles- stability - extinction- chaos - periodic fluctuations What factors control whether predator/prey interactions are stable? What factors control whether predator/prey interactions are stable?

Stabilizing Factors influencing stability Destabilizing Type III functional response Refugia Generalist predator Low predator efficiency Complex systems multiple predator spp. multiple prey spp. prey switching Complex systems multiple predator spp. multiple prey spp. prey switching Time lags Specialist predator High predator efficiency Simple systems

Summary ● Factors that influence coexistence: predator efficiency, system complexity refugia, time lags ● Factors that influence coexistence: predator efficiency, system complexity refugia, time lags ● Predation involves energy and matter flowing from one species into another (+ -). ● Predation involves energy and matter flowing from one species into another (+ -). ● Holling’s Type I, II, III curves ● Generalist vs. specialist, numerical vs. functional ● Predation can: act as an agent of selection structure communities regulate populations ● Predation can: act as an agent of selection structure communities regulate populations