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Objectives - Chapter 14 1. 2. 3. 4. What is an exploitative interaction? Define Functional response Define Numerical response Describing predator/prey interactions mathmatically (Lotka Volterra models) Exploitation (Predation, etc.) • Most important biological interactions Consumption of one organism (or part thereof) by another Exploitation (Predation, etc.) Predator and prey Kill and consume Exploitation (Predation, etc.) Herbivore and plant Consume, but may not kill Exploitation (Predation, etc.) Parasite and host Consume, but may not kill, reducing fitness H. Bogert with Leeches Hirudinea Leech Leech Parasites • Eat only one or two different organisms during a lifetime--- as opposed to other types of predators (e.g., grazers that eat a large number of plants) • Host and habitat are the same!!! • Leopold - “parasites kill far more organisms than we know” - selection pressure Exploitation (Predation, etc.) Parasitoid and insect Consume and kill Exploitation (Predation, etc.) Pathogen Disease, debilitating conditions of host Exploitation Many relationships not clear cut E.g., Competition between two organisms where one eats the other. Exploitation Many relationships not clear cut E.g., Herbivore killing plant it feeds on Exploitation (Predation, etc.) Definitions of each are problematic---Common to all interactions: One organism living at the expense of another. Responses of Consumer Species to Variation In the Abundance of Their Food Species As the density of the food species increases, the consumer species responds by: 1. Increasing the rate at which they eat the food species. “Functional Response” In Type 1 exploitation interactions, time required to find prey (search time) is the only factor limiting consumption rate. Increasing abundance of food organism proportionally reduces searching time, increasing rate of prey consumption. Consumption rate increases until consumers cannot eat any faster (Satiation) Consumption Rate Theoretical Functional Response Curves Satiation Lo Prey Density Hi In Type 2 exploitation interactions, consumption rate is influenced by two separate processes: Searching “Handling” At low prey density, searching time limits consumption rate. At moderate prey density, handling time limits consumption rate. At high prey density, predator consumption rate limited by satiation. Consumption Rate Theoretical Functional Response Curves Satiation Lo Prey Density Hi Theoretical Functional Response Curves In Type 3 exploitation interactions, the consumer eats multiple food species. When a food species is rare, the consumer may ignore it and focus on consuming more common species. As a food species becomes more abundant, the consumer switches to eating more of that species. Prey Switching and Learning Curve Limit Prey Consumption Here Responses of Consumer Species to Variation In the Abundance of Their Food Species As the density of the food species increases, the consumer species responds by: 2. Increasing population size due to increased survivorship and reproduction AND immigration from surrounding areas. “Numerical Response” Predator Responses Numerical Response: 1. Effect of prey on predator reproduction: • Increased food (prey) • Increased growth rate, survivorship • Earlier reproduction, increased offspring/female, increased females • Increased R and r, increased # predators Predator Responses Numerical Response: 2. Effect of prey density on predator migration Increased food Residents remain Increased # predators Predators attracted Numerical Response-Field Examples Brown Lemming 1951 1-5/acre 1952 15-20 1953 70-80 Numerical Response-Field Examples Brown Lemming 1951 1-5 1952 15-20 1953 70-80 Pomarine Jaeger uncommon breeding breeding no breeding 4/mi2 18/mi2 Numerical Response-Field Examples Brown Lemming Pomarine jaeger Short-eared Owl 1951 1-5 1952 15-20 1953 70-80 uncommon no breeding breeding 4/mi2 breeding Absent one record breeding 3-4/mi2 18/mi2 Numerical Response-Field Examples 1951 1-5 1952 15-20 1953 70-80 uncommon no breeding breeding 4/mi2 breeding Short-eared Owl Absent one record Snowy Owl Scarce no breeding breeding .2-.5/mi2 many non breeding 3-4/mi2 breeding .2-.5/mi2 few non Brown Lemming Pomarine jaeger 18/mi2 Responses of Consumer Species to Variation In the Abundance of Their Food Species As the density of the food species increases, the consumer species responds by: 3. Combination of #1 and #2. “Combined Response” Mini Summary: To regulate the food species population, the consumer population must be able to eat food organisms faster than they can reproduce, as determined by: 1. Consumption rate: (Functional Response). 2. Consumer Species Rate of Increase: (Numerical Response) 3. Combined Response of Consumer Species 4. Consumer Efficiency: Number of food organisms required to produce a new consumer organism. Lotka Volterra Predator-Prey Model Prey Model - Figure 14.16 dNh/dt = rhNh - pNhNp dNh/dt = Rate of prey population change rh = intrinsic growth rate of prey p = ingestion efficiency Nh = density of prey Np = density of predators Lotka Volterra Predator-Prey Model Predator Model – Fig. 14.16 dNp/dt = cpNhNp - dpNp dNp/dt = rate of predator change c = production efficiency of predator p = ingestion efficiency Nh = density of prey dp = death rate of predator Np = density of predators Lotka Volterra Predator-Prey Model Predator population Predator decreasing Predator increasing Prey population Lotka Volterra Predator-Prey Model Predator isocline Predator population Predator decreasing Predator increasing Prey population Lotka Volterra Predator-Prey Model Predator population Prey decreasing Prey increasing Prey population Lotka Volterra Predator-Prey Model Predator population Prey decreasing Prey increasing Prey population Prey isocline Lotka Volterra Predator-Prey Model Predators decreasing Predator population Prey decreasing Predators increasing Prey decreasing Predators decreasing Predators increasing Prey increasing Prey increasing Prey population Lotka Volterra Predator-Prey Model Predator population Prey population Lotka Volterra Predator-Prey Model Predator population Prey population Lotka Volterra Predator-Prey Model Predator population Prey population Predator-Prey Model Question: 1. Are prey species populations being regulated by density dependent or density independent controls? 2. What about the predator species? Summary for Today • Types of exploiters • Functional response • Numerical response predator reproduction predator migration Lotka Volterra predator-prey model
