objectives - chapter 14

Objectives - Chapter 14

1. What is an exploitative interaction?

2. Define Functional response

3. Define Numerical response

4. Describing predator/prey interactions mathmatically (Lotka Volterra models)

Exploitation (Predation, etc.)

• Most important biological interactions - Consumption of one organism (or part thereof) by another


Predator and prey

Kill and consume


Herbivore and plant

Consume, but may not kill


Parasite and host

Consume, but may not kill, reducing fitness

H. Bogertwith

Leeches

Hirudinea

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


Parasitoid and insect

Consume and kill


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


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”

Theoretical Functional Response Curves

In Type 1 exploitation interactions, time required to find prey (search time) is the only factor limiting consumption rate.

Satiation

Increasing abundance of food organism proportionally reduces searching time, increasing rate of prey consumption.

Consumption rate increases until consumers cannot eat any faster (Satiation)

Lo Prey Density Hi

Co

nsu

mp

tio

nR

ate


In Type 2 exploitation interactions, consumption rate is influenced by two separate processes:

Searching“Handling”

Satiation

At low prey density, searching time limits consumption rate.

At moderate prey density, handling time limits consumption rate.

Lo Prey Density HiLo Prey Density Hi C

on

sum

pti

on

Rat

e

At high prey density, predator At high prey density, predator consumption rate limited by consumption rate limited by satiation.satiation.


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



2. Increasing population size due to increased survivorship and reproduction AND immigration from surrounding areas.

“Numerical Response”

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

Predator Responses

Increased food

Increased # predators

Predators attractedResidents remain

1951 1952 1953

Brown Lemming 1-5/acre 15-20 70-80

Numerical Response-Field Examples

1951 1952 1953

Brown Lemming 1-5 15-20 70-80

Pomarine Jaeger uncommon breeding breeding

no breeding 4/mi2 18/mi2


1951 1952 1953Brown Lemming 1-5 15-20 70-80

Pomarine jaeger uncommon breeding breeding


Short-eared Owl Absent one record breeding3-4/mi2


1951 1952 1953Brown Lemming 1-5 15-20 70-80

Pomarine jaeger uncommon breeding breeding


Short-eared Owl Absent one record breeding3-4/mi2

Snowy Owl Scarce breeding breedingno breeding .2-.5/mi2 .2-.5/mi2

many non few non




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.

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



Prey population

Predatorpopulation Predator

increasingPredator

decreasing


Prey population

Predatorpopulation

Predator isocline

Predatorincreasing

Predatordecreasing

Prey population

Predatorpopulation

Preyincreasing

Preydecreasing



Prey population

Predatorpopulation

Prey isoclinePrey

increasing

Preydecreasing

Prey population

Predatorpopulation

Preyincreasing

Preydecreasing

Preyincreasing

Preydecreasing

Predatorsincreasing

Predatorsdecreasing

Predatorsincreasing

Predatorsdecreasing



Prey population

Predatorpopulation

Question:

1. Are prey species populations being regulated by density dependent or density independent controls?

2. What about the predator species?

Predator-Prey Model

• Types of exploiters

• Functional response

• Numerical response

predator reproduction

predator migration

Lotka Volterra predator-prey model

Summary for Today

objectives - chapter 14

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