Lecture 7: Predation, Parasites, and Pathogens

Types of predation

1. Herbivory

2. Parasitism

3. Carnivory

4. Cannibalism

What influences prey availability?

1. Presence of alternative, preferred prey

2. Size of prey population

3. Vulnerability of different age and sex classes

4. Predator-prey specialization → adapted to one kind of prey

5. Environment and efficiency of predators catching prey

Predator Behaviour

1. Change in prey density

2. Change in predator density (competition)

3. Differences in the degree of clumping of prey

Types of responses

1. Functional response → how are individual predators behaving while feeding

2. Numerical Response → changes in population numbers in response to prey. Reproduction, immigration, and emigration.

3. Growth rate of the resource in relation to resource abundance

Functional Response

Important variables:

• Na = prey eaten per unit time

• h = handling time

• Ts = search time

Predator searching → the role at which predators encounter prey depends on density

Total response curves:

• Type I

• Type II

• Type III

Type I response curve

number of prey found will increase with prey density

• Linear relationship

• Most simplistic and realistic

Assumptions:

• Search randomly for prey

• Unlimitied appetite

• Constant amount of time searching for prey

Type II response curve

decreasig proportion of prey eaten as prey densities rise

• More curved graph

• More like logistic models

Assumptions:

• Limited by capacity to process food

• Search efficiency not constant

• Processing of food and search are mutually exclusive behaviours

Type III response curvve

number of prey caught increases slowly at low prey densities, but quickly at intermediate densities, before levelling out at high densities.

• Prey switching

• Search image

Prey switching

2+ different types of prey

Search image

predators will memorize image of prey, which makes it easier to find and acquire. Birds especiialy do this

Numerical Response

trend of predator numbers against prey density

Increase in prey density → increased predator survival and fecundity → increase in predation population → more prey consumed

What might prey do to avoid predation?

• Migration

• Herding and spacing → safety in numbers

• Birth synchrony → individuals time to have all offspring at once. Predator swamping

Management Implications

• Predation of rare species

• Predators as biological control agents

• Effect of harvesting on prey species

Parasites

Feed on living hosts, don’t always kill them

• Microparasites → virusis, fungi, bacteria (tend to multiply really quickly)

• Macroparasites → anthropods (fleas, ticks), nematodes, cestodes (tapeworms) (can reproduce, but not through multiplication)

Epidemiology

incidence, distribution, and potential control of disease.

Host Populations

1. Susceptibles → haven’t been infected but could be

2. Infected → activelly have parasite/disease

3. Recovered → had parasite/disease and got over it

Types of parasites/diseases

1. Endemic parasites → adapted to their host

• can cause enzootic disease

• chronic impacts on host, not always fatal

2. Epizootic disease → parasites that cause large outbreaks

• short term, major, and fatal

• Equivalent to epidemic diseases in humans

• Eg. Sylvatic plague in black-tailed prairie dogs

How do diseases spread?

• Traits of parasite and host

• Interactions with food and predators

• Human introductions (Eg. EIDs)

• Emerging Infectious Diseases (EIDs) → appearance of new diseases

What are the 3 main pathways of EIDs?

1. Jump from domestic animals to wildlife populations

2. Direct human intervention through translocation of host or parasite

3. No human or domestic animal associations

Parasites and species interactions

• Competition → superior competitors may become infected

• Reducing predation → reduce the efficiency of predators and herbivores

• Increasing prey susceptibility → increase availability of prey for predators

Management Implications

• Transmission to and from humans and domesticated animals

• Invasive species and pests

• Endangered species

• Regulating populations (Eg. House finch may help level out numbers/thin out)