Biotic Interactions Part II

Predation

Consumption of an organism by another (prey must be alive when predator first attacks it)

*Not included detritivore

Predation enhances

Fitness of predator and reduces fitness prey (± interaction) the

Three key reasons predation is vital in ecology

1) Restricts abundance and distribution of prey population

2) Influences/determines community organization 

3) Its a major selective force

Native Species

Usually on an island, no natural adaptations for predators/prey.

Red Queen Hypothesis 

(Van Valen 1973) 

Predators (Coevolution) 

Continuously strive to improve in capturing, killing and consuming prey efficiently. 

Preys (coevolution)

Constantly improving skills to fight against or evade capture + consumption by predators 

Examples of Adaptations in Predators

• Birds of prey have keen eyesight

• Camouflage allows predators to blend in 

• Venomous snakes have poisonous venom

• Treefrogs have special pads on feet. 

• King snakes are immune to venom of venomous snakes

Two ways to classify predators

1) Classifications #1: Based on taxonomy/trophic level.

• Easy to understand BUT not useful.

2) Classifications #2: Function or mechanism involved in the predatory behavior. 

• Provides info about rate that predator plays in ecosystem/community. 

Classification 1

• Omnivores - Autotrophs/heterotrophs

• Herbivores - Autotrophs digest cellulose

• Carnivores - Heterotrophs capture and kill prey. 

Classification 2 

A) True Predators - Kill prey, several different prey (eat only parts).

B) Grazers - Attack a great # of prey, remove only part of each prey individual (rarely lethal). Effect on the prey individual variable.

C) Parasites - Consume parts of prey (host). Attacks are rarely lethal, [] one or very few prey. 

D) Parasitoids - (Insects - Hymenoptera and Diptera). Body invaders (Wasp larva). 

Types of Model

• The Lotka-Volterra model of Predation (Alfred Lotka and Vito Volterra 1927-1928) 

• The Lotka-Voltera model of Predator-Prey relationships 

Effects of predator-prey relationships on population growth (Condition)

This model excludes causes of cannibalism or intraspecific predation

Equation (prey and predation)

Predator:

dN/dt = -cpP

Prey:

dp/dt = rp

Predator-Prey Lotka-Volterra (assumptions) 

1) Feeding interactions between specialist predator and its prey 

2) Predator/prey move randomly

3) Greater probability of encounters between predator and prey

Shape assumptions of Predator/prey lotka volterra.

• If NO predator population, prey population increases with exponential growth model. 

• Absence of prey, assume predator population decline exponentially (Natural death rate (cp). 

Predator/prey oscillations cycles in abundance

Assumes dynamics of both species are highly related. (ex; snow shoe hare and Canadian Lynx)