THE BEHAVIOUR OF PREDATORS

THE BEHAVIOUR OF PREDATORS The food of Predators is determined by 1. The type of prey – preference (selection) 2. The density of the prey

THE BEHAVIOUR OF PREDATORS Predators show a PREFERENCE when they select prey: Preference is shown when the proportion of a food type in the diet is higher than the proportion available to the animal

Wagtails select (red) a smaller size of fly than that available (green)

THE BEHAVIOUR OF PREDATORS Predators show SWITCHING when a prey type is initially rare then becomes abundant when rare the predator ignores it when common the predator shows preference

Predators are selecting if red line is above broken line

THE BEHAVIOUR OF PREDATORS The food of Predators is determined by 2. The density of the prey Animals eat more when there is more available to eat. This is called the FUNCTIONAL RESPONSE. Identified by C.S. (Buzz) Holling 1959 (from UBC). The functional response is the relationship between the amount a single predator eats relative to the density of prey available The simple relationship is a TYPE I

TYPE I FUNCTIONAL RESPONSE – Reindeer eating lichens

SATIATION and HANDLING Reasons for changes in food intake rate 1. There is a finite stomach capacity - satiation 2. There is a finite amount of time in a day to handle prey. Handling time includes: Catching Killing Eating Digesting With high numbers of prey eventually all time is taken up with handling. Results in a curve called the TYPE II FUNCTIONAL RESPONSE

The different types of FUNCTIONAL RESPONSE Density ->

TYPE II FUNCTIONAL RESPONSE

Type II Functional Response of Bay-breasted warblers to outbreaks of spruce budworm larvae – eastern Canada

TYPE II FUNCTIONAL RESPONSE - lynx feeding on snowshoe hares, northern Canada

TYPE II FUNCTIONAL RESPONSE - kestrels feeding on voles Bank voles feeding on shrubs

TYPE III FUNCTIONAL RESPONSE Occurs when the prey is initially rare and the predator ignores it, then switches to eating this prey when it becomes more common. Results in an S-shaped curve

TYPE III FUNCTIONAL RESPONSE

TYPE III FUNCTIONAL RESPONSE – harriers (raptors) feeding on grouse chicks

NUMERICAL RESPONSE Reasons why numbers level off as prey density increases: 1. Searching efficiency declines due to interference between predators – often with insects 2. Territoriality - sequesters space and limits numbers - another form of interference

Predatory mites searching leaves for prey mites = prey/min

NUMERICAL RESPONSE

NUMERICAL RESPONSE – warbler breeding numbers relative to food density

NUMERICAL RESPONSE – wolf numbers relative to moose density, Ontario

TOTAL RESPONSE By multiplying the proportion of prey population killed by each predator (Functional response) and the number of predators we get the total proportion of prey killed by the predator population, called the TOTAL RESPONSE %Total killed by the predator population (TR) = %killed by one predator x number of predators

Total response – Woodpeckers feeding on beetle larvae

Total response – Warblers feeding on spruce budworm larvae

Total response – mice and shrews feeding on sawfly cocoons (a kind of wasp) Total response – wolves feeding on moose in Ontario

Inverse density dependent predation of small predators on bird nests in forest fragments - eastern forests of USA = Type II FR

Total response and prey recruitment - Type II FR C is stable B is unstable Total response = % predation %

TOTAL RESPONSE TYPE II NOTES 1. Occurs when there is a Type II functional response 2. The predator has another food source, the primary prey on which it depends 3. There is no refuge for the prey There can be different levels of predation, with different consequences: Curve i). System stabilizes at C, predator cannot eliminate prey Curve ii) There is a stable point at C, and an unstable threshold at B. If prey numbers are reduced below B for some other reason, then predators can cause extinction of Curve iii) Highest level of predation – above the prey recruitment curve at all prey densities. This system cannot exist except as a transition phase to extinction. There are no stable points.

RED FOX – supported by rabbits could eliminate the smaller Marsupials in Australia

MOOSE – spread through BC and support higher populations of wolves

WOLF

CARIBOU – in BC reduced to extinction by wolves which are maintained by Moose

Caribou in BC forests - r declines faster at small numbers due to Inverse density dependent predation from wolves

Total response and prey recruitment - Type III FR % Prey NET recruitment Total response = % predation % Prey density

TOTAL RESPONSE TYPE III NOTES 1. Occurs when there is a Type III functional response 2. The predator depends on this prey, the primary prey 3. The predator cannot cause extinction because at low prey densities predation is density dependent. There is always a stable point at A There can be different levels of predation, with different consequences: Curve i). System stabilizes at A, predators regulate prey at all prey densities Curve ii) There is a stable point at C, predators eat starving prey. Curve iii) There are two stable points A,C and an unstable boundary B between them. If high prey numbers are below B the system collapses to A. Alternatively if low prey numbers are allowed to increase above B then system outbreaks to C.