1. THE BEHAVIOUR OF PREDATORS

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

3. 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

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

5. 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

6. Predators are selecting
if red line is above
broken line

7. 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

8. TYPE I FUNCTIONAL RESPONSE –
Reindeer eating lichens

9. 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

10. The different types of FUNCTIONAL RESPONSE
Density ->

11. TYPE II FUNCTIONAL RESPONSE

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

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

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

15. 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

16. TYPE III FUNCTIONAL RESPONSE

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

18. 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

19. Predatory mites searching leaves for prey mites
= prey/min

20. NUMERICAL RESPONSE

22. NUMERICAL RESPONSE – warbler breeding numbers relative to food density

23. NUMERICAL RESPONSE – wolf numbers relative to moose density, Ontario

24. 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

27. Total response – Woodpeckers feeding on beetle larvae

28. Total response – Warblers feeding on spruce budworm larvae

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

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

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

33. 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.

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

35. MOOSE – spread through BC and
support higher populations of wolves

36. WOLF

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

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

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

40. 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.