Can generalists predators be a effective bio-control agents?

1. Some business to take care of:
-- Go to your lab this week. Read through Chapter 4, as well as Chapter 12
BEFORE lab.
-- There is a new lab on Tuesday afternoon. If you wish to switch to this lab,
we can allow some movement this week. However, it needs to be done
unofficially, so that it doesn’t require drop-add. Check with me, if you wish to
switch to this early evening lab.
-- Lecture powerpoints can be downloaded from website, along with lots of
other really good stuff. http://bio.fsu.edu/~miller/BSC3402L/
-- There are always lots of seminars on campus. If you have aspirations for
graduate school or are just curious, we encourage you to attend. This week,
there is:
-- January 15: Dr. George D. Weiblen, University of Minnesota, St. Paul
Ecological specialization of tropical insect herbivores: insights from phylogeny and
population genetics
-- January 16: Dr. George D. Weiblen, University of Minnesota, St. Paul
Lessons in conservation politics from Papua New Guinea
Both are at 4:00 in this room.

2. I. Purpose of this Course
II. The Scientific Method
III. What are Foragers?
A. Definition of foraging:
-- All behaviors related to obtaining resources
-- Resources are things that increase fitness.
Fitness is relative reproductive contribution
to future generations

3. III. What are Foragers?
A. Definition of foraging:
B. Types of Resources -- different types of
foragers and foraging is associated with
different resources. The “Big 3” categories
are (in no order):
1. Food
2. Sex
3. Shelter

4. III. What are Foragers?
A. Definition of foraging:
B. Types of Resources
1. Food
2. Sex
3. Shelter

5. There are at least six types of predators, based on how they
get their food. These include:
a. true predators
b. grazers
c. parasites
d. parasitoids
e. detritivores
f. plants!

6. True predators kill prey immediately and generally consume
many prey during their lifetime

7. Grazers only consume part of prey, generally without killing, but
also generally consume many prey during their lifetime

8. Human louse
Human flea
Adult heartworms
in dog heart
Parasites consume only part of prey, don't kill, generally live in or
on one to few hosts during lifetime.

9. Anaphes flavipes
(cereal beetle
parasitoid)
Pseudacteon curvatus, a
South American species
that parasitizes fire ants
in the saevissima
complex
Parasitoid from
film “Aliens”
Parasitoids are usually insects with a free living adult which
forage for a living host on or in which to lay eggs. Larvae usually
kill host. Often disgusting.

10. Scavengers consume dead or rotting flesh (note distinction!).

11. Plants don’t fall into these categories well because they have
abiotic resources, but they clearly forage for these resources.
Hydrocotyle bonariensis

12. Carnivorous plants are active true predators

13. III. What are Foragers?
A. Definition of foraging:
B. Types of Resources
1. Food (different types of foragers)
2. Sex
3. Shelter

14. sex

15. sex
Rock-Paper-Scissors
In side-blotched lizards, males
can have either orange, blue, or
yellow throats. Orange males
guard large sites with many
females and are dominant over
blue males, that guard smaller
sites with fewer females. Blues
dominate over yellows, which
actually resemble females.
Yellows, however are quite
good at sneaking into orange’s
large territories and mating with
orange’s females.

16. III. What are Foragers?
A. Definition of foraging:
B. Types of Resources
1. Food
2. Sex
3. Shelter

17. shelter

18. III. What are Foragers?
IV. Decision making by foragers.
A. Types of Decisions
B. Balancing Decisions are based on costs/benefits
C. Optimal Diet Model
D. Spatial Distributions of Resources

19. IV. Decision making by foragers.
A. Types of Decisions
-- what to consume?
-- when?
-- how?
-- where?
-- ultimately must balance out different needs
such as food vs. sex or eating vs. being eaten
(remember Lima’s squirrel exp.)
-- The point is that foragers must make a lot of decisions,
often quickly and often combining different needs and
constraints.

20. IV. Decision making by foragers.
A. Types of Decisions
B. Balancing Decisions: costs and benefits
1. Benefits -- resources already discussed,
including food, shelter, and matings.
Must increase fitness.
2. Costs are usually time, energy and
survival. Time is important because it
could be spent garnering more food,
shelter, or mates).
3. Which is more important, Benefits or Costs?
For some organisms, it is just benefits (e.g. “energy maximizers”,
such as hummingbirds). For others, it may be costs (e.g., “time
minimizers”). But, usually, it is some combination of both.

21. IV. Decision making by foragers.
A. Types of Decisions
B. Balancing Decisions: costs and benefits
1. Benefits
2. Costs
3. Which is more important?
If both are important:
-- could use overall benefit (B-C)
-- B/C ratio useful because units don’t
need to match. Example, Energy/time

22. III. What are Foragers?
IV. Decision making by foragers.
A. Types of Decisions
B. Balancing Decisions are based on costs/benefits
C. Optimal Diet Model
D. Spatial Distributions of Resources

23. IV. Decision making by foragers.
C. Optimal Diet Model
1. Logic:
-- foragers see a series of potential prey
-- which to eat and which to ignore?
-- depends on their rank in B/C.
It is thought that many predators are able to estimate
the B/C for each prey type. They can then specialize on
the prey types with higher B/C and ignore the rest

24. IV. Decision making by foragers.
C. Optimal Diet Model
1. Logic
2. Mathematical Model
Consider a predator’s options when it sees a food item. If it
eats that item (call it item i), then it will get benefit Ei (the
energy from item i). The costs are just those associated with
catching and consuming the item hi (called “handling costs”).
So, the value of that item for the predator is

25. IV. Decision making by foragers.
C. Optimal Diet Model
1. Logic
2. Mathematical Model
Now, if the predator decides to skip that prey and search for
another, then the expected value of the next prey would be
the environmental average E, with the average costs (h),
PLUS the costs of searching for the next item, called s. So
the next item has a different value:
First item: Second item:

26. IV. Decision making by foragers.
C. Optimal Diet Model
1. Logic
2. Mathematical Model
So, clearly the predator should take a prey when it sees it if:
Otherwise, the predator should keep searching. And, note
that an experienced predator should know all these values
and, so , should be able to make good decisions, on
average.

27. 3. Predictions based on Ei/hi > E/(s+h)
a. If average search times are long and handling times are
short, then forager should take most prey that it sees --
be a GENERALIST.
b. If search times are short and handling times long, then
predators should be SPECIALIST, taking only high E/h
items.
c. More productive habitats (short s) should lead to more
specialized diets.
d. The abundance of prey not taken should have no effect
on selection of individual prey. That is, the right hand
side of the equation has no s, so ignore low E prey.
(Lousy prey are always lousy, even if common).

28. IV. Decision making by foragers.
C. Optimal Diet Model
1. Logic
2. Mathematical Model
3. Predictions
4. Evidence: an example with fish
Werner, E. E., and D. J. Hall. 1974. Optimal foraging and
the size selection of prey by the bluegill sunfish (Lepomis
macrochirus). Ecology 55:1042-1052.

29. Werner, E. E., and D. J. Hall. 1974. Optimal foraging and
the size selection of prey by the bluegill sunfish
(Lepomis macrochirus). Ecology 55:1042-1052.
Earl Werner fed Daphnia to bluegill sunfish. He gave the
fish Daphnia of three different sizes. He predicted that if
he gave the fish a low density of prey, they should eat
anything. But, if he gave them a higher density, they
should more and more become specialists on just the
better (larger) Daphnia.

30. Optimal diet model would predict that as prey become more
abundant, predators should become more picky (specialists).

31. Example Study for the Week
Goss-Custard, J. D. 1977. Optimal foraging and the size selection of worms by
redshank, Tringa totanus, in the field. Animal Behaviour 25:10-29

32. Their “optimal” prey was
around 7 mm in length.
The most abundant prey
is actually larger.
The redshanks are taking
smaller, less numerous
prey because of the
higher benefit/cost ratio

33. Read the Bee Lab Chapter before lab!
Chapters 4 (not 5) and 12

34. Sutherland, W. J. and R. A. Stillman. 1988. The
foraging tactics of plants. Oikos 52:239-244.
-- long nodes in bad patches, short in good
-- straight in bad patches, turn in good
-- don’t branch in bad environments, do in good