Foragers: Types of Resources and Decision Making

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

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

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. Hydrocotylebonariensis

12. Carnivorous plants are active true predators

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

17. shelter

18. What are Foragers? 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. What are Foragers? 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) If average search times are long and handling times are short, then forager should take most prey that it sees -- be a GENERALIST. If search times are short and handling times long, then predators should be SPECIALIST, taking only high E/h items. More productive habitats (short s) should lead to more specialized diets. 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 (Lepomismacrochirus). 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 (Lepomismacrochirus). 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