Resource Acquisition & Allocation Optimal Foraging Theory

1. Resource Acquisition & AllocationOptimal Foraging Theory

2. Resource Acquisition & AllocationForaging tactics and efficiency • Foraging has costs (exposing yourself as a prey item) and takes time/energy • An optimal foraging tactic maximizes the difference between foraging profits and their costs • This should be under very strong natural selection!

3. Resource Acquisition & Allocation • Consider the benefits/costs of chasing prey that are of relatively poor nutritional value • What about the cost/benefit associated with caloric return (small vs. large; easy vs. hard) • Natural routes should be favored • Good locations should be checked • These will vary across the landscape

4. Resource Acquisition & AllocationOptimal Foraging Theory • Numerous aspects of OFT can be neatly summarized into a series of assumptions • A) environmental structure is repeatable, with some statistical expectation of finding a particular resource (such as a habitat, microhabitat, and/or prey item)

5. Resource Acquisition & AllocationOptimal Foraging Theory • b) food items can be arranged in a continuous and unimodal spectrum, such as size distributions of insects • c) similar animal phenotypes are usually closely equivalent in their harvesting abilities (e.g intermediates); also similar sized prey are only slightly less efficient than the optimal sized prey

6. Resource Acquisition & AllocationOptimal Foraging Theory • d) the principle of allocation applies, and no one phenotype can be maximally efficient on all prey types (trade-off in efficiencies) • e) an individual’s economic goal is to maximize its intake of food resources

7. Resource Acquisition & AllocationOptimal Foraging Theory • MacArthur breaks foraging down into four phases: • 1) deciding where to search • 2) searching for palatable food items • 3) upon locating a potential food item, deciding whether or not to pursue it • 4) pursuit itself, with possible capture and eating

8. Resource Acquisition & AllocationOptimal Foraging Theory • Search and pursuit efficiencies are largely determined by the preceding assumptions about foraging morphology • Thus MacArthur only consider 1 and 3 • 1) deciding where to search • 2) searching for palatable food items • 3) upon locating a potential food item, deciding whether or not to pursue it • 4) pursuit itself, with possible capture and eating

9. Resource Acquisition & AllocationOptimal Foraging Theory • Where to search can largely be the result of previous foraging attempts • Which prey items to select is also relatively straightforward; however, one does has to decide whether to pursue it or continue searching for something better

10. Resource Acquisition & AllocationOptimal Foraging Theory • Ultimately, the predator will chase again, so then the real question becomes whether they will find another, better prey item in the time required to capture and ingest the first prey item

11. Resource Acquisition & AllocationOptimal Foraging Theory • Many animals spend the majority of the effort searching for prey, but relatively little capturing and eating small prey items (e.g. “searchers”)

12. Resource Acquisition & AllocationOptimal Foraging Theory • Conversely, many animals spend little time searching, but a great deal of time/effort in capturing it • Consequently, pursuers should generally be more selective and more specialized than searchers

13. Resource Acquisition & AllocationOptimal Foraging Theory • Currently the currency for which OFT operates is energy gained/time • Incorporating limiting nutrients or predation risk have not been widely incorporated

14. Resource Acquisition & AllocationOptimal Foraging Theory • Carnivorous animals forage in a number of interesting ways • ‘sit and wait’ vs. ‘actively foraging’

15. Resource Acquisition & AllocationOptimal Foraging Theory • What conditions are required to support a sit-and-wait strategy (1 or more) • 1) relatively high prey density • 2) high prey mobility • 3) low predator energy requirements

16. Resource Acquisition & AllocationOptimal Foraging Theory • For the ‘searchers’, prey density and mobility are also important, but the spatial distribution of prey is paramount

17. Resource Acquisition & AllocationOptimal Foraging Theory • Even for groups that appear relatively consistent, subtle differences show why this paradigm has conceptual value

18. Resource Acquisition & AllocationOptimal Foraging Theory • There are some general correlates between these foraging modes

19. Resource Acquisition & AllocationOptimal Foraging Theory

20. Resource Acquisition & AllocationOptimal Foraging Theory • Herbivores can similarly be viewed • Herbivores spend relatively little energy in finding their prey, but more breaking down the chemical compounds and absorbing the nutrients

21. Resource Acquisition & AllocationOptimal Foraging Theory • Because carnivore prey is composed of readily available proteins, lipids, and carbs(and easily digestible), carnivores can afford to expend considerable effort in searching for their ‘optimal’ prey

22. Resource Acquisition & AllocationOptimal Foraging Theory • Many carnivores have extremely efficient (and elaborate) capturing aparatii

23. Resource Acquisition & AllocationOptimal Foraging Theory • Holling estimated the diameter of prey item that should be optimal for a praying mantid of a particular size

24. Resource Acquisition & AllocationOptimal Foraging Theory • He then offered a hungry mantid prey items that varied in size. They were reluctant to attack small or large prey items

25. Resource Acquisition & AllocationOptimal Foraging Theory • Because small organisms are disproportionately more abundant than large ones, most predators encounter and eat many more small items than large ones, irrespective of their own size (although must still be energetically profitable) • Who (size) should have a larger diet breadth?

26. Resource Acquisition & AllocationPhysiological Ecology • Environmental physiology is how organisms function within, adapt and respond to, and exploit their physical environments • PE’s are primarily interested in the immediate functional and behavioral mechanisms by which organisms cope with their abiotic environments • Mutual constraints between physiology and ecology dictate that both must evolve together

27. Resource Acquisition & AllocationPhysiological Ecology • Homeostatis: the maintenance of a stable internal state across a range of environmental conditions • Can be achieved by physiological means and/or behavioral • Many factors need to be controlled besides temperature: humidity, light intensity, and various concentrations (e.g. pHs, salts)

28. Resource Acquisition & AllocationPhysiological Ecology • What is the benefit of all of this?

29. Resource Acquisition & AllocationPhysiological Ecology • Physiological Optima and Tolerance Curves • Physiological processes proceed at different rates under different conditions • They typically look like bell-curves

30. Resource Acquisition & AllocationPhysiological Ecology • Performance curves

31. Resource Acquisition & AllocationPhysiological Ecology • Performance curves can sometimes be altered during the lifetime of an individual, especially as it becomes exposed to different ambient external conditions • Clearly tolerance curves change over evolutionary time, but little is known about the evolution of tolerance acclimation

32. Resource Acquisition & AllocationPhysiological Ecology • Performance or tolerance is often sensitive to two or more environmental variables • For example, temperature and humidity can impact the performance of many things

33. Resource Acquisition & AllocationEnergetics • A relatively high % of food passes through the gut unused (80 to 90) • Food is digested and assimilated and some is used for respiration and metabolic activity • The remainder is incorporated into the animal concerned as secondary productivity (growth or reproduction)

34. Resource Acquisition & AllocationEnergetics • Ingestion = assimilation + egestion • Assimilation = productivity + respiration • Productivity = growth + reproduction • The total amount needed per unit time for maintenance increases with increasing body mass

35. Resource Acquisition & AllocationEnergetics • Metabolic rates vary on several key aspects

36. Resource Acquisition & AllocationEnergetics • Because small organisms have a very high SA/vol ratio, they have a much higher metabolic rate (scaled to mass)

37. Resource Acquisition & AllocationEnergetics • Because energy is required to maintain a constant internal body temperature, homeotherms have considerably higher metabolic rates, as well as higher energy needs than poikilotherms (approximating temperature is that of the environment) of the same body mass • Related terms: endotherm & ecotherm

38. Resource Acquisition & AllocationEnergetics • The vast majority of animals are ectothermic and all plants are as well • Some of the larger poikilotherms are at times at least partially endothermic • Behavior allows for increased efficiencies

39. Resource Acquisition & AllocationEnergetics • Because of the energy requirements to maintain a constant body temp no matter what the conditions, endotherms have considerably higher metabolic rates

40. Resource Acquisition & AllocationEnergetics • There is a distinct lower limit on body size for endotherms (2-3; humm and shrew…niche?)

41. Resource Acquisition & AllocationEnergetics

42. Resource Acquisition & AllocationEnergetics