Resource Acquisition & Allocation Optimal Foraging Theory

Resource Acquisition & Allocation Foraging 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!

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

Resource Acquisition & Allocation Optimal 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)

Resource Acquisition & Allocation Optimal 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

Resource Acquisition & Allocation Optimal 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

Resource Acquisition & Allocation Optimal 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

Resource Acquisition & Allocation Optimal 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

Resource Acquisition & Allocation Optimal 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

Resource Acquisition & Allocation Optimal 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

Resource Acquisition & Allocation Optimal 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”)

Resource Acquisition & Allocation Optimal 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

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

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

Resource Acquisition & Allocation Optimal 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

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

Resource Acquisition & Allocation Optimal Foraging Theory Even for groups that appear relatively consistent, subtle differences show why this paradigm has conceptual value

Resource Acquisition & Allocation Optimal Foraging Theory There are some general correlates between these foraging modes

Resource Acquisition & Allocation Optimal 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

Resource Acquisition & Allocation Optimal 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

Resource Acquisition & Allocation Optimal Foraging Theory Many carnivores have extremely efficient (and elaborate) capturing aparatii

Resource Acquisition & Allocation Optimal Foraging Theory Holling estimated the diameter of prey item that should be optimal for a praying mantid of a particular size

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

Resource Acquisition & Allocation Optimal 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?

Resource Acquisition & Allocation Physiological 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

Resource Acquisition & Allocation Physiological 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)

Resource Acquisition & Allocation Physiological Ecology What is the benefit of all of this?

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

Resource Acquisition & Allocation Physiological Ecology Performance curves

Resource Acquisition & Allocation Physiological 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

Resource Acquisition & Allocation Physiological 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

Resource Acquisition & Allocation Energetics 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)

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

Resource Acquisition & Allocation Energetics Metabolic rates vary on several key aspects

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

Resource Acquisition & Allocation Energetics 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

Resource Acquisition & Allocation Energetics 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

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

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

Resource Acquisition & Allocation Energetics