Academic journal article Cognitive, Affective and Behavioral Neuroscience

Decision Ecology: Foraging and the Ecology of Animal Decision Making

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Decision Ecology: Foraging and the Ecology of Animal Decision Making

Article excerpt

In this article, I review the approach taken by behavioral ecologists to the study of animal foraging behavior and explore connections with general analyses of decision making. I use the example of patch exploitation decisions in this article in order to develop several key points about the properties of naturally occurring foraging decisions. First, I argue that experimental preparations based on binary, mutually exclusive choice are not good models of foraging decisions. Instead, foraging choices have a sequential foreground-background structure, in which one option is in the background of all other options. Second, behavioral ecologists view foraging as a hierarchy of decisions that range from habitat selection to food choice. Finally, data suggest that foraging animals are sensitive to several important trade-offs. These trade-offs include the effects of competitors and group mates, as well as the problem of predator avoidance.

Foraging in Patches

In an alpine meadow, a worker bumblebee plows through the air. Its large body and implausibly small wings remind one of an enormous but absurdly miniaturized transport plane. Like their better known relatives the honeybees, bumblebees live in colonies and collect pollen and nectar to feed their developing brood. Foraging bumblebees visit flowers, of course, flying to them and crawling into them to find pools of nectar. A natural meadow is not a uniform floral carpet. Instead, the bumblebee finds flowers in clumps. Most plants, for example, present a small cluster of flowers together on a single stalk called an inflorescence. What sorts of decisions does the bumblebee need to make as it moves through this world of flowers and flower clumps? Of course, it must somehow choose which inflorescence to visit and which flower to visit on the inflorescence. A somewhat less obvious problem is the necessity of deciding whether to stay and exploit another flower on this inflorescence or to leave and find a new inflorescence to exploit.

Many-probably most-animals face leave-versus-stay decisions like this. To understand the advantages or disadvantages of leaving or staying, we need to know how the bee accrues food as it spends time exploiting the inflorescence. Typically, the bee will acquire food fairly quickly at first, so that we would see a roughly linear relationship between nectar gained and the time spent exploiting the inflorescence. This cannot last, because the bee's exploitation eventually depletes the inflorescence, so our plot of gains versus time will start to bend downward (Figure 1) and must ultimately asymptote to some maximum that is set by the limited resources of the inflorescence. So patches exhibit diminishing returns; fresh, unexploited patches yield food quickly, but food gains per unit time inevitably decline. Consider two possible strategies: A patch-exploiting bumblebee could make short visits that "skim the cream," moving quickly on to fresher patches elsewhere. At the other extreme, our bumblebee could exploit each inflorescence thoroughly, working the inflorescence to extract every last dreg of nectar. Which should the bumblebee do?

To answer this question economically, we want to compare the value of staying to the value of leaving. We can use the relationship between exploitation time and food gains discussed earlier to find the value of staying. Obviously enough, if this relationship shows diminishing returns, the value of staying for one more time interval must also decline steadily. To find the value of leaving, however, we need to consider things beyond the current patch. We need to know the value of the bee's options elsewhere: What can it gain if it leaves the patch? This depends on the overall richness of the bee's habitat. In a rich habitat with lots of inflorescences dripping with nectar, the value of leaving is obviously higher than in a poor habitat, where low-quality inflorescences are few and far between. With these elements in mind, the reader can probably piece the whole story together. …

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