Foraging

Animals acquire resources in countless ways. Temporal perception is useful in many of them. For example, speciation mechanisms are undoubtedly related to competitive exclusion in competition for resources. This provides a force for sympatric speciation via resource partitioning in time. In this case, animals forage at different times of day but still eat the same foods, as is observed in several species of tern, lizards, crustaceans, and gastropods (Schoener, 1970, 1974). This reduces competition while simultaneously economizing resource acquisition in a kind of temporal ideal free distribution (for a description of the ideal free distribution in space, see Milinski and Parker, 1991). Whether these behaviors are learned remains to be established.

An area that seems most promising for the discovery of event timers in the wild is in the empirical testing of optimal foraging theory. A basic assumption of optimal foraging theory is that animals recognize something about resource dis tribution (the psychophysical evidence for this was discussed in Section 4.2.2). This recognition can be more or less behaviorally plastic, depending on the cognitive faculties of the animal. If resource distribution is relatively stable over time, a species may evolve a patch departure schedule that is based on generations of trial and error without regard for the present environmental conditions. At the other extreme, animals with event timers could measure the rate of food intake at different patches or with different foods and compare them to optimize foraging schedules in the future. Animals could also measure the time between patches and incorporate this information into the overall strategy. This updating of foraging behavior based on prior information is commonly referred to as Bayesian foraging (Getty and Krebs, 1985; Killeen et al., 1996). This is in direct contrast to the assumptions of the marginal value theorem, which assumes that animals know resource distribution, transit, and handling times even before they begin foraging (Charnov, 1976; Valone and Brown, 1989). While the marginal value theorem provides a useful null model against which to compare animal behaviors, it does not require an event timer per se, as animals may evolve to forage at optimal schedules. However, when resource distributions change over the lifetime of the animal, an event timer will be required for animals to appropriately update their Bayesian expectations. The study of Bayesian foraging behavior in organisms amenable to molecular and genetic study would provide another promising inlet into the mechanisms involved in sensing and integrating information about temporal intervals into future behavior patterns.

Bayesian foraging behavior is also likely to be ubiquitous. Many animals require patch assessment before they can make optimal foraging decisions (Valone and Brown, 1989). Constraints on forager memory and resource changes over time force the reinvestigation of patches (Belisle and Cresswell, 1997). Animals use recent information about temporal aspects of resource distribution to make decisions about patch departure. Among central place foragers, there is a positive correlation between distance traveled to the foraging site and the patch residence time (see Bateson, this volume; Kacelnik, 1984).

Studies of risk-sensitive foraging show the ability of animals to detect the variance of resource acquisition even when the mean is unchanged (Real and Caraco, 1986). For example, honeybees prefer stable rewards to unstable rewards, regardless of the mean. This requires an event timer. The adaptive explanation for stable vs. unstable preferences is described by Bateson (this volume).

The data on animal preferences do notentirely corroboratethetheory ofrisk-sensitive foraging (Bateson and Kacelnik, 1998; Ha et al., 1990; Stephens, 1980). Explanations for this are based on cognitive constraints related to time perception and memory. Animals may discount time in different ways, depending on past experience or genetic predisposition, or they may average rate intake over different intervals. Animals also have certain constraints on their abilities to discriminate event times, as typified by Weber's law (Bateson and Kacelnik, 1998; described in Section 4.2.1). I suggested earlier that animals may suffer from distorted perceptions of time based on intake rate. The consequences for rate-biased time perception have been described by Hills and Adler (2002).

The order of experiences also appears to play a role in event timing. A kind of first impression among animals, called side bias, sometimes confounds psychophys-ical results (Ha et al., 1990). Side bias generally refers to some unknown force controlling the animal's behavior. Experimenters typically make an effort to remove these animals from the analyses. Nonetheless, every animal may experience this kind of bias with variable time reinforcement schedules. Large initial rewards could lead to particularly strong cognitive bias. A series of large rewards might also instill a memory of a rare event that keeps the animal coming back. Exactly how the temporal sequence of events establishes memory biases is still an open question.

Another temporal factor in foraging is the effect of time horizons (Krebs and Kacelnik, 1984). Time horizons affect the behaviors of animals that are able to anticipate the ends of foraging bouts. Late in the day an animal may choose to continue foraging in a poor patch because it does not have enough time to get to a better one. A mechanism to avoid this problem involves organizing a series of patches in time and visiting them so as to maximize resource gain over the duration.

Traplining fits the criteria of serial patch arrangement. It is a behavior seen in bats and a number of birds and frugivorous primates. It involves following a pre-specified path during the daily foraging bout (Bell, 1991). Time horizons undoubtedly affect traplining schedules, but once scheduled, traplining provides a short-term answer to the time horizon problem. A similar behavior pattern is cropping. Cropping involves visiting locations at intervals that allow for resource replenishment. Cody (1971) observed various species of finches cropping seeds in the Mohave Desert at the base of a mountain range. These birds moved their foraging sites to different distances from the mountain each day, scheduling revisitation rates to match replenishment rates. Insect-eating shore birds also appear to crop along the shore. Consistent with these observations, lab experiments on cache recovery in scrub jays (Aph-elocoma coerulescens) show that they can learn and recall what, where, and when information about stored food items for up to 5 days (Clayton and Dickinson, 1998). In some manifestations of cropping, an event timer could help an animal know when to return to a foraging site.

Exploring EFT

Exploring EFT

EFT stands for Emotional Freedom Technique. It works to free the user of both physical and emotional pain and relieve chronic conditions by healing the physical responses our bodies make after we've been hurt or experienced pain. While some people do not carry the effects of these experiences, others have bodies that hold onto these memories, which affect the way the body works. Because it is a free and fast technique, even if you are not one hundred percent committed to whether it works or not, it is still worth giving it a shot and seeing if there is any improvement.

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