Examples

Example 1: Rufous Hummingbirds

Carpenter et al. (1983) found a way to test optimal foraging theory, using Rufous Hummingbirds. These hummers establish feeding territories during stops on their 2000-mile migration between their breeding grounds in the Pacific Northwest and their wintering habitat in southern Mexico. They zealously guard those territories, driving off hawkmoths, butterflies, other hummers, and even bees that might compete for the nectar. In addition, they deplete the nectar resources around the periphery of their territories as early in the day as they can, in order to out-compete other nectar-sippers that might try to sneak a drink at the territory edge.

When half of the flowers in a territory were covered with cloth so the birds could not drain them, Carpenter and her co-workers found that the resident hummer increased its territory size. This showed that territoriality was tied to the availability of nectar, and that the bird could in some way assess the amount of nectar it controlled. Then, by substituting a sensitive scale topped by a perch for the territory-holder's traditional perch, they were able to measure the bird's weight each time it alighted. The researchers found that the hummers optimized their territory size by trial and error, making it larger or smaller until their daily weight gain was at a maximum. In this case of migrant-territorial hummers, theory accurately predicted how a bird behaves in nature.

Example 2: Optimal clam selection by northwestern crows (Alcock, 1997) Richardson and Verbeek (1986) noticed that crows in the Pacific Northwest often leave lit-tleneck clams uneaten after locating them. The crows dig the clams from their burrows, but they often leave the smaller ones on the beach and only bother with the larger ones, which they drop on the rocks and eat. Their acceptance rate increases with prey size: they open and eat only about half of the 29-mm-long clams they find, while consuming all clams in the 32-33 mm range. The two researchers determined that the most profitable clams were the largest, not because they broke more easily, but because they contained more calories than smaller clams. By considering the caloric benefits from clams of different sizes and the costs of searching for, digging up, opening, and feeding on clams, the authors were able to construct a mathematical model based on the assumption that crows would select an optimal diet, in this case one that maximized their caloric intake. The model predicted that clams approximately 28.5 mm in length would be opened and eaten half the time, given the search costs required to find clams of different sizes; the crows behavior shows that they agree with researchers' match (Figure 8.11). Their work was based on optimal foraging theory.

The optimal foraging theory at the light of ecosystem principles The optimal foraging theory clearly complies with the Ecological Law of Thermodynamics. The fact that prey abundance influences consumers' selectivity and that diets are broad when prey are scarce and narrow if food is abundant, as a function of search for food time, is clearly translated by "... If more combinations and processes are

Clam length (mm)

Figure 8.11 Optimality model of prey selection in relation to prey size. The curve represents the predicted percentages of small to large clams that crows should select for consumption after locating, based on the assumption that the birds attempt to maximize the rate of energy gain per unit of time spent foraging for clams. The solid circles represent the actual observations, showing the model's predictions were supported (Richardson and Verbeek, 1986).

Clam length (mm)

Figure 8.11 Optimality model of prey selection in relation to prey size. The curve represents the predicted percentages of small to large clams that crows should select for consumption after locating, based on the assumption that the birds attempt to maximize the rate of energy gain per unit of time spent foraging for clams. The solid circles represent the actual observations, showing the model's predictions were supported (Richardson and Verbeek, 1986).

offered to utilize the Exergy flow, the organization that is able to give the highest Exergy under the prevailing circumstances will be selected or by if more combinations and processes are offered to utilize the free energy flow, the organization that is able to give the greatest distance away from thermodynamic equilibrium under the prevailing circumstances will be selected". Both examples can, therefore, be easily explained by the same ecosystem principles.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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