Theories of optimality involve a mathematical model of cost and benefit
analysis that can give quantitative predictions about an animal's behavior.
These hypotheses can be tested experimentally or through comparative
phylogeny. By no means are these models fully accurate;
each comes with certain assumptions and variations that are not included in
these simple models. But we can often use the models to predict behavior to a
reasonably certain degree.
To some degree, animals display the ability to modify their behavior so that
they receive an optimal balance of benefits and costs. Costs can include
danger, loss of valuable time, and wasted energy. Benefits are usually counted
in terms of net energy intake (consumed calories) per unit time or number of
offspring produced. In this section, we will focus on optimal foraging methods
to achieve the highest net energy intake. We will discuss reproductive fitness
and the production of offspring in the next
section.
Contingency Theory
Contingency Theory, also called the prey choice model, predicts what an
animal will do when it encounters a particular food. Should the animal eat what
he has, or search for a more profitable food item? We do not often imagine
animals refusing to eat the food in front of them to search for other items, but
this does occur. Shorecrabs, for instance, eat muscles that become increasingly
difficult to crack open as their size increases. Crabs will pass up large
muscles, which would take too much time and energy to crack, to search for
smaller muscles. This way, the crab can spend less time and energy handling
their food, and, even though they pass up the massive meals, will increase their
net food intake.
Models similar to that just described for the Shorecrab can include several food
choices, though the math involved can quickly complicated; we will focus on the
simpler version with two food types.
PARARAPH
For the purpose of the model, we will define the following terms:
-
energy (E) is the net number of calories obtained by consuming the
food item.
-
Handling time (h) is the amount of time required to handle the food
between the time it is encountered to the time it is consumed. Handling time
can include cracking a shell, digging it out of the ground, or manipulating the
item.
-
Search time (s) is the mean expected time between encounters of items
of the same food type. Search time depends on the abundance of the item and the
ease of locating it.
-
total time foraging (T) is the sum of searching and handling times.
The model we are building is concerned with profitability, the energy gained
divided by the time spent handling it (E/h) for a single food source, and the
maximum energy gained per total time foraging (E/T) when there are multiple food
sources.
Using the Model
Food choice 1 is scarce, but is highly profitable, meaning it will yield a high
amount of energy with a low handling time. E/h for food 1 is therefore quite
high. However, because we are trying to maximize both E/h and E/t, we must also
take into account the time it takes to find the very scarce food choice 1.
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