Is this mobbing behavioradaptive?

What is an adaptation?It is a heritable trait that:

spread as a result of naturalselection and has been maintained

by selection to the present, or

is currently spreading relative toalternative traits because of

natural selection

In all such cases, the trait mustconfer (in the past and/or present)

higher reproductive success (i.e., fitness)on the individuals that express it

Examples of indirect and direct measures usedby behavioral ecologist to examine fitness consequences

of traits thought to be adaptations

How could you test the proposition that mobbing is adaptive?

In light of this vulnerable situation, Tinbergen hypothesized that the mobbing behavior is an anti-predator adaptation. By threatening and

distracting predators, gulls reduce the chances of the predators attacking their eggs and/or nestlings

Note that the gull chick is ina rudimentary nest on theon the ground, surrounded byother nests.

Also note that thenest is easily located and accessed by aerial and groundpredators

Effectiveness of mobbing in preventing egg-eating predatorsfrom finding eggs (by Hans Kruuk)

In this experiment, the frequency of intense mobbing attacks (red circles) on crowsincreased when these predators were within the borders of a nesting colony. As mobbing

increased, the percentage of hen eggs discovered and eaten (blue circles) decreased.

This test examines the fitness consequences of the mobbing behavior. Does it providean indirect or direct measure of the behavior’s fitness consequences?

How could the test be improved?

One powerful approach for testing adaptationist hypothesesis called the comparative method

This involves testing predictions about the evolutionof a trait by examining animals other than the species

whose characteristics are under investigation

For instance, one could test a logicalprediction of the mobbing hypothesis:

If the mobbing behavior represents ananti-predator adaptation, then gulls that nest in predator-free habitats

should not show the mobbing behavior

Logic of the comparative method

Nestingbirds

Using gull phylogeny as a tool for examining the originof mobbing behavior

Hypothesis A requires one switch (from ground nesting to

cliff nesting)

Hypothesis B requires two switches (from cliff nesting to

ground nesting and then back again)

Occam’s Razor: belief that simplerexplanations are more likely to be

correct that complex ones