is this mobbing behavior adaptive? - columbia university€¦ · is this mobbing behavior adaptive?...
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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
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