Biology Reference
In-Depth Information
the mayflies mostly remain beneath rocks during the day and usually only
forage on exposed surfaces and drift in the water column at night (McIn-
tosh and Townsend 1994). These nocturnal patterns of behavior were
retained when mayflies from brown trout streams were tested in experi-
mental streams without fish or with galaxiids. Other stream invertebrates
may also have experienced similar evolutionary shifts (Townsend 2003).
Thus, in a little more than a century, brown trout predation has led to
evolutionary shifts in activity patterns of at least one native New Zealand
invertebrate.
Exploiters and the Exploited: The Red
Queen Hypothesis
Introduction of alien predators, parasites, or disease agents often creates
abruptly new relationships between these types of organisms and their
prey or hosts. In evolutionary terms, the exploitation of one species by an
organism of a higher trophic level tends to follow the Red Queen
Hypothesis (Van Valen 1973). This hypothesis, named for a character in
Lewis Carroll's topic
Through the Looking Glass
, states that the members of
an exploitation interaction tend to establish an evolutionary stand-off, in
which improvements in exploitation ability by the one member are
matched by improvements in defense by the other. Or, as the Red Queen
put it,“Now, here, you see, it takes all the running you can do just to stay
in the same place.”
The introduction of alien predators, parasites, or disease agents may
create a situation in which native prey or host species are subjected to
new, more intense patterns of exploitation. The same can be true when
alien prey or host species are confronted with alien enemies that they have
not previously encountered. In some cases, these new interactions may
lead to extirpation or extinction of the prey or host (see chapter 16). In
other cases, they may lead to rapid evolutionary adjustments by the prey
or host to the new selective pressures.
Evolutionary Adaptation to Predators and Parasitoids
by Native Invertebrates
Several good examples of evolutionary adaptation by native invertebrate
prey species to alien predators are available. The European green crab
(
Carcinus maenas
) was introduced to the North American east coast in the
early 1800s, and has now spread along the coast from New Jersey to Nova
