Biology Reference
In-Depth Information
added to the sampling program. Three duck species were found to feed
heavily on mussels: lesser scaup (
Aythya affinis
), greater scaup (
A. marila
),
and bufflehead (
Bucephala albeola
).
Beginning in 1993 and continuing through 1995, the abundance of
mussels in Long Point Bay declined, dropping to a biomass of only 758
tons in 1995.The abundance of the three major duck predators on mus-
sels grew correspondingly over the sampling period. In 1986, prior to the
mussel invasion, waterfowl days spent in Long Point Bay for the two scaup
species combined were 38,500 and for the bufflehead 4,700. By 1997,
waterfowl days for scaup had grown to 3.5 million and for bufflehead to
67,000. From 1993 through 1995, when mussels were declining, the three
duck species were estimated to have consumed a minimum of 39-46% of
the mussel biomass annually.
Ecological and Evolutionary Responses to
Invasive Aliens
The above example shows a strong ecological response to invading zebra
and quagga mussels in only one location. Nevertheless, it emphasizes the
fact that the native biotic community does respond to an invasive alien in
a fashion that tends to integrate it into the food web.The aquatic ecosys-
tem of Long Point Bay probably will never return to its pre-mussel state,
but a new state, in which the mussel population is intimately linked with
native species by ecological and evolutionary adjustments, will eventually
develop.
Over evolutionary time, invasive species tend to become integrated
into the new biotic community in such a way that their initial impacts are
softened. Integration occurs through the processes of coevolution and
counteradaptation. Coevolution is the mutual evolutionary adaptation of
two or more species to each other: herbivore with plant, predator with
prey, and parasite with host.These evolutionary sequences eventually may
lead to patterns of mutual benefit for the interacting species. Counter-
adaptation is a related concept and refers to the total of evolutionary
adjustments by members of the native community to the new invader.
These adjustments may involve improved defenses, refined competitive
capabilities, or adaptations for exploiting the new community member.As
we have seen, the invading species is also evolving adjustments to the
physical and biotic conditions it encounters.
The sum total of these biotic adjustments constitutes the organization
that exists in biotic communities. Major questions in evolutionary ecol-
