Biology Reference
In-Depth Information
ogy concern the importance of coevolution and counteradaptation in
communities and the time scale on which they develop and change.The
degree of biotic organization varies greatly, tending to be low in commu-
nities of habitats that exhibit extreme physical conditions or frequent dis-
turbance and substantial in communities of habitats that are equitable and
stable.
Ecological Adjustments
Ecological adjustments tend to precede evolutionary adjustments. Many
plants, for example, show induced responses to herbivory, such as altered
growth form or production of deterrent chemicals (Agrawal 1998).Thus,
native plants may respond quickly to introduced herbivores. As we have
seen (chapter 15), introduced plants typically acquire native herbivores
and introduced animals a set of native predators and parasites. Zebra mus-
sels are beginning to show ecological pressure from a variety of predators,
as indicated by the example at the beginning of this chapter. Many native
fish, including freshwater drum (
Aplodinotus grunniens
), redear sunfish
(
Lepomis microlophus
), pumpkinseed (
Lepomis gibbosus
), copper redhorse
(
Moxostoma hubbsi
), and river redhorse (
Moxostoma carinatum
), have teeth
and chewing pads that enable them to crush and eat zebra mussels
(French 1993). The freshwater drum now feeds heavily on zebra mussels
in Lake Erie (Morrison et al. 1997). In Arkansas, blue catfish (
Ictalurus fur-
catus
) feed heavily on zebra mussels for part of the year, apparently swal-
lowing them whole (Magoulick and Lewis 2002). Other native fish, as
well as the introduced common carp (
Cyprinus carpio
), also consume zebra
and quagga mussels to some degree.
Zebra mussels have also been colonized by freshwater sponges in many
locations. Heavy growth of such sponges on the shells of mussels has sig-
nificant negative impacts on growth and survival of zebra mussels (Ric-
ciardi et al. 1995; Lauer and Spacie 2000). A few native North American
trematodes also have been found to infect zebra mussels (Molloy et al.
1997), although the diversity of parasites in North America is far below
that in the Old World.
A similar example is provided by the imported fire ant (
Solenopsis
invicta
), which has dramatically affected populations of native ants and
other arthropods (Gotelli and Arnett 2000). In a 1987 study in Texas,
Porter and Savignano (1990) found that the fire ant had reduced native
ant diversity by 50% and had reduced the abundance of many other
arthropods. Morrison (2002) repeated the study in 1999. He found that
