Biodiversity of Freshwaters - Freshwater Ecology: Concepts and Environmental Applications - page 194

EXAMPLE 10.2.
Calculating Expected Numbers of Species after a Habitat Reduction

A developer wants to decrease the area of a small lake in Wisconsin from 90
to 10 ha. Given that data from Tonn and Magnuson (1982) can be used to
calculate values of c

0.3325 for lakes of similar size, cal-
culate the expected number of fish species for each size of lake.

2.211 and z

For a 90-ha lake log S log 2.211 0.3325 log (90) 0.994,

so S 9.9 species of fish

For a 10-ha lake log S log 2.211 0.3325 log (10) 0.677,

so S 4.8 species of fish

Thus, we can expect that half the fish species will be supported in the
smaller lake. This calculation ignores other possible factors, such as what
type of habitat will be present after the lake is altered and the variance in
the predictive relationship (fairly high). It also does not tell us which species
will survive. However, such relationships are useful for illustrating the idea
that the size, as well as the quality of habitat, is an important parameter in
conserving biodiversity.

very low levels of disturbance, only late successional species are competi-
tive. At intermediate levels of disturbance, both types of species can be
found, and diversity is at a maximum. The problem with the intermediate
disturbance hypothesis is that it provides no a priori way to establish rel-
ative disturbance intensity among communities. This hypothesis will be dis-
cussed in greater detail in Chapter 18.
Disturbances by humans can also cause variations in species diversity.
Assessing changes in types and numbers of species present forms the basis
of several indices of biotic integrity. Use of such indicators is described in
Chapter 14.

INVASIONS OF NONNATIVE SPECIES

Invasion by species introduced by humans is probably the most per-
manent form of pollution. Dispersal of species is one of the less recognized
forms of global change instigated by humans (Vitousek et al., 1996). Once
an invader becomes established, eradicating it is almost impossible. I do not
know of any examples of eradication of an aquatic pest species once it has
become established in a large area (although some species may be success-
fully controlled to low numbers). Understanding the ecology of ecosystems
is essential to managing invasive species (Mack et al., 2000). As humans in-
crease speed and frequency of global travel and move more materials across
international boundaries, the probability for transport of undesirable species
increases dramatically. Humans have created a world without borders for
many species (Mack et al., 2000) and rates of human-caused species