Biodiversity of Freshwaters - Freshwater Ecology: Concepts and Environmental Applications - page 183

10 Biodiversity
of Freshwaters
Measures of Diversity
Temporal and Spatial Factors Influencing Evolution of Freshwater
Organisms
Short-Term Factors Influencing Local Distribution of Species
Invasions of Nonnative Species
Extinction
What Is the Value of Freshwater Species Diversity?
Summary
Questions for Thought
Describing patterns of and controls on distribution of organisms is cen-
tral to the study of ecology and historically has been the focus of much lim-
nological study. An entire field, conservation biology, is now dedicated to
the science of conserving organisms. We are living in a time of unprece-
dented rates of human-caused extinction, particularly in freshwater habitats
(Cairns and Lackey, 1992). Efforts to save species require knowledge of dis-
tribution of organisms in their habitats. In addition to causing many species
to go extinct and threatening many more, people are introducing exotic
species into habitats at very high rates. This leads to direct negative effects
on humans and often harms the ecosystems that exotic species invade.
In this chapter, I discuss measures of diversity and how and why di-
versity varies among and within habitats, and I describe some particularly
spectacular cases of high diversity. Extinction caused by humans and in-
troduction of exotic organisms will also be discussed.
MEASURES OF DIVERSITY
The simplest measure of diversity is species richness, the total number
of species found in an area. Another important aspect of diversity is how
183