Biodiversity of Freshwaters - Freshwater Ecology: Concepts and Environmental Applications - page 200

keeping a canary in the mine. When the bird dies it is time to get out or in-
crease the ventilation. When numerous species go extinct, this could indi-
cate that the ability of Earth to support life is endangered (Lawton, 1991).
However, basing arguments for conserving species purely on economic
and utilitarian grounds is dangerous. Many species may exist that have no
economic value and are not essential to ecosystem function. Many species
are not attractive to the general public, unless they have big eyes or flashy
coloration. Do these species deserve to be extinct? It is common in public
debate over listing a species as endangered to hear the question, “Aren't
people more important than animals?” I suspect what is usually meant in
this case is that an individual believes his or her right to make money the
way he or she wants is more important than the right of a species to ex-
ist. If the immediate past is any gauge, species will continue to be driven
to extinction, regardless of their value.

SUMMARY

1. Several aspects of diversity are used by ecologists, including the
number of species (richness), evenness, within-habitat ( ) diversity,

) diversity.
2. Evolution ultimately drives diversity. Aquatic habitats that have been
in existence for long periods of time, such as some tectonic lakes and
old river basins, tend to have high diversity and many endemic species.
Spatial segregation of habitats also influences species evolution.
3. Over short-term timescales (decades and centuries), factors other than
evolution may influence diversity, including size of habitat,
connectivity of habitats, habitat disturbance, sources of new species,
species interactions, productivity, and species introductions.
4. Human-caused species introductions are common forms of pollution in
aquatic environments. Some of these invading species have serious
economic and ecological impacts on the communities that are invaded.
Most successful invasions are difficult or impossible to reverse.
5. Humans are causing extinction of existing species at rates from
hundreds to millions of times greater than the evolution of new
species is occurring. Many of us alive today will likely witness the
disappearance of half or more of the biodiversity on Earth, including
many species in aquatic habitats.

and between-habitat (

QUESTIONS FOR THOUGHT

1. Why are temperate lakes generally relatively species poor?
2. What are the evolutionary advantages of very long diapause periods?
3. Are there more species of large than small animals?
4. Should conservation be based on local diversity (e.g., if a species is
rare in one state and common in another, should it be conserved
where it is already rare)?
5. What is the benefit of an ecosystem-based method of conservation?
6. Should DNA samples of endangered species be stored?
7. How might genetic diversity be different than species diversity,
particularly in microbial species?