Lecture Notes: Oct. 9

Endangered Species and Habitat Protection

Our textbook wraps the endangered species issue into the broader theme of loss of biodiversity and leads that off with a look at loss of forests as a key habitat loss that causes species extinction. But since many endangered species reside in the Western U.S., I thought we ought to pay more attention to endangered species per se, the ones that get listed and protected under the Endangered Species Act. Thus we have a recitation on endangered species, and a lecture based on these notes.

Here are the key points that will be discussed in class:

1. The difference between "Endangered" (near extinction) and "Threatened" (trends portend extinction sometime in the future) under the 1973 Endangered Species Act.

2. The factors that tend a species toward endangerment:

· limited range (endemic to limited areas);

· small population (limited breeding success, and/or genetic degradation due to in-breeding);

· isolated;

· narrow habitat requirements (habitat specificity)

· Non-adaptive behavior

3. The main human causes of species loss:

· the biggest is habitat destruction and fragmentation;

· hunting (for sport and food), including illegal poaching;

· purposeful exterminaiton

· pollution (e.g., DDT in bird shells reduces reproduction success);

· introduction of exotics (may out-compete or prey on endemic species);

4. Focus on habitat destruction and degradation:

We discussed the notion of "island biogeography" and the relationship between habitat "island" size and species diversity. In a given habitat, the size of habitat available is directly proportional to the number of species (bio-diversity) that that habitat can support for the long term. Another way of looking at this is that if the size of a habitat is reduced, hen the probability of species loss increases.

As landscapes are "fragmented" by human development the patches become smaller, and can support fewer species and fewer numbers of individual members of species. Smaller patches also suffer more "edge effect"---whereby the habitat near the edge of the patch is compromised (meaning it is less useful to species who need that habitat) because processes from the "matrix" in which the patch is embedded work their way into the patch (e.g., wind, predation, pollution, etc.). This effectively reduces the patch size even further.

Patch configuration on the landscape also matters--as they become further separated species are less able to move from patch to patch, so patches arrayed in

"corridors" are more useful than patches simply randomly distributed across the landscape.

These landscape ecology principles suggest several management goals:

1. protect all habitat you can, and maintain or recreate habitat patches as large as possible---try to improve the habitat in the patch;

2. where possible, maintain or recreate habitat patches in corridors connecting larger patches;

3. remove barriers (roads, developments, etc.) between patches -- or at least make the barriers more "permeable" to species (e.g., design roads so that species can cross them (or go under them) safely.