With this lecture we begin more concrete discussions of principles related to the design of conservation reserves or reserve systems and to conservation programs directed either at multiple species or at entire systems. We'll talk more about the history of reserve design and the purposes reseve systems serve in a couple of weeks. For now it's enough to know that there are four broad purposes such reserves may serve:
Conservation reserves are needed because of the enormous impact that human beings have on this planet. As I've said repeatedly in this course, we cannot choose to have no impact. We can only choose the type of impact we will have. Of course, when we think of the impact we have, we tend to focus on the direct and obvious impacts:
As we saw early in this course, human activities dominate many of the earth's ecosystems. We manage them for agriculture or forest products, pave them for shopping malls, convert them to housing developments, and extract their resources for our consumption. Our activities fix more nitrogen than all biotic and abiotic sources, fertilizing the entire planet [9]. Not only do our activities directly diminish the amount of relatively undisturbed habitat available to other species, not only do they modify the character even of remote habitats that never see a bulldozer or chain saw, in areas where bulldozers and chainsaws are common our actions create islands of undisturbed habitat in a sea of human-dominated ones.
When we think of habitat destruction, the tropical rainforest almost always leaps to mind. When we think of habitat fragmentation, however, we need look no further than our own backyard (Figure 1).
As Figure 1 makes clear, habitat fragmentation has several related effects:
