Preservation of natural diversity: the problem of extinction prone species

As concerned citizens and biologists we are anxious to understand how natural diversity can be maintained in a world of rapidly diminishing re-sources-resources that are important to the livelihood of human beings as well as to the 2 million or so other creatures with which we share this planet. Some day, of necessity, man must reestablish a steady state with nature. Where on the scale of population this steady state will lie and how we shall arrive there are difficult questions that are being forced upon us with an ever greater urgency by an accelerated pace of world events. With certainty the stressful transition period which we are entering now will impose extraordinary pressures on virtu-ally all existing species, not the least on our own. In developing a rational plan for the preservation of diversity we must be guided by an understanding of processes that unfold on an evolutionary time scale: the birth and death of species, the waxing and waning of whole faunas and floras, and the invasive replacement of archaic assemblages by more modern ones. Such dynamic facets of evolution have traditionally been the province of paleontologists and historical biogeo-graphers. Biologists concerned with liv-ing organisms and present day distribu-tions have too frequently assumed a sta tic view of evolution. Only in the past decade or so with the rise of what might be called dynamic biogeography have we come to realize that these long-term processes can be successfully studied on a contemporary basis. The intellectual cornerstone of these ad