The Role of Climatic Change in the Design of Biological Reserves: The Paleoecological Perspective for Conservation Biology

The design of areas (refuges, reserves, or preserves) to conserve the biological diversity of terrestrial ecosystems in the face of unprecedented habitat destruction has primarily been based on the equilibrium theory of island biogeography (MacArthur & Wilson 1967). The equilibrium models and others such as the passive sampling, random placement, and habitat heterogeneity hypotheses (for discussion see Boecklen & Simberloff 1986:250) are designed for the climatic and environmental conditions of the region today. They do not take into consideration the potential response of the biota to future longand short-term climatic changes, although there have been some exceptions (Hamilton 1981; Peters & Darling 1985). Hunter et al. (page 375) use a paleovegetational perspective to address specific recommendations for the design of nature preserves. Specifically, they emphasize the individualistic responses of taxa to past environmental changes rather than a community, or holistic, response. The significance of including contingencies for climatic change in designing biological reserves is clearly illustrated by the Holocene archeological and paleontological record of the eastern Sahara. Today, this area is one of the largest hyperarid expanses on Earth. During the early Holocene (8,000-10,000 years ago), "climatic conditions supported extensive vegetation, a Sudanic biome, perhaps, which would have had many microenvironmental zones [with a parkland megafaunall available for exploitation by [widespread] pre-Neolithic and Neolithic [human] groups" (McHugh et al. 1988:3031). In fact, during the middle Neolithic (ca. 6,200 years B.P.), the Nubian desert supported organized human villages, which subsisted on hunting and gathering as well as agriculture (Wendorf, Close, & Schild 1985). Although this is a fairly long span of time (thousands of years), many of the significant environmental changes may have happened within shorter time spans (hundreds of years). As illustrated in the hypothetical model by Peters & Darling (1985:709, Fig. 2), biological preserves designed for this area under early Holocene conditions would have been completely obliterated by climatic changes in the latter part of the Holocene. The late Holocene environmental changes may appear extreme and, perhaps, serve as a worst-case scenario, but large-scale environmental changes, coincident with a major extinction event, have occurred in North America and other parts of the world during the last 12,000 years (Martin & Klein 1984). The paleoecological record of the late Quaternary provides a baseline against which predictions for the future can be measured. There are two divergent theoretical ways to model the response of biotas to climatic and environmental changes. If groups of organisms ("communities") respond to environmental changes as intact units, then the communities we observe today might be quite old geologically, allowing for extensive coevolution. Planning for the preservation of the communities would be quite straightforward appropriate areas would be set aside as reserves and these communities would merely track environmental change. The Pleistocene refuge model (e.g., Haffer 1969; Moreau 1963; Simpson & Haffer 1978; Vuilleumier 1971), in which areas were postulated to have harbored mesic communities during periods of regional aridity in the tropics, is primarily based on the premise of the community response concept. These models have been broadly applied to the design of biological preserves.