Lecture © Andrew McAdam
BIOL 606 Session, University of Alberta, April 11, 2001
It is an evolutionary fact that species come into existence and subsequently go extinct, but it is also clear that the process of speciation cannot possibly keep pace with contemporary rates of extinction. We are in the midst of the 6th Mass Extinction (see Tatarnic, March 14). Although decisions regarding conservation priorities are largely socio-political there remains a clear role for scientists to provide sound information for decision-makers. With the understanding that conservation of anything is itself a success regardless, how should we prioritize our limited conservation efforts?
Brian Bowen presented a tripolar framework of systematic, ecological, and evolutionary perspectives on conservation, which correspond roughly to priorities based on bioheritage, biodiversity function or service, and potential for future speciation (Bowen, 1999). From the systematics perspective, individual taxonomic units are of value because of the information they provide on previous evolutionary events. Each species has its own unique set of characters that have evolved in response to previous environmental conditions. In preserving species, we are preserving information about previous conditions and the evolutionary process that has led to contemporary forms. The systematic perspective then values both taxonomic rank and distinctiveness (May, 1990). Sole representatives of higher taxonomic groups ('living fossil'), such as the tuatara, have sets of characters that are highly distinct and, therefore, receive higher conservation priority. Because of the central importance of taxonomic rank to the systematic approach, there are large consequences to taxonomic promotion or demotion. For example, recent molecular data proposing the demotion of black turtles to sub-species or population status has generated much controversy because of the potential implications for conservation programs for these turtles (see Conservation Forum, Conservation Biology, October, 1999, including Karl and Bowen, 1999). While the definition of units (such as species or sub-species) may help to focus conservation attention, we must preserve more than just the suite of characters or perhaps only the one or two diagnostic characters that differentiate taxonomic groups. Units can be preserved in zoos, on museum shelves or in laboratory freezers, but process cannot. The ecological and evolutionary perspectives on conservation emphasise process over units.
From an ecological perspective, biodiversity plays an integral role in ecosystem function or services and a decrease in biodiversity threatens an impairment of function. Organisms are valued for the unique service they provide to ecosystems or to humans directly and not for their unique morphology or behaviour per se. For example, the priority of maintaining a top feline predator in south Florida superseded that of preserving the distinct lineage of the Florida panther in the recent decision to supplement decreasing populations of Florida panther with a separate sub-species from Texas (Bowen, 1999). The connection between diversity and ecosystem function has interested ecologists for much of the last half century and more recent experiments have found controversial evidence in support of this connection (McCann, 2000), but more needs to be done to identify causality and the generality of these results.
Finally, an evolutionary perspective focuses not on bioheritage or current function but on the potential for future speciation. In this case, the goal is to identify groups with a high potential for future radiation. Potential radiations may come from species rich groups such as African cichlids, or from historically isolated populations identified as evolutionarily significant units (ESU's; Ryder, 1986; Moritz, 1994), which may represent incipient species. Whether species-rich groups have a high potential for speciation or are simply dead-end lineages of highly specialized local forms is not at all clear.
If we wish to conserve more than units, then much more needs to be done to improve our understanding of the process we are hoping to maintain. Species come into existence, are important components of ecosystems and at some point go extinct. However, we currently know very little about the role most species play in ecosystem function and are unable to predict future radiations. So, while a process approach to conservation may be a worthy academic pursuit, we are left with the immediate task of trying to salvage what diversity we can, using whatever tools are available.
Bowen, B.W., 1999. Preserving genes, species, or ecosystems? Healing the fractured foundations of conservation policy. Mol. Ecol. 8: S5-S10.
Karl, S.A. and Bowen, B.W., 1999. Evolutionary Significant Units versus Geopolitical Taxonomy: Molecular Systematics of an Endangered Sea Turtle (genus Chelonia). Cons. Biol. 13: 990-999.
May, R.M., 1990. Taxonomy as destiny. Nature, 347: 129-130.
McCann, K.S., 2000. The diversity-stability debate. Nature, 405: 228-233.
Moritz, C., 1994. Defining 'Evolutionarily Significant Units' for conservation. TREE 9: 373-375.
Ryder, O.A., 1986. Species Conservation and Systematics: the Dilemma of Subspecies. TREE 1: 9-10.
Renner, S.S. 1999. Circumscription and phylogeny of the Laurales: evidence from molecular and morphological data. American Journal of Botany. 86(9): 1301-1325