The negative effect of fragmentation is a cornerstone of the policy recommendations, research agenda and fiscal priorities of conservation biology (Lubchenco et al. 1991
). In our work, we separated the effects of fragmentation from that of area loss. The results suggest that fragmentation has no consistent or significant effect on species diversity. Fahrig (2003)
reports that most studies claiming that fragmentation leads to loss of diversity do not separate fragmentation from area. However, Fahrig lists 17 studies that do strive to achieve this separation. She concludes that they do not support the hypothesis that fragmentation reduces diversity. This is our conclusion too. Nevertheless, we looked at each of these 17 studies. Many deal only with a single species. Some deal with abundances; many deal with flying species not well isolated by the fragments; and one uses an analytical technique now known to be faulty. So we do not claim that they parallel and support our own. Yet we do endorse Fahrig's conclusion and have followed her recommendation to separate the two variables from each other.
The results of Tscharntke et al. (2002)
support our conclusion that fragmentation does not have a negative effect on species diversity. In the latter study, small grassland fragments showed higher species diversities—of butterflies, legume-feeding herbivores and of rape-pollen beetles and their parasitoids—than did those same groups in larger grassland fragments (and see references within Tscharntke et al. 2002
). However, this latter study did not explicitly analyse the effect of habitat loss relative to that of fragmentation per se
processes on total species diversity, which is the purpose of our study.
The question of fragmentation was introduced to help design nature reserves using the theory of island biogeography (Wilson & Willis 1975
). The scale of our study is smaller, involving not islands but patches of mainland. Yet, just as fragmentation seems not to matter at the latter scale, it appears not to matter at the island scale (Lomolino 1994
; Rosenzweig 2004
). Theoretically, it also does not matter at the scale of whole continents, i.e. a world divided into n
separate biogeographical provinces should have about the same steady-state species diversity as an undivided one (Rosenzweig 2001
). So the hypothesis that fragmentation depresses the number of species would appear to be one of those reified doctrines that Slobodkin (2001)
However, fragmentation will retain considerable importance for the conservation of individual species that require unbroken tracts for territories. These species may well be among the most charismatic, exerting an influence on decision making well beyond their contribution to species numbers. Even supposing that we are correct in our conclusion, even if we are right to expect that other species from the available pool can be expected to take the place of the charismatic ones that may disappear owing to fragmentation, society will not be satisfied. Nor, in our opinion, should it be. The simple number of species is hardly the sole matter of conservation importance. Nonetheless, fragmentation studies would seem best focused on those charismatic species likely to be endangered by fragmentation, and more general claims of fragmentation's severe consequences viewed with great caution.