A Conceptual Genealogy of Fragmentation Research: From Island Biogeography to Landscape Ecology

Abstract

The concept of habitat fragmentation has become an important theme in conservation research, and it is often used as if fragmentation were a unitary phenomenon. However, the concept is ambiguous, and empirical studies demonstrate a wide variety of direct and indirect effects, sometimes with mutually opposing implications. The effects of fragmentation vary across organisms, habitat types, and geographic regions. Such a contrast between a schematic concept and multifaceted empirical reality is counterproductive. I analyzed the stabilization of the schematic view of fragmentation by the early 1980s, using a genealogical narrative as a methodological approach. The main assumptions behind the schematic view were: (1) fragments are comparable to oceanic islands; (2) habitats surrounding fragments are hostile to a majority of the organisms; and (3) natural pre-fragmentation conditions were uniform. The stabilization loop of this view was supported by the reduction of empirical research to species-area curve fitting, which always produced expected results. I present a model of the dynamics of fragmentation research that shows the schematic, island-biogeographic view as an ''intellectual attractor.'' Since the 1980s, the theoretical presuppositions of the schematic view have been challenged, and empirical research has become multifaceted. Fragments of a particular habitat type are viewed as elements in a heterogeneous landscape rather than ''islands'' surrounded by a hostile ''sea.'' However, the island metaphor is still used in conservation contexts in the shape of speciesarea curves. It is backed by a presupposition that human-influenced environments are essentially different from so-called ''natural'' environments, but this is unfounded. My suggestion is that our perspective should be broadened still further so that habitat fragmentation is viewed as a particular form of human-induced environmental degradation; I discuss both theoretical and practical implications of this suggestion.Instead of an essentially continuous forest cover, with infrequent meadow-like openings along watercourses or small grasslands where fires had been unusually severe, the landscape now presents the aspect of a savana, with isolated trees, small clumps or clusters of trees, or small groves scattered in a matrix of artificial grassland of grains and pasture grasses, unstable and frequently devoid of plant cover as a result of regular plowing.

What you find depends on where you look: responses to proximate habitat vary with landscape context

“…Studies of fragmentation and the effects of patch area, isolation, shape, or other metrics should account for, or even control for, landscape context in the study design. This conclusion should not be surprising, as it has long been clear that birds respond to landscapes at a range of scales (Wiens 1995, Lee et al 2002, and that species occurrence is influenced by the nature of the matrix composition, as well as by a habitat area itself (Ricketts 2001, Haila 2002. Our results further indicate that it is insufficient to describe habitat responses without reference to habitat availability in the larger context.…”

Managing Landscapes for Conservation Under Uncertainty

“…The island model suggests reserves close together are better than reserves far apart, and the patch-corridor-matrix model further suggests that reserves connected by a corridor are better than isolated reserves (see reviews and critiques by Gilbert 1980, Burgman et al 1988, Simberloff 1988, Doak and Mills 1994, Haila 2002, Manning et al 2004. However, it is difficult to find simple guidelines built on these concepts that result in effective conservation strategies in a variety of circumstances for a range of species.…”

Efectos de la estructura del paisaje y de la vegetación en la diversidad de murciélagos filostómidos (Chiroptera: Phyllostomidae) de Oaxaca, México

“…Estas transformaciones se han manifestado como pérdida y fragmentación de extensas regiones de vegetación nativa (Vitousek et al 1997). La fragmentación se define como la transformación de un hábitat de gran tamaño en numerosos fragmentos de área menor, aislados por una matriz de hábitat distinto al original (Wilcove et al 1986; Andrén 1994) y es considerado un proceso de degradación ambiental humana-inducida a escala de paisaje Haila 2002). Se ha observado que taxa distintos responden de manera diferencial a la fragmentación del hábi-tat (Fahrig 2003).…”