The debate about the effects of habitat fragmentation: causes and consequences

Abstract

Understanding how species respond to the increasing loss and fragmentation of natural ecosystems has never been more urgent. Nowadays there is consensus on the negative impact of habitat loss on biodiversity. However, the effect of habitat fragmentation is strongly debated. In this review, we propose a scheme that evaluates the causes and consequences of this debate. We suggest that it is caused by the use of different definitions and conceptualizations of fragmentation (distal causes), which promote the use of different study methods (proximate causes). Some studies consider fragmentation as a process that is inseparable from habitat loss and other local threats (e.g., edge and isolation effects), and measure its effects at the site, patch, or landscape scales, without controlling necessarily the effects of habitat loss at the landscape scale. Others consider fragmentation as a pattern that describes the configuration of the habitat in the landscape, the effects of which can and should be evaluated independently of the effect of habitat amount (i.e., fragmentation per se), using the landscape as the unit of analysis. Consequently, the former group of studies concludes that fragmentation has strong and negative effects on biodiversity, while the latter group concludes that these effects are generally weak, and positive when significant. Understanding the causes and consequences of this debate is critical to apply more appropriate conservation measures.