Ecological Responses to Habitat Edges: Mechanisms, Models, and Variability Explained

Abstract

Key Words ecological boundary, ecotone, edge effect, effective area model, core area model, habitat fragmentation ■ Abstract Edge effects have been studied for decades because they are a key component to understanding how landscape structure influences habitat quality. However, making sense of the diverse patterns and extensive variability reported in the literature has been difficult because there has been no unifying conceptual framework to guide research. In this review, we identify four fundamental mechanisms that cause edge responses: ecological flows, access to spatially separated resources, resource mapping, and species interactions. We present a conceptual framework that identifies the pathways through which these four mechanisms can influence distributions, ultimately leading to new ecological communities near habitat edges. Next, we examine a predictive model of edge responses and show how it can explain much of the variation reported in the literature. Using this model, we show that, when observed, edge responses are largely predictable and consistent. When edge responses are variable for the same species at the same edge type, observed responses are rarely in opposite directions. We then show how remaining variability may be understood within our conceptual frameworks. Finally, we suggest that, despite all the research in this area, the development of tools to extrapolate edge responses to landscapes has been slow, restricting our ability to use this information for conservation and management.

Ecosystem decay of Amazonian forest fragments: implications for conservation

“…Laurance 1997, Didham 1997a, Ries et al 2004. The BDFFP has helped to reveal the remarkable diversity of edge effects in fragmented rainforests, which alter physical gradients, species distributions, and many ecological and ecosystem processes (Figure 3).…”

“…Edge effects in fragmented forests are evidently additive, whereby forest adjoined by two or more nearby edges suffers greater edge effects than does forest adjoined by just a single edge (Malcolm 1994, Ries et al 2004, Fletcher 2005). In the BDFFP study area, an additive-edge model better predicts structural changes to forest fragments than does a single-edge model (Malcolm 1994).…”

Non‐random food‐web assembly at habitat edges increases connectivity and functional redundancy

“…Land-use change is increasing the prevalence of habitat edges (Ries et al 2004;Haddad et al 2015), and juxtaposing natural communities against anthropogenic assemblages with which they may…”

“…These habitat edges can influence patterns of species abundance, distribution and diversity (Dyer and Landis 1997;Ewers and Didham 2008;Murphy et al 2016), alter dispersal processes (Duelli et al 1990;Macfadyen and Muller 2013) and even interactions among species (Fagan et al 1999;Ries et al 2004;). Species interactions underpin many important ecosystem functions and services (Klein et al 2003;Macfadyen et al 2011), and they are frequently altered by changes in the…”

Sample based estimation of landscape metrics; accuracy of line intersect sampling for estimating edge density and Shannon’s diversity index

“…It is a robust metric and is recommended as a fragmentation index (Li et al 1993, Saura andMartinez-Millan 2001). Depending on species under consideration the edge length in a landscape can have negative, positive and neutral impacts (Ries et al 2004). There is a relationship between such landscape structures and ecological processes (Turner 1989) and the metrics are useful for understanding these relations (Leitão et al 2006).…”