Corridors for Conservation: Integrating Pattern and Process

Corridors are commonly used to connect fragments of wildlife habitat, yet the identification of conservation corridors typically neglects processes of habitat selection and movement for target organisms. Instead, corridor designs often are based on binary patterns of habitat suitability. New technologies and analytical tools make it possible to better integrate landscape patterns with behavioral processes. We show how resource selection functions can be used to describe habitat suitability with continuous and multivariable metrics and review methods by which animal movement can be quantified, analyzed, and modeled. We then show how the processes of habitat selection and movement can be integrated with landscape features using least-cost paths, graph theory, and step selection functions. These tools offer new ways to design, implement, and study corridors as landscape linkages more objectively and holistically. 317 A nn u. R ev . E co l. E vo l. Sy st . 2 00 6. 37 :3 17 -3 42 . D ow nl oa de d fr om a rj ou rn al s. an nu al re vi ew s. or g by U ni ve rs ity o f C al if or ni a D av is o n 02 /2 0/ 09 . F or p er so na l u se o nl y. ANRV292-ES37-12 ARI 17 October 2006 7:21 Corridor: regions of the landscape that facilitate the flow or movement of individuals, genes, and ecological processes Matrix: component of the landscape that is neither patch nor corridor INTRODUCTION Corridors are cornerstones of modern conservation. Traditionally, corridors have been viewed as linear strips of habitat that facilitate the movement of organisms through landscapes (Puth & Wilson 2001). Corridors, often in association with the charismatic megafauna whose populations they are designed to conserve, are a fundamental component of wildland conservation, particularly in North America where many regional and several continental-scale corridor initiatives are underway (Nelson et al. 2003, Noss 2003). International corridors foster new levels of transboundary conservation, elevating corridors from an ecological to a political and socioeconomic tool (Zimmerer et al. 2004). Despite the widespread application of corridors, much current practice causes them to fall far short of their conservation promise. On-theground applications of corridors usually are based on simplistic depictions of habitats that are assumed to provide the associated ecological processes. Typically, corridor applications proceed with little species-specific information and limited evaluation, and they are rarely published or reviewed in scientific journals (Vos et al. 2002; but see Beier et al. 2006). In some cases, corridors, selected for their political appeal, are being plunked down willy-nilly on landscapes that already have been carved up for other purposes. This makes the provision of practical corridor guidelines for managers as big a challenge today as it was over a decade ago (Hobbs 1992). A grizzly bear (Ursus arctos) tagged as “99” and his victim provide a compelling study in the failings of this approach. This young male bear wandered into the fringes of the burgeoning town of Canmore, Alberta, in late May, 2005. After showing indifference to human encounters, it was captured on a local golf course and relocated by government conservation officers. A week later, “99” was detected in a designated wildlife corridor above the town of Canmore, one that was a scant 1000 m wide, perforated with human-use trails, and sandwiched between a recently built golf course and steep slopes above the townsite. By day’s end, both the bear and a young woman were dead, and the world tuned in to Alberta’s first grizzly-caused human fatality in seven years. Critics were quick to blame the wildlife policy that relocated the bear. But the bigger failing occurred years previously with the designation of the corridor. Corridors based on scant biological data supported Canmore’s rapid development during the 1990s, obliterating much of the wildlife habitat in this montane valley. Too little fertile and connected habitat remains in the valley that contains Canmore to support grizzly bear movement to adjacent protected areas in the Canadian Rocky Mountains (Herrero 2005). Indeed, examining movements of three other grizzly bears in this area suggests that the designated corridors actually are avoided, and the oft-assumed distinction between corridor and matrix is not apparent (Figure 1a). Despite various planning guidelines supporting corridor designations (BCEAG 1999), the corridor designs in Canmore require important modifications, at least for grizzly bears. We suggest that more sophisticated approaches to corridor designs not only are possible but essential if corridors are to realize their potential for conserving biodiversity. Although they have limitations (reviewed by Hilty et al. 2006), corridors have been promoted widely as a conservation strategy. Since their introduction as a tool for game management in the 1940s (reviewed by Harris & Scheck 1991), over 700 318 Chetkiewicz · St. Clair · Boyce A nn u. R ev . E co l. E vo l. Sy st . 2 00 6. 37 :3 17 -3 42 . D ow nl oa de d fr om a rj ou rn al s. an nu al re vi ew s. or g by U ni ve rs ity o f C al if or ni a D av is o n 02 /2 0/ 09 . F or p er so na l u se o nl y. ANRV292-ES37-12 ARI 17 October 2006 7:21