Connectivity 101

“Man is always marveling at what he has blown apart, never at what the universe has put together, and this is his limitation.”

— Loren Eiseley

By Gary M. Tabor and Katie Meiklejohn

The combination of habitat loss and landscape fragmentation poses one of the greatest threats to biodiversity conservation. Its global magnitude has challenged ecologists and conservation biologists to delve into the complexities of ecological integrity while establishing priorities that protect and/or restore intact, connected landscapes.

Increases in the number of endangered species and the patterns of global extinction are in part the result of habitat loss and landscape fragmentation. These threats isolate populations by disrupting the migration and dispersal of species – vital life-history processes for sustaining population health and species persistence – and alter ecological elements such as fire, stream flow, drought, and species interactions.

Climate change is now exacerbating the negative cumulative impacts of habitat loss and fragmentation. Local climate disturbances will further alter long-term ecological cycles like fire, drought, and flood as well as seasonal temperature and precipitation patterns. Because these changes will ultimately shift in the distribution and abundance of plant and animal communities, landscape fragmentation will impede the ability of many species to respond, move, and/or adapt to climate-related impacts.

A recent review of the scientific literature indicates that the top recommendation for counteracting the negative consequences of habitat loss, fragmentation, and climate change on wildlife is to maintain landscape connectivity sufficient to sustain natural patterns of wildlife movement and permit adaptation.

Not All Connectivity Is Equal

To achieve and maintain connectivity on the ground, it is critical to distinguish between structural connectivity and functional connectivity. Structural connectivity refers to the physical pattern of habitat and potential connections between areas of habitat within the landscape. It is the geometry of habitat fragments – their orientation and degree of separation – as well as the quality of the developed lands separating these fragments (i.e. urban, agricultural, forested, etc.). This geometry is important because it influences the willingness of wildlife species to move between patches of habitat.

By contrast, functional connectivity refers to the actual movement of individual organisms through the landscape and the degree to which each landscape facilitates or impedes this movement. Because it refers to the ways species utilize natural systems to move through the landscape – rather than how people perceive patterns of connection –functional connectivity must inform landscape planning and management efforts.

It helps to envision a functionally connected landscape as an assemblage of habitat “islands” (the result of fragmentation) surrounded by “matrix” (less preferred habitat). Anything qualifies as matrix – clear cuts, agricultural land, suburban sprawl. But because species vary in their willingness to pass through less preferable habitats, meaningful conservation planning and management projects must evaluate connectivity from the perspective of the individual target species.

As a result, land managers need to define species’ habitats accurately. Important components of this definition include identifying the scale at which species use a given habitat, describing the extent of this use at both local and regional levels, and understanding how species respond to different elements of the landscape. For instance, gray wolves, a generalist species, will readily move through a variety of land-cover types, whereas a forest specialist like the Canada lynx will not, leaving them more susceptible to the isolating effects of fragmentation and habitat loss. Such variations in species-response characteristics to landscape fragmentation mean that the processes associated with functional connectivity are both species- and landscape-specific.

Giving Shape to Corridors and Linkages

Habitat corridors are conservation tools that enable land managers to restore and maintain connectivity. Historically, the term ‘corridor’ referred to linear strips of land, but this strict interpretation fails to define connectivity from the species’ perspective.

More recent interpretations acknowledge that corridors may or may not be linear – their form depends on the needs and characteristics of the species for which they are designed and on the landscapes in which they occur. We can thus define habitat corridors as tracts of intact land intended to facilitate the movement of individual wildlife species between areas of core habitat. Do note, however, that while the terms “corridor” and “linkage” are often used synonymously, linkage technically refers to lands intended to promote the movement of multiple species, whereas corridors highlight the needs of individual species.

Approaches to securing habitat corridors and linkage zones include federal designations, special management strategies, smart-growth strategies, conservation easements, and land purchase. Once corridors are protected, habitat restoration, monitoring of wildlife movement patterns, and management of ongoing human activities in the area are generally required to maintain the integrity and functionality of landscapes.

Numerous organizations concentrate on corridor efforts In North America, noteworthy initiatives include:

On a global scale, other prime examples of conservation projects focusing on functional connectivity include the Great Eastern Ranges Initiative (formerly Alps to Atherton) in Australia, the Terai Arc Landscape Project focused on southern Asia’s tigers,  Africa’s Albertine Rift Initiative, and the Green Belt Initiative across Europe.

Connecting with Public Policy

The value of landscape connectivity as a driver of sustainability for both human and natural systems has become better understood in recent years. In fact, the profile of connectivity strategies has risen quickly among state and federal decision-makers, particularly in relation to policies around climate change and energy development. The Western Governors Association’s Wildlife Corridors Initiative and the federal designation of the Path of the Pronghorn migration corridor illustrate a wider appreciation of such strategies, and the current administration is actively engaging organizations like Freedom to Roam to provide connectivity language for insertion into upcoming natural-resources and climate-change bills.

The momentum building for connectivity conservation around the globe is encouraging. However, effective connectivity projects require careful design to address the specific characteristics and needs of target species. Furthermore, implementing this approach does not provide a panacea, and it must be combined with additional conservation strategies aimed at mitigating other drivers like habitat loss, fragmentation, and global climate change.


Trained as a veterinarian and ecologist, Gary Tabor is a conservation catalyst who has worked on behalf of large landscape conservation for the past 25 years. His most notable initiatives include championing theYellowstone to Yukon effort. Gary co-founded the Freedom to Roam initiative, now part of the World Wildlife Fund, with Patagonia Company and promoted the Western Governors Association’s Wildlife Corridors Initiative. Gary serves on the Board of Governors for Society for Conservation Biology.

Having earned a Master’s in conservation biology, Katie Meiklejohn now lives in Montana where she is pursuing a career in wildlife conservation and indulging her passion for mountain sports. Katie has a long-standing interest in finding solutions to large-scale issues like habitat fragmentation and climate change.

References

Beier, P. et al. 2008. Forks in the road: choices in procedures for designing wildland linkages. Conservation Biology. 1-16.

Chetkiewicz, C-L. B. et al. 2006. Corridors for conservation: integrating pattern and process. Annual Review of Ecology, Evolution and Systematics. 317-342.

Heller, N. and E.S. Zavaleta. 2008. Biodiversity management in the face of climate change: a synthesis of 20 years of recommendations. Biological Conservation. 14-32.

Additional Resources

Crooks, K.R. and M. Sanjayan. 2006. Connectivity Conservation. Cambridge University Press.

Damschen, E.L. et al. 2006. Corridors increase plant species richness at large scales. Science. 1284-1286

Fahrig, L. 2003. Effects of habitat fragmentation on biodiversity. Annual Review of Ecology, Evolution and Systematics. 487-515.

Hess, G.R. and R.A. Fischer. 2001. Communicating clearly about conservation corridors. Landscape and Urban Planning.195-208.

Hilty, J., W.Z. Lidicker Jr. and A.M. Merenlender. 2006. Corridor Ecology: The Science and Practice of Linking Landscapes for Biodiversity Conservation. Island Press.

Parmesan, C. and G. Yohe. 2003. A globally coherent fingerprint of climate change impacts across natural systems. Nature. 37-42.

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