Wild Side : Make the connection
By Matt Pelikan
Published: December 31, 2008
In coming years, expect to see the emerging concept of "landscape connectivity" shape conservation thinking on Martha's Vineyard. Growing out of recent ecological research, the idea of connectivity shifts the conservation focus from individual properties to the landscape as a whole. While the quality of each protected property still matters, the ease with which wildlife moves among the protected areas becomes a focus of attention.
Wildlife needs connectivity for many reasons, and on many scales. Long-distance migratory species require connectivity across hemispheres; shorebirds, for example, are famous (and sadly vulnerable) for requiring vast, predictable, resource-rich stopover sites to refuel on their epic journeys. Many species of plants and invertebrates, in contrast, live in relatively small, transient sub-populations scattered across suitable habitat. Ideally, a fairly steady flow of dispersing individuals augments or replaces sub-populations that fail. For these species, even narrow barriers of unsuitable habitat can break a viable population into non-viable fragments.
The importance of connectivity is heightened by climate change. Every species has a range of temperature in which it is capable of flourishing. As the climate warms, the ranges of species will have to shift northward, move up in elevation, or concentrate in areas with cool microclimates. Without sufficient connectivity for the gradual transition of entire species, the future will be one of steadily declining biodiversity.
Martha's Vineyard offers fertile ground for applying the idea of connectivity to conservation planning. At present, we are blessed with a fine and growing network of protected lands; on much of Martha's Vineyard, surrounding unprotected land remains in largely natural condition, providing many of the same benefits as the protected property while also connecting conservation areas.
But development - including new roads, new houses (especially ones with large lawn areas), and energy infrastructure - can degrade the connections among conservation land, separating small wildlife populations and fragmenting larger ones. This separation is a vital matter. Larger populations are inherently more stable than smaller ones; they contain more genetic diversity, giving them more flexibility, and they are simply less likely to be wiped out entirely by a single event.
The amount of connectivity you see in a landscape depends entirely on what you're trying to connect, and why. The veery, for example, a songbird related to the wood thrush, may be the fussiest and least numerous of Martha's Vineyard's regularly breeding birds. I can't imagine that more than a half-dozen pairs nest each year, always in wooded stream drainages in Chilmark and West Tisbury - a number and a specificity that puts this species at high risk for extirpation from Martha's Vineyard.
But suitable drainages lie close together, and the intervening land is itself heavily wooded. This is a bird that migrates back and forth to South America; I can't imagine it views the space between potential nest sites as much of an obstacle. The species may be rare here, but from a conservation perspective, landscape connectivity is probably not its problem. Its low numbers and low density probably stem from a regional decline, or simply from the fact that veeries don't think much of the habitat we have to offer.
The spotted salamander, which requires predator-free, often transient woodland pools for breeding, presents a different case. Salamanders typically disperse only short distances from where they hatch (though as with most species, individuals vary widely in how far they roam). Since their breeding pools are not a common landscape feature in the best of times, even a natural landscape looks fragmented to a salamander. Your odds of making it to the next pool by random dispersal are not good (though better than zero). And the arrival of outsiders to enrich your gene pool, or replace your pool's population if you and your colleagues have all died at once, is a correspondingly rare (if essential) event.
But add a few paved roads to the picture. Studies have shown that salamanders (and many other smaller animals) avoid crossing roads. Pavement is unfamiliar, exposed to predators and steel-belted radials, abrasive, often hot, perhaps chemically repugnant to something like a salamander; one study of red-backed salamanders found that even an unpaved road turned back 50 percent of the individuals that encountered it. So between deterrence and mortality, even a few heavily traveled roads may carve a salamander's landscape into unconnected fragments, leaving each pool's population to wink out, permanently, inevitably, as the result of some unlucky coincidence.
So while connectivity alone doesn't ensure adequate conservation, conservation without connectivity is precarious at best. For many Vineyard species (and for many migratory species that use Martha's Vineyard or its waters), Martha's Vineyard offers few meaningful barriers. But many other species may already be on a trajectory toward local extinction, their populations cracked into nonviable fragments by habitats they can't or won't venture across.
