Habitat corridors offer another way for managing ecosystems beyond the immediate boundaries of core protected areas. In the past, most species lived in landscapes of well-connected habitats, but human activities increasingly fragment these habitats into smaller and smaller patches. The concept of wildlife corridors was developed to minimize the impact of fragmentation and enhance connectivity. Corridors are linear strips of land linking habitat patches. Ideally, they allow species to move among different areas for breeding, birthing, feeding, roosting, annual migrations, and dispersal of young animals away from their parents and to escape from predators or disturbance. Corridors may be a natural feature of a landscape, such as a riverbank, or they may be created intentionally to connect existing protected areas that are too small to sustain wide-ranging or area-sensitive species (such as cougars, grizzly bears, and tigers). Corridors can be many sizes, from a narrow hedgerow only a few meters long to wide swaths of habitat and protected areas, such as the Yellowstone to Yukon initiative, spanning 3,200 kilometers.
Simply selecting habitats that appear to be connected on a map does not ensure they are useful as corridors. Effective corridors need to consider what species will use them and what dispersal patterns those species follow. The habitat, width, length, and location, and the human activities in the area are important considerations in corridor design. Monitoring of corridors that pass under or over roadways in Banff National Park's Bow Valley has revealed that ungulates and carnivores prefer different corridor designs. Grizzly bears did not use corridors that were close to human settlements, preferring those near streams or drainage areas. Elk, in contrast, preferred corridors far from carnivores and with clear visibility and adapted quickly to the road bypasses. Corridors are also important for small and mobile species, like birds and insects. Studies of a threatened bird in the southeastern United States, the Bachman's sparrow, found that corridors allowed higher colonization rate of certain patches.
Understanding natal dispersal patterns can be helpful to corridor design. Mammals typically disperse less than the diameter of five home ranges. Based on this, Harrison (1992) suggested minimum corridor widths based on species' home range sizes, ranging from 22 km for wolves in Alaska to 0.6 km for deer in Minnesota. Seasonal migration patterns are also an important consideration in identifying corridors.
Given that there are limited funds for conservation, some have questioned the value of corridors relative to other options as a conservation strategy (Simberloff et al., 1992). One concern is that corridors may actually lead animals into unsuitable habitats or may facilitate the spread of invasive species into core habitat areas. Human activities (such as hunting, livestock, and grazing) or roads may also interfere with the effectiveness of corridors.
Unfortunately, the study of real wildlife corridors (versus model corridors) is relatively new, and the full utility of corridors remains unknown. The few studies that do exist, however, generally suggest that well-designed corridors can be effective conservation tools for some species in certain landscapes (Beier and Noss, 1998).
—Daniel Brumbaugh and Melina F. Laverty
See also: Benthos; Communities; Coral Reefs; Dams; Habitat Tracking; Nurseries; Preservation of Species Bibliography
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