ABSTRACT
In 1978, the “ecological trap hypothesis” postulated that avian nest predation rates were density dependent, and that the greater density of nests near edges leads to a concomitant increase in depredation rates of avian nests near edges.[7] Much of the interest in the negative infl uence of edge effects in the 1980s was due to population declines in neotropical migratory birds that nest in North America.[8] Nest success is vital to long-term avian population dynamics,[9] therefore determining which factors infl uence nest predation is essential for biologists hoping to successfully manage avian populations. Reviews of avian nest predation studies in the mid-to late-1990s found that most, but not all, studies found evidence of increased nest predation near edges.[10,11] However, evidence of an edge effect on nest predation rates is not restricted to birds, as painted turtles (Chrysemys picta) can have greater nest predation rates near water edges.[12]
Although there is strong evidence that avian (and other taxa) nest success can be lower for some species near edges, there appear to be many factors that affect nest
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success,[10] which can include nest type,[13] plot age,[14] predator densities,[15] plot size,[16] and among the most important factors-landscape context.[17] One of the major challenges for biologists hoping to understand the impact of edge effects on wildlife populations is disentangling the effects of habitat fragmentation on avian nesting success at multiple spatial scales, including edge, patch, and landscape.[17,18] There is considerable confusion or disagreement about whether or how different stand types or ages of forest (e.g., recently harvested patches surrounded by mature forest) constitute a “fragmentation” of that larger habitat patch or landscape. In forested landscapes, some biologists feel that forest harvesting does not necessarily “fragment” larger forest patches or forested landscapes, but rather represents a patch with a different disturbance history and resulting structure.
