Ecological trap

Abstract: Organisms often rely on environmental cues to make behavioral and life-history decisions. However, in environments that have been altered suddenly by humans, formerly reliable cues might no longer be associated with adaptive outcomes. In such cases, organisms can become ‘trapped' by their evolutionary responses to the cues and experience reduced survival or reproduction. Ecological traps occur when organisms make poor habitat choices based on cues that correlated formerly with habitat quality. Ecological traps are part of a broader phenomenon, evolutionary traps, involving a dissociation between cues that organisms use to make any behavioral or life-history decision and outcomes normally associated with that decision. A trap can lead to extinction if a population falls below a critical size threshold before adaptation to the novel environment occurs. Conservation and management protocols must be designed in light of, rather than in spite of, the behavioral mechanisms and evolutionary history of populations and species to avoid ‘trapping' them.

Abstract: Observations of 21 species of open-nesting passerines breeding in contiguous field and forest habitats at Rose Lake Wildlife Research Area, Michigan, were made during 1974 and 1975. Data were collected on nest dispersion, clutch-size, and fledging success in relation to the field-forest edge. Losses of eggs or nestlings were attributed to predation, inclement weather, Brown-headed Cowbird (Molothrus ater) parasitism, nest desertion, hatching failure, and adult death. Each bird species seemed to have a preferred distance from the habitat discontinuity that was used as a nest site. Furthermore, nests were not uniformly distributed on the area. Over one-half of the nests were found within ?15 m of the habitat discontinuity. Seventy-five percent of the nests belonged to birds characteristic of mixed breeding habitats, i.e., birds requiring an open overstory canopy with elevated singing and observation perches and dense cover near the ground for nesting and feeding. These mixed-habitat species also accounted for the increase in avian species nesting near edges. Based on Kendall rank and partial rank correlation tests, increasing numbers of nests and the percentage of total clutches ^3 eggs were found to be negatively correlated with increasing distance from the habitat discontinuity. Correlation between fledging success and increasing distance from the edge was positive and highly significant. Of the several mortality factors investigated, predation and cowbird parasitism were found to be the most important. The increased predation rate with decreased distance from the edge was attributed primarily to a functional response to higher numbers of nests and a greater activity of potential nest predators in the vicinity of the habitat discontinuities. Our results indicate that habitat suitability decreases with increasing numbers of nests toward the narrow field-forest edges. Although such abrupt habitat discontinuities did attract a variety and abundance of birds characteristic of habitats with mixed life-form, these discontinuities seemed to function as "ecological traps" by concentrating nests and thereby increasing density-dependent mor? tality. Ironically, the cowbird was also a victim of the increased predation rate. As these man-made forest edges are of recent origin, they are perhaps unrepresentative of the ecological niche in which these species evolved, and thus they may be poorly adapted to cope with the increased nest predation.

Abstract: The concept of the ecological trap, a low-quality habitat that animals prefer over other available habitats of higher quality, has appeared in the ecological literature irregularly for over 30 years, but the topic has received relatively little attention, and evidence for traps remains largely anecdotal. Recently, however, the ecological trap concept has been the subject of a flurry of theoretical activity that is likely to raise its profile substantially, particularly in conservation biology. Ecological trap theory suggests that, under most circumstances, the presence of a trap in a landscape will drive a local population to extinction. A number of empirical studies, almost all of birds, suggest the existence of traps and demonstrate the difficulties of recognizing them in the field. Evidence for ecological traps has primarily been found in habitats modified by human activities, either directly (e.g., through the mowing of grassland birds' nests) or indirectly (e.g., via human-mediated invasion of exotic species), but some studies suggest that traps may occur even in relatively pristine areas. Taken together, these theoretical and empirical results suggest that traps may be relatively common in rapidly changing landscapes. It is therefore important for conservation biologists to be able to identify traps and differentiate them from sinks. Commonly employed approaches for population modeling, which tend to assume a source-sink framework and do not consider habitat selection explicitly, may introduce faulty assumptions that mask the effects of ecological traps and lead to overly optimistic predictions about population persistence. Given the potentially dire consequences of ecological traps and the accumulating evidence for their existence, greater attention from the community of conservation biologists is warranted. In particular, it is important for conservation biologists and managers to incorporate into conservation planning an explicit understanding of the relationship between habitat selection and habitat quality.

Abstract: When an animal settles preferentially in a habitat within which it does poorly relative to other available habitats, it is said to have been caught in an "ecological trap" Although the theoretical possibility that animals may be so trapped is widely recognized, the absence of a clear mechanistic understanding of what constitutes a trap means that much of the literature cited as support for the idea may be weak, at best Here, we develop a conceptual model to explain how an ecological trap might work, outline the specific criteria that are necessary for demonstrating the existence of an ecological trap, and provide tools for researchers to use in detecting ecological traps We then review the existing literature and summarize the state of empirical evidence for the existence of traps Our conceptual model suggests that there are two basic kinds of ecological traps and three mechanisms by which traps may be created To this point in time, there are still only a few solid empirical examples of ecological traps in the published literature (although those few examples suggest that both types of traps and all three of the predicted mechanisms do exist in nature) Therefore, ecological traps are either rare in nature, are difficult to detect, or both An improved library of empirical studies will be essential if we are to develop a more synthetic understanding of the mechanisms that can trigger maladaptive behavior in general and the specific conditions under which ecological traps might occur