Ecological traps

Ecological traps are scenarios in which rapid environmental change leads organisms to prefer to settle in poor-quality habitats. The concept stems from the idea that organisms that are actively selecting habitat must rely on environmental cues to help them identify high-quality habitat. If either the habitat quality or the cue changes so that one does not reliably indicate the other, organisms may be lured into poor-quality habitat.

Ecological traps are thought to occur when the attractiveness of a habitat increases disproportionately in relation to its value for survival and reproduction. The result is preference of falsely attractive habitat and a general avoidance of high-quality but less-attractive habitats. For example, Indigo buntings typically nest in shrubby habitat or broken forest transitions between closed canopy forest and open field. Human activity can create 'sharper', more abrupt forest edges and buntings prefer to nest along these edges. However, these artificial sharp forest edges also concentrate the movement of predators which predate their nests. In this way, Buntings prefer to nest in highly altered habitats where their nest success is lowest.

While the demographic consequences of this type of maladaptive habitat selection behavior have been explored in the context of the sources and sinks, ecological traps are an inherently behavioral phenomenon of individuals. However, ecological traps can have far-reaching demographic consequences for species with large dispersal capabilities, such as the grizzly bear (Ursus arctos) The ecological trap concept was introduced in 1972 by Dwernychuk and Boag and the many studies that followed suggested that this trap phenomenon may be widespread because of anthropogenic habitat change.

As a corollary, novel environments may represent fitness opportunities that are unrecognized by native species if high-quality habitats lack the appropriate cues to encourage settlement; these are known as perceptual traps. Theoretical and empirical studies have shown that errors made in judging habitat quality can lead to population declines or extinction. Such mismatches are not limited to habitat selection, but may occur in any behavioral context (e.g. predator avoidance, mate selection, navigation, foraging site selection, etc.). Ecological traps are thus a subset of the broader phenomena of evolutionary traps.

As ecological trap theory developed, researchers have recognized that traps may operate on a variety of spatial and temporal scales which might also hinder their detection. For example, because a bird must select habitat on several scales (a habitat patch, an individual territory within that patch, as well as a nest site within the territory), traps may operate on any one of these scales. Similarly, traps may operate on a temporal scale so that an altered environment may appear to cause a trap in one stage of an organism’s life, yet have positive effects on later life stages. As a result, there has been a great deal of uncertainty as to how common traps may be, despite widespread acceptance as a theoretical possibility. However, given the accelerated rate of ecological change driven by human land-use change, global warming, exotic species invasions, and changes in ecological communities resulting from species loss, ecological traps may be an increasing and highly underappreciated threat to biodiversity.

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