Ecological traps

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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. More specifically, traps are thought to occur when the attractivenss of a habitat increases relative 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. 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 phenomena (Robertson and Hutto 2006). The ecological trap concept was introduced over 30 years ago by Dwernychuk and Boag (1972) and the many studies that followed suggested that this trap phenomenon may be widespread due to anthropogenic habitat change (see references in Schlaepfer et al. 2002, Battin 2004, and Robertson and Hutto 2006).

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 (i.e. “undervalued resources”, Gilroy and Sutherland 2007). Theoretical (Delibes et al. 2001, Donovan and Thompson 2001, Kokko and Sutherland 2001) and empirical studies (Dwernychuk and Boag 1972, Weldon and Haddad 2005, Robertson and Hutto 2007) 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). As such ecological traps are a subset of the broader phenomena of evolutionary traps (Schlaepfer et al. 2002).

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 (Misenhelter and Rotenberry 2000). 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 (Schlaepfer et al. 2002). 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 (Robertson and Hutto 2006). 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.

One recent addition to the literature on ecological traps is by (Robertson and Hutto 2006), which provided guidelines for demonstrating the existence of an ecological trap. They asserted that a study would have to show a preference for one habitat over another (or equal preference) and that the population in the preferred habitat (or equally preferred habitat) had a lower fitness (i.e., did not do as well in terms of survival and/or reproduction). The authors found that very few of the published articles that claimed to show the existence of an ecological trap met these criteria, perhaps because it is very difficult to demonstrate habitat preference. One study that was successful was able to show that Indigo Buntings preferred nesting in “winged” patches (with two narrow corridors projecting from opposite ends of the patch) over rectangular patches, despite a higher rate of nest predation (Weldon and Haddad 2005). The authors found a higher percentage of older, presumably dominant male Indigo Buntings in the winged patches. The preference for the patches with more edge, combined with its much lower nest success rate, indicated that these patches were indeed ecological traps.

Because ecological and evolutionary traps are still very poorly understood phenomena, many questions about their proximate and ultimate causes as well as their ecological consequences remain unanswered. Are traps simply an inevitable consequence of the inability of evolution to anticipate novelty or react quickly to rapid environmental change? How common are traps? Do ecological traps necessarily lead to population declines or extinctions or is it possible that they may persist indefinitely? Under what ecological and evolutionary conditions should this occur? Are organisms with certain characteristics predisposed to being "trapped"? Is rapid environmental change necessary to trigger traps? Can global warming, pollution or exotic invasive species create traps? Embracing genetic and phylogenetic approaches may provide more robust answers to the above questions as well as providing deeper insight into the proximate and ultimate basis for maladaptation in general (see Crespi 2000). Because ecological and evolutionary traps may lead to population declines, traps are an important research priority for conservation scientists. Given the rapid current rate of global environmental change, traps may be far more common that is realized and it will be important to examine the proximate and ultimate causes of traps if management is to prevent or eliminate traps in the future.

[edit] References

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