Ecological trap

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 phenomenacite journal |last=Robertson |first=B.A. |authorlink= |coauthors=Hutto, R.L. |year=2006 |title=A framework for understanding ecological traps and an evaluation of existing evidence |journal=Ecology |volume=87 |pages=1075-1085 ] . The ecological trap concept was introduced over 30 years ago by Dwernychuk and Boagcite journal |last=Dwernychuk |first=L.W. |authorlink= |coauthors=Boag, D.A. |year=1972 |title=Ducks nesting in association with gulls-an ecological trap? |journal=Canadian Journal of Zoology |volume=50 |pages=559-563 ] and the many studies that followed suggested that this trap phenomenon may be widespread due to anthropogenic habitat changecite journal |last=Schlaepfer |first=M.A. |authorlink= |coauthors=Runge, M.C. and Sherman, P.W. |year=2002 |title=Ecological and evolutionary traps |journal=Trends in Ecology and Evolution |volume=17 |pages=474-480 ] cite journal |last=Battin |first=J. |authorlink= |coauthors= |year=2004 |month= |title=When good animals love bad habitats: Ecological traps and the conservation of animal populations |journal= Conservation Biology |volume=18 |issue= |pages=1482-1491 |id= |url= |accessdate= |quote= ] .

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”)fact|date=September 2008 . Theoreticalcite journal |last=Delibes |first=M. |authorlink= |coauthors=Gaona, P. and Ferreras, P. |year=2001 |title=Effects of an attractive sink leading into maladaptive habitat selection |journal=American Naturalist |volume=158 |pages=277-285 ] and empirical studiescite journal |last=Weldon |first=A.J. |authorlink= |coauthors=Haddad, N.M. |year=2005 |title=The effects of patch shape on Indigo Buntings: Evidence for an ecological trap |journal=Ecology |volume=86 |pages=1422-1431 ] 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.

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 scalescite journal |last=Misenhelter |first=M.D. |authorlink= |coauthors=Rotenberry, J.T. |year=2000 |title=Choices and consequences of habitat occupancy and nest site selection in sage sparrows |journal=Ecology |volume=81 |pages=2892-2901 ] . 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.

A recent addition to the literature on ecological traps provides guidelines for demonstrating the existence of an ecological trap. A study must show a preference for one habitat over another (or equal preference) and that individuals selecting the preferred habitat (or equally preferred habitat) have lower fitness (i.e., experience lower survival or reproductive success). To date, there appear to be few well-documented examples of ecological trap, but this paucity may, in part arise from the practical difficulty of demonstrating habitat preference in wild organisms. 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. 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.

Polarized light pollution is perhaps the most compelling and well-documented cue triggering ecological trapsfact|date=September 2008 . Orientation to polarized sources of light is the most important mechanism that guides at least 300 species of dragonflies, mayflies, caddisflies, tabanid flies, diving beetles, water bugs and other aquatic insects in their search for the water bodies they require for suitable feeding/breeding habitat and oviposition sitesfact|date=September 2008 . Because of their strong linear polarization signature, artificial polarizing surfaces (e.g., asphalt, gravestones, cars, plastic sheeting, oil pools, windows) are commonly mistaken for bodies of waterfact|date=September 2008 . Light reflected by these surfaces is often more highly polarized than that of light reflected by water, artificial polarizers can be even more attractive to polarotactic aquatic insects than a water bodyfact|date=September 2008 and appear as exaggerated water surfaces acting as supernormal optical stimuli. Consequently, dragonflies, mayflfies, caddisflies and other water-seeking specieis actually prefer to mate, settle, swarm and oviposit upon these surfaces than available water bodies.

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 generalfact|date=September 2008 . 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.

References

Crespi, B.J. 2001. The evolution of maladaptation. Heredity 84: 623 - 629

Gilroy, J.J., and W.J. Sutherland. 2007. Beyond ecological traps: perceptual errors and undervalued resources Trends in Ecology and Evolution 22(7):351-6.

Horváth G and Kriska G. 2008. Polarization vision in aquatic insects and ecological traps for polarotactic insects. In: Lancaster J and Briers RA (Eds.) Aquatic Insects: Challenges to Populations. pp. 204-229, Wallingford, Oxon, UK: CAB International Publishing.

Horváth G and Zeil J. 1996. Kuwait oil lakes as insect traps. Nature 379: 303-304.

Horváth G, Bernáth B and Molnár G. 1998. Dragonflies find crude oil visually more attractive than water: Multiple-choice experiments on dragonfly polarotaxis. Naturwissenschaften 85: 292-297.

Horváth, G., Kriska, G., Malik, P., and B.A. Robertson. In press. Polarized light pollution: A new kind of ecological photopollution. Frontiers in Ecology and the Environment.

Horváth G, Malik P, Kriska G and Wildermuth H. 2007. Ecological traps for dragonflies in a cemetery: the attraction of Sympetrum species (Odonata: Libellulidae) by horizontally polarizing black gravestones. Freshwater Biol 52: 1700-1709.

Kriska G, Horváth G and Andrikovics S. 1998. Why do mayflies lay their eggs en masse on dry asphalt roads? Water-imitating polarized light reflected from asphalt attracts Ephemeroptera. J Exp Biol 201: 2273-2286.

Kriska G, Malik P, Szivák I and Horváth G. 2008. Glass buildings on river banks as "polarized light traps" for mass-swarming polarotactic caddis flies. Naturwissenschaften 95: 461-467.

Schwind R. 1991. Polarization vision in water insects and insects living on a moist substrate. J Comp Physiol A 169: 531-540.

Further reading

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