Cases in which rapid environmental change triggers animals to actually prefer inferior habitats are known as ecological traps. Ecological traps occur when nocturnally-active insects are attracted away from more natural habitats to artificial night lights where they experience depleted energy stores and elevated risk of predation. However, night lighting can also become polarized through reflection from asphalt or other smooth, dark man-made objects, and this attracts aquatic insects to maladaptively oviposit on these objects that they perceive as supernormally attractive water bodies. We designed a field-based experiment to 1) estimate the relative importance of unpolarized versus polarized LED light in guiding nocturnal terrestrial and emergent aquatic insects into ecological traps. We captured insects using oil traps that varied in the percentage of LED night lighting they polarized, and that were shaded and directed downward or unshaded and directly and broadly visible. Experiments were conducted on the banks of five rivers in New York state.
Results/Conclusions
All terrestrial and aquatic taxa were captured in greater numbers in traps associated with unshaded lighting; shading reduced captures of both groups by approximately 75%. Patterns of capture among shading and polarization treatments indicated that that none of the nine terrestrial insect families we captured used polarized light in guiding their habitat selection behavior, while 5 of the 12 aquatic insect families we captured did so, weighting polarized vs. unpolarized light in diverse, but maladaptive ways. Our results illustrate that two forms of light pollution can interact in creating ecological traps, that additively or synergistically in different taxa, and that both terrestrial and aquatic insects exhibit a broad taxonomic predisposition ecological traps formed by light pollution. This study illustrates a first experimental model system by which conservation scientists can investigate the sensory-cognitive mechanisms that trigger ecological traps and expose ways to eliminate them or mitigate their impacts on native species.