Negative Phototaxis Results from Avoidance of Light and Temperature in Stream Salamander Larvae
Forest removal is a global threat to amphibian diversity. Declines occur within these areas, but many amphibians also avoid moving into or through disturbed areas. Understanding which cues result in avoidance may provide targets for preservation of amphibian occupancy and population connectivity. Negative phototaxis is known from many amphibians, but light can serve as a cue or as a proxy for other environmental cues like temperature. This study sought to evaluate whether larval salamander habitat selection was influenced most by light or temperature cues. Because some individuals choose to remain in deforested habitat, we also assessed whether differences in habitat selection existed between individuals from forested and deforested habitat. Using a laboratory experiment, we found that salamanders use both light and temperature cues for habitat selection. Although salamanders demonstrated larger responses to temperature, they were willing to move into warmer habitats to avoid light. Individuals from deforested regions preferred brighter and warmer areas than individuals from forested regions although plasticity was higher with respect to light relative to temperature. We also noted that salamander thermal preferences were lower than daytime temperatures in small (< 60 m) deforested regions. Overall, a combination of light and thermal cues following forest removal may contribute to avoidance of deforested regions, but more research is necessary to understand why some salamanders continue to occupy warm and bright-disturbed areas.Abstract
Habitat selection results with respect to A) distance from light or ice bath and B) temperature for larval Desmognathus quadramaculatus individuals from forested and deforested stream patches. Boxplots reflect the mean, quartiles, and outlying values. When temperature and light cues were placed in conflict, that is where movement toward shade would require movement toward warmer temperatures, salamanders used both cues to locate themselves within light and temperature gradients.
Stream temperatures from an upstream-forested reach versus a downstream deforested reach. Stream temperatures within canopy gaps are on average 0.72 ± 0.02°C warmer than upstream forested reaches and can increase more than 5°C during the day. The canopy gap at this site is 55 m in length.
Frequency with which individuals selected distance from light A) or temperatures B) during the 12 observations of habitat selection. Frequencies were obtained using 30-cm categories for distance from light in light-cue–only treatments and 5°C categories for temperature in temperature-only treatments. Individual selection frequencies are shown with their best fitting curve.
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