Invertebrate and vertebrate predation rates in a hyperarid ecosystem following an oil spill

Thermal conditions determine lizards' response to oil contamination in a desert habitat

A unique, hyper-arid habitat in southern Israel was polluted by crude oil in 2014. Surveys following the event found that some species of local lizards avoid the oil, while other species were found more frequently in polluted plots. These results raised the question: why do species react differently to oil-polluted soil? We evaluated how soil type, thermal conditions, and food availability interacted to shape habitat preferences of three lizard species. Generally, thermal conditions determined habitat selection and preferences for contaminated or clean soils, while the effects of food availability were weak. The diurnal Acanthodactylus opheodurus avoided artificial heating sources, perhaps to avoid hot soil during warm hours. Both nocturnal Stenodactylus species showed a preference for higher temperature treatments. While crude oil is considered harmful, ectotherms may not recognize it as a danger and may be attracted to it due to its thermal properties, which may create an ecological trap.

Sphingid caterpillars conspicuous patches do not function as distractive marks or warning against predators

To avoid predation by visual predators, caterpillars can be cryptic to decrease detectability or aposematic to warn predators of potential unpalatability. However, for some species, it is not clear if conspicuous patches are selected to avoid predation. For example, Pandora sphinx (Eumorpha pandorus, Lepidoptera: Sphingidae) caterpillars are assumed to be palatable and have both cryptic (green, brown) and conspicuous (orange, red) color morphs. Five lateral, off-white to yellow patches on either side may serve as a warning for predators or to draw attention away from the caterpillar's form to function as distractive marks. We conducted a field study in three temperate fragmented forests in Massachusetts to investigate the potential utility of E. pandorus coloration and conspicuous patches. Using four plasticine caterpillar prey model treatments, green and red with and without lateral conspicuous patches, we tested the effects of color, patch patterning, and seasonality on attack rates by a variety of taxa. We found that 43% of the prey models (n = 964) had bite marks by an array of predators including arthropods (67.5%), birds (18.2%), rodents (11.5%), and large mammals (2.8%). Arthropods as dominant predators align with conclusions from previous studies of prey models placed near ground level. Attack rates peaked for arthropods in late August and early September but were more constant across trials for vertebrates. Arthropods, a heterogeneous group, as indicated by the variety of bite marks, showed significantly higher attack rates on green colored prey models and a tendency of higher attack on solid (non-patch patterned) prey models. Vertebrates, more visually oriented predators, had significantly higher attack rates on red colored prey models and patch patterned prey models. Thus, our results did not suggest that conspicuous patch patterning reduced predation and therefore, we did not find support for the distractive mark hypothesis or warning hypothesis. Further, our study shows clear contrasting interpretations by different predators regarding visual defensive strategies.