Dryness increases predation risk in efts: support for an amphibian decline hypothesis

Abstract

One hypothesis for amphibian declines is that increased dryness attributed to global climate change exposes amphibians to greater biotic threat and, consequently, greater mortality. But, little is known about behavioral responses of terrestrial amphibians to dry conditions alone or in combination with biotic threats. We used field observations and laboratory experiments to test the response of efts (terrestrial juveniles) of the eastern red-spotted newt, Notophthalmus viridescens, to separate and combined desiccation and predation risks. When only at risk of desiccation, efts moved into shade, traveled down slope, decreased activity, and adopted water-conserving postures. Efts also significantly reduced the rate of water loss by huddling and were attracted to chemical cues from conspecific efts but not from conspecific adults. Thus, efts have a variety of behaviors that reduce the risk of dehydration associated with climate change. When faced only with a predation risk, represented by adult and eft newt tissue extracts (alarm chemicals), efts reduced their activity and avoided alarm cues from both sources. When exposed to combined desiccation and predation risks, efts were less active than when exposed to either risk separately and avoided adult tissue extracts, but not eft extracts. These results suggest that under dry conditions, conspecific tissue extracts contain both attractive (huddling) and repulsive (predator-related) chemical components that induce offsetting behavioral responses. This is the first study to demonstrate moisture-dependent responses to conspecific rinses and alarm substances, underscoring the importance of considering environmental moisture and animal hydration in studies examining responses to conspecific odors and/or alarm chemicals. These results support the hypothesis that elevated dehydration risk may compromise anti-predator behavior and exacerbate amphibian population declines.

Abiotic and biotic influences on the dispersal behavior of metamorph cane toads (Bufo marinus) in tropical Australia

“…Similar findings have been reported for the eastern red-spotted newt, Notophthalmus viridescens (Rohr and Madison, 2003). When subjected to desiccation risk, these amphibians adopt behaviors such as huddling together to reduce effective surface area to volume ratios (potentially explaining why metamorphs in our experiments desiccated less in the presence of conspecifics and why toad metamorphs aggregate in dry conditions: see above).…”

“…Evidently, the trade-off between desiccation risk and predator aversion elicits variable responses among amphibians, although this may depend on the degree of dehydration experienced. Rohr and Madison (2003) did not quantify dehydration rates, but metamorph cane toads in our study suffered on average a 10.7% reduction in mass to avoid cannibals on a dry substrate. As cane toad metamorphs can survive at least a 50% reduction in body mass (Child, 2007), the desiccating power of our experimental environment may have been too low to significantly hamper increased movement in the presence of a cannibal.…”

The response to the social environment reveals sex-dependent behavioural syndromes in the Bosca’s newt (Lissotriton boscai)

“…Most studies of behavioural syndromes have focused on the repeatability of mating behaviours in birds (Bell et al 2009), and attention to the role of the social environment on behavioural correlations has been paid only recently (Rohr and Madison 2003;Aragón et al 2006a;Cote and Clobert 2007;Magnhagen and Bunnefeld 2009). Furthermore, sex differences in behavioural repeatability is relatively unexplored and mainly focused on a reproductive context in birds (Bell et al 2009).…”

Predator diversity, intraguild predation, and indirect effects drive parasite transmission

“…Given that I. verticalis consumed tadpoles, that many amphibians possess alarm chemicals that can reduce their activity and affect their space use (38,39), and that activity and cercarial avoidance are well-documented anticercarial behaviors (35-37), we hypothesized that I. verticalis density would decrease tadpole activity, increasing metacercarial infections. Indeed, I. verticalis was the only species that significantly reduced activity in monospecific tanks relative to controls (Fig.…”