Predator-prey interactions shape thermal patch use in a newt larvae-dragonfly nymph model

Is thermal sensitivity affected by predation risk? A case study in tadpoles from ephemeral environments

Changes in environmental temperature may induce variations in thermal tolerance and sensitivity in ectotherm organisms. These variations generate plastic responses that can be analyzed by examining their Thermal Performance Curves (TPCs). Additionally, some performance traits, like locomotion, could be affected by other factors such as biological interactions (e.g., predator-prey interaction). Here, we evaluate if the risk of predation modifies TPCs in Mendoza four-eyed frog (Pleurodema nebulosum, Burmeister, 1861) and Guayapa's four-eyed frog (Pleurodema guayapae, Barrio, 1964), two amphibian species that occur in ephemeral ponds in arid environments. We measured thermal tolerances and maximum swimming velocity at six different temperatures in tadpoles under three situations: control, exposure to predator chemical cues, and exposure to conspecific alarm cues. TPCs were fitted using General Additive Mixed Models. We found that curves of tadpoles at risk of predation differed from those of control mainly in thermal sensitivity parameters. Our work confirms the importance of biotic interactions have in thermal physiology.

Impacts of predator-induced behavioural plasticity on the temperature dependence of predator-prey activity and population dynamics

Predation is a key ecological interaction affecting populations and communities. Climate warming can modify this interaction both directly by the kinetic effects of temperature on biological rates and indirectly through integrated behavioural and physiological responses of the predators and prey. Temperature dependence of predation rates can further be altered by predator-induced plasticity of prey locomotor activity, but empirical data about this effect are lacking. We propose a general framework to understand the influence of predator-induced developmental plasticity on behavioural thermal reaction norms in prey and their consequences for predator-prey dynamics. Using a mesocosm experiment with dragonfly larvae (predator) and newt larvae (prey), we tested if the predator-induced plasticity alters the elevation or the slope of the thermal reaction norms for locomotor activity metrics in prey. We also estimated the joint predator-prey thermal response in mean locomotor speed, which determines prey encounter rate, and modelled the effect of both phenomena on predator-prey population dynamics. Thermal reaction norms for locomotor activity in prey were affected by predation risk cues but with minor influence on the joint predator-prey behavioural response. We found that predation risk cues significantly decreased the intercept of thermal reaction norm for total activity rate (i.e. all body movements) but not the other locomotor activity metrics in the prey, and that prey locomotor activity rate and locomotor speed increased with prey density. Temperature had opposite effects on the mean relative speed of predator and prey as individual speed increased with temperature in predators but decreased in prey. This led to a negligible effect of body temperature on predicted prey encounter rates and predator-prey dynamics. The behavioural component of predator-prey interaction varied much more between individuals than with temperature and the presence of predation risk cues in our system. We conclude that within-population variation in locomotor activity can buffer the influence of body temperature and predation risk cues on predator-prey interactions, and further research should focus on the magnitude and sources of behavioural variation in interacting species to predict the impact of climate change on predator-prey interactions and food web dynamics.

The dicey dinner dilemma: Asymmetry in predator-prey risk-taking, a broadly applicable alternative to the life-dinner principle

Forty years ago, the 'life-dinner principle' was proposed as an example of an asymmetry that may lead prey species to experience stronger selection than their predators, thus accounting for the high frequency with which prey escape alive from interaction with a predator. This principle remains an influential concept in the scientific literature, despite several works suggesting that the concept relies on many under-appreciated assumptions and does not apply as generally as was initially proposed. Here, we present a novel model describing a very different asymmetry to that proposed in the life-dinner principle, but one that could apply broadly. We argue that asymmetries between the relative costs and benefits to predators and prey of selecting a risky behaviour during an extended predator-prey encounter could lead to an enhanced likelihood of escape for the prey. Any resulting advantage to prey depends upon there being a behaviour or choice that introduces some inherent danger to both predator and prey if they adopt it, but which if the prey adopts the predator must match in order to have a chance of successful predation. We suggest that the circumstances indicated by our model could apply broadly across diverse taxa, including both risky spatial or behavioural choices.

Thermoregulatory strategies in an aquatic ectotherm from thermally-constrained habitats: An evaluation of current approaches

Many ectotherms employ diverse behavioral adjustments to effectively buffer the spatio-temporal variation in environmental temperatures, whereas others remain passive to thermal heterogeneity. Thermoregulatory studies are frequently performed on species living in thermally benign habitats, which complicate understanding of the thermoregulation-thermoconformity continuum. The need for new empirical data from ectotherms exposed to thermally challenging conditions requires the evaluation of available methods for quantifying thermoregulatory strategies. We evaluated the applicability of various thermoregulatory indices using fire salamander larvae, Salamandra salamandra, in two aquatic habitats, a forest pool and well, as examples of disparate thermally-constrained environments. Water temperatures in the well were lower and less variable than in the pool. Thermal conditions prevented larvae from reaching their preferred body temperature range in both water bodies. In contrast to their thermoregulatory abilities examined in a laboratory thermal gradient, field body temperatures only matched the mean and range of operative temperatures, showing thermal passivity of larvae in both habitats. Despite apparent thermoconformity, thermoregulatory indices indicated various strategies from active thermoregulation, to thermoconformity, and even thermal evasion, which revealed their limited applicability under thermally-constrained conditions. Salamander larvae abandoned behavioral thermoregulation despite varying opportunities to increase their body temperature above average water temperatures. Thermoconformity represents a favored strategy in these ectotherms living in more thermally-constrained environments than those examined in previous thermoregulatory studies. To understand thermal ecology and its impact on population dynamics, the quantification of thermoregulatory strategies of ectotherms in thermally-constrained habitats requires the careful choice of an appropriate method to avoid misleading results.