Cold-blooded animals, such as insects, reptiles and fish, rely on their surroundings to warm their bodies to temperatures needed for basic activities, such as foraging for and digesting prey. Under warmer conditions, foraging and digestion typically occur more rapidly than they would under cooler conditions. Thus, global warming is expected to make cold-blooded predators “hungrier”, increasing the rate at which they hunt for and consume their prey, thereby strengthening their overall effects on prey species and potentially reducing prey densities in the wild.
However, warming temperatures can also affect other aspects of an animal’s physiology that can influence the way that predators and their prey interact. In particular, warmer temperatures accelerate the rate at which organisms grow and develop. By doing so, warming can limit the amount of time that individual prey spend in life stages or at sizes that are particularly vulnerable to their predators. For example, like many insects, mosquitoes undergo metamorphosis, growing from an aquatic larval stage to an airborne adult stage. Mosquito predators that are restricted to aquatic habitats, such as dragonfly nymphs or fish, can only feed on larval mosquitoes.
Warming can therefore simultaneously affect the predator-prey interaction in opposing ways – speeding up the rate at which the predator consumes prey, but limiting how much time the predator has to consume prey before they “escape” the predator’s reach. So whether warming will lead to fewer or greater numbers of prey surviving will depend on which player – predator or prey – is most strongly affected by rising temperature.
We used a series of short-term experiments to build a mathematical model describing the effects of temperature on predation of larval mosquito prey (Aedes atropalpus, the rock pool mosquito) by dragonfly nymphs (Pachydiplax longpennis, the blue dasher; and Erythemis simplicicollis, the eastern pondhawk). We use the model to demonstrate that warmer temperatures can have varied effects on how many mosquito larvae survive to become adults, depending on the relative effects of warming on the predator and prey. When temperature had stronger effects on the rate at which the dragonfly nymphs foraged, then fewer mosquito larvae survived to adulthood at warmer temperatures. However, when temperature had stronger effects on the mosquito larvae’s development rate, then more mosquito larvae survived to adulthood at warmer temperatures. Our results suggest that predicting how warming will impact predator-prey interactions – and thus, how warming will influence the densities of important prey such as mosquitoes – will require careful consideration of how both predator and prey species respond to warmer temperatures.