Prey behavioural time budgets create seasonality in predator diets and prey mortality rates

Background/Question/Methods

Predator prey interactions are most commonly described in the context of functional responses, where what predators are eating is dependent primarily on prey densities. In this view prey switching is strictly considered a density driven phenomenon. However, not all behavioural states expressed by prey in space and time have the same vulnerability to predation thus creating time budgets that are a mixture of safe and dangerous periods. As such, prey availability for predators should be strongly influenced by prey behaviour and not just densities. Here we explore how spatiotemporal variation in the behaviour of species within a food web impacts prey vulnerability, predator-prey interactions and life history parameters. We focus on seasonality of interactions, a scale at which densities can be relatively constant but behavioural time budgets are highly variable. We combine analysis of novel biologging data collected on Canada lynx, snowshoe hares, and red squirrels with a revisit of other well characterized predator-prey systems to generate new theory on how temporal variation in the spatiotemporal structure of prey behaviour shapes predator diets and prey mortality rates.

Results/Conclusions

We found a clear seasonal pattern in lynx diets that corresponds with temporal variation in red squirrel and snowshoe hare behavioural time budgets. Consumption of red squirrels by lynx reduced to nothing as squirrel activity decreased in the winter leaving snowshoe hares that remain active as the sole prey. This behaviourally dependent prey selection by lynx has cascading effects on seasonal patterns in prey mortality rates, with snowshoe hares having low mortality in summer when other species are active and high mortality rates in winter when hare activity is higher than other prey. Red squirrels have the opposite seasonal pattern with mortality rates mirroring activity (both highest in summer). A broader examination of predator diets from other well characterized systems confirms that seasonality in diets is common in the natural world with patterns in prey selection corresponding to spatiotemporal variation in prey time budgets. This work highlights that behaviour, and not just density, determines availability of prey for predators. The consideration of temporal variation in prey time budgets when investigating predator prey systems greatly improves our understanding of predator prey interactions by providing theoretical explanations for previously inexplicable patterns in diets and mortality rates.