Quantifying predator functional responses under field conditions reveals interactive effects of temperature and interference with sex and stage

Abstract

Predator functional responses describe predator feeding rates and are a core component of predator-prey theory. Although originally defined as the relationship between predator feeding rates and prey densities, it is now well known that predator functional responses are shaped by a multitude of factors. Unfortunately, how these factors interact with one another remains unclear, as widely used laboratory methods for measuring functional responses are generally logistically constrained to examining a few factors simultaneously. Furthermore, it is also often unclear whether laboratory derived functional responses translate to field conditions. Our goal was to apply an observational approach for measuring functional responses to understand how sex/stage differences, temperature, and predator interference interact to influence the functional response of zebra jumping spiders on midges under natural conditions. We used field feeding surveys of jumping spiders to infer spider functional responses. We applied a Bayesian model averaging approach to estimate differences among sexes and stages of jumping spiders in their feeding rates and their dependencies on midge densities, temperature, and predator interference. We find that females exhibit the steepest functional responses on midges, followed by juveniles, and then males, despite males being larger than juveniles. We also find that sexes and stages differ in the temperature dependence of their space clearance (aka attack) rates. We find little evidence of temperature dependence in females, whereas we find some evidence for an increase in space clearance rate at high temperatures in males and juveniles. Interference effects on feeding rates were asymmetric with little effect of interference on male feeding rates, and effects of interference on females and juveniles depending on the stage/sex from which the interference originates. Our results illustrate the multidimensional nature of functional responses in natural settings and reveal how factors influencing functional responses can interact with one another through behavior and morphology. Further studies investigating the influence of multiple mechanisms on predator functional responses under field conditions will provide an increased understanding of the drivers of predator-prey interaction strengths and their consequences for communities and ecosystems.

Quantifying predator functional responses under field conditions reveals interactive effects of temperature and interference with sex and stage

“…All data and code for their analyses are permanently archived on Zenodo https://doi.org/10.5281/zenodo.6426222 (Coblentz, 2022).…”

Predator feeding rates may often be unsaturated under typical prey densities

“…Gilg et al, 2006;Messier, 1994;Moleón et al, 2012;Moustahfid et al, 2010;Nielsen, 1999;Nilsen et al, 2009). However, other studies show saturated feeding rates at only one or a few observations at the highest observed prey densities (Angerbjörn, 1989;Coblentz et al, 2022;Korpimaki & Norrdahl, 1991;Quinn et al, 2003;Redpath & Thirgood, 1999;Sundell et al, 2000) or little to no evidence of feeding rate saturation (Beardsell et al, 2021(Beardsell et al, , 2022Coblentz et al, 2021;Novak, 2010;Novak et al, 2017;Preston et al, 2018). Therefore, it is currently unclear how saturated feeding rates are likely to be in general.…”