Predator-prey interactions under thermal pressure

Abstract

Ectotherms' ecological performance is directly linked to their thermal environment, many of which are warming due to climate change. If predator and prey thermal niches differ, warming may impact the intensity of predator-prey interactions, with subsequent effects on their populations. To determine how warming may impact predator-prey interactions, I fit and compared maximum swim speed thermal performance curves (TPCs) of Dytiscidae predaceous diving beetles (Tribe Agabini) and their prey, Wood Frog (Lithobates sylvaticus) and Eastern Gray Treefrog (Dryophytes versicolor) tadpoles. I then used climate change projections and measures of pond water temperature to determine how relative swim speeds of predators and prey may change in the future. Due to a lack of predicted future water temperature data, I established an air-water temperature relationship by fitting a generalized linear model (GLM) to 2024 air and water temperatures from 5 sites north of Thunder Bay, Ontario. I then used predicted air temperature data for 2025-2100 and my GLMs to get predicted water temperatures for the next 75 years. TPC comparisons between Agabini predators and tadpole prey revealed that predators have a performance advantage over D. versicolor tadpoles at warmer temperatures, but not L. sylvaticus tadpoles. Agabini beetle thermal optimum (Topt) (28.6 ± 1.6 ºC) was also significantly greater than D. versicolor (24.2 ± 0.9 ºC, p = 0.025), but not significantly different from L. sylvaticus (25.7 ± 3.2 ºC, p = 0.163). Agabini beetle 80% thermal tolerance breadth (Tbr(80%)) (13.5 ± 0.9) was significantly narrower than D. versicolor (18.1 ± 0.9, p = 0.040) but not significantly different from L. sylvaticus (19.1 ± 2.7, p = 0.162). Predictions showed that pond temperatures will increase through time, giving Agabini beetle predators an increasing performance advantage over D. versicolor over the next 75 years. However, due to similar performance measures between L. sylvaticus and the predators, their interaction will not be impacted by temperature changes over the next 75 years. These results show variability between predator-prey pairs in the same environment. When the predator's performance advantage over their prey increases, it may result in increased predation pressure and reduced prey populations, while other predator-prey interactions will be unaffected. Thus, as climate change alters thermal regimes, predator-prey interactions will be altered, but not between all predator-prey pairs.