Spatial extinction or persistence: landscape-temperature interactions perturb predator-prey dynamics

Recognising that species interact across a range of spatial scales, we explore how landscape structure interacts with temperature to influence persistence. Specifically, we recognise that few studies indicate thermal shifts as the proximal cause of species extinctions; rather, species interactions exacerbated by temperature result in extinctions. Using microcosm-based experiments, as models of larger landscape processes, we test hypotheses that would be problematic to address through field work. A text-book predator-prey system (the ciliates Didinium and Paramecium) was used to compare three landscapes: an unfragmented landscape subjected to uniform temperatures (10, 20, 30 degrees C); a fragmented landscape (potentially hosting metapopulations) subjected to these three temperatures; and a fragmented landscape subjected to a spatial temperature gradient (-10 to 30 degrees C) - despite the prevalence of natural temperature ecoclines this is the first time such an analysis has been conducted. Initial thermal response-analysis (growth, mortality, and movement measured between 10 and 30 degrees C) suggested that as temperature increased, the predator might drive the prey to extinction. Thermal preferences (measured at 5 temperatures between 10 and 30 degrees C), indicated that both predator and prey preferred warmer temperatures, with the predator exhibiting the stronger preference, suggesting that cooler regions might act as a prey-refuge. The landscape level observations, however, did not entirely support the predictions. First, in the unfragmented landscape, increased temperature led to extinctions, but at the highest temperature (where the predator growth can be reduced) the prey survived. Second, at high temperatures the fragmented landscape failed to host metapopulations that would allow predator-prey persistence. Third, the thermal ecocline did not provide heterogeneity that improved stability; rather it forced both species to occupy a smaller realized space, leading toward extinctions. These findings reveal that temperature-impacted rates and temperature preferences combine to drive predator-prey dynamics and persistence across landscapes.