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

Abstract

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°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°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°C) suggested that as temperature increased, the predator might drive the prey to extinction. Thermal preferences (measured at 5 temperatures between 10 and 30°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.

Temperature alters the shape of predator–prey cycles through effects on underlying mechanisms

“…In our study, both predator and prey populations went deterministically extinct by the end of the experiment at all temperatures, consistent with the typical behavior of Didinium and Paramecium without stabilizing environmental factors introduced to the microcosms (Luckinbill, 1973;DeLong & Vasseur, 2013;Salt et al, 2017). Although extinctions occurred earlier in warmer temperatures, the system did not undergo major qualitative shifts such as from stable to unstable or from having a fixed point equilibrium to having oscillations, which are common predictions from theory (Vasseur & McCann, 2005;Amarasekare, 2015).…”

“…Full-size  DOI: 10.7717/peerj.9377/ fig-4 period and amplitude of Didinium-Paramecium caudatum dynamics (Salt et al, 2017). Yet by considering a broad range of temperatures, we also found that some of these dynamic shifts themselves may be unimodal rather than monotonically changing.…”

“…Here we examine the predator-prey cycles of the ciliate Didinium nasutum (hereafter Didinium) foraging on the ciliate Paramecium bursaria (hereafter Paramecium) as they pass through a population cycle. The Didinium-Paramecium predator prey system is a classic laboratory tool for studying predator-prey dynamics (Gause, 1934;Luckinbill, 1973;Salt, 1974;Jost & Ellner, 2000;Minter et al, 2011;Montagnes et al, 2012;DeLong & Vasseur, 2013;Li et al, 2013;Li & Montagnes, 2015;Salt et al, 2017). The advantages of this system are clear: short generation times, small spatial footprint, specialization of Didinium on Paramecium making for a very strong predator-prey interaction, and ease of estimating population abundances.…”

Multi‐scale responses to warming in an experimental insect metacommunity

“…As a result, temperature-induced increases in functional connectivity could increase diversity at both local and regional scales within metacommunities (Cadotte & Fukami, 2005;Verreydt et al, 2012). Although previous experiments investigating the effect of warming on metacommunity dynamics have maintained tractability by warming local patches while manipulating dispersal rates (Limberger, Low-D ecarie, & Fussmann, 2014;Thompson et al, 2015), allowing warming to simultaneously alter both local species interactions and species' movement between patches would provide a critical next step toward understanding the full impact of warming in spatially structured environments (Salt, Bulit, Zhang, Qi, & Montagnes, 2016).…”

Microbial grazers may aid in controlling infections caused by aquatic zoosporic fungi

“…food saturated on suitable prey) at 18 °C, for each species. Data were obtained from a various sources at a range of temperatures[59][60][61][62][63][64][65][66] and were converted to rates at 18 °C by two methods, either assuming a Q10 of 2 or that growth rate varies linearly with temperature at a rate of 0.07 r (d -1 ) °C -1[67].…”