Contributions of mean temperature and temperature variation to population stability and community diversity

Abstract

Future climate changes are predicted to not only increase global temperatures but also alter temporal variation in temperature. As thermal tolerances form an important component of a species’ niche, changes to the temperature regime have the capacity to negatively impact species, and therefore, the diversity of the communities they inhabit. In this study, we used protist microcosms to assess how mean temperature, as well as temporal variation in temperature, affected diversity. Communities consisted of seven species in a multitrophic food web. Each ecosystem was inoculated with the same abundances of each species at the start of the experiment, and species densities, Hill's numbers (based on Shannon diversity), the number of extinctions, and the probability the microcosm contained predators were all calculated at the end of the experiment. To assess how mean temperature and temperature fluctuations affect stability, we also measured population densities through time. We found that increased temporal variation in temperature increased final densities, increased Hill's numbers (at low mean temperatures), decreased rates of extinctions, and increased the probability that predators survived till the end of the experiment. Mean temperatures did not significantly affect either the number of extinctions or the probability of predators, but did reduce the positive effect of increased temporal variation in temperature on overall diversity. Our results indicate that climatic changes have the potential to impact the composition of ecological communities by altering multiple components of temperature regimes. However, given that some climate forecasts are predicting increased mean temperatures and reduced variability, our finding that increased mean temperature and reduced temporal variation are both generally associated with negative consequences is somewhat concerning.

Spatiotemporal thermal variation drives diversity trends in experimental landscapes

“…positive effect of the 'sub-optimal' conditions induced by temperature variance Martin & Huey, 2008), promoting diversity at the middle phase of the experiment. These differences were driven by increased abundances of Bursaria truncatella and Homalozoon vermiculare (Figure S2; Figure 4a), in agreement with previous findings that temporal thermal variation also increases predator survival (Hammill & Dart, 2022). This indicates the potential for temporal thermal variation to buffer against species loss, providing evidence for hypothesis 1b at the experiment's midpoint.…”

“…We opted not to acclimate the stocks prior to experiment set‐up because the average temperature of each landscape over a 24‐h period was 20°C, the same temperature that the stocks were kept at. Additionally, we chose to control for average patch temperature at the landscape level because, as recent evidence has shown (Hammill & Dart, 2022 ), mean temperature interacts with temperature variation. Our four temperature regimes manipulated either spatial variation in temperature, temporal variation in temperature, both spatial and temporal variation, or neither (acting as a control).…”

The effect of single versus successive warm summers on an intertidal community

“…If environmental stress occurs over a prolonged period, or if repeated stressors occur in rapid succession, there can be stronger negative consequences on organism survival and fitness (Bible et al 2017;Ma et al 2018;Siegle et al 2022). At the community level, repeated stressors that occur with limited intervening time for recovery can produce more homogenous (Hammill and Dart 2022) and depauperate (Dal Bello et al 2019) communities. Even if recovery can occur between stressors, an initial stressor may engender susceptibility to subsequent stressors (Marshall and Sinclair 2015, Siegle et al 2018, Jackson et al 2021, Sun et al 2022, perhaps by eroding the energy stores available for coping with secondary stressors.…”

Temperature change and biodiversity influence community stability differently in birds and fishes

“…Other aspects of TC include the variation in inter-annual temperature (variability) [9][10][11][12] , the temporal trend 13 , and extreme heat waves 5,14,15 . Nevertheless, to our knowledge, no study has considered these different aspects together in analyses of community stability.…”