Linking species traits and demography to explain complex temperature responses across levels of organization

Abstract

Microbial communities regulate ecosystem responses to climate change. However, predicting these responses is challenging because of complex interactions among processes at multiple levels of organization. Organismal traits that determine individual performance and ecological interactions are essential for scaling up environmental responses from individuals to ecosystems. We combine protist microcosm experiments and mathematical models to show that key traits—cell size, shape, and contents—each explain different aspects of species’ demographic responses to changes in temperature. These differences in species’ temperature responses have complex cascading effects across levels of organization—causing nonlinear shifts in total community respiration rates across temperatures via coordinated changes in community composition, equilibrium densities, and community–mean species mass in experimental protist communities that tightly match theoretical predictions. Our results suggest that traits explain variation in population growth, and together, these two factors scale up to influence community- and ecosystem-level processes across temperatures. Connecting the multilevel microbial processes that ultimately influence climate in this way will help refine predictions about complex ecosystem–climate feedbacks and the pace of climate change itself.

Feedbacks between size and density determine rapid eco-phenotypic dynamics

“…Following previous work (Abrams 1977; Abreu et al . 2019; Lax, Abreu & Gore 2020; Wieczynski et al . 2021), we included an additional mortality term in the ecological dynamics, mN , to account for regular loss of individuals from the population through sampling.…”

“…Following previous work (Abrams 1977;Abreu et al 2019;Lax, Abreu & Gore 2020;Wieczynski et al 2021), we included an additional mortality term in the ecological dynamics, "#, to account for regular loss of individuals from the population through sampling. This additional mortality term has been shown to better describe the ecological dynamics of a microbial microcosm with frequent sampling, like ours (Abreu et al 2019;Lax, Abreu & Gore 2020).…”

“…In protists, we expect changes in body size to be at least partly caused by plasticity because reproduction (cell division) is tightly linked to ontogenetic changes in body size (cells grow then divide when a critical size is attained). However, T. pyriformis also reproduces extremely fast (∼4 generations per day) and exhibits wide standing variation in body size (Wieczynski et al . 2021), so rapid evolutionary change is also possible.…”

“…In protists, we expect changes in body size to be at least partly caused by plasticity because reproduction (cell division) is tightly linked to ontogenetic changes in body size (cells grow then divide when a critical size is attained). However, T. pyriformis also reproduces extremely fast (~4 generations per day) and exhibits wide standing variation in body size (Wieczynski et al 2021), so rapid evolutionary change is also possible. Therefore, to distinguish the impacts of plasticity and evolution on changes in body size, we fit alternative mathematical models (Plasticity Model, Eco-Evolutionary Model, and Plasticity + Eco-Evo Model) to our experimental time series and use model selection to infer which one best explains our data.…”

Increasing temperature weakens the positive effect of genetic diversity on population growth

“…Here, we address this issue in a model microbial system, the globally distributed protist Tetrahymena thermophila . These organisms play an important role in the global carbon cycle that ultimately determines the pace of climate change (i.e., the microbial loop; Gao et al, 2019; Karhu et al, 2014; Rocca et al, 2021) and are easy to grow in temperature‐controlled laboratory conditions (Fjerdingstad et al, 2007) making them an ideal system to understand how temperature may influence ecological processes (Petchey et al, 1999; Wieczynski et al, 2021).…”