Abstract
AbstractSpecies interactions, environmental conditions, and stochastic processes work in concert to bring about changes in community structure. However, the relative importance of specific factors and how their combined influence affects community composition remain largely unclear. We conducted a multi‐factorial experiment to (1) disentangle the direct and interaction‐mediated effects of environmental conditions and (2) augment our understanding of how environmental context modulates species interactions. We focus on a planktonic system where interactions with phytoplankton effect changes in the composition of bacterial communities. Further, light and temperature conditions can influence bacteria directly as well as through their interactions with phytoplankton. Epilimnetic bacteria from two humic lakes were combined with phytoplankton assemblages from each lake (home or away) or a no‐phytoplankton control and incubated for 5 d under all combinations of light (surface, ~25% surface irradiance) and temperature (five levels from 10° to 25°C). Observed light effects were primarily direct, while phytoplankton and temperature effects on bacterial community composition were highly interdependent. The influence of temperature on aquatic bacteria was consistently mediated by phytoplankton and most pronounced for bacteria incubated with “away” phytoplankton treatments, likely due to the availability of novel phytoplankton‐derived resources. The effects of phytoplankton on bacterial community composition were generally increased at higher temperatures. Incorporating mechanisms underlying the observed interdependent effects of species interactions and environmental conditions into modeling frameworks may improve our ability to forecast ecological responses to environmental change.
Highlights
Species interactions, environmental conditions, and stochastic processes affect the abundance, diversity, and distribution of organisms in the environment
When Trout Bog (TB) bacteria were incubated with their “home” phytoplankton, there was a significant interaction between light and temperature
Significant light effects were not detected when bacteria were combined with phytoplankton from the “away” lake
Summary
Environmental conditions, and stochastic processes affect the abundance, diversity, and distribution of organisms in the environment. Effects of environmental conditions on a population include direct effects that can potentially be characterized by singlespecies observations and experiments as well as indirect effects that depend on species interactions and require more community-focused approaches to detect and predict (Gilman et al.2010). The outcome (e.g., mutualism, parasitism) and strength of interspecific interactions can change depending on environmental conditions as well as community composition (He et al 2013, Chamberlain et al 2014). To predict how communities will respond to seasonal environmental fluctuations and long-term changes in climate, it is necessary to account for species interactions that mediate and are affected by environmental conditions. Interaction-mediated effects of environmental change have consequences for local abundances and geographic distribution as well as phenology
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