OOS 31-6 - Rate of environmental change across levels of ecological organization: an experimental perspective

Background/Question/Methods
Experimental ecology has recently begun to grapple with incorporating temporal aspects of global change into experimental designs; however, there is no widely used framework, often precluding the translation of results between systems and across levels of ecological hierarchy. Theoretical work has suggested that depending on the rate of change (RoC) of an environmental driver, the nature of biological responses can be profoundly modified. Although seemingly intuitive, data on driver RoC effects are scarce and difficult to synthesize. To address this gap, we (1) performed a systematic literature review to identify publishing trends in studies reporting on the RoC of global change drivers from the level of individual organisms to ecosystems and (2) experimentally investigated the influence of temperature RoC on soil fungal individuals and interactions. In our experiment work, we implemented a multidimensional temperature treatment design that included a gradient of different RoCs (imitating instantaneous, daily and seasonal temperature changes) and two different heat stress levels compatible with possible climate change scenarios. We applied two different analytical approaches (dose-based and event-based) for distinguishing the effects of magnitude and RoC on individual and interactive responses.

Results/Conclusions
Our systematic literature review revealed a dearth of studies at the community and ecosystem levels and limited experimental data above the level of individual organisms. Few studies applied a gradient RoC approach, with most using only “abrupt” and “gradual” treatments, impeding insights into nonlinear trends and system thresholds. In our experimental study, we found that slower temperature RoC buffered negative effects of heat stress on fungal growth, but did not alter thermal limits. This means that different performance curves would be expected under different temperature RoCs. Fungal responses to temperature RoC correlated with traits relating to mycelial architecture and thermal limits. More instances of competitive exclusion were observed under faster RoCs, while more ties were observed under slower RoCs, particularly for intermediate competitors. In our work we provide a framework for experimental RoC studies, recommended reporting parameters, and a template experimental design that can be applied to any organism (group) and/or level of ecological organization. The need to investigate multiple RoCs, magnitudes and organism groups to make robust conclusions can lead to ‘combinatorial explosion’ in experiments; however, this potential problem also provides the opportunity for theoreticians and experimentalists to cooperate to generate targeted hypotheses for experimental work.