Sequential stressor mesocosm experiment - fish x warming

Cumulative impacts of multiple extreme and novel environmental changes on
communities are often the result of asynchronous rather than simultaneous
exposures to such stressors. Yet, the importance of temporal dynamics
remains a major knowledge gap in multiple stressor ecology, lacking theory
or evidence. We provide a conceptual template for predicting the
ecological importance of the order in which consecutive stressors occur
(i.e. an exposure order effect) based on correlated species responses.
Negative correlation of species responses is hypothesized to increase,
while positive correlation is expected to reduce, exposure order effects
of consecutive stressors on communities. Towards a proof of concept, we
experimentally exposed planktonic communities from fishless mountain lakes
to different temporal sequences of two stressors, namely invasive
sportfish and elevated water temperatures. Both stressors suppressed the
same resident top predator and large grazers while eliciting positive
responses from smaller tolerant taxa, attesting to their interchangeable
effects across species based on size selection. As a result, reversal of
the order of exposure to the two stressors did not alter their combined
effects on community composition and function. Our findings suggest that
the order in which consecutive stressors occur may not matter to a
community if ecological memory of either stressor induces tolerance of the
other.