<div>10 June 2022</div><div><b>Editor-in Chief</b> , Ecology Letters</div><div>Dear Dr Thrall,</div><div>Please find attached our manuscript entitled “Fluctuating fortunes:
stressor synchronicity and fluctuating intensity influence biological
impacts”, which we are submitting to <i>Ecology Letters</i> as a
letter.</div><div>The study of multiple stressors has exploded in the last decade. Yet,
most manipulative experiments continue to apply stressors under static
conditions, ignoring how dynamic environments influence the intensity
and synchronicity of stressor presence and, consequently, the effect on
biological responses. Unless we improve our understanding of the impact
of multiple stressors under more realistic conditions, predictions of
future effects and efforts to mitigate effects may be less than
adequate.</div><div><b>Novelty statement:</b> This manuscript helps to address this
challenge by first developing a generalisable conceptual model of how
the type of interaction between stressors (i.e., antagonistic, additive,
synergistic) can influence the effect of variable stressor intensity
(i.e., fluctuations) and synchronicity (i.e., timing of fluctuations).
We then test and validate this model experimentally by evaluating the
effects of variable stressor intensity and synchronicity on plant growth
and physiology. We compare responses to those under static stressor
conditions, considered the ‘standard’ method in multiple stressor
experiments.</div><div>We find that variable stressor intensity and synchronicity does affect
biological responses, with the effect dependent on the response
variable, the stressor intensity, and the type of interaction between
stressors. For instance, fluctuating stressors reduced plant biomass
36% more than static stressors at the highest intensities, but there
are no such differences observed for photosynthetic capacity.</div><div>Our study demonstrates the importance of considering variability in
stressor intensity and synchronicity in multiple stressor experimental
designs. Ultimately, this approach will help us to better understand and
accurately predict cumulative stressor effects within a real-world
context. And we believe our generalisable conceptual model will be of
broad interest to the readership of <i>Ecology Letters.</i></div><div>All data used in this analysis are contained in the manuscript, and code
for analysis will be made available
on the lead author’s GitHub page.</div><div>The authors declare no conflicts of interest and confirm this manuscript
is not being considered for publication elsewhere. Its submission has
been approved by all authors and all persons entitled to authorship have
been so named.</div><div>Thank you for your consideration.</div><div>Sincerely,</div>