Do Species’ Abundances become More Spatially Variable with Stress?

The relationship between stress and population variability is essential for predicting whether communities will exhibit stability and resilience when faced with stress. Stress is generally considered to increase biological variability, even before mean responses exhibit change. However, generalities related to spatial variability of populations have not emerged, as large-scale perturbations tend to reduce variability in affected areas (i.e., a homogenising effect), and a posi- tive relationship between mean and variance is expected at all scales. To investigate whether stress does increase the spa- tial variability of macrobenthic species abundances, we analysed the response of survey and experimental data, collected over a variety of space (50 m to 5 km) and time scales (15 d to 15 yr), to two different stressors. We observed no consis- tent increase in variability as a response to stress, even within studies. Moreover, a complex relationship was observed be- tween spatial variance and mean abundances that was not represented by a simple power law. However, one consistent re- sponse was observed across stressors and study type; the number of common species exhibiting changes (either increases or decreases) to their spatial variability, beyond natural levels, increased with stress. It seems likely that having species within a community whose spatial variability responds in different ways to stress (rather than spatial variability of all spe- cies increasing) may be crucial to smoothing out tensions between species and increasing resilience.