Do Species' Abundances become More Spatially Variable with Stress?

Abstract

Abstract: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 positive relationship between mean and variance is expected at all scales. To investigate whether stress does increase the spatial 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 consistent increase in variability as a response to stress, even within studies. Moreover, a complex relationship was observed between spatial variance and mean abundances that was not represented by a simple power law. However, one consistent response 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 species increasing) may be crucial to smoothing out tensions between species and increasing resilience.

Rates of post-larval bedload dispersal in a non-tidal soft-sediment system

“…Hewitt & Thrush 2009). This measure of homogeneity in distribution was calculated for both ambient abundance and absolute dispersal rates.…”

“…Nevertheless, in marine ecosystems, dispersal and colonization processes are still poorly known (Cowen & Sponaugle 2009). The relative contribution of local, regional, or global dispersers has profound implications for community dynamics and resilience to disturbance (Palmer et al 1996, Whitlatch et al 1998, Thrush et al 2009). Despite the global dispersal potential of many species, short-dispersing fauna are also common, especially in soft-sediment ecosystems (Grantham et al 2003).…”

Protection Enhances Community and Habitat Stability: Evidence from a Mediterranean Marine Protected Area

“…Rising temporal and spatial variability is often a subtle outcome of human disturbance on ecological systems [7] – [9] , undermining community structure, leading to decreased resilience and to increased potential for regime shifts [10] . Regime shifts are largely unpredictable due to the inherent complexity of ecological systems [11] .…”

Increasing heterogeneity of sensitive assemblages as a consequence of human impact in submarine caves

“…More localized anthropogenic disturbance like human frequentation can determine changes both in single response variables (e.g., total number of species or individuals, diversity indices, biomass, or abundance of a single species) (e.g., Sala et al 1996;Garrabou et al 1998) and in the multivariate structure of marine assemblages (see Milazzo et al 2002 for a review). However, anthropogenic disturbance can also affect local heterogeneity, and increasing variability in pattern of distribution of benthic assemblages are considered to be a sensitive response, occurring before gross changes in mean abundance (Hewitt and Thrush 2009).…”