Temporal variability of a single population can determine the vulnerability of communities to perturbations

Abstract

1. Many aspects of global change affect the variability of species population densities, in terms of both the magnitude and pattern of density fluctuations. However, we have limited empirical understanding of the consequences of altered temporal variability of populations, independent of changes in their mean densities, for the structure and stability of natural communities and the responses of ecosystems to additional stressors. 2. We used a field experiment to test the effects of altered temporal variability of a single consumer species on community structure and stability. Specifically, we manipulated the temporal variability of populations of a key grazer species on temperate rocky shores (Littorina littorea), independent of their mean densities, over 12 months and measured the responses of algal communities in terms of multiple measures of structure and stability. Further, we tested whether consumer variability determined the effects of an additional perturbation, elevated sedimentation, on algal communities. 3. The effects of sedimentation on the structure and stability of algal communities were regulated by the temporal variability of consumer populations. In particular, elevated sedimentation led to a decrease in algal evenness, but only when consumer densities were held constant, and resulted in a decrease in the rate of local algal extinctions, but only when consumer temporal variability was increased. 4. Independent of sedimentation, increased temporal variability of consumer populations led to a shift in algal assemblage structure and affected the stability of algal communities in terms of both compositional turnover and resistance to environmental perturbations. Further, these effects varied according to the temporal pattern of consumer density fluctuations. 5. Synthesis. Our results demonstrate that changes in the temporal variability of a single species can modify multiple aspects of both the structure and stability of natural communities and alter their responses to perturbations. However, the effects of consumer variability cannot be predicted without knowledge of the temporal pattern of density fluctuations. These findings have profound implications for our understanding of the effects of multiple disturbances on ecosystems.

Community temporal variability increases with fluctuating resource availability

“…We further tested the relationship between the relative abundance of dominant species and community stability. The results showed that temporal stability of protozoan community increased significantly with the relative abundance of dominant protozoan species, C. Striatum , further supporting the importance of dominant species in stabilizing communities (also see refs 12 and 19, 20, 21, 22). However, the lack of a statistically significant positive relationship between community temporal stability and dominant algal species ( S. opoliensis ) suggested that community-wide species asynchrony was more likely to play a vital role in regulating temporal stability of resident algal community.…”

“…In particular, the observation that resident communities receiving low-magnitude pulses were more stable than resident communities receiving high-magnitude pulses might be explained by the fact that when the pulse events continued for the entire experiment (i.e., with longer duration), there was more time for the acclimation of the dominant species to the new conditions. As a result, well-adapted dominant species with relatively stable populations could contribute significantly to community stability2122. We further tested the relationship between the relative abundance of dominant species and community stability.…”

“…Additionally, component species with less variable population dynamics could contribute to less variable communities. This is particularly true when the stable presence of a few dominant species directly facilitates the process of stability propagation from the population level towards higher organizational levels121819202122.…”

Navigating the complexity of ecological stability

“…; Mrowicki et al . ). Many of the most globally important disturbances in nature are of this kind (Fig.…”

“…Directionality measures the trajectory of change, which can be highly dynamic and variable in terms of its mean and variance. Both can elicit distinct ecological responses (Bertocci et al 2005;Benedetti-Cecchi et al 2006;Garc ıa Molinos & Donohue 2010Pincebourde et al 2012;Mrowicki et al 2016). Many of the most globally important disturbances in nature are of this kind ( Fig.…”