Stabilizing effects in temporal fluctuations: management, traits, and species richness in high‐diversity communities

Abstract

The loss of biodiversity is thought to have adverse effects on multiple ecosystem functions, including the decline of community stability. Decreased diversity reduces the strength of the portfolio effect, a mechanism stabilizing community temporal fluctuations. Community stability is also expected to decrease with greater variability in individual species populations and with synchrony of their fluctuations. In semi-natural meadows, eutrophication is one of the most important drivers of diversity decline; it is expected to increase species fluctuations and synchrony among them, all effects leading to lower community stability. With a 16-year time series of biomass data from a temperate species-rich meadow with fertilization and removal of the dominant species, we assessed population biomass temporal (co)variation under different management types and competition intensity, and in relation to species functional traits and to species diversity. Whereas the effect of dominant removal was relatively small (with a tendency toward lower stability), fertilization markedly decreased community stability (i.e., increased coefficient of variation in the total biomass) and species diversity. On average, the fluctuations of individual populations were mutually independent, with a slight tendency toward synchrony in unfertilized plots, and a tendency toward compensatory dynamics in fertilized plots and no effects of removal. The marked decrease of synchrony with fertilization, contrary to the majority of the results reported previously, follows the predictions of increased compensatory dynamics with increased asymmetric competition for light in a more productive environment. Synchrony increased also with species functional similarity stressing the importance of shared ecological strategies in driving similar species responses to weather fluctuations. As expected, the decrease of temporal stability of total biomass was mainly related to the decrease of species richness, with its effect remaining significant also after accounting for fertilization. The weakening of the portfolio effect with species richness decline is a crucial driver of community destabilization. However, the positive effect of species richness on temporal stability of total biomass was not due to increased compensatory dynamics, since synchrony increased with species richness. This shows that the negative effect of eutrophication on community stability does not operate through increasing synchrony, but through the reduction of diversity.

Functional differences stabilize beetle communities by weakening interspecific temporal synchrony

“…On a species‐pair basis, Lepš et al. () found similar negative relationship between species dissimilarity (based on several traits) and synchrony. In experimental plant communities, Roscher et al.…”

“…On the contrary, in an experimental grassland (Lepš et al. ), plant species richness itself explained 67% of total community variability, but this relationship is partially caused by experimental fertilization of some plots, which decreased species richness and destabilized the community. The negative relation between species richness and community variability may be a simple consequence of the statistical averaging of not completely synchronous populations (Doak et al.…”

“…), or decreases (Lepš et al. ), with nutrient addition. For wild‐animal populations, weather variability (Mutshinda et al.…”

Competition among functional groups increases asynchrony of their temporal fluctuations in a temperate grassland

“…() synchrony. This is true regardless of whether the weighted or unweighted form was used (Lepš et al., ) as weighting does not play a role if there are just two components. Perfect synchrony (corresponding to a correlation coefficient value +1) among the individual components of a community is in reality not achievable.…”

“…As far as we know, our data are the only removal experiment where the two components and their mixture have been available for more than 10 years, thus enabling reliable estimates of variability and synchrony. We are aware that there is very probably some stabilization within functional groups, caused by the asynchrony of individual species within functional groups (Lepš et al., ). Thus, we are not able to decide unequivocally whether the lower variability of forbs is due to a higher stability of their individual species, or because this group is more (functionally) diverse.…”