Increasing synchrony opposes stabilizing effects of species richness on terrestrial communities

Abstract

Aim Ecological theory has predicted that species richness should stabilize communities, with mechanisms including species synchrony and population variability determining the net impacts. While these theories have been supported empirically, results can be sensitive to taxonomic bias as studies are often focussed on plants. Trophic differences between consumers and primary producers can lead to varying stabilizing effects of species richness. Here, we compared the impact of species richness on community variability in four taxonomic groups: terrestrial birds, mammals, invertebrates and plants. Location Global. Method Using data from 6763 time series globally (BioTIME) for four terrestrial taxa, we quantified community and population variability and species synchrony based on abundance fluctuations over time. Results Species richness destabilized communities through increasing synchrony and stabilized communities through reducing population variability in all taxa. Such opposing effects weakened the net impacts of species richness on communities. Population variability had higher importance relative to synchrony in plant communities. By contrast, synchrony had more comparable (or even higher) importance compared with population variability in animal communities. When synchrony and population variability were not controlled, stabilizing impacts of species richness were detected in plant communities only. Main Conclusions Our results highlight how species richness drives stabilizing and destabilizing mechanisms simultaneously across all taxa, with strong taxonomic variation in the relative importance of these mechanisms in regulating community variability. This questions the generality of previous findings on stabilizing impacts of species richness based on limited taxonomic coverage. Additionally, our results indicate the need to understand how the importance of stabilizing and destabilizing mechanisms differs in determining community variability across organisms and environments.

Tree species identity, canopy structure and prey availability differentially affect canopy spider diversity and trophic composition

“…Further, variability of horizontal gap sizes decreased spider functional richness and isotopic ranges, indicating a limited trophic diversity of consumed prey. This may indicate that high structural complexity promotes functional similarity of spiders via spatial partitioning and increased abundance of prey with high trophic similarity (Müller et al 2018 ; Tsang et al 2023 ). Yet, this similarity can be mediated by canopy gaps, as we also found an increase in contrasting trophic traits (isotopic divergence) with larger horizontal gap size, and increasing functional evenness with variation in horizontal gap size.…”

“…The latter underlines that multiple heterogeneity attributes might have differing relationships with canopy arthropods and that in sum, intermediate habitat heterogeneity might balance positive and negative impacts (Heidrich et al 2020 ; Swart et al 2020 ). This would also lead to higher ecological stability of communities via even occupation of dissimilar niches (Godoy et al 2018 ; Tsang et al 2023 ).…”