Tscheulin, T. | bioRxiv Science

bioRxiv2021

Relationship Between Inter-individual Variation in Circadian Rhythm and Sociality: A case Study Using Halictid Bees

The bee family Halictidae is considered to be an optimal model for the study of social evolution due to its remarkable range of social behaviors. Past studies in circadian rhythms suggest that social species may express more diversity in circadian behaviors than solitary species. However, these previous studies did not make appropriate taxonomic comparisons. To further explore the link between circadian rhythms and sociality, we examine four halictid species with different degrees of sociality, three social species of Lasioglossum, one from Greece and two from Puerto Rico, and a solitary species of Systropha from Greece. Based on our previous observations, we hypothesized that species with greater degree of sociality will show greater inter-individual variation in circadian rhythms than solitary species. We observed distinct differences in their circadian behavior that parallel differences across sociality, where the most social species expressed the highest inter-individual variation. We predict that circadian rhythm differences will be informative of sociality across organisms.

animal behavior and cognition↗

bioRxiv2020

An invasive plant species enhances biodiversity in overgrazed pastures but inhibits its recovery in protected areas

Anthropogenic environmental change exposes biological communities to concurrent stressors (e.g., changes in climate and land-use, overexploitation, biotic invasions) that frequently persist over prolonged periods. Predicting and mitigating the consequences of human action on nature therefore requires understanding how exposure to multiple interacting stressors alters biological communities over relevant (e.g., multi-decadal) time periods. Here, we explore the effects of overgrazing and plant species invasion on plant community diversity and ecosystem functioning (productivity), as well as the patterns of recovery of plant communities following cessation of grazing pressure. In a Mediterranean pasture system, we utilized a "natural" experiment involving long-term exclusion of grazers (for 15-25 years in parks) and also conducted short-term grazing-exclusion and invasive species removal experiments. Our results reveal that invasion by a grazing-resistant plant (prickly burnet) has net positive effects on plant diversity under overgrazing conditions but inhibits the recovery of biodiversity once grazing ceases. Furthermore, while the diversity-productivity relationship was found to be positive in pastures, the interactive effects of overgrazing and species invasion appear to disrupt ecosystem functioning and inhibit the recovery of pasture productivity. These findings highlight the potential for prolonged exposure to anthropogenic stressors, such as overgrazing, to cause potentially-irreversible changes in biological communities that, in turn, compromise ecosystem functioning and resilience. In such cases, sustainable ecosystem management may require direct intervention to boost biodiversity resilience against centennial overgrazing.

ecology↗