Indirect effects of an ecosystem engineer: how the Canadian beaver can drive the reproduction of saproxylic beetles

Ecosystem engineers cause biodiversity spill-over: Beavers are associated with breeding bird assemblages on both wetlands and adjacent terrestrial habitats

The influence of ecosystem engineers on habitats and communities is commonly acknowledged in a site-bounded context, i.e. in places directly affected by the presence of the focal species. However, the spatial extent of the effects of such engineering is poorly understood, raising the question as to what impact they have on ecosystems situated beyond the species' direct influence. Beavers Castor spp., iconic ecosystem engineers, are capable of significantly transforming aquatic ecosystems. Their presence boosts biodiversity in adjacent aquatic and riparian habitats, but as a result of cascading processes, beavers may affect terrestrial habitats situated beyond the range of their immediate activity. Our study investigates the breeding bird assemblage along a spatial gradient from the water to the forest interior on central European watercourses modified and unmodified by beavers. The results show that beaver sites are characterized by a higher species richness and abundance of breeding birds than unmodified watercourses. Such sites also host a different species pool, as 27 % of the recorded bird species occurred exclusively on the beaver sites. The effect of the beaver's presence on the bird assemblage extended to adjacent terrestrial habitats located up to 100 m from the water's edge, where the species richness and abundance was higher and the species composition was substantially modified. We also found a positive correlation between the total area of beaver wetland and the numbers of bird species and individuals recorded. Our study adds to the general understanding of the spatial context of the ecosystem engineering concept, as the changes brought about by engineers have an influence beyond the area of their immediate occurrence. Our work also has implications for landscape planning and management, where existing beaver sites with terrestrial buffer zones may constitute a network of biodiversity hotspots.

A Biodiversity Boost From the Eurasian Beaver (Castor fiber) in Germany’s Oldest National Park

Freshwater ecosystems are among the most threatened ecosystems on the planet. Beavers are important engineers in freshwater ecosystems and reintroduction programs have enabled the recovery of beaver populations in several European countries, but the impact on biodiversity conservation is still unclear. We studied the effects of beavers on the terrestrial biodiversity of eight taxonomic groups by comparing beaver ponds with river and forest habitats in a mountain forest ecosystem in Central Europe. Among the 1,166 collected species, 196 occurred exclusively at beaver ponds, 192 in plots at the river, and 156 in the forest plots. More species of conservation concern were found at the beaver ponds (76) than on the river (67) and forest (63) plots. Abundances of bats and birds were higher at the beaver ponds than at the river or forest sites. The number of bird species at the beaver ponds was higher than at the river. The community composition of birds, beetles, and true bugs differed significantly between the beaver ponds and river plots, and for seven taxonomic groups it differed significantly between the beaver ponds and forest plots. An indicator species analysis revealed eight indicator species for the beaver pond but none for the river and forest plots. Our results demonstrate that beavers, as ecological engineers, increase habitat heterogeneity in mountain forests and thereby promote biodiversity. The expansion of beaver populations into these ecosystems should thus be supported, as it may serve as a biotic restoration tool.

Groundcovers and Rain Shelters Alter Co-Occurrence Patterns among Ground Beetle Communities in an Organic Raspberry Crop

Simple Summary

Rain shelters and reflective groundcovers improve the economic and environmental sustainability of organic fruit crops affected by a number of plant pathogens. In this study, we examined whether these structures also affect the communities of species that inhabit the soil surface, particularly ground beetles, in organic red raspberry crops. Our results indicate that ground beetle species richness, activity and functional traits differed in the presence of rain shelters and reflective groundcovers, but these effects were relatively minor. Thus, this study suggests that these structures, which have known benefits against plant pathogens, had no detrimental impact on ground beetle communities.

Abstract

The use of rain shelters and reflective groundcovers has been shown to improve the economic and environmental sustainability of organic fruit crops prone to rain-driven epidemics of phytopathogens. Here, we tested whether these structures affect communities of epigean species. To this end, we studied rain shelters and white, synthetic reflective groundcovers placed in a red raspberry organic cropping system in New Brunswick, Canada, during two subsequent summers to assess their independent and combined effects on ground beetles (Coleoptera: Carabidae). 18,445 ground beetles belonging to 54 species were collected. Rain shelters and reflective groundcovers altered patterns of ground beetle species richness, activity density and functional diversity compared to the control, but to a limited extent. Thus, this study suggests that these structures, which have known benefits against phytopathogens, have no detrimental impact on epigean fauna.

The Pitfalls in the Path of Probabilistic Inference in Forensic Entomology: A Review

To bridge the gap between experimentation and the court of law, studies in forensic entomology and other forensic sciences have to comply with a set of experimental rules to generate probabilistic inference of quality. These rules are illustrated with successional studies of insects on a decomposing substrate as the main example. The approaches that have been used in the scientific literature to solve the issues associated with successional data are then reviewed. Lastly, some advice to scientific editors, reviewers and academic supervisors is provided to prevent the publication and eventual use in court of forensic studies using poor research methods and abusing statistical procedures.

Size matters: When resource accessibility by ecosystem engineering elicits wood-boring beetle demographic responses

Episodic natural disturbances play a key role in ecosystem renewal, and ecological engineering could do so by transforming resource accessibility. While such coupling creates nontrophic and lasting interactions between resource consumers and ecosystem engineers, it is unclear how large the disturbance must be to sustain such coupling. Natural disturbances that occur from the ecological engineering by the Canadian beaver (Castor canadensis) modulate deadwood dynamics in many forest ecosystems. Relying on such episodes of fresh woody debris, primary wood-boring beetles, organisms that dig tunnels into those debris for reproduction, act as important deadwood decomposers in the ecosystem. Here, we investigate how the age and size of beaver disturbances act as predictors for primary wood-boring beetle abundance and species richness around beaver-altered habitat patches. To do so, we sampled beetles around 16 beaver-disturbed and unaltered watercourses within the Kouchibouguac National Park (Canada) and modeled beetle demographic responses to site conditions and their physical characteristics, distance from the watercourse, deadwood biomass, and the geographical location of the sites. Our results indicate that the size of the disturbance is positively associated with beetle abundance, which highlights unique deadwood dynamics inherent to large beaver ponds. The role of beavers in forest ecosystems by reaching multiple taxa at multiple spatiotemporal scales further exemplifies the need to study nontrophic interactions and their complex consequences in ecosystem management.