Lily M. Thompson | Search USGS

USGS2026

Null models reveal differing drivers of multidimensional beta diversity change in invaded metacommunities

Aim Invasion-driven changes in beta diversity (Δβ) are multifaceted (taxonomic, functional, and phylogenetic) and are comprised of three components (total beta diversity, replacement, and richness difference); therefore, they represent a nine-dimensional phenomenon. Invasion-driven trajectories of multidimensional Δβ are inconsistent and can vary based on the geographic origin of nonnative species, native community structure, and site attributes. Here, we examine the drivers of multidimensional Δβ to better understand how nonnative species alter biodiversity. Location 1023 wadable-stream fish communities across the conterminous United States. Methods We characterized nine dimensions of Δβ as changes in local contribution to beta diversity (ΔLCBD) derived from pairwise beta diversity of all 1023 sites between contemporary and native-only assemblages at each site. We used redundancy analysis and variance partitioning to identify and estimate the relative importance of 18 Δβ drivers related to nonnative species origin, propagule pressure, abiotic factors, and native community structure. We compared results between those from raw and null model standardized LCBD. Results We found an overall trend of taxonomic homogenization due to nonnative species occurrences. However, null model standardization revealed inconsistent directional change in functional and phylogenetic Δβ, and also revealed Δβ patterns and drivers that differed from those of raw values. Sites did not contribute evenly to overall Δβ trends, with nonnative species origin and native community structure explaining the most variation in ΔLCBD (16% and 15% respectively). Nonnative occurrences, regardless of origin, contributed to taxonomic homogenization, with the magnitude of change dependent on origin. Native community structure dictated the direction of phylogenetic Δβ, with phylogenetically distinct sites contributing to homogenization. Conclusions Our findings demonstrate the utility in using LCBD to identify site-level drivers of Δβ and the need for null model standardization of multidimensional Δβ metrics. Additionally, our results show that spatially explicit definitions of nonnative species are needed to gain robust estimates of Δβ.

conterminous United States↗

USGS2024

Range-wide salamander densities reveal a key component of terrestrial vertebrate biomass in eastern North American forests

Characterizing the population density of species is a central interest in ecology. Eastern North America is the global hotspot for biodiversity of plethodontid salamanders, an inconspicuous component of terrestrial vertebrate communities, and among the most widespread is the eastern red-backed salamander, Plethodon cinereus . Previous work suggests population densities are high with significant geographic variation, but comparisons among locations are challenged by lack of standardization of methods and failure to accommodate imperfect detection. We present results from a large-scale research network that accounts for detection uncertainty using systematic survey protocols and robust statistical models. We analysed mark–recapture data from 18 study areas across much of the species range. Estimated salamander densities ranged from 1950 to 34 300 salamanders ha −1 , with a median of 9965 salamanders ha −1 . We compared these results to previous estimates for P. cinereus and other abundant terrestrial vertebrates. We demonstrate that overall the biomass of P. cinereus , a secondary consumer, is of similar or greater magnitude to widespread primary consumers such as white-tailed deer ( Odocoileus virginianus ) and Peromyscus mice, and two to three orders of magnitude greater than common secondary consumer species. Our results add empirical evidence that P. cinereus , and amphibians in general, are an outsized component of terrestrial vertebrate communities in temperate ecosystems.

Biology Letters↗