The geography of biodiversity change in marine and terrestrial assemblages

Abstract

Human activities are fundamentally altering biodiversity. Projections of declines at the global scale are contrasted by highly variable trends at local scales, suggesting that biodiversity change may be spatially structured. Here, we examined spatial variation in species richness and composition change using more than 50,000 biodiversity time series from 239 studies and found clear geographic variation in biodiversity change. Rapid compositional change is prevalent, with marine biomes exceeding and terrestrial biomes trailing the overall trend. Assemblage richness is not changing on average, although locations exhibiting increasing and decreasing trends of up to about 20% per year were found in some marine studies. At local scales, widespread compositional reorganization is most often decoupled from richness change, and biodiversity change is strongest and most variable in the oceans.

Temperature-related biodiversity change across temperate marine and terrestrial systems

“…Finally, a weaker link between assemblage responses and temperature change on land may be due to other factors, such as land-use change and moisture availability, posing stronger constraints on local biodiversity. Nonetheless, the smaller magnitude or slower responses of terrestrial species to temperature change 5,12,15,24,36,37 , combined with the faster rates of warming on land, indicate a potentially higher risk of climatic debt (i.e. response lags) among terrestrial versus marine taxa 3,12,14,19,36,38–40 .…”

“…Our analyses provide a first step towards explaining divergent patterns of assemblage-level biodiversity change across the planet 24,41 . Overall, our results provide strong support the prediction that divergent biodiversity trajectories across latitude may arise as a consequence of global warming, with polar and temperate regions likely acting as “sinks”, and tropical regions as “sources” 6,8,31 .…”

“…sampled at a given time), and the number of samples can vary among years within each study. As the spatial extent varies among studies, we gridded those studies that had large extents and multiple sampling locations into hexagonal cells of ~96km 2 ; many studies were not partitioned because they were contained within a single cell 24 . Specifically, each sample was assigned to different combinations of study ID x grid cell based on their latitude and longitude, resulting in new assemblage time series (each with multiple samples across years).…”

“…Specifically, for each study we allocated individual samples to 96 km 2 hexagonal grid cells based on their location (Methods; 24 ). For studies with large extents, we created new equal-extent assemblage time series by allocating the samples to different grid-cell by study combinations (thus keeping the integrity of each sample and study within each grid cell).…”

Trait-based responses to land use and canopy dynamics modify long-term diversity changes in forest understories

“…However, the most common metrics used to monitor biodiversity change do not necessarily capture the processes leading to biodiversity change. Although species extinction rates are estimated to be high above background levels globally (Barnosky et al, 2011), several studies have shown that regional-to-local-scale diversity can actually remain stable or even increase with time (Sax and Gaines 2003;Dornelas et al 2014;Vellend et al 2013;McGill et al 2015;Blowes et al 2019;Steinbauer et al 2018). Plot-scale species richness is thought to be strongly controlled by regional species abundance distributions (Supp & Ernest, 2014) .…”