On the shape and origins of the freshwater species–area relationship

Abstract

The species–area relationship (SAR) has over a 150‐year‐long history in ecology, but how its shape and origins vary across scales and organisms remains incompletely understood. This is the first subcontinental freshwater study to examine both these properties of the SAR in a spatially explicit way across major organismal groups (diatoms, insects, and fish) that differ in body size and dispersal capacity. First, to describe the SAR shape, we evaluated the fit of three commonly used models, logarithmic, power, and Michaelis–Menten. Second, we proposed a hierarchical framework to explain the variability in the SAR shape, captured by the parameters of the SAR model. According to this framework, scale and species group were the top predictors of the SAR shape, climatic factors (heterogeneity and median conditions) represented the second predictor level, and metacommunity properties (intraspecific spatial aggregation, γ‐diversity, and species abundance distribution) the third predictor level. We calculated the SAR as a sample‐based rarefaction curve using 60 streams within landscape windows (scales) in the United States, ranging from 160,000 to 6,760,000 km2. First, we found that all models provided good fits (R2 ≥ 0.93), but the frequency of the best‐fitting model was strongly dependent on organism, scale, and metacommunity properties. The Michaelis–Menten model was most common in fish, at the largest scales, and at the highest levels of intraspecific spatial aggregation. The power model was most frequent in diatoms and insects, at smaller scales, and in metacommunities with the lowest evenness. The logarithmic model fit best exclusively at the smallest scales and in species‐poor metacommunities, primarily fish. Second, we tested our framework with the parameters of the most broadly used SAR model, the log–log form of the power model, using a structural equation model. This model supported our framework and revealed that the SAR slope was best predicted by scale‐ and organism‐dependent metacommunity properties, particularly spatial aggregation, whereas the intercept responded most strongly to species group and γ‐diversity. Future research should investigate from the perspective of our framework how shifts in metacommunity properties due to climate change may alter the SAR.

Resource quantity and quality differentially control stream invertebrate biodiversity across spatial scales

“…To explore resource-diversity relationships at a larger, aggregated spatial scale (hereafter 'regional' scale), we created a 1000 km radius window around each site to identify sites within the same 'region'. We chose 1000 km because this spatial extent encompasses regional processes of organismal diversity and ecological processes across an array of ecosystems (Cheruvelil et al, 2013;Mittelbach et al, 2001;Passy et al, 2022). We then calculated a new value for each site based on the average of all sites included within the window.…”

Environmental Factors Shape the Differences in Biodiversity-Area Relationships in Riverine Macroinvertebrates of Two Rivers in the Tibetan Plateau in China

“…The biological significance of two parameters (c and z) for SAR models has attracted the interest of biogeographers and ecologists [15,17,18]. As c is the expected species per unit area, it can be considered a measure of α-diversity [4].…”

“…Habitat types in SAR studies in freshwater SARs have mostly focused on lakes [34,35], ponds [36], and wetlands [37], and the taxonomic focus of the studies is more on fishes [38] than other aquatic organisms. In streams and rivers, fewer SAR studies are focused on taxonomic diversity [18]. The parameters of the log-log form of SAR can be influenced by both habitat characteristics and the biological characteristics of the organisms that are present [18].…”

“…In streams and rivers, fewer SAR studies are focused on taxonomic diversity [18]. The parameters of the log-log form of SAR can be influenced by both habitat characteristics and the biological characteristics of the organisms that are present [18]. Streams and rivers are among the most threatened ecosystems in the world [39] and therefore should be the subject of additional studies on this topic.…”

Climate‐associated variation in the drivers of benthic macroinvertebrate species–area relationships across shallow freshwater lakes

“…However, these winter fish kills are less likely to occur in tropical regions, meaning that the intensity of fish predation may vary less with lake area in these regions (Yu et al., 2021). To date, few studies have elucidated how climate may mediate the relative influence of passive sampling, more individuals and/or disproportionate effects shaping ISARs in freshwater insular ecosystems (but see Drakare et al., 2006; Passy et al., 2023).…”