Abstract
We investigated whether the equilibrium theory of island biogeography (ETIB) can be applied to the meiofauna of groundwater‐fed springs. We tested whether copepod species richness was related with spring area, discharge, and elevation. Additionally, five hypotheses are tested based on species distribution patterns, dispersal ability, and life‐history characteristics of several guilds (stygobiotic, nonstygobiotic, cold stenotherm, and noncold stenotherm species). Thirty springs in the central Apennines (Italy) were considered. A multimodel selection procedure was applied to select best‐fit models using both ordinary least‐squares regressions and autoregressive models. Mantel tests were used to investigate the impact of spatial autocorrelation in determining interspring similarity (ßsor), pure turnover (ßsim), intersite nestedness (ßnest = ßsor − ßsim), and matrix nestedness (measured using NODF and other metrics). Explicit consideration of spatial correlations reduced the importance of predictors of overall species richness, noncold stenotherm species (both negatively affected by elevation), cold stenotherm species, and nonstygobiotic species, but increased the importance of area for the stygobiotic species. We detected nested patterns in all cases, except for the stygobites. Interspring distances were positively correlated with ßsor and ßnest (but not with ßsim) for the entire data set and for nonstygobiotic, cold stenotherm, and noncold stenotherm species. In the case of stygobites, interspring geographical distances were marginally correlated with ßsor and no correlation was found for ßsim and ßnest. We found support for ETIB predictions about species richness, which was positively influenced by area and negatively by elevation (which expresses the size of source of immigrants). Low turnover and high nestedness are consistent with an equilibrium scenario mainly regulated by immigration and extinction. Stygobites, which include many distributional and evolutionary relicts, have a low capability to disperse through the aquifers and tend to be mainly confined to the springs where they drifted out and were trapped by springbed sediments.
Highlights
| METHODSThe studied springs are located in the central Apennines (Abruzzo region). Climate is continental, with average annual precipitation ranging from 700 to 1,000 mm
We considered two levels of diversity: species richness recorded in each spring and β-diversity of copepods (Crustacea, Copepoda, Figure 1)
For the nonstygobiotic species (Figure 4g–i), we found that interspring distances were significantly correlated with overall species dissimilarity, pure turnover, and nestedness
Summary
The studied springs are located in the central Apennines (Abruzzo region). Climate is continental, with average annual precipitation ranging from 700 to 1,000 mm. Using the entire data set, both overall species dissimilarity among springs and the nestedness component were correlated with interspring geographical distances (r = .481, p < .0001 for ßsor and r = .437, p < .0001 for ßnest, respectively), whereas the pure turnover component (ßsim) was not correlated with geographical distances (r = −.021, p = .819) (Figure 4a–c). In the case of the noncold stenotherm species (Figure 4m–o), interspring distances were correlated with both overall species dissimilarity and the nestedness component (r = .441, p < .001 for ßsor and r = .381, p < .017 for ßnest, respectively), but not with the pure turnover (ßsim) component (r = −.001, p = .993) Overall, these results support Predictions #3 and #4. All indices but matrix temperature showed a nonnested pattern for the stygobiotic species (Table 4), in accordance with Prediction #3
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