Different mechanisms drive beta diversity of freshwater fishes across similar ecoregions in India (original) (raw)

Aquatic Sciences

Abstract

As an important component of overall diversity, β-diversity is driven by spatial and temporal variability of several ecological factors. While changes to β-diversity can be the result of a combination of these factors, it is still unclear whether the same driving factors govern regions with similar β-diversity. We studied lower–middle-order streams in two river basins (three of them located in the state of Madhya Pradesh ‘MP’ and four located in West Bengal ‘WB’) in India, approximately 1600 km apart. Fish abundance and environmental data were collected from 2015 to 2017. While spatial variables constructed from geographic or fluvial distances are often used in evaluating dispersal effects, studies using terrain properties are relatively fewer. In tropical stream systems, which can undergo drastic seasonal transformations, terrain properties along with distances are likely to influence dispersal. Heterogeneity indices for both environment (Environmental heterogeneity, EH) and topography (Topographic heterogeneity, TH) were calculated. Influence of environmental and spatial variables (fluvial distance and TH) on β-diversity was modeled using dbRDA (distance-based redundancy analysis). β-diversity did not vary across seasons (i.e., temporally) in either regions, but did vary across streams (i.e., spatially). MP had a higher TH while WB displayed greater EH. Both regions showed a positive beta diversity–environmental heterogeneity relationship and EH–TH relationship across streams. Although both basins rest in the tropics, different mechanisms seem to explain community assembly. Variation partitioning showed a stronger influence of environmental filtering on fish communities in WB, and dispersal limitation reflected by spatial factors in MP. Our findings highlight that different mechanisms can drive β-diversity within the same tropical realm and the need to consider the role of topography, along with traditionally acknowledged spatial descriptors, in studies exploring the mechanisms driving β-diversity of fishes in riverine ecosystems.

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