Land use effects on the co-occurrence patterns of streams ichthyofauna in the eastern Amazon

Abstract

In this manuscript, we aimed to answer: 1) which environmental and spatial processes are determinant for the patterns of co-occurrence of fish in Amazonian streams, and 2) which variables are responsible for the positive and negative associations between species pairs. For this, we sampled 32 Terra-Firme forest streams in a basin affected by different land uses in the eastern Amazon. In each stream, we measured environmental metrics for its physical characterization; estimated the percentage of land cover of the drainage network; and sampled the ichthyofauna. We also analyzed associations (positive or negative) between pairs of species and whether these associations were determined by physical habitat characteristics and the percentage of vegetation cover, spatial dispersal or biotic interactions, using a classical null model approach complemented by spatial tests and of environmental characteristics of the sites occupied by members of each pair of species. Most of the patterns of ichthyofauna co-occurrence occurred at random, composed mainly of rare species, which may be due to the specificity of these species or because the still forested and highly heterogeneous areas of the region may be acting as a mosaic, together with less aggressive land uses such as agriculture, generating these random pairs. Meanwhile, 32 species (41.03%) formed 613 non-random aggregated or segregated pairs (20.41% of the total pairs), composed mainly of species of intermediate frequency and abundance in the region and with different niches and guilds and determined by biotic interactions, environmental filters’ action and/or by limiting species dispersal.