Exploring community assembly among Javanese and Balinese freshwater shrimps (Atyidae, Palaemonidae) through DNA barcodes

Species proliferate through evolutionary mechanisms but coexist through ecological dynamics. As such, it might be expected that mechanisms of speciation and species maintenance jointly influence the settlement of ecological communities, a process called community assembly. Disentangling the relative contribution of evolutionary and ecological dynamics might be a difficult task, particularly so for the tropical biotas due to their extreme diversity and large knowledge gaps. Here, we explore genetic diversity and distribution of 23 freshwater shrimp species of the genera Caridina and Macrobrachium in Sundaland to examine patterns of species co-occurrence based on 1583 observations across 19 sites in Java and Bali islands. DNA-based species delimitation methods applied to 204 cytochrome oxidase I sequences detected 30 operational taxonomic units and a few cases of deep intraspecific divergence. Species co-occurrence and phylogenetic community structure show no departure from expectations under a random distribution of species in landscapes and support a lottery model of community assembly. Species age estimates expand beyond the geological settlement of Sundaland, suggesting that species proliferation and community assembly are driven by mechanisms acting at distinct spatial and temporal scales.