Community assembly and species coexistence in Sulawesi’s stream fishes

• Applicant: Dr. Fabian Herder
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2018 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 407494669

Stream fish communities are species assemblages that developed in the highly dynamic, heterogeneous environments of natural watercourses. Species composition and richness of such communities typically varies on different scales, from altitudinal gradients to microhabitats, and is also affected by the geographic history of the environment. Community assembly theory provides an integrative framework for assessing the processes that underlie species coexistence, but the current understanding of the mechanisms of coexistence in complex tropical freshwater fish faunas remains highly fragmentary. The stream fish fauna of the Indonesian island Sulawesi is a promising model to address current hypotheses on coexistence in such species assemblages. Sulawesi’s faunal history is characterized by spatial isolation from neighbouring biotas, and the island’s topography supports numerous rather small drainages with a diverse fauna of freshwater fishes, from obligate freshwater species to lineages with marine larval states, to fishes that migrate among freshwaters and the sea. Recent paleo-geological advances suggest that Sulawesi is a composite of old paleo-islands, interconnected by younger expansions. The project proposed takes advantage of the natural replicates of coastal stream fish communities in Sulawesi, nested on or among the formerly separated paleo-islands. The general goal is to understand the processes that shape coexistence in complex stream fish communities. Two central hypotheses aim at disentangling these processes: (i) Species assembly is predominantly shaped by environmental filtering and spatial isolation; (ii) Functional traits enable species coexistence on a local scale, and vary along environmental gradients. For testing these hypotheses, individual fishes and data on their habitat use will be collected from 63 stream sites, covering significant altitudinal gradients with an array of habitats, across the largest paleo-islands and their expansions. Habitat use will be quantified by point abundance sampling, complemented by the analysis of functional traits, feeding niches, and phylogenetic diversity. Combined, the data obtained allow inferring in detail the processes that shape complex fish communities, in the case of a larger tropical island.

• DFG Programme: Research Grants
• Co-Investigators: Professor Dr. Jost Borcherding; Dr. Matthias Geiger