Linking animal contests and community structure using rockpool fishes as a model system

Summary Competition for limiting resources is a fundamental and well‐established driver of niche partitioning, which in turn promotes species coexistence and biodiversity. Although contests are a well‐known behavioural mechanism by which organisms compete over limiting resources, there has been surprisingly little application of contest theory to understanding interspecific interactions, niche partitioning, species coexistence and biodiversity. We investigated the link between contest dynamics and community structure using two intertidal rockpool fishes,Bathygobius cocosensis(Gobiidae) andLepidoblennius haplodactylus(Tripterygiidae), as model species. We assessed the abundance and distribution of the two species on intertidal rocky shores of South‐East Australia, and whether distribution patterns were related to abiotic variables. We then conducted interspecific contest experiments between pairs ofB. cocosensisandL. haplodactylusof varying size and sex under high and low dissolved oxygen levels to assess the competitive dominance of the species. To relate these results to community structure, we quantified temporal patterns of rockpool fidelity of each speciesin situ. Field surveys revealed thatB. cocosensiswas most prevalent in rockpools with higher dissolved oxygen, andL. haplodactyluswas most prevalent in rockpools that contained noB. cocosensis. Contest experiments revealed thatB. cocosensisdisplayed higher resource holding power thanL. haplodactylusregardless of size asymmetry, sex or dissolved oxygen concentration, although contest intensity was influenced by relative body size of competing individuals. Furthermore, the microhabitat preference ofL. haplodactyluswas modulated in the presence ofB. cocosensis. In the field,B. cocosensisdisplayed higher rockpool fidelity thanL. haplodactylus. In light of these findings, we propose thatB. cocosensisis the superior competitor but persistence of both species is likely facilitated by low‐cost contest resolution strategies, plasticity in microhabitat preference, negative spatial co‐variation and interspecific variation in dispersal and corresponding home range sizes. By using contest theory to understand the dynamics of interspecific contests, insight has been gained into how habitat is partitioned, species coexist and ultimately how biodiversity is maintained. A lay summary is available for this article.