DOI: 10.5061/dryad.5mkkwh733
title: The macroecology of reef fish agonistic behaviour

description: Understanding the interplay between processes operating at large and small
 spatiotemporal scales in shaping biotic interactions within biological
 communities remains challenging. Recent studies illustrate how phenotypic
 specialization, species life-history traits and/or resource partitioning
 recurrently underlie the structure of mutualistic interactions in
 terrestrial ecosystems along large latitudinal gradients of biodiversity.
 However, we know considerably less about how local processes interact with
 large-scale patterns of biodiversity in modulating biotic interactions in
 the marine realm. Considering agonistic behaviour as a proxy for contest
 competition, we empirically investigate whether the structure of reef fish
 agonistic interactions is conserved across a 34,000-km longitudinal
 gradient of biodiversity. By sampling coral reefs using standardized
 remote underwater video, we found recurrent patterns of fish agonistic
 behaviour in disparate communities distributed across five biogeographic
 provinces of the Pacific and Atlantic oceans. While the sheer number of
 species increases with regional richness, the number of aggressive
 disputes at the habitat scale is similar across communities. We then
 combined generalized linear models and network theory to reveal that, the
 emergent structure of local agonistic networks was not modular but instead
 recurrently display a nested structure, with a core of highly interactive
 site-attached herbivores of the Pomacentridae family. Therefore, despite
 the increase in the number of species involved in agonistic interactions
 toward speciose communities, the network structure is conserved along the
 longitudinal richness gradient because local disputes are mostly driven by
 closely-related, functionally-similar species. These findings suggest that
 evolutionary and local processes interact in modulating reef fish
 agonistic behaviour and that fine-scale niche-partitioning can structure
 the ecological networks in marine ecosystems.
description: We surveyed seven tropical reefs over a 34.000 km longitudinal
 gradient of biodiversity: four at the Atlantic (Rocas Atoll, Abrolhos,
 Curaçao, Yucatán) and three at the Indo-Pacific Ocean (Moorea, Fiji,
 Bali). We designed a standardised study to record data on reef fish
 behaviour using Remote Underwater Video (RUV) sampling. We carried out the
 same sampling effort in all localities to control for possible influence
 of sampling on the relationships between agonistic behaviour and species
 richness across communities. Our standardised sampling effort (87.5h of
 footage) consisted of 50 video samples per locality. A remote video sample
 consisted of a 15-min shot by a high-definition camera, fixed and focused
 over a 2m² reef area previously chosen at random by a free diver. To
 encompass the local habitat heterogeneity, we sampled three different
 sheltered shallow reefs with depths between 2–10 m in each
 locality. We identified all reeef fish species and
 recorded all agonistic interaction events between them occurring in the
 central 10 min of each video sample (the first and last 2.5 min were
 discarded to remove any potential disturbance by the observers). We
 considered an agonistic interaction as a chasing event between individual
 fish—a behaviour that is well-documented as representative of disputes for
 food resources, territory and/or mating opportunities. We focused on
 species larger than 5 cm in total length because identification of smaller
 individuals in remote video analysis can be unprecise.
 We investigated the distribution of agonistic interactions among
 reef fishes across localities using the network formalism. For each
 locality, we combined the data from all 50 video samples to create an
 asymmetrical binary adjacency matrix in which
 elements <i>a<sub>ij</sub></i>=1 represented the
 agonistic behaviour of reef fish species <i>i</i>towards the
 species<i>j, a<sub>ji</sub></i>=1 the behaviour
 of <i>j</i>towards <i>i</i>,
 and <i>a<sub>ij</sub></i>=<i>a<sub>ji</sub></i>=0 when species never interacted. These one-mode directed networks depicted species as nodes colour-coded by taxonomic families connected by links indicating the direction of the agonistic interaction (outward=actor, inward links=receptor).  We related the number of agonistic interactions performed by species of all localities to key descriptors of reef fish agonistic behaviour—taxonomic family, trophic groups, and home range. Since our study focuses on macroecological scale patterns, we classified fish species into broad functional groups. We considered five trophic groups based on their primary diets—herbivores, carnivores, omnivores, planktivores, and invertebrate feeders—and three categories of home range—site-attached (less than 5m<sup>2</sup>), small home range (within reef) and mobile (between reefs).
description: We provide a table of reef fish richness recorded across spatial
 scales and seven adjacency matrices of reef fish agonistic behaviour from
 seven tropical reefs in the Atlantic and Indo-Pacific Oceans: Rocas Atoll,
 Abrolhos, Curaçao, Yucatán, Moorea, Fiji and Bali. The species richness
 table comprises the total number of reef fish species observed in the
 remove underwater videos, and number of species observed interacting
 agonistically across spatial scales and localities. The total number of
 species in all video samples  (local scale - 100m<sup>2</sup>)
  and the average of the total number of reef fish species registered on
 each video sample( habitat scale - 2m<sup>2</sup>) were
 detected for each locality. The seven adjacency matrices describe the
 one-mode directed networks of agonistic interactions among reef fish
 species on each locality (across all 50 video samples, local scale -
 100m<sup>2</sup>), whose scientific names are given in
 the rows and columns.