DOI: 10.5061/dryad.w9ghx3fx8
title: Body size mediates trophic interaction strength of novel fish assemblages under climate change

description: Ecological similarity plays an important role in biotic interactions.
 Increased body size similarity of competing species, for example,
 increases the strength of their biotic interactions. Body sizes of many
 exothermic species are forecast to be altered under global warming,
 mediating shifts in existing trophic interactions amongst species, in
 particular for species with different thermal niches. Temperate rocky
 reefs along the southeast coast of Australia are climate hotspots and now
 house a mixture of temperate native fish species and poleward
 range-extending tropical fishes (vagrants), creating novel species
 assemblages. Here, we studied the relationship between body size
 similarity and trophic overlap between individual temperate native and
 tropical vagrant fishes. Dietary niche overlap between vagrant and native
 fish species increased as their body sizes converged, based on both
 stomach content composition (short-term diet), stable isotopes analyses
 (integrated long-term diet) and similarity in consumed prey sizes. We
 conclude that the warming-induced faster growth rates of tropical
 range-extending fish species at their cool-water ranges will continue to
 converge their body size towards and strengthen their degree of trophic
 interactions and dietary overlap with co-occurring native temperate
 species. The strengthening of these novel competitive interactions are
 likely to drive changes to temperate food web structures and reshuffle
 existing species community structures.
description: We used a small hand net and a mixture of ethanol and clove oil
 to capture juveniles of six native temperate species (<em>Ambassis
 jacksoniensis</em><em>,</em> <em>Atypichthys
 strigatus</em>, <em>Microcanthus strigatus</em>,
 <em>Parma microlepis</em>, <em>Pempheris
 affinis</em>, <em>Trachinops taeniatus</em>) and of
 three tropical vagrant species (<em>Abudefduf
 sexfasciatus</em>, <em>A. vaigiensis</em>,
 <em>Pomacentrus wardi</em>) along the southeast coast of
 Australia between latitudes 30.8º and 36.8ºS. For
 stomach content analysis, the entire gut was removed from each frozen
 fish, and the abundance of each prey item (excluding vegetation) inside
 the stomach was visually counted, their maximum lengths measured, and
 identified at family level using a stereo microscope. Autotroph prey items
 including algae and seagrass were grouped together, as the partly digested
 vegetation could not be identified, and their contribution to the diet was
 estimated as a count. Then, we calculated Bray-Curtis similarity index
 using on stomach contents. For stable isotope analysis,
 white muscle tissue free from scales, skin and bone was extracted from
 each fish, and freeze-dried for at least 36 hrs in individual Eppendorf
 tubes. Dried tissue was ground using a ball mill. Powdered muscle tissues
 of each fish were weighed in tin capsules individually and analysed for
 stable δ<sup> 15</sup>N and δ<sup>13</sup>C
 isotope, using a Nu Instruments NuHorizon Continuous Flow IRMS (CF-IRMS)
 at the University of Adelaide. We then calculated Euclidean similarity
 index based using stable isotope signatures. For prey
 size similarity, we calculated proportional similarity in median prey size
 per fish stomach.
description: # Body size mediates trophic interaction strength of novel fish
 assemblages under climate change
 [https://doi.org/10.5061/dryad.w9ghx3fx8](https://doi.org/10.5061/dryad.w9ghx3fx8) Dataset provides 1) Bray-Curtis similarity index based on stomach contest, 2) Euclidean similarity index based using stable isotope signatures, and 3) proportional similarity in median prey size per fish stomach. Please refer our paper for experimental procedures, data collection, analysis and results. ## Description of the data and file structure Three datasets have seven columns, and first five columns contain variables that are same across three datasets (1-5) and remaining sixth (6) and seventh (7) columns contains distance indexes. Brief description of column names are as indicated below; 1\) ID1: Identifier of species 1 in comparison 2\) ID2: Identifier of species 2 in comparison 3\) Species_pair: Abbreviated names of two species in comparison 4\) Site: Abbreviated name of sampling site where species 1 and species 2 were collected from 5\) Affinity: Identifier for species group (i.e., Vagrant, Novel or Native group) 6\) Bray_similarity: Bray-Curtis similarity index based on stomach contest 6\) Euclidean_Similarity: Euclidean similarity index based using stable isotope signatures 6\) Prop.Similarity_Mediam_Prey: Proportional similarity in median prey size per fish stomach 7\) Prop_Similarity_Fish_Size: Proportional similarity in fish size For abbreviation, please refer our Figure S2 for site names and Figure S4 for species names.