Abstract
Niche-related processes (e.g., density or niche-breadth compensation and competition) are fundamental to a broad understanding of community ecology and ecosystem functioning. Most evidences of competition are from controlled indoor trials with few species, and it remains a challenge to estimate competition among multiple species in the field. Here, we analyze stable isotopes and distributional data from 51 fish taxa in six locations in the southwestern Atlantic to predict intraspecific trophic pressure (ITP) and the potential competitive strength among species in a trophic-based framework. We used two proxies built upon 2-dimensional isotopic space (δ13C vs. δ15N), its predicted overlap, and fish density to calculate winner and loser taxa in potential paired interspecific competitive interactions. The intraspecific proxy indicated that cryptobenthic fishes are under high among-individual trophic pressure (high densities and small niche sizes). Also, cryptobenthic behavior together with feeding specialization and extremely small-sizes were the most important traits related to low success in interspecific simulations. Although cryptobenthic fishes face strong competitive pressures, there are some known inherent trade-offs to cryptobenthic life such as trophic and habitat use specializations. These seem to compensate and ensure coexistence among cryptobenthic fishes and non-cryptobenthic species. Habitat loss/degradation via urbanization, invasive species and climate-change-driven sea-level rise can reduce the suitability of habitat and increase competition on cryptobenthic species, especially in shallow reefs and intertidal shores.
Highlights
Competition is one of the most important driving forces shaping life forms, from microbes to large-sized plants and animals (Gause, 1934; Simberloff, 1982; Connell, 1983; Xavier and Foster, 2007; Bonin et al, 2015)
The evaluation of interspecific interactions using the species competition proxy (SCP) indicated that the potentially inferior competitors were Coryphopterus sp., Starksia multilepis, and Storrsia olsoni at Rocas, Abudefduf saxatilis, Gobioclinus kalisherae, and Entomacrodus vomerinus at Noronha, Malacoctenus brunoi, Tomicodon sp. and Mugil curvidens at Trindade (Supplementary Figure 1), Gobiesox barbatulus, Sphoeroides testudineus and Thalassophryne nattereri at Salinópolis, Omobranchus punctatus, Acanthurus chirurgus and Sparisoma axillare at Jericoacoara, and Sparisoma axillare, Stegastes variabilis, and Coryphopterus glaucofraenum at Anchieta (Supplementary Figure 2)
We have shown that a diverse group of abundant species, the feeding-specialists of cryptobenthic behavior, is extremely vulnerable to interspecific competition and presents high rates of relative intraspecific trophic pressure (ITP) for resources
Summary
Competition is one of the most important driving forces shaping life forms, from microbes to large-sized plants and animals (Gause, 1934; Simberloff, 1982; Connell, 1983; Xavier and Foster, 2007; Bonin et al, 2015). The understanding of how the struggle for space and resources occurs drew Darwin’s attention on the mechanisms involved in the coexistence and contests within and among species (Darwin, 1859). In his seminal book Darwin dedicated one chapter to the discussion of the mechanisms behind one species becoming victorious over another and on the role of natural selection in a competition spectrum (Darwin, 1859). The search for estimates of niche overlap (on a spatial or trophic basis) have shed light on competition measurements and supported the majority of ecological inferences regarding potential competition assessments (Hutchinson, 1961, 1978; MacArthur, 1968; Bonin et al, 2015)
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