Quantification of intraspecific and interspecific competition in fish species of the Aegean Sea

ICES Journal of Marine Science, 2024, Vol. 81, Issue 2, 334–347 https://doi.org/10.1093/icesjms/fsad201 Received: 4 April 2023; revised: 22 November 2023; accepted: 23 November 2023 Advance access publication date: 22 December 2023 Original Article Quantification of intraspecific and interspecific competition in fish species of the Aegean Sea Martha Koutsidi 1,* , Alexis Lazaris1 , Panagiota Peristeraki2 , George Tserpes2 , Evangelos Tzanatos 1 1 Department of Biology, University of Patras, Patras GR26504, Greece Hellenic Centre for Marine Research, Institute of Marine Biological Resources and Inland Waters, P.O. Box 2214, Heraklion GR71003, Greece ∗ Corresponding author. Department of Biology, University of Patras, Patras GR26504, Greece. Tel: +6945607337; E-mail: Abstract Competition shapes species coexistence and community assembly, playing a central role in maintaining biodiversity and ecosystem resilience. Here, we used an asymmetric competition index that quantifies the possible competitive effect of a species on any other, using southern Aegean Sea nekton biomass from the Mediterranean International Trawl Survey dataset, combined with data on six traits relevant to trophic ecology and spawning. We modeled the effect of selected haul-level covariates on the competition index, and we indicated competition variation across depth and habitats. Most species experienced stronger inter- than intra-specific competition. Both the higher-than-expected significance of interspecific competition (in comparison to intraspecific that is generally anticipated to be higher) and the existence of an extensive network of multiple competitive interactions indicated, are associated with high biodiversity, combined to the absence of dominance by one or a few species in the community (no species is disproportionally highly abundant in comparison to others); the latter may be relevant to community stability and resilience. The quantification of competition across marine ecosystems can help predict how fish communities will respond to future resource availability and environmental conditions. Keywords: fish; intraspecific competition; interspecific competition; Meditteranean Sea Introduction Competition is the negative interaction between individuals or populations for limited shared resources (Cody et al., 1975). It limits population densities, through control of survival, growth or reproduction. Competition is a fundamental ecological process shaping population dynamics, species coexistence and community structure (Xia et al., 2020). It can play an important role in habitat selection, foraging behaviour, growth, and recruitment (Munday et al., 2001). Competition includes an intraspecific and an interspecific component which refer to the negative effect of individuals of a species on individuals of the same or a different species, respectively. The strength of intraspecific competition is often a limiting factor of population size (BoströmEinarsson et al., 2013), exerting selective forces central to species biology with a vital role in limiting populations, eliminating unfit genes, and driving evolution (Ward et al., 2006). Conversely, individuals may exhibit low intraspecific overlap in resource use, either because competition has led to resource partitioning or because of different preferences (Munday et al., 2001). Species niches and resulting interspecific competition are shaped by resource diversity, quantity and availability (Costa-Pereira et al., 2018) which change seasonally or spatially and can be influenced by productivity and human activities (Araújo and Costa-Pereira, 2013). Resource limitation and niche overlap may create high intraspecific or interspecific competition; the former is generally believed to be more intense because of high niche overlap between conspecifics. Competition between species is asymmetric (i.e. the competitive effect of species-A on species-B is not equivalent to that of species-B on species-A). It often leads to the exclusion of inferior competitors from mutually preferred habitats (Young, 2004). Therefore, inferior competitors survive better when superior competitor abundance is reduced. The density of both intra- and interspecific competitors varies by habitat and may influence the access to resources, creating ecological opportunities and interactions (Wagner et al., 2014). An understanding of the potentially complex competitive relationships is vital to predict community response to changes in resource availability (Bonin et al., 2009). This may be challenging in ecosystems with high biodiversity, like the Mediterranean Sea (Myers et al., 2000). Different resource availability is expected to promote individual specialization between populations (Darimont et al., 2009). Because individuals vary in their degree of specialization, a population can contain individuals that use a narrow (specialists) or a broader (generalists) subset of available resources (Roughgarden, 1972). A population consisting of various ecologically specialized phenotypes (of higher niche variation) has lower intraspecific competition (Swanson et al., 2003). High biodiversity can affect interspecific competition as many species coexist and compete for resources. The aim of this study was to create an asymmetric competition index that quantifies the possibility of competition among fishes given limited resources availability based on community composition and biological traits. We used this index derived from an eastern Mediterranean trawl survey dataset to © The Author(s) 2023. Published by Oxford University Press on behalf of International Council for the Exploration of the Sea. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. 2 335 Fish species of the Aegean Sea determine the relative intensity of pairwise competitive relationships and to investigate: (i) Whether competition varies across space and time, (ii) which species pairs are the main competitors and whether intraspecific or interspecific competition is the main component, and whether (iii) intraspecific and (iv) interspecific competition change across depth and habitat types. Materials and methods Fish community dataset Traits dataset We evaluated competition for food resources and spawning habitat by using six biological traits. We used four traits relevant to trophic ecology: size, trophic level, diet and feeding type, and two reflecting spawning habitat use: spawning period and habitat -for the relevance of these traits for competition see e.g. Hobbs and Munday (2004); Ward et al. (2006). Within each trait, 2–5 categories (modalities) were created using information from the bibliography for each species (Table 1). In our dataset, aiming to incorporate interspecific hete (...truncated)