Diet patterns of water green frogs (Pelophylax esculentus complex) in mixed population systems in Serbia

From Firenze University Press Journal: Acta Herpetologica

Katarina V. Breka, Institute of Zoology, Faculty of Biology, University of Belgrade

Milan Plećaš, Institute of Zoology, Faculty of Biology, University of Belgrade

Nikola Vesović, Institute of Zoology, Faculty of Biology, University of Belgrade

Katarina Stojanović, Institute of Zoology, Faculty of Biology, University of Belgrade

Boris Dudić, Institute of Zoology, Faculty of Biology, University of Belgrade

Srđan Z. Stamenković, Institute of Zoology, Faculty of Biology, University of Belgrade

Frogs have an important position in the trophic net-work by regulating the populations of invertebrates and other groups of organisms on which they feed (Hock-ing and Babbitt, 2014). Larval stages feed on algae and detritus and, as primary consumers, influence the ecosys-tem structure and function by altering algal communi-ties, patterns of primary production, and organic matter dynamics in a variety of freshwater habitats (Kupferberg, 1997; Flecker et al., 1999). Within trophic webs, adult frogs occupy an intermediate position and are involved in aquatic and terrestrial food webs as both prey and predator of various taxa due to their complex life history (McCoy et al., 2009). Frogs are reported as prey for vari-ous vertebrates and invertebrates, but also as predators of invertebrates and some vertebrate species (e.g., small liz-ards, snakes, birds, mammals, and other anurans) (Toledo et al., 2007).Green frogs are semi-aquatic ambush (“sit and wait”) predators (Moore and Biewener, 2015) that feed both during the day and at night (Cogãlniceanu et al., 2000). The success of this strategy depends on factors such as prey density, prey mobility, and energy requirements of the predator (Moore and Biewener, 2015). According to the requirements of optimal foraging theory, animals with such a strategy must be generalists across the spec-trum and opportunists in prey selection to maximize energy intake per unit of time (Pianka, 2000; Glaudas et al., 2019). Information about dietary habits and trophic inter-actions are the key determinants of the structure and dynamics of ecological niches in coexisting species (Lunghi et al., 2022). They are necessary for basic under-standing of the life history of anurans and the fluctuation patterns of their populations (Anderson et al., 1999), for identifying environmental conditions and habitat changes (Batista et al., 2011), and for designing and implementing management and conservation strategies for species that require protection (Stuart et al., 2004). Although some species among anurans are considered specialists (Simon and Toft, 1991), frogs are mainly considered generalists and opportunists (e.g., ÇiÇek and Mermer, 2007; Almei-da-Gomes et al., 2007). In generalist species, aspects such as phylogeny, foraging mode, prey availability and abundance, and morphological constraints to capture and ingest a particular type of prey, may be related to resource partitioning among species (Lima, 1998; Vignoli et al., 2009). In addition, community niche micro-differ-entiation of both frog taxa and prey may be influenced by anthropogenic activities that can affect ecological interac-tions (Albrech and Gotelli, 2001).Serbia is populated by all three taxa of the Pelophy-lax esculentus complex: Pelophylax ridibundus (P. r i d), Pelophylax lessonae (P. l e s), and their hybrid Pelophylax esculentus (P. e s c). Throughout its range, mixed popu-lations in which all three taxa of the P. esculentus com-plex coexist in the same locality are generally rare (“REL population systems”, named after the initial letters of the taxa that compose them) (Suriadna et al., 2020). In Ser-bia, these population systems are detected in a few areas along the Danube (Krizmanić and Ivanović, 2010). We believe that REL population systems provide the oppor-tunity to study all three taxa living in syntopy and shar-ing the same resources. Although they are likely to have similar ecological needs, they should have measur-able differences in resource use that reduce the possibil-ity and/or extent of competition between taxa and thus promote coexistence (Costa-Pereira et al., 2019). Before the clarification of the taxonomic status of green frogs (Berger, 1973) and the advent of molecular identification techniques, field identification of taxa in this complex was difficult (see Breka et al., 2020). We note that most trophic studies treated green frogs as a single unit with-out considering possible dietary differentiation within the complex (e.g., Lőw and Tӧrӧk 1998; Cogălniceanu et al., 2000). Trophic studies on green frogs have mostly been reported for populations with a single taxon (e.g., Šimić et al., 1992; Mollov, 2008; Sas et al, 2009), while only a few have reported on diet in mixed populations where at least one parental species coexists with the hybrid taxon — LE or RE population systems (Sas et al., 2007; Ferenti et al., 2009), and a few on diet in REL systems (Popović et al., 1992; Paunović et al., 2010; Karaica et al., 2016). More recently, field studies on green frogs have been conducted on population systems based on inter-taxon differences, especially when considering implications for effective conservation and management of altered aquatic and wetland habitats (Jośko and Pabijan, 2020).The aim of the present study was to (1) provide the necessary data for an overview of the diet composition of the P. esculentus complex in Serbia in REL population systems; (2) determine the dietary pattern and niche breadth for each taxon at three sites with different habitat quality and anthropogenic pressure; (3) determine whether there are niche shifts in the composition of the staple diet and/or dietary partitioning between three taxa in syntopic population systems of green frogs.

DOI: https://doi.org/10.36253/a_h-13529

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