Is resource partitioning the key? The role of intra‐interspecific variation in coexistence among five small endemic fish species (Characidae) in subtropical rivers

Abstract

This study focused on intra and interspecific variations in the diet of small species in the Pelotas River, upper Uruguay River ecoregion. We tested the hypothesis that five small characids coexist via resource partitioning. Samplings were performed quarterly between August 2013 and May 2014 at 14 sites in the Pelotas River basin, using gillnets of different mesh sizes, seines, cast nets and electrofishing. In this study, the contents of 1,253 stomachs were analysed from Astyanax dissensus, A. paris, A. saguazu, A. xiru and Bryconamericus patriciae. The main food resources consumed were aquatic insects, leaves, seeds and detritus. There were significant seasonal intra and interspecific variations in the use of food resources by the five species. Permutational analysis of multivariate dispersions results indicated significant differences in individual intraspecific variability between the sampled periods, with the highest values found in November and February because of an increase in allochthonous resources (leaves and seeds). Besides this, significant differences in the proportions of consumption of allochthonous and autochthonous were observed. The trophic niche breadth was significantly different among the species, such that in August, the species had narrower niche breadths. In the other periods, the highest niche breadth values were due to an increase in the consumption of allochthonous items. Diet overlap was low (< 0.4) between 62% of the species pairs. The small characid species showed pronounced changes in resource use and intra and interspecific variations indicating resource partitioning. These factors appear to be essential in species interactions and for coexistence.

Morphological traits correlated with resource partitioning among small characin fish species coexisting in a Neotropical river

“…In a previous study, high diet segregation among abundant characid species in samples from the main channel of the Pelotas River was found (Neves et al, 2018). However, such an understanding of the morphological keystone of trophic differentiation is currently lacking for these opportunistic characins.…”

“…The Pelotas River stands out as an area of ecological importance because its fauna has a high degree of endemism. However, hydroelectric potential and agroindustrial development are main risk to this biodiversity (Neves et al, 2018). In the study area (Figure 1), the sites sampled encompassed segments of the main channel of the Pelotas River (eight reaches) that presented altitude and width ranges of 990–782 and 35–150 m respectively, while in sampling sites located in tributaries (six reaches), these ranges were 990–787 m (altitude) and 15–55 m (width).…”

“…The large variations in rainfall in these regions (Feow, 2018), occurring either seasonally (dry and rainy seasons) or due to short‐term events (episodic storm events), are additional factors that lead to flow and current velocity disparities at the scale of both mesohabitats and the entire landscape. These variables mediate the types of potential food resources carried into the river system and also lead to consequent changes in the dynamics of autochthonous resources and their availability (Brambilla, Uieda, & Nogueira, 2019; Brett et al, 2017; Giling, MacNally, & Thompson, 2015; Neves, Silva, Baumgartner, Baumgartner, & Delariva, 2018; Roach, 2013). This landscape and its underlying forces create a rich environment for niche partitioning or specialisation, which is generally expected to increase the number of species that can stably coexist there (Leibold, Urban, De Meester, Klausmeier, & Vanoverbeke, 2019; Schoener, 1974) and also potentially promote the evolution of morphological and ecological diversity.…”

“…In addition, fish of the family Characidae exhibit many diverse trophic modes (Hyatt, 1979). The genera Astyanax and Bryconamericus (“lambaris”; genera incertae sedis in Characidae) (Lima et al, 2003) form one of the fish clades most abundant in which dietary plasticity has been particularly well documented by previous studies (Bonato, Burress, Fialho, & Armbruster, 2018; Delariva, Hahn, & Kashiwaqui, 2013; Kokubun, Bonato, Burress, & Fialho, 2018; Oricolli & Bennemann, 2006; Pini et al, 2019; Portella, Lobón‐Cerviá, Manna, Bergallo, & Mazzoni, 2017; Silva, Gubiani, Neves, & Delariva, 2017) and has also been associated with the exploitation of alternative and seasonally varying resources in tropical systems (Neves et al, 2018; Silva, Gubiani, & Delariva, 2014).…”

Temporal shifts in intraspecific and interspecific diet variation: effects of predator body size and identity across seasons in a stream community

“…According to classic niche theory, increased dissimilarity in resource use should lead to decreased competition (MacArthur and Levins 1967, File et al 2012). Thus, seasonal shifts in intra- and interspecific diet variation, such as those caused by changes in prey availability, should theoretically coincide with changes in the strength of competition (Zaret and Rand 1971, Chase and Leibold 2003, Correa and Winemiller 2014, Neves et al 2018). For instance, Zaret and Rand (1971) suggest that increased interspecific competition during the dry season when food resources in tropical streams are low provides a good explanation for seasonal diet shifts in characin fishes.…”