Patterns of co-occurrences in a killifish metacommunity are more related with body size than with species identity

Abstract

Body size may be more important than species identity in determining species interactions and community structure. However, co-occurrence of organisms has commonly been analysed from a taxonomic perspective and the body size is rarely taken into account. On six sampling occasions, we analysed patterns of killifish co-occurrences in nestedness (tendency for less rich communities to be subsamples of the richest), checkerboard structure (tendency for species segregation), and modularity (tendency for groups to co-occur more frequently than random expectation) in a pond metacommunity located in Uruguay. We contrasted co-occurrence patterns among species and body size-classes (individuals from different species were combined into size categories). The analysis was performed at two spatial scales: ponds (communities) and sample units within ponds. Observed nestedness was frequently smaller than the null expectation, with significantly greater deviations for body size-classes than for species, and for sample units than for communities. At the sample unit level, individuals tended to segregate (i.e. clump into a checkerboard pattern) to a larger extent by body size rather than by taxonomy. Modularity was rarely detected, but nevertheless indicated a level of taxonomic organization not evident in nestedness or checkerboard indices. Identification of the spatial scale and organization at which ecological forces determine community structure is a basic requirement for advancement of robust theory. In our study system, these ecological forces probably structured the community by body sizes of interacting organisms rather than by species identities.

Ontogenetic variations and feeding habits of a Neotropical annual fish from southern Brazil

“…Arim et al (2010), Canavero et al (2013) and Ortiz & Arim (2016) observed a clear spatial segregation in annual fishes of different body size classes in temporary ponds in Uruguay, where the main determinants of the assembly structure appear to be the differences in the trophic niche and the opposing interactions between size classes. Thus, spatial segregation by body size classes could allow coexistence by reducing intraspecific interactions (Canavero et al, 2013), and we believe that it may be happening in the population studied here. In addition, we also believe that the available food items were sufficiently abundant (Gerking, 1994;Dias & Fialho, 2009, not being the cause of competition, allowing the feeding patterns observed in C. fulgens in this temporary flooded area, although the availability of food resources was not evaluated in the present study.…”

“…Ontogenetic feeding changes are well known in fishes (Wootton, 1999;Amundsen et al, 2003) and have been recorded in some Cynolebiidae species (Santos-Filho, 1997;Laufer et al, 2009;Abilhoa et al, 2010b;Canavero et al, 2013;Keppeler et al, 2013Keppeler et al, , 2015Cavalheiro & Fialho, 2016;Ortiz & Arim, 2016). These ontogenetic changes in annual fish populations may reduce a potential intraspecific competition for prey items through diet segregation or by reducing direct interactions through spatial and/or temporal segregation (Laufer et al, 2009;Canavero et al, 2013;Ortiz & Arim, 2016), since is known that competitive interactions are stronger among individuals of similar body sizes (Santos-Filho, 1997;Canavero et al, 2013;Ortiz & Arim, 2016).…”

“…These ontogenetic changes in annual fish populations may reduce a potential intraspecific competition for prey items through diet segregation or by reducing direct interactions through spatial and/or temporal segregation (Laufer et al, 2009;Canavero et al, 2013;Ortiz & Arim, 2016), since is known that competitive interactions are stronger among individuals of similar body sizes (Santos-Filho, 1997;Canavero et al, 2013;Ortiz & Arim, 2016). The ontogenetic changes in diet between size classes of C. fulgens might occur as a consequence of the increase in body size (Arim et al, 2010), and not as a response for minimize intraspecific competition in this studied population.…”

“…The juveniles and adults cynolebiids with similar morphology may present segregated diets, occuping different trophic niches, or may reduce intraspecific interferences by feeding at different times and/or microhabitats, reinforcing the role of interactions influenced by body size as an important determinant in the interactions between species and the structure of the food chain in this temporary system (Laufer et al, 2009). Arim et al (2010), Canavero et al (2013) and Ortiz & Arim (2016) observed a clear spatial segregation in annual fishes of different body size classes in temporary ponds in Uruguay, where the main determinants of the assembly structure appear to be the differences in the trophic niche and the opposing interactions between size classes. Thus, spatial segregation by body size classes could allow coexistence by reducing intraspecific interactions (Canavero et al, 2013), and we believe that it may be happening in the population studied here.…”

“…Despite the large diversity of the Cynolebiidae family (Costa, 2008) and the vulnerability of some species Rosa & Lima, 2008), ecological characteristics such as feeding, reproduction, behavior patterns, growth, species richness and abundance of annual fishes in temporary environments are poorly known (Arenzon et al, 1999(Arenzon et al, , 2001(Arenzon et al, , 2002Errea & Danulat, 2001;Shibatta & Rocha, 2001;Shibatta, 2005Shibatta, , 2006García et al, 2008;Laufer et al, 2009;Arim et al, 2010;Gonçalves et al, 2011;Canavero et al, 2013;Lanés et al, 2013Lanés et al, , 2014aLanés et al, , b, 2016Keppeler et al, 2013Keppeler et al, , 2015Ortiz & Arim, 2016).…”