Ecological correlates of the distribution limits of two poeciliid species along a salinity gradient

Abstract

Identifying the environmental factors responsible for the formation of a species' distribution limit is challenging because organisms interact in complex ways with their environments. However, the use of statistical niche models in combination with the analysis of phenotypic variation along environmental gradients can help to reduce such complexity and identify a subset of candidate factors. In the present study, we used such approaches to describe and identify factors responsible for the parapatric distribution of two closely‐related livebearer fish species along a salinity gradient in the lowlands of Trinidad, West Indies. The downstream distribution limits of Poecilia reticulata were strongly correlated with the brackish–freshwater interface. We did not observe significant phenotypic variation in life‐history traits for this species when comparing marginal with more central populations, suggesting that abrupt changes in conditions at the brackish–freshwater interface limit its distribution. By contrast, Poecilia picta was present across a wide range of salinities, although it gradually disappeared from upstream freshwater localities. In addition, P. picta populations exhibited an increase in offspring size in localities where they coexist with P. reticulata, suggesting a role for interspecific competition. The parapatric distribution of these two species, suggests that P. reticulata distributions are limited by an abiotic factor (salinity), whereas P. picta is limited by a biotic factor (interspecific competition). Similar parapatric patterns have been previously described in other systems, suggesting they might be a common pattern in nature. © 2013 The Linnean Society of London

Ecological, evolutionary and human‐mediated determinants of poeciliid species richness on Caribbean islands

“…On small Caribbean islands that contain several poeciliid species (all of which became established by colonization as opposed to in situ speciation), a similar pattern is observed. On Trinidad and Tobago, the closely related P. reticulata and P. picta exhibit a parapatric distribution (Torres-Dowdall et al, 2013). Poecilia reticulata's range extension into lowland rivers seems to be limited by its relative intolerance of brackish and saltwater.…”

“…Poecilia reticulata's range extension into lowland rivers seems to be limited by its relative intolerance of brackish and saltwater. Poecilia picta is found across a wide range of salinities but its gradual disappearance in more upstream (freshwater) habitat seems to be driven by interspecific competition with P. reticulata (Torres-Dowdall et al, 2013). Likewise, on the island of Grenada there are two species of the same genus: P. reticulata and P. vivipara.…”

Shared and unique patterns of phenotypic diversification along a stream gradient in two congeneric species

“…In stream ecosystems, salinity, water velocity, temperature regimes, and dissolved oxygen are of particular importance1114. Other studies found interactions between biotic and abiotic variables to predict species distributions along environmental gradients3741, as exemplified by the study of Torres-Dowdall et al 42,. who examined ecological factors explaining the parapatric distribution of the congeners P. reticulata and P. picta in the lowlands of Trinidad.…”

“…who examined ecological factors explaining the parapatric distribution of the congeners P. reticulata and P. picta in the lowlands of Trinidad. It appears as if the distribution of P. reticulata is limited by an abiotic factor (increasing salinity), whereas that of P. picta is limited by a biotic interaction (interspecific competition with P. reticulata )42.…”

Ecology and the diversification of reproductive strategies in viviparous fishes

“…We assumed that competitive interactions for the focal species primarily occur with other species of the family Poeciliidae (Alberici da Barbiano et al . 2010; Torres-Dowdall et al . 2013) and that the intensity of competition is a function of the number of coexisting species.…”