Reproductive strategies of Amazonian stream fishes and their fine-scale use of habitat are ordered along a hydrological gradient

Abstract

Macroecological comparisons have shown that habitat characteristics have a major influence on the evolution of life-history strategies of fishes in large river systems. Specifically, habitat variability and predictability seem to forge the reproductive strategies of fishes into a trilateral continuum with three main types: seasonal, opportunistic and equilibrium. Despite the usefulness of such a broad categorisation, large-scale patterns of trait distribution should ultimately be influenced by selection at smaller (i.e. individual) spatial scales. However, the scarcity of studies developed at the organismal scale leaves gaps in our understanding of how habitat characteristics affect life history and behavioural tactics of stream fishes. We examined the fine-scale spatial distribution of fishes in pristine Amazonian headwater streams over a full seasonal cycle to test whether segregation into main channel and associated temporary pond habitats was predictably related to hydrological variation and species' life-history traits. Most species could not be unambiguously assigned to one of the three end points of the trilateral continuum, but seemingly occupied instead the intermediate multivariate space between the end points. However, species were clearly ordered along a gradient of relative habitat use, ranging from strict channel dwellers throughout the hydrological cycle to pond specialists, with some species occupying the ponds at high water levels. Hydrological effects on habitat use were significantly related to species' reproductive strategies, with the strongest responses found in species with large eggs and seasonally concentrated reproduction, which were most abundant in ponds at high water levels. We suggest that trophic limitations and hydrological characteristics of Amazonian headwater forest streams may severely limit the seasonal strategy, one of the end points of the trilateral model. The species-specific habitat segregation reported here adds to the list of mechanisms, such as miniaturisation and isolation by distance, previously postulated to contribute to high diversity of stream fish faunas in the Amazon basin. © 2013 John Wiley & Sons Ltd.