Abstract
The present study compares the reproduction, condition and size of the small characiform fish, Characidium pterostictum, sampled at close sites differing in severity of flash flood effects. Data were obtained from seasonal samples in two sites situated 8 km apart in the same stream. In the upstream site, habitat is more severely affected by flash floods than in the downstream site, and this difference was hypothesized to produce differences in life history and individual reproduction trade-off patterns, as predicted by life-history theory. The results provided evidence for small-scale spatial variation in life-history and trade-off patterns within the studied population. At the most severely disturbed site, C. pterostictum displayed a trade-off pattern that favored reproductive life-span (e.g., larger size, higher and seasonally stable condition, larger mean size of mature females) over instantaneous reproductive output (lower gonadosomatic index), while the opposite pattern was observed in the less disturbed site. Because of the differences in disturbance effects between each sampling site, these results suggest that within-stream variability in the severity of hydrological disturbance can influence life-history patterns at small spatial scales. An implication of the results is that fish occupying areas that are hydrologically more variable within a stream are not necessarily at an energetic or reproductive disadvantage, but may be simply under environmental conditions that favor distinct patterns of energy allocation (or trade-offs) and population persistence, as predicted by life-history theory. Therefore, plasticity in life-history is expected to be common in stream fish populations that are widespread in a stream system with spatially variable or patchy habitat characteristics.
Highlights
Streams are heterogeneous environments where physical and temporal variability influence biotic patterns and processes, including fish life-history (Poff & Ward, 1990)
The present study compares the reproduction, condition and size of the small characiform fish, Characidium pterostictum, sampled at close sites differing in severity of flash flood effects
Investigating small-scale spatial variation in life-history is important for understanding how stream fish populations persist under the environmental variability (Magalhães et al, 2003), since mortality is locally variable within streams (Lobón-Cerviá & Rincón, 2004)
Summary
Streams are heterogeneous environments where physical and temporal variability influence biotic patterns and processes, including fish life-history (Poff & Ward, 1990). In fish populations facing high environmental variability or adverse conditions (e.g., food limitation), there is a trade-off between individual survival and reproduction (Winemiller, 2004), with some species sacrificing egg production for growth, while others sacrifice condition to maintain fecundity (Link & Burnett, 2001). Investigating small-scale spatial variation in life-history is important for understanding how stream fish populations persist under the environmental variability (Magalhães et al, 2003), since mortality is locally variable within streams (Lobón-Cerviá & Rincón, 2004). To cope with local variability in habitat conditions, fish can exhibit different energy allocation patterns among survival, growth, and reproduction (Lobón-Cerviá & Rincón, 2004). A general prediction is that fish inhabiting highly variable habitats are affected by density-independent mortality, and tend to exhibit shorter longevity, smaller body size and earlier maturity, in comparison with less variable environments (Schlosser, 1990; Magalhães et al, 2003; Danylchuk & Tonn, 2006)
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