Temporal Demographic Patterns in Amazonian Upland Shrimps Related to Stream Hydraulics and Precipitation

ABSTRACT Reports of seasonal patterns in reproduction are uncommon for Amazonian upland‐stream shrimps (Caridea: Palaemonidae), since changes provoked by heavy rainfall in these systems are not as marked as in large rivers. Differences in the proportion of ovigerous females throughout the year are subtle and seem to be more a result of responses to environmental variation than interspecific competition. Despite these shrimp species reproducing continuously throughout the year, peaks of reproductive activity are believed to occur during the rainy season, as in large rivers, since changes in main‐channel hydraulics favour dispersion and habitat/food availability. Seasonal size variation due to variation in reproduction or mortality can also occur throughout the year, and recruitment is frequent during ebb and drought. Therefore, if any temporal pattern exists, reproductive activity is expected to be related to seasonal changes in precipitation and stream hydraulic features. To address these questions, we investigated whether upland stream shrimps show temporal patterns of size variation and reproduction (based on the proportion of ovigerous females) and whether precipitation and stream hydraulic features are correlated with the proportion of ovigerous females. We detected minimal mean‐size variation throughout the months for all species; thus, size changes do not follow a temporal pattern in our time series. A non‐random temporal pattern in the proportion of ovigerous females was found only for Pseudopalaemon amazonensis , but none of the measured predictors was related to this proportion. Despite the lack of a consistent temporal effect, the number of ovigerous Macrobrachium inpa showed a significant positive relationship with stream flow. Our findings confirm that Amazonian upland‐stream shrimp species reproduce continuously throughout the year, but non‐random temporal patterns of reproduction occur in some species. Size variation did not show any temporal pattern in our time series. Stream flow was found to be positively related to reproduction in one species. These results add evidence to shrimp reproductive ecology research on how local changes in stream velocity can affect shrimp species reproduction. Moreover, further investigation is still needed to predict future effects of water level variation on shrimp species traits as climate change advances.