ABSTRACT
This study assesses the effect of vegetation structure on the subtropical invertebrate communities in contrasting sampling dates of macrophyte populations in the RAMSAR site of Iberá wetlands, South America. Invertebrates associated with the submersed Egeria najas and the floating rooted Pontederia azurea were chosen to provide a model involving different microhabitat complexity. The results suggest that vegetation structure provided by the two macrophyte species supported significant differences in the density of animals, with invertebrate abundance of E. najas twice as high as on P. azurea. Abundance showed no significant differences in both contrasting sampling dates, growth and decline. Our result clearly showed invertebrates exclusively associated with each macrophyte species, as well different invertebrate taxa dominating in each sampling date (decline: Cladocera; growth: Aphididae, Belostomatidae and Planorbidae). We also show that working at the taxonomic levels of family could be a sensible trade-off between taxonomic identification effort versus reaching reliable and useful results for environmental monitoring and natural resource management in highly diverse subtropical wetlands. Our results emphasize the role of vegetation structure on invertebrate communities, as well suggest that the growth cycle of macrophyte populations could be a relevant variable influencing these animals in pristine subtropical wetlands.
Subject(s)
Invertebrates , Wetlands , Animals , Argentina , South America , Environmental MonitoringABSTRACT
Geometric morphometric methods are powerful tools to discriminate between closely related ostracods taxa as well as to study the relationship between their morphological variations, taxonomy and paleoecology. In this study, valve outline analysis allows the discrimination between the non-marine ostracod C. silvestrii and R. whatleyi juveniles, pointing out differences in the posterior valve area and surface ornamentation. Modern female specimens of C. silvestrii from 23 sites located in a spatial transect (41 to 51 °S) exhibited extensive morphological variability, on the basis of which three morphotypes (acuminated, transitional, subtruncated) were determined. Multivariate analyses showed that acuminated and transitional shapes are not arranged in groups but the subtruncated morphotype, previously described as E. cecryphalium, seems to be associated with low water conductivity (372 µS cm-1), dominant cold (5 ºC) and windy (8.6 m s-1) climatic conditions. The fossil cluster which included nine cores spanning the last 15.6 kyr, only covered acuminated and transitional shapes, which may indicate that these lineages might be older than the subtruncated morphotype. In addition, morphological differences between reproduction modes suggested that parthenogenetic females exhibit de posterior margin more acuminate than sexual females. These results set the ground for more precise ecological and paleoenvironmental studies in Patagonia.
