The rapid degradation of wetlands worldwide accentuates the urgent need for ecological data to help manage and protect the threatened biodiversity in the remaining often-fragmented wetlands. In the Neotropics where fragmentation is common, environmental factors structuring aquatic macroinvertebrate communities are poorly known. We tested the hypothesis that physical features, such as wetland area, habitat diversity, water depth and temperature, and water and sediment chemistry are important correlates with richness, density and composition of wetland macroinvertebrate assemblages in Brazil. If so, do these correlations differ between summer and winter? A total of 16 895 individuals across 61 families were collected. Richness was positively associated with habitat diversity and water depth and negatively associated with water temperature. Macroinvertebrate density was negatively associated with water depth, and positively correlated with habitat diversity, percentage of sediment organic matter and water conductivity. Macroinvertebrate composition was associated mainly with wetland area and habitat diversity in the wetlands studied; these relationships persisted in both seasons. Our data illustrate environmental factors that potentially structure and maintain aquatic macroinvertebrate biodiversity in southern Brazil wetlands, and should be managed because 90% of these ecosystems have already been lost as a result of human activities.

The expansion of rice fields is one of the main human activities responsible for the decline of natural wetlands throughout the world. However, rice fields have been recognized as having considerable potential value for many aquatic species. In this sense, an important question from the point of view of biodiversity conservation is the adequacy of these agricultural wetlands as an integrated managed landscape that contributes to maintain a rich biodiversity. The two main questions of this study were: (1) Do richness, density, and composition of macroinvertebrates differ in rice fields with different management practices (flooded and dry)?; and, (2) Do richness, density and composition of macroinvertebrates change in rice fields over the rice cultivating phases? Six collections were carried out in six rice fields with different management practices after cultivation (three dry and three flooded during the fallow phase). The macroinvertebrates were sampled using a corer (7.5-cm diameter) inserted 10 cm into the substratum of the rice fields. We recorded 6,425 macroinvertebrates, comprising 71 macroinvertebrate taxa. Macroinvertebrate richness and density varied over the rice cultivating cycle. The different management practices adopted after cultivation did not influence the macroinvertebrate richness and density; however, they influenced composition. Thus, the mosaic created by the variation of flooded and dry rice fields would provide the setting for a greater number of taxa within the agricultural landscape. The difference in taxa composition between flooded and dry rice fields is an interesting result in terms of biodiversity conservation. Rice producers could maintain part of their agricultural land flooded during the fallow phase. These management practices adopted could be an important strategy for biodiversity conservation in areas where the natural wetlands were converted into rice fields.

Irrigated rice fields in southern Brazil remain without surface water for 2 years during the fallow phase. The present study tested the hypothesis that the hydrologic regime adopted in rice fields of southern Brazil does not compromise the viability of resting stages of aquatic invertebrates. Dry sediment samples were collected from 9 rice fields with different durations of the fallow phase: 20 days, 1 year, and 2 years after the harvesting period. A total of 2,853 invertebrates distributed across 40 taxa emerged after rewetting dry sediments over the experiment duration (58 days). The dominant invertebrates were microcrustaceans represented by 1,041 individuals and 17 species. Invertebrate richness and density on rice fields fallowed (i.e., dried) for 1 year were greater than that for rice fields drained 20 days and 2 years. Aquatic invertebrate composition varied between rice fields fallowed for 20 days compared to those that remained dry for 1 or 2 years. The existence of viable resting stages in dry rice sediments over all stages of the fallow phase should help guide wetland restoration initiatives in southern Brazil.

Exotic pine invasion influences native wetland assemblages by changing environmental conditions such as hydrological regime and physicochemical characteristics. The expansion of cultivated pine has been a concern in southern Brazil and its impacts on aquatic biodiversity are poorly known. We tested the hypotheses that: (1) pine invasion decreases aquatic macroinvertebrate richness and abundance, modifying composition and macroinvertebrate functional feeding groups in ponds; and (2) β-diversity between natural and pine ponds is determined mainly by species nestedness. Five ponds in native grassland and five in a pine-planted matrix were sampled seven times from 2007 to 2009. The pine ponds had reduced macroinvertebrate richness and abundance, and different taxa and functional feeding groups. Comparing ponds in natural and cultivated pine areas, β-diversity as determined by nestedness did not differ from the value resulting from the turnover. Reduction of surface in ponds in pine areas may be one of the main causes for the lower macroinvertebrate richness and abundance because many taxa do not have adaptations to tolerate or escape the dry phase. Our results suggest that pine invasion has a negative impact on macroinvertebrate structure in southern Brazil coastal ponds.

Metacommunity organisation in temporary ponds is assembled by spatiotemporally varying processes that are also contingent on the species' dispersal ability and scale of observation. Aquatic insects are useful models to study the relative contribution of environmental and spatial factors to community assembly in view of the differing dispersal ability existing in the species from this group. We assessed the metacommunity organisation of aquatic insects and subsets of strong-and weak-flying insects in relation to environmental (habitat structure; water chemistry; climate) and spatial factors in temporary ponds ranging along a latitudinal gradient in southern Brazil. Local and climate environmental factors (water chemistry and temperature) along with fine-scale spatial factors were the main drivers of the total insect community, although their relative importance shifted between subsets of weak-and strong-flying insects. The composition of strong-flying insects was structured by climate and fine-scale spatial factors, while weak-flying insects, by local (water chemistry) and spatially structured climate. This suggests that strong-flying insects showed stronger signatures of mass effects at finer scales, while weak-flying insects were more strongly affected by species sorting coupled to local environmental factors and regional climate. In summary, our results indicate that the relative importance of assembly processes for metacommunity organisation of aquatic insects in temporary ponds is contingent on dispersal ability.