Bet-hedgers commit to the hedge: Zooplankton in ephemeral semiarid wetlands of tropical Brazil that widely spread risk.

Bet-hedging is an ecological risk-aversion strategy in which a population does not commit all its effort toward a single reproductive event or specific environmental condition, and instead spreads the risk to include multiple reproductive events or conditions. For aquatic invertebrates in dry wetlands, this often takes the form of some propagules hatching in the first available flood, while remaining propagules hatch in subsequent floods (the "hedge"); this better ensures that a subset of propagules will hatch in a flood of sufficient duration to successfully complete development. Harsh environmental conditions are believed to promote an increased reliance on bet-hedging. Bet-hedging studies have typically been restricted to single sites or single populations. Community-level assessments may provide more robust support for the range of hatching strategies that exist in nature. Here, we tested whether freshwater zooplankton assemblages inhabiting ephemeral and unpredictable wetlands of a semiarid zone of tropical Brazil employ hatching strategies suggestive of bet-hedging; few efforts have addressed bet-hedging in the tropics where the unique conditions may influence the strategy. We collected dry sediments from six ephemeral wetlands, and flooded them across a sequence of three hydrations under similar laboratory conditions to assess whether hatching patterns conform to some of the predictions of the bet-hedging theory. We found that taxa showing hatching patterns akin to bet-hedging associated with delayed hatching numerically dominated the assemblages that emerged from dry sediments, although there was large heterogeneity in the hatching rate among sites and across taxa. While some populations distributed their hatching across all three floods and committed most of their hatching fraction to the first hydration, others committed as much or more effort to the second hydration (the "hedge") or the third hydration (another substantial "hedge"). Thus, in the harsh study wetlands, hatching patterns akin to bet-hedging associated with delayed hatching were common and occurred at multiple temporal scales. Our community assessment found that a commitment to the "hedge" was greater than the current theory would predict. Our findings have broader implications; bet-hedger taxa seem especially well equipped to tolerate stress if conditions become harsher as environments change.

Perils of life on the edge: Climatic threats to global diversity patterns of wetland macroinvertebrates.

Climate change is rapidly driving global biodiversity declines. How wetland macroinvertebrate assemblages are responding is unclear, a concern given their vital function in these ecosystems. Using a data set from 769 minimally impacted depressional wetlands across the globe (467 temporary and 302 permanent), we evaluated how temperature and precipitation (average, range, variability) affects the richness and beta diversity of 144 macroinvertebrate families. To test the effects of climatic predictors on macroinvertebrate diversity, we fitted generalized additive mixed-effects models (GAMM) for family richness and generalized dissimilarity models (GDMs) for total beta diversity. We found non-linear relationships between family richness, beta diversity, and climate. Maximum temperature was the main climatic driver of wetland macroinvertebrate richness and beta diversity, but precipitation seasonality was also important. Assemblage responses to climatic variables also depended on wetland water permanency. Permanent wetlands from warmer regions had higher family richness than temporary wetlands. Interestingly, wetlands in cooler and dry-warm regions had the lowest taxonomic richness, but both kinds of wetlands supported unique assemblages. Our study suggests that climate change will have multiple effects on wetlands and their macroinvertebrate diversity, mostly via increases in maximum temperature, but also through changes in patterns of precipitation. The most vulnerable wetlands to climate change are likely those located in warm-dry regions, where entire macroinvertebrate assemblages would be extirpated. Montane and high-latitude wetlands (i.e., cooler regions) are also vulnerable to climate change, but we do not expect entire extirpations at the family level.

Does taxonomic and numerical resolution affect the assessment of invertebrate community structure in New World freshwater wetlands?

The efficiency of biodiversity assessments and biomonitoring studies is commonly challenged by limitations in taxonomic identification and quantification approaches. In this study, we assessed the effects of different taxonomic and numerical resolutions on a range of community structure metrics in invertebrate compositional data sets from six regions distributed across North and South America. We specifically assessed the degree of similarity in the metrics (richness, equitability, beta diversity, heterogeneity in community composition and congruence) for data sets identified to a coarse resolution (usually family level) and the finest taxonomic resolution practical (usually genus level, sometimes species or morphospecies) and by presence-absence and relative abundance numerical resolutions. Spearman correlations showed highly significant and positive associations between univariate metrics (richness and equitability) calculated for coarse- and finest-resolution datasets. Procrustes analysis detected significant congruence between composition datasets. Higher correlation coefficients were found for datasets with the same numerical resolutions regardless of the taxonomic level (about 90%), while the correlations for comparisons across numerical resolutions were consistently lower. Our findings indicate that family-level resolution can be used as a surrogate of finer taxonomic resolutions to calculate a range of biodiversity metrics commonly used to describe invertebrate community structure patterns in New World freshwater wetlands without significant loss of information. However, conclusions on biodiversity patterns derived from datasets with different numerical resolutions should be critically considered in studies on wetland invertebrates.

Climate- versus geographic-dependent patterns in the spatial distribution of macroinvertebrate assemblages in New World depressional wetlands.

Analyses of biota at lower latitudes may presage impacts of climate change on biota at higher latitudes. Macroinvertebrate assemblages in depressional wetlands may be especially sensitive to climate change because weather-related precipitation and evapotranspiration are dominant ecological controls on habitats, and organisms of depressional wetlands are temperature-sensitive ectotherms. We aimed to better understand how wetland macroinvertebrate assemblages were structured according to geography and climate. To do so, we contrasted aquatic-macroinvertebrate assemblage structure (family level) between subtropical and temperate depressional wetlands of North and South America using presence-absence data from 264 of these habitats across the continents and more-detailed relative-abundance data from 56 depressional wetlands from four case-study locations (North Dakota and Georgia in North America; southern Brazil and Argentinian Patagonia in South America). Both data sets roughly partitioned wetland numbers equally between the two climatic zones and between the continents. We used ordination methods (PCA and NMDS) and tests of multivariate dispersion (PERMDISP) to assess the distribution and the homogeneity in variation in the composition of macroinvertebrate assemblages across climates and continents, respectively. We found that macroinvertebrate assemblage structures in the subtropical depressional wetlands of North and South America were similar to each other (at the family level), while assemblages in the North and South American temperate wetlands were unique from the subtropics, and from each other. Tests of homogeneity of multivariate dispersion indicated that family-level assemblage structures were more homogeneous in wetlands from the subtropical than the temperate zones. Our study suggests that ongoing climate change may result in the homogenization of macroinvertebrate assemblage structures in temperate zones of North and South America, with those assemblages becoming enveloped by assemblages from the subtropics. Biotic homogenization, more typically associated with other kinds of anthropogenic factors, may also be affected by climate change.

Ecology of Terrestrial Arthropods in Freshwater Wetlands.

The terrestrial arthropod fauna of wetlands has been largely ignored by scientists compared to other ecological elements, yet these organisms are among the most important influences on the ecology of these systems, with the vast majority of the biodiversity in wetlands found among the terrestrial arthropods. Wetlands present a range of habitat for terrestrial arthropods, with unique faunas being associated with soils and ground litter, living-plant substrates, and peatlands. Myriapoda, Araneae, Collembola, Carabidae, Formicidae, and assorted herbivorous Coleoptera and Lepidoptera are the terrestrial arthropod groups that most influence the ecology of wetlands. Despite their success, most terrestrial arthropods possess fairly rudimentary adaptations for life in wetlands, with most simply moving to higher ground or up vegetation during floods, although some species can tolerate immersion. Many terrestrial arthropods are environmentally sensitive and show considerable promise as bioindicators of wetland ecological conditions.

Freshwater release into estuarine wetlands changes the structure of benthic invertebrate assemblages: A case study from the Yellow River Delta.

Freshwater releases to wetlands degraded by excessive soil salinity in estuarine areas have been widely used to restore vegetation and maintain biodiversity of the wetland ecosystems. However, freshwater release also alters the physical and chemical properties of the water body, having a profound impact on the ecology of restored wetland ecosystems. In this study, physical and chemical parameters of water quality were compared between restored and non-restored tidal wetlands after 10 years of freshwater release in the Yellow River estuary. In addition, benthic invertebrates were used as bioindicators to reveal the effects of freshwater release on estuarine wetland ecology. The results showed that there was a significant difference in salinity between restored and non-restored wetlands (P < 0.05), which led to differences in the composition of benthic invertebrate communities (ANOSIM P < 0.001). The primary components of benthic invertebrate community were insects in restored wetlands, and in non-restored tidal wetlands the primary components were annelids, crustaceans, and gastropods. More long-term monitoring research of the impacts of freshwater introduction on degraded estuarine wetland ecosystems is needed to fully assess consequences.

Detrimental effects of a novel flow regime on the functional trajectory of an aquatic invertebrate metacommunity.

Novel flow regimes resulting from dam operations and overallocation of freshwater resources are an emerging consequence of global change. Yet, anticipating how freshwater biodiversity will respond to surging flow regime alteration requires overcoming two challenges in environmental flow science: shifting from local to riverscape-level understanding of biodiversity dynamics, and from static to time-varying characterizations of the flow regime. Here, we used time-series methods (wavelets and multivariate autoregressive models) to quantify flow-regime alteration and to link time-varying flow regimes to the dynamics of multiple local communities potentially connected by dispersal (i.e., a metacommunity). We studied the Chattahoochee River below Buford dam (Georgia, U.S.A.), and asked how flow regime alteration by a large hydropower dam may control the long-term functional trajectory of the downstream invertebrate metacommunity. We found that seasonal variation in hydropeaking synchronized temporal fluctuations in trait abundance among the flow-altered sites. Three biological trait states describing adaptation to fast flows benefitted from flow management for hydropower, but did not compensate for declines in 16 "loser" traits. Accordingly, metacommunity-wide functional diversity responded negatively to hydropeaking intensity, and stochastic simulations showed that the risk of functional diversity collapse within the next 4 years would decrease by 17% if hydropeaking was ameliorated, or by 9% if it was applied every other season. Finally, an analysis of 97 reference and 23 dam-affected river sites across the U.S. Southeast suggested that flow variation at extraneous, human-relevant scales (12-hr, 24-hr, 1-week) is relatively common in rivers affected by hydropower dams. This study advances the notion that novel flow regimes are widespread, and simplify the functional structure of riverine communities by filtering out taxa with nonadaptive traits and by spatially synchronizing their dynamics. This is relevant in the light of ongoing and future hydrologic alteration due to climate non-stationarity and the new wave of dams planned globally.

Congeneric Predaceous Diving Beetle Species Fail to Segregate in a Floodplain System: A Case of Amplified Sympatry.

Coexistence of closely related species has long been a focus of biologists in their efforts to explain mechanisms that drive community assembly. Dytiscidae (predaceous diving beetles) are a group that shows a particularly high affinity for sympatry despite their relatedness. Our objective was to investigate the degree of overlap among Neoporus (Guignot) species (Coleoptera: Dytiscidae) in floodplains of the southeastern United States. We sampled two floodplain habitats (permanent oxbow lakes and temporarily flooded pools) of the Altamaha River (Georgia, USA) for Neoporus species over three years. Six species of Neoporus were collected during our study, and a significant amount of overlap (spatial and temporal) was documented. Analysis suggested that none of the species exhibited a preference toward one habitat type or the other. Temporally, no striking patterns of segregation emerged. No negative correlations between species were documented, but neither were significant positive correlations found. This absence of distinct patterns suggests a lack of segregation among Neoporus species in floodplains of the Altamaha River. While Dytiscidae in general appears to be a particularly sympatric group of organisms, overlap among congeneric species within the family has been documented less frequently. Our study provides new insight into the degree to which dytiscids are capable of coexisting in space and time.

Functional and phylogenetic relatedness in temporary wetland invertebrates: current macroecological patterns and implications for future climatic change scenarios.

In freshwater ecosystems, species compositions are known to be determined hierarchically by large to small­scale environmental factors, based on the biological traits of the organisms. However, in ephemeral habitats this heuristic framework remains largely untested. Although temporary wetland faunas are constrained by a local filter (i.e., desiccation), we propose its magnitude may still depend on large-scale climate characteristics. If this is true, climate should be related to the degree of functional and taxonomic relatedness of invertebrate communities inhabiting seasonal wetlands. We tested this hypothesis in two ways. First, based on 52 biological traits for invertebrates, we conducted a case study to explore functional trends among temperate seasonal wetlands differing in the harshness (i.e., dryness) of their dry season. After finding evidence of trait filtering, we addressed whether it could be generalized across a broader climatic scale. To this end, a meta-analysis (225 seasonal wetlands spread across broad climatic categories: Arid, Temperate, and Cold) allowed us to identify whether an equivalent climate-dependent pattern of trait richness was consistent between the Nearctic and the Western Palearctic. Functional overlap of invertebrates increased from mild (i.e., Temperate) to harsher climates (i.e., Arid and Cold), and phylogenetic clustering (using taxonomy as a surrogate) was highest in Arid and lowest in Temperate wetlands. We show that, (i) as has been described in streams, higher relatedness than would be expected by chance is generally observed in seasonal wetland invertebrate communities; and (ii) this relatedness is not constant but climate-dependent, with the climate under which a given seasonal wetland is located determining the functional overlap and the phylogenetic clustering of the community. Finally, using a space-for-time substitution approach we suggest our results may anticipate how the invertebrate biodiversity embedded in these vulnerable and often overlooked ecosystems will be affected by long-term climate change.