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

Revised New World bioregions and environmental correlates for vectors of Chagas disease (Hemiptera, Triatominae)

The subfamily Triatominae includes a group of hematophagous insects, vectors of the parasite Trypanosoma cruzi, which is the etiological agent of Chagas disease, also known as American trypanosomiasis. Triatomines occur in the Old and New World and occupy diverse habitats including tropical and temperate areas. Some studies suggest the distributions of triatomines group into three or four regions. This study objectively determined bioregions focused specifically on New World Triatominae, using clustering and ordination analysis. We also identified indicator species by bioregion and investigated relationships among bioregions and environmental variables using redundancy analysis and multivariate regression trees. We delineated seven bioregions specific to Triatominae and linked each with indicator species. This result suggests more biogeographical structure exists than was revealed in earlier studies that were more general, subjective, and based on older taxonomic and distributional information. Precipitation, elevation, and vegetation were important variables in the delimitating bioregions. This implies that more detailed study of how these factors influence triatomine distributions could benefit understanding of how Chagas disease is spread.

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.

Structural and functional development of twelve newly established floodplain pond mesocosms

Ecosystems are complex structures with interacting abiotic and biotic processes evolving with ongoing succession. However, limited knowledge exists on the very initial phase of ecosystem development and colonization. Here, we report results of a comprehensive ecosystem development monitoring for twelve floodplain pond mesocosms (FPM; 23.5 m × 7.5 m × 1.5 m each) located in south-western Germany. In total, 20 abiotic and biotic parameters, including structural and functional variables, were monitored for 21 months after establishment of the FPMs. The results showed evolving ecosystem development and primary succession in all FPMs, with fluctuating abiotic conditions over time. Principal component analyses and redundancy analyses revealed season and succession time (i.e., time since ecosystem establishment) to be significant drivers of changes in environmental conditions. Initial colonization of both aquatic (i.e., water bodies) and terrestrial (i.e., riparian land areas) parts of the pond ecosystems occurred within the first month, with subsequent season-specific increases in richness and abundance for aquatic and terrestrial taxa over the entire study period. Abiotic environmental conditions and aquatic and terrestrial communities showed increasing interpond variations over time, that is, increasing heterogeneity among the FPMs due to natural environmental divergence. However, both functional variables assessed (i.e., aquatic and terrestrial litter decomposition) showed opposite patterns as litter decomposition rates slightly decreased over time and interpond differences converged with successional ecosystem developments. Overall, our results provide rare insights into the abiotic and biotic conditions and processes during the initial stages of freshwater ecosystem formation, as well as into structural and functional developments of the aquatic and terrestrial environment of newly established pond ecosystems.

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.

Large-scale geographical and environmental drivers of shallow lake diatom metacommunities across Europe

Disentangling the relative role of species sorting and dispersal limitation in biological communities has become one of the main issues for community ecologists and biogeographers. In this study, we analysed a data set of epiphytic diatoms comprising 34 lakes from six European countries. This data set covers a relatively large latitudinal gradient to elucidate which processes are affecting the distribution of diatom communities on a broad spatial extent. Our results show strong environmental effects on the composition of the diatom communities, while the spatial factor effects were weak, emphasising that compositional variation was mainly due to species turnover. Our data support information from the literature that local abiotic factors are the main predictors controlling the compositional variation of diatom assemblages in European shallow lakes. More specifically, changes in species composition were driven mainly by nutrient content in Northern Europe, whereas lakes located in Southern Europe were more affected by conductivity and lake depth. Our results solve pending questions in the spatial ecology of diatoms by proving that species turnover is stronger than nestedness at any spatial scale, and give support to the use of epiphytic diatoms as biological indicators for shallow lakes.

Context-dependent resistance of freshwater invertebrate communities to drying

More freshwater ecosystems are drying in response to global change thereby posing serious threat to freshwater biota and functions. The production of desiccation-resistant forms is an important adaptation that helps maintain biodiversity in temporary freshwaters by buffering communities from drying, but its potential to mitigate the negative effects of drying in freshwater ecosystems could vary greatly across regions and ecosystem types. We explored this context dependency by quantifying the potential contribution of desiccation-resistance forms to invertebrate community recovery across levels of regional drying prevalence (defined as the occurrence of drying events in freshwaters in a given region) and ecosystem types (lentic, lotic) in temporary neotropical freshwaters. We first predicted that regional drying prevalence influences the selection of species with desiccation-resistant forms from the regional species pools and thus increases the ability of communities to recover from drying. Second, we predicted lentic freshwaters harbor higher proportions of species with desiccation-resistant forms compared to lotic, in response to contrasted hydrologic connectivity. To test these predictions, we used natural experiments to quantify the contribution of desiccation-resistant forms to benthic invertebrate community recovery in nine intermittent streams and six geographically isolated temporary wetlands from three Bolivian regions differing in drying prevalence. The contribution of desiccation-resistant forms to community recovery was highest where regional drying prevalence was high, suggesting the species pool was adapted to regional disturbance regimes. The contribution of desiccation-resistant forms to community recovery was lower in streams than in wetlands, emphasizing the importance of hydrologic connectivity and associated recolonization processes from in-stream refuges to recovery in lotic systems. In all regions, the majority of functional traits were present in desiccation-resistant taxa indicating this adaptation may help maintain ecosystem functions by buffering communities from the loss of functional traits. Accounting for regional context and hydrologic connectivity in community recovery processes following drying can help refine predictions of freshwater biodiversity response to global change.

Land-use type and intensity differentially filter traits in above- and below-ground arthropod communities

Along with the global decline of species richness goes a loss of ecological traits. Associated biotic homogenization of animal communities and narrowing of trait diversity threaten ecosystem functioning and human well-being. High management intensity is regarded as an important ecological filter, eliminating species that lack suitable adaptations. Below-ground arthropods are assumed to be less sensitive to such effects than above-ground arthropods. Here, we compared the impact of management intensity between (grassland vs. forest) and within land-use types (local management intensity) on the trait diversity and composition in below- and above-ground arthropod communities. We used data on 722 arthropod species living above-ground (Auchenorrhyncha and Heteroptera), primarily in soil (Chilopoda and Oribatida) or at the interface (Araneae and Carabidae). Our results show that trait diversity of arthropod communities is not primarily reduced by intense local land use, but is rather affected by differences between land-use types. Communities of Auchenorrhyncha and Chilopoda had significantly lower trait diversity in grassland habitats as compared to forests. Carabidae showed the opposite pattern with higher trait diversity in grasslands. Grasslands had a lower proportion of large Auchenorrhyncha and Carabidae individuals, whereas Chilopoda and Heteroptera individuals were larger in grasslands. Body size decreased with land-use intensity across taxa, but only in grasslands. The proportion of individuals with low mobility declined with land-use intensity in Araneae and Auchenorrhyncha, but increased in Chilopoda and grassland Heteroptera. The proportion of carnivorous individuals increased with land-use intensity in Heteroptera in forests and in Oribatida and Carabidae in grasslands. Our results suggest that gradients in management intensity across land-use types will not generally reduce trait diversity in multiple taxa, but will exert strong trait filtering within individual taxa. The observed patterns for trait filtering in individual taxa are not related to major classifications into above- and below-ground species. Instead, ecologically different taxa resembled each other in their trait diversity and compositional responses to land-use differences. These previously undescribed patterns offer an opportunity to develop management strategies for the conservation of trait diversity across taxonomic groups in permanent grassland and forest habitats.