Do latitudinal gradients exist in New Zealand stream invertebrate metacommunities?

Novel Insights to Be Gained From Applying Metacommunity Theory to Long-Term, Spatially Replicated Biodiversity Data

Global loss of biodiversity and its associated ecosystem services is occurring at an alarming rate and is predicted to accelerate in the future. Metacommunity theory provides a framework to investigate multi-scale processes that drive change in biodiversity across space and time. Short-term ecological studies across space have progressed our understanding of biodiversity through a metacommunity lens, however, such snapshots in time have been limited in their ability to explain which processes, at which scales, generate observed spatial patterns. Temporal dynamics of metacommunities have been understudied, and large gaps in theory and empirical data have hindered progress in our understanding of underlying metacommunity processes that give rise to biodiversity patterns. Fortunately, we are at an important point in the history of ecology, where long-term studies with cross-scale spatial replication provide a means to gain a deeper understanding of the multiscale processes driving biodiversity patterns in time and space to inform metacommunity theory. The maturation of coordinated research and observation networks, such as the United States Long Term Ecological Research (LTER) program, provides an opportunity to advance explanation and prediction of biodiversity change with observational and experimental data at spatial and temporal scales greater than any single research group could accomplish. Synthesis of LTER network community datasets illustrates that long-term studies with spatial replication present an under-utilized resource for advancing spatio-temporal metacommunity research. We identify challenges towards synthesizing these data and present recommendations for addressing these challenges. We conclude with insights about how future monitoring efforts by coordinated research and observation networks could further the development of metacommunity theory and its applications aimed at improving conservation efforts.

The biogeography of Streptomyces in New Zealand enabled by high-throughput sequencing of genus-specific rpoB amplicons

We evaluated Streptomyces biogeography in soils along a 1200 km latitudinal transect across New Zealand (NZ). Streptomyces diversity was examined using high-throughput sequencing of rpoB amplicons generated with a Streptomyces specific primer set. We detected 1287 Streptomyces rpoB operational taxonomic units (OTUs) with 159 ± 92 (average ± SD) rpoB OTUs per site. Only 12% (n = 149) of these OTUs matched rpoB sequences from cultured specimens (99% nucleotide identity cutoff). Streptomyces phylogenetic diversity (Faith's PD) was correlated with soil pH, mean annual temperature and plant community richness (Spearman's r: 0.77, 0.64 and -0.79, respectively; P < 0.05), but not with latitude. In addition, soil pH and plant community richness both explained significant variation in Streptomyces beta diversity. Streptomyces communities exhibited both high dissimilarity and strong dominance of one or a few species at each site. Taken together, these results suggest that dispersal limitation due to competitive interactions limits the colonization success of spores that relocate to new sites. Cultivated Streptomyces isolates represent a major source of clinically useful antibiotics, but only a small fraction of extant diversity within the genus have been identified and most species of Streptomyces have yet to be described.

Increasing climate-driven taxonomic homogenization but functional differentiation among river macroinvertebrate assemblages

Global change is increasing biotic homogenization globally, which modifies the functioning of ecosystems. While tendencies towards taxonomic homogenization in biological communities have been extensively studied, functional homogenization remains an understudied facet of biodiversity. Here, we tested four hypotheses related to long-term changes (1991-2016) in the taxonomic and functional arrangement of freshwater macroinvertebrate assemblages across space and possible drivers of these changes. Using data collected annually at 64 river sites in mainland New Zealand, we related temporal changes in taxonomic and functional spatial β-diversity, and the contribution of individual sites to β-diversity, to a set of global, regional, catchment and reach-scale environmental descriptors. We observed long-term, mostly climate-induced, temporal trends towards taxonomic homogenization but functional differentiation among macroinvertebrate assemblages. These changes were mainly driven by replacements of species and functional traits among assemblages, rather than nested species loss. In addition, there was no difference between the mean rate of change in the taxonomic and functional facets of β-diversity. Climatic processes governed overall population and community changes in these freshwater ecosystems, but were amplified by multiple anthropogenic, topographic and biotic drivers of environmental change, acting widely across the landscape. The functional diversification of communities could potentially provide communities with greater stability, resistance and resilience capacity to environmental change, despite ongoing taxonomic homogenization. Therefore, our study highlights a need to further understand temporal trajectories in both taxonomic and functional components of species communities, which could enable a clearer picture of how biodiversity and ecosystems will respond to future global changes.

Biodiversity patterns across taxonomic groups along a lake water-depth gradient: Effects of abiotic and biotic drivers

Understanding biodiversity patterns and the role of biotic attributes in governing these patterns remains one of the most important challenges in ecology. Here, taking water depth in Lake Lugu as a typical geographical gradient, we studied how these different taxa, that is bacteria, diatoms and chironomids, respond to the water depth and environmental gradients using molecular and morphological methods. We further evaluated the relative importance of water depth, environmental variables and biotic attributes in explaining biological characteristics, such as biomass, species richness, and community composition. The biomass of chironomids and the richness of bacteria and chironomids showed a nonlinearly decreasing pattern associated with increased water depth, while biomass and species richness of diatoms showed U-shaped and hump-shaped patterns, respectively. The three taxonomic groups all showed increasing dissimilarity with water depth changes, and there was clear cross-taxon congruence among the variations in community composition. Abiotic variables were pivotal in structuring biological characteristics; however, the biotic attributes also explained a unique portion of their variations. This suggests that biotic interactions significantly influenced the patterns of biomass, species richness, and community compositions along the water depth gradient for the three taxonomic groups studied. Our results provide new evidence that biotic attributes could help in predicting the biodiversity of aquatic communities along geographical gradients, such as water depth.

Lake regionalization and diatom metacommunity structuring in tropical South America

Lakes and their topological distribution across Earth's surface impose ecological and evolutionary constraints on aquatic metacommunities. In this study, we group similar lake ecosystems as metacommunity units influencing diatom community structure. We assembled a database of 195 lakes from the tropical Andes and adjacent lowlands (8°N-30°S and 58-79°W) with associated environmental predictors to examine diatom metacommunity patterns at two different levels: taxon and functional (deconstructed species matrix by ecological guilds). We also derived spatial variables that inherently assessed the relative role of dispersal. Using complementary multivariate statistical techniques (principal component analysis, cluster analysis, nonmetric multidimensional scaling, Procrustes, variance partitioning), we examined diatom-environment relationships among different lake habitats (sediment surface, periphyton, and plankton) and partitioned community variation to evaluate the influence of niche- and dispersal-based assembly processes in diatom metacommunity structure across lake clusters. The results showed a significant association between geographic clusters of lakes based on gradients of climate and landscape configuration and diatom assemblages. Six lake clusters distributed along a latitudinal gradient were identified as functional metacommunity units for diatom communities. Variance partitioning revealed that dispersal mechanisms were a major contributor to diatom metacommunity structure, but in a highly context-dependent fashion across lake clusters. In the Andean Altiplano and adjacent lowlands of Bolivia, diatom metacommunities are niche assembled but constrained by either dispersal limitation or mass effects, resulting from area, environmental heterogeneity, and ecological guild relationships. Topographic heterogeneity played an important role in structuring planktic diatom metacommunities. We emphasize the value of a guild-based metacommunity model linked to dispersal for elucidating mechanisms underlying latitudinal gradients in distribution. Our findings reveal the importance of shifts in ecological drivers across climatic and physiographically distinct lake clusters, providing a basis for comparison of broad-scale community gradients in lake-rich regions elsewhere. This may help guide future research to explore evolutionary constraints on the rich Neotropical benthic diatom species pool.