A macroecological perspective of diversity patterns in the freshwater realm

Department of Biology, University of Oulu, Oulu, Finland
Freshwater Biology (Impact Factor: 3.93). 08/2011; 56(9):1703 - 1722. DOI: 10.1111/j.1365-2427.2011.02610.x

ABSTRACT Summary1. The aim of this paper is to review literature on species diversity patterns of freshwater organisms and underlying mechanisms at large spatial scales.2. Some freshwater taxa (e.g. dragonflies, fish and frogs) follow the classical latitudinal decline in regional species richness (RSR), supporting the patterns found for major terrestrial and marine organism groups. However, the mechanisms causing this cline in most freshwater taxa are inadequately understood, although research on fish suggests that energy and history are major factors underlying the patterns in total species and endemic species richness. Recent research also suggests that not all freshwater taxa comply with the decline of species richness with latitude (e.g. stoneflies, caddisflies and salamanders), but many taxa show more complex geographical patterns in across-regions analyses. These complexities are even more profound when studies of global, continental and regional extents are compared. For example, clear latitudinal gradients may be present in regional studies but absent in global studies (e.g. macrophytes).3. Latitudinal gradients are often especially weak in the across-ecosystems analyses, which may be attributed to local factors overriding the effects of large-scale factors on local communities. Nevertheless, local species richness (LSR) is typically linearly related to RSR (suggesting regional effects on local diversity), although saturating relationships have also been found in some occasions (suggesting strong local effects on diversity). Nestedness has often been found to be significant in freshwater studies, yet this pattern is highly variable and generally weak, suggesting also a strong beta diversity component in freshwater systems.4. Both geographical location and local environmental factors contribute to variation in alpha diversity, nestedness and beta diversity in the freshwater realm, although the relative importance of these two groups of explanatory variables may be contingent on the spatial extent of the study. The mechanisms associated with spatial and environmental control of community structure have also been inferred in a number of studies, and most support has been found for species sorting (possibly because many freshwater studies have species sorting as their starting point), although also dispersal limitation and mass effects may be contributing to the patterns found.5. The lack of latitudinal gradients in some freshwater taxa begs for further explanations. Such explanations may not be gained for most freshwater taxa in the near future, however, because we lack species-level information, floristic and faunistic knowledge, and standardised surveys along extensive latitudinal gradients. A challenge for macroecology is thus to use the best possible species-level information on well-understood groups (e.g. fish) or use surrogates for species-level patterns (e.g. families) and then develop hypotheses for further testing in the freshwater realm. An additional research challenge concerns understanding patterns and mechanisms associated with the relationships between alpha, beta and gamma components of species diversity.6. Understanding the mechanistic basis of species diversity patterns should preferably be based on a combination of large-scale macroecological and landscape-scale metacommunity research. Such a research approach will help in elucidating patterns of species diversity across regional and local scales in the freshwater realm.

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    ABSTRACT: Questions: Are community composition and species richness of aquatic macrophytes determined primarily by local (habitat heterogeneity and water quality) or regional patterns (climate) at regional scale? Do two macrophyte functional groups (i.e. emergent and submerged macrophytes) respond similarly to local and regional patterns? Are lake macrophytes and explanatory variables geographically structured? Location: The US state of Minnesota Material: The community composition and species richness of aquatic flora was studied using presence-absence data in 454 lakes, covering the entire US state of Minnesota. In addition, community composition and species richness of emergent and submerged macrophytes was investigated separately. Methods: Variation partitioning based on partial redundancy analysis and partial linear regression was used to study the relative roles of water quality, habitat heterogeneity, climate and sampling effort in explaining community composition and species richness of lake macrophytes, respectively. Results: Macrophyte community composition and species richness (all taxa and two functional groups) were explained by water quality and climate. Alkalinity and total phosphorus from water quality variables affected most community composition of aquatic flora and macrophytes species richness decreased with increasing concentrations of these two variables. Maximum temperature of the warmest month and mean annual temperature affect most plant community composition, whereas species richness had a negative relationship with minimum temperature of the coldest month. Most significant explanatory variables (e.g. alkalinity, total phosphorus and temperature) were geographically structured showing a latitudinal change. Conclusions: Community composition and species richness of macrophytes were congruently influenced by regional (climate) and local patterns (water quality) at regional scale. Community composition and species richness of helophytes and submerged macrophytes were explained by environmental gradient to equal degree. The latitudinal change in the most significant environmental variables was related to calcareous soils and intensive agriculture, which were situated in the southern part of the state. Macrophyte species richness showed a reversed latitudinal gradient, which was likely due to high nutrient concentrations found in southern latitude lakes. Water quality primarily filters species from regional species pool, allowing only species tolerating high nutrient concentration, like invasive plants, to survive in southern latitudes.
    Journal of Vegetation Science 01/2015; · 2.82 Impact Factor
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    ABSTRACT: 1. Regional faunas are structured by historical, spatial and environmental factors. We studied large-scale variation in four ecologically different beetle groups (Coleoptera: Dytiscidae, Carabidae, Hydrophiloidea, Cerambycidae) along climate, land cover and geographical gradients, examined faunal breakpoints in relation to environmental variables, and investigated the best fit pattern of assemblage variation (i.e. randomness, checkerboards, nestedness, evenly-spaced, Gleasonian, Clementsian). We applied statistical methods typically used in the analysis of local ecological communities to provide novel insights into faunal compositional patterns at large spatial grain and geographical extent.2. We found that spatially-structured variation in climate and land cover accounted for most variation in each beetle group in partial redundancy analyses, whereas the individual effect of each explanatory variable group was generally much less important in accounting for variation in provincial species composition.3. We also found that climate variables were most strongly associated with faunal breakpoints, with temperature-related variables alone accounting for about 20% of variation at the first node of multivariate regression tree for each beetle group. The existence of faunal breakpoints was also shown by the “elements of faunal structure” analyses, which suggested Clementsian gradients across the provinces, i.e., that there were two or more clear groups of species responding similarly to the underlying ecological gradients.4. The four beetle groups showed highly similar biogeographical patterns across our study area. The fact that temperature was related to faunal breakpoints in the species composition of each beetle group suggests that climate sets a strong filter to the distributions of species at this combination of spatial grain and spatial extent. This finding held true despite the ecological differences among the four beetle groups, ranging from fully aquatic to fully terrestrial, and from herbivorous to predaceous species.5. The existence of Clementsian gradients may be a common phenomenon at large scales, and it is likely to be caused by crossing multiple species pools determined by climatic and historical factors on the distributions of species.This article is protected by copyright. All rights reserved.
    Journal of Animal Ecology 09/2014; · 4.84 Impact Factor
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    ABSTRACT: SUMMARY 1. Beta diversity modelling has received increased interest recently. There are multiple definitions of beta diversity, but here we focus on variability in species composition among sampling units within a given area. This facet can be described using various approaches. Some approaches ignore the spatial scale of the area considered (i.e. region limits) while some consider different region limits as a starting point for the analysis of beta diversity. 2. We focused specifically on the beta diversity-environmental heterogeneity relationship in running waters. First, we present two conceptual models, which assume either (1) strong environmental control among localities (riffle sites in our case) within each region unit (a region unit encompasses a species pool, and can be a stream or a basin or an ecoregion) or (2) that the spatial level of a region unit affects the relative importance of mechanisms affecting variability in species composition among localities (i.e. among riffle sites) within each region unit. Second, we compared three recent studies that used similar methods to examine the beta diversity-environmental heterogeneity relationship, but which were based on different region units, comprising sets of streams or sets of basins or sets of ecoregions. 3. Our conceptual framework assumes that environmental control is not likely to be the sole mechanism affecting variability in community composition among localities within each region unit, but it is likely to be most important when dispersal rates are intermediate (i.e. among localities within a basin). In contrast, if dispersal rates are very high (i.e. among localities within a stream) or very low (i.e. among localities within an ecoregion), environmental control is in part masked by high dispersal rates or is prevented from occurring because not all species can reach all localities, respectively. Such scale dependency in the relative strength of environmental control might therefore transcend spatial scales from individual region units to the strength of the beta diversity-environmental heterogeneity relationship. We emphasise that the beta diversity-environmental heterogeneity relationship can only be tested across multiple region units. The results of three case studies are consistent with these predictions. Specifically, the beta diversity-environmental heterogeneity regression was highly significant across multiple basins, but not across multiple streams or across multiple ecoregions. 4. We suggest that researchers take spatial scale and region unit level explicitly into account when inferring the mechanisms structuring ecological communities and mapping variation in beta diversity. We also propose a unified terminology for studies examining the beta diversity-environmental heterogeneity relationship in running waters because inconsistent terminology is likely to hamper the progress of our science.
    Freshwater Biology 11/2014; · 3.93 Impact Factor

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