Diversity Patterns Associated with Varying Dispersal Capabilities as a Function of Spatial and Local Environmental Variables in Small Wetlands in Forested Ecosystems

The diversity of species on a landscape is a function of the relative contribution of diversity at local sites and species turnover between sites. Diversity partitioning refers to the relative contributions of alpha (local) and beta (species turnover) diversity to gamma (regional/landscape) diversity and can be influenced by the relationship between dispersal capability as well as spatial and local environmental variables. Ecological theory predicts that variation in the distribution of organisms that are strong dispersers will be less influenced by spatial properties such as topography and connectivity of a region and more associated with the local environment. In contrast, the distribution of organisms with limited dispersal capabilities is often dictated by their limited dispersal capabilities. Small and ephemeral wetlands are centers of biodiversity in forested ecosystems. We sampled 41 small and ephemeral wetlands in forested ecosystems six times over a two-year period to determine if three different taxonomic groups differ in patterns of biodiversity on the landscape and/or demonstrate contrasting relationships with local environmental and spatial variables. We focused on aquatic macroinvertebrates (aerial active dispersers consisting predominantly of the class Insecta), amphibians (terrestrial active dispersers), and zooplankton (passive dispersers). We hypothesized that increasing active dispersal capabilities would lead to decreased beta diversity and more influence of local environmental variables on community structure with less influence of spatial variables. Our results revealed that amphibians had very high beta diversity and low alpha diversity when compared to the other two groups. Additionally, aquatic macroinvertebrate community variation was best explained by local environmental variables, whereas amphibian community variation was best explained by spatial variables. Zooplankton did not display any significant relationships to the spatial or local environmental variables that we measured. Our results suggest that amphibians may be particularly vulnerable to losses of wetland habitat in forested ecosystems as they have high beta diversity. Consequently, the loss of individual small wetlands potentially results in local extirpations of amphibian species in forested ecosystems.

Temporal changes in threatened ephemeral claypans over annual and decadal timescales in south-west Australia

The vegetation of the ephemeral claypans of south-west Australia were first described over 100 years ago. Since then they have been almost totally cleared for agriculture and urban development and are currently listed as critically endangered. These claypans have many similarities with ephemeral wetlands found in other Mediterranean climate regions with significant species turnover both within and between claypans and fine scale patterning highly correlated with micro-topography. Although annual variation in species composition was apparent there was also a consistent trend of increasing exotic taxa richness due to higher recruitment rates. This increasing exotic richness is of note, as the major threat to these communities is the invasion by a small number South African taxa, which can establish dense monocultures across these wetlands. Over the last two decades these invasive taxa have spread into 37% of the previously non-invaded quadrats. As remnant size was not a good predictor of their occurrence all remnants should be considered vulnerable. Management of these invasive taxa will be the major conservation issue in these threatened wetlands into the future.

A multiscale, hierarchical, ecoregional and floristic classification of arid and semi-arid ephemeral wetlands in New South Wales, Australia

Describing, classifying and quantifying vegetation communities is fundamental for understanding their current distribution, rarity, interrelationships and ecosystem functions. In the present study, we apply a consistent objective classification system for ephemeral wetlands of arid and semi-arid areas of New South Wales (NSW), Australia. Our approach uses a two-step statistically based, hierarchical, multiscale classification of environmental data at broad scales and floristics data at intermediate scales. At broad scales, ecoregionalisation methods were used to describe three wetland macrogroups. Within these groups, we performed unsupervised analyses of 640 floristic survey plots using the Bray–Curtis algorithm, clustering by group averaging and testing of clusters using similarity profile analysis (SIMPROF). From this we delineated 18 vegetation groups with class definition based on a combination of diagnostic and non-diagnostic similarity percentage analysis (SIMPER) outputs and dominant taxa. We show that a consistent classification system can be effectively created for subsets of vegetation that have adequate plot data within a general matrix that is poorly sampled if outputs are restricted to appropriate scales of resolution. We suggest that our approach provides a stable and robust classification system that can be added to as more data become available.