"Species Trait" Approaches for Theoretical and Applied Issues in Freshwater Communities III
Presiding: L Bache, University of California, Berkeley; N Bonada, University of Barcelona
NB31F-01 INVITED 08:30h
Ecological Trait Composition of Freshwater Fish Across Gradients of Environmental Variability in North-Eastern Australia
North-eastern Australia encompasses 18o of latitude, monsoonal/tropical to sub-tropical/temperate climates, geomorphologically diverse rivers, and flow regimes with markedly varied seasonality, constancy and predictability. Fish assemblages in the region vary in relation to the predictability of aquatic habitat availability and other topographic, climatic and/or biogeographic factors. This paper examines how environmental, biogeographic and phylogenetic factors may constrain ecological trait composition at local and regional scales. We derived 17 categories of ecological traits to describe the morphology, behaviour, habitat, life history and trophic characteristics of 114 fish species from 64 river basins. Trait composition varied substantially across the region. The number of riffle dwelling species, maximum size and longevity of fishes was greater in the hydrologically predictable and constant rivers of the Wet Tropics region than in more unpredictable or seasonal environments. The importance of herbivory was also greater in the tropics. Historical biogeographic and phylogenetic factors may confound our ability to understand the role of environmental factors in determining spatial variation in ecological trait composition. Understanding the functional linkages between environmental drivers of fish species distributions via their ecological characteristics should provide a foundation for predicting future impacts of environmental change in a region of Australia subject to increasing human pressures.
NB31F-02 INVITED 08:45h
Species Traits and Assemblage Structure Across Anthropogenic Environmental Gradients in Streams of Southeastern Michigan
Recent studies suggest that analyses of biological assemblages summarized by phenotypic traits (trophic, life cycle, habit, and stressor tolerance) may be more insightful than taxon-based analyses, and that landscape features, like anthropogenic land use, may act as filters that can be linked to assemblage differences when summarized by traits. Common fish species and macroinvertebrate taxa collected from 46 streams in southeastern Michigan were summarized by traits, and principal component analysis (PCA) was used to identify biological gradients. Three axes explained a majority of variation in trait characteristics for both groups of organisms. Axes that explained the most variation in fish and macroinvertebrates were interpreted as gradients in ecological integrity because each was strongly, positively weighted by intolerant taxa and trait specialists. However, only the axis summarizing macroinvertebrate integrity was correlated with taxon diversity and richness; the fish axis was not correlated with either measure. Instead, a different fish axis, which emphasized the inclusion of fluvio-lacustrine species, was correlated with diversity, implying that stream fish diversity was elevated by lentic conditions. Investigations of relationships of axes with habitat variables re-enforces the view that environmental features, acting as filters, have a strong influence on assemblage structure when traits are considered.
NB31F-03 09:00h
Linking Species Traits to the Abiotic Template of Flowing Waters: Contrasting Eco physiologies Underlie Displacement of Zebra Mussels by Quagga Mussels in a Large River-Estuary
The St. Lawrence River-Estuary was the gateway of entry for dreissenids to North America and holds some of the oldest populations. The St. Lawrence also has four distinct physical-chemical water masses (a regional scale abiotic template) that both species inhabit. Despite their ecological similarities, quagga mussels are supplanting zebra mussels in much of their shared range. In order to try to better understand the changing distributions of these two species we compared glycogen, shell mass and tissue biomass in each of the water masses. This comparative physiological combined with experimental approaches (estuarine salinity experiments and reciprocal transplants) showed that while quagga mussels should dominate in most habitats, that abiotic/bioenergetic constraints in two regions (the Ottawa River plume and the freshwater-marine transition zone) might prevent them from dominating these locations. These findings are an example of how the interaction of landscape scale abiotic heterogeneity and a species-specific physiology can have strong impacts of distribution of biota large rivers.
NB31F-04 09:15h
Alternative Approaches for Evaluating the Effects of Environmental Gradients on Stream Invertebrates
Taxonomic optima, i.e., the environmental conditions at which peak abundance is expected, are widely used to analyze assemblage response to environmental gradients. Typically analyses consider how the mean optima for an assemblage change over a gradient. In this study we consider how other characteristics of the assemblage vary. We ask two questions. First, how does variability in assemblage optima change over an environmental gradient? Second, is there a trade-off between environmental generalists, i.e., genera having a wide range of occurrence, and specialists, i.e., genera having a narrow range of occurrence, over these gradients? We use data collected in the U.S. EPA Environmental Monitoring and Assessment Program for benthic invertebrate assemblage and stream characteristic information. Optima estimates for genera are derived from logistic regression models over environmental gradients in streams. Assemblage characteristics are based on the distribution of these optima for genera occurring at a site. These results suggest alternative approaches for evaluating the effects of environmental gradients on stream biota.