"Species Trait" Approaches for Theoretical and Applied Issues in Freshwater Communities II
Presiding: L Bache, University of California, Berkeley; N Bonada, University of Barcelona
NB14F-01 INVITED 15:30h
Relationships Between Traits of Stream Assemblages and Hydraulics
The objective of this contribution is to provide a comparative discussion, across spatial scales (microhabitat, reach) and biological groups (fish, macroinvertebrates), of previous results concerning the relationships between traits of stream assemblages and hydraulics. At the microhabitat scale, some traits related to morphology or longevity respond to hydraulics 'consistently' for fish and macroinvertebrates. Responses of feeding habits and locomotion patterns are more specific to macroinvertebrates. Relationships between traits and hydraulics are generally weak at the microhabitat scale. Only trends can be observed at this scale, where assemblages are unsteady and partly random. Relationships between traits and hydraulics at the reach scale are stronger than those observed at the microhabitat scale, for both fish and macroinvertebrates. They are generally consistent with relationships observed at the microhabitat scale. Therefore, repeated microhabitat constraints may have a strong impact on the structure of assemblages in stream reaches. Tracks for improving our models of functional responses to hydraulics include using more appropriate definitions of microhabitat characteristics, using more quantitative descriptions of species traits, and using models that can reflect alternative strategies to adapt to the environment.
NB14F-02 INVITED 15:45h
Comparing Community Trait Patterns of Macroinvertebrates in Mediterranean and Temperate Regions.
Streams in mediterranean regions have highly seasonal discharge patterns, with predictable torrential floods and severe droughts. In contrast, discharge variations are less extreme in temperate regions and intermittent flow conditions are uncommon. Given that regional or large-scale filters should determine the local trait composition of communities, we hypothesize that climatic differences between mediterranean and temperate regions cause differences in macroinvertebrate trait patterns (e.g. in traits that favor drought resistance and drought recovery). Using published and unpublished data, we assembled the abundance of macroinvertebrate genera of 100 sites in the Mediterranean Basin region and 100 sites in the European temperate region and linked these abundances to published information on 63 categories of 11 biological traits. Significant differences were found between regions for almost all traits, with an overall variability in trait composition of 17%. Surprisingly, resistance forms did not discriminate mediterranean and temperate regions. In comparison with temperate regions, mediterranean regions had smaller size individuals with more than one reproductive cycle per year, reflecting a higher resilience capability of macroinvertebrates. The higher proportion of swimmers and spiracles breathers can be explained by the dominance of lentic habitats during drought in mediterranean regions.
NB14F-03 INVITED 16:00h
Long-term Temporal Variation in Biological Traits of Benthic Macroinvertebrates in California Mediterranean-Climate Streams
The temporal variation of biological traits of benthic macroinvertebrates was analyzed using three long-term macroinvertebrate data sets (7, 8, and 20 years). We used 19 fuzzy-coded biological traits (e.g., maximum size, life cycle duration, and respiration mode) to describe temporal variation of biological traits and the relationships between trait composition and total annual precipitation, discharge, and near-bed hydraulics. Post wet-season (spring) samples were taken from 8 streams (1st-3rd order)in northern California, where the climate is mediterranean and precipitation shows high interannual variability. We used multivariate ordination to compare trait composition between years, and regression to determine the relationship of traits to rainfall, discharge, and sheer stress. Temporal variation in biological traits was significantly correlated with total annual rainfall and sheer stress, suggesting that both long-term and local, short-term patterns in environmental conditions influence trait composition. However, total annual rainfall best explained the interannual variation in individual traits (e.g., aerial respiration) and overall trait composition. For example, moderate body size (5-10 mm) and streamlined body shape were positively correlated with total rainfall, whereas aerial dispersal and diapause was negatively correlated with total rainfall.
NB14F-04 INVITED 16:15h
A Comparison of Structural and Functional Approaches to Determine Land-use Effects on Grassland Stream Communities
Effective catchment management in the face of land-use alteration depends on our ability to quantify ecologically significant changes and to discriminate between varying levels of impact. We compare the efficacy of traditional structural indices of change (species composition) with functional measures based on the representation of species traits (including life-history, trophic and morphological features) in an analysis of grassland streams along a gradient of agricultural development (ungrazed native tussock, grazed tussock, extensively grazed pasture, intensive dairy and deer farming). Only 8 of 60 invertebrate taxa demonstrated a significant separation across the land-use gradient wherease 23 of 53 trait modalities did so. Traits associated with population resilience (small size, short generation time, single individual reproduction) became more prevalent with increasing development while gill bearing and the tendency to lay unattached eggs became less prevalent. Multivariate analyses involving species or trait composition were all able to discriminate land uses, but more of the overall between-land use variance was accounted for by trait composition. Rather than simply recording a loss or reduction of species, our functional approach was able to identify sensitive life-history characteristics and provide direct evidence of causative mechanisms, facilitating the development of targeted management actions.
NB14F-05 INVITED 16:30h
The Interaction Between Plant Life History Traits and the Riverine Landscape: a Stochastic Simulation Approach
At the level of the watershed, the riverine habitat represents a spatially distributed yet interconnected landscape element. The spatial organization of the riverine landscape determines the distribution and extent of habitats and the interconnectivity influences how species access riverine habitat elements. A central question is what and how characteristics of a species affect its performance in the context of a river network. We used a spatially explicit, stochastic simulation modeling approach to explore how interconnectivity and complexity of the stream network potentially interacts with life history traits in determining riparian plant species persistence and abundance. We varied life history traits and stream network complexity in a factorial design. For each factorial combination, a new species was introduced to an established riparian community. We evaluated the new species and the community responses using various metrics including rate of spread and abundance. Interaction strengths varied between different life history traits depending on network complexity, but persistence and success of a new species was determined by the combination species life history traits not a single or combination of a few traits. This work underscores the need to better understand life histories using multiple pathways of investigation including models, field and experimental approaches.
NB14F-06 INVITED 16:45h
Functional Redundancy as a Stabilising Feature of Vegetation in Shallow Lakes
There is no abstract associated with this presentation.