Trait and abundance patterns in two marine molluscs: the influence of abiotic conditions operating across multiple spatial scales

摘要

Theoretical mechanisms describing species abundance distributions should also underpin geographic variation in life-history traits. However, recent studies suggest that abundance and trait patterns may not co-vary and may respond differently to abiotic conditions acting at different spatial scales. We examined patterns in abundance and body size of 2 estuarine molluscs, the arkshell Anadara trapezia and the mudsnail Batillaria australis, across their wide distributions in eastern Australia. We related abundance and body size patterns to abiotic variables including water temperature, pH, salinity, sediment redox and dissolved oxygen content at multiple spatial scales. Two hypotheses were tested: (1) geographic patterns in abundance and body size do not co-vary, and (2) patterns in abundance are more strongly influenced by abiotic conditions occurring at a large spatial scale (e.g. across latitudinal gradients) whereas body size is more strongly influenced by variation in abiotic conditions occurring at smaller scales. The influence of spatial scale and associated abiotic variables on abundance and body size distributions was determined using multiple linear regression, ANOVA and variance component analyses. Geographic variation in abundance and body size were independent of each other in both species. Abiotic variation across latitudinal gradients was the strongest predictor of abundance, but factors that varied substantially at local scales (e.g. dissolved oxygen and sediment redox) were the strongest predictors of body size. Our data indicate that geographic patterns in body size and abundance can be disconnected from each other, most likely due to differential responses to abiotic variation acting at different spatial scales.