Distribution of megabenthic gastropods along environmental gradients: the mid-domain effect and beyond

Abstract

We analysed the distribution patterns of megabenthic species of marine molluscs from the Uruguayan shelf in relation to 3 interacting gradients, namely depth, salinity and temperature of sea bottom waters. Our results were generated from a data set comprising the complete list of megabenthic gastropods (adult shell length > 50 mm; 22 species) from a study area that encompassed latitudes from 34 to 39°south, between 4 and 800 m depth. Multiple regressions were used to evaluate the contribution of 3 classes of explanatory variables to gastropod richness at sampling points along the gradients: (1) geometric constraints on the distribution of species' tolerance ranges for environmental variables (the mid-domain effect, MDE), (2) the species-area effect driven by the spatial extent of scaled environmental variables, and (3) the environmental variables themselves. In addition, we explored multivariate explanations for the bathymetric pattern of gastropod species richness, incorporating depth-based area, temperature, salinity and geometric constraints as predictor variables. Examination of Moran's I for regression residuals confirmed that results were not biased by spatial autocorrelation. Overall, the environmental variables per se were the most important contributors to the observed patterns. However, a significant signature of the MDE was revealed, by the entry of geometric constraints into nearly all models. In contrast, the species-area effect was less important. These results suggest that: (1) MDE may operate in any kind of bounded gradient, (2) both stochastic and deterministic processes are responsible for the pattern observed, and (3) the relative contribution of the MDE to the patterns is dependent on the gradient considered and the way in which species richness is measured. KEY WORDS: Mid-domain effect · Species richness · Continental shelf · Gastropods · UruguayResale or republication not permitted without written consent of the publisher

The mid‐domain effect: it's not just about space

“…Colwell & Lees, ). However, only six studies have actually employed mid‐domain models to inspect richness responses along non‐spatial gradients, including sea temperature (Brayard et al ., ; Beaugrand et al ., ), estuarine temperature and salinity (Carranza et al ., ), light (Lusk et al ., ) and time (Morales et al ., ; Tiwari et al ., ). All six studies found evidence for a non‐spatial mid‐domain effect.…”

Coexistence patterns of benthic gastropods on the Uruguayan shelf

“…However, this is not a general pattern (Sanders et al 2007). In the system here studied, although sediment features of sea bottom are relatively constant (Correia et al 1996), salinity, temperature and other oceanographic characteristics are highly variable in time and space, both in a seasonal and interannual basis, and indeed affect benthic gastropod community structure (Ortega and Martínez 2007, Carranza et al 2008a, 2008b ,2008c, 2008d). Nonetheless, it is still unclear if the variability in oceanographic conditions can be considered as a true disturbance for the assemblages under study.…”

One, two and three-dimensional geometric constraints and climatic correlates of North American tree species richness

“…Our results show that the magnitude of the contribution can be quite substantial and that MDE alone predicts species richness very well over at least two thirds of the domain. Other researchers have also found that when included in a multivariate framework, geometric constraints are an important contributor to observed species richness patterns (Storch et al 2006, Carranza et al 2008.…”