Hydroperiod, predators and the distribution of physid snails across the freshwater habitat gradient

Abstract

1. Studies of species distributions across environmental gradients further our understanding of mechanisms regulating species diversity at the landscape scale. For some freshwater taxa the habitat gradient from small, shallow and temporary ponds to large, deep and permanent lakes has been shown to be an important environmental axis. Freshwater snails are key players in freshwater ecosystems, but there are no comprehensive studies of their distributions across the entire freshwater habitat gradient. Here we test the hypothesis that snail species in the family Physidae are distributed in a non-random manner across the habitat gradient. We sampled the snails, their predators and the abiotic environment of 61 ponds and lakes, spanning a wide range in depth and hydroperiod. Temporary habitats had the lowest biomass of predators. Shallow permanent ponds had the highest biomass of invertebrate predators but an intermediate fish biomass. Deep ponds and lakes had the highest fish biomass and intermediate invertebrate biomass.Five species of physids occurred in the regional species pool and 60 of the 61 ponds and lakes surveyed contained physid snails. Each pond and lake contained an average of just 1.2 physid species, illustrating limited membership in local communities and substantial among-site heterogeneity in species composition. 3. Physids showed strong sorting along the habitat gradient, with Physa vernalis found in the shortest hydroperiod ponds and Aplexa elongata, P. gyrina, P. acuta and P. ancillaria found in habitats of successively greater permanence. When organised into a siteby-species incidence matrix with sites ordered according to their hydroperiods, we found the pattern of incidence to be highly coherent, showing that much of the heterogeneity in species composition from one pond to another is explained by hydroperiod. We also found that the number of species replacements along this gradient was higher than random, showing that replacement is more important than nesting in describing species composition in ponds of different hydroperiod. 4. Discriminant analysis showed that pond depth, invertebrate biomass and fish biomass were the best predictors of species composition. Analysis of these niche dimensions showed that P. vernalis and A. elongata were most successful in shallow, temporary ponds with few predators. P. gyrina and P. acuta were typically found in ponds of intermediate depth and high predator abundance. P. ancillaria was found in the deepest lakes, which had abundant fish predators but few invertebrate predators. Of the five species considered, P. ancillaria, P. vernalis and A. elongata were relatively specialised with regard to key habitat characteristics, P. gyrina was moderately generalised and P. acuta was remarkably generalised, since it alone occurred across the entire freshwater habitat gradient. The exceptional habitat breadth of P. acuta stands in contrast to distributional studies of other freshwater taxa and deserves further attention.

How did this snail get here? Several dispersal vectors inferred for an aquatic invasive species

“…Kefford & Nugegoda, 2005;Turner & Montgomery, 2009). It is known as a rapid (re)coloniser of freshwater systems where it is exposed to variable environmental conditions (Chlyeh et al, 2006).…”

Winning the biodiversity arms race among freshwater gastropods: competition and coexistence through shell variability and predator avoidance

“…Neurobiological studies of predator recognition are identifying physiological mechanisms with increased precision (e.g., Orr et al, 2007Orr et al, , 2009Lukowiak et al, 2008). Other studies are determining the tradeoffs in risk and vulnerability for not responding under different environmental conditions typical of food webs when predators interact with their various gastropod prey (e.g., Turner & Montgomery, 2009;Wojdak & Trexler, 2010).…”

“…Inter-and intra-specific competitions can be influenced by selective predation as well as by a lack of sufficient concentrations of dissolved calcium or persistence of well buffered, deep inland waters. These attributes are widely documented geographically both in deep, ancient lakes and in many other freshwater ecosystems (e.g., Boss, 1978;Lodge et al, 1987;Økland, 1990;Hutchinson, 1993;Rundle et al, 2004;Turner & Montgomery, 2009;Brown & Lydeard, 2010). New information is integrated into these earlier studies on how abiotic and physiological variables as well as introductions of non-native species can alter the relative importance of adaptations to avoid selective predation.…”

Failure of Transmission of Low-Pathogenic Avian Influenza Virus Between Mallards and Freshwater Snails: An Experimental Evaluation

“…Tadpole snails (Physa acuta and Physa gyrina) are found throughout North America in virtually all freshwater habitats (Dillon et al, 2005;Turner and Montgomery, 2009). These snails feed exclusively on algae and detritus on the sediment (Dillon, 2000;Vaughn, 2009), and accumulate hepatotoxins through ingestion of cyanobacteria, which they likely transmit to predators (Zurawell et al, 1999).…”