No abstract

Summary1. The concept of metacommunity is based on the hypothesis that species occurrence depends on species dynamics and interactions on local and regional scales via the movements of individuals between localities. Metacommunity approaches are currently being applied to pond breeding taxa such as amphibians. 2. Given that animal movement is also influenced by the physical quality of the matrix to be crossed to reach a breeding habitat and by the affinity of the species for specific terrestrial habitats, matrix characteristics may enhance or hinder dispersal success. These characteristics would, in turn, affect the composition of larval assemblages at local level and, consequently, determine metacommunity structure and dynamics. 3. Here we compared the structures and dynamics of two metacommunities with the same pool of anurans along similar freshwater gradients in two regions that are well differentiated in terms of their respective terrestrial matrix. 4. Abundance of tadpole species and species assemblage in the two regions were determined principally by local processes (at pond level); however, the structure and dynamics of the communities differed. In one region species abundance was explained in part by landscape factors and consequently showed lower co-occurrence and lower colonization rates (species sorting models) indicating that terrestrial habitat could restrict animal movements, whereas in the other region higher co-occurrence and higher colonization rates (mass effect models) indicated low dispersal limitations.

In a field survey the distribution of pond-breeding anuran species and their potential large predators was investigated along a freshwater habitat gradient, ranging from ephemeral pools to permanent ponds. In a laboratory experiment predator-induced plasticity was examined for all tadpole species to test whether the plastic response of ephemeral and temporary pond species differs from that of permanent pond species. Desiccation and predation pose conflicting demands; reduced activity lowers the risk of death by predation but increases the risk of death by desiccation. It was expected that species from time-constrained habitats would display a morphotype that would reduce vulnerability to invertebrate predators, thus allowing these species to maintain a high level of activity, whereas species from permanent ponds would avoid predation both morphologically and behaviourally. Species distribution and predator composition along the hydroperiod gradient differed. Variations between ephemeral and temporary ponds can be attributed to hydroperiod differences and the presence of large invertebrate predators in temporary ponds, whereas the contrasts between temporary and permanent ponds can only be attributed to the hydroperiod, since the presence and abundance of top predators are similar in both habitat types. With the exception of bufonids, all species showed predator-induced plasticity in agreement with previous studies. Tadpole species differed in the integration of the phenotypic traits measured, but differences observed between species could not be attributed only to habitat. Species from temporary habitats showed an expected response, with a low reduction of activity in comparison with the rest of the species. The lack of general patterns in the morphological changes suggests that species within the same habitat type did not converge on similar phenotypes, perhaps due to functional constraints on differences in microhabitat use in the water column.

It is predicted that climate change will drive extinctions of some reptiles and that the number of these extinctions will depend on whether reptiles are able to change their distribution. Whether the latitudinal distribution of reptiles may change in response to increases in temperature is unknown. We used data on reptile distributions collected during the 20th century to analyze whether changes in the distributions of reptiles in Spain are associated with increases in temperature. We controlled for biases in sampling effort and found a mean, statistically significant, northward shift of the northern extent of reptile distributions of about 15.2 km from 1940-1975 to 1991-2005. The southern extent of the distributions did not change significantly. Thus, our results suggest that the latitudinal distributions of reptiles may be changing in response to climate change.

We investigated the autumnal diet of the brown trout Salmo trutta, in a Prepyrenean stream (NW Iberian Peninsula) focusing on intraspecific dietary differences related to size and sex. The diet of trout included 18 types of prey, with Plecoptera and Ephemeroptera nymphs and Diptera larvae as the most consumed taxa. Large trout ate larger prey, than did small trout, and also increased the consumption of terrestrial-surface prey with respect to aquatic-benthic prey. As terrestrial-surface preys were larger than aquatic-benthic prey, the size-related differences in the diet of trout were related to gape-limitations. Although male and female trout did not differ in size, we found that males foraged on a more diverse type of prey than females, probably owing to male territoriality during the reproductive period. This study provides new evidence of dietary plasticity in the brown trout and confirms the importance of local dietary studies to better understand factors which drive trophic ecology of predators.