Amphibious Taxa Research Articles

Macrozoobenthos communities from two types of land-water transition zones in a European lowland dam reservoir

We investigated the abundance, diversity and taxonomic composition of macrozoobenthos from the land-water interfaces of a lowland dam reservoir developing on sandy and organic-rich substrata. We also checked the possibilities of the occurrence of the edge effect consisting in increased abundance and diversity of the commu- nity developing in the transition zone between two habitats, as well as in the presence of taxa specifi c for only that zone. The study area was the middle part of the Wocawek Reservoir (the lower Vistula River, central Poland). In 2002-2003, we sampled air-exposed (above the water line, at the water line) and submerged (0.5 m and 1 m depth) sites from a sandy area situated in the fl ooded part of the reservoir and a small cove overgrown with macrophytes, with sediments rich in organic matter. In the organic-rich sediments, biodiversity and abundance were higher at the exposed sites than at the submerged ones. Furthermore, we found numerous specifi c taxa, which occurred only in the land-water interface of the organic-rich habitat (semi-terrestrial Diptera, terrestrial and amphibious Oligo- chaeta, Endochironomus sp. (impar group), Valvata cristata, Anisus contortus and Coleoptera larvae). Thus, all symptoms of the edge effect were observed there. On the other hand, the sandy shore was a simple transition zone. Some symptoms of the edge effect appeared (high biodiversity and the presence of a few amphibious taxa) but the abundance was extremely low compared with that found at the submerged sites. Individuals inhabiting the sandy transition zone formed accidental assemblages, widely differing from one sample to another. The homogeneous unstable land-water interface on the sandy shore is a poor habitat for macroinvertebrates, which are washed out by wave action, have no protection against air exposure and freezing, and their substratum may be totally destroyed in winter by ice drifting downstream. On the other hand, organic-rich sediments are more stable and provide much better protection and food conditions for the fauna living near the water line.

Using multi-scale species distribution data to infer drivers of biological invasion in riparian wetlands

Aim:? Biological invasion is a major conservation problem that is of interest to ecological science. Understanding mechanisms of invasion is a high priority, heightened by the management imperative of acting quickly after species introduction. While information about invading species’ ecology is often unavailable, species distribution data can be collected near the onset of invasion. By examining distribution patterns of exotic and native plant species at multiple spatial scales, we aim to identify the scale (of those studied) that accounts for most variability in exotic species abundance, and infer likely drivers of invasion. Location:? River Murray wetlands, south-eastern Australia. Methods:? A nested, crossed survey design was used to determine the extent of variation in wetland plant abundance, grazing intensity and water depth at four spatial scales (reaches, wetland clumps, wetlands, wetland sections), and among three Depth-strata. We examined responses of exotic and native species groups (grouped into terrestrial and amphibious taxa), native weeds and 10 individual species using hierarchical ANOVA. Results:? As a group dominated by terrestrial taxa, exotic species cover varied at reach-, wetland- and section-scales. This likely reflects differences in abiotic characteristics and propagule pressure at these scales. Groups based on native species did not vary at any scale examined. Cover of 10 species mostly varied among and within wetlands (patterns unrelated to species’ origin or functional group), but species’ responses differed, despite individual plants being similar in size. While flora mostly varied among wetlands, exotic cover varied most among reaches (26%), which was attributed to hydrological modification and human activities. Main conclusions:? Multi-scale surveys can rapidly identify factors likely to affect species’ distributions and can indicate where future research should be directed. By highlighting disproportionate variation in exotic cover among reaches, this study suggests that flow regulation and human-mediated dispersal facilitate exotic plant invasion in River Murray wetlands.

Paleoecology of the Quarry 9 vertebrate assemblage from Como Bluff, Wyoming (Morrison Formation, Late Jurassic)

Quarry 9 is among the richest microvertebrate localities in the Morrison Formation, having thus far produced the remains of dozens of Late Jurassic taxa. Because this lenticular claystone deposit records such a high diversity of contemporaneous species, it provides an exceptionally detailed view of their paleoecology and local paleoenvironment. In this study, we reexamined the entire Quarry 9 collection, totaling more than 3700 specimens, and developed a revised faunal list that was used to determine taxonomic and ecological diversities. Comprehensive abundance data were collected as well, revealing significant discrepancies between the most diverse and most abundant groups. Amphibious taxa (crocodilians and turtles) were very abundant, and seemed to fill an important ecological role as “connectors” between the terrestrial and aquatic food webs. In contrast, small terrestrial taxa (small theropods, mammals, and small reptiles) were very diverse, highlighting their central placement within the terrestrial food web. Lithologically and sedimentologically, the deposition of Quarry 9 occurred in a low-energy pond or swamp, an interpretation supported by the available taphonomic data.

Données microanatomiques sur la conquête de l'environnement terrestre par les vertébrés

Microanatomical data and the conquest of land by vertebrates. The compactness profile of femoral cross-sections and body size of 46 species of lissamphibians was studied to assess the relationship between lifestyle (aquatic, amphibious or terrestrial) and bone compactness. Two tests that incorporate phylogenetic information (permutational multiple linear regression incorporating phylogenetic distances and concentrated changes tests) show that the return to an aquatic lifestyle is associated with an increase in the compactness of the femur and an increase in body size. However, amphibious taxa cannot be distinguished from terrestrial ones on the only basis of size or compactness. Mathematical equations obtained from our data using logistic regression with phylogenetic weighting are used to infer the lifestyle of four early stegocephalians from the Permian and the Triassic. The results are generally congruent with prevailing palaeontological interpretations, which suggests that this method could be applied to infer the lifestyle of early taxa whose lifestyle is poorly understood. To cite this article: M. Laurin et al., C. R. Palevol 5 (2006) .

The evolution of long bone microstructure and lifestyle in lissamphibians

The compactness profile of femoral cross-sections and body size of 105 specimens of 46 species of lissamphibians was studied to assess the effect of lifestyle (aquatic, amphibious, or ter- restrial). Several tests that incorporate phylogenetic information (permutational multiple linear re- gression incorporating phylogenetic distances, logistic regression using phylogenetic weighting, concentrated-changes tests) show that the return to a fully aquatic lifestyle is associated with an increase in the compactness of the femur and an increase in body size. However, amphibious taxa cannot be distinguished from terrestrial ones solely on the basis of size or compactness. Body size and compactness profile parameters of the femur exhibit a phylogenetic signal (i.e., closely related taxa tend to be more similar to each other than to distantly related taxa). Mathematical equations obtained from our data by using logistic regression with phylogenetic weighting are used to infer the lifestyle of four early stegocephalians. The results are generally congruent with prevailing paleontological interpretations, which suggests that this method could be applied to infer the lifestyle of early taxa whose lifestyle is poorly understood.

Cranial morphology and affinities of Microbrachis, and a reappraisal of the phylogeny and lifestyle of the first amphibians

ABSTRACT An anatomical study of Microbrachis reveals inaccuracies in previous studies, especially in the palate and cranial proportions. The vomer and the pterygoid reach the midline anteriorly, and the postorbital does not appear to reach the tabular. The skull is higher in our cranial reconstruction than previously thought. A phylogenetic analysis of early stegocephalians places Microbrachis at a fairly basal position in the clade that includes “microsaurs,” lysorophians, and lissamphibians. This analysis corroborates previous suggestions that lissamphibians are part of a clade that includes the taxa classically referred to as “lepospondyls,” and that seymouriamorphs and temnospondyls are not part of Tetrapoda. Statistical tests on another recent amphibian phytogeny reveal that its different placement of the origin of lissamphibians is not statistically more parsimonious than the placement that we suggest. Our analysis also suggests that the first evolutionary radiation of amphibians took place in an aquatic environment because most of the first groups of amphibians to have differentiated, namely adelogyrinids, nectrideans, and Microbrachis, appear to have been aquatic or amphibious taxa. However, the lifestyle of many early amphibians is difficult to assess.