Snake diets and the deep history hypothesis

The structure of animal communities has long been of interest to ecologists. Two different hypotheses have been proposed to explain origins of ecological differences among species within present‐day communities. The competition–predation hypothesis states that species interactions drive the evolution of divergence in resource use and niche characteristics. This hypothesis predicts that ecological traits of coexisting species are independent of phylogeny and result from relatively recent species interactions. The deep history hypothesis suggests that divergences deep in the evolutionary history of organisms resulted in niche preferences that are maintained, for the most part, in species represented in present‐day assemblages. Consequently, ecological traits of coexisting species can be predicted based on phylogeny regardless of the community in which individual species presently reside. In the present study, we test the deep history hypothesis along one niche axis, diet, using snakes as our model clade of organisms. Almost 70% of the variation in snake diets is associated with seven major divergences in snake evolutionary history. We discuss these results in the light of relevant morphological, behavioural, and ecological correlates of dietary shifts in snakes. We also discuss the implications of our results with respect to the deep history hypothesis. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 476–486.     

Future climate‐driven shifts in distribution of Calanus finmarchicus

Calanus finmarchicus is a key‐structural species of the North Atlantic polar biome. The species plays an important trophic role in subpolar and polar ecosystems as a grazer of phytoplankton and as a prey for higher trophic levels such as the larval stages of many fish species. Here, we used a recently developed ecological niche model to assess the ecological niche (sensu Hutchinson) of C. finmarchicus and characterize its spatial distribution. This model explained about 65% of the total variance of the observed spatial distribution inferred from an independent dataset (data of the continuous plankton recorder survey). Comparisons with other types of models (structured population and ecophysiological models) revealed a clear similarity between modeled spatial distributions at the scale of the North Atlantic. Contemporary models coupled with future projections indicated a progressive reduction of the spatial habitat of the species at the southern edge and a more pronounced one in the Georges Bank, the Scotian Shelf and the North Sea and a potential increase in abundance at the northern edge of its spatial distribution, especially in the Barents Sea. These major changes will probably lead to a major alteration of the trophodynamics of North Atlantic ecosystems affecting the trophodynamics and the biological carbon pump.     

Separating the effects of climate and vegetation on evapotranspiration along a successional chronosequence in the southeastern US

We combined Eddy‐covariance measurements with a linear perturbation analysis to isolate the relative contribution of physical and biological drivers on evapotranspiration (ET) in three ecosystems representing two end‐members and an intermediate stage of a successional gradient in the southeastern US (SE). The study ecosystems, an abandoned agricultural field [old field (OF)], an early successional planted pine forest (PP), and a late‐successional hardwood forest (HW), exhibited differential sensitivity to the wide range of climatic and hydrologic conditions encountered over the 4‐year measurement period, which included mild and severe droughts and an ice storm. ET and modeled transpiration differed by as much as 190 and 270 mm yr^?1, respectively, between years for a given ecosystem. Soil water supply, rather than atmospheric demand, was the principal external driver of interannual ET differences. ET at OF was sensitive to climatic variability, and results showed that decreased leaf area index (L) under mild and severe drought conditions reduced growing season (GS) ET (ET_GS) by ca. 80 mm compared with a year with normal precipitation. Under wet conditions, higher intrinsic stomatal conductance (g_s) increased ET_GS by 50 mm. ET at PP was generally larger than the other ecosystems and was highly sensitive to climate; a 50 mm decrease in ET_GS due to the loss of L from an ice storm equaled the increase in ET from high precipitation during a wet year. In contrast, ET at HW was relatively insensitive to climatic variability. Results suggest that recent management trends toward increasing the land‐cover area of PP‐type ecosystems in the SE may increase the sensitivity of ET to climatic variability.     

Environmental media and shape asymmetry: a case study on turtle shells

Although physical features of the environment are known to influence shape, to date, the effects of many environmental conditions on asymmetry remain unexamined. The present study aimed to examine the relationship between asymmetry and the fluid media (air versus water) that an organism inhabits and, subsequently, to use these findings to test a novel hypothesis that fluid environments can impose selective forces acting to constrain asymmetry to maintain or enhance biomechanical function. We examined carapace asymmetry in 114 species (69 aquatic and 45 terrestrial) from the chelonian superfamily Testudinoidea. The results obtained indicate that environment is correlated with the degree of asymmetry, but in different directions for the two clades that comprise the Testudinoidea. Within the Testuguria, aquatic turtles have lower levels of asymmetry than terrestrial turtles, which is consistent with our proposed biomechanical hypothesis. This pattern was not observed within the Emydidae, possibly due to the much shorter time that terrestrial taxa in this clade have existed. Nevertheless, the present study provides the first evidence for a relationship between fluid media and asymmetry in any taxonomic group.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 483–489.     

Northern map turtles (Graptemys geographica) derive energy from the pelagic pathway through predation on zebra mussels (Dreissena polymorpha)

1. Zebra mussels ( Dreissena polymorpha ) derive their energy from the pelagic energy pathway by filtering plankton. Because zebra mussels occur in high densities in littoral habitats, they potentially constitute an important trophic link between littoral consumers and pelagic energy sources. Northern map turtles ( Graptemys geographica ) are widespread in North America and consume zebra mussels.
2. We used stable isotopes analyses to quantify the flow of energy from the pelagic pathway to northern map turtles and to infer the contribution of zebra mussels to map turtle biomass. We then built a bioenergetic model to estimate the annual intake of zebra mussels by northern map turtles in Lake Opinicon, Ontario, Canada.
3. Stable isotopes analyses indicated that zebra mussels constitute between 0% and 14% of the diet of males and between 4% and 36% of the diet of females. Assuming that zebra mussels account for all of the pelagic contribution, we estimated that map turtles consume 3200 kg of zebra mussels annually. Because female map turtles are much larger than males and consume more zebra mussels, they are responsible for 95% of the zebra mussel biomass ingested annually.
4. The pelagic pathway supports an important part of the standing crop biomass of map turtles in Lake Opinicon. We highlight the importance of freshwater turtles in lake ecosystems. Unravelling the trophic interactions mediated by freshwater turtles will lead to a more integrated picture of lake ecosystems.     

Life history variation between species of the relictual genus Borderea (Dioscoreaceae): phylogeography, genetic diversity, and population genetic structure assessed by RAPD markers

The genus Borderea consists of two species, B. pyrenaica and B. chouardii, taxa which have been previously considered as conspecific due to their overall close morphology. These two sole species of the rare genus of Dioscoreaceae are endemic to the Pyrenees (Spain, France). This mountain range likely operated as a refugium for these plants during the last glaciations. B. chouardii is only known from a single population in the Spanish Prepyrenees and has been classified as at risk of extinction in the Red List of Endangered Species (IUCN); B. pyrenaica shows a narrow distribution range in the central Pyrenees and Prepyrenees. We analysed genetic variation, population structure and differentiation in these two taxa using RAPD markers. Our study was conducted on the same seven populations for which very low levels of genetic differentiation were detected previously through allozyme analysis. By contrast, high levels of genetic variability were detected through the RAPD hypervariable markers. Twelve RAPD primers produced 112 distinct bands in the 397 surveyed individuals, totalling 395 different RAPD phenotypes. Only four bands were monomorphic across all samples of Borderea, whereas 21 of the polymorphic bands were species‐specific (20 for B. chouardii, and one for B. pyrenaica). The largest genetic distances were those between the B. chouardii and the B. pyrenaica phenotypes. An analysis of molecular variance showed greater variance between groups (B. chouardii vs. B. pyrenaica, 76.08%) than within groups (3.60%). RAPD band specificity, phenotypic distances, and the partitioning of variance all support the taxonomic separation of the two species. Statistical evaluation of within‐ and among‐population RAPD genetic variability in B. pyrenaica showed that genetic variability was higher within populations (>80%) than among them. No clear pattern of RAPD differentiation could be observed among the six studied populations of this taxon though slight differences in genetic diversity could be observed in the more isolated Prepyrenean populations compared with the more widespread Pyrenean ones. These results suggest a recent postglacial origin of the present B. pyrenaica populations. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80 , 483–498.     

Characterization of polymorphic microsatellites in the castration parasite plant‐ant Allomerus octoarticulatus cf. demerarae (Formicidae: Myrmicinae)

Fifteen microsatellite loci were isolated from the Peruvian tropical plant‐ant Allomerus octoarticulatus cf. demerarae (Hymenoptera: Myrmicinae) and their polymorphism was characterized. High levels of within‐population variation were observed at most loci, with number of alleles ranging from one to 21, and heterozygosity from 0 to 1 per population sample. Cross‐species amplification of these loci was also tested in one other species of the ant genus Allomerus (Allomerus decemarticulatus), displaying similar life history.     

Intersimple sequence repeat (ISSR) variation in Lactoris fernandeziana (Lactoridaceae), a rare endemic of the Juan Fernández Archipelago, Chile

Sixteen populations and 89 individuals of Lactoris fernandeziana were examined for variation in intersimple sequence repeat (ISSR) banding patterns. The species is a rare endemic of Masatierra Island in the Juan Fernández Archipelago, and is the only member of the endemic family Lactoridaceae. Five populations showed a single genotype whereas the other 11 populations had from two to 16 multilocus genotypes. Over 73% of the ISSR diversity occurred across populations, with only about 27% within populations. Diversity among populations results from the presence of different subsets of loci within each population rather than unique loci within populations; only two populations displayed novel loci, with one and three in each. Levels of differentiation at ISSR loci among populations are not correlated with geographic distance on Masatierra; rather, the pattern of variation is mosaic. The presence of differentiated local populations is concordant with the geitonogamous breeding system of the species and suggests low levels of long distance pollen or seed dispersal. The mosaic pattern of ISSR variation on Masatierra may result, in part, from drift and inbreeding in small populations following fragmentation of a once more continuous distribution of Lactoris with the formation of canyons by erosion. Also, the generation of new ISSR loci by mutation could occur with rare, sporadic gene flow among populations accounting for the mosaic pattern of variation and the paucity of unique alleles within populations. The ISSR results for Lactoris suggest that studies of morphological, ecological and physiological features may elucidate differentiation among populations of L. fernandeziana . Field studies have demonstrated that plants occur both in the dense forest understory and in the full sunlight in forest openings.     

How do soil fauna and soil microbiota respond to beech forest growth?

The dynamics and performance of soil biota during forest rotation were studied in monoculture beech stands forming a chronosequence of four different age-classes(30,62,111,153 yr).Biomass was monitored in major groups of microflora,microfauna,mesofauna,and macrofauna.Resource availability(litter layer,soil organic mater),biomass of the two dominant decomposer groups(microflora,earthworms)as well as the biomass of mesofauna and microfauna were found to remain quite stable during forest succession.Nevertheles...