ECOLOGIE DES TRICOTS RAYES DE NOUVELLE-CALEDONIE

Les organismes vivants utilisent des ressources pour vivre, croître et se reproduire.Derrière ce lieu commun se cache une théorie importante en Ecologie : la théorie desTraits d'Histoire de Vie (voir Stearns 1992, par exemple). Selon cette théorie, lesindividus optimisent l'utilisation de ressources limitées (ressources alimentaires,habitat, mais aussi partenaire sexuel entre autres) afin de maximiser des traits telsque la croissance, la survie ou la reproduction. Dans le cadre de la théorie de lasélection naturelle, les individus favorisés sont ceux qui adoptent les stratégiesd'acquisition des ressources les plus efficaces dans un environnement donné. Ceconcept très simple est extrêmement puissant pour comprendre l'écologie et lavariété des stratégies adoptées par les espèces, les populations ou les individus.Cette théorie est d'ailleurs centrale en Ecologie Evolutive (Stearns 1992)

Thirsty sea snakes forsake refuge during rainfall

International audienceVertebrates living in dry or salty habitats spend significant amounts of time and energy maintaining their hydro-mineral balance; any opportunity to drink fresh water should reduce such expenses. However, to find fresh water, individuals are generally forced to leave the safe and buffered conditions that prevail in their refuges. Therefore, they must face harsh environmental conditions and increased predation risks.We examined this trade-off in the field, using a very large dataset gathered on amphibious sea snakes that confront periodic droughts.The study was carried out on different islets in the lagoon of New Caledonia. As expected, sea kraits remain concealed most of the time under rocks or within burrows during dry weather. They select precise time windows to move rapidly between the sea and the land, thereby minimizing the time spent in the open. Rainfall triggered massive disruptions of this rhythm: many snakes quickly forsook their shelter to drink in the open, and remained almost motionless until satiety. Interestingly, they adopted specific and unusual postures to drink. They perched on the top of rocks that were benefiting from run

Climate and foraging mode explain interspecific variation in snake metabolic rates

The energy cost of self-maintenance is a critical facet of life-history strategies. Clarifying the determinant of interspecific variation in metabolic rate (MR) at rest is important to understand and predict ecological patterns such as species distributions or responses to climatic changes. We examined variation of MR in snakes, a group characterized by a remarkable diversity of activity rates and a wide distribution. We collated previously published MR data (n = 491 observations) measured in 90 snake species at different trial temperatures. We tested for the effects of metabolic state (standard MR (SMR) versus resting MR (RMR)), foraging mode (active versus ambush foragers) and climate (temperature and precipitation) while accounting for non-independence owing to phylogeny, body mass and thermal dependence. We found that RMR was 40% higher than SMR, and that active foragers have higher MR than species that ambush their prey. We found that MR was higher in cold environments, supporting the metabolic cold adaptation hypothesis. We also found an additive and positive effect of precipitation on MR suggesting that lower MR in arid environments may decrease dehydration and energetic costs. Altogether, our findings underline the complex influences of climate and foraging mode on MR and emphasize the relevance of these facets to understand the physiological impact of climate change

Determinants of dietary specialization: a comparison of two sympatric species of sea snakes

International audienceWhy do some predator species specialize on only a single type of prey whereas others take a broad range? One critical determinant may be the ontogenetic range of body sizes of the predator compared to that of its prey. If any single prey taxon spans only part of the range of prey sizes ingestible by the predator, then the predator will be more likely to take multiple prey taxa. We exploit a model system that provides a robust opportunity to test this hypothesis. We studied two sympatric species of predatory sea snakes, similar in size and general ecology that feed on anguilliform fishes from different habitats in the Great Lagoon of New Caledonia. Eel species from soft-bottom habitats must construct their own burrows, and thus tend to be more slender-bodied and less variable in body size than eel species that inhabit variable-sized crevices among hard coral. As a result, a laticaudine sea snake species (Laticauda saintgironsi) that feeds on hard-coraldwelling eels relies primarily on a single prey species: juveniles take young eels whereas adults consume adult eels of the same species. In contrast, a laticaudine species (L. laticaudata) that forages on soft-bottom eels switches its prey ontogenetically: juveniles take small eel species whereas adults consume large eel species. Thus, habitat-imposed constraints on the range of body sizes within each prey taxon generate a striking difference in the degree of dietary specialization of two closely related, sympatric predator species

Using biotic interactions in broad-scale estimates of species’ distributions

International audienceAim: To examine the combined effect of abiotic and biotic factors on species distri-butions in a marine environment. Specifically, we aim to account for the effects of trophic interactions at broad scales in ecological niche models (ENMs) of sea kraits (Laticauda: Reptilia) by including the potential distribution of food resources as pre-dictor variables.Location: Oceania and Southeast Asia.Methods: First, we outline a simple method to generate biotic interaction variables for ENMs. We then test whether ENMs that include biotic interactions perform bet-ter than ENMs based on abiotic variables only.Results: The models based on biotic interactions (i.e. trophic interactions) and abi-otic variables slightly outperformed the models informed only by abiotic variables. We found a strong relationship between prey species richness and probability of distribution of predator (sea kraits). The models that included potential distributions of prey species as predictor variables showed an increase in proportion of pixels predicted present and a decrease in omission error, compared with models based only on abiotic variables.Main conclusions: Distribution estimates of predator species at broad scales are more accurate if calibration of ENMs includes relevant biotic variables (prey species richness, in this study). Hence, when data are available, biotic variables should be included in ENMs

Chapter 12. Sea snakes. A handbook of techniques

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Midwife toads (Alytes obstetricans) select their diurnal refuges based on hydric and thermal properties

International audienceMost amphibians use both aquatic and terrestrial habitats. While the aquatic phase attracted considerable interest, terrestrial habitat use is often less investigated. We studied diurnal refuge selection in the Midwife toad in Western central France. We used a factorial design and tested the effect of refuge type (wood versus rubber boards) and substrate (wet sawdust versus bare soil). Most animals were observed under refuges with sawdust substrate. An interaction between refuge type and temperature was detected with higher presence probability under rubber refuges at low temperature. Conflicting hydric and thermic requirements are likely determinants of the observed pattern

Refining model estimates of potential species’ distribution to relevant accessible areas

International audienceDispersal is an important, yet overlooked phenomenon when studying species’ distributions using ecologicalniche models (ENMs). Here, we use species’ dispersal limits to evaluate and refine ENM estimates only to theareas accessible to the species within the study region and, thereby, enhance the model interpretations. First,we ran multiple ENMs to estimate the distribution of sea krait species in both marine and terrestrialenvironments. Second, we estimated dispersal of the sea kraits using a cost analysis approach. Finally, weoutline a new approach that combines dispersal models and ENMs with the purpose of estimating theaccessible range when projecting species’ distribution estimates outside the known species range. We foundthat only a small proportion of the area the ENMs were projected over was accessible to sea kraits. Themajority of the suitable areas for sea kraits are within the accessible area. Outside the accessible area, there isonly a very limited suitable area for sea kraits. Our results suggest that when dispersal is taken into account,sea kraits seem to occupy most of their suitable available niche and that they may be unable to colonize muchof the area outside of their dispersal ranges. Using dispersal estimates to refine species’ distribution pre-dictions is a useful tool for refining the area of focus when ENM results are interpreted. Estimating species’dispersal also helps evaluate the ability of the models to predict the species’ distributions in areas that are notaccessible to the species and, hence, the potential commission error represented by overpredictio

Traffic noise exposure affects telomere length in nestling house sparrows

International audienceIn a consistently urbanizing world, anthropogenic noise has become almostomnipresent, and there are increasing evidence that high noise levels canhave major impacts on wildlife. While the effects of anthropogenic noiseexposure on adult animals have been widely studied, surprisingly, therehas been little consideration of the effects of noise pollution on developingorganisms. Yet, environmental conditions experienced in early life can havedramatic lifelong consequences for fitness. Here, we experimentally manipulatedthe acoustic environment of free-living house sparrows (Passerdomesticus) breeding in nest boxes. We focused on the impact of such disturbanceon nestlings’ telomere length and fledging success, as telomeres(the protective ends of chromosomes) appear to be a promising predictor oflongevity.We showed that despite the absence of any obvious immediate consequences(growth and fledging success), nestlings reared under traffic noiseexposure exhibited reduced telomere lengths compared with their unexposedneighbours. Although the mechanisms responsible for this effect remain tobe determined, our results provide the first experimental evidence that noisealone can affect a wild vertebrate’s early-life telomere length. This suggeststhat noise exposure may entail important costs for developing organisms