49 research outputs found
Trophic experiments to estimate isotope discrimination factors
No full text: 1. In Caut, Angulo & Courchamp (2008a) rats were fed with experimental diets of distinct isotopic values (_13C and _15N) in order to infer the discrimination factors. We showed negative relationships between discrimination factors and diet isotopic values. In Caut, Angulo & Courchamp (2009), our aim was to generalise these relationships to other taxonomic groups with a view to providing ecologists with a general and flexible method to obtain discrimination factors for diet reconstruction studies when difficult to obtain otherwise. 2. Perga & Grey (2010) claims that there is an artefact of experimental design (due to protein contents) and partly reanalyzes our data, taking into account the type of diet (mixed or not; carnivorous, omnivorous or herbivorous). However, (i) the role of protein content through isotopic routing is not clear; (ii) a reanalysis of our data shows that the relationships between discrimination factors and diet isotopic values remain significant even when following Perga's suggestions. 3. Auerswald et al. (2010) criticized the imprecise definitions, mathematical artefacts and invalid statistical analysis of Caut, Angulo & Courchamp. (2009). However, (i) their arguments are not new; they challenge the use of stable isotope in ecological trophic studies in general, and lack both alternative suggestions and ecological perspective; (ii) none of their statistical and mathematical objections has a significant effect on the results. 4. Synthesis and applications. Neither reply reflects the current context of debate. The complementarity between experimental studies and their application in field studies is indispensable for the use of stable isotopes in ecology. Protocols should be very well assessed in order to represent field conditions with accuracy. Further analyses are necessary to remove some of the flaws in the use of stable isotopes (carrying out an in-depth analysis of isotopic routing, turnover and dynamic during trophic experiments to ensure accurate attainment of equilibrium), but none of the issues raised by Perga & Grey (2010) and Auerswald et al. (2010) alter our main conclusions.Peer reviewe
Isotope incorporation in broad-snouted caimans (crocodilians)
No full textSummary
The trophic ecology and migration of vertebrate species have been increasingly studied using stable isotope analysis. However, this approach requires knowledge on how dietary isotopic values are reflected in consumers' tissues. To date, this information has only been obtained for a handful of ectotherms; in particular, little is known about crocodilians. In this study, diet-tissue discrimination factors (DTDFs) and carbon and nitrogen stable isotope turnover rates were estimated for plasma, red blood cells (RBCs), and muscle obtained from broad-snouted caimans (Caiman latirostris). Individuals were fed two different control diets for 189 days. DTDFs for δ15N (Δ15N) and δ13C (Δ13C) ranged from −2.24‰ to 0.39‰ and from −0.52‰ to 1.06‰, respectively. Isotope turnover rates in tissues, expressed as half-lives, ranged from 11 to 71 days, with plasma<muscle<RBCs. Δ15N was found to be particularly small, even when compared to values found for other ectotherms, a result that may be linked to the unique excretion physiology of crocodilians. These stable isotope incorporation data should help inform future interpretations of isotopic values obtained in the field for this taxon
Satellite transmitter attached to a black caiman’s head.
No full textPhotograph of a male black caiman (Melanosuchus niger; M2; TL = 3.2 m) with an Argos satellite transmitter glued to the front of its head. Reprinted with permission from S Caut.</p
Study site and scientific platform.
No full textLocation of the Kaw Marshes within French Guiana and picture of the scientific platform (6 x 4 meters) with its two metal boats. Reprinted with permission from S Caut.</p
Use of biological invasions and their control to study the dynamics of interacting populations
No full textInfluence of sex, size and trophic level on blood Hg concentrations in Black caiman, Melanosuchus niger (Spix, 1825) in French Guiana
No full textInternational audienceMercury (Hg) is a contaminant that is impacting ecosystems worldwide. Its toxicity is threatening wildlife and human populations, leading to the necessity of identifying the most affected ecosystems. Therefore, it is essential to identify pertinent bioindicator organisms to monitor Hg contamination. In this study, we determined the stable carbon and nitrogen isotope ratios in the red blood cells (RBCs), and the total Hg concentration in total blood of 72 Melanosuchus niger in French Guiana. The goals of our study were to assess the level of Hg contamination in total blood of Black caimans and to further investigate the influence of individual traits (i.e., sex, size/age, diet) on Hg concentrations. Mercury concentration in total blood of Black caimans ranged from 0.572 to 3.408 μg g−1 dw (mean ± SD is 1.284 ± 0.672 μg g−1 dw) and was positively correlated to individual body size and trophic position . We did not find any sexual or seasonal effects on Hg concentrations in the blood. The use of blood of M. niger is relevant to determine Hg concentrations within the population and suggests that this species can be used as a bioindicator for environmental contamination. In addition, our results emphasize trophic position as a major source of Hg variation and further suggest that it is essential to take trophic position into account for future studies
Native predators living in invaded areas: responses of terrestrial amphibian species to an Argentine ant invasion
No full textPredator–prey interactions play a key role in the success and impacts of invasive species. However, the effects of invasive preys on native predators have been poorly studied. Here, we first reviewed hypotheses describing potential relationships between native predators and invasive preys. Second, we examined how an invasive prey, the Argentine ant (Linepithema humile), affected a native terrestrial amphibian community. In the field, we looked at the structure of the amphibian community in invaded versus uninvaded areas and characterized amphibian trophic ecology. The amphibian community sampled seemed to show a species-dependent response in abundance to invasion: adults of the natterjack toad (Bufo calamita), the species demonstrating the highest degree of ant specialization, were less abundant in invaded areas. Although available ant biomass was significantly greater in invaded than in uninvaded areas (only Argentine ants occurred in the former), amphibians consumed relatively fewer ants in invaded areas. In the lab, we quantified amphibian consumption of Argentine ants versus native ants and assessed whether consumption patterns could have been influenced by prior exposure to the invader. The lab experiments corroborated the field results: amphibians preferred native ants over Argentine ants, and prior exposure did not influence consumption. Differences in preference explained why amphibians consumed fewer Argentine ants in spite of their greater relative availability; they might also explain why the most ant-specialized amphibians seemed to avoid invaded areas. Our results suggest the importance to account for predator feeding capacities and dietary ranges to understand the effects of invasive species at higher trophic levels.Peer Reviewe
Stable Isotopes Reveal Trophic Partitioning and Trophic Plasticity of a Larval Amphibian Guild
No full textTemporary ponds are highly variable systems where resource availability and community
structure change extensively over time, and consequently the food web is highly dynamic.
Amphibians play a critical role both as consumers and prey in aquatic communities and yet
there is still little information on the trophic status of most amphibians. More importantly, little
is known about the extent to which they can alter their trophic ecology in response to changing
conditions.We experimentally investigated the effects of increased amphibian density,
presence of intraguild competitors, and presence of native and invasive predators (either
free or caged) on the trophic status of a Mediterranean amphibian guild, using stable isotopes.
We observed variations in δ13C and δ15N isotopic values among amphibian species
and treatments and differences in their food sources. Macrophytes were the most important
food resource for spadefoot toad tadpoles (Pelobates cultripes) and relatively important for
all anurans within the guild. High density and presence of P. cultripes tadpoles markedly
reduced macrophyte biomass, forcing tadpoles to increase their feeding on detritus, algae
and zooplankton, resulting in lower δ13C values. Native dytiscid predators only changed the
isotopic signature of newts whereas invasive red swamp crayfish had an enormous impact
on environmental conditions and greatly affected the isotopic values of amphibians. Crayfish
forced tadpoles to increase detritus ingestion or other resources depleted in δ13C. We
found that the opportunistic amphibian feeding was greatly conditioned by intra- and interspecific
competition whereas non-consumptive predator effects were negligible. Determining
the trophic plasticity of amphibians can help us understand natural and anthropogenic
changes in aquatic ecosystems and assess amphibians’ ability to adjust to different environmental
conditions.Peer reviewe
Stable isotope biplot of each amphibian species and sources of the experiment.
No full text<p><i>δ</i><sup>15</sup>N and <i>δ</i><sup>13</sup>C values (mean ‰ <b>±</b> SD) of the amphibians included in this study (<i>Hyla meridionalis</i>, <i>Pelobates cultripes</i>, <i>Pelophylax perezi</i>, and <i>Triturus pygmaeus</i>) pooled across all experimental treatments for a general view of differences in trophic status among species. Resources are also shown as means <b>±</b> SD. The discrimination factors were added to the sources and not subtracted to the consumers to allow different discrimination factors to be assigned to different sources.</p
Overview of the experimental treatments specifying name, acronym, number of replicates and details of each treatment.
No full text<p>Overview of the experimental treatments specifying name, acronym, number of replicates and details of each treatment.</p
