Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The extent of the global human footprint [ 1 ] limits our understanding of what is natural in the marine environment. Remote, near-pristine areas provide some baseline expectations for biomass [ 2, 3 ] and suggest that predators dominate, producing an inverted biomass pyramid. The southern pass of Fakarava atoll—a biosphere reserve in French Polynesia—hosts an average of 600 reef sharks, two to three times the biomass per hectare documented for any other reef shark aggregations [ 4 ]. This huge biomass of predators makes the trophic pyramid inverted. Bioenergetics models indicate that the sharks require ∼90 tons of fish per year, whereas the total fish production in the pass is ∼17 tons per year. Energetic theory shows that such trophic structure is maintained through subsidies [ 5–9 ], and empirical evidence suggests that sharks must engage in wide-ranging foraging excursions to meet energy needs [ 9, 10 ]. We used underwater surveys and acoustic telemetry to assess shark residency in the pass and feeding behavior and used bioenergetics models to understand energy flow. Contrary to previous findings, our results highlight that sharks may overcome low local energy availability by feeding on fish spawning aggregations, which concentrate energy from other local trophic pyramids. Fish spawning aggregations are known to be targeted by sharks, but they were previously believed to play a minor role representing occasional opportunistic supplements. This research demonstrates that fish spawning aggregations can play a significant role in the maintenance of local inverted pyramids in pristine marine areas. Conservation of fish spawning aggregations can help conserve shark populations, especially if combined with shark fishing bans.
ISSN: 0960-9822

hal-01359391
https://hal-univ-perp.archives-ouvertes.fr/hal-01359391
DOI : 10.1016/j.cub.2016.05.058

Éditeur(s) : HAL CCSD Ecological Society of America
Résumé : CABI:20153174020
Understanding how plants are constructed - i.e., how key size dimensions and the amount of mass invested in different tissues varies among individuals - is essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The BAAD contains 259634 measurements collected in 176 different studies, from 21084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01-100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric equations (except in very large trees where biomass was estimated from detailed sub-sampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem cross-section including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area, wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the world's vegetation.
ISSN: 0012-9658

hal-01535227
https://hal.archives-ouvertes.fr/hal-01535227
DOI : 10.1890/14-1889.1
PRODINRA : 306122

Éditeur(s) : HAL CCSD Royal Society, The
Résumé : International audience
Individuals can play different roles in maintaining connectivity and socialcohesion in animal populations and thereby influence population robustnessto perturbations.We performed a social network analysis in a reef shark populationto assess the vulnerability of the global network to node removal underdifferent scenarios. We found that the network was generally robust to theremoval of nodes with high centrality. The network appeared also highlyrobust to experimental fishing. Individual shark catchability decreased as afunction of experience, as revealed by comparing capture frequency and sitepresence. Altogether, these features suggest that individuals learnt to avoidcapture, which ultimately increased network robustness to experimentalcatch-and-release. Our results also suggest that some caution must be takenwhen using capture–recapture models often used to assess population sizeas assumptions (such as equal probabilities of capture and recapture) maybe violated by individual learning to escape recapture.
EISSN: 1471-2954

hal-01561754
https://hal-univ-perp.archives-ouvertes.fr/hal-01561754
DOI : 10.1098/rsbl.2016.0824