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Baraloto C.,French National Institute for Agricultural Research | Couteron P.,Institute pour la Recherche et le Developpement
Biotropica | Year: 2010

We examined fine-scale heterogeneity of environmental conditions in a primary rain forest in French Guiana to describe variation in microhabitats that plants may experience during establishment. We characterized both the range as well as the spatial structuring of 11 environmental factors important for seedling establishment in six hexagonal sampling grids, one each in gap and understory sites at three points representing the predominant geomorphic units in this primary forest. Each grid contained 37 sampling points separated by 31 cm-20 m. Monte-Carlo tests of semivariograms against complete spatial randomness indicated that for many variables in all six sampling grids, spatial dependence did not exceed 1 m. A principal component analysis of all sampling points revealed a lack of spatial microhabitat structure, rather than homogeneous patches associated with canopy structure or geomorphology. Our results suggest that ample fine-scale spatial heterogeneity exists to support the coexistence of plant species with differential abiotic requirements for regeneration. © 2010 The Author(s). Journal compilation © 2010 by The Association for Tropical Biology and Conservation. Source

Kuhn C.E.,National Oceanic and Atmospheric Administration | Tremblay Y.,Institute pour la Recherche et le Developpement | Ream R.R.,National Oceanic and Atmospheric Administration | Gelatt T.S.,National Oceanic and Atmospheric Administration
Endangered Species Research | Year: 2010

The foraging strategies of diving marine species are often categorized into 3 fundamental groups (epipelagic, mesopelagic, and benthic foraging) based on diving, habitat use, and diet studies. Because these foraging strategies are influenced by the distribution and behavior of the prey being targeted, we would expect search behavior and space use to differ depending on the strategy employed. Since northern fur seals Callorhinus ursinus display both epipelagic and benthic foraging strategies, they were an ideal model to test the hypothesis that fine-scale movement and space-use patterns will vary when animals use markedly different foraging strategies. Dive bouts were characterized into foraging strategies based on numerous dive parameters (depth, duration, etc.). For each strategy, we compared movement patterns (e.g. transit rate and path straightness) and space use (area-restricted search [ARS] zones) around St. Paul Island, Alaska, USA. Nearly all dive parameters were significantly different between foraging strategies (epipelagic vs. benthic). In addition, epipelagic bouts were more sinuous and covered a greater total distance than benthic bouts. However, the greater distances traveled in epipelagic bouts were due to longer bout durations, as transit rates were not different between the 2 strategies. On average, <2 ARS zones were identified per trip, and the characteristics of epipelagic and benthic ARS zones were not different. By combining dive behavior with precise at-sea locations, this study has provided a greater understanding of the fine-scale foraging behavior of northern fur seals. Monitoring changes in foraging behavior over time and comparing behavior among populations with differing population trajectories may provide more clues as to why northern fur seal numbers on St. Paul Island continue to decline. © Inter-Research 2010. Source

Costalago D.,Institute pour la Recherche et le Developpement | Costalago D.,Nelson Mandela Metropolitan University
Vie et Milieu | Year: 2015

In the Atlantic Ocean, small pelagic fish occasionally execute long distance migrations before they become adults. However, in the Mediterranean Sea, the populations of the most common small pelagic fish, anchovy and sardine, seem to be generally more confined to relatively small areas. Particularly in the NW Mediterranean, local environmental conditions, such as mesoscale events, wind forcing or river run-offs, can contribute to shaping the dispersal patterns of fishes, especially in their early life stages. Intrinsic factors such as dietary preferences, swimming abilities or feeding behavior can also play an essential role in the distribution of the populations in the region. Some studies have been done in the NW Mediterranean in order to elucidate which factors are playing the main roles in the dispersal and in the ecology of anchovy and sardine larvae and juveniles. Nevertheless, a holistic evaluation of all the potential attributes conditioning the distribution of early life history anchovy and sardine is lacking. It is therefore necessary to clearly highlight the most determinant biological and environmental features for the dispersion of the early life stages of anchovy and sardine in the NW Mediterranean. This review of the state-of-the-art in the distribution and the trophic ecology of the larvae and juveniles of these populations, pointing out the main methods utilized, will also help to identify some of the major gaps of knowledge and discrepancies that might conduce to future research. Source

Zydelis R.,Duke University | Zydelis R.,DHI Water - Environment - Health | Lewison R.L.,San Diego State University | Shaffer S.A.,University of California at Santa Cruz | And 15 more authors.
Proceedings of the Royal Society B: Biological Sciences | Year: 2011

Fisheries by catch is a recognized threat to marine mega fauna. Addressing by catch of pelagic species however is challenging owing to the dynamic nature of marine environments and vagility of these organisms. In order to assess the potential for species to overlap with fisheries, we propose applying dynamic habitat models to determine relative probabilities of species occurrence for specific oceanographic conditions. We demonstrate this approach by modelling habitats for Laysan (Phoebastria immutabilis) and black-footed albatrosses (Phoebastria nigripes) using telemetry data and relating their occurrence probabilities to observations of Hawaii-based long line fisheries in 1997-2000. We found that modelled habitat preference probabilities of black-footed albatrosses were high within some areas of the fishing range of the Hawaiian fleet and such preferences were important in explaining by catch occurrence. Conversely, modelled habitats of Laysan albatrosses overlapped little with Hawaii-based long line fisheries and did little to explain the by catch of this species. Estimated patterns of albatross habitat overlap with the Hawaiian fleet corresponded to by catch observations: black-footed albatrosses were more frequently caught in this fishery despite being 10 times less abundant than Laysan albatrosses. This case study demonstrates that dynamic habitat models based on telemetry data may help to project interactions with pelagic animals relative to environmental features and that such an approach can serve as a tool to guide conservation and management decisions. © 2011 The Royal Society. Source

Vannucchi P.,University of Florence | Sage F.,University Pierre and Marie Curie | Phipps Morgan J.,Cornell University | Remitti F.,University of Modena and Reggio Emilia | Collot J.-Y.,Institute pour la Recherche et le Developpement
Geochemistry, Geophysics, Geosystems | Year: 2012

Convergent plate boundaries accommodate intraplate displacement within a ∼100-1000 m thick shear zone. Marine geophysicists typically define this zone, the subduction channel (SC), as the sedimentary layer between the downgoing oceanic crust and the base of the upper plate. Geologists and modelers, instead, perceive the SC as a specific type of shear zone. The original theory of SCs was developed when the net accretion of marine sediments to the forearc was thought to typify a convergent margin. While erosive margins were briefly mentioned, their mechanics were not discussed in any detail. We now realize that subduction erosion is taking place at roughly half of the modern subduction margins. Here we review and revise the theory of erosive SCs (1) to unify this concept across disciplines, focusing on the meaning of the channel's boundaries; (2) to redefine the portions of the forearc included in the SC concept; and (3) to better idealize this dynamic system where material supply to the channel, fluid content, and the heterogeneity of deformation all influence the SC's upper and lower boundaries. Migration of the channel boundaries controls the downdip variation of tectonic mechanisms that shape the margin. Within the shallow, <15 km deep part of the SC, a gradual change of physical properties defines three zones; zone 1 of rapid fluid dewatering, zone 2 of overpressure, and zone 3 with metamorphic fluid release. A SC is a dynamic feature with along-strike and downdip variations caused by changes in channel material, in trapped fluid contents, and in interplate boundary geometry. Copyright 2012 by the American Geophysical Union. Source

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