339 research outputs found
Warm and fertile sub-humid conditions enhance litterfall to sustain high soil respiration fluxes in a mediterranean cork oak forest
Soil respiration is a major component of the global carbon budget and Mediterranean ecosystems have usually been studied in locations with shallow soils, mild temperatures, and a prolonged dry season. This study investigates seasonal soil respiration rates and underlying mechanisms under wetter, warmer, and more fertile conditions in a Mediterranean cork oak forest of Northern Tunisia (Africa), acknowledged as one of the most productive forests in the Mediterranean basin. We applied a soil respiration model based on soil temperature and relative water content and investigated how ecosystem functioning under these favorable conditions affected soil carbon storage through carbon inputs to the soil litter. Annual soil respiration rates varied between 1774 gC m(-2) year(-1) and 2227 gC m(-2) year(-1), which is on the highest range of observations under Mediterranean climate conditions. We attributed this high soil carbon flux as a response to favorable temperatures and soil water content, but this could be sustained only by a small carbon allocation to roots (root/shoot ratio = 0.31-0.41) leading to a large allocation to leaves with a multiannual leaf production, enhanced annual twig elongation (11.5-28.5 cm) with a reduced leaf life span (<1 year) maintaining a low LAI (1.68-1.88) and generating a high litterfall (386-636 gC m(-2) year(-1)). Thus, the favorable climatic and edaphic conditions experienced by these Mediterranean cork oak forests drove high soil respiration fluxes which balanced the high carbon assimilation leading to a relatively small overall contribution (10.96-14.79 kgC m(-2)) to soil carbon storage
Recent expansion of marine protected areas matches with home range of grey reef sharks
Dramatic declines in reef shark populations have been documented worldwide in response to human activities. Marine Protected Areas (MPAs) offer a useful mechanism to protect these species and their roles in coral reef ecosystems. The effectiveness of MPAs notably relies on compliance together with sufficient size to encompass animal home range. Here, we measured home range of 147 grey reef sharks, Carcharhinus amblyrhynchos, using acoustic telemetry in New Caledonia. The distribution of home range was then compared to local MPA sizes. We report a home range of 12 km2 of reef for the species with strong differences between adult males (21 km2), adult females (4.4 km2) and juveniles (6.2 km2 for males, 2.7 km2 for females). Whereas local historic MPA size seemed adequate to protect reef shark home range in general, these were clearly too small when considering adult males only, which is consistent with the reported failure of MPAs to protect sharks in New Caledonia. Fortunately, the recent implementation of several orders of magnitude larger MPAs in New Caledonia and abroad show that recent Indo-Pacific MPAs are now sufficiently large to protect the home ranges of this species, including males, across its geographical range. However, protection efforts are concentrated in a few regions and cannot provide adequate protection at a global scale
Low fuel cost and rising fish price threaten coral reef wilderness
Wilderness areas offer unparalleled ecosystem conditions. However, growing human populations and consumption are among factors that drive encroachment on these areas. Here, we explore the threat of smallâscale fisheries to wilderness reefs by developing a framework and modeling fluctuations in fishery range with fuel costs and fish prices. We modeled biomass of four fishery groups across the New Caledonian archipelago, and used fish and fuel prices from 2005 to 2020 to estimate the extent of exploited reefs across three fishing scenarios. From 2012 to 2018, maximum profitable range increased from 15 to over 30 hr from the capital city, expanding to reefs previously uneconomic to fish, including a UNESCO heritage site. By 2020, over half of New Caledonian (âŒ17% global) wilderness reefs will become profitable to fish. Our results demonstrate that remoteness from humans should not be considered protection for wilderness coral reefs in the context of rising fish prices
Isolation and no-entry marine reserves mitigate anthropogenic impacts on grey reef shark behavior
Reef sharks are vulnerable predators experiencing severe population declines mainly due to overexploitation. However, beyond direct exploitation, human activities can produce indirect or sub-lethal effects such as behavioral alterations. Such alterations are well known for terrestrial fauna but poorly documented for marine species. Using an extensive sampling of 367 stereo baited underwater videos systems, we show modifications in grey reef shark (Carcharhinus amblyrhynchos) occurrence and feeding behavior along a marked gradient of isolation from humans across the New Caledonian archipelago (South-Western Pacific). The probability of occurrence decreased by 68.9% between wilderness areas (more than 25âhours travel time from the capital city) and impacted areas while the few individuals occurring in impacted areas exhibited cautious behavior. We also show that only large no-entry reserves (above 150âkmÂČ) can protect the behavior of grey reef sharks found in the wilderness. Influencing the fitness, human linked behavioral alterations should be taken into account for management strategies to ensure the persistence of populations
Les méthodes expérimentales dans la recherche en Management International.
International audienceLes methodes expeĆimentales dans la recherche en management international RESUME Les mĂ©thodes expĂ©rimentales sont depuis longtemps employĂ©es en Sciences naturelles afin de tester une hypothĂšse en contrĂŽlant les conditions d'expĂ©rimentation. Ces mĂ©thodes ont Ă©tĂ© reprises en Sciences Ă©conomiques et de gestion ces derniĂšres dĂ©cennies, et sont devenues une rĂ©fĂ©rence dans certaines sous-disciplines comme le marketing. Or, les expĂ©rimentations restent rares dans la recherche en management international. Dans ce chapitre, nous prĂ©sentons les difficultĂ©s, mais aussi les avantages des mĂ©thodologies expĂ©rimentales dans cette sous-discipline Ă travers l'exemple du projet InterCCom, portant sur la compĂ©tence interculturelle. GrĂące au dĂ©veloppement d'un jeu sĂ©rieux informatisĂ© dans le cadre de ce projet, les comportements des membres d'une Ă©quipe internationale virtuelle sont mesurĂ©s, ce qui permettra de rĂ©ponse Ă des problĂ©matiques de recherche variĂ©es
Environmental DNA reveals tropical shark diversity in contrasting levels of anthropogenic impact
Sharks are charismatic predators that play a key role in most marine food webs. Their demonstrated vulnerability to exploitation has recently turned them into flagship species in ocean conservation. Yet, the assessment and monitoring of the distribution and abundance of such mobile species in marine environments remain challenging, often invasive and resource-intensive. Here we pilot a novel, rapid and non-invasive environmental DNA (eDNA) metabarcoding approach specifically targeted to infer shark presence, diversity and eDNA read abundance in tropical habitats. We identified at least 21 shark species, from both Caribbean and Pacific Coral Sea water samples, whose geographical patterns of diversity and read abundance coincide with geographical differences in levels of anthropogenic pressure and conservation effort. We demonstrate that eDNA metabarcoding can be effectively employed to study shark diversity. Further developments in this field have the potential to drastically enhance our ability to assess and monitor elusive oceanic predators, and lead to improved conservation strategies
Environmental DNA illuminates the dark diversity of sharks
In the era of âAnthropocene defaunation,â large species are often no longer detected in habitats where they formerly occurred. However, it is unclear whether this apparent missing, or âdark,â diversity of megafauna results from local species extirpations or from failure to detect elusive remaining individuals. We find that despite two orders of magnitude less sampling effort, environmental DNA (eDNA) detects 44% more shark species than traditional underwater visual censuses and baited videos across the New Caledonian archipelago (south-western Pacific). Furthermore, eDNA analysis reveals the presence of previously unobserved shark species in human-impacted areas. Overall, our results highlight a greater prevalence of sharks than described by traditional survey methods in both impacted and wilderness areas. This indicates an urgent need for large-scale eDNA assessments to improve monitoring of threatened and elusive megafauna. Finally, our findings emphasize the need for conservation efforts specifically geared toward the protection of elusive, residual populations
Functional diversity of sharks and rays is highly vulnerable and supported by unique species and locations worldwide
Elasmobranchs (sharks, rays and skates) are among the most threatened marine vertebrates, yet their global functional diversity remains largely unknown. Here, we use a trait dataset of >1000 species to assess elasmobranch functional diversity and compare it against other previously studied biodiversity facets (taxonomic and phylogenetic), to identify species- and spatial- conservation priorities. We show that threatened species encompass the full extent of functional space and disproportionately include functionally distinct species. Applying the conservation metric FUSE (Functionally Unique, Specialised, and Endangered) reveals that most top-ranking species differ from the top Evolutionarily Distinct and Globally Endangered (EDGE) list. Spatial analyses further show that elasmobranch functional richness is concentrated along continental shelves and around oceanic islands, with 18 distinguishable hotspots. These hotspots only marginally overlap with those of other biodiversity facets, reflecting a distinct spatial fingerprint of functional diversity. Elasmobranch biodiversity facets converge with fishing pressure along the coast of China, which emerges as a critical frontier in conservation. Meanwhile, several components of elasmobranch functional diversity fall in high seas and/or outside the global network of marine protected areas. Overall, our results highlight acute vulnerability of the worldâs elasmobranchsâ functional diversity and reveal global priorities for elasmobranch functional biodiversity previously overlooked
Uso do Ăndice de vegetação por diferença normalizada (NDVI) na avaliação do desenvolvimento de cafeeiros do Sul de Minas Gerais
O objetivo deste trabalho foi de observar o Ăndice de vegetação por diferença normalizada (NDVI) em cafezais de Lavras, sul de Minas Gerais ao longo do tempo para utilização desta variĂĄvel como ferramenta no manejo das lavouras. Foi realizado o estudo em cafezal no campus da Universidade Federal de Lavras (UFLA) no perĂodo de fevereiro de 2014 a março de 2015. Trinta plantas de Coffea arabica L, cv CatuaĂ IAC 144 com 6 anos de idade foram avaliadas semanalmente o NDVI em trĂȘs posiçÔes e conteĂșdo de clorofila total em 4 posiçÔes. Os dados obtidos foram submetidos Ă anĂĄlise de sĂ©rie temporal e cada variĂĄvel foram submetidos Ă anĂĄlise de correlação de Person (r). Os resultados indicam que Nas plantas de cafĂ© valores de NDVI variaram em função da posição da planta e da Ă©poca da medida, enquanto para NDVI e conteĂșdo de clorofila total foi observada uma correlação negativa. Contudo, a sĂ©rie temporal do NDVI Ă© uma ferramenta Ăștil no manejo de cafezais no sul de Minas Gerais
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