Rare Species Support Vulnerable Functions in High-Diversity Ecosystems

Around the world, the human-induced collapses of populations and species have triggered a sixth mass extinction crisis, with rare species often being the first to disappear. Although the role of species diversity in the maintenance of ecosystem processes has been widely investigated, the role of rare species remains controversial. A critical issue is whether common species insure against the loss of functions supported by rare species. This issue is even more critical in species-rich ecosystems where high functional redundancy among species is likely and where it is thus often assumed that ecosystem functioning is buffered against species loss. Here, using extensive datasets of species occurrences and functional traits from three highly diverse ecosystems (846 coral reef fishes, 2,979 alpine plants, and 662 tropical trees), we demonstrate that the most distinct combinations of traits are supported predominantly by rare species both in terms of local abundance and regional occupancy. Moreover, species that have low functional redundancy and are likely to support the most vulnerable functions, with no other species carrying similar combinations of traits, are rarer than expected by chance in all three ecosystems. For instance, 63% and 98% of fish species that are likely to support highly vulnerable functions in coral reef ecosystems are locally and regionally rare, respectively. For alpine plants, 32% and 89% of such species are locally and regionally rare, respectively. Remarkably, 47% of fish species and 55% of tropical tree species that are likely to support highly vulnerable functions have only one individual per sample on average. Our results emphasize the importance of rare species conservation, even in highly diverse ecosystems, which are thought to exhibit high functional redundancy. Rare species offer more than aesthetic, cultural, or taxonomic diversity value; they disproportionately increase the potential breadth of functions provided by ecosystems across spatial scales. As such, they are likely to insure against future uncertainty arising from climate change and the ever-increasing anthropogenic pressures on ecosystems. Our results call for a more detailed understanding of the role of rarity and functional vulnerability in ecosystem functioning

The Fish Communities of a Coral Reef Transect

As a contribution to the discussion on the causes of the high fish species diversity found on coral reefs, a coast-to-sea transect has been studied in the lagoon of Moorea Island (French Polynesia) in order to uncover the spatial scales at which recurrent assemblages (i.e., communities) can be identified. The transect was divided into 22 stations where fishes were sampled. According to the null hypothesis (chaos), the fish species should be distributed at random along the transect. This was tested first by a method of constrained clustering that performs a statistical test of cluster fusion, based on a null hypothesis that corresponds to chaos. Groups of stations were found with, at most, a 5% chance of resulting from a random distribution of species among the groups. The distribution of species among the stations pro vided a second test of the null hypothesis; the observed number of ubiquitous species was found to be significantly smaller than expected under the hypothesis of chaos and, in the same way, the species limited to a single group of stations were found to be significantly more numerous than expected under chaos. Both patterns are consistent with reports from other reefs of the Indo-Pacific

Biodiversity Research on Coral Reef and Island Ecosystems: Scientific Cooperation in the Pacific Region.

v. ill. 23 cm.Quarterl

Anthropogenic stressors, inter-specific competition and ENSO effects on a Mauritian coral reef

Much of the western Indian Ocean suffered widespread loss of live coral in 1998 and interest is now focussed on the indirect effects of this coral loss on other components of the ecosystem, in particular fishes. However, it is just as important to identify changes in fish assemblages at locations that did not suffer coral mortality to understand local versus regional drivers. We surveyed benthic and fish communities on a reef flat in Mauritius five times between 1994 and 2005. The design allowed for comparison through time, along the coast and between inshore and offshore reef locations. The benthic community demonstrates a clear trend along the coast, likely in response to a dredged water ski lane, but little change through time. Branching Acropora colonies dominate much of the live coral and best explain patterns in the fish assemblage (P < 0.01). Few changes in overall fish species richness through time were identified, and observed changes were within fishery target families rather than species reliant on live coral. Departure from expected levels of taxonomic distinctness suggests degradation in the community associated with the dredged ski lane. Non-metric multi-dimensional scaling of the fish assemblage demonstrates a similar pattern to that seen in the benthos; greater differences along the coast (Global R = 0.34) than through time (Global R = 0.17) and no trend between reef positions. SIMPER analysis identified two species of Stegastes as the main drivers of trends in the MDS plot and the most dominant of these, S. lividus, appears to be reducing species richness of the remaining fish community. The study highlights Mauritius as a regional refugia of thermally-sensitive corals and specialised fish, suggesting a need for careful management. \u

The capture and culture of post-larval fish and invertebrates for the marine ornamental trade

Governments, non-government organizations, and other stakeholders are striving to develop practices, policies, and vehicles to make the tropical marine ornamental trade sustainable. Small-scale fisheries based on post-larval capture and culture (PCC) promise to contribute to this goal by (1) removing the risk of damaging corals (inherent in harvesting adults of target species established on reefs) by collecting post-larvae with light traps, nets, and purpose-built temporary shelters as they settle from the plankton to the substrate; and (2) translating the high mortality of post-larvae at settlement into high rates of survival in culture. Possible concerns about overfishing of post-larvae, harvesting the juveniles after they have run the gauntlet of predation at settlement, and the large proportion of bycatch can be eliminated or greatly alleviated by restricting the size and quantity of fishing gear, designing it to retain bycatch alive, and releasing bycatch at times and places that minimize predation. However, special caution is needed when PCC is used at small, isolated islands with self-replenishing populations. Although PCC is environmentally friendly, its contribution to the ornamental trade is expected to be limited. Large variation in the abundance and species composition of settling post-larvae among years, the logistics and costs of operating labor-intensive operations in remote locations, and competition with responsible enterprises harvesting wild adults or producing ornamentals in hatcheries are expected to constrain the viability and market share of dedicated PCC enterprises. PCC is expected to have the greatest uptake by part-time artisanal fishers in developing countries with infrastructure for exporting marine ornamentals. Such fishers are more immune to temporal variation in the supply of post-larvae—they can engage in PCC when valuable post-larvae are abundant and switch to other sources of income when they are scarce. Livelihood opportunities for smallholders could be enhanced through promotion of the environmental benefits of PCC among hobbyists maintaining marine ornamentals

A Framework for Assessing Impacts of Marine Protected Areas in Moorea (French Polynesia).

v. ill. 23 cm.QuarterlyMarine Protected Areas (MPAs) have been promoted as effective management tools to protect biodiversity at local and global scales, but there remains considerable scientific uncertainty about effects of MPAs on species abundances and biodiversity. Commonly used assessment designs typically fail to provide irrefutable evidence of positive effects. In contrast, Before-After- Control-Impact (BACI) designs potentially remedy many of these problems by explicitly dealing with both spatial and temporal variation. Here, we document the historical context of implementation and the scientific assessment of MPAs recently established at eight sites around the island of Moorea, French Polynesia. In 2004, we designed and implemented a monitoring plan that uses a BACIPaired Series (BACIPS) design to quantify the effect of the MPAs. Twice per year, we monitor fish, corals, and other benthic invertebrates at 13 sites (eight within MPAs and five outside MPAs) around Moorea, in three distinct reef habitats (fringing, barrier reef, and outer slope). We present statistical analyses of data collected during five surveys ( July 2004 to July 2006), before the initiation of enforcement. We also assessed the potential of our program to detect future responses to the established MPA network. Our estimates of biomass for five categories of fishes (Acanthuridae, Chaetodontidae, Serranidae, Scaridae, and fisheries target species) within MPA sites generally track estimates in paired Control sites through time. Estimated statistical power to detect MPA effects (a 192% biomass increase within the MPA) was high at the MPA network scale but varied among taxonomic categories and reef habitats: power was high on the reef outer slope and lower in the lagoon, and generally high for acanthurids and chaetodontids. It did not vary significantly between sites. We discuss limitations of our approach (shared by all MPA assessments to date) and describe solutions and unique opportunities to redress these limitations in French Polynesia

Hierarchical drivers of reef-fish metacommunity structure

Coral reefs are highly complex ecological systems, where multiple processes interact across scales in space and time to create assemblages of exceptionally high biodiversity. Despite the increasing frequency of hierarchically structured sampling programs used in coral-reef science, little progress has been made in quantifying the relative importance of processes operating across multiple scales. The vast majority of reef studies are conducted, or at least analyzed, at a single spatial scale, ignoring the implicitly hierarchical structure of the overall system in favor of small-scale experiments or large-scale observations. Here we demonstrate how alpha (mean local number of species), beta diversity (degree of species dissimilarity among local sites), and gamma diversity (overall species richness) vary with spatial scale, and using a hierarchical, information-theoretic approach, we evaluate the relative importance of site-, reef-, and atoll-level processes driving the fish metacommunity structure among 10 atolls in French Polynesia. Process-based models, representing well-established hypotheses about drivers of reef-fish community structure, were assembled into a candidate set of 12 hierarchical linear models. Variation in fish abundance, biomass, and species richness were unevenly distributed among transect, reef, and atoll levels, establishing the relative contribution of variation at these spatial scales to the structure of the metacommunity. Reef-fish biomass, species richness, and the abundance of most functional-groups corresponded primarily with transect-level habitat diversity and atoll-lagoon size, whereas detritivore and grazer abundances were largely correlated with potential covariates of larval dispersal. Our findings show that (1) within-transect and among-atoll factors primarily drive the relationship between alpha and gamma diversity in this reef-fish metacommunity; (2) habitat is the primary correlate with reef fish metacommunity structure at multiple spatial scales; and (3) inter-atoll connectedness was poorly correlated with the nonrandom clustering of reef-fish species. These results demonstrate the importance of modeling hierarchical data and processes in understanding reef-fish metacommunity structure

Effects of marine protected areas on recruitment processes with special reference to Mediterranean littoral ecosystems

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Rare Species Support Vulnerable Functions in High-Diversity Ecosystems

Around the world, the human-induced collapses of populations and species have triggered a sixth mass extinction crisis, with rare species often being the first to disappear. Although the role of species diversity in the maintenance of ecosystem processes has been widely investigated, the role of rare species remains controversial. A critical issue is whether common species insure against the loss of functions supported by rare species. This issue is even more critical in species-rich ecosystems where high functional redundancy among species is likely and where it is thus often assumed that ecosystem functioning is buffered against species loss. Here, using extensive datasets of species occurrences and functional traits from three highly diverse ecosystems (846 coral reef fishes, 2,979 alpine plants, and 662 tropical trees), we demonstrate that the most distinct combinations of traits are supported predominantly by rare species both in terms of local abundance and regional occupancy. Moreover, species that have low functional redundancy and are likely to support the most vulnerable functions, with no other species carrying similar combinations of traits, are rarer than expected by chance in all three ecosystems. For instance, 63% and 98% of fish species that are likely to support highly vulnerable functions in coral reef ecosystems are locally and regionally rare, respectively. For alpine plants, 32% and 89% of such species are locally and regionally rare, respectively. Remarkably, 47% of fish species and 55% of tropical tree species that are likely to support highly vulnerable functions have only one individual per sample on average. Our results emphasize the importance of rare species conservation, even in highly diverse ecosystems, which are thought to exhibit high functional redundancy. Rare species offer more than aesthetic, cultural, or taxonomic diversity value; they disproportionately increase the potential breadth of functions provided by ecosystems across spatial scales. As such, they are likely to insure against future uncertainty arising from climate change and the ever-increasing anthropogenic pressures on ecosystems. Our results call for a more detailed understanding of the role of rarity and functional vulnerability in ecosystem functioning

Degradations anthropiques des zones frangeantes des recifs coralliens polynesiens, influences sur l'ensemble de l'ecosysteme, incidences sur les peuplements ichtyologiques

INIST RP 185 (2481) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc