Why are anopheline mosquitoes not present in the Seychelles?

<p>Abstract</p> <p>Background</p> <p>Species of anopheline mosquitoes are largely distributed over emerged lands around the world and, within the tropics, few areas are without these insects, which are vectors of malaria parasites. Among the exceptions is the Seychelles archipelago in the western Indian Ocean. However, in the Aldabra island group, located in the extreme western portion of the archipelago, <it>Anopheles gambiae s.l. </it>was introduced, leading to massive proliferation and then elimination, with the most recent autochthonous malaria cases recorded in 1931.</p> <p>Methods</p> <p>In order to re-examine the absence of anopheline mosquitoes in the Seychelles, an entomological field survey was conducted in December 2008 at 17 sites on four granitic islands, including Mahé and Praslin, and ten sites on coralline atolls in the extreme west, including Aldabra.</p> <p>Results</p> <p>No evidence of larval or adult anophelines was found at the surveyed sites, which supports their absence in the Seychelles.</p> <p>Conclusions</p> <p>In the granitic islands of the Seychelles, the climate is favourable for anophelines. However, these islands are protected by their remoteness and prevailing seasonal winds. In addition, stagnant freshwater, required in anopheline larval development, is relatively uncommon on the granitic islands because of the steep slopes. In the southwestern atolls (Aldabra and Providence-Farquhar groups), the presence of a long dry season of up to nine months and the total absence of permanent natural freshwater prevents the breeding of anophelines and their successful colonization. The Seychelles does not have any native land mammals and like in other parts of the world (Antarctica, Iceland, New Caledonia, Central Pacific islands) their absence is associated with the lack of anophelines. This suggests an obligatory relationship for anophelines to feed on terrestrial mammals, without alternative for blood-feeding sources, such as bats, birds and reptiles.</p

Comparative use of three methods for estimating the population size of a transferred island endemic: the endangered Seychelles White-eye Zosterops modestus

Post-release monitoring is an important aspect of species transfers, providing a basis for conservation and management actions to achieve long-term survival of the species. Between 2001 and 2003, the Seychelles White-eye Zosterops modestus became established on Frégate Island following the transfer of 37 adult colour-ringed birds from Conception Island. Capture and colour ringing of birds was undertaken at regular intervals to keep the majority of the population banded. As the population grew, sampling methodologies became necessary to estimate its size accurately. Here, we compare the results obtained between November 2005 and January 2006 using three different methods: (1) capture–mark–relocate (NOREMARK); (2) point-transect with ‘distance sampling’, and (3) direct systematic surveys. Fifty point counts of 10 min each were conducted and replicated three times. The estimate by capture–mark–relocate was 77 individuals (72–83; P < 0.05) with better precision over distance sampling: 78 individuals (44–136; P < 0.05). The result from direct systematic surveys (81) indicated that estimates obtained with the two indirect methods were reliable. Based on present and previous method comparisons, we recommend using the capture–mark–relocate method for its higher precision and the NOREMARK program to determine sizes of island populations with a significant proportion of marked individuals.OSTRICH 2011, 82(2): 87–9

Survival rates of a tropical island endemic following conservation introduction on a rehabilitated island: the case of the endangered Seychelles White-eye

Survival rates of the endemic Seychelles White-eye Zosterops modestus were investigated in a small transferred population on Frégate Island, Seychelles. The population has been studied since the first conservation introduction of 37 Seychelles White-eyes in 2001-2003, in an attempt to secure the long term future of this critically endangered species. Re-sighting data of 206 birds from direct systematic surveys were analysed with Cormack-Jolly-Seber (CJS) models using the software MAR K 5.1. Here we present the first robust estimates of adult annual survival published for this species. We also attempted to provide a preliminary survival rate of first-year birds. Adult survival probability (φ) was found to be 76 % in our best-supported model, and survival was constant over time. Annual adult survival rate did not differ significantly between the transferred white-eyes (φ = 72, n = 31) and the Frégatois (those born on Frégate) (φ = 78, n = 175), nor did it between males (φ = 77, n = 117) and females (φ = 74, n = 86). Juvenile survival rate could not be modelled due to insufficient data on chicks marked at the nest or shortly after fledgling. However, 24 out of 27 (89 %) white-eyes marked as chicks/ fledglings on Frégate between 2002 and 2008 survived to one year old, indicating potentially high juvenile survival rates, comparable to the adults. More data are needed on marked chicks/ fledglings to determine reliable and robust juvenile survival rates through modelling. Our study revealed the importance of having good monitoring design, regular, systematic and long-term data collection for such transferred populations, which will aid in the estimation of reliable survival rates along with other demographic and ecological parameters. We recommend the continued collection of both protocol-driven and empirical data, as well as an increased effort to estimate juvenile survival rates which will lead to more accurate assessments of population status. Close monitoring of transferred threatened birds on small islands offers further opportunities to better understand fundamental principles of population dynamics and ecology in these environments.Taux de survie d’un endémique insulaire tropical après introduction pour la conservation sur une île réhabilitée : le cas de l’Oiseau-lunettes des Seychelles, espèce en danger. L’Oiseau-lunettes des Seychelles Zosterops modestus est une espèce endémique hautement menacée des Seychelles, confinée à l’origine dans les deux îles de Mahé et Conception. Ses populations ont subi au cours du XXe siècle un déclin drastique, vraisemblablement lié à l’introduction du Rat noir Rattus rattus et peut-être aussi à la destruction ou dégradation des forêts indigènes, et comptaient seulement 300 oiseaux environ en l’an 2000. Pour sauver cette espèce en danger critique d’extinction, 37 individus ont été transférés sur l’île de Frégate entre 2001 et 2003, et depuis, cette population a été suivie régulièrement chaque année. À partir de 206 données de recaptures visuelles nous avons estimé les taux de survie de ces oiseaux à l’aide du logiciel MARK 5.1 en utilisant les modèles de Cormack-Jolly-Seber (CJS), et présentons ici les premières estimations robustes des taux annuels de survie adulte publiés pour cette espèce. Nous avons aussi tenté d’estimer les taux de survie pour les oiseaux de première année. La probabilité de survie des adultes (φ) était de 76 %, et fut constante sur la période étudiée. Ce taux de survie annuel des adultes ne fut pas notablement différent entre les oiseaux-lunettes transférés (φ = 72 %, n = 31) et ceux nés sur Frégate (φ = 78 %, n = 175), ni entre les mâles (φ = 77 %, n = 117) et les femelles (φ = 74 %, n = 86). Il n’a pas été possible de modéliser le taux de survie des juvéniles faute de données suffisantes sur les poussins bagués au nid ou juste après l’envol. Cependant, 24 sur 27 (89 %) de ceux-ci ont survécu à leur première année, ce qui indiquerait un taux de survie élevé et comparable à celui des adultes. Nous recommandons que l’on poursuive la collecte des données démographiques sur ces oiseaux à travers un protocole bien défini et aussi de façon empirique, et qu’une attention plus particulière soit donnée à l’estimation de la survie des juvéniles afin de permettre des évaluations démographiques plus précises sur cette population. Le suivi rapproché d’oiseaux menacés réintroduits dans des petites îles offre aussi l’opportunité de mieux comprendre les principes fondamentaux régissant la dynamique et l’écologie des populations en général.Henriette Elvina, Rocamora Gérard. Survival rates of a tropical island endemic following conservation introduction on a rehabilitated island: the case of the endangered Seychelles White-eye. In: Revue d'Écologie (La Terre et La Vie), tome 67, n°2, 2012. pp. 223-236

Conservation introductions as a tool for the recovery of endangered island species: territoriality and demography of the Seychelles white-eye Zosterops modestus on Frégate Island

La réintroduction constitue un outil de gestion des populations menacées d extinction. L Oiseau-lunettes des Seychelles a été introduit à des fins de conservation dans trois îles: Frégate (2001 et 2003), l Ile du Nord et Cousine (2007) Nous avons suivi le développement des nouvelles populations introduites (principalement Frégate) et des populations sources (Conception et Mahé). Nous montrons d abord que l espèce a établi à Frégate des territoires relativement larges (moyenne: 1.34 ha), de type agrégés et localisés principalement dans des forêts de feuillus. La méthode du Core-weighting kernel est la plus efficace pour mesurer la superficie des territoires. Nos résultats confirment que la période de reproduction se prolonge sur toute l année à Frégate (contre 9 mois à Conception), ainsi que la reproduction des oiseaux dès l age d un an. Je rapporte également le premier cas suspecté de polyterritorialité pour l espèce. La deuxième partie de la thèse traite de dynamique des populations. Nous recommandons l utilisation d une méthode de capture-recapture pour estimer les effectifs et du logiciel NOREMARK pour analyser les données. Nous démontrons que la survie adulte à Frégate est élevée (76%), et que la croissance de la population est très sensible à ce paramètre. Les populations à Frégate, Ile du Nord et Conception augmentent mais celles de Mahé et Cousine déclinent. Néanmoins, la population mondiale est de 550-650 oiseaux en 2009-2010, contre 280-390 en 1997, ce qui montre l efficacité d une stratégie de conservation basée sur la création de nouvelles populations dans plusieurs îles.Conservation introduction can be used as a tool to establish self-sustaining populations of species threatened with extinction. The endemic Seychelles white-eye (Zosterops modestus) originally confined to Conception and Mahé islands (280-390 individuals in 1997) was transferred to Frégate (37 birds in 2001-2003), Ile du Nord (25 birds in 2007) and Cousine (23 birds in 2007) islands. The development of transferred and source populations has been monitored, particularly on Frégate. Part 1 of this thesis shows that territories on Frégate are spatially aggregated, relatively large (mean 1.34 ha) and predominantly found in broad-leaf forest. The Core-weighting kernel was the most efficient method in measuring territory size. We confirm the extended year-round breeding season on Frégate (only c.9 months on Conception), as well as reproduction of first-year birds. We also reveal the first case of suspected polyterritoriality for this species. Part 2 focuses on population demography and trends. We recommend the use of capturemark- relocate techniques to estimate population size and of programme Noremark for data analysis. We show that the species has high adult survival rates (76%) and that population growth rate (1.18) is most sensitive to this parameter. Conception, Frégate and North populations are increasing, whilst Cousine and Mahé are experiencing alarming declines. In 2009-2010, the global population stood at 550-650 individuals. We evaluate the efficiency of these introductions and conclude that creating new island populations has been advantageous for the species and offers more scope for the metapopulation to grow.PARIS-Museum Hist.Naturelle (751052304) / SudocSudocFranceF

Suivi spatio-temporel des communautés d'arthropodes (effets de l'éradication des rats et tentative de réintroduction d'un insecte rare dans des îles en cours de réhabilitation des Seychelles)

Ce travail vise en premier lieu a étudier l impact de divers facteurs du milieu et de l éradication des rats sur les communautés d Arthropodes d une sélection d îles. Pour cela, nous avons suivi les peuplements d invertébrés en utilisant principalement pièges-fosses et points de comptage sur feuilles. La situation géographique de l île et le type de substrat semblent déterminants mais aucun facteur n apparaît dominant et ceux agissant à une microéchelle pourraient avoir une influence insoupçonnée. Sur les îles granitiques, l abondance, la richesse et la diversité en invertébrés diminuent fortement après l éradication des rats, laissant supposer une facilitation (probablement indirecte) des rongeurs sur les peuplements d invertébrés, en particulier pour les Hémiptères Auchénorhynches (P<0,001). Sur l île corallienne échantillonnée, en revanche, l éradication entraîne une augmentation significative (p<0,05) de l abondance en Araignées (P<0,01), en Coléoptères (P<0,05) et en Formicidés (P<0,05). Ces réactions contraires seraient liées à la structure de l écosystème perturbé, notamment à la présence d animaux insectivores pouvant être limités par les rats. Nous avons ensuite tenté l introduction à fins de conservation d un insecte endémique rare, la Phyllie des Seychelles Phyllium bioculatum (Phasmatodea, Phylliidae). Des difficultés sont survenues pendant l élevage et certaines phyllies, réintroduites en semiliberté, ont été tuées par des prédateurs inconnus. Notre expérience pourra cependant servir de base à de futurs projets de réintroduction d insectes dans l Océan Indien, où elle fut une première. Enfin, nous avons découvert deux espèces du genre Cratopus (Curculionidés) nouvelles pour la science et ainsi contribué à l inventaire de l entomofaune locale.This work aims primarily at studying the impact of various factors, and particularly the eradication of rats, on Arthropod assemblages in a sample of islands. We monitored populations of invertebrates using mainly pitfall traps and leaf point counts. Island geographical location and type of substrate seem important, although no factor appears dominant, hence microfactors (at microhabitat level) might well have an unsuspected influence. On granitic islands, invertebrate abundance, richness and diversity decreased sharply after rat eradication, suggesting a likely indirect facilitation on the invertebrate populations by rodents, particularly for Auchenorrhyncha (Hemiptera) (P<0,001). On the coralline island studied, however, eradication resulted in a significant increase (p <0.05) in the abundance of Spiders (P <0.01), Coleoptera (P <0.05) and Formicidae (P <0.05). These opposite reactions are probably related to the structure of the disturbed ecosystems, particularly to the presence of insectivorous animals which may be limited by rats (birds, reptiles, large insects). Our second objective was to attempt a first conservation introduction of the rare endemic Seychelles leaf-insect Phyllium bioculatum (Phasmatodea: Phylliidae). There were difficulties during the captive breeding phase and the released leaf-insects, reintroduced with a semi-captive procedure, disappeared or were found killed by unknown predators. However, this experience, which was the first documented conservation introduction attempt in the Indian Ocean, can serve as a basis for future similar projects. Finally, we discovered two species of Cratopus (Curculionidae) new to science and thus contributed to the inventory of the local entomofauna.PARIS-Museum Hist.Naturelle (751052304) / SudocSudocFranceF

Introduced mammals on Western Indian Ocean islands

The diversity of introduced mammals and their introduction history varies greatly across the Western Indian Ocean (WIO) islands, from ancient introductions in the past millennia on islands off the East coast of Africa where extant terrestrial native mammal communities exist, to very recent invasions in the past decades on islands in the Mascarene archipelago. We compile the distribution of 16 introduced mammal taxa on 28 island groups comprising almost 2000 islands. Through an exhaustive literature review and expert consultation process we recorded all mammal eradications, and species recoveries which could be attributed to introduced mammal eradication or control. All island groups have been invaded by mammals, and invasive cats and rats in particular are ubiquitous, but cultural contingency has also led to regional invasions by other mammals such as lemurs, civets and tenrecs. Mammal eradications have been attempted on 45 islands in the WIO, the majority in the Seychelles and Mauritius, and where successful have resulted in spectacular recovery of species and ecosystems. Invasive mammalian predator eradication or control in association with habitat management has led to improved conservation prospects for at least 24 species, and IUCN red-list down-listing of eight species, in the Mascarene Islands. Future island conservation prioritisation in the region will need to take account of global climate change and predicted sea-level rises and coastal inundation. Greater investment and prioritisation in island conservation in the region is warranted, given its high biodiversity values and the extent of invasions

Predicting the Presence of Leptospires in Rodents from Environmental Indicators Opens Up Opportunities for Environmental Monitoring of Human Leptospirosis

International audienceLeptospirosis, an environmental infectious disease of bacterial origin, is the infectious disease with the highest associated mortality in Seychelles. In small island territories, the occurrence of the disease is spatially heterogeneous and a better understanding of the environmental factors that contribute to the presence of the bacteria would help implement targeted control. The present study aimed at identifying the main environmental parameters correlated with animal reservoirs distribution and Leptospira infection in order to delineate habitats with highest prevalence. We used a previously published dataset produced from a large collection of rodents trapped during the dry and wet seasons in most habitats of Mahé, the main island of Seychelles. A land use/land cover analysis was realized in order to describe the various environments using SPOT-5 images by remote sensing (object-based image analysis). At each sampling site, landscape indices were calculated and combined with other geographical parameters together with rainfall records to be used in a multivariate statistical analysis. Several environmental factors were found to be associated with the carriage of leptospires in Rattus rattus and Rattus norvegicus, namely low elevations, fragmented landscapes, the proximity of urbanized areas, an increased distance from forests and, above all, increased precipitation in the three months preceding trapping. The analysis indicated that Leptospira renal carriage could be predicted using the species identification and a description of landscape fragmentation and rainfall, with infection prevalence being positively correlated with these two environmental variables. This model may help decision makers in implementing policies affecting urban landscapes and/or in balancing conservation efforts when designing pest control strategies that should also aim at reducing human contact with Leptospira-laden rats while limiting their impact on the autochthonous fauna