Academic literature on the topic 'Ecology – Seychelles – Cousine Island'

SummaryThe Seychelles Warbler was once a highly threatened single-island endemic species with a population of 26 individuals confined to Cousin Island in the inner Seychelles. Following long-term management of Cousin, the population steadily recovered to around 300- 360 birds. Given the vulnerability of one small island in the Indian Ocean, the possibility of establishing the species on additional islands had been proposed as a priority conservation measure. This paper describes the successful translocation of 29 Seychelles Warblers from Cousin to Aride, summarizes the ecological studies carried out prior to, during and after the translocation and documents the subsequent establishment of the new population. It is considered that the Seychelles Warbler will soon no longer be a globally threatened species.

The distribution of the forest tree Pisonia grandis (Nyctaginaceae) coincides with seabird colonies on small tropical islands. Its seeds are enclosed in a calyx exuding extremely sticky resin which adheres strongly to feathers. Birds are obviously seed-dispersal vectors, but the multi-seeded infructescences frequently entangle birds, often fatally. On Cousin Island, Seychelles, I investigated the production, germination, survival, and tolerance to seawater of Pisonia seeds, and the occurrence of entanglement with birds. Fresh seeds had high germination success (62–87% in experimental trays), but seedling survival in Cousin's forests was low (0.1% of 6020 seeds survived as seedlings after 2–8 mo). Some seeds tolerated 30 min daily immersions in seawater (8–15% germination after 14–28 d treatment), but not continuous immersion in seawater (reduced germination after 5 d and none after 12 d). Inter-island dispersal is likely via living unencumbered seabirds carrying a few seeds, but not on floating carcasses. Seeds attached to carcasses did not have improved germination or survival. Intra-island propagation is almost entirely vegetative, with negligible local seed dispersal. Pisonia plants therefore do not benefit from fatal entanglements. The extreme stickiness of the seeds evidently evolved to resist removal by seabirds and so facilitate long-distance dispersal. The mortality of some potential vectors is an unfortunate consequence, but has little impact on the large populations of tree- and ground-nesting seabirds which nest in or under these trees.

Thesis (PhD)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Invasive species are among the most important global conservation threats. Their management is one of the key conservation challenges that will have to be addressed in the next few decades. The study of real invasions and their management in natural ecosystems provides an opportunity to gain important information on theoretical and applied aspects of biological invasions. This project focuses on the broader ecological context of invasive ant management in an ecologically sensitive island habitat. The thesis has three main components: 1) assessing the role of the invasive ant Pheidole megacephala in the ecosystem and evaluating its threat to the system, 2) evaluating a low-impact management program for the ant, and 3) using a community-level approach to assess ecosystem response to ant removal. The ant occupied almost 30% of the island‘s total land area and reached extremely high densities in some areas. The ant was associated with exotic hemipteran scale insects through trophobiotic mutualisms that facilitated high ant and hemipteran abundances. The highly destructive scale insect Pulvinaria urbicola was among the hemipterans that benefited from ant attendance. High levels of hemipteran feeding resulted in dieback of functionally important and threatened native Pisonia trees, which represented a significant threat to the forest ecosystem. A management program was initiated in response to this threat, consisting of baiting with selective hydramethylnon-based bait delivered in bait stations, accompanied by detailed pre-and post-baiting monitoring. The method was highly effective at suppressing the ants, whilst preventing bait uptake by non-target organisms. It was also cost-effective and adaptable to ant density in the field, but was only effective over short distances. The method may be applicable to other sensitive environments with similar challenges. After ant control, the ant-scale mutualism was decoupled and the Pu. urbicola population collapsed. There were variable responses in different taxa to the removal of these highly abundant exotic species, the most important of which was the recovery in Pisonia trees. Shoot condition and foliage density improved and there was a decrease in sooty mold. Herbivory on Pisonia increased due to recovery of native canopy herbivores, but the overall impact was far less than that of the exotic hemipterans. Soil surface arthropods, a group that may have been vulnerable to the treatment method, were unaffected by baiting. Instead, they increased significantly after ant removal, confirming the ant‘s impact on other arthropods. Other ant diversity and non-ant arthropod abundance increased post-baiting, including the endemic ant Pheidole flavens farquharensis and some functionally important insects such as the Indian cockroach. Natural enemies that interacted predictably with the mutualists were influenced by management. Predators of hemipterans increased significantly after ant removal and were instrumental in the scale population collapse, whereas parasitoids of hemipterans that benefited from the mutualism declined. Additionally, groups that were unrelated to the mutualism were indirectly influenced by management. The natural enemy assemblage as a whole showed recovery to pre-invasion conditions. The study shows how widely interconnected and influential the ant was in the ecosystem. It highlights the threat of the species in natural systems as well as the complex responses following invasive ant removal. Yet, it also demonstrates the potential to safely and effectively manage the species, thereby raising the opportunity for ecosystem recovery.
AFRIKAANSE OPSOMMING: Indringerspesies is van die belangrikste globale bedreigings vir natuurbewaring. Hulle bestuur is van die grootste bewaringsuitdagings wat in die volgende paar dekades aangespreek moet word. Die studie van werklike invalle en hul bestuur in natuurlike ekosisteme bied 'n geleentheid om belangrike inligting te verkry oor teoretiese en toegepaste aspekte van biologiese indringing. Hierdie projek fokus op die breër ekologiese konteks van uitheemse mier bestuur in 'n ekologies sensitiewe eiland habitat. Die tesis het drie hoofkomponente: 1) die beoordeling van die rol van die indringer mier Pheidole megacephala in die ekosisteem en evaluering van sy bedreiging vir die sisteem, 2) die evaluering van 'n lae-impak bestuursprogram vir die mier, en 3) die gebruik van 'n gemeenskaps-vlak benadering om ekosisteem reaksie op mierverwydering te assesseer. Die mier het byna 30% van die totale landoppervlak van die eiland beslaan en het in party areas baie hoë digthede bereik. Die mier was geassosieer met uitheemse dopluis spesies in mutualismes wat hoë mier en dopluis getalle gefasiliteer het. Die hoogs beskadigende dopluis Pulvinaria urbicola was een van die spesies wat bevoordeel is deur die mutualisme. Hoë vlakke van dopluis voeding het die terugsterwe van funksioneel belangrike, bedreidge inheemse Pisonia bome veroorsaak, wat ʼn groot bedreiging vir die ekosisteem verteenwoordig het. ‗n Bestuursprogram is geïmplimenteer as gevolg van hierdie bedreiging, wat bestaan het uit selektiewe hidrametielnoon-gebaseerde lokaas wat in die veld geplaas is in lokaashouers, vergesel deur intensiewe monitering voor en na lokaasplasing. Die metode was hoogs effektief in die onderdrukking van die miere en het lokaasinname deur nie-teiken organismes verhoed. Dit was ook koste-effektief en aanpasbaar volgens mierdigtheid in die veld, maar was slegs effektief oor kort afstande. Die metode mag van toepassing wees in ander sensitiewe omgewings met soortgelyke uitdagings. Na mierbeheer is die mier-dopluis mutualisme ontkoppel en die Pu. urbicola bevolking het drasties verminder. Daar was verskillende reaksies in verskillende taxa tot die verwydering van die oorvloedryke eksotiese spesies, maar die belangrikste reaksie was die herstel van Pisonia bome. Spruittoestand en blaardigtheid het verbeter en daar was ʼn afname in roetskimmel. Herbivorie op Pisonia het toegeneem as gevolg van ʼn herstel in inheemse herbivore, maar die algehele impak was veel minder as dié van die eksotiese dopluis. Grondoppervlak gelidpotiges, 'n groep wat kwesbaar kon wees vir die behandelingsmetode, was onaangeraak deur die lokaas, maar het beduidend na mierverwydering vermeerder. Mierdiversiteit het vermeerder en die Seychelles endemiese mier Pheidole flavens farquharensis is hervestig. Ander gelidpotiges het ook vermeerder, insluitend funksioneel belangrike spesies soos die Indiese kakkerlak. Natuurlike vyande wat geassosieer was met die mutualiste is beïnvloed deur die mierbestuur. Predatore van dopluis het beduidend toegeneem na mierverwydering en was hoogs betrokke by die vermindering van dopluis, terwyl parasiete van dopluis, wat voordeel getrek het uit die mutualisme, gedaal het. Daarbenewens is groepe wat onverwant was aan die mutualisme indirek beïnvloed deur mierbestuur. Die algehele natuurlike vyand gemeenskap het herstel na pre-indringing toestand. Die studie toon hoe wydverbind en invloedryk die mier was in die ekosisteem. Dit beklemtoon die bedreiging van die spesies in natuurlike stelsels asook die komplekse reaksies wat uitheemse mierverwydering volg. Tog demonstreer dit die potensiaal om die spesies veilig en doeltreffend te bestuur, en sodoende die geleentheid vir ekosisteemherstel te skep.

Introduction Seabird life history strategies are often characterised by high adult survival, delayed maturity at breeding, low clutch sizes and variable reproductive output (Schaffner 1990, Bowler et al. 2002, Hockey and Wilson 2003, Ramos et al. 2005). At low latitudes seabirds have small clutches, large eggs and long incubation and fledging periods (Hockey and Wilson 2003), and clutch size has been related to food availability and predation risk (Shea and Ricklefs 1996). Primary production in tropical marine ecosystems is generally considered to be low and seasonal, and food may be scarce, especially at oceanic islands (Hockey and Wilson 2003). Avian predators on small islands are generally few, but predators may be attracted to seabird eggs and chicks when large numbers of seabirds are breeding at high densities (Schaffner 1991, Hockey and Wilson 2003). Although most tropical islands are free of large indigenous mammalian predators, predation by smaller terrestrial predators like crabs and skinks occurs (Schaffner 1991, Ramos et al. 2005). Intra- and interspecific competition between breeding birds may also lower breeding success (Bowler et al. 2002, Ramos et al. 2005). Cousine Island is one of the smallest islands in the Seychelles archipelago. Seven tropical seabirds breed at the island; two of the least common are the White Tern Gygis alba and the White-tailed Tropicbird Phaethon lepturus. An estimated 1 000–1 500 pairs of White Terns and 450–850 pairs of White-tailed Tropicbirds breed on this island (Skerret et al. 2001). White Terns are tree-nesting birds that lay a single egg on an exposed fork or in an artificial structure, whereas White-tailed Tropicbirds are ground nesters that breed in a shady and sheltered crevice (Schaffner 1991, del Hoyo et al. 1996, Bowler and Pillay 2000). The incubation period of White Terns is 34–36 d (five weeks) and the nestling period 68 d (seven weeks), whereas the incubation period of the White-tailed Tropicbird is 40–42 d (six weeks) and the nestling period 77–85 d or 11–12 weeks (del Hoyo et al. 1996, Higgins and Davies 1996). Both species exhibit life-history traits specific to tropical island breeding. Each species has a clutch size of one and nesting success is generally low, from 30–50% for White-tailed Tropicbirds (Schaffner 1991, Ramos and Pacheco 2003) and 29–40% for White Terns (Vanderwerf 2003). The aim of this study was to compare the reproductive parameters of White Terns and White-tailed Tropicbirds on Cousine Island and investigate if egg or chick failures were associated with different stages of the incubation and nestling periods. The study also examined the associations between reproductive parameters and nest types (White Terns), the two monsoon seasons and nest reuse. We postulate reasons for observed differences in the measured parameters between the two species

Cette étude analyse la quasi-totalité du cycle de vie de deux espèces de puffins sympatriques, le puffin tropical (Puffinus bailloni, PT) et le puffin du Pacific (P. pacificus, PP) nichant sur Aride Island (Seychelles). L’objectif est de comprendre les interactions existantes entre ces espèces, ainsi que l’influence de l’environnement, au sein de la colonie et dans le milieu marin. Le nombre de couples ont était estime à 15,000 pour le PP et 30,000 pour le PT (où la population est probablement en déclin). Ils sélectionnent davantage des zones escarpées avec des végétations basses. Les PP montrent également une préférence pour les zones rocheuses avec un sol profond. Les PT nichent pendant toute l’année mais de manière plus intensive en fin de saison de reproduction des PP et le taux d'échec de la reproduction est maximal durant la période où les deux espèces nichent en même temps. Dans le milieu marin, il-y-a une ségrégation spatiale entre les deux espèces, exploitant des zones d’alimentation bien distinctes hors saison de reproduction et se distinguant également dans leur comportement alimentaire (profondeur de plonge). Dans la colonie les deux espèces sont en concurrence sur le site de reproduction mais les PP semblent être de meilleurs compétiteurs. Nous proposons la mise en place de mesures de conservation pour les deux espèces, mais favorisant spécialement les PT
The procellariiformes are one of the most endangered orders in the world. In addition, information on population estimates, trends, movements at sea and population dynamic is lacking for many species. We analysed almost the full life cycle of two sympatric species: the tropical (Puffinus bailloni, TS) and the wedge-tailed shearwater (P. pacificus, WS) breeding at Aride Island (Seychelles), in order to understand the interactions between them and the environment both at sea and in the colony. We assessed habitat selection, abundance, distribution and breeding success of the two species at the colony and the habitat selection and distribution at sea. The population was 15,000 and 30,000 pairs for WS and TS respectively; the TS is possibly in decline. Both species selected steep and lowly vegetated areas; the WS also selected boulder-like zones. The TS nests year-round but it has a peak of breeding at the end of the WS breeding season and its failure rate is higher when the two species co-exist. We found spatial, rather than ecological, segregation between the two species at sea in both foraging behaviour (diving depth) and inter-breeding areas. On land they are likely to compete for breeding sites with the WS often over competing the TS. We then suggest future conservation plans focused on both species but especially on the TS

Cousine Island, Seychelles, is of major conservation significance as it is relatively pristine, and apparently the only tropical island over 20 ha with no alien invasive mammals. Such mammals, especially rodents, can impact substantially on arthropod faunas. This study focuses on the arthropods of the island that live in fallen logs and litter. The dominant log species are Pisonia grandis (Summerhayes, 1932), Ficus spp. and Cocos nucifera (Linnaeus, 1952). Stage of decomposition and forest type in which the logs occurred significantly influenced the composition and structure of the assemblages. Young logs were significantly richer in species than older logs, possibly due to the greater resources and more varied microhabitats in the younger logs. Log type was also important for arthropod species richness and abundance. Although P. grandis and Ficus spp. logs did not differ significantly, these two log types did differ greatly from C. nucifera which had a higher arthropod species richness, composition and abundance. However, these differences were only significant for recently fallen logs. As the logs decayed, their arthropod assemblages converged. Nevertheless, each log type had some arthropod species not present in another log type. This is important in terms of conservation, especially in the case of C. nucifera, which, according to one school of thought, should be removed from some Seychelles islands as it is considered an alien invasive. Arthropod assemblages in woody litter differed in composition depending on forest type in which they occurred. These woody litter assemblages were generally dissimilar to those in logs in the same forest type. Leaf litter was extremely poor in arthropod species. Species richness, both in logs and litter, was comparable to figures from temperate lands, possibly because the rich, topical fauna was ameliorated by small island size. As the logs are home to several Seychelles endemic species, their conservation is essential. Furthermore, as they are also the food base of certain threatened Seychelles vertebrates, their conservation is about conservation of a food chain on this unique tropical island.
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

Thesis (DTech. degree in Nature Conservation.)--Tshwane University of Technology, 2010.
Hawksbill sea turtles (Eretmochelys imbricata) have been reduced by more than 80% worldwide in the last century and are considered critically endangered. Although nesting populations have been subject to numerous studies, there is a considerable lack of knowledge pertaining to the in-water behaviour and ecological functions of wild foraging hawksbill populations. This is especially true for the Western Indian Ocean as important topics such as habitat use and dietary items have scarcely been explored. Between 2006 and present, more than 178 hours of in-water observations of foraging hawksbill activity was recorded on a small insular reef at D'Arros Island, Seychelles. Most of the 827 sightings were of known, resident turtles (> 90%), facilitating analyses on both a population and individual level. Habitat types were identified and described, turtle densities estimated, population dynamics established, home ranges calculated, food items identified, food intake quantified, feeding behavior described, food resources quantified, diet selectivity indices calculated, intra/interspecific competition quantified and activity and dive patterns were described.