Restoration ecology of the Seychelles giant millipede

[摘要] ENGLISH ABSTRACT: The loss and degradation of habitat is recognised as the greatest threat to invertebrate biodiversity. Restoration practices have the potential to reduce these impacts. The Seychelles giant millipede (SGM), Sechelleptus seychellarum, is a threatened and functionally important macro-detritivore endemic to the Seychelles granitic islands. The broad objective of this dissertation was to investigate selected aspects of the restoration ecology of the SGM, with the intention of making practical restoration recommendations that can be used to assist in the conservation of this species. This study was carried out on Cousine Island, Seychelles between 1998 and 2009, in the context of the large-scale plant community restoration that has taken place on the island. Large fluctuations in millipede population densities were found between 1998 and 2009. In 2002, 2003, 2005 and 2007 millipede densities were low, while densities were high in 1998 and 2009. Although the SGM is active all year round, its surface activity was positively correlated with rainfall, with density high during the high rainfall period (i.e. October – April) and low during the low rainfall period (i.e. May – September). Female:male:juvenile ratios were ~ 3:1:1. The implications are that translocations should preferably be done in years of high millipede densities and during the wet season. Alien coconut trees did not affect SGM density, but negatively affected its foraging behaviour, whereas bamboo stands negatively affected both its density and foraging behaviour. The SGM showed feeding preferences for Pisonia grandis and Ficus sp. leaf litter types. Alien bamboo and coconut pose a varied threat to the SGM, and their removal and replacement by indigenous forest species (e.g. P. grandis and Ficus sp.) should form part of an island's restoration programme. SGM density was an order of magnitude lower in the restored area compared to the natural forest. In contrast, SGM physical condition improved significantly in the restored area, as vegetation structure increased. Furthermore, SGM behaviour in the restored area switched from a predominantly walking to a predominantly feeding behaviour over the study period, resulting in the forest restoration programme on Cousine increasing the foraging area of the SGM by 43%. SGM spatial density did not significantly correlate with edaphic and litter properties, but did positively correlate with the toposcape (i.e. elevation and granitic rock cover). Granite rock crevices in forest covered areas were important diurnal refuges for the SGM, as microclimate conditions in non-forest covered rock refuges were unsuitable. SGM physical condition was significantly lower in non-shaded crevices compared to those shaded by forest. Low granite rock cover in the restored forest limited the SGM colonisation of this area in large numbers, despite canopy cover in the restored forest being comparable with that in the reference natural forest. As most restoration practices are primarily vegetation-based, this study demonstrates that such an approach can be inadequate for restoring habitat for target invertebrates, as many species' habitat requirements extend beyond that of vegetation. For the SGM, selecting restoration sites that already have abundant rock cover would be the most practical way to increase SGM habitat through forest restoration practices. Taking into consideration the habitat requirements of target invertebrates can help in setting or redirecting restoration goals and thus enhance the conservation value of such practices.

[发布机构] Stellenbosch University