Nestedness in insular floras:spatiotemporal variation and underlying mechanisms

Aims Nestedness is a characteristic of insular metacommunity structure.Relatively few studies,however,have attempted to evaluate temporal changes in nestedness,or elucidate the mechanisms underlying nestedness.I evaluated both spatial and temporal patterns of nestedness in the insular floras of four archipelagoes of small islands in the Bahamas and the potential underlying environmental gradients.Methods The NODF(a nestedness metric based on overlap and decreasing fill)and the matrix temperature measure,T,were used to quantify nestedness in insular floras on small islands near Abaco,Andros,Great Exuma and the Exuma Cays,Bahamas.Two different null models were employed for each nestedness measure.Six environmental variables were evaluated in relation to nestedness by ordering islands according to gradients and recalculating NODF scores.Important Findings All archipelagoes were significantly nested.Nestedness among sites contributed more to overall nestedness than did nestedness among species.NODF scores varied among archipelagoes,but were surprisingly constant over time.Ordering islands by vegetated area yielded the highest nestedness scores for three archipelagoes;ordering islands by protection from exposure yielded the highest nestedness score for one archipelago.Nestedness scores varied little over time even though species compositions changed,indicating that extinctions occurred in a deterministic manner.The relative importance of area suggests extinction is an important mechanism in producing nestedness.Attempting to determine the relative importance of immigrations or extinctions requires some assumptions,however,and both processes are likely cumulative in most cases.

An early evaluation of translocation actions for endangered plant species on Mediterranean islands

In situ conservation is widely considered a primary conservation strategy. Plant translocation, specifically, represents an important tool for reducing the extinction risk of threatened species. However, thus far, few documented translocations have been carried out in the Mediterranean islands. The CareMediflora project, carried out on six Mediterranean islands, tackles both short-and long-term needs for the insular endangered plants through in situ and ex situ conservation actions. The project approach is based on using ex situ activities as a tool to improve in situ conservation of threatened plant species.Fifty island plants(representing 45 taxa) were selected for translocations using common criteria.During the translocations, several approaches were used, which differed in site selection method, origin of genetic material, type of propagative material, planting method, and more. Although only preliminary data are available, some general lessons can be learned from the experience of the CareMediflora project. Among the factors restricting the implementation of translocations, limited financial resources appear to be the most important. Specific preliminary management actions, sometimes to be reiterated after translocation, increase the overall cost, but often are necessary for translocation success. Translocation using juvenile/reproductive plants produces better results over the short term,although seeds may provide good results over the long run(to be assessed in the future). Regardless,plant translocation success can only be detected over long periods; therefore, proper evaluation of plant translocations requires a long-term monitoring protocol. Care-Mediflora project represents the first attempt to combine the existing approaches in a common plant conservation strategy specifically focusing on the Mediterranean islands.