Study

Changes in the vegetation and reptile populations on Round Island, Mauritius, following eradication of rabbits

  • Published source details North S.G., Bullock D.J. & Dulloo M.E. (1994) Changes in the vegetation and reptile populations on Round Island, Mauritius, following eradication of rabbits. Biological Conservation, 67, 21-28.

Summary

European rabbits Oryctolagus cuniculus, introduced to Round Island (151 ha) in the 19th century caused extensive damage to native vegetation and soil erosion. To conserve the native flora and fauna (including many endangered species) rabbit eradication was undertaken. Changes in the vegetation and reptile populations on Round Island are described in 1982 (when rabbits abundant) and 1989 (three years after their eradication).

Vegetation surveys: In July/August 1989, vegetation was surveyed using the same methods as in 1975 and 1982. Percentage ground cover was estimated along transects in three representative areas. Species cover was estimated in 15 permanent quadrats (1 x 3 m to 5 x 5 m in size) established in 1975. The two commonest trees (both natives), the fan palm Lantania loddigesii and screwpine Pandanus vandermeerschii, were censused in four areas. The two endangered endemic palms, bottle palm Hyophorbe lagenicaulis and hurricane palm Dictyosperma album var. conjugatum were censused by detailed searches.
 
Reptile surveys: In 1989, abundance indices of six reptile species were determined using the same methods as in 1975 and 1982, i.e. mainly daytime counts. For three species more active at night (Round Island boa Casarea dussumerii, Gunther's geckoPhelsuma guentheri and Serpent Island gecko Nactus serpensinsula) timed searches of suitable habitat were conducted dusk to midnight.

Vegetation: Changes in cover and composition (attributed to rabbit eradication) included increase in regeneration of three native tree species. The most obvious change between 1982 and 1989 was a marked increase in extent and density of Latania thicket. In 1989, for the first time, large numbers of Hyophorbe seedlings (< 20 mature palms >< 1979-1989) were observed with a small but increasing number of juveniles. Status of the rarest palm, Dictyosperma, did not change between 1982 and 1989; only two trees survive and no seedlings were found.
 
In 1989, there was a widespread increase of the introduced grass Chloris barbata (and also the herb Boerhavia spp.) with 2-12% cover in survey areas (negligible cover in 1982). There were also marked local increases in frequency and/or cover of several recently introduced or non-native species
 
Reptiles: Increases of the endemic reptiles (five threatened) were evident and particularly marked for N.serpensinsula (a 20-fold increase; from 10 individuals in 1982 to 210 in 1989), with C.dussumerii (363%; 8 to 37), Telfairs skink Leiolopisma telfairii (114%; 465 to 993), Mauritius ornate day gecko P.ornata (109%; 562 to 1,173) P.guentheri (85%; 41-76) and Bojer's skink Gongylomorphus (Scincus) bojerii (54%; 883 to 1,363). In the absence of any other dramatic ecological changes since 1982, these increases are attributed to increases in habitat and food availability following rabbit removal.
 
 
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