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Individual study: Vegetation response to temporary reduction of European rabbit Oryctolagus cuniculus numbers and eradication of feral goats Capra hircus on Round Island, Mauritius

Published source details

North S.G. & Bullock D.J. (1986) Changes in the vegetation and populations of introduced mammals of Round Island and Gunner's Quoin, Mauritius. Biological Conservation, 37, 99-117

Summary

Native palm savannas have been lost on mainland Mauritius. Some remnant palm savanna persists on two offshore islands, Round Island (151 ha) and Gunner's Quoin (65 ha). Vegetation on Round Island has been degraded by introduced European rabbits Oryctolagus cuniculus and feral goats Capra hircus, and associated erosion. Vegetation on Gunner's Quoin (65 ha) has been severely degraded by introduced mammals, invasive plants and possibly fire. Vegetation surveys were undertaken on Round Island in July/August 1975 (after near eradication of goats) and July/August 1982 (goats eradicated and rabbit control undertaken).

Plant surveys: Surveys focussed on monitoring endangered endemic palm (Palmae) and screwpine (Pandanus) populations which constitute the last real remnant of Mauritian palm savanna. Individuals of selected species were counted and placed into one of four height classes: 1) 0.1-1.2 m; 2) 1.2-3 m; 3) 3-4; 4) >4 m.
 
Goat eradication: Shooting gradually reduced the goat population from around 100 in 1950, with the last sightings of two males in February 1978.
 
Rabbit control: In 1974, the rabbit population was estimated at 2,000-3,000. In December 1976, 883 rabbits (a ‘high proportion’ of the population) were shot.

Goat eradication and temporary reduction in rabbit numbers (by January 1978, rabbits described as ‘numerous as ever') allowed some ground vegetation and palm regeneration. Surviving mature Latania palms were estimated at about 150 years old (probably the last to become established before rabbit and goat grazing prevented regeneration). Hyophorbe and Dictyosperma had declined much more (possibly as their seedlings are more palatable to rabbits and goats). Compared to 1975, the 1982 survey revealed a marked increase in Class 2 Latania (579 vs. 2,533; +338%), and a decrease in Class 4 (12,897 vs. 3,426; - 73%) individuals. This is assumed a consequence of reduced rabbit numbers between 1975 and 1977, long enough to allow increased regeneration.
 
Other changes possibly associated with declines and eventual eradication of goats occurred; notably, there was increase in ground cover between surveys, predominantly of species (e.g. Ipomoea, Tylophora and Vetiveria) unpalatable to rabbits but eaten by goats.
 
 
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