Open AccessFeral sheep on Socorro Island: facilitators of alien plant colonization and ecosystem decay
Author(s) -
Walter Hartmut S.,
Levin Geoffrey A.
Publication year - 2008
Publication title -
diversity and distributions
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.918
H-Index - 118
eISSN - 1472-4642
pISSN - 1366-9516
DOI - 10.1111/j.1472-4642.2007.00407.x
Subject(s) - ecology , alien , introduced species , habitat , geography , invasive species , ecosystem , colonization , vegetation (pathology) , transect , range (aeronautics) , biological dispersal , biology , political science , law , composite material , medicine , population , materials science , demography , pathology , sociology , politics , citizenship
The paper examines the role of feral sheep ( Ovis aries ) in facilitating the naturalization of alien plants and degrading a formerly robust and stable ecosystem of Socorro, an isolated oceanic island in the Mexican Pacific Ocean. Approximately half of the island is still sheep‐free. The other half has been widely overgrazed and transformed into savannah and prairie‐like open habitats that exhibit sheet and gully erosion and are covered by a mix of native and alien invasive vegetation today. Vegetation transects in this moderately sheep‐impacted sector show that a significant number of native and endemic herb and shrub species exhibit sympatric distribution patterns with introduced plants. Only one alien plant species has been recorded from any undisturbed and sheep‐free island sector so far. Socorro Island provides support for the hypothesis that disturbance of a pristine ecosystem is generally required for the colonization and naturalization of alien plants. Sheep are also indirectly responsible for the self‐invasion of mainland bird species into novel island habitats and for the decline and range contraction of several endemic bird species.