Effects of Introduced Plants and Animals on Island Vegetation: Examples from Galápagos Archipelago

Abstract

Island ecosystems are particularly vulnerable to biological invasions. Since the early 1800s, humans have introduced to the GaIapagosIslands animals andplants that threaten the native vegetation Goats are the most abundant and destructive feral animals. Endemic members of the Cactaceae and Asteraceae have been reduced drastically. A control program has completely eradicated goats on several islands, where vegetation has returned but sometimes the species composition diyfers from the original. Hunting continues on Santiago, where 80,000 goats exist, and fenced quudrats protect some native plants. Cattle damage vegetation, particularly the endemic sbrub, Miconia robinsoniana, by trampling and grazing. Ranchers on several islands have been urged to fence in cattle. Wild pigs dig up and eat the roots of tuoodyplants and some rare orchids. Donkeys trample and eat grasses and shrubs. Control of pigs has started; there is no control of donkeys. Between 20 and50 introduced

Threat of Invasive Alien Plants to Native Flora and Forest Vegetation of Eastern Polynesia

“…It forms densely shaded monospecific stands from near sea level up to 1,300 m elevation and occupies the belt between 1,500 and 2,500 mm of rainfall per year, including pristine, undisturbed cloud forest habitats (Meyer 1996). It is noteworthy that most of the species cited here are also dominant invaders in other tropical oceanic islands such as the Hawaiian Islands (c. W. Smith 1985, Medeiros et al 1995), the Mascarene Islands (see, e.g., MacDonald et al 1991, Strahm 1999, and the Galapagos Islands (Schofield 1989). Other potentially serious invasive plants in the native wet forests of eastern Polynesia are introduced ornamental plants belonging to the genera Hedychium (Zingiberaceae), especially H. flavescens on some of the highest summits of Rarotonga and in wet valleys of Rapa Iti; Passifiora (Passifloraceae); and Rubus (Rosaceae), with several species known to be dominant plant invaders in other tropical islands in the Pacific (Meyer 2000) and in the Indian Ocean.…”

Goat grazing, its interactions with other herbivores and biodiversity conservation issues

“…Feral goats are considered a pest in semiarid rangelands in Australia (Parkes et al, 1996), where their commercial harvest is suggested as an economic opportunity, but also as a tool to minimize their negative impacts on both agricultural production and native species and habitats (Choquenot et al, 1998). Goats have been eradicated from at least 120 islands worldwide (Campbell and Donlan, 2005) where their introduction has frequently resulted in ecosystem degradation and biodiversity loss (Coblentz, 1978;Schofield, 1989). Within the Aldraba Island (Seychelles), a World Heritage site, their eradication started once their numbers increased and prompted concern for the future of the local biota (Coblenz et al, 1990).…”

Consequências ecológicas da fragmentação florestal na amazônia

“…A teoria ecológica sugere que habitats de alta diversidade, como as florestas tropicais, devem ser menos sujeitos às invasões do que habitats de menor diversidade (Tilman 1997). Ilhas com poucas espécies, por exemplo, tendem a ter maior número de invasões do que as áreas continentais mais ricas em espécies (Schofield 1989). Apesar disso, várias espécies exóticas ou generalistas foram capazes de invadir fragmentos de floresta na Amazônia, os quais são relativamente ricos em espécies.…”