Conservation on Volcán Alcedo (Galápagos): terrestrial invertebrates and the impact of introduced feral goats

Abstract

Diversity, composition and community structure of terrestrial macroinvertebrates were compared along an altitudinal gradient on Volcán Alcedo (Isabela, Galápagos), sampled at nine sites in April 1986 and 1996. This volcano has recently suffered a population explosion of introduced feral goats, which have transformed large parts of the former forest and scrub into grassland, especially at higher elevations. Species diversity showed highest values for the lower arid part of the volcano with little change between 1986 and 1996. At higher elevations, diversity was generally lower, but the 1996 data revealed increased values compared with 1986. Species composition and relative abundance in samples from the lower arid and transition zones differed between periods, whereas at higher elevation this difference was masked by the effects of introduced goats. There was a decrease of high altitude specialist species (including several endemics) and a significant increase of more xerophilic species in overgrazed sites. Both the temporary increase in habitat heterogeneity and availability of dead wood explain the observed recent increase in species richness on goat-damaged sites. Firm and quick action to reduce the feral goat numbers could still restore the initial state and conserve most of the natural diversity of Volcán Alcedo.