Abstract
Islands, especially small oceanic islands, are highly sensitive to the introduction of alien biota. As islands have often been stopovers in the early development of international trade, there have been many opportunities for the introduction of alien organisms. As island food webs are simple, the addition of species can destabilise them (trophic interference) causing the collapse of normal trophic interactions and potentially the extirpation of whole ecosystems. In St Helena the native ecosystems were largely destroyed by events set in train after human discovery of the island, particularly the introduction of the goat. Ecosystem repair is challenging: total eradication of invasives can be problematic. If total eradication is impossible, classical biological control is an alternative. Gene drive biological control is an emerging technology that may be used in future. One consequence of wholesale ecosystem destruction is that many island species are ‘ultra‐rare’ (reduced to total populations of 10 individuals or less). In such cases, inbreeding may have caused fitness problems compounding extinction risk. In such cases, genetic rescue may be required, via the deliberate beneficial increase of the allele pool from other populations or even other species via adaptive introgression.
Key Concepts
- Island ecosytems are vulnerable to introduced species.
- Terrestrial mamals do not disperse well and are absent from oceanic islands.
- Introduced species, especially mammalian herbivores and carnivores, destabilise existing trophic structure (trophic interference) and can lead to the collapse of ecosystems.
- Total eradication of invasives, or their biological control, can sometimes be possible to eliminate or mitigate the effect of invasives.
Keywords: trophic levels; food webs; invasive species; genetic rescue; genetic viability; adaptive introgression; conservation genomics; biological control; endonuclease gene drive; gene drive biological control (GDBC)
