Introduced species in the Maltese Islands

Abstract

The aim of this paper is to review the situation regarding the introduction of non-native species of flora and fauna into the Maltese Islands and their surrounding waters. The introduction of non-native species is not a new phenomenon -- indeed it is a natural process in ecosystems, particularly island ones. Most oceanic islands are initially colonised by species coming from ‘overseas’. Those invaders that manage to gain a foothold and survive to breed and spread, eventually become the native biota. Invariably this biota will evolve characteristics that adapt it to the particular environment it is now living in, which may be substantially different from that of its native environment. Some island populations will eventually become so different from their ‘exotic’ ancestors that they become new species in their own right -- species that occur only on the particular island on which they live, that is, endemic. Continental islands, such as the Maltese Islands, are somewhat different since they may become connected to the continental mainland during sea-level lows, allowing easy access of mainland biota. During sea-level highs, the islands become cut off from the mainland and the biota becomes stranded. For example, in the case of the Maltese Islands, they received their initial biota when they were connected to the Sicilian mainland towards the end of the Miocene, and then became separated at the beginning of the Pliocene, some five million years ago (THAKE, 1985; GIUSTI et al., 1995). For those species with limited powers of dispersal, the island populations continue to evolve independently of their mainland ancestors, and here too endemic forms may arise. Superimposed on this, there is an influx of those mainland species which manage to cross the water.