Alien species pathways to the Galapagos Islands, Ecuador

Abstract

Alien species, one of the biggest threats to natural ecosystems worldwide, are of particular concern for oceanic archipelagos such as Galápagos. To enable more effective management of alien species, we reviewed, collated and analysed all available records of alien species for Galápagos. We also assembled a comprehensive dataset on pathways to and among the Galápagos Islands, including tourist and resident numbers, tourist vessels, their itineraries and visitation sites, aircraft capacity and occupancy, air and sea cargo and biosecurity interceptions. So far, 1,579 alien terrestrial and marine species have been introduced to Galápagos by humans. Of these, 1,476 have become established. Almost half of these were intentional introductions, mostly of plants. Most unintentional introductions arrived on plants and plant associated material, followed by transport vehicles, and commodities (in particular fruit and vegetables). The number, frequency and geographic origin of pathways for the arrival and dispersal of alien species to and within Galápagos have increased over time, tracking closely the increase in human population (residents and tourists) on the islands. Intentional introductions of alien species should decline as biosecurity is strengthened but there is a danger that unintentional introductions will increase further as tourism on Galápagos expands. This unique world heritage site will only retain its biodiversity values if the pathways for invasion are managed effectively.

Fig 1. The Galápagos Islands in relation to mainland South America.

The Galápagos Islands and mainland Ecuador showing air (grey lines) and sea routes (black lines), ports, tourism sites (black crosses) and fishing sites (open circles). The remote and rarely visited northernmost islands (Darwin and Wolf) are omitted for clarity of presentation.

Fig 2. Number of alien species (AS) and number of vectors.

Normalised sum of alien species (AS), residents, tourists (national and foreign), plane passengers (PAX), flights, boats (tourist+cargo) and, cargo per decade in the Galápagos Islands, Ecuador.

Fig 3. Accumulated number of alien species introduced by different pathways per decade.

Fig 4. Correlation of the cumulative number of recorded alien species versus the number of Galápagos residents from 1833–2015 (R² = 0.97) (red circles) and number of tourists that have arrived to Galápagos 1979–2015 (R² = 0.93) (blue triangles).