Protecting Island Animals And Ecosystems
Island ecosystems are sources of rich biodiversity, but are also incredibly fragile and sensitive to human interference. Plants on islands are often reliant on frugivorous (fruit-eating) animals to disperse their seeds, but several islands have recorded extinctions of more than half of their frugivorous animals. In this study, researchers sought to understand what qualities of islands makes them more or less resilient to human activity, as well as what frugivore traits are associated with likelihood of extinction.
74 islands were examined in this study, ranging across 20 archipelagos. Oceanic islands were chosen due to their higher sensitivity and unique native species, and the study was restricted to the tropics and subtropics due to plants’ higher reliance on animal seed dispersal at these latitudes. Several island qualities were recorded: area, distance to mainland, maximum elevation, average temperature and precipitation, and amount of land surrounding the island.
For the purposes of this study, the researchers considered be any animal with fruit as a part of their diet to be frugivorous. They limited themselves to birds, reptiles, and mammals. Three animal traits were recorded: body mass, quantity of fruit in diet (low, medium, or high), and ability to fly (able or unable). Both living and extinct species were recorded, with information gathered from existing databases. In cases where information was unavailable from any existing databases, primary literature was consulted. For each island, the researchers calculated pre-extinction species richness in order to compare it to current species richness.
The three most important island characteristics found were distance to mainland, island area, and maximum elevation. In other words, small, mountainous islands that were very far away from the mainland were most likely to experience extinctions. For animal traits, the researchers found that large, flightless animals were the most likely to go extinct. Extinctions were found to decrease average community body mass by an average of 37%, with the largest extinct animals found to be reptiles and birds. Tortoises, giant lizards, flightless waterfowl, and the dodo are all examples of large frugivores that were found to have gone extinct on the islands studied.
The researchers speculate that smaller islands are less tolerant of disruption due to limited resources, which also explains why mountainous islands are more prone to extinction – they have less available habitat. Isolated islands are also more likely to contain unique animals, and the researchers note that gigantism and flightlessness are (or were) more common on isolated islands than in other environments. Larger animals are more prone to extinction due to their larger energy and space requirements, and flightless animals are more prone due to their inability to escape hunters or terrestrial predators like dogs and cats.
Preserving island ecosystems is critical to biodiversity and the field of biology itself. Charles Darwin formulated his theory of evolution in large part due to observing the unique animals found on the Galapagos Islands. Islands are a sort of natural laboratory, in which animals are (largely) cut off from outside influence. Destroying communities like the Galapagos hinders scientific exploration into evolution and biology, and could have consequences for our own species.
The researchers stress that the effects of the loss of large frugivores are not understood because of an overall lack of studies in this area. More research must be done to understand how the loss of these animals affects sensitive island ecology. If we are to protect our sensitive island communities, we need to protect frugivores from extinction, and we should place a higher priority on small, isolated islands and large, flightless animals. In areas where large frugivores have gone extinct, replacing them with similar living species may become necessary.