Island ecology
As a result, island ecosystems comprise 30% of the world’s biodiversity hotspots, 50% of marine tropical diversity, and some of the most unusual and rare species.
Because they are simple systems, islands provide an opportunity to study processes of extinction that can be extrapolated to larger ecosystems.
Island populations are small and exhibit low genetic variability (see founder effect), but are isolated from the predators and competitors that they initially evolved with.
Some of these unique adaptations are reflected in charismatic island species such as the Malagasy hippopotamus, Komodo dragon, or pygmy mammoths.
The collection of differences in morphology, ecology, physiology and behaviour of insular species compared to their continental counterparts is termed Island syndrome.
Because the distributions of these populations are limited by their island habitats, they tend to have fewer individuals than their mainland counterparts and lower genetic variation.
[16] Today there are over 500 million people on islands, all dependent on local resources either directly (traditional use) or indirectly (ecotourism revenue).
Overharvesting of ocean fauna is particularly troubling as yields of coral reef fish species are an important food source for island populations.
Humans have contributed to globalization and decreased effective isolation of island communities, allowing for invasion of exotic species.
Feral cats and dogs have also greatly diminished native vertebrate populations on islands, through both predation and disease.
The higher impact of introduced and nonnative species on islands is largely a result of lower biodiversity levels (Platenburg et al.).
However, islands’ vulnerability to introduced species is also due to agricultural, economic, and health differences as compared to continental land (Russel et al.).
The smaller land area and population sizes of islands compared to continents create greater vulnerability to the impacts of introduced species (Russel et al.).
There are many examples of animal species such as birds, reptiles, and aquatic insects being harmed by the introduction of predators such as rats, cats, and ants.
At a colony in Hawaii, at least 20% of wedge-tailed shearwater eggs were taken by mynas, dark-plumaged birds of the starling family (Towns et al.).
The Cuban tree frog is known for its ability to survive under harsh conditions, and it is highly adaptable, as it will eat a wide variety of organisms (Platenberg).
In contrast to the accidental introduction of the Cuban treefrog, the cane toad was deliberately introduced to control agricultural pests (Platenberg).
In general, when the introduction of a nonnative species results in extinction, the ecosystem experiences losses in some trophic levels (Platenberg).
This phenomenon is seen in New Zealand, where the loss of bird species may have changed dynamics in avian-induced vegetation communities and impacted abundances of forest plants (Platenberg).
Pacific rats, for example, were thought to be causing the local extinction of large, nocturnal ground-dwelling lizards, and they were assumed to have minimal effect on diurnal species, those that sleep at night, such as shore skinks (Wood et al.).
This can be due to sea level rise, the intrusion of salt water into freshwater habitats, or species inability to adapt to increasing temperatures and extreme weather events.
[20] In more isolated areas, such as the Southern Ocean Islands, indirect effects such as invasive species and global warming can play a greater role in influencing populations than overexploitation, pollution and habitat loss.
[23] Other directions include habitat restoration, and eradication of introduced predators, ungulates, and exotic plants (via hunting, removal or biological control).
On many islands, scientists and managers are studying traditional practices of indigenous populations as potential conservation solutions.
In some cases, limited-take systems that serve the community may provide a better alternative to fully closed protected areas, if there are not enough resources for proper enforcement.
