Increasing travel, trade, and tourism associated with globalization and expansion of the human population have facilitated intentional and unintentional movement of species beyond natural biogeographical barriers, and many of these alien species have become invasive. Invasive alien species (IAS) are considered to be one of the main direct drivers of biodiversity loss at the global level1, 2
. It is clear that IAS can produce substantial environmental and economic damage, and their negative effects are exacerbated by climate change, pollution, habitat loss and human-induced disturbance. Increasing domination by a few invasive species increases global homogenization of biodiversity, reducing local diversity and distinctiveness.
IAS can change the community structure and species composition of native ecosystems directly by out-competing indigenous species for resources. IAS may also have important indirect effects through changes in nutrient cycling, ecosystem function and ecological relationships between native species. IAS can also cause cascading effects with other organisms when one species affects another via intermediate species, a shared natural enemy or a shared resource. These chain reactions can be difficult to identify and predict. Furthermore, aggregate effects of multiple invasive species can have large and complex impacts in an ecosystem.
Invasive species may also alter the evolutionary pathway of native species by competitive exclusion, niche displacement, hybridization predation, and ultimately extinction. IAS themselves may also evolve due to interactions with native species and with their new environment.
IAS can directly affect human health. Infectious diseases are often IAS imported by travellers or vectored by exotic species of birds, rodents and insects. IAS also have indirect health effects on humans as a result of the use of pesticides and herbicides, which infiltrate water and soil.