answers: human travel
context: translocations of species have also been proposed in the interest of genetic conservation, which advocates the introduction of new individuals into genetically depauperate populations of endangered or threatened species. The above examples highlight the intent of humans to introduce species as a means of incurring some benefit. While these benefits have in some cases been realized, introductions have also resulted in unforeseen costs, particularly when introduced species take on characteristics of invasive species. Unintentional introductions occur when species are transported by human vectors. Increasing rates of human travel are providing accelerating opportunities for species to be accidentally transported into areas </s> in sparse and eroded ecosystems, which then promotes the growth and reestablishment of native species. Another benefit of non-native species is that they can act as a substitute for an existing ecosystem engineer. In many cases, non-native species can be introduced to fill a niche that had previously been occupied by a native species. Many non-native species have similar characteristics and functions and can keep an ecosystem functioning properly without collapse. An example of this is the Aldabra giant tortoises, which were introduced on several small islands and have successfully taken over the roles of herbivore and seed disperser. The </s> and is increasing because of tourism and globalization. This may be particularly true in inadequately regulated fresh water systems, though quarantines and ballast water rules have improved the situation. Invasive species may drive local native species to extinction via competitive exclusion, niche displacement, or hybridisation with related native species. Therefore, besides their economic ramifications, alien invasions may result in extensive changes in the structure, composition and global distribution of the biota of sites of introduction, leading ultimately to the homogenisation of the world's fauna and flora and the loss of biodiversity. Nevertheless, it is difficult to unequivocally attribute extinctions to
question: most exotic species are introduced into a new environment accidentally as a result of