Final answer:
Exotic species are particularly threatening to islands and marine ecosystems because of their isolation and distinctive species compositions, which are not adapted to deal with introduced predators or competitors. Conservation efforts aim to protect these vulnerable ecosystems by preventing and controlling invasive species.
Step-by-step explanation:
Exotic species, also known as invasive species, represent a substantial threat to certain types of ecosystems, particularly those that are geographically isolated or have a high rate of endemism. Islands and marine ecosystems, due to their isolation and unique species compositions, tend to be highly susceptible to the disruptive effects of exotic species. For example, the introduction of an exotic predator in an island setting can decimate local fauna that have not evolved to cope with new predators. Similarly, in marine ecosystems, species like the zebra mussel (Dreissena polymorpha) have caused significant ecological disruption. In these environments, the exotic species often have no natural predators, allowing them to spread unchecked and outcompete, predation or otherwise harm native species.
Conservation efforts often focus on protecting such fragile ecosystems by trying to prevent the introduction of invasive species and, when possible, by working to remove or control them if they become established. It is also important for conservationists to consider ecosystem diversity and to plan ecological preserves that include a variety of ecosystems in order to support a greater range of species, including those that are endemic and potentially more vulnerable to invasive species.