Tropical species are accustomed to living in a small temperature range and thus may be unable to cope warming temperatures. Many species appear to be living at or near their temperature optimum that lets them thrive. Even changes of a few degrees could upset the balance. Once the temperature gets above the thermal optimum, fitness levels will most likely decline, and there may not be much they can do about it. Previous studies focused on plants and habitats in the Arctic but it now appears that global warming could have a dramatic impact on tropical species.