The distinct ecological importance of species supports functional diversity and has a direct bearing on the species composition of the site, and therefore on overall biodiversity. For example a keystone species will be more important than other species for conserving overall biodiversity. Similarly a species of tree in a tropical rainforest which supports a large number of endemic invertebrate fauna and provides food to vertebrates would make a greater contribution to global biodiversity than an alpine plant in a temperate country which has much less species dependant on it for survival.