One million species are under threat of extinction worldwide, primarily due to adverse human impact. The loss of a species is an ethical tragedy, but additionally, it can have dramatic effects on the functioning of ecosystems on Earth. In each ecosystem, species have their roles. These roles depend on the characteristics of the species, like their size, weight, shape, reproductive capacity or the food resources they use. If some species are similar, they can sometimes substitute each other and keep the ecosystem going even if one of them is lost. However, the accumulated loss of many species can lead to ecosystem degradation with a direct adverse effect on human well-being.