The niches of nearly all species are narrow in at least one and often several ways. Anolis lizards eat only live arthropods, as we saw in Chapter 46, and not plants, fungi, or dead organisms, though these resources are available in their habitats. Similarly, among the small birds that live in woodlands, there are warblers that hunt insects among the leaves in the trees, thrushes that seek insects in the soil underneath, and woodpeckers that find insects under bark. Each kind of bird is a member of a diverse family of related species that all seek insect prey.

Usually, some aspect of the niches of closely related species is similar (all Anolis lizards are alike in their dietary preferences for small live prey), and so are evolutionary conserved. This observation is called phylogenetic niche conservatism. It is commonly seen and speaks to the strong influence of evolutionary history in shaping at least some aspects of the niches of organisms.