Discuss two factors that may trigger an adaptive radiation and provide an example of each.

Adaptive radiation is the process in which a single ancestral species evolves into a wide array of descendant species that are adapted to a variety of different ecological niches. There are several factors that can trigger adaptive radiation, but two key factors are the availability of ecological opportunity and the presence of key innovations.

Ecological opportunity refers to the availability of unoccupied or underutilized ecological niches that can be exploited by a population. When a population encounters a new environment with abundant resources and few competitors, it can lead to rapid speciation and the evolution of diverse species. An example of this is the adaptive radiation of Darwin's finches in the Galapagos Islands. These finches diversified into multiple species with different beak shapes and feeding habits in response to the availability of various food sources and ecological niches on the different islands.

Key innovations are traits or adaptations that allow a population to exploit new resources or habitats. When a population evolves a key innovation, it can lead to the rapid diversification of descendant species as they exploit the new opportunities provided by the innovation. An example of this is the adaptive radiation of mammals during the Cenozoic era. The evolution of key innovations such as the development of placental reproduction and the ability to exploit diverse food sources allowed mammals to rapidly diversify and occupy a wide range of ecological niches.

In both of these examples, the availability of ecological opportunity and the presence of key innovations triggered adaptive radiation, leading to the evolution of diverse descendant species adapted to different ecological niches.