#Radiation island hawaii drivers#

On Maui and the Big Island, for example, several species within the silversword alliance have adapted to the drier environments of higher elevations. The fruit of this plant has sticky appendages that could easily have allowed the seeds of an ancestral plant to hitch a ride on a migratory bird.Īs with the drosophilids, the descendents of the original colonizing species diversified dramatically as they underwent multiple founder events and spread into new environments. Today the closest non-Hawaiian relative of the silversword alliance is a small, daisy-like plant called a tarweed that grows on the west coast of North America. In fact, all appear to be descended from a single ancestral species that arrived on the Hawaiian islands millions of years ago ( Panel 3). In the 1980s, biologists studying the genetics of these species realized that they are far more closely related than they appear. They occupy habitats ranging from near sea level to the upper limits of vegetation on mountains and from semiarid desert areas to thick rainforests. The 30 members of the alliance include trees, shrubs, mats, vines, and the rare and magnificent flowering silverswords that live on the high slopes of Haleakala in Maui and Mauna Kea in the Big Island (see Figure 13). The 30 species of plants belonging to what is called the silversword alliance are a superb example.įor decades, botanists had known that all of these species are related because their leaves and flowers share certain characteristics, which is why the species are termed an “alliance.” But in other ways the plants are so different that the nature of this relationship remained obscure. While the adaptive radiation of the drosophilids in Hawaii has resulted in a remarkable number of species, other radiations have produced descendants with an even greater range of physical characteristics.

Taking all these processes into account, and testing how they operate in different systems, may allow us to identify universal principles underlying adaptive radiation.Many Other Species Have Undergone Adaptive Radiations in Hawaii All of the above mechanisms seem to have played a role in giving rise to the exceptional diversity of morphological, ecological and behavioral traits represented among the many species of Hawaiian Tetragnatha. Still others show evidence for character displacement by close relatives, often resulting in convergent evolution of stereotyped ecomorphs. Others have shifted into new environments and evolved traits that appear to be adaptive in those environments.

Several clades appear to have diversified in allopatry under a narrow range of ecological conditions, highlighting the role of niche conservatism in speciation. Among the lineages that make up this remarkable radiation, we find evidence for multiple diversification modalities. We present the most taxonomically comprehensive phylogenetic hypothesis to date for this group, using 10 molecular markers and representatives from every known species across the archipelago.

#Radiation island hawaii drivers#

Here, we characterize the ways these different drivers contribute to present-day diversity patterns, using the exemplary adaptive radiation of Hawaiian long-jawed orbweaver ( Tetragnatha) spiders. Diversification may occur via several mechanisms including non-adaptive divergence, adaptation to novel environments, or character displacement driven by competition. However, different adaptive radiations show a variety of different patterns, making it difficult to come up with universal rules that characterize all such systems. Adaptive radiation provides the ideal context for identifying and testing the processes that drive evolutionary diversification.