Adaptations and diversification on isalnds
Island research has been helping scientists understand the evolutionary process ever since Darwin returned from the Galapagos. This is because islands are suited perfectly with the mechanisms for species formation and adaptive radiation-- they're like laboratories of evolution.
Darwin's research on the Galapagos islands led him to the conclusion that species are not independently formed. Three observations contributed to this realization, the first of which was the fact that related populations on neighboring islands varied in appearance. Second, Darwin noticied that inhabitants of an island are more related to other inhabitants of adjacent land forms, rather than those occupying similar environments in other places in the world. Third, upon returning to England, John Gould informed Darwin that the various kinds of birds in the Galapagos that were though to belong to different families, were in fact members of the same family. Would Darwin have come back with the same knowledge and insight as he did after visiting the Galapagos, if he had instead journeyed to another island? Perhaps, but Darwin was extremely lucky in stumbling upon the diverse species found on the Galapagos.
The reason islands are so special is because of their small size, distinct boundaries, and abundance of inhabitants. All of these traits make it easier for scientists to observe and interpret patterns of evolution. Groups of islands are even better for observing evolutionary diversification, because they serve as replicates in which general can be sperated from unique evolutionary outcomes. Also, since many islands emerge/ have emerged fairly recently, they serve as blank slates for colonization and diversification. Not only are most islands new, but many are distant from other land masses, allowing for independent and unconstrained evolutionary divergence.
A big question that many scientists are asking is about speciation. Does it occur before ecological divergence and coexistence, or does divergence cause speciation? The answer is close to being found, most research has been conducted on islands. An important fact that scientists noticed is that speciation occurs on some islands but not on others. It has been found that small islands formerly connected to larger land masses experience significantly more speciation than islands who have been singular since their emergence. But small islands in general have little speciation, which suggests that pressure from natural selection is not enough to spilt one species into two. Divergence is the driving force of speciation. However, other factors also influence speciation, including the dgree of isolation of a particular island.
Adaptive radiation, in the context of ecological opportunity, comes from speciation and adaptation. The beginning of it all is the colonization of a new or species-poor environment. Sympatry of two or more species creates competition for resources, and natural selection takes over by favoring certain adaptations. Morphological divergence and resource speccialization occurs as a result. Islands are again, favored areas to study adaptive radiation because pairs of species occur in sympatry on some islands and alone on others.
Darwin's time spent on the Galapagos foreshadowed many of these evolutionary theories, including divergence of populations in allopatry and the diversification that occurs during adaptive radiations. Continued research conducted on islands has further increased our understanding of evolution; the geographical and evolutionary dynamics of biotas on islands and extinction in particular. Darwin was not able to recognize these things at the time, but his observations and recordings served as important tools for scientists of today to continue their development on the theory of evolution. Most of what we know today can still be attributed to Darwin's original insights.