Initial Colonizing Species

Initial Colonizing Species—Adaptive Radiation

Before humans discovered the Hawaiian Islands, relatively few species managed to reach the isolated island chain. The first colonizing species that somehow found their way to the remote archipelago of the Hawaiian Islands may have been birds blown off course, insects carried by the wind, or seeds floating on the water.

Seeds were also carried to the Islands in the feathers and stomachs of birds, while mud on the birds’ feet also carried tiny eggs of land snails and other species. Some plants, insects, reptiles, and other species may have reached the Hawaiian Islands by rafting over the vast Pacific Ocean on logs or other floating debris. These species were somehow able to cross thousands of miles of ocean and reach the Hawaiian Islands, then reproduce and become established, eventually adapting to their new Hawaiian habitats.

Populations of species that established themselves in the Hawaiian Islands often became separated from one another, spreading out and taking advantage of different ecological opportunities. For example, a single finch bird species spread out and utilized various food sources. Some of the birds fed on insects while others ate seeds or flower nectar. The bird populations eventually became divided, with each group taking advantage of different food sources.

Over many generations these different bird populations evolved specialized beaks to take advantage of their specific food sources. The separated sub-populations became unique species, and each of these endemic Hawaiian species uniquely adapted to its particular habitat.

The single species of finch birds that evolved into many new species of honeycreepers is an example of the evolutionary process of adaptive radiation, which results in new species development—in this case a single species evolving into more than 50 unique species and subspecies of Hawaiian honeycreepers, some with beaks designed for probing bark and grasping insects, others better suited for eating fruit or sipping nectar.

This evolutionary process of adaptive radiation also occurred in plant species. For example, some coastal plants such as naupaka kahakai (Scaevola sericea, beach naupaka) first took hold in coastal areas after the seeds floated here. Eventually the plants grew at higher and higher elevations up the sides of the Hawaiian Islands’ volcanic slopes, and these higher elevation plants developed variations in their leaves and other characteristics that increased their chances of survival in the different habitats.

As the beach naupaka species expanded its range and began to grow at higher elevations, six new naupaka species evolved on the slopes of Hawaiian volcanoes. These higher elevation species are now known as naupaka kuahiwi (Scaevola species), and are very different from the original coastal naupaka species that first colonized the Hawaiian Islands.

Over hundreds of thousands, and even millions of years, the plants, birds, insects, and sea life that became established in the Hawaiian Islands evolved into thousands of new species with unique traits that aided their survival in the Island habitats.

The rich tropical soils of the Hawaiian Islands as well as abundant sunlight and plenteous water provided all of the key ingredients of life, creating an isolated tropical paradise able to produce the fascinating variety of species that now inhabit the air, land and water of the Hawaiian Islands.

The Hawaiian Islands today remain a natural showcase of active biological and geological processes. The active volcanoes of the Hawaiian Islands continue to create new land even as rains erode the islands back into the sea. Thousands of rare and endangered plants, animals, and marine species found nowhere else continue to thrive in native Hawaiian ecosystems. Unfortunately, many of these species cling to existence in their diminishing native habitats, and face a variety of threats to their continued survival.

Scientists consider the Hawaiian Islands a living laboratory, and come to the Islands from all over the world to study the Islands’ species and scientific processes. The endemic species of the Hawaiian Islands are the ongoing record of millions of years of evolution and also a precious living testament to the complex processes of evolutionary biology occurring over millions of years on a relatively tiny group of islands surrounded by thousands of miles of ocean.