The Beagle and Darwin’s Finches

Ecology is, in simple terms, the science that investigates the profusion and distribution of organisms and the interaction between both the physical and biotic environment. The habitat of an organism governs its suitability and the reaction to that organism’s ecological setting is contingent upon its genetic make up ~ a product of evolution.
G. Evelyn Hutchinson’s work, The Ecological Theater and the Evolutionary Play describes this interplay between the science of ecology and evolution.

Darwin’s second voyage of the Beagle arrived on the Galápagos Islands in September 1835. The Archipelago is a cluster of 13 islands about 600 miles west of Ecuador. This archipelago is volcanic and quite possibly mantle plume, or columns of hot rock rising from under the earth’s crust. More seismic activity is witnessed on the western part of the archipelago, where the youngest of the 13 islands are located. On these young islands earthquakes and lava flows are commonplace. There are two distinct seasons on the Galapagos. The dry season (July to December)is noted by fog and mist that hovers on higher elevations. Most rainfall occurs in March and April and the hot season runs from January through June. Seasonal change varies relative to weather and oceanographic conditions. Each island exhibits slight variance in physical environment and vegetation, due to its geographic location, size and geomorphology.

Darwin discovered that 13 species of finches inhabited the Archipelago. A member of the Passerene group, the subfamily Geospizinae of the finch family tend not to fly over water as a general rule, and so populations on one island would be, for the most part, isolated from populations on another island. Seeds comprise a large percentage of the finch’s natural diet. The finch’s bill or beak is used to crack the seeds, prior to consumption, however, the ability to crack various seeds is predicated on the size of the bill.

Vegetation varies with the season, thus seeds vary in size, relative to plant variety and abundance. Environmental factors would predicate the avilability and size of the seeds ~ some season plants would produce large seeds, and alternatively, at times they'd produce smaller seeds. But in order to survive, finches must secure nourishment and since they have only the local habitat within which to forage, they must live off the availability of food and develop coping mechanisms, to remain alive.

Remarkably, these finches developed distinct anatomical changes, most notably in the size and shape of their beaks and their behaviour. The finches beak adapted so that it could be used to crack seeds in one region, or probe for nectar imn another or forage for insects where they were the abundant source of nourishment. Yet, all finches on the Galapagos had evolved from a single species of ground-dwelling finch in South America. A diverse species had formed relative to habitat and food source ~ ground and tree-dwelling seed eaters and tree-dwelling insect eaters. This became the subject of further research on Darwin’s natural selection and adaptive radiation.

Camarhynchus pallidus, or the Woodpecker Finch, uses a twig or cactus spine as a foraging tool. Typically, woodpeckers use a long tongue to retrieve insects, but this finch uses the tool to compensate for its short tongue. The tool is manipulated to dislodge insect prey from trees. A superbly intelligent and talented bird, it even carefully selects a twig or a cactus spine according to shape, size and the particular need.

So how does this discussion of ecology and Geospizinae morphology have to do with this story? Of course, the process described above takes place over generations, so I’m naturally taking some license here in suggesting that this could be apparent in a short timeframe. Nonetheless, survival is predicated upon fitness ~ fitness of the consumer, be it the primary or secondary consumer. An organism adapts to its environment in order to continue to be successful in securing required nourishment. In the case of a more hostile environment, a successful or fit species develops different traits to accomplish this. As with the woodpecker finch, when neither the bill nor the tongue is naturally adequate enough to survive, he employs a device, scavenged from its habitat, to use as a tool.