Science / Medicine : Galapagos Isles Remain a Science Lab : Evolution: Wellspring of Darwin’s theories 145 years ago, life on the isolated archipelago continues to be studied by researchers.
“Both in space and time, we seem to be brought somewhat near to that great fact--that mystery of mysteries--the first appearance of new beings on this Earth.”
The words, written by a young Charles Darwin in 1845, were describing the Galapagos Islands.
Nearly a century and a half later, the storied archipelago 600 miles off the Ecuadorean mainland remains a fertile natural laboratory for scientists exploring animals, plants and geology. Evolution, long synonymous with Darwin’s work here, remains a unifying theme.
Exotic birds and prehistoric-looking reptiles are the biggest draws for the researchers who flock to the Charles Darwin Research Station to conduct their field inquiries. More than 400 scientific missions have visited the islands since the station was established by an alliance of international conservation groups in 1960.
The diverse “Darwin’s finches,” the giant tortoises from which the islands take their name, boobies of various hues, saltwater-snorting marine iguanas and playful fur seals are among the animals that continue to provide scientists with insights into natural selection and adaptation.
Research is also being conducted to determine how to preserve this fragile ecosystem in the face of increased tourism and immigration.
The Galapagos are conducive to scientific exploration because a limited number of species have evolved in this nearly pristine setting remote from the mainland and, in large measure, from human incursion. And the islands’ isolation from one another in many cases has led to the emergence of different species on different islands.
In addition, a lack of natural predators has left the animals fearless of outside species, including humans and, therefore, easily accessible for study in the wild. Finally, rapidly changing climatic conditions on the volcanic islands allow researchers to chart how various species adapt to their environment over short time periods.
The Galapagos “are sort of a microcosm of what goes on everywhere,” says Craig MacFarland, president of the Charles Darwin Foundation for Galapagos Isles. But “it’s a simpler system so it’s easier to understand and describe the dynamics.”
Darwin’s observation of the tortoises, mockingbirds and finches on the various islands, for example, set in motion thoughts that eventually led to his landmark theory that the fittest of any species survive through a process of evolution.
At any given time today, MacFarland says, there are about five research missions in the islands, in addition to a scientific staff of 15 at the Darwin station. Some scientists pursue “knowledge for knowledge’s sake"--much of which can also be applied to conservation efforts--while others conduct research directly aimed at the preservation of flora and fauna, much of it unique to the Galapagos.
At the research station, a program to breed tortoises in captivity before releasing them into the lush, green highlands has helped increase their numbers dramatically.
Howard L. Snell, an assistant professor of biology and curator of herpetology at the University of New Mexico, has engaged in both pure research and preservation endeavors.
Snell, who has performed research in the Galapagos since 1977, has studied, among other things, how land iguanas retain a stable size through the process of natural selection.
Initially, he found that larger females produced more offspring that survived than did smaller females. But when droughts followed an El Nino--unusually warm waters, which take a harsh toll on sea life, combined with significantly increased rainfall--Snell discovered that larger iguanas were the first to starve because they needed more food, which was scarce.
Hence, strong natural selection pressures tend to work, under different conditions, against the evolution of iguanas that are either larger or smaller than the norm. The iguanas--avid sunbathers whose expression appears to that of a wry smile--have a arithmetic mean length of 15.7 inches as adults.
More recently, Snell has undertaken a four-year project in conjunction with the Darwin Foundation to document the islands’ biological diversity as well as the human impact on the archipelago. The data will be given to the Ecuadorean government and the Galapagos National Park Service for use in charting tourism and development policy.
Dave Anderson, an evolutionary ecologist at UC Davis, started working in the Galapagos as a research assistant to Princeton University biologist Peter Grant and has been conducting his own work since 1983. Grant is a leader in Galapagos research through his work with finches and other birds.
Anderson is studying fratricide--the ultimate in sibling rivalry--among masked boobies. Unlike other sea birds that raise a single offspring from a single egg, these striking white and black boobies lay two eggs each breeding cycle.
Generally, the older of the two chicks wastes little time pulling or shoving its weaker sibling out of the nest. Too feeble to get back, the infant dies of exposure or starvation. The parents do not interfere.
The reason the masked boobies lay two eggs, Anderson says, is that they have a relatively low rate of successful egg hatching. The second egg is insurance in case the first fails. The birds don’t lay more than two eggs, however, because the physical cost of producing additional eggs is not worth the limited benefit, Anderson hypothesizes.
In an effort to determine whether the parents could raise both chicks, Anderson matched two equal-size chicks in a single nest. He was able to do this because the boobies treat any chick in their nest as their own.
By carefully managing the chicks’ growth to prevent one from gaining an upper hand, Anderson found that the parents would indeed raise both offspring until they could make it on their own.
The success rate of getting at least one chick to fledge increased from 58% in the single chick brood to 93% in the two-chick broods. Why, then, does this not happen naturally? The answer, Anderson says, is the need to prevent the population from outstriping the food supply.
Stephen Kress, a research biologist for the Audubon Naturalist Society and an ornithological laboratory associate at Cornell University, is engaged in a project to enhance the survival chances of an endangered species, the dark-rumped petrel.
Petrels, crow-sized sea birds with pink, webbed feet, build nests on the ground in soil burrows. The eggs have a long 52-day incubation period; newborns take another three months to fledge. This leaves both vulnerable to introduced predators--pigs, cats and especially rats.
Kress and his partner, Richard Podolosky, have sought to counter this danger by creating 220 artificial petrel nests in an extinct volcano--a more protected environment--on Santa Cruz Island. The scientists played recordings of petrel sounds-- cacky-poooo is a favorite--to persuade the birds that others petrels had already deemed the site safe.
Over the past three summers, more than 70% of the burrows have been visited by petrels, Kress said. Last summer, four pairs bred in the created nests--although the chicks were killed by rats. Undaunted, Kress says that even a single rat can do this kind of damage.
“This is only an experiment,” Kress cautioned. “This is not necessarily a solution.”
‘One Is Astonished at the . . . . Creative Force’
Charles Darwin spent five weeks in the Galapagos as a young naturalist aboard the ship Beagle in 1835. He combined his observations of species on the islands and their counterparts on the South American mainland when he published “Origin of Species” in 1859.
Darwin noted particularly the numerous species of finches, giant tortoises, mockingbirds and plants on the various islands of the archipelago. This diversity of unique species on islands so near to each other yet so varied in their environmental conditions planted seeds of doubt in Darwin’s mind about the accepted biblical account of creation.
“One is astonished at the amount of creative force, if such an expression may be used, displayed on these small, barren and rocky islands,” Darwin wrote of the Galapagos, “and still more so, at its diverse yet analogous action on points so near each other.”
The 13 varieties of finches, for instance, display specialized beak structures and feeding habits, each suited to the conditions on its respective island.
Some eat seeds, others insects or leaves; some remove ticks from tortoises and some drink blood from sea birds.
All of the sparrow-sized birds evolved from a common ancestor. This helped lead Darwin to his theory that, as a species adapts to its environmental conditions, “favorable variations would tend to be preserved and unfavorable ones to be destroyed. The result of this would be the formation of new species.”