Caught in a Booby Trap

How did the blue-footed booby evolve those lovely blue feet? Genetic analysis shows that the blue-footed booby shared a recent common ancestor with the grey-footed Peruvian booby of coastal South America. Unlike the latter, whose diet includes anchovies and sardines, the blue-footed booby is a sardine specialist that feeds by plunge diving exclusively into cold-water upwellings, like those of the Cromwell current. Sardines normally abound in Galápagos, but not anchovies—the strong currents quickly carry away their young. But sardines are also rich in blue-green coloring agents (carotenes) that show up in the feet of successful booby divers. Hence it’s an uncanny “fit” of the blue-footed booby to island conditions is uncanny: did it evolve in Galápagos from continental ancestors who followed trade winds west? The species also regulates brood sizes in relation to sardine supply via flexible siblicide, which surely helps in coping with ENSO. It shares siblicide with its close Galápagos relative, the Nazca booby, as well as aggressive NAV behavior in which nonparental adult visitors peck at innocent, unrelated chicks until they bleed or drown. New evidence from brown boobies—another close relative—suggests that this behavior evolved as a result of benefits from survival cannibalism during extreme El Niños.

Galápagos Derailed

The same species of Galápagos rail, a 6-inch insectivorous ground bird, has been reported on all eight islands with a highland humid zone. Evidence suggests that the rail colonized Galápagos at roughly the same time as giant tortoises, which evolved into 15 species with life spans of 150 years. So why is there just one species of rail? The question is especially germane given reports of the rail’s “reduced flight ability” (as is true of many island-dwelling rails), which would effectively isolate different island populations. And why has the species survived when so many similar rails have succumbed to human influence on other Pacific islands? The human history of Galápagos helps to answer these questions. Two things have saved the Galápagos rail from extinction: (1) It remains capable of flying between islands, which explains why it failed to differentiate like tortoises. (2) There have been massive efforts to eradicate or control invasive species, restoring habitat for rails to repopulate.

“An Inexplicable Confusion”

While visiting Galápagos, the young Charles Darwin was confused by the similarity of various finches he observed. We now understand that what we see as different finch species are “species before speciation is complete.” The confusion is inherent: many of them remain similar enough to form fertile hybrids. But a robust difference exists between the groups of ground finches and tree finches, raising the question, what prompted the evolution of that clear distinction? The primary habitats for tree finches are tree species of the wonderful Galápagos daisy genus, Scalesia, that dominate the forests of the humid areas of various islands. Did the evolution of daisies into trees influence the evolution of differences between ground and tree finches? For that matter, how did highland trees evolve from lowland shrubby daisies, thus forming the highland habitat for tree finches? Several lines of evidence, including a contemporary interaction analysis of various birds and trees, suggest that the giant daisies of Galápagos and the tree species of Darwin’s finches coevolved.

The “Secret Recipe” of Galápagos

Galápagos tortoises demonstrate the special “creative force” of evolution in the archipelago, having radiated into 15 species—each with a characteristic shell shape—within the last 3.2 million years. Formed over an active mid-ocean volcanic hotspot, Galápagos islands have also changed dramatically in the same period, providing new and diverse “petri dishes” for tortoise evolution. In these new homes, which are low, dry islands, where the tortoise’s main food is prickly pear cactus (which has concurrently evolved a protective treelike stature), tortoises evolved impressive new features, including saddlebacked shells and extra-long limbs. On all the islands where they occur, tortoises serve as “ecological engineers,” building suitable niches for themselves (and incidentally for other species). In the case of domed-shell tortoises, those niches include tortoise-maintained wallows, meadows, and migration trails. Heavily hunted in Galápagos history, most tortoise species are rebounding today, some from tortoises rediscovered in the novel places they had been carried by early mariners in their quest for food.

Tough Times for the Loneliest Albatross

The waved albatross of Galápagos, the world’s only tropical albatross, has survived millennia of flying in low-velocity winds by foraging relatively short distances to the Peruvian upwelling. The advent of longline fishing along the coast of Peru and recent changes in El Niño have caught the albatross in a demographic pinch, rendering it critically endangered since 2007. Because reproductive pairs lay only a single egg per year under the best of circumstances, the conservation challenges are noteworthy and all the more serious because recurrent El Niño events shut down the albatrosses’ food supply. Effective conservation measures include human intervention to save “marooned” and abandoned eggs, to change longlining practices in the Peruvian coastal fishery, and to provide safe refugia on a small island off the coast of Ecuador where hungry albatrosses can raise chicks even closer to the upwelling. But until our efforts suffice to reduce greenhouse gas emissions and the growing severity of El Niño events, we shall all have an albatross hanging around our necks: the beautiful waved albatross of Galápagos.

One Big Social‒Ecological System

Galápagos is no longer the “little world within itself” that Darwin visited: it is now one big social‒ecological system (SES): the evolutionary fitnesses of all, or nearly all, Galápagos organisms are today a joint product of natural conditions and human activity. But this also makes Galápagos an effective microcosm. At first glance, the place seems totally unique: it is small and isolated, its habitats are extreme, its wildlife is peculiar, and its initially tiny human population is diverse and growing rapidly. But on a larger scale, are those not all true about Earth itself? The small size and isolation of Galápagos may exacerbate some threats and challenges, its position in the heartland of El Niño may exaggerate the swings and changes of contemporary climate, and its land area for human use is close to a record low (3%, although human impact reaches to every corner of the archipelago), but these conditions make both problems and solutions show up faster in Galápagos than elsewhere. Galápagos is now a valuable test bed for the sustainability challenges facing the whole of planet Earth.

Beautiful on the Inside

Marine iguanas stand in stark contrast to the Galápagos rails. They vary enormously in space by size and color, supporting classification into 11 subspecies (whereas rails are monotypic). And they vary in time, especially males, which change to bright colors in the mating season—some to the point of being bright red and green “Christmas iguanas.” They vary over time in an additional special way: iguanas shrink up to 20% (or 2.7 inches) during the food scarcity of El Niño events. They have evolved the capacity to shut down their normal stress response when the ocean gets warm, thus becoming quiescent and riding out the storm. The larger the iguanas, the more they shrink and the longer they survive. Furthermore, nearly all marine iguana subspecies have increased in size since 1905, while, at the same time, climate change has made El Niño events stronger and longer. Could climate change be driving the evolution of larger marine iguanas? Will iguanas be able to keep up as El Niño worsens?

Not Earthbound Misfits After All

This chapter explores two delightfully unique, flightless seabirds: the Galápagos cormorant, one of the world’s most unusual organisms, and the Galápagos penguin, the only penguin to swim in the Northern Hemisphere. Three themes stand out: first, in pre-settlement Galápagos, neither species suffered great disadvantage because of flightlessness. Having no terrestrial predators allowed both species to nest on land near water’s edge, to specialize in diving for prey in the rich, cool Cromwell upwelling, and to prosper during over a million years of flightless life in Galápagos. Second, from very different evolutionary origins, the two seabirds evolved a fascinating evolutionary convergence in the archipelago—not their flightlessness per se, because penguins were already flightless when they arrived. Instead, there are striking similarities in their uniquely opportunistic mating practices, including the cormorant’s very unusual facultative polyandry. Third, does the older flightless specialist, the penguin, have the advantage when El Niño causes food supply to falter, or does the advantage go to the cormorant, the seabird specifically retooled by evolution for conditions in Galápagos? Forty years of census data show that penguins react slightly more quickly to ENSO and with more population flux, but that both species show impressive reproductive resilience.

Fishing in a Common Pool

By 1992, overfishing along the South American coast prompted a large migration to Galápagos of fishers, middlemen, and buyers, who began a “gold rush” harvest of brown sea cucumbers (a spiny marine organism) for the lucrative Asian market. Attempts to regulate that harvest by the government of Ecuador and the Galápagos National Park Service provoked more than a decade of protests and violence, which were only curbed when fishers were given an effective role in decision-making. But because the brown sea cucumber requires a minimum density for reproduction—an example of the Allee effect—it proved too challenging for the first participatory management system, which failed, but it led to a simpler system that continues successfully today. Galápagos is proving to be a showcase not simply for genetic evolution but also for the cultural evolution of new forms of governance, ideally including sustainability that it can then model for the world.

Out of the Ordinary

Galápagos stands out for its vast collection of extreme life: the world’s only tropical albatross, its only flightless cormorants, and its marine iguanas; three colorful species of boobies; and 15 species of giant tortoises, one on each major volcano, except for one especially large volcano that has two. Each of these organisms has evolved adaptations to the unique rigors of life in an isolated archipelago on the equator. As Galápagos has recently grown ever more connected to the world system, many species’ adaptations have become vulnerabilities in the face of human-induced change. Fortunately, long before people arrived, evolution also endowed native species with forms of resilience to local perturbations like El Niño events and periodic droughts. The eight case studies in this book highlight these vulnerabilities and resiliences and argue that the mismatch between them, stemming from human impact, is the core conservation challenge today.