Welcome to Superoceras, a blog about science and natural history, slightly biased towards paleontology and zoology, but inclusive of all sciences. Started in October of 2009, my goal is to communicate scientific knowledge (and the occasional piece of nonsense) in an informative and entertaining manner. Feel free to contact me with questions, comments, concerns, or criticism at superoceras(at)gmail(dot)com, and follow me on Twitter @Superoceras for all that and more in 140 characters or less!

Wednesday, February 09, 2011

In Darwin's Footsteps: Field Studies in the Galápagos Archipelago (Part 1)

A humble explorer, pointing towards the Pinnacle Rock of Isla Bartolomé.

On 27 December, 1831, The HMS Beagle set sail on what would become one of the most influential voyages of all time. On board was a young gentleman naturalist who, despite suffering from seasickness on a regular basis, kept detailed notes, collected valuable specimens, and made keen observations on the geology, biology, anthropology and ecology of many of the southern continents and islands. This man was Charles Darwin, and it was on this second voyage of the Beagle that he first began his musings on his theory of evolution.

A Galápagos marine iguana heats up after a swim on a pāhoehoe flow on Isla Isabela.

The most famous stop on Darwin's voyage was undoubtedly the Galápagos Archipelago. It was here that he encountered giant tortoises, friendly mockingbirds, and "impish" marine iguanas. Today, visitors to the islands can still encounter these unique animals. A few years back, I was lucky enough to become one of those visitors. Naturally, I thought that Darwin Week would be a perfect opportunity to share some of the things I learned (and photos I took) while I explored "Las Islas Encantadas".

A brown pelican (our guide Billy's favorite animals in the archipelago) on the red cliffs of Isla Rábida.

Despite their location on the Equator, visitors to the Galápagos Archipelago should not expect a hot, tropical climate. The temperature is relatively mild, ranging from 19-30° C annually (remarkably cooler than it can be in the Washington, D.C. area in the height of the summer). It’s also very arid, with little annual rainfall, even in the wet season. From late June through December, the Galápagos experience their cool, dry season known as garúa. It is marked by cooler temperatures, choppier seas, and winds blowing in from the southeast. The physical manifestation of the garúa comes as a heavy mist that forms 300-600 m above sea level and hovers around the tops of volcanic cones. This is an awesome sight to witness from above or below, and as a result of this mist, the highland regions of the islands receive more precipitation than the lowlands. This precipitation concentrates itself on the southern and eastern faces of the islands, where the wind blows and collects it.

Garúa descends on the uplands of Isla Rábida.

The waters of the Galápagos are also remarkably cool. Even though I was warned of this beforehand, the first time I snorkeled I was still shocked by just how cold it was, even in a wetsuit. This is a direct result of local oceanic currents and the process of upwelling. The Humbolt and Peru Currents bring cold Antarctic water on a one-way trip to the islands, as there is no landmass between to intercept it. These currents move that colder water away from South America and west towards the Galápagos, causing upwelling in coastal waters. As offshore winds blow warm surface water away from the islands, the cool water coming in wells up from beneath to replace it, keeping the water chilly year round.

The lichen covered ʻaʻā of Isla Tintorera almost resembles the fin of the islands namesake, the whitetip reef shark.

The Galapágos Islands are a world unto themselves. Seperated from mainland South America by 1,000 km, they have been relatively isolated for the majority of their short geological history. The result of oceanic hotspot volcanism, many of the islands are actually the tops of submarine volcanos (with the exception of some of the eastern islands, which are composed of uplifted submarine lava). The effects of this volcanic activity can be seen all over the island chain. Beautiful flows of pāhoehoe lava cover the beaches of Isabela Island, where the small island of Tintorera off its shore are covered in jagged ʻaʻā lava. Bartolomé is littered with spatter cones and lava tubes, and has the remains of a tuff cone (Pinnacle Rock) and a sunken volcanic crater. Rábida and Santiago's shores are covered in volcanic sand beaches - the result of erosion by wind and water - and sport volcanic cones as well. And for all of you structural geologists out there, there are even fault bound, down dropped blocks of land (known as graben) on the northern tip of Santa Cruz. All of these examples provide a series of snapshots that help one visualize the gradual formation of these islands over time.

A pretty sick lava tube, just hanging out on Isla Bartolomé.

On Tintorera Island, the beaches are made up of black basalt mixed with medium sized coral fragments. On San Cristóbal, parts of the beach are comprised solely of bivalve and gastropod shells, and the spines of echinoids. Almost any beach you set foot upon that is not red, brown, or black, is probably made up of quartz sand and the wave washed, ground up remains of marine organisms. Even the white sand beaches of some of the islands are the result of thousands of years of parrotfish eating and digesting coral and defecating the tiny sand like particles until they amass unto a shoreline. Many species of parrotfish frequent the shallow waters around the islands, and are responsible for this type of deposition. Whether it is from the gradual erosion of shells and spines, or the bowel movements of actinopterygians, the remains of living organisms regularly become part of the non-living environment.

Grey mat plant covers the slopes of Isla Bartolomé on the walk up to the Pinnacle Rock Overlook.

The Galápagos are home to species of flora and fauna, some of which are very familiar, and other of which are unique to the islands themselves. Many have evolved adaptations to help them survive in this admittedly hostile environment, and some have helped shape it. Take for example, the lava cactus (Brachycereus nesioticus). These pioneer plants are often found on fresh lava flows, taking root and surviving where most other plants cannot. On islands like Bartolomé, B. nesioticus grow in abundance on the western side of the island, where there is nothing more than volcanic rock and grey matplant (Tiquilia nesiotica). Plants like these take root places other plants cannot, break up rock into soil, and upon their death, add nutrients to the land that less rugged plants can then use to sustain themselves. Over time, forests will grow where only lava flows existed, like in the highlands of Santa Cruz, where Scalesia pedunculata, the tree sized daisy, flourishes.

A lava cactus, paving the way for the future, on Isla Bartolomé.

In the Galápagos, adaptations like those possessed by the lava cactus often culminate in the divergence of a new species. Because of the isolated location of the islands, any breeding population of organism that makes it there from the mainland and manages to survive is reproductively isolated as well. As I mentioned, many species of plant and animal found in the Galápagos are uniquely endemic to the islands, and are found no where else on Earth even though they have very close relatives on the mainland. The Galápagos dove (Zenaida galapagoensis) is very similar to the mourning dove (Zenaida macroura) of the Americas, and shares a common ancestor with them, but is unique, and only found in the Galápagos. This allopatric speciation can be seen in many Galápagos species, like the lava gull (Leucophaeus fuliginosus), the Galápagos hawk (Buteo galapagoensis), the Hood mockingbird (Mimus macdonaldi), and the 13 infamous species of “Darwin’s finches” that can only be found in the Galápagos. In the case of the finches, the adaptive radiation of one isolated species of finch resulted in the divergence of multiple new species, each taking up a unique ecological niche in the absence of competitors. This particular case of geographical isolation and speciation is the most evident example of its kind seen in the Galápagos, which is perhaps why it is one of he most well known examples as well.

This Galápagos dove on Isla Seymour Norte looks remarkably like the mourning doves that visit my bird feeder every morning.

In the interest of keeping content manageable, I think I’ll go ahead break here and finish up with part two tomorrow. I apologize in advance if it seems a bit disjointed, or too rigid. Everything written here comes from notes (both lecture and field) that I have scribbled all over various journals and pads of paper, so I’m trying to make it connect as well as possible. Stay tuned for more on the Galápagos.

Galápagos sea lions rest on the black sand beaches of Isla Santiago.

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