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ISLANDS AND THEIR LESSONS IN BIODIVERSITYi -Jack R. Holt

ISLAND OF THE The of the dodo is representative of modernity in several ways, not the least of which is that the event occurred on a small island. -David Quammen (1996) When I was in London five years ago I had one day to stay in the city before our plane left for New York. With all of London to choose from, what does one do in one day? Well, for me there was no question. I had to go to the British of Natural History. The main attraction was its collection of . I walked throughout the museum, and then paused at a of that had become extinct during historic times. There was a stuffed , once so numerous in North America that their flocks blackened the sky as they flew over. Nearby, there was a Dodo, another pigeon. This was large. In fact everything about this was large except its wings. Its skeleton indicated that the Dodo was flightless. Not only were its wings short, but its breast bone was too small to support muscles. Clearly, it could not fly, and its reconstruction made it look even more comical with a bald face and a body covered with fluffy down-like (see Figure 1). Portuguese sailors discovered the Dodo's Island in 1510. The island, a small point of land in the east of , became known as . The earliest record of the Dodo was in 1598. By 1681, the last Dodo had been killed. Isolated island seem to favor the of flightless birds (as well as miniature and giant reptiles). Birds probably become flightless because birds that lose their ability to fly are not selected against in habitats with plenty of food and no predators. Thus, on its little island in the Indian Ocean, the Dodo was a successful . However, when Portuguese sailors began to kill them for FIGURE 1. Top: A reconstruction of the dodo food, they brought their associates like pigs and that emphasizes the stubby wings and stocky rats. Together with the wholesale slaughter, body of this large . Bottom: An destruction of forests and nests, the last Dodo articulated skeleton of a dodo. died in 1681, only 83 years after it was first sighted. Mauritius and similar isolated islands are volcanic and therefore can be made very far from continental land masses (and their biota). The island also is surrounded by a large fringing . Although volcanic activity seems to have been quiet for the past million years, the island continues to grow through the accretion of limestone by the growth of coral.

ARCHIPELAGOS AND BARRIERS Islands have had two distinct modes of origin – they have either been separated from continents of which they are but detached fragments, or they have originated in the ocean and have never formed part of a continent or any large mass of land. -Alfred R. Wallace (1880) Unlike Mauritius, Puerto Rico is part of a chain of islands (archipelago) called the Greater FIGURE 2. A relief map of Puerto Rico. Antilles and forms a boundary between the Atlantic and the Caribbean. Like Mauritius, Assateague Island is quite different from Puerto Rico was formed by volcanic activity and Puerto Rico. It is part of the North American is surrounded by a fringing coral reef. However, continent and formed by the outwash of its geology is older and much more complex. sediments from the eastern seaboard and their Puerto Rico seems to have been formed from the reallocation by ocean currents. Barrier islands floor of the Atlantic Ocean around 190 million are long and narrow bits of land with narrow years ago. Originally, It was an arc of volcanic strips of different environments. Most of the islands that coalesced. Around it in the shallow wave action occurs on the ocean side. The sea, reef builders made thick deposits of mainland side of the barrier island is marsh and limestone. bay (see Figure 3). This history can still be seen in the landforms of the island. The ancient island arc is now a mountain chain that runs east to west across Puerto Rico. On the north and south are areas of limestone from the reef-builders. This geological mosaic creates a large number of habitats in a small area. In fact, the island is only about 100 miles long (E-W) and 40-50 miles wide (N-S). In that relatively small area (3,515 mi2), Puerto Rico has rain forests, dry forests, mangrove swamps, coral reefs, etc. Consider the number of bird species in Puerto Rico. The island has about 280 species of living birds (both residents and migrants). All the rest of the United States has about 650 species of birds. Thus, the number of birds in Puerto Rico may be less than half that of the rest of the US, but the surface area of Puerto Rico is less than one-tenth that of Pennsylvania FIGURE 3. Top: Map of Assateague Island. (46,058mi2). Since the surface area of the 2 Note the long, thin aspect of the island. North is United States is about 3,787,425 mi , Puerto to the left. Bottom: Diagram of a barrier island Rico has 469 times more bird species per square that illustrates the open ocean, island, bay and mile than does the rest of the US! mainland. Barrier islands also serve to dampen Consider what that means in the context of wave action thereby changing the character of bidiversity. The numbers indicate that the the marsh than fringes the bay. destruction of a square mile in Puerto Rico has a much greater impact on bird species than the loss of a square mile in central Pennsylvania.

By and large, barrier islands like Assateague are dynamic; that is, they are constantly changing. Consequently, permanent construction on them often is a lesson in futility. The dynamic nature of the island can be seen on the beach where black peat and blackened clam The beach and main dune. shells from an ancient marsh continually erode in the surf. That is because the island is slowly rolling over itself toward the mainland as it has done since its formation at the end of the last ice age. As you walk from the beach and dunes toward the bay, you encounter a forest dominated by long-leaf pine. The forest, in turn abruptly changes to marsh. Pine trees grow on higher ground with less chance of salt water intrusion.

Scrub behind main dune. All of these different zones occur in an area that is sometimes less than a mile across. The diversity of allows nearly 300 species of birds to occur there. Although the island has a high diversity of plants and animals, a barrier island like Assateague is too close to the mainland to have unique species (This includes the ponies and Sitka Deer, animals that are artificially maintained and controlled). Unique or endemic island species occur on isolated islands like Mauritius.

Long-leaf pines with marsh in the foreground. AMONG THE FIRST TO STUDY ISLANDS Note how the height of the trees rises the farther Mr. Darwin appears to have been the first writer they are from the bay (to the right). who called attention to the number and importance, both from a geological and a biological point of view, of oceanic islands. -Alfred R. Wallace (1880) The Galapagos Islands (Figure 5) are much like Mauritius in that they are volcanic and rise from a very deep ocean bottom. Unlike Mauritius, though, the Galapagos are an archipelago and relatively close to . Although the islands lie on the equator, they are bathed by a cold water current Salt marsh, one of the most productive so that coral does not grow on them. This island on earth. chain is relatively young and many of the FIGURE 4. Illustrations of the beach, dunes, organisms that inhabit it show clear affinities scrub, pine forest, and salt marsh in a straight with those of the South American continent. line across the barrier island. These characteristics helped to give some of the important clues about the A walk across the island will take you operation of evolution. through several distinct environments (see The Galapagos Islands are true desert Figure 4). The leading edge of the island is a islands. The surrounding cold current causes the sandy beach that is delimited by a main dune. air to dry out so rains rarely fall. In this harsh Other smaller dunes occur in the area environment relatively few species live on the immediately behind the main dune. This area island surface, but the surrounding waters are looks almost like a desert with some cactus and teeming with life. Thus, a species of Iguana has scrubby plants. taken to the sea and feeds on algae. Another amphibious oddity is the Galapagos , an that these areas must have been connected to animal whose ancestors must have traveled their respective continents when ocean water northward on the Antarctic current. levels were lower as they must have been during The Beagle circumnavigated the globe the great ice ages. during Darwin’s five-year voyage. After the ship left the Galapagos, it headed across the Pacific toward Australia. On the way, Darwin visited many other oceanic islands, many of which had coral reefs, most of which were atolls. One of the first books that Darwin wrote after his return to England was The Structure and Distribution of Coral Reefs in 1842. In it he described the distribution of coral islands and differentiated between islands with fringing reefs and islands with atoll lagoons. He speculated that atolls came from fringing reefs that grew on a subsiding (see Figure 6). As the water level rose relative to the volcano, the coral grew higher on the mountain until all that could be seen was a ring of coral islands surrounding a lagoon.

FIGURE 6. An illustration of Darwin’s theory of the formation of coral atolls. During a period of growth, a volcano has a fringing reef, which as the volcano sinks (or the ocean rises), the coral continues to grow up along the sides of the mountain. If the mountaintop is under water, all that is left is the ring of coral islands surrounding a lagoon.

He divided the region according to the distribution of animals on the islands. Wallace drew an imaginary line (now called Wallace's

FIGURE 5. Map of the Galapagos Archipelago Line; see Figure 8). An Asian dominated the area to the west of the line while an from Darwin (1871; originally 1845). Australian fauna dominated to the east.

In Wallace's words: While Darwin speculated about the origins "In this archipelago there are two distinct of islands and ruminated on the island biota, rigidly circumscribed which differ as Alfred Russel Wallace (see Figure 7) lived for much as do those of Africa and South years in the islands of the Malay Archipelago America and more than those of Europe and and studied its island life first hand. Wallace North America; yet there is nothing on the traveled all over the region collecting, observing, map or on the face of the islands to mark and writing. His most striking and enduring their limits. The boundary line passes observation was that islands that shared the between islands closer together than others continental margin with Asia were dominated by belonging to the same group. I believe the Asian species. Those islands that occurred on western part to be a separated portion of the continental margin of Australia were continental Asia while the eastern part is a dominated by Australian species. He explained fragmentary prolongation of a former west Pacific continent. In mammalia and birds, He saw the most striking aspect of the the distinction is marked by genera, families, relationship when he traveled from Bali, an and even orders confined to one region; island off the tip of Java. Its birds and mammals insects by a number of genera and little were clearly Asian. However, Lombock, only 25 groups of peculiar species, the families of miles away by sea, had and marsupials insects having generally a very wide or typical of Australia. universal distribution." East of the Wallace Line, he sought the Also from The Malay Archipelago, Volume 1. ultimate prize, the Bird of Paradise (see Figure 9). Species had been described from of birds that had been collected by native bird hunters. Their preparations were fairly good and preserved the delicate . However, they considered the feet to be useless, and threw them away. They were so skillful at sewing the that western taxonomists thought that the birds had no feet. In fact one was named Paridisaea apoda (the footless paradise bird). Footless or not, the delicate plumage was almost of another world. He succeeded in catching many of the birds and even discovered a new Bird of Paradise that was named for him, Semioptera Wallacei. During the eight years that Wallace spent as an explorer in the Maluccas, he collected 125,600 specimens and traveled 14,000 miles. In the mean time, the idea of Natural Selection FIGURE 7. Alfred Russel Wallace at the turn of (the key to modern evolutionary thought) came the century. to him as it had come to Charles Darwin 20 years earlier. Still, Darwin had not published the concept and Wallace's manuscript from the Spice Islands convinced Darwin to begin writing The Origin of Species.

FIGURE 9. Illustrations of the Red Bird of Paradise.

Upon his return to England, Wallace settled down to a life of cataloging his enormous collection and writing. His most influential book FIGURE 8. Wallace's map of the islands around in his day was The Malay Archipelago, Celebes from Wallace (1892). I added the dotted published in 1869. However, his most enduring line to indicate Wallace's line separating the work might have been Island Life, published in Asian and Australian faunas. 1880. This book helped to establish Biogeography as a discipline in the developing of the forest, he would encounter science of . He did no more exploring about 50 species of in any hectare (about 2.5 after this and lived as an eccentric, but fruitful acres). The amazing thing is that in hectares scientist until his on November 7, 1913. very close together, each with about 50 species Thus, the study of islands, a study that of ants, there would be only about 30-40 species produced the foundation for the fact of evolution in common. Thus, the number of species seemed and the theory of natural selection languished for to be as important as the particular species more than 50 years. Island studies did continue present. to support evolutionary biology by studying their endemic species. However, the direction of island studies changed and gained momentum when two American ecologists, Edward O. Wilson and Robert H. MacArthur, adopted it.

ISLAND BIOGEOGRAPHY Many of the principles graphically displayed in the Galapagos and other remote archipelagos apply in lesser or greater degree to all natural habitats. -R.H. MacArthur and E.O. Wilson (1967) In 1954 E.O. Wilson (Figure 10) was given the opportunity to go to New Guinea and study the diversity of tropical ants there. Wilson had begun as a budding naturalist when he was a young man in Alabama. However, a childhood accident had left him blind in one , so he had trouble using a microscope. Wilson claimed that he was inspired to study ants in the when, as a 10-year old boy, he read the following passage from National Geographic in 1934: I remember one Christmas day at the

Mina Carlota, in the Sierra de Trinidad FIGURE 10. E. O. Wilson collecting ants in the of Cuba. When I attempted to turn over tropics. a large rock to see what was living underneath, the rock split in the middle, Back in 1943 Philip J. Darlington, a mentor and there, in the very center, was a half of Wilson at Harvard, had noticed a relationship teaspoonful of brilliant green metallic between the size of islands and the number of ants glistening in the sunshine. They reptiles that occurred there. Cuba, about 40,000 proved to be an unknown species. square miles supported 76-84 species of reptiles He enjoyed insects, but during World War II and amphibians. Whereas, Puerto Rico (4,000 and its aftermath, insect pins were hard to get. square miles) had about 39-40 reptiles and Although pinning preserves most insects, some, amphibians. It appeared that as the land area like ants, are usually preserved in alcohol. Thus, dropped by a factor of 10, the number of species E.O. Wilson began to study ants in an academic that the area could support was cut in half. setting. He stuck with them and studied under Darlington’s study produced the data in Table 1. some of the most important names in insect Wilson had known of Darlington’s work. biology and evolutionary theory. As a graduate However, his own work on ants seemed to student, Wilson collected ants across the U.S., indicate that the number of species in a given and was then was funded to go to Cuba. area was the important characteristic. Thus, it New Guinea was even more exciting. could be tested. Wilson, a taxonomist and Finally, he was going to a place where very little population biologist, teamed up with a brilliant collecting had been done. He described the ecologist, Robert H. MacArthur (1930-1972; excitement and intensity with which he collected Figure 11), to explore that question. in the tropical forests. Then, a remarkable insight came to him. He noticed that in any area TABLE 1. Data generated by Darlington that 1883 with such force that it erased all life from suggests a relationship between the size of an what was left of the island. Fortunately for island and the number of reptile species on that science the Dutch began to do periodic island. inventories of plants and animals on the island. Area (square miles) Number of species Given its size, MacArthur and Wilson estimated 40,000 76-84 that it should have about 30 species of birds. 4,000 39-40 Their island studies convinced them that extrinsic factors also came into play in 400 [20 estimated] determining the number of species. For 40 9 example, the distance from a mainland source 4 5 could profoundly affect the number of species

that can get to the island. They realized that the MacArthur completed his doctoral work number of species on the island had to be the under the direction of the legendary G. Evelyn consequence of an equilibrium between the loss Hutchinson at Yale University. He worked on of species due to extinction and the gain in the evolutionary ecology of closely related species from colonization (and evolution over a flycatchers (birds) in the forests of New England. very long time). Also, they realized that the He employed careful observations and united number of species depended upon the group in them with sophisticated mathematics in the style question. That is, an island of a particular size of Hutchinson. and distance from a mainland would have

different stable numbers of insects, reptiles, birds and trees. Also, a definite species gradient exists from the equator to the poles. The number of species drops precipitously even from the sub tropics to the temperate zone. This is one of the explanations for the differences in bird species numbers between Pennsylvania and Puerto Rico. Why this happens still is a mystery, but, clearly, only islands in the same latitude can be compared. Why are areas correlated so well with specific numbers of species? Perhaps because larger areas have more habitats in which to house more species. This answer, while simple, is quite powerful as an explanatory tool and as a heuristic, a theory that generates more questions. They began to realize, as had Wallace, that many different types of environments behave as islands. For example, a pond is an “aquatic island” within a terrestrial environment. The same holds true for plots of prairies and strips of state forests. MacArthur and Wilson understood that large islands of prairies or rainforest in Amazonia were necessary to maintain their rich

Figure 11. Robert Helmer MacArthur Image biological diversity. Put another way, a one or from: two-acre prairie would have only the shadow of http://www.nceas.ucsb.edu/~alroy/lefa/MacArth the diversity that a ten thousand-acre prairie ur.html would have. Thus, to save biological diversity in stable environments, we need to set aside large One of the first tests of the species-area island tracts. In 1967 Wilson and MacArthur concept involved a careful inventory of living published The Theory of Island Biogeography things on the island of Krakatoa. This was a and changed the way that we view landscape and small island in Indonesia (in the Sunda Straits the preservation of isolated environments. between Sumatra and Java, also part of the To illustrate the power of this theory, I Malay Archipelago) whose volcano exploded in graphed Darlington's data from Table 1 in Figure 12. This time I transformed the data with the log latitude. However the slopes of the line change function. The line flattened into a straight line. from one kind of organism to the next. What Thus, it would be possible to predict the number does that mean? Ecologists really don't know. of expected reptile species on any sized island in Nevertheless, the relationship is a powerful tool the Caribbean. The relationships seem to be in determining questions like what sized plot is constant when considering the same type of necessary to maintain 90% of the tree species in living thing (lizard, bird, tree, etc.) at the same a particular type of forest.

FIGURE 12. A log-log graph of Darlington's data (from Table 1). Note that the curve flattens out to a straight line.

ISLANDS AND ANSWERS meticulous notes. Then, grand discoveries like Unlike experimental biologists, evolutionary the mechanisms of evolution and island biologists well versed in natural history have an biogeography can happen. abundance of answers from which to pick and Of the founders of Island Biogeography, choose. What they most need are the right MacArthur died too young from renal cancer but questions. They look for the best stories nature continues to have an impact on ecology through has to tell us, because they are above all, his students. Wilson remains a premier naturalist storytellers. -Edward O. Wilson 1994 and has championed controversial theories in Darwin, Wallace, Darlington, Wilson, evolution and ecology. He has become one of MacArthur and many other naturalists were the strongest voices today for the preservation of brought to truths of evolution and ecology biological diversity because he is such a good through their studies of island life. Most of all storyteller. they asked good questions because they sought For us today, some of the most important out nature's stories. Most of these naturalists stories are those of the Dodo, Bird of Paradise, came to ecology through a love of collection, but and similar island creatures. Odd birds such as collection alone is empty because it is all the those can evolve and exist on islands question and no story. The story comes when because, although diversity may be high, the the collection begins to make sense. That total number of species that an island can support happens through careful observation and is lower simply because the land area of an island is smaller than that of a continent. So, on developed the theory of evolution and the very small islands like Mauritius and Lombok, intellectual mystery of The Wallace Line. species have a very limited range and are usually We lose more than wildlife in destroying small in number. Therefore, it is not surprising nature, we lose our humanity. that of all the birds that have become extinct Indeed, we are affected spiritually, as she since the demise of the Dodo, 90% have been concludes. However, we are also affected island birds. materially because we are among the living This lesson is a very important one as we things on this planet. carve up forests and other natural habitats on I stumbled onto some NASA images of the continents. In effect, the eastern deciduous earth several days ago. I was reminded of the forest has become an archipelago across the Apollo 8 mission and the first time that I had northeastern U.S. As those island habitats seen the entire disk of our planet. Launched become isolated and smaller, they can no longer December 21, 1968. Apollo 8 was the first flight support the number of species that the whole of the giant Saturn V with a crew. Frank eastern deciduous forest once could. Thereby, Borman, James A. Lovell Jr., and William A. the whole becomes simplified and Anders circled the moon 10 times on Christmas degraded. Eve and Christmas Day. I was a senior in high In considering the biodiversity situation in school and this was my last Holiday season the Malay Archipelago (now Indonesia), Penny while I still lived at home. The moon's surface van Oosterzee in a book about the Wallace Line was gray and dull, but the earth looked like a concluded: tiny blue island in the great black sea of space. "This book has been a great joy and a great What will we do with this precious island? sadness to write. If Wallace were to retrace Will we continue to splinter, simplify, and his journey today, in truth he would have degrade its ecosystems? Will we learn the lesson found little to inspire him. And without of the Dodo? inspiration it is doubtful he would have

Island earth. The arrow indicates the location of the island of Mauritius.

Sources that I used to write the essay: Darwin, Charles R. 1897 (originally 1842. The Beddall, Barbara G., ed. 1969. Wallace and Structure and Distribution of Coral Reefs. Bates in the Tropics, an Introduction to the 3rd edition. D. Appleton & Co. New York. Theory of Natural Selection. Collier- Darwin, Charles R. 1871 (originally, 1845). Macmillan Ltd. London. Journal of Researches into the Natural Bowler, Peter J. 1992. The Fontana History of History and Geology of the Countries the Environmental Sciences. Fontana Press. Visited During the Voyage of the H.M.S. London. Beagle Under the Command of Cpat. Fitz Darlington, Philip J. 1957. Zoogeography, The Geographical Distribution of Animals. John Wiley and Sons, Inc. New York. Roy, R.N. New Edition. D. Appelton & Co. Van Oosterzee, Penny. 1997. Where World New York.1 Collide. The Wallace Line. Cornell Darwin, Charles R. 1859. The Origin of Species University Press. Ithaca, NY. by Means of Natural Selection. The Wallace, Alfred R. 1874. The Malay corrected copyright edition (1902). John Archipelago, The Land of the Orang-Utan Murray. London. and the Bird of Paradise..MacMillan and Darwin, Charles R. 1958 (first published in 1892 Co. London. as edited by Francis Darwin). The Wallace, Alfred R. 1892. Island Life or the Autobiography of Charles Darwin and Phenomena and Causes of Insular Faunas Selected Letters. Dover Publications, Inc. and Floras. Macmillan and Co. London. New York. Wallace, Alfred R. 1895. A Narrative of Travels Darwin, Francis, ed. 1896. The Life and Letters on the Amazon and Rio Negro. 5th edition. of Charles Darwin, Including an Ward, Lock, & Bowden. London. Autobiographical Chapter. Vol. 1&2. D. Wilson, Edward O. 1984. Biophilia. Harvard Appleton & Co. New York. University Press. Cambridge, Mass. Holt, Jack R. and Patricia Nelson. 2001. Paths of Wilson, Edward O. 1992. The Diversity of Life. Science, Explorations for Science Students W.W. Norton and Co. New York. and Educators. Kendall/Hunt Publishing Co. Wilson, Edward O. 1994. Naturalist. Island Dubuque, Iowa. Press/ Shearwater Books. Washington, D.C. Loewenberg, Bert J., ed. 1959. Charles Darwin: INTERNET SOURCES ACCESSED NOV 1997 Evolution and Natural Selection, an Alfred Russel Wallace. Anthology of the Writings of Charles http://www.iol.ie/~spice/alfred.htm Darwin. Beacon Press. Boston. Caribbean Island Arcs. MacArthur, Robert H. and Edward O. Wilson. http://qualibou.upr.clu.edu/MRCE.html 1967. The Theory of Island Biogeography. Dodo. IN: Levin, Simon A. and Henry S. Horn, http://www.amnh.org/Exhibition/Exhibition/ eds. Monographs in Population Biology. Treasures/Dodo/dodo.html Princeton University Press. Princeton, NJ. Mason, Stephen F. 1962. A History of the i In writing this essay, I pulled together material Sciences. Collier Books. New York. from two different published essays: Ants and Quammen, David. 1996. The Song of the Dodo, Archipelagoes and and Birds of Paradise. Island Biogeography in an Age of . Scribner. New York. Raby, Peter. 1996. Bright Paradise, Victorian Scientific Travelers. Princeton University Press. Princeton, NJ. Raffaele, H.A. 1989. A Guide to the Birds of Puerto Rico and the Virgin Islands, revised edition. Princeton University Press. Princeton, NJ. Rosenzweig, Michael L. 1997. Species Diversity in Space and Time. Cambridge University Press. Cambridge, UK. Shepard, A. & D. Slayton. 1994. Moon Shot, The Inside Story of America's Race to the Moon. Turner Publishing Co. Atlanta. Trefil, James and Robert Hazen. 1995. The Sciences, An Integrated Approach. John Wiley & Sons, Inc. New York. Udvardy, Miklos D.F. 1969. Dynamic Zoogeography. Van Nostrand Reinhold Co. New York.

1 This book is known also as The Voyage of the Beagle and Journal of Researches.