Distributional Ecology of New Guinea Birds Author(s): Jared M. Diamond Reviewed work(s): Source: Science, New Series, Vol. 179, No. 4075 (Feb. 23, 1973), pp. 759-769 Published by: American Association for the Advancement of Science Stable URL: http://www.jstor.org/stable/1735788 . Accessed: 22/12/2012 20:00 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Association for the Advancement of Science is collaborating with JSTOR to digitize, preserve and extend access to Science. http://www.jstor.org This content downloaded on Sat, 22 Dec 2012 20:00:09 PM All use subject to JSTOR Terms and Conditions Species lliversity on Islands If one were to count all the animal or plant species occurring within an area of I hectare, the result would vary greatly dependng on the location of the census area. The species total would DistributionalEcology generally be much higher in the tropics than in the temperate zones, higher at of New GuineaBirds the base of a mountainthan at the sum- mit, higher on a large island than on a small island, and higher on an island Recent ecological and biogeographicaltheories can near a continent than on a remote island. It is important to understand be tested on the bird communitiesof New Guinea. this variation if, for example, one is establishinga system of national parks JaredM. Diamond to ensure survival of as many native species as possible. Islands such as those of the southwest Pacific lend themselves well as test areas for a quantitativetheory of species diversity As indicated by frequent references understood.New Guinea has served as because each island represents a sepa- in the syntheses of zoogeography by the bird colonizationsource for the thou- rate experiment, and because most in- Wallace;(l), of evolution by Mayr (2), sands of islandsof the southwestPacific; sular variation in species diversity can and of ecology by MacArthur (3), the and New Guinea itself behaves as an be predicted from values of only two tropical island-continentof New Guinea "islandarchipeSagos' for montane birds, or three readily measuredvariables. We and its birds have played a special role since its mountain ranges are isolated shall see that the diversity of bird in advancing our understandingof ani- from each other by a i'sea" of unin- species on most Pacific islands is in a mal populations. This role developed habitablelowlands. The numberof bird state of dynamic equilibrium that is, partly because birds are the best known, species on these oceanic islands and the diversity is determined by the most easily observed and identifiedani- mountain islands varies with area and island's present physical characteristics mals, and partly because of unique isolation, providing innumerable "ex- and is independent of the island's his- advantagesof New Guinea itself New periments of nature" whereby the tory. However, on some islands, the Guinea provides a range of habitats niche of a given species can be studied species diversity may also reflect the from tropicalrain forest to glacierswith- as a function of the competing species island's recent history. in distances of less than 16 kilometers, pool. The number of land and freshwater a range of elevations of over 50()0 Within the past decade, new para- bird species coexisting on each tropical meters, and an equatorialposition that digms introsluced by MacArthur and island of the southwest Pacific varies minimizes seasonal migration with its Wilson and their co-workers(3-7) have from 1 for some isolatedkatolls up to associated complications. The rugged revolutionized our understanding of 513 for New Guinea itself. This varia- topography, which isolates populations some central questions of ecology, such tion is due partly to the greater variety in adjacent valleys or on adjacent as: Why do diSerent localities support of habitatspresent on the larger islands. mountains, has promoted speciation very different numbers of animal or However, even within a given habitat within small areas of a single land mass plant species? What determines the type (for example, in tropical lowland by essentiallythe same mechanismsthat distribution of a given species? How rain forest) there are great differences underlie speciation on large continents. do related species manage to coexist? among islands in the number of bird In New Guinea's expanses of forest un- These questions are not only of basic species to be found. These differences disturbed by man, niche interrelations scientific interest but are also of prac- are largely predictablefrom an island's retain a simplicity and beauty lost in tical importance in formulating con- area, its distancefrom New Guinea, and altered environments,and distributional servation policies. Furthermore, the its elevation (13). patterns illustrating many intermediate concepts of MacArthurand Wilson are Figure 1 shows the number of bird stages in evolution and in niche dis- proving increasingly helpful in under- species S occurring at sea level on placement are readily identified. The standing human populations. In this islands between 8 and 500 km from number of breeding bird species, 513, article I discuss these questions in the New Guinea, as a function of island is large enough to give rise to the com- light of my studies of New Guinea area A (expressedas squarekilometers). plex interactions characteristicof con- birds, conducted during six expeditions Over a 3-millionfold range of areas the tinental faunas, but not s-o large as to to New Guinea and other islands of the results fit the power function- be overwhelming.In spite of the physi- southwestPac;fic (8-15). A recent book cal difficuIties of exploration in New discussesin detail many of the examples 5-12.3A022 (l) Guinea, the distributionand taxonomy summarized here (15). Many patterns with an average error of 19 percent. of its bird species are by now fairly well observed in New Guineaibirdsare rele- Thus, a tenfold increase in area in- vant to other groups of animals in other creases species diversity by somewhat The author is professor of physiology at the parts of School of Medicine, University of California, the worlds especially in the less than a factor of 2. The numbered Los Angeles 90024. tropics. deviant points represent islands in var- 23 FEBRUARY 1973 7ss This content downloaded on Sat, 22 Dec 2012 20:00:09 PM All use subject to JSTOR Terms and Conditions ious stages of "relaxation,"as will be As a test of the equilibriumtheory, t represents time. Let us assume con- explained. in 1968 and 1969 I resurveyedthe land stant coefficients Ki and Ke, (expressed l n Fig. 2 l ha\e plotted, as a func- and freshwater birds of a temperate as year- l ), respectively- tion of island distance D from New archi,oelago and of a tropical island E= Ke S(t) (3) whose birds had been surveyed50 years Gllillea, the ratio of an island's actual I = Ki [S -S(t)] (4) S at sea level to the S value predicted previously:the nine Channel Islands off dS/dt = l-E KiS*:- from the island's area and Eq. l. This southern California (9), and Karkar (Ki + Kc)S(t) ( 5) ratio decreases exponentially with dis- Island off northern New Guinea (l 2). where S: is the mainland species pool. tance, by a factor of 2 for each 2600 On each island I found that between At equilibrium (dS/dt = O), the species km from New Guinea. Thus, the most 17 and 62 percentof the species present diversity S(.(, is given by remote islands of the southwest Pacific 50 years ago had disappeared,and an (Mangareva and the islands of the approximatelyequal number of species Seq = KiS/(Ki + Kc) Pitcairn group, 8()()0 to 9200 km from absent 50 years ago had immigrated. (6) Relaxation to equilibriumfrom an ini- have a bird species diver- Thus, the species diversityhad remained New Guinea) tial species diversity S(O) that differs that of islands of in dynamic equilibrium;Terborgh and sity only 12 percent from St, is described by: similar size near New Guinea. Faaborg (17) obtained similar results in the The mollntains of the higher south- for the birds of Mona Island [S(t) - S(sq]/[S(O) - Se] = e tXtr (7) west Pacific islands harbor additional West Sndies.While a few of the extinc- where "relaxationtime" tl. is given by bird species not occurring at sea level. tions and immigrationsin these studies On the average, each 1000 m of eleva- were related to effects of man, most of tl = (Ki + Ke) l (8) tion L enriches an island's avifauna by the changes were of the random kind a number of montane species equal to expected in the abselace of a human The relaxation time is the length of 8.9 percent of its avifauna at sea level. role. As predicted f rom colonization time requiredfor the departureof spe- Thus, bird species diversity on the New theory (4), most of the extinctions in- cies diversity from equilibrium, IS(t)- Guinea satellite islands may be sum- volved populations that were rare 50 S(ll, to relax to 1/e (or 36.8 percent)of marized by the empirical formula years ago because of such factors as the initial departure,15(°)-Se,ll, where recency of colonization, small island e is the base of naturallogarithms.