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
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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. Actu- >N= (12.3) ( I + 0.089 L/ 1000) X size, presence of well-establishedcom- ally, this treatment is only a crude ap- be- (e-D/'"")(A0 22) (2) peting species or small area or margi- proximation of the real situation, nal suitabilityof island habitat. Among cause K( and Ki prove to be functions. Similarly, species diversity in other tlaeChannel Islandsthe calculatedmini- Of S(t). However, by applying Eqs. plant and animal groups on other mum turnover rates, expressed as the 3 to 8 to island faunas we can deduce islands increases with island area and percentageof island species immigrating the form of these functions, stipulate decreases with distance from the colo- or becoming extinct per year, range some conditionsfor an improvedmodel, nization source. These two trends con- from 1.2 percent per year for the and come to some conclusions about stitute the fundamental law of island smallest or most barren islands down the distribution of bird species. biogeography.The exponent of area is to 0.3 percent per year for the largest As an example of an "experimentof generally in the range 0.20 to 0.34 island. nature"that permitsestimation of S(0), (4. l 6). Since the S and A values for Kar- S(.
This content downloaded on Sat, 22 Dec 2012 20:00:09 PM All use subject to JSTOR Terms and Conditions lowland species at equilibrium (from conclusions can be drawn (13). I(i)With characteristically colonize mainland Eq. l) but actually has 135. If we take decreasing island area, extinction rates "second-growth"habitats (transient veg- Eq. 7 and substituteS(0) = 325, S(t) = increase (yielding shorter calculated tr etational stages during regrowth of a 135, Seq= 65, and t = 10,000 years, values) because of smaller population forest clea'ring).Subsequent immigrants we obtain a relaxation time of 7,600 sizes. Thus, among land-bridge islands are drawn from a mainland species years for the avifauna of Misol. the calculated tr for the'relict popula- pool comprised of progressivelypoorer Relaxation times can also be esti- tions decreases from 9000 years for an colonists. Exp-ressedmathematically, K mated from four other types of "ex- island of area 7800 km2 (Aru), to 6;l00 on'a given island is a decreasing func- perimentsof nature."These are: the fis- years for 450 km2 (Batanta),and to 2630 tion of S(t). ;(iY) The probability of sion of a large island into two smaller yearsifor 145 km2 (Pulu Adi). Species extinction is much higher for recently islandsbecause of rising sea levels flood- diversities on small land-bridge islands arrived immigrants 'that still have a ing a- low isthmus; contraction in an do not show an excess over equilibrium low population'density, than for estab- island'sarea because of rising sea levels; values (Fig. 1) because relaxation times lished species'that-have saturatedavail- gradual extinction, from land-bridge for these islands are much shorter than able island habitats. islands, of relict populations of those the 10,000 years that have elapsed since New Guinea lowland species that never severing of the land bridges. (ii) On cross water gaps of more than 8 km supersaturated islands certain species Patchiness of Species Distributions . . . . or even 50 m (such species must have are especially prone to extinction and reached the islands at the time of the tend consistentlyto disappearfirst. The Among the characteristicsof tropical land bridge, and were isolated without resultingrelease of the remainingspecies species that'distinguishthem from their possibility of recolonization after sub- from competition tends to increase high-latitudecounterparts'are the lesser mergence of the land bridge) (l3); and their population densities and to de- tendency of tropical'species to disperse, recolonization of volcanic islands such crease their risk of extinction.Expressed their subjection to greater niche com- as Krakatau, Long? and Ritter, after mathematically,K} on a given island pression' by interspecific competition, cataclysmic eruptions totally destroyed is an increasing function of Sl(t). (iii) and their lower extinction and higher the fauna. The -species that arrive first -at an speciation rates. All these character- From ca]culated relaxation times ob- initia]l.yempty island tend to be'certain istics contribute to the striking tropical . . . . tained by these methods for 19 New species with consistently superior dis- phenomenon called "patchiness"(3, 7, Guinea satellite islands, the following perlsal abilityn such as those that 15). Whereas the local presence or
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l l 100 1000 10,000 100,000 1,000,000 Area (km2) Distance (km) Fig. 1 (left). Number of resident land and freshwater bird species on New Guinea ssatellite islands, plotted as an funotion of island area' on a' double logarithmic scale. Symbols: *, islands on whch species diversity is presumed to be at equiliblrium (the' remaining, numbered islands are in various s-tages of "relaoxation"after displacement of species diversity from an equilib- rium value); , exploded volcanic island!s (1, Long); O, contracted islands (2, Goodenough; 3, Fergusson);' + land-bridge islands (4, Aru;- 5, Waigeu; -6, lapen; 7, S;alawati; 8, Misol; 9, Batanta; 10, Pulu' Adi; 11, 'Ron; 12, {Sohildpadj- d3, island fragments split ofT from a larger -island by flooding of an isthmus ( 13, Batjan- 14, Amboina- 15, New Hanover- 16, Tidore). The straight line was fitted by leiast'mean squ'aresthrough points for all 'is]ands except the'land-bridge islands. No,te that the number of species increases with area; and thait deviations Sforrelaxing islands are more marked for 'llargeislands than for small islands, 'because of high extinction rates and short relaxation times on the latter. [After Diamond (13)] ' Fi'g. 2 (right). Ordi- nate (logarithmic scale), number of resident land and freshwater bird 'species (S) on tropical southwest Pacific islands more than 500 km from New Guinea,' divided by number of species expected' on an is]and of equivalent area iess 'than 500 km from New Guinea (calculated from Eq. 1). Abscissa^,island distance from New Guinea. The'graph shows that species diversity de- cl eases by a factor of 2 per 2600 ktn. [After Diamond ( l3') g 23 FEBRUARY 1973 761
This content downloaded on Sat, 22 Dec 2012 20:00:09 PM All use subject to JSTOR Terms and Conditions an extreme degree, such that they occur at a few widely separatedlocalities but are absent in similar habitatsover most of New Guinea (15). For instance, the flycatcher Poecilodryas placens is known from six scattered areas, where it inhabitsrain forestswith a well-shaded understoryof small saplings in locally flat terrain up to 1000 m above sea 6°S- IJSS - level. The species is absent from hun- dreds of well-explored iocalities with similarhabitat elsewhere in New Guinea. Most of these very local species in New Guinea fall Into one of two cate- gories: distinctive "monotypic genera" l l s l with no close relatives (that is, genera Fig. 3. Distribution of the Papuan tree creeper, Cliszzactezis 1eucopSzaea, in the moun- consisting only of a single isolated tains of New Guinea. Although mountains and forests with similar tree bark extend species), or members of large genera uninterrupted for 1600 km, and although there is no other New Guinea bird in the consisting of many eccalogicallysimilar same family, this bark-feeding species has a distribution gap (unshaded area) of 400 km in the middle of its range (hatched area). [After Diamond (15)1 species. The highly fragmented distri- butions of these species suggest that they are slowly becoming extinct, either absence of temperate-zonespecies can habitat requirements, since a skeptic because they are the last survivors of generally be predicted from knowledge can always claim that some unspecified unsuccessful evolutionary lines (mono- of their particularhabitat requirements, factor has been overlooked. However, typic genera), or because they cannot many tropical species are patchily dis- many of the examples of patchy distri- compete with several ecologically simi- tribu-tedwith respect to the available bution that I describe briefly below and lar relatives in the same genus. habitat-that is, they may be absent in detail elsewhere (15) involve well- 3 ) Complementary checkerboard at a considerable fraction of the lo- studied species which appear to have ranges. Some local absences of species calitles oSering a suitable habitat for distinct and readity defined require- are correlated with the presence of them. Temperate-zone biologists, be- ments, and which are ubiquitous in ecologically similar congeners, indicat- cause they are rarely confronted with habitats meeting these requirementsin ing that one-to-one competitive exclu- examples of such patterns, often many geographical areas of New sion occurs in New Guinea mainland assume that the evidence for patchiness Guinea. Since there do seem to be habitats as on oceanic islands. For ex- in the tropics can be dismissed as some generalizations emerging about ample, the extensive midmontanegrass- an artifact of inadequate exploration patchiness, it is becoming increasingly lands, which are a by-productof human or insufficiently understood habitat unnecessary to invoke unspecified fac- agricultureduring the last few centuries, requirements.To prove that a species tors as an explanation. have been colonized in irregularcheck- actually is locally absent rather than There are four main types of patchy erboardfashion by eight Lonchurafinch just overiooked is certainly more diffi- distribution. species native to other habitats. Each cult than to prove that it is present. 1) Distributionalgaps in a continuous midmontane area supports only' one Fortunately, the documentation of habitat. The ICentralDividing Range of finch species over a considerable local patchy distributionsin New Guinea has New Guinea provides an uninterrupted range of grass types and heights, alti- been facilitated by many New Guinea expanse of montane forest for 1600 tudes, and rainfall conditions,'but the natives who possess a detailed knowl- km. Nevertheless, 18 montane bird areas inhabited by a given species are edge of local birds. Some natives were species that would otherwise be uni- often scattered hundreds of kilometers able to name (in their native languages) formly distributedhave a distributional apart. Evidence indicates that in each and accurately describe in advance all gap of several hundredkilometers some- instance the first arrival became estab- bird species that I eventually located where along the Central Range (Fig. lished over a local area and was able to in their areas; they could distinguish 3 ) . For instance, the finch Lonchura exclude potential subsequent colonists at a distance obscure sibling species in montana occurs commonly in large of the seven other species, but the such taxonomically difficult genera as flocks throughout the alpine grasslands identity of each locally successful Sericornis; and could accurately de- of western and eastern New Guinea, colonist depended partly on chance scribe other species known to them only where it is the only specialized seed- (15). In the slightly more complex situa- from single individuals observed up eating bird, yet it is absent in the alpine tion illustrated in Fig. 4 ("compound to 10 years previously (14, 15). When grasslandof centralNew Guinea, which checkerboard exclusion"), each local such "walking encyclopedias" of bird has similar grass and an otherwise area can support coexisting populations lore confirm the permanent local similar avifauna (15). Large distribu- of any two species out of three potential absence of a species that is regularlyen- tional gaps in a continuous habitat also colonists, and the identity of the locally cotlnteredin other areas, one can have occur in the New Guinea lowlands. missing third species varies irregularly. corfidence that the species is actually The interpretationof these remarkable 4) Distributionalislands on a main- absent and not merely overlooked. It patterns is discussed below. land. Comparisonof mountainsseveral is even more difficult to prove that a 2) Very local distributions.The dis- kilometers apart within the same range locality really does meet all of a bird's tributionsof many species are patchy to invariably reveals faunal differences
762 SCIENCE, VOL. 179
This content downloaded on Sat, 22 Dec 2012 20:00:09 PM All use subject to JSTOR Terms and Conditions that cannot be explained by differences in habitat (15). For example, species characteristicof lowerlmontane forest at 800 to 1100 m were compared on four peaks of the North Coastal Range. In order of decreasing.area and sum- mit elevation, the mountains and their numberof lower montane species were: Menawa (1890 m high), 45 lower mon- tane species at 800 to 1100 m ; Nibo (1560 m), 36 species; Somoro (1420 m), 34 species; and Turu (1140 m), 26 spe- cies. The four mountainshad structural- ly similar forest at 800 to 1100 m, but the smaller mountains had less area of such forest and, correlated with this, fewer bi'rdspecies characteristic-of this Fig. 4. Compound checkerboard exclusion: distributions of three Melidecteshoney- forest. Similar findings have been de- eaters. O, MeZidectesochromelas; B, M. belfordi;R, M. sufocrissalissuperspecies. Most scribed for Andean birds and North mountainous areas of New Guinea SUppO1t two species with mutually exclusive alti- American mammals ( 19 ) . These pat- tudinal ranges. At each locality depicted on the map of New Guinea, the letters above and below indicate the species present at higher and lower altitudes, respectively. The terns are reminiscent of the funda- identity of the locally missing thind species is subject to irregular geographical variation. mental species: area relation of island biogeography(see page 760). Evidently, dispersal rates of birds betwee.n' New tional gaps in a continuous habitat may decline in species B following an inva- Guinea mountains separated from each persist for long periods of time, albeit sion of its close competitor A may per- other by valleys a few kilometers wide as nonequilibrium phenomena. For mit B's other close competitor C to are so low that the peaks behave as example, the finch Lonchura montana increase, depressing the population of islands. (discussedabove3 may have disappeared C's competitor D and ultimately affect- from the alpine grassland of central ing species ecologically far removed New Guinea severalmillennia ago, when from A. Correlated with the greater Significanceof Patchiness the area of this habitat was reduced by diversity of species in the tropics than encroachment of forest; and this finch at higher latitudes is the fact that tropi- While much remains bafRing about may disperse too slowly to have refilled cal species have more closely packed patchy distributions in the tropics, the whole gap since then. In the more niches than their temperate counter- such distributionsappear to be caused seasonal temperate latitudes, by con- parts, such that the local survival of a by the synergistic'effects of two charac- trast, the annual north-southmigrations, given species may be criticallydependent teristics.of tropical species compared to and the postbreeding wanderings of on the mix of competitorsas well as on temperate-zone species. These are ' the many nonmigratoryspecies, flood suit- the suitabilityof the habitat (3, pp. 231 lower dispersalrates of tropical species, able habitats with potential colonists of ff3. Thus, competition may stabilize which prolong the existence of distri- most species each iyear. Mortality due some distributionalgaps indefinitely. butional gaps as temporary or non- to climatic fluctuations in temperate These considerations help us to un- equilibriumphenomena; and the greater Iatitudesplaces a premium on dispersai derstand the differing numbers of pressure from interspecificcompetition, ability to recolonize vacated territories, species on differentcontinents. Low dis- which stabilizes gaps' as indefinitely whereas the greater stability of the persal may allow localized populations miaintainedor equiiibrium phenomena. tropics selects against dispersal. of disappearingspecies to linger, rela- That the mean dispersal distances of Effects of interspecific competition tively undisturbedby influx of competi- many New Guinea bird species are less on local distributionare easiest to rec- tors, for long periods of time before than' several kilometers is indicated (i) ognize in the one-to-one situation of final extinction. Conversely, low disper- by the absences of montane species on simple checkerboard exclusion, where sal favors high rates of speciation, since mountains separatedby several kilome- species A, for example, occurs only in the first stage of speciation depends on ters from populations of the same the absence of species B and vice versa, the effectiveness of geographical bar- species on other mountains; (ii) by the or in compound checkerboard exclu- riers or distributionalgaps (Fig. 8). Be- numerous species absent on oceanic sion, where species A occurs only in the cause the number of species at equilib- islands a few kilometers or even only a absence of either species B or species C. rium on a continent depends on a few meters from the New Guinea main- The eompetitors in these situations are balance between speciation rates and land (13); and (iii) by the presence of usually, t-houghnot always, close rela- extinction rates, tropical habitatsshould distinct subspecies or even semispecies tives within the same genus. It is more be expected to have a greater number on mountains separated by valleys sev- diicult to determinethe connections in of species at equilibrium than habitats eral kilometers wide or on islands so-calied diffuse competition, where the at higher latitudes (Fig. 5). Further- separated by straits several kilometers absence of a species is due to the com- more, with increasing continental area, wide. Once a species has become local- bined efdfectsof many species, each extinction rates should decrease (be- ly extinct for whateverreason, immigra- somewhatdistantly related to the absent cause of larger population sizes and tion from populations in immediately species and potentially overlapping it more local refuges), and speciation rates contiguousareas is so slow that distribu- ecologically only in part (3, 10). A should increase (because of more popu- 23 FEBRUARY 1973 763
This content downloaded on Sat, 22 Dec 2012 20:00:09 PM All use subject to JSTOR Terms and Conditions _ . _ _ _ _ b
Fig. 5. Speciation rates (solid curves) and E1 their altitudinal range (Fig. 6). With extinction rates (dashed curves3 on a JZ sa increasingelevation C. mglrinabecomes single land mass, as a inction of the number of species (abscissa). The ordi- l / increasinglyabundant until it- suddenly n?te is the tota1'number of species pro- U disappears at 1643 m an altitude not duced through speciat-ionor lost through *ov- ir far above its altitude of masimum extinction per 10S000 years. The inter- abundance.At this elevation C. rohsttz section of the curves (N1,^1V2) determines Or X, §e suddenly appears near its masimum the number of species at equilibrium. The S2 abundance and becomes progressively speciation cu'rve'is approximately linear, o o / / / because the probability'of speciation of a less common toward Mt. KarinluiSs given species'is appro:ximatelyindependent a.O summit. Prolonged observations at the of the presence' of other species but ex- transition altitude showed that the tWQ tinction rates increase sharply as more O a / /< f species ,are interspecifically territorial species are packed,-together, ()n a large AS-_ */ * tropical land massn high' speciation 3nates at 1643 mn and no individual of either (curve Sl) and 1QW e,xtinction rates (EI) N2 N:I: species was ever found transgressingthe yield' a high nvimberof species at equilib- Number of species range of the other. There is no change rium (N1). On a similar-'sizedtemperate in vegetationat this altitude the nearest lancl mass or a smaller tropical Iand mass, lower speciation rates (S2?=and higher ex- i'ecotone' (a border 'between forest tinction rates' (E2) yield fewer species at The best understoodsegregating r mecha- types) lies 338 m higher. In all, the equilibrium ( N2 ) . nism among New Guinea birds depends New Guinea avifauna contains about on altitude and involves an inlteresting 45 pairs, 13 trios and 3 quartets of behaviolnal. response., . relatedspecies which ]replaceeach other lations isolated over greater distances). Altitudinxxl segregation. O]n New altitudinally with similar abruptness. Thus, one should also expect more Guinea mountains not disturrbed by For a given species pair the transition species at equilibriumin a large center man, forest extends uninterrupt:ed from altitude shows minor local variation of speciation, such as the Amazon sea level to timberline at around 3800 correlatedwith local conditionsof rain- Basin, than in a small center, such as m. Many bird species especialEly those fall, exposure, and slope but no-sys- New Guinea (Fig. 5). witk no closely related speciess in the tematic geographicalvariation overNew areanexhibit gradual changes iin abun- Guinea'. Altitudinal sequences with . . . . dance with altitude. However in many sharp transitions also occur among Ecological Segregationof Species other instances one finds sequeences of birds in the Peruvian Andes (21) and two, three or even four closel f rela-ted on all large mountainous islands of A central problem of ecology con- species replacing each other, abruptly Indonesia eind the southwest Pacific. cerns community- organization: How with altitude (15)* For examptleS Cr- Stric,ttransitions may be vi,olatedby are resourcesdivided among the species teroseelis murina and CratterosceZis young birds: when one finds an indi- of an ecological community and what robusta, two abundantand ver y similar vidual outside the normal altitudinal . . mutual arrangements permit the c o- warblersthat glean for insects ]near the range of its species it generally proves existence of closely related species (20)? ground dif3er ecologically m ainly in to be a juvenile or an immature bird.
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- .! 2000 *; :: ::#S Fig. 6. Altitudinal ranges of the warblers CraterosceZisrobmsta C. robusta *. (*) and C. murina (0) on the'west ridge of Mt. KarimuiS New Guinea. On the left, eacRhmark represents one individual C. murina g g heard, seen, or collected at the given altitude''(the paucity of - 1 SOO - records at 650 to 1050 m results from my. having spent little a time at this altitude). The right-hand side gives ' the relat;ve 3 / o abundance in ' the whole avlfa.una-that is the percentage of ._ bird individuals of all species estimated as being C. robust or C5 C. m7lrin. The two species replace 'each other abruptly at 1643 O m, ard each species reaches'its masimum abundance near tEs [000 r altitude. Many other .species show equally sharp'.transitions although the altitude of masimum abundance frequently differs frc>n the altitude 'at which the species transibion occurs oW 500-
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This content downloaded on Sat, 22 Dec 2012 20:00:09 PM All use subject to JSTOR Terms and Conditions Among New Guinea birds generally, altitude species may expand simultane- they are assumed to be distinct species. there is a characteristicDaltitudinal ously into the range of a missing They may also develop slightly diSerent dependence of population structure. middle-altituderelative. altitudinal ranges. Typically, immature birds are found Reconstructionof the process of spe- 4) Both populations reexpand geo- in a fringe at the bottom of the ciation provides the other test for com- graphically until their geographiclal altitudinalrange; somewhat higher, one petition and clearly demonstrates the ranges abut but--do not overlap. There finds immature birds plus nonbreeding origin of altitudinal sequences ( 15) . is no or little interbreeding, proving adults, with females usually appearing Speciation occurs when an initially that the populations are in fact distinct at lower altitudes than males; next continuous population breaks up into species. comes the optimal part of the species' geographical isolates, the isolates S ) Each species begins to expand range, with breeding adults of both diverge, reestablish geographical con- geographically into the range of the sexes; and, finally, another fringe of tact and perfect their reproductive other, so that there is geographical immature birds but few adults appears isolating mechanisms, and finally rein- overlap ("sympatric" distribution) for at the upper altitudinal limit of some vade each other's geographical ranges a short distance. Within the zone of but not all species. This population if there are sufficient ecological dif- sympatry the two species segregate structure is manifested to an extreme ferences to permit coexistence (2). altitudinally,each being confined to the degree by some birds of paradise, While the slowness of evolution rarely altitudinal range in which it is com- whose displaying adult males may be- permits following a given species petitively superior to the other. The compressed into the top 180 m of the through this process with time, the narrower altitudinal range inside than altitudinal range, with adult females distribution patterns of diSerent New outside the zone of sympatry is a clear and especially immature birds being Guinea montane species represent demonstration of niche compression found up to 1000 m below the lowest "snapshots" of seven different stages due to competition. adult male. in a continuous speciation process 6 ) Expansion continues, and the UItimately the altitudinal sequences (Fig. 8): western species reaches the eastern end are related to differential adaptations 1) A single montane species extends of New Guinea and overruns the entire that are continuous functions of alti- from the western to the eastern end geographicalrange of its eastern sibling tude, one species being preferentially of New Guinea, oiccupying the same species. The eastern species has given adapted to higher altitudes, cooler tem- altitudinal range at all longitudes. up the upper (or lower) part of its peratures,and more montanevegetation 2) The local population in one area altitudinal range throughout its whole than the other species. But the very dies out, so that the east-west dis- geographical range7 and there is no sharpnessof the transitionsimplies that tribution becomes discontinuous. altitudinal overlap. competition superimposes a special 3) The eastern and western popula- 7) The eastern species continues to behavior pattern on these differential tions, now isolated, diverge sufficiently expand until it has reached the western adaptations,since the transitionsdo not that they would probably not inter- end of New Guinea. The two species coincide with sharp changes in tem- breed if contact were established;hence, are now sympatric over the entire perature or vegetation. That is, each length of New Guinea, with mutually species must be capable of surviving exclusive altitudinal ranges. Evolution over a wider altitudinal range than it 4000- Mt. Mt. may then continue in the direction of actually inhabitsand must be excluding Wilhelmina Michael Mt. Saruwaged either stage 8a, 8b, or 8c. related species from the range in which 8a) Stages 1 through 7 may be re- it is competitively superior to them. To peated one or two more times to yield confirm this ,.X..'.'...i..'V..X.'T--T' interpretation, the local ..'.-'.-."-.'-'ly.'S-iT-'..i:series of three or four closely related poptllation of one member of a se- - .T..T,i1..Xi:0f,00i; 3000- .. species ....- sympatric over the whole of quence would have to be removed in -i.-0,-.-X-00-..,;i.X--0ft;: ti.'---iX'TS'-0.Xt-itA.,X,-tNew Guinea but occupying mutuallyex- order to ascertain whether the adjacent - ,.,i,,,i,,,,,,000t,t,,,,f,.;clusive altitudinal ranges. species would expand their altitudinal a) ..;;.;fX00.;TS,,;fE4i,!00X ,...t,--0f."t.,f-'T,',;d,'T,,lL;8b) Two species that have become ranges. This test of competition arises 3 ._ 0'-'."i't-'TiX'T-i'sympatric with mutually exclusive in 0.. New Guinea under two types of zr: iTE.-40;-0T'tT-'.iT.X.';.'tl.italtitudinal ranges may diverge in other .0T,,-T,T,';ttEt;0'S-'t;00tl-07 naturally occurring conditions. 2000- -,000t,-;i..0f-,X,0X-0tT;tniche parameters besides altitudinal The first test of niche expansion .t,,000;-Xti.-E,;i...-,;X..t.,.preference (for example7 they may associated with Tit-'t;-S't"t'.'.;.-t;-.X:-;X.:00 relief of competition iS.Xt;:ti,0T,:fE.t ..l,lyTlL,0 develop differentdiets or foraging tech- occurs on small or isolated mountains -00t-'T-'TiT-'tt.ti".t;000.-i; niques), so that partial altitudinalover- or islands (8, 10, 15). Because of the .=L lap as well as complete geographical dependence of species diversity on 1000 / overlap becomes possible. area and isolation and because of the 8c) Each species becomes genetically of random element in colonization, one molded to its compressed altitudinal or another member of an altitudinal Fig. 7. Altitudinal ranges of the honey- range to a degree such that the range sequence may be missing on such a eaters PtiZop)ora perst)iata (diagonally now reflects innate survival ability hatched bar) and P. guisei (solid bar) on "mountainisland." As shown in Fig. 7, rather than competitive compression, a under these three New Guinea mountains. On Mt. circumstancesa low-altitude Michael, where both species are present, gap between the ranges of the two species may expand into the range of their altitudinal ranges are mutually ex- species develops, and neither species a missing high-altituderelative, a high- clusive. On Mt. Wilhelmina, where P. expands altitudinallyon removal of the altitude species may expand into the guisei is absent, and on Mt. Saruwaged, other. where P. pe)striata is absent, the remain- range of a missing low-altituderelative, ing species takes over most or all of the This process seems to be the principal and a high-altitudespecies and a low- altitudinal range of its missing relative. mechanism by w'nichthe rich diversity 23 FEBRUARY 1973 765
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of bird species in the mountains of ducing such transitions, one would this overlap band the neighbor of a l!Jew Guinea evolved out oiTthe low- expect two competing,territorial species given individual would as likely belong lands (15). with different altitudinaladaptations to to the other species as to the same What is the significance of sharp replace each other in an overlap Iband species, whereas in the distributionsof altitudinal transistions? If there were which would consist of a mosaic of Fig. 6 each individual is surrounded o special behavioral mechanism pro- territories of the two species (2Z). ln by individuals czf the same species. In fact, altitudinal segregation of con- generic species on mountainousPacific Stage Stage islands with fewer than 66 species 3000- 3000- fW always involves broad overlap bands, 1 C) and sharp transitionsoccur only on the z 2000 more species-rich islands. This contrast suggests two selective pressures under- {ooo- 1 000 - lying sharp transitions.First, in species- poor areas the niche of a given spe cies is nearly as fbroad as permitted o] O- loy its intrinsic adaptationsand is little compressedby interspecificcompetitione 3000- 3000 - - 7 Under these conditions the success oiTa 2 dispersingjuvenile in colonizing a new 2000 2000- territory will depend mainly on visible features of the environment.In species- 1000- 1000- rich areas,'however,the task-of identi- fying a territory that offers a high probability of breeding success for a O- given species becomes much more 3000- -- - 3000- difficult, since success now depends 8a critically on the presence and abun- - 3 dance of many other competingspecies. a 2000- s 1 M This in effect would requirea dispersing 3 1000- 111111 juvenile to perform a faunal survey in ._ 1000- addition to merely judging the appear- : ance of the habitat. Second, a selective O- O- pressure may arise from the difficulty 3000- - of finding mates in a species-richcom- 3000- 8b munity where many species are rare. 4 Thus, I postulate that, on species-rich 2000- 2000- islands but not on species-poorislands, _ dispersingyoung birds are programmed 1000- genetically, or they learn by early
10P0- , S experience, to seek out habitats where
O- their species is already established, O- rather than habitats where they will be 30Q0- n surrounded by individuals of other 3000- - 1 18c species. The presence of individualsof -t 5 their own species becomes the only 2000- 2000- - reliable indicator that the habitat is suitable for them. By waiting in the 1000- 1 dooo-sts5ssIIsIazIIIIIIIIIIIIIID juvenile fringe or "kindergarten"at the lower or upper limit of the O I | ' 1 f o altitudinal range, the juveniles are in 132 138 444 150 132 138 144 150 a ringsideposition from which they can eventually seize an optimal territory Longitude (°E) vacated by an adult. h Otherspatial segregating mechanisms Fig. 8. Stages in the evoltltionary transformation of one species into two species with mutually exclusive altitudinal ranges. See text for details. In each diagram altitudina],I Two further ecological segregating range is plotted as a function of longitude for some species or pairs of species in thee mechanisms, vertical stratificationand mountains of New Guinea. Thus, in stages 1 through 4 there is neither geographica]t1 habitat segregation,resemble altitudinal nor altitudinal overlap, in stages 5 through 8a and 8c there is geographical but noh segregation in that closely related altitudinal overlap, and in stage 8b both geographical and altitudinal overlap. Eackd species become sorted out spatially. such distributional pattern represents a "snapshot"of a diSerent stage in speciation and permits reconstruction of the whole process. Examples of species in each stage are:: Bird species are more stratified 1, Ifrita kowaldi; 2, Climactesis leucop11aea;3, Melidectes nouXuysi and M. princepsi; vertically in the New Guinea forest 4, ..Parotialawesi and P. carolae; 5, Pac11ycep1lalopsispoifosoma and P. 1zattamensis;6 Ael blyo)nis macg}egoriae and A . subala}is; 7, Ducula rufigaste} and D. c11alsonotaI' than in forests with fewer bird species 8a, Eupetes caerulescens, E. castanonotus, and E. Ieucostictus; 8b, Neopsittacus mus but similarvegetational structure. Thus, schenbroekii and N. pullicauda; 8c, MeZiphagaanaloga and M. orienfalis. standard bird nets 2 m in height and 766 SCIENCE, VOL. 179
This content downloaded on Sat, 22 Dec 2012 20:00:09 PM All use subject to JSTOR Terms and Conditions resting on the ground catch only about concentratedtoward the main branches, medium-sized bird of relative weight half of the forest species locally present the smaller birds toward the periphery +/2.73 = 1.65 can coexist successfully in New Guinea montane rain forest but (Fig. 9). Among congeners sorting by with both the large species and with all species in the species-poorrain forest size in New Guinea, the ratio between the small species. Thus one finds a of New Zealand. Some of the species the weights of the larger bird and the sequence of three or more species in New Guinea forage only in the smaller bird is on the average 1.90; it rather than just two species of such canopy; others forage regulalrlyat 4 to is never less than 1.33 and never more different sizes. For example, the eight 15 m above- the ground but never than 2.73. Species with similar habits fruit pigeons of the genera Ptilinopus descend to 2 m and hence are never and with a weight ratio less than 1.33 and Ducula coexisting in the lowland caught in nets; and others forage only are too similar to coexist locally (that forests of New Guinea form a graded on the ground or up to a height of is, to share territories)and must segre- size sequence over a 16-fold range in 2 m. As in the case of altitudinal gate spatially. For instance, the cuckoo- weight (Fig. 9). ranges, vertical foraging ranges expand shrikes Coracina tenuirostris and C. May and MacArthur (6) predicted on species-poor mountains or islands papuensis segregate by habitat on New on theoretical grounds that sprecies where vertically abutting competitors Guinea, where their average weights segregatingalong a single niche dimen- are absent (10) . are 73 grams and 74 grams, respec- sion in a Ructuatingenvironment must Some congeners become sorted by tively, but they often occur together in maintain a certain minimum niche dif- occupying different habitat types, often the same tree on New Britain, where ference. This minimum spacing seems to the mutual exclusion of each other. their respective weights are 61 g and in fact to have been reached in nature For example, whereas there is only one 101 g. New Guinea has no locally by those bird species that segregate species of barn owl (genus Tyto) in coexisting pairs of species with similar according to size. Thus, on Pacific most parts of the world, New Guinea habits and with ia weight ratio ex- islands with 30 to 50 bird species, has three species: Tyto capensis in ceeding 2.73, presumably because a the ratio between the weights of pairs grassland, T. alba in partly wooded of birds segregating by size is approxi- areas, and T. tenebricosa in forest. mately 4, but this ratio has already Among species sorting by habitat, spa-- been compressed to 2 on islands with 163 Fruit (mm) tial expansion is a frequent response to 123 / 100 species. On New Guinea (513 the absence of competing congeners species) the average value of this _< /t
23 FEBRUARY 1973 767
This content downloaded on Sat, 22 Dec 2012 20:00:09 PM All use subject to JSTOR Terms and Conditions Some General Features of Competition increase linearly or even more rapidly The consequences of the species- with species diversity,so that an island area relation (Fig. 1) should be taken Despite the abundant distributional with few species also has a low density into considerationduring the planning evidence for competition between New of individuals (11). However, on the of tropical rain forest parks (13). In a Guinea bird>;species, one rarely sees Pearl Islands oS Panama, total popula- geographical area that is relatively a member of one territorial species tion densities of birds are even higher homogeneouswith regard to the fauna, fightinga member of another territorial than on the Panama mainland l(25). one large park would be preferable to species. Once territoriesare established, Part of the difference between these an equivalent area in the form of fighting simply does not pay: the win- two sets of results may depend on several smaller parks. Continuous non- ner as well as the loser may be injured, whether the island colonists are as forest strips through the park (for or both combatants may attract the well adapted to the available habitat example, wide highway swaths) would attention of a predator. Even among as are the mainland species they re- convert one rain forest "island" into migrant North American thrushes that place. Also, the low populationdensities two half-size islands and should be must reestablish their territories each on the New Guinea satellite islands, avoided. If other considerationsrequire spring, interspecific chases and aggres- and on old isolated islands such as that an area be divided into several sive behavior disappear within a week Madagascar (26) and New Zealand, small parks, connecting them by forest after arrival on the breeding grounds may reflectgenetic deteriorationin their corridors might significantly improve (24). In tropicalrain forest, where many isolated populations, because of small their conservation function at little bird species are permanently resident gene pools, reduced intraspecific and further cost in land withdrawn from and are relativelylong-lived, and where interspecific competition, and (fre- development. visibility inside the forest is poor, quently) short populationsurvival times Modern ecological studies may also neighboring individuals may confine to extinction (1.1). be relevant to the understiandingof their aggressive behavior for years to human populations. For instance, songs and calls a.nd simply learn to during a long period of human evolu- avoid each others foraging space. Conclusions tion there appear to have been not one Species that colonize species-poor but two coexistent hominid lines in islands, where they are freed of com- The concepts by which MacArthur Africa, the A ustralopithecusrobustus- petition from close relatives, often and Wilson have transformed the A . boisei l("Zinjanthropus') line, which broaden the spatial parameters of the science of ecology in the past decade, became extinct, and the A ustralo- niche by immedia.telyoccupying a wider and the results of ecological studies pithecusafricanus-A. habilis line, which range of habitats, altitudes, or vertical such as mine on New Guinea bird led to Homo sapiens (27). The need to foraging positions. However, the col- communities, have implications for maintain niche differences between onists rarely expand their diets or conservation policies. For example, these lines must have provided one of range of foraging techniquesuntil after primary tropical rain forest, the most the most important selective pressures relatively long periods of time on an species-rich and ecologically complex on the ancestors of modern man in evolutionary scale (11). This combina.- habitat on earth, has for millions of the late Pliocene and early Pleistocene. tion of spatial elasticity with tactical years served as the ultimate evolu- Thus, any attemptto understandhuman and dietary conservatismreRects partly tionary source of the world's dominant evolution must confront the problem of the degree of genetic programming plant and animal groups. Throughout what these ecological segregating underlying the stereotyped foraging the tropics today, the rain forests are mechanismswere. To what extent were strategies of birds, and partly the being destroyed at a rate such that contemporaneous species of the two economics of feeding. Given a certain little will be left in a few decades. lines separated by habitat, by diet, by set of inflexible tactics, the economics When the rain forests have been re- size difference, or by foraging tech- of energy yield and energy expenditure duced to isolated tracts separated by nique, and were their local spatial dis- in foraging dictate the diet but leave open country, the distributionof obli- tributions broadly overlapping or else to the individualthe decision about the gate rain forest species will come to sharpenedby behavioralinteractions as space in which the tactics can be applied resemble bird distributions on New in the case of the Craterosceliswarblers profitably(3, chap. 3). Guinea land-bridgeislands after sever- of Fig. 6? To take another example, How does the combined population ing of the land bridges.The smaller the there are striking parallels between the density of all bird species on an island tract, the more rapidly will forest present distributionsof human popula- compare with the combined population species tend to disappear and be re- tions and of bird populations on the density on a mainland?That is, istands placed by the widespread second- islands of Vitiaz and Dampier straits have fewer species than mainla.nds,but growth species that least need protec- between New !Guineaand New Britain. the types of competitive release we tion (13). This ominous- process is Some of these islands were sterilized have examined mean that the island illustrated by Barro Colorado Island, by cataclysmic volcanic explosions colonists frequentlyhave broaderniches a former hill in Panama that became within the last several centuries. The and higher populationdensities than on an island when construction of the birds that recolonizedthese islandshave the ma.inland.How well does competi- Panama Canal flooded surrounding been characterizedas coastal and small- tive release compensate on islands for valleys to create Gatun Lake. In the island specialists of high reproductive the population densities of missing succeeding 60 years several forest bird potential, high dispersal powers, and mainland species? Studies on this species have already disappearedfrom low competitive ability, unlike the geo- problem of density compensation have Barro Colorado and been unable to graphically closer, competitively su- provided conSicting results. In the New recolonize across the short intervening perior, slowly dispersing, and breeding Guinea area, total population densities water gap from the forest on the nearby birds of mainlandNew Guinea.(10, 11, in similar habitats on different islands shore of G;atunLake. 13). It remains to be seen whether 768 SCIENCE, VOL. 179
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the people of the Vitiaz-Dampier ibid., p. 603; E. O. Wilson, Evolution 13, 2(). D. Lack, Ecol*geial Isolation in Birds (Har- 122 (1959); Amer. Natur. 95, 169 (1961); vard Univ. Press, Cambridge,Mass., 1971). islands, the Polynesians, and other and D. S. Simberloff, Ecology 50, 267 21. J. W. Terborgh, Ecology 52, 23 (1971). human populationsthat colonize insular (1969). 22. M. L. Cody, ibid. 51, 455 (1970). 6. R. M. May and R. H. MacArthur, Proc. Nat. 23. ; --Is Anzer. Ncxtltr. or unstableh;abitats also have distinctive Acad. Sci. U.S.A. 69, 1109 (1972). 102> t07 (19683. 7. E. O. Wilson, Psyche 65, 26 (1958). 24. D. H. MorsefiWilson Bull. 83, 57 (1971). poptllationecologies. 8. J. M. Diamond, A mer. Mus. Nol . No. 2284 25. R. H. MacArthur, J. M. Diamond, J. R. (1967); Explorers J. 46, 210(1968); Karr, Ecology 53, 330 (1972). References and Notes and J. W. Terborgh, Auk 85, 62 (1968); J. M. 26. J. R. Karr, personal communication. Diamond, Amer. Mtes. Nos!. No. 2362 (1969); 27. D. Pilbeam, The A scent of Man (Macmillan, 1. A. R. Wallace, The Geographical Distribution J. Terborgh and J. M. Diamond, Wilson Bull. New Yorks 1972); L. S. B. Leakey, Nalure of Animals (Macmillan, London, 1876). 82, 29 (1970). 209, 1279 (1966), F. C. Howell, ibid. 223, 2. E. Mayr, Systematics and the Origin oJ 9. J. M Diamond, Proc. Nat. Acad. Sci. U.S.A. 1234 (1969); W. Schaffer, Amer. Natllr. 102, ,Species (Columbia Ulliv. Press, New York, 64, 57 (1969). 559 ( l 968). 1942); Arlimal Species and Eltolution (Harvard 10. -, ibid. 67, 529 (1970). Z8. l thank R. H. MacArthurand J. W. Terborgh, Univ. Press Cambridge, Mass., 1963). 11. , ibid., p. 1715. for stimulatingdiscussions; the National Geo- 12. -, ibid. 68, 2742 (1971). graphic Society, Explorers Club, American 3. R. H. MacArthur, Geographical Ecology 13. , ibid. 69, 3199 (1972). (Harper & Row, New Philosophical Society, Chapman Fund, and York, 1972). 14. , Science 151, 1102 (1966). Sanford Trust of the American Museum of 4, - -- and E. O. Wilson, The T}teory ot Natural History, and Alpha Helix New Guinea [sland Biogeogra phy (Princeton Univ. Press, ot New Guinea (Nuttall Ornithological Club Programof the National Science Foundation, Prunceton, N.J., 1967). Cambridge, Mass., 1972). for support; M. Cody, A. Grinnell, S. 5. - Is Elfolution 17, 373 (1963); R. H. Mac- 16. F. W. Preston, Ecology 43, 185 (1962). Kaufman-Diamond,S. Krasne, and G. Szabo, Arthur and R. Levins, Proc. Nat, Acad. Sci. 17. J. Terborgh and J. Faaborg, Atlk, in press. for criticismof the manuscript;D. Amador,for U.,S.A. 51, 1207 (1964); R. -H. MacArthur, Biol. 18. R. F. Fl}nt, Glacial and Pleistocene Geolog> permission to use facilities of the American Rev. Cambridge 40, 510 (1965)- -- , H. (Wiley, New York, 1957). Museum of Nattlral History; and more resi- Recherfi M. Cody, Amer. Natur 100, 319 19. F. Vuilleumier, Amer, Natxr. 104, 373 (1970); dents of New Guinea than can be mentioned (1966?; R. H. MacArthtlr and E. Pianka, J H. 13rown ihid. 105, 467 (1971). hy name. tor makinv ficldworkpossible.
ecological health, and can indeed bring out potentialitiesof the earth which re- main unexpressed in the state of wil- derness.
H* e The disastrous ecological consequen- umanlzlng the Earth ces of many past and present human activities point to the need for greater Rene J. Dubos knowledge and respect of natural laws. This view is succinctly expressed by Barry Commoner in his fourth law of ecology: "Nature knows best." I shall first discuss the limitations of this law. When left undisturbed, all environ- How gray and drab, unappealingand which were most Rourishingin antiq- ments tend toward an equilibriumstate unsignificant,our planet would be with- uity are now among the poorest in the called the climax or mature state by out the radiance of life. If it wereCPnot world. Some of their most famous cities ecologists. Under equilibrium condi- covered with living organisms the sur- have been abandoned;lands which were tions, the wastes of nature are constant- face of the earth would resemble that once fertile are now barren deserts. ly being recycled in the ecosystem, of the moon. Its colorful and diversified Disease, warfare, and civil s;trifehave which becomes thereby more or less appearance is largely the creation of certainly played important roles in the self-perpetuating. In a natural forest, microbes, plants, and animals which collapse of ancient civilizations;but the for example, acorns fall to the ground endlessly transform its inanimate rocks primarycause was probablythe damage and are eaten by squirrels,which in turn and gases into an immense variety of caused to the quality of the soil and to may be eaten by foxes or other preda- organic substances. Man augments still water supplies by poor ecological prac- tors; the dead leaves and branches the further this diversification by altering tices. Similarly today, the environment excrements of animaIs, are utilized by the physical characiterIsticsof the land, is being spoiled in many parts of the microbes, which return their constitu- changing the distribution of living world by agricultural misuse or over- ents to the soil in the form of humus things, and adding human order and use, by industrial poisoning, and of and mineral nutrients. More vegetation fantasy to the ecologtcal determinism course by wars. grows out of the recycled materials, of nature. The primary purpose of the recent thus assuring the maintenance c)f the Many of man's interventionsinto na- United Nations Conference on the Hu- ecosystem. ture have, of course, been catastrophic. man Environment, held in Stockholm When applied to such equilibrated History is replete with ecological dis- in June 1972, was to formulate gIobal systems, the phrase "Natureknows best' asters caused by agriculturaland indus- approaches to the correction and pre- is justified, but is in fact little more trial mismanagement. The countries vention of the environmental defects than a tautology. As used in this resultingfrom man's mismanagementof phrasesthe word nature simply denotes The author is a professor emeritus of the Rockefeller University, New York 10021. This the earth. I shall not discuss the techni- a state of affairs spontaneouslybrought article is the text of the B. Y. Morrison MemoriaI cal lecture, sponsored by the Agricultural Research aspects of-these problems,but rather about by evolutionary adaptation re- Service of the U.S. Department of Agriculture. shall try to look beyond them and pre- sulting from feedbacks which generate The lecture was delivered at the annual meeting of the AAXS, 29 December 1972, in Washington sent facts suggesting that man can ac- a coherent system. There are no prob- D.C. Reprints may be obtained from Dr. Robert tually improve on nature. In my opin- lems in undisturbed nature; there are Nelson, Public lnformation Office, Agrlcultural Research Service, U.S. Department of Agriculture ion, the human use of natural resources only solutions, precisely because the Washington, D.C. 20250. and of technology is compatible with equilibrium state is an adaptive state. 23 FEBRUARY 1973 - 769
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