Untitled Page 002 [manoa.hawaii.edu]manoa.hawaii.edu/hpicesu/book/1988_chap/09.pdf · Plants and animals ancestral to our native Hawaiians ecies of today (a total of about 1,000 colonized

ISLAND ECOSYSTEMS

Hawaiian organisms clearly comprise a highly si nificant rt of the natural, cu~fura/, a n d inte//ecrua/ i l ~ r ~ t a g e ofihepeopgof rile United Srarcs and ofthe worid.

Lloyd I*. Loope

Islands have long fascinated biologists and have contributed greatly to development of the science of biology. Charles Darwin's five-week vistt to the Galapaps Islands in 1835, as part of an exploratory voyage around the world, was crucial in his subsequent development of the theory of evolution. In the second edition of his journal, ubhhed in 1845. Darwin made a famous pronouncement about thc hearing oPthe Galapagos islands on the origin of species:

Thc archipchgo is a littlc world within itsell, or rather a satsllite altached rn Antcrimfi. w h c n ~ s it lhlr dcriwd i t icw s1nw colnnists. and has received rhc gctwal charxtcr ol' ils indigenous prududions. Conridcring the small sizc of these islands, \vr: icel lhc marc astonished ill the numbcr of thcir aboriginal beings, and 81 lhsir cunlined rangc. Sccing rvwy height crnwncd w i ~ h its crater, and the houndarirs ufmost lava-strums still diaisct, wc arc led to 1rclia-x Ihal within a pcrkd geologically rcant the unbroken occan war hcrr: sprcad out. llence hoth in rpwc and time, wc rccm to be bruufiht rorncahar near to that grwl Art--that myslcry of mytcrics--the Ersr appurance of new bcings no this cnnh.

Oceanic islands, r~articularlv the Hawaiian and Galananos archioelams. - . continue to serve a< &cia1 5ite;for modern evo1utiona~u;dies. ~ o n t i n u ~ n ~ evolutionary rtudies oicndemic island hintn arc dependent on [he survival of a mcanitieIul samnle of olants and animals. Hawaiian oreanisms clearlv cornpxe a GE.hlu iiinifica;~: part of the natural, cc:tur~l. a d inrel:ectcal ' heri~age o i t . ~c pcrq,.e of the L ~nile~l Slaws and of the awrltl.

DEVELOPMENT OF ISLAND IXOSYSTEMS THHOUCH TIME

Islands are n~icrocosms of the biosphere in space and time, with evolu- tion proceeding in partial isola~ion from that on continetlts and othcr islands. In the Hawaiian Idands, localed ovcr 2,500 mi (4,000 km) from the nearest continent, this isolation from other lands was, until recently, almost complete. The first volcanncs of the island chain rose from the central part of the ances- tral Pacific Ocean ahout 70 million years ago. Individual islands were formed.

matured, and eroded to sea level in a cycle lasting about 10 million years. New islands were continuallv heinr formed as the Pacific Plate drifted northwestward. The main Hawaiian Islands now range in age from under amilliou years (Hawai'i) to 5.8 milliot~ years (Kaua'i). Recent biological cvi- dence suggests that ancestors of Hawai'i's diverse endemic pomace or vinegar flies (Drosophilidae) werc resent in the island chain 40 million years ago (Beverlqand Wilson 39857. '

Plant seeds and animals from other lands reach newly formed volcanic islands verv rarelv. through a limited varietv of means--floatinn in the ocean or carried by air currents-or birds. In the case of the Cialapag& Islandb, "onIv'603 mi (06.5 km) from the tnainland of Sour11 America. !izards, ro- dents, and ants were ablc to colonize. oresumdiv hv riding 'rafts ' of veaeta- tion washed down tropical rivers. 1n yontrast, thksegro~pi did not reach the *waiian islands until man brought them. Plants and animals ancestral to our native Hawaiians ecies of today (a total of about 1,000 colonized the Hawaiian %lands at the rate of about one years over the 70,000,000-year history of the Archipelago. Islands nearer to a continental source area are colonized much more rapidly. In the Galqmgos lslantls, for example, about 1,000 species ancestral In the native species of the Galapagos today arrived at a rate of about one species in 3,000 yean over a period of about 3,000,000 years.

A developing isolated archipelago such as Hawai'i, with high ninuntains, tropical climate, and abundant rainfall, provided a rzmarkahle opportunity for the plants and animals that managed to arrive eariy. These vtrung island sosvstems were verv sirnole. comnosed of onlv a few soecies. his cnndi- tionalloncd the occ;~rren'ce nl thicvolutionaiy called adaptite rndislion in many groups. Biological vacanc'es existed and bpccle developed lo fil l these vilcancirs. With a scarcltv of forest tree species in tile devel- ouine flora. herbaceous ancestors ~roduced tree-like hescendants. From a;o<mol~ iinch-like ancestor, ~he '~awai ian hokycreepers (1)repanidinae) evol\a! dozens of diverse species, each adapted to specialmed feeding and together expioit1n9 a wide iange of insect and plmt foods (prooucinp: a\ Zinmernar (lY'0) said. "s~ckle-bilied nectar suckers. grosbeak-like seed- crackers. heay-hil!ed fruit-eaters. sharp-billed Insect catchers. some dmo\t wood~ecker-like and others almost oa%ot-like in habit"). Atnone the insects and h'irds. largely protected from iniense predntioo, many flight& forn~r tlewlnped frtm otherwice flip,hted groups. In one group, the gcometrid moths (or "inch\vormr"), herbivoroui anceitori orndwcd iredaccoos descendants. i)ther such adaptive shins anlong ~ a w a h Ilom &d fauna were numerous.

Over millions of years, ecosystems of the Fla\r.aiian Islands hecanie incrensinnlv r~ch in suecies nf nll~nts and aninrals. as new eenclic stocks

is1i11ds were rrodetl ncarei andnearer to sea level. massive extinction of snecies occurred. Hrnvevcr. manv lineaees survived and continued to evolve . ~~ ~

~ ~ . on vounyrr islands. produci~r:: drverse i&nd rcos)stem% with bpccie,well adapted to their en\.ironmetrts. Raud evolution. through founder effects (the establishmet~t of small numheis of indi\lduals with'onlv :t nortion of the Qenetlc variah~l~t! ilva~ldhle In the cntlre pol~~dation), geneilc dottlenecks (extreme redwtmn of oopdatinn numbers and a m , ~ b d ~ t y throurh catastroph~c events), and relaxed nilural sc.lection in generally favorable s i t~k ions ,

. is characteristic nf some species groups.

DISRUPTION OF ISLAND ECOSYSTEM DEVELOPMENT

7he processes of coloniwtion and island evolution continued uninter- rupted until Polynesians the 4th century A.D. They brought dozens of new altered ecolo 'cal condi lions through use of fire of land Z r agriculkre. Changes accelerated with in 1778 A.D. The entomologist Zimmcrman (1970) characterized these changes a s follows:

This extraurdinaw Hawaiian biula would haw continued its rcmartahle adaciivc ~ ~ ~ -. . .-- '~ - radialion at a rapd ralc had man no! cau~crl ils reccnt decirnarion. Now a drar. tic new \cr nfun~~vumhlc cundilions farm thc delicalcly adapted hima, a d a large fraction of it is dnorncrl to cncrn~inalion. What thc fukrc holds'for it w w n n ~ prcdicl, md m shall nu1 know enyhing like it again. Many of its dorioui prduas. the fruit nf user, haw alrcad" vnishcd, and its ww mountains arc being washcd back into ihc sea *hen= thcy came.

Plants and animals of the Galapagos Islands and many other islands of the world face a similar uncertain future due to chanued ecoloeical condi- cons. Having evolved in long isolation from the continial challeSge of many of the evolutionary forces th:tt shape conrinentsl plants and animals -including such forces as hnwsing and trampling by hooved mammals, prc- dation by rodents and anls, virulent diseases, and frequent and intense fire- island organisms are highly vulnerable when such forces m e introduced to their environments.

NEEDS FOR THE FUTURE

We Ilaw a fairly gocd ~ e n e r a l understanding of i4and ecmy\tents. Wc know t h a ~ , .although thev i~wxllv poczess swnewhal fewer component species than climatinllv Ccrrn~arahle c~;ntit~ental ecnsvstems and mivlack tawnnomic groups of orgar~sms hpor t an t elsewhere, 1hc.sarne basic ecdogical principles apply to island ecosystems as to ecosystems everywhere. We know that small populationr, rare forms, and rapid evolution are characteristics of oceanic tslands. We are becoming increasiltgly aware of the vulnerability of islands to human disturbance and to inv:aions of in t r~duced species. Scientists need to accelerate their studies of island organisms hefore many more of [hem dis- amear. as well as to addrchs hetter the tooic of conservation biolonv of -, i&d species and ecosytems. Actively managed n;.rional parks 2nd reserves ?n islands seem to procide the only opportuni!~ for hng-term survival of 1s:ar.d ecos\s!erns. Lonu-rertn research and ~ r t o n ~ ~ o r i n e will ue r e a i r e d to support rninagement p;;,gran~s. Research on techniq;es to contrh~ the n ~ o s t damaging d i e n species will always be among rhe highest of prioril~es. Per- haps ironically, intervention by man through mana ~etnent of alien species seems t o provide the only possible antidote to the b :tndora's hox of ~n l ro - duced species and other disturbances 1)rought hy m:ttt. In order for stuch Programs to succeed, strong commitment hy managers and ade tiate funding will be required. I n order to assure adequate commitment and(Eundingfor these programs in the future, education of the puhlic to the importance, uniqueness, and wlncrability of island species is prohably the most esscntial requirement.

Important References

Re\rc.erlcy, S.H., and A.C. Wilson. 1985. Aneiemr origin for Hawaiian Drosophilinilc inferrcd from prnlcia mrnparisvns. Prncecditt~s, ~Ymio,tolAcodrr,r.y ofSci~~tccr, US.A. 82:4753-4757.

Cislqui3.S. 1965. IrlorrdLilr; A.hrn1uml H~.$loryof~l~c Islmdso/fl~c World. Natural Hislory Ptcss, (hrden Cily, New York.

Carlquist, S. 1974. Islu~td Biolu~. Coltrmbia Univ. Prug Ncw Ynrk. Carson. ILL, and A.R. Templeton. 19x1. (icnctic rcsolulinns in rckrion 10 spccialion

phcnumcna: Ihc founclinguf new pnpulalions. An,irulReview ($Ecolon mtii Syclc~nnli(:s 1507-131.

Prinecwn, Ncw Jcrsey. James. H.F.. and S.L. Olson. 1083. Flinhtlcss birds. Naficral Hiskwv 92(9l:%)-10.

- . . . ~ a r n c i and Row. New York.

1lonohlu. Zimmcrman, E.C. I(97O. Aclilptivc radixinn in 1l;waii with spccial rckrcncc to insects.

Biafrnpico ?(l):X-$8.