Table Of ContentSelbyana 14: 21-22
ARTHROPOD ABUNDANCE AND COMMUNITY
STRUCTURE ASSOCIATED WITH OHIA CANOPY
FOLIAGE (METROSIDEROS POLYMORPHA)
FROM THE HAWAIIAN ISLANDS:
DATA FROM TWO STUDIES
ROBERT W. PECK
Department of Zoology, University of Hawaii, Honolulu, Hawaii 96822
INTRODUCTION within Hakalau Forest National Wildlife Refuge
(NWR), at 1,900 m, on the windward slope of
Recent work in tropical forest canopies has Mauna Kea. Here, ohia varies markedly in its
revealed that most arthropod communities are growth form depending upon the extent of can
highly diverse, with many species showing host opy cover. In closed canopy areas, trees have a
tree specificity, and maintaining restricted geo straight, pole-like form, with foliage concentrat
graphic and ecological ranges. Little information ed at the top, and form a nearly continuous forest
exists regarding the mechanisms that form and canopy. In open canopy areas, where ohia are
maintain these communities, although it has been widely spaced, trees become massive, with fo
suggested that patterns of community structure, liage extending from the top to more than half
such as guild organization, may exist (Moran & way to the ground. These differences in forest
Southwood 1982). The structure and patterns of structure, which may have arisen from events
arthropod communities within insular faunas are such as natural gap formation, logging, and cattle
even less well known. Two factors suggest that grazing, have led to a mosaic of forest types.
arthropod communities in island forests, such as Between May 1991 and March 1992, foliage was
those of the Hawaiian Islands, may differ. First, sampled and arthropods collected from both for
the extreme isolation of the islands has resulted est types via a pole-mounted branch clipper. This
in a disharmonic fauna, differing greatly in high study, which also looked at habitat-limiting fac
level taxonomic diversity. Approximately 50% tors for insectivorous birds, concentrated on bio
of the world's insect orders and 15% of the fam mass differences of arthropods between the two
ilies are native to the archipelago. Second, Ha areas.
waiian wet forests tend to be dominated by a Gagne's work took place within and adjacent
small.number of canopy-forming tree species. to Hawaii Volcanoes National Park, on Mauna
Over large areas, one or two species may com Loa. His sites were relatively undisturbed, closed
prise the canopy. How these factors have influ canopy forests, that differed in elevation. The
enced the composition of Hawaii's arthropod lower elevation site (Thurston lava tube; 1,195
community is not yet fully understood. m) was located eight miles south of a higher el
This paper summarizes data on the structure evation site (Kilauea Forest Reserve; 1,600 m).
of the arthropod community associated with the Between March 1971 and May 1973, ohia can
dominant wet forest canopy tree in Hawaii, ohia opies were fogged using synergized pyrethrum,
(Metrosideros po!ymorpha). Two studies are pre approximately every other month.
sented. First, my recent study compared the fo
liage community within two nearly contiguous
REsULTS AND DISCUSSION
areas differing in extent of canopy cover, forest
structure, and tree growth morphology. The sec Within Hakalau Forest (NWR), ohia foliage
ond study was from the work of the late Dr. from the open canopy area supported a greater
Wayne Gagne (Gagne 1979, Gagne & Howarth arthropod biomass than an equal amount of fo
1975), and allows comparison of two relatively liage in the closed canopy area. Although all taxa
pristine forests, similar in structure, but differing followed this trend, only spiders and overall bio
in elevation. mass were found to differ significantly. Spiders
contributed the greatest biomass in both areas,
followed by caterpillars, hemipterans, psocop
METHODS
terans, and homopterans. The pattern of com
Both studies took place within mid-elevation munity structure is similar in both areas, with
wet forests (1,900-3,000 mm rain/year) on the no difference in the relative abundance of the
Island of Hawaii. The influence of habitat struc arthropod groups. These data suggest that can
ture on arthropod communities was investigated opy cover, understory structure and ohia growth
21
22 SELBYANA [Volume 14
morphology have little effect on the composition spiders, and the relative insignificance of chew
of the fauna, but do influence the biomass of ers. Although caution is necessary when com
arthropods the foliage supports. paring studies where slight differences in meth
Canopy fogging data from Mauna Loa re odology or guild placement can have a large effect,
vealed between-elevation similarities as well as these data suggest that the guild structure of ar
differences. Psocopterans, hemipterans, and ho thropods associated with ohia foliage may be
mopterans were numerically important at both unique among tropical forest canopies.
elevations, while caterpillars, neuropterans and
orthopterans were least numerous. However,
ACKNOWLEDGMENTS
collembola ranked second in abundance at the
lower elevation site, but were rare at higher el I thank Frank Howarth for help with Wayne
evations; spiders were more common at higher Gagne's data. Financial support was provided to
than lower elevations. When taxa were placed R.W.P. from Hawaii Audubon Society, Sigma
into feeding guilds, between-site similarities and Xi, and John D. and Catherine T. MacArthur
differences reflected the distribution of the dom Foundation (to L. Freed, R. Cann, and S. Co
inant groups. At both sites, detritivores were nu nant).
merically dominant, followed by sap-suckers (see
Gagne 1979, Gagne & Howarth 1975 for guild
LITERATURE CITED
assignments). Predators were important at both
areas, but much more so at higher elevation, with BASSET Y. AND A. H. ARTHINGTON. 1992. The ar
spiders contributing greatly to this difference. thropod community of an Australian rainforest
Fungivores and tourists were few at both sites. tree: abundance of component taxa, species rich
Many of Hawaii's unique forest ecosystems ness and guild structure. Aust. J. Ecol. 17(1): 89-
98.
have been highly modified or destroyed, partic
GAGNE W. C. 1979. Canopy-associated arthropods
ularly at lower elevation. Major contributing fac
in Acacia koa and Metrosideros poiymorpha tree
tors include land use practices and competition
communities along an altitudinal transect on Ha
and predation from alien species. Data from the waii Island. Pacific Insects 21(1): 56-82.
Kilauea Forest Reserve site (selected for study --AND F. C. HOWARTH. 1975. Arthropods as
due to its pristine nature) revealed that all but sociated with foliar crowns of structural domi
the tourist guild have been invaded by alien ar nants. In D. MUELLER-DoMBOIS, K. W. BRIDGES,
thropod species. Their impact on the native com AND H. L. CARSON, eds., Island ecosystems: bio
munity is unknown. logical organization in selected Hawaiian com
munities. Hutchinson Ross, Stroudsburg, Penn
To compare patterns of Hawaii's insular ar
sylvania.
thropod community with other areas, a guild
MORAN V. C. AND T. R. E. SOUTHWOOD. 1982. The
comparison of the fogging data was made to for
guild composition of arthropod communities in
ests in Borneo (Stork 1987) and Australia (Basset trees. J. Anim. Ecol. 51(1): 289-306.
& Arthington 1992). More differences than sim STORK N. E. 1987. Guild structure of arthropods from
ilarities were found, but the Kilauea Forest Re Bomean rain forest trees. Ecol. Ent. 12(1): 69-80.
serve did show similarities to the Australian for
ests with the dominance of sap-suckers and
