International Biological Program Technical Reports (1970-1975)

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The Pacific Cooperative Studies Unit & The Hawaii-Pacific Islands Cooperative Ecosystems Studies Unit
University of Hawaii at Manoa
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Honolulu, HI 96822-2279

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    Canopy-associated arthropods in Acacia koa and Metrosideros tree communities along the Mauna loa Transect
    (Island Ecosystems IRP, U.S. International Biological Program, 1976-06) Gagne, Wayne C
    The spatial distribution and zonation of canopy-associated arthropods of Acacia koa and Metrosideros tree communities along an altitudinal transect on the east flank of Mauna Loa was determined by insecticidal fogging of the canopy with pyrethrum. Eight sites were on the Mauna Loa Transect, which has been intensively sampled by IBP participants in the Island Ecosystems IRP. Two sets of transect zones were determined on the basis of arthropod distribution. The influence of environmental and biotic factors, plant community structure and climate are interpreted according to distribution patterns. The distribution of arthropod groups coincided quite closely with vascular plant communities of the transect as defined by other studies. The composition, spatial distribution, and environmental relationships of arthropod canopy communities along the Mauna Loa Transect are compared with the situation pertaining along other lower elevational transects to sea level in Hawaii Volcanoes National Park as well as with other ecosystems in order to further characterize the arthropod canopy community. Host specificity, vegetation structure, competition between ecological homologs, and climate appeared to have the most important influence on population density and spatial distribution patterns of the arthropod taxa studied.
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    Spatial Distribution of Bird Species on the East Flank of Mauna Loa
    (Island Ecosystems IRP, U.S. International Biological Program, 1975-10) Conant, Sheila
    Eleven transects in ten different types of plant communities found along an altitudinal gradient on the east flank of Mauna Loa were sampled monthly using the "count x detectability" method of censusing birds. Eight of these sites were on the Mauna Loa Transect, which has been intensively sampled by IBP participants in the Island Ecosystems IRP. Frequency, density and distribution of the 29 bird species encountered are discussed. Data on species presence and density at each site were used to construct community (sampling site) ordinations based on similarity indices and species ordinations based on two-way tables. The results of these analyses provided the basis for the objective definition of transect zones for those sites located on the Mauna Loa Transect. The transect zones objectively defined by avian community analyses were almost identical to those based on analyses of plant communities on Mauna Loa. The habitats selected by each bird species are discussed. Optimum habitats as a reflection of maximum density are described for each species. At least two types of environmental factors associated with the altitudinal gradient appear to be important influences on patterns of avian spatial distribution: 1) continuously varying environmental factors (e.g., rainfall, temperature, gradual transitions from one plant community to another); 2) habitat discontinuities (narrow ecotones, abrupt changes in vegetation structure). Competition is briefly discussed as a factor that may affect density and distribution of some bird species. In some cases (e. g., 'Apapane, 'I’iwi) it is apparent that very specific factors (e.g., blooming time and amount in certain important food plants such as Metrosideros and Sophora) strongly influence the distribution and local abundance of a few bird species. However, vegetation structure appeared to be the single most important influence on population density and patterns of spatial distribution of the bird species studied.
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    Ecology of Fungi in Wildland Soils along the Mauna Loa Transect
    (Island Ecosystems IRP, U.S. International Biological Program, 1975-11) Stoner, Martin F. ; Stoner, Darleen K. ; Baker, Gladys E.
    The distribution of fungi in soils along the Mauna Loa Transect was determined by an approach employing specific fungal reference genera, selective isolation methods, and a combination of analytical techniques. Two sets of transect zones were determined on the basis of fungal distribution. The influence of environmental factors, particularly those relating to soil, vascular plant communities, and climate, are interpreted according to distribution patterns. The distribution of fungal groups coincided clearly with vascular plant communities of the transect as defined by other studies. Features of the structure, stability, and development of fungal communities, and of the ecological roles of certain fungi are indicated by the results. The composition, spatial distribution, and environmental relationships of fungal communities along the Mauna Loa Transect are compared with situations in other insular and continental ecosystems in order to further characterize and elucidate the ecology of the Hawaiian soil-borne mycoflora. An overall evaluation of the research indicates that the selective methods employed to evaluate fungal distribution represent an effective approach to ecosystem analysis on a broad scale.
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    The Use of Sheep Wool in Nest Construction by Hawaiian Birds
    (Island Ecosystems IRP, U.S. International Biological Program, 1975-09) van Riper, Charles III
    The utilization of sheep wool as a nesting material was examined from 1969 through 1975 on the island of Hawaii. Of the 10 bird species studied, six incorporated wool into their nests. Both introduced and endemic birds use wool, with a significantly greater usage by endemic birds. Use of wool in nest construction appears correlated with the intricacy of the nest that a species builds, with a significant difference between degree of usage in complex and simple nests. Roughly built nests, like those of the Cardinal (Cardinalis cardinalis), contained no wool whereas the complex nest of the Elepaio (Chasiempis sandwichensis) had a great deal of wool. Wool is apparently used by the birds because it is a readily available material in certain areas, and because of its binding quality. The wool is gathered from tufts that snag on branches as the sheep pass or from dried skins on the ground. The amount of wool utilized in each nest varies both interspecifically and intraspecifically, but in all nests only the body of the nest contained wool, the lining always being of other materials. A separate study was conducted to determine if wool is used only when available nearby or is a sought-after material. Only the Elepaio was found to consistently travel distances to procure wool, whereas the other species studied used it only when available within their territories.
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    Plant-Pollinator Interactions in Hawaii: Pollination Energetics of Metrosideros collina (Myrtaceae)
    (Island Ecosystems IRP, U.S. International Biological Program, 1976-04) Carpenter, F Lynn
    The most abundant tree species in much of the undisturbed Hawaiian forests was the subject of a two year study on plant-pollinator interaction and energetics. The purposes of the study were 1) to determine the roles of insects and of some endemic Hawaiian birds in the pollination of the tree, Metrosideros collina, 2) to test the hypothesis that maximal outbreeding and seed set occur at intermediate levels of nectar availability, 3) to understand the adaptive significance of profuse flowering in this species, and 4) to compare the pollination ecology of this species and the degree of specialization in the plant-pollinator community with those of similar mainland systems. Endemic Hawaiian birds (Drepanididae) are essential for high levels of fruit set and outbreeding in M. collina. Fruit set was much higher in redflowered individuals when birds were allowed to use inflorescences than when only insects used them. This is apparently caused by partial self-incompatibility, such that maximal fruit set occurs only with outbreeding, the primary agents of which are the birds. The predominant flower color in the population, the dimensions of floral parts, and copious nectar secretion adapt this species to bird pollination. However, insects effect moderate amounts of pollination and fruit set. The open flower and the color- and scent-variability within the population may be adaptations for insect pollination in the event that bird pollination fails. The population seems to have differentiated along an elevational gradient, with adaptations for bird pollination increasing proportionally with elevation. The generalization of the pollination strategy is on both an individual and populational basis, and enables M. collina to be the good colonizer that successional patterns and its own geographical distribution show it to be. Red-flowered individuals are partially self-compatible, but yellow-flowered individuals are totally self-compatible. The yellow-flowered morph may be evolving autogamy. At this stage its breeding system is intermediate between autogamy and outbreeding, with geitonogamy being encouraged due to 1) increased attractiveness to insects relative to the high energy birds by means of color and scent cues, and 2) increased nectar flow which satiates pollinators. Furthermore, yellow-flowered individuals have a floral structure that facilitates transferal of pollen to stigmas in the same inflorescence by means of small size pollinators, or even without the aid of a pollinator. A model is derived that predicts the selective results of various degrees of pollinator limitation on nectar productivity. Bird numbers are more constant relative to nectar availability than would be expected by random sorting, although temporary deficits and surpluses of these pollinators occur: their inability to respond instantly to changes in the intensity of bloom introduces lags into the system, and these have important consequences for pollination, outbreeding, and gene flow. During some times of the year pollinators are limiting to M. collina, and intraspecific competition occurs. Maximal fruit set and outbreeding do occur at intermediate nectar availabilities. Interspecific competition between species of trees for pollinators is a potential selective force that may explain the character displacement and staggering of flowering seasons of several tree species in the Hawaiian forests. Comparison with a similar but more diverse forest community in New Zealand and with mainland tropical forests suggests that the length of flowering season per tree species is inversely related to the number of tree species competing for pollinators. Profuse flowering in M. collina results in lowered fruit set per inflorescence because of decreased outbreeding, but the total number of fruits set per tree is probably high because of partial self-compatibility in most individuals. Thus, the M. collina system does not help explain profuse flowering in mainland tropical species that are totally self-incompatible. In comparison with mainland communities, the degree of specialization in the plant-pollinator relationship seems to be less in Hawaiian forests, although more information is needed on the Hawaiian lobelias and Sophora chrysophylla before such a statement should be made with any certainty.
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