Mauna Kea Ant Survey

Principal Investigators
Peter T. Oboyski and Paul C. Banko

Affiliation
Pacific Island Ecosystems Research Center, U.S. Geological Survey - Biological Resources Division / Pacific Cooperative Studies Unit - University of Hawaii

Introduction
Five species of ants are documented from upper elevations of Mauna Kea (Wetterer, et. al. 1998). Linepithema humile, the argentine ant, (max. elev. 2640m) and Cardiocondyla venustula (max. elev. 2430) were the most common and widespread above 2000m. Three other species, Pheidole megacephala, the bigheaded ant, (max. elev. 1770), Tetramorium bicarinatum (max. elev. 1820), and Monomorium pharaonis (max. elev. 1930) were all collected below 2000m. Two other species, Tapinoma melanocephala, and Hypoponera opapiceps were also discovered by Oboyski (unpublished data) within the Pohakuloa Training Area on the saddle between Mauna Loa and Mauna Kea.

Two species, L. humile and P. megacephala, are of particular concern because of their aggressive and invasive nature. Also of concern is C. venustula, which along with L. humile, has been documented within the boundaries of the core population of palila (Loxioides bailleui), an endangered Hawaiian honeycreeper.

It is unclear what impact, if any, these ants have on the biology of palila. Each of these ants consumes other arthropods and sugars, such as from flower nectaries, as a regular part of their diets. The direct impact of ant foraging could be the reduction of food resources available to birds in the form of insects and spiders. Ants may reduce plant productivity by deterring pollinators and tending sap-sucking homopterans, which may limit plant resources, such as flowers and seeds, available to native bird and insect species.

To better understand what negative impacts these ants have on palila it is necessary to know the current distribution of each ant species. By comparing the current distributions to those of previous studies it is possible to determine if ant ranges are spreading or contracting. Given this information a control and monitoring plan can be outlined.

Objectives
To determine the distribution of ant species in select areas of Mauna Kea.
To compare the current distribution of ant species to that of previous studies.
To compare arthropod communities within and outside areas of ant infestation.
To provide information for the design of a control program.

Methods
Study Area: The study area is located along the southwestern slope of Mauna Kea, Hawaii from 1700 to 2500 m elevation. This area was focused on because its proximity to the highest density of palila, a federally listed endangered bird species. Habitat type changes with elevation. The lowest elevations within the study area are predominantly native grasses (Eragrostis) with occassional native shrubs (Chenopodium). Mid-elevations are dominated by native shrubs (Chenopodium, Dodonaea). The highest elevations are dominated by mixed native trees (Sophora, Myoporum) and shrubs (Chenopodium, Dodonaea). Substrate types range from ashy sand at lower elevations to course sand and weathered basalt outcroppings at higher elevations. Rainfall averages from 30 to 50 cm per year with higher elevations receiving more moisture.

Sampling: Baiting for ants follows approximately the methods of Wetterer et. al. (1998) (see also Fellers & Fellers 1982). Transects were laid from Saddle Road (~1700-1900 m) projecting towards the summit of Mauna Kea to an elevation of 2000-2500 m. Transects were spaced ~500 m apart at their origins. Stations were spaced 200 m apart along each transect. At each station three portions of canned tuna fish (approximately 2 grams per portion) were placed on clear plastic disks (~6 cm diameter) within a 10-meter radius of the station and marked by a flag. Stations were revisited after two to four hours at which time the number of ants visiting each plastic disk during a five-minute period was estimated.

Once distributions of each species are delimited semi-annual monitoring will be initiated to detect distribution changes. Pitfall traps will be set within and outside ant infestations to examine the ground fauna in these areas. Traps will be opened for a two-week period twice per year. The abundance of each species collected will be tabulated and used to compare arthropod communities within and outside ant infestations.

Results
This is a research project in progress. No data is currently available for presentation.

Contact
For more information please contact
Pete Oboyski, Entomologist
USGS-BRD
PO Box 44
Hawaii Volcanoes National Park, HI 96718
(808) 967-7396 ext.227
Pete_Oboyski@USGS.gov