Availability of food resources, distribution of invasive species, and conservation of a Hawaiian bird along a gradient of elevation

Abstract

Aim We evaluated how an elevation gradient affects: (1) the availability of food required by a specialist seed-eater, Loxioides bailleui Oustalet (Drepanidinae), or palila, and hence the distribution of this endangered Hawaiian bird, and (2) the distribution of alien threats to Loxioides populations, their primary foods, and their dry-forest habitat, and hence strategies for their conservation.Location We worked throughout the subalpine forest that encircles Mauna Kea Volcano, Hawai'i Island, but we focused our studies mainly on the western slope between 2000 and 3000 m elevation, where the gradient of elevation was greatest and palila were most abundant.Methods We determined phenology and productivity patterns of the endemic dry-forest tree species, Sophora chrysophylla (Salisb.) Seem. (Fabaceae), or m a amane, which provides Loxioides with most of their food, and another common endemic tree, Myoporum sandwicense A. Gray (Myoporaceae), or naio, which provides some resources, along a 786-m elevation gradient at monthly intervals for 10 years (Sophora only). We also determined the availability each month of moth larvae (Lepidoptera) for that were important in the diet of nestling and adult palila. In addition, we documented the incidence of parasitism on moth larvae by several wasp (Hymenoptera) and fly (Diptera) species, and we determined the distribution of predatory wasps and ants (Hymenoptera), which potentially threaten insect prey of birds. Percentage cover of alien grass species that pose fire threats in palila habitat and other weeds were assessed during one survey. Small mammal abundance and distribution were determined by trapping during three (rodent) or five (carnivore) surveys.Results Sophora flower and seed (pod) availability varied predictably along the elevation gradient, with about 4 months separating peaks in reproduction at high and low elevations. This, together with highly variable production of flowers and pods within elevation strata, resulted in Sophora resources being available to Loxioides throughout the year on the western slope of Mauna Kea. Sophora produced flowers and pods more seasonally where gradients of elevation were short; thus, resources were available less consistently. In contrast, Myoporum produced flowers and fruits with little variation with respect to season or elevation. The availability of important insect prey of Loxioides was also related to elevation, in part because threats to Lepidoptera larvae from parasitic wasps were generally less at higher elevations. Threats to insect prey from predatory ants was also less at higher elevations but the abundance of predatory wasps was not related to elevation. Several weeds that pose the most serious threats to Loxioides habitat were more abundant at mid and low elevations, and alien grass cover was somewhat greater at mid elevation, thereby increasing fire risks in the

Altered Ecologies: Fire, climate and human influence on terrestrial landscapes: Terra Australis 32

“…Ancient Polynesian and subsequent European colonists introduced many exotic species now naturalised in the Pacific Islands (Rinke 1986;Wiles et al 1997;Richardson et al 2000;). Introduced fauna prey on or harass native species (Thorsen et al 2000;Thibault et al 2002;Blanvillain et al 2003;Yap and Sodhi 2004), and compete with endemic animals for food (Banko et al 2002;Hansen et al 2002).…”

Biology and Impacts of Pacific Island Invasive Species. 11.Rattus rattus,the Black Rat (Rodentia: Muridae)

“…data) and the highest elevations (in most cases >3,000 m) (Amarasekare 1994). On Hawai'i Island, Amarasekare (1994) did not find R. rattus above 2,837 m, which is approximately the vegetation boundary in the alpine desert ecosystem; R. rattus generally occurs in low abundances near those upper elevations (less than one individual/ ha at 2,100 -2,500 m [Amarasekare 1993]; 0.2 individuals/trapnight at 1,785 -2,600 m [Banko et al 2002]). Poa foliosa tussock grassland is the principal habitat for R. rattus on Macquarie Island (55° S), probably because it provides year-round food, shelter, and a slightly warmer microhabitat than outside the tussock canopy (Pye et al 1999).…”

Survival of Feral Cats,Felis catus(Carnivora: Felidae), on Mauna Kea, Hawai'i, Based on Tooth Cementum Lines

“…Our study was based on the assumption that tooth cementum data reflect a pattern of annual formation and therefore age. This assumption is supported by (1) the presence of cementum lines in the teeth, (2) one recaptured cat that deposited at most one line per year, and (3) the seasonality in subalpine Mauna Kea, which is observed in māmane tree phenology (Banko et al 2002), temperature, and rainfall ( Juvik et al 1993) that may Lower CI set to zero when predicted negative (ages 7-11). induce annulus formation.…”

“…For example, cementum lines in rhesus monkeys (Macaca mulatta) were correlated with dry periods and presumably caused by episodes of lower food abundance or quality (Kay and Cant 1988). Given the unimodal patterns of māmane tree phenology (Banko et al 2002) and rainfall on Mauna Kea ( Juvik et al 1993), we predicted that feral cats would form annual cementum lines regardless of endogenous or exogenous control.…”

“…Both sites are dry subalpine woodlands, and species abundance and plant phenology vary along an elevation gradient (Banko et al 2002). The dominant vegetation includes māmane (Sophora chrysophylla) and naio (Myoporum sandwicense) trees, with pū kiawe (Leptecophylla tameiameiae) and 'āheahea (Chenopodium oahuense) shrubs.…”