Critically Endangered Fijian Crested Iguana (Brachylophus vitiensis) Shows Habitat Preference for Globally Threatened Tropical Dry Forest

Abstract

Tropical dry forests are a unique and threatened ecosystem in the Pacific and globally. In Fiji, the endangered Fijian crested iguana (Brachylophus vitiensis) is endemic to tropical dry forests. Yadua Taba Island contains one of the best remaining stands of tropical dry forest in the Pacific along with the largest (and only secure) population of B. vitiensis in Fiji and has been proposed as a translocation source for iguana conservation. In this study we determined the major vegetation types on Yadua Taba and identified forest habitat preferences of B. vitiensis to (1) characterize the island's habitats for tropical dry forest regeneration monitoring and (2) understand which forest types are preferred by iguanas for future translocation projects. Vegetation data were collected using reconnaissance, entitation, line transects, and aerial photos. Iguana abundance data were collected by nocturnal surveys of permanent transects. Six major vegetation types were identified of which tropical dry forest was the largest (46% of the island), followed by a combination of rocky cliff-shrubland/grassland vegetation (26%). Our conservative estimate of B. vitiensis population size on Yadua Taba is 12,000 iguanas, the majority of which occur in tropical dry forest. Superabundance of the dry forest understory tree Vavaea amicorum, the favorite fruit species of iguanas, may help account for the high density of iguanas observed. These results highlight the ecological link between tropical dry forest and B. vitiensis and emphasize the importance of rehabilitation or conservation of tropical dry forest habitat in potential iguana translocation sites as part of the management plan for B. vitiensis throughout the Fiji Islands.Tropical dry forest generally occurs in seasonally dry tropical regions where the average annual rainfall is less than 2,000 mm. In addition, tropical dry forests usually experience dry seasons (monthly rainfall < 100 mm) that stretch over 3 months or more (Mooney et al. 1998). In the Pacific, tropical dry forest has been recorded from Australia, New Guinea, the Solomon Islands, Vanuatu, New Caledonia, Fiji, and Hawai'i (Keppel and Tuiwawa 2007). Due to a combination of factors including fire, grazing by goats, introduction of invasive plant species, and clearing for agriculture (e.g., sugarcane, coconut, and pineapple plantations), very few, usually small, patches of tropical dry forest remain in tropical dry areas. As such, tropical dry forests are now considered one of the most endangered tropical ecosystems globally ( Janzen 1988, Lerdau et al. 1991 One of the best examples of tropical dry forest in Fiji and in the Pacific is found on Yadua Taba Island, a National Trust of Fiji Reserve in the northwest of Fiji. Over the past 25 yr, goats have been removed from the island, fires have been banned, and anthropogenic activities greatly restricted, which have increased the extent and improved the condition of tropical dry forest on Yadua Taba. In addition to having the only protected tropical dry fore...

Spatial Ecology of the Critically Endangered Fijian Crested Iguana, Brachylophus vitiensis, in an Extremely Dense Population: Implications for Conservation

“…As a result, female iguanines often are distributed in order to maximize their access to resources, and males are distributed in relation to females [32], [36], [38]. As with other herbivores in harsh habitats, FCI also are likely to be energetically constrained by the digestion of plant material and the high variability of available food over time [11], [12]. This may then impact on the size of home range a male can energetically afford to defend.…”

“…1). The 70 ha island is volcanic in origin, with varied terrain supporting a range of vegetation types dominated by tropical dry forest (TDF) [9], [11], [12], [14], [15]. The climate is highly seasonal with the island receiving the majority of its annual rainfall during the wet season, from November to April, though the timing and intensity of the wet season varies between years.…”

“…All three species are of serious conservation concern but little is known of either B. fasciatus or B. bulabula . In contrast, the critically endangered B. vitiensis has been the subject of several ecological studies because it still exists in extremely high density on one small island [8], [10], [11], [12]. The nationally protected Fijian island of Yadua Taba is the last stronghold of B. vitiensis, and over 10,000 individuals still survive on this 70 ha island (Fig.…”

Forest Plant and Bird Communities in the Lau Group, Fiji

“…Quantitative descriptions of WP forest communities exist for Tonga [22] , [23] , [24] , [25] , Samoa [26] , [27] , [28] , [29] , and western Fiji [30] , [31] , and in a few cases have been related to habitat quality for vertebrates [32] , [33] , [34] . In this paper we examine variation in species composition of woody plant and bird communities in forests on the Lau islands of Lakeba, Nayau, and Aiwa Levu.…”

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“…in dry light forest, ripe fruit. This fruit is said to be the favorite food of the Fijian crested iguana (Morrison et al 2009). Illn: USEE 15, Atlas pl.…”