Spatial ecology of the critically endangered Fijian crested iguana, Brachylophus vitiensis, in an extremely dense population: implications for conservation

The Critically Endangered Fijian crested iguana, Brachylophus vitiensis, occurs at extreme density at only one location, with estimates of >10,000 iguanas living on the 70 hectare island of Yadua Taba in Fiji. We conducted a mark and recapture study over two wet seasons, investigating the spatial ecology and intraspecific interactions of the strictly arboreal Fijian crested iguana. This species exhibits moderate male-biased sexual size dimorphism, which has been linked in other lizard species to territoriality, aggression and larger male home ranges. We found that male Fijian crested iguanas exhibit high injury levels, indicative of frequent aggressive interactions. We did not find support for larger home range size in adult males relative to adult females, however male and female residents were larger than roaming individuals. Males with established home ranges also had larger femoral pores relative to body size than roaming males. Home range areas were small in comparison to those of other iguana species, and we speculate that the extreme population density impacts considerably on the spatial ecology of this population. There was extensive home range overlap within and between sexes. Intersexual overlap was greater than intrasexual overlap for both sexes, and continuing male-female pairings were observed among residents. Our results suggest that the extreme population density necessitates extensive home range overlap even though the underlying predictors of territoriality, such as male biased sexual size dimorphism and high aggression levels, remain. Our findings should be factored in to conservation management efforts for this species, particularly in captive breeding and translocation programs.This work was supported by the International Iguana Foundation, the Australian National University (field work grant), the Federation of Australian Women (Georgina Sweet fellowship), the Ecological Society of Australia (student research award) and the Taronga Foundation

Predation of the critically endangered Fijian crested iguana (Brachylophus vitiensis) by the swamp harrier (Circus approximans)

The Fijian crested iguana (Brachylophus vitiensis) is the largest extant lizard in Fiji, where it enjoys life in the absence of any mammalian predators. On the only island where this iguana is abundant, the only predator appears to be the swamp harrier (Circus approximans), which is non-selective in its iguana prey, catching individuals in a similar proportion to their size availability. Here we report on the first observation of a reptile being the major prey item of the swamp harrier

Spatial ecology of the critically endangered Fijian crested iguana, Brachylophus vitiensis, in an extremely dense population: implications for conservation.

The Critically Endangered Fijian crested iguana, Brachylophus vitiensis, occurs at extreme density at only one location, with estimates of >10,000 iguanas living on the 70 hectare island of Yadua Taba in Fiji. We conducted a mark and recapture study over two wet seasons, investigating the spatial ecology and intraspecific interactions of the strictly arboreal Fijian crested iguana. This species exhibits moderate male-biased sexual size dimorphism, which has been linked in other lizard species to territoriality, aggression and larger male home ranges. We found that male Fijian crested iguanas exhibit high injury levels, indicative of frequent aggressive interactions. We did not find support for larger home range size in adult males relative to adult females, however male and female residents were larger than roaming individuals. Males with established home ranges also had larger femoral pores relative to body size than roaming males. Home range areas were small in comparison to those of other iguana species, and we speculate that the extreme population density impacts considerably on the spatial ecology of this population. There was extensive home range overlap within and between sexes. Intersexual overlap was greater than intrasexual overlap for both sexes, and continuing male-female pairings were observed among residents. Our results suggest that the extreme population density necessitates extensive home range overlap even though the underlying predictors of territoriality, such as male biased sexual size dimorphism and high aggression levels, remain. Our findings should be factored in to conservation management efforts for this species, particularly in captive breeding and translocation programs

Diet and habitat preferences of the Fijian crested iguana (Brachylophus vitiensis) on Yadua Taba, Fiji: implications for conservation

The Fijian crested iguana (Brachylophus vitiensis) is restricted to tropical dry forest habitat and has been extirpated from over 80% of its original range primarily because of habitat destruction. A large population on Yadua Taba island has been proposed as a source for iguana translocations. This study aimed to determine the dietary and habitat requirements of the herbivorous B. vitiensis on Yadua Taba to identify essential tree species. Between September 2005 and June 2006 we examined the diet of B. vitiensis using faecal analyses, while perch preferences were examined using field surveys. Faecal analyses identified 26 plant species in the diet of B. vitiensis, while field surveys recorded iguanas in 33 tree species. The most common diet species largely overlapped with the most common perch species. There were no major seasonal shifts, sex differences, or age-class variations in diet or perch preferences. These results suggest that while B. vitiensis occurs in and consumes several plant species on Yadua Taba, it is primarily dependent on only a few species. To improve translocation success, future translocations of B. vitiensis need to ensure that these important tree species are present at new sites

Injury rates by sex and size class for <i>B. vitiensis.</i>

<p>For example the first line, a total of 118 adult males were surveyed of which 96 (81.9%) had some type of visible injury, 59 (50%) had missing toes, 68 (57.5%) exhibited bite marks, 36 (30.3%) had lost at least one dorsal crest spine, and 31 (26.3%) had lost a portion of tail.</p

Analyses of sexual dimorphism in adult <i>B. vitiensis.</i>

<p>Data collected from animals >160 mm SVL on Yadua Taba. Results are shown for unpaired t tests and for ANCOVA where sex is the factor and SVL the covariate. Raw data shown but all statistical tests were performed on natural log transformed data.</p

The minimum convex polygon 85% peeled ranges for all adult males with ≥6 sightings.

<p>The minimum convex polygon 85% peeled ranges for all adult males with ≥6 sightings.</p

The minimum convex polygon 85% peeled core home ranges for a) adult females with ≥6 sightings (n = 32), and b) adult males with ≥10 sightings (n = 36), occupying the 50×50 m study site.

<p>The black points represent female range centers in both cases.</p

Summary of home range measures in <i>B. vitiensis</i> for adult males with 10 or more sightings (n = 36) and adult females with 6 or more sightings (n = 32).

<p>As an example, on the first line, a mean of 3.95 females are found in a male’s home range, 27.49% of male space is shared with at least one female, the index of overlap pressure of females on males is 1.22 and males overlap a mean of 28% of the home range of overlapping females.</p