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

Morrison SF, Biciloa P, Harlow PS, Keogh JS - PLoS ONE (2013)

Bottom Line: 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.Intersexual overlap was greater than intrasexual overlap for both sexes, and continuing male-female pairings were observed among residents.

View Article: PubMed Central - PubMed

Affiliation: Division of Evolution, Ecology & Genetics, Research School of Biology, The Australian National University, Canberra, ACT, Australia.

ABSTRACT
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.

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Location of Yadua and Yadua Taba Islands, Fiji, showing the village of Denimanu on Yadua and the research site on Yadua Taba.
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pone-0073127-g001: Location of Yadua and Yadua Taba Islands, Fiji, showing the village of Denimanu on Yadua and the research site on Yadua Taba.

Mentions: True iguanas (iguanines) are primarily a New World group with the exception of the three living species in the genus Brachylophus. Brachylophus occur in the South Pacific Ocean archipelagos of Fiji and Tonga and are the sister clade to the rest of the iguaninae [7]. Most members of the iguaninae are large, terrestrial, and herbivorous, but the surviving Brachylophus species instead are medium sized (182–235 mm maximum snout vent length) and arboreal, with B. fasciatus (Lau banded iguana) occupying dry forests in Tonga and eastern Fiji, B. bulabula (Fijian banded iguana) occupying mesic forests in central Fiji, and B. vitiensis (Fijian crested iguana) occurring in dry forests in western Fiji [7], [8], [9]. 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. 1) [8], [9], [10,]. This site provided an excellent opportunity to study the spatial ecology and behavioral interactions of the critically endangered iguana in its natural habitat. For herbivorous lizards living in optimal habitats, population densities can increase greatly and potentially impact on home range size [4], [13]. The impact of the extreme population density at our study site on the behavioral ecology of the Fijian crested iguana was of particular interest.


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

Morrison SF, Biciloa P, Harlow PS, Keogh JS - PLoS ONE (2013)

Location of Yadua and Yadua Taba Islands, Fiji, showing the village of Denimanu on Yadua and the research site on Yadua Taba.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3760881&req=5

pone-0073127-g001: Location of Yadua and Yadua Taba Islands, Fiji, showing the village of Denimanu on Yadua and the research site on Yadua Taba.
Mentions: True iguanas (iguanines) are primarily a New World group with the exception of the three living species in the genus Brachylophus. Brachylophus occur in the South Pacific Ocean archipelagos of Fiji and Tonga and are the sister clade to the rest of the iguaninae [7]. Most members of the iguaninae are large, terrestrial, and herbivorous, but the surviving Brachylophus species instead are medium sized (182–235 mm maximum snout vent length) and arboreal, with B. fasciatus (Lau banded iguana) occupying dry forests in Tonga and eastern Fiji, B. bulabula (Fijian banded iguana) occupying mesic forests in central Fiji, and B. vitiensis (Fijian crested iguana) occurring in dry forests in western Fiji [7], [8], [9]. 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. 1) [8], [9], [10,]. This site provided an excellent opportunity to study the spatial ecology and behavioral interactions of the critically endangered iguana in its natural habitat. For herbivorous lizards living in optimal habitats, population densities can increase greatly and potentially impact on home range size [4], [13]. The impact of the extreme population density at our study site on the behavioral ecology of the Fijian crested iguana was of particular interest.

Bottom Line: 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.Intersexual overlap was greater than intrasexual overlap for both sexes, and continuing male-female pairings were observed among residents.

View Article: PubMed Central - PubMed

Affiliation: Division of Evolution, Ecology & Genetics, Research School of Biology, The Australian National University, Canberra, ACT, Australia.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus