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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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Related in: MedlinePlus

The minimum convex polygon 85% peeled ranges for all adult males with ≥6 sightings.
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pone-0073127-g003: The minimum convex polygon 85% peeled ranges for all adult males with ≥6 sightings.

Mentions: The mean home range size of the 36 adult male residents for which we had ten or more sightings was 64.36±8.31 m2, and for 32 adult females with six or more sightings was 59.87±12.63 m2. There was no significant difference in mean adult home range size between adult male and female residents (n = 68, t = 0.03, P = 0.76). There was extensive home range overlap within and between the sexes, with both females and males overlapping with multiple individuals (Table 2; Fig. 2). While males with ≥10 sightings were used for analysis (Fig. 2b) we also mapped the potential home range for males with ≥6 sightings to better visualize the degree of the density and overlap of animals in this population (Fig. 3). As the home range size of adult males increased, they overlapped a greater proportion of the home ranges of neighboring resident males (Pearson’s, n = 36, r = 0.62, P<0.001) and resident females (Pearson’s, n = 36, r = 0.41, P = 0.02). Likewise, female encroachment onto the home ranges of other resident females (Pearson’s, n = 32, r = 0.40, P = 0.02) and males (Pearson’s, n = 32, r = 0.38, P = 0.04) increased with focal female home range area. Heavier resident females (BM) were overlapped by fewer other females (Pearson’s, n = 32, r = −0.56, P<0.01), and males (Pearson’s, n = 32, r = −0.48, P = 0.01) than lighter females. Also, there was a trend for the percentage of a resident female’s home range covered by other resident females to decrease as BM of the focal female increased (Pearson’s; n = 32, r = −0.37, P = 0.05).


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)

The minimum convex polygon 85% peeled ranges for all adult males with ≥6 sightings.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0073127-g003: The minimum convex polygon 85% peeled ranges for all adult males with ≥6 sightings.
Mentions: The mean home range size of the 36 adult male residents for which we had ten or more sightings was 64.36±8.31 m2, and for 32 adult females with six or more sightings was 59.87±12.63 m2. There was no significant difference in mean adult home range size between adult male and female residents (n = 68, t = 0.03, P = 0.76). There was extensive home range overlap within and between the sexes, with both females and males overlapping with multiple individuals (Table 2; Fig. 2). While males with ≥10 sightings were used for analysis (Fig. 2b) we also mapped the potential home range for males with ≥6 sightings to better visualize the degree of the density and overlap of animals in this population (Fig. 3). As the home range size of adult males increased, they overlapped a greater proportion of the home ranges of neighboring resident males (Pearson’s, n = 36, r = 0.62, P<0.001) and resident females (Pearson’s, n = 36, r = 0.41, P = 0.02). Likewise, female encroachment onto the home ranges of other resident females (Pearson’s, n = 32, r = 0.40, P = 0.02) and males (Pearson’s, n = 32, r = 0.38, P = 0.04) increased with focal female home range area. Heavier resident females (BM) were overlapped by fewer other females (Pearson’s, n = 32, r = −0.56, P<0.01), and males (Pearson’s, n = 32, r = −0.48, P = 0.01) than lighter females. Also, there was a trend for the percentage of a resident female’s home range covered by other resident females to decrease as BM of the focal female increased (Pearson’s; n = 32, r = −0.37, P = 0.05).

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