Browsing by Author "Shirk, Philip"
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Item Abundance and roosting ecology of chameleons in the Eastern Arc Mountains of Tanzania and potential effects of harvesting(2011-12) Patrick, David A.; Shirk, Philip; Vonesh, James R.; Harper, Elizabeth B.; Howell, KimHarvesting of chameleons from the East Usambara Mountains of Tanzania for the exotic pet trade is of concern due to the high rates of habitat loss in this region and the fact that many of the species are endemic or near endemic to this isolated montane forest. Export of the majority of chameleons found in the East Usambaras is regulated by their listing under CITES Appendix II. To ensure harvesting is sustainable, however, greater knowledge of the ecology of species is needed. We conducted this study in and around Amani Nature Reserve in the East Usambara Mountains during August 2009. We used transects on the forest edge and interior to gather baseline data relating to the ecology of chameleons and to assess if any effects of harvesting on populations could be detected. We compared abundance of chameleons between forest edge and interior, the age/size of species, and sex-ratios between these two habitat types. We observed 108 chameleons during surveys, representing seven species. Some species were restricted to forest interior while others were only found on forest edges. When comparing age/size and sex ratios of the most valued species for the exotic pet trade, Trioceros deremensis, we found a strong female sex-bias in adults only, and that adult females were larger than adult males. This is in contrast to reports in published literature showing that males are capable of growing larger than females. Based on the low abundance of some species, we suggest careful consideration of future export quotas under CITES. Further investigation into the potential reasons for the size and sex-ratios of T. deremensis is also needed.Item Community and population-level responses of an Afromontane chameleon assemblage to forest fragmentation(2012-08) Shirk, Philip; Patrick, David A.; Howell, Kim; Harper, Elizabeth B.Background/Question/Methods Habitat modification in the form of fragmentation and loss is a leading cause of biodiversity decline. The basic predictions from island biogeography theory that species richness and population size decrease with declining area and increased isolation have received considerable support. However much of this research has focused on birds and mammals in temperate regions or the Neotropics, limiting our ability to generalize to other taxa and regions. Reptiles in particular are understudied and have not yet shown the clear response of other taxa. Here we examine the community and population-level responses of an Afromontane chameleon assemblage to forest fragmentation. The East Usambara Mountains of Tanzania have high rates of endemicity in a forested landscape fragmented by logging, tea plantations, and small-scale farming. Remaining fragments have been isolated for approximately 80 years, making it unlikely that short-lived species retain any extinction debt. Within this fragmented habitat are eight species of chameleon, many of which are of conservation concern. We used repeated distance-based sampling in a large forest block and 11 forest fragments in order to estimate species’ densities and overall richness. This allowed us to quantify the population and community-level responses to habitat fragmentation while accounting for differences in detectability. Results/Conclusions Chameleon richness decreased with both decreasing fragment size and with increasing isolation. The chameleon communities of 10 of the 11 forest fragments were subsets of the community of the largest block sampled, suggesting that smaller fragments contribute little to landscape-level biodiversity. The densities of Trioceros deremensis, Rhampholeon temporalis, and the combination of Kinyongia matschiei and K. vosseleri are better predicted by fragment area alone than by any model including isolation, but species’ responses differ. R. temporalis shows a strong decrease in density with decreasing fragment area, while T. deremensis’ density decreases only slightly with decreasing fragment area. Neither species was found in the two smallest forest fragments (<3.5 ha), suggesting that each has a similar fragment area threshold. Kinyongia spp., which are commonly found in disturbed habitat, show an increase in density as fragment area decreases. Due to the alteration of chameleon communities in smaller fragments, with declines in species richness and species-dependent changes in density, several small blocks are not equivalent to a single large block. A possible functional cause for this non-equivalency is altered vegetation characteristics in smaller fragments. In some cases the vegetation variables are more strongly correlated with species’ density than is fragment area.Item Impact of Habitat Alteration on Endemic Afromontane Chameleons: Evidence for Historical Population Declines Using Hierarchical Spatial Modelling(2014-09) Shirk, Philip; Linden, Daniel W.; Patrick, David A.; Howell, Kim; Harper, Elizabeth B.; Vonesh, James R.Aim We map estimated historical population declines resulting from species-specific models of sensitivity to habitat fragmentation for three forest-depen-dent chameleons.Location East Usambara Mountains, Eastern Arc Mountains, Tanzania.Methods We surveyed three chameleon species (Rhampholeon spinosus, Rham-pholeon temporalis and Trioceros deremensis) along 32.2 km of transects andused a hierarchical, distance-sampling model to estimate densities. The modelincluded habitat characteristics at the landscape (patch) and local (transect)scales while accounting for detectability. By analysing the model in a Bayesianframework, we were able to propagate error through the entire analysis andobtain exact solutions despite small sample sizes. We then used our estimatedrelationships between habitat and density to project chameleon population sizesacross current and historical land cover maps of the study area (230 km2),giving an estimate of the impact of anthropogenic habitat alteration on thesespecies.Item Shirk et al 2014 Supporting Information(2014-09) Shirk, Philip; Linden, Daniel W.; Patrick, David A.; Howell, Kim; Harper, Elizabeth B.; Vonesh, James R.