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Diversity and Distributions

Impact of habitat alteration on endemic Afromontane chameleons: evidence for historical population declines using hierarchical spatial modelling

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Abstract

Aim

We map estimated historical population declines resulting from species-specific models of sensitivity to habitat fragmentation for three forest-dependent chameleons.

Location

East Usambara Mountains, Eastern Arc Mountains, Tanzania.

Methods

We surveyed three chameleon species (Rhampholeon spinosus, Rhampholeon temporalis and Trioceros deremensis) along 32.2 km of transects and used a hierarchical, distance-sampling model to estimate densities. The model included habitat characteristics at the landscape (patch) and local (transect) scales while accounting for detectability. By analysing the model in a Bayesian framework, we were able to propagate error through the entire analysis and obtain exact solutions despite small sample sizes. We then used our estimated relationships between habitat and density to project chameleon population sizes across current and historical land cover maps of the study area (230 km2), giving an estimate of the impact of anthropogenic habitat alteration on these species.

Results

Species’ densities increased in larger patches and further from patch edges and varied seasonally. Local vegetation characteristics had significant relationships with expected chameleon densities, though effect sizes were small. Estimates of total current population sizes varied by two orders of magnitude among species, but each was 49–79% higher than detection-naïve estimates. All three declined from estimated historical levels by approximately 60% in the study area, approximately one-third more than would be expected from forest loss alone. Remaining populations of the study species are predominantly located in protected nature reserves, so the future of these species will likely be determined by the degree of protection offered by the nature reserves.

Main conclusions

Habitat loss and fragmentation have greatly reduced forest-dependent chameleon population sizes in the East Usambara Mountains. Populations of these species in other areas are experiencing higher rates of habitat loss. Efforts aimed at ensuring the efficacy of protected forests may be a key to conserving remaining populations.

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