The Cross River Gorillas (Gorilla gorilla diehli) at Mawambi Hills, South-West Cameroon: Habitat Suitability and Vulnerability to Anthropogenic Disturbance

Abstract

Only about 300 individuals of the Cross River gorilla (CRG; Gorilla gorilla diehli) survive today. The subspecies is endemic to approximately 12–14 sites at the Cameroon-Nigeria border, and is critically endangered. To understand survival prospects of the CRG at Mawambi Hills, Cameroon, a maximum entropy (MaxEnt) distribution model was used to predict the distribution of gorillas. Overall, 24% of the study area was predicted to be suitable for gorillas. The most important predictors of gorilla distribution were elevation as a surrogate for accessibility (52.4%), distance to nearby villages which represents proximity to anthropogenic disturbance (22.7%), and slope steepness as a proxy for security (19.4%). Gorillas mainly occupied slopes of steep hills and avoided areas of human disturbance. To evaluate the spatial relationship between gorilla distribution and human activities, the predicted habitat suitability map was overlaid with a kernel density map of human activities. A positive correlation was found between locations of human activity and suitable habitat for gorillas (r = 0.5). This suggests that anthropogenic pressures in previously unused forest areas are increasing as a result of resource depletion at lower altitudes, consequently putting the gorillas at greater risk. Conservation management plans that seek to reduce human encroachment into habitats preferred by gorillas such as steep hills will probably contribute to gorilla survival.

Variation in behavioral traits of two frugivorous mammals may lead to differential responses to human disturbance

“…This indicates that elevation may be a good determinant for the choice of a nesting site by chimpanzees, where the areas with intermediate values of elevation are more suitable. In contrast, Etiendem, Funwi‐Gabga, Tagg, Hens, and Indah (2013) found that elevation was an important predictor of the Cross River gorilla distribution at Mawambi Hills.…”

Evaluating the potential effectiveness of alternative management scenarios in ape habitat

“…Agents were assigned predetermined distances from their village of origin which they had to reach before returning home. These distances were randomly chosen from a normal distribution with a mean of zero and a standard deviation of 10 km, chosen because in the study area most of the human activity originating from villages happens within c. 10 km (Etiendem et al 2013;Imong et al 2014a). When agents on their way home reached within three cells of their village of origin (540 m, roughly corresponding to the median radius of settlements in the study area) they changed their direction after a new distance to be reached was randomly chosen as above.…”

Taxonomic Tapestries: The Threads of Evolutionary, Behavioural and Conservation Research

“…The less numerous subspecies -and in fact the least numerous gorilla subspecies -is the Cross River gorilla (Gorilla gorilla diehli) found at the Nigeria/Cameroon border and listed as Critically Endangered by the IUCN Red List (2014.2). There are approximately 250-300 individuals living, however, these are distributed in 12-14 small and fragmented populations (Etiendem et al, 2013). The most pressing threats are the destruction or modification of habitat resulting in further isolation of small populations and hunting for the bushmeat and pet trade.…”