title: Assessment of landscape-scale distribution of sympatric great apes in African rainforests: concurrent use of nest and camera-trap surveys.
abstract: Information on the distribution and abundance of sympatric great apes (Pan troglodytes troglodytes and Gorilla gorilla gorilla) are important for effective conservation and management. Although much research has been done to improve the precision of nest-surveys, trade-offs between data-reliability and research-efficiency have not been solved. In this study, we used different approaches to assess the landscape-scale distribution patterns of great apes. We conducted a conventional nest survey and a camera-trap survey concurrently, and checked the consistency of the estimates. We divided the study area (ca. 500 km²), containing various types of vegetation and topography, into thirty 16-km² grids (4 km × 4 km) and performed both methods along 2-km transects centered in each grid. We determined the nest creator species according to the definitions by Tutin & Fernandez [Tutin & Fernandez, 1984, Am J Primatol 6:313-336] and estimated nest-site densities of each species by using the conventional distance-sampling approach. We calculated the mean capture rate of 3 camera traps left for 3 months at each grid as the abundance index. Our analyses showed that both methods provided roughly consistent results for the distribution patterns of the species; chimpanzee groups (parties) were more abundant in the montane forest, and gorilla groups were relatively homogeneously distributed across vegetation types. The line-transect survey also showed that the number of nests per nest site did not vary among vegetation types for either species. These spatial patterns seemed to reflect the ecological and sociological features of each species. Although the consistent results may be largely dependent on site-specific conditions (e.g., high density of each species, distinct distribution pattern between the two species), conventional nest-surveys and a subsequent check of their consistency with independent estimates may be a reasonable approach to obtain certain information on the species distribution patterns. Further analytical improvement is necessary for camera-traps to be considered a stand-alone method.
authors.affiliation: Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto City, Kyoto, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nakashima
authors.forename: Yuji
authors.initials: Y
authors.lastname: Iwata
authors.forename: Chieko
authors.initials: C
authors.lastname: Ando
authors.forename: Chimene
authors.initials: C
authors.lastname: Nze Nkoguee
authors.forename: Eiji
authors.initials: E
authors.lastname: Inoue
authors.forename: Etienne-Francois Okoue
authors.initials: EF
authors.lastname: Akomo
authors.forename: Philippe Mbehang
authors.initials: PM
authors.lastname: Nguema
authors.forename: Thierry Diop
authors.initials: TD
authors.lastname: Bineni
authors.forename: Ludovic Ngok
authors.initials: LN
authors.lastname: Banak
authors.forename: Yuji
authors.initials: Y
authors.lastname: Takenoshita
authors.forename: Alfred
authors.initials: A
authors.lastname: Ngomanda
authors.forename: Juichi
authors.initials: J
authors.lastname: Yamagiwa
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D006071:Gorilla gorilla / Q000502:physiology*; D006702:Homing Behavior; D002679:Pan troglodytes / Q000502:physiology*; D011157:Population Dynamics; D012919:Social Behavior
keywords: Gabon; camera trap; distance sampling; nest; sympatric apes