Impacts of human activity on mammals 949


FIG. 1 Location of the study area and camera-trap grid, in place during August– November 2017, across the community forest and adjacent production forest in the buffer zone of the Dja Biosphere Reserve, Cameroon.


Methods


Survey design We placed a systematic grid of 30 camera traps (Bushnell, Overland Park, USA) set 1 km apart across the village, sur- rounding community forest and adjacent production forest. There was no logging within the surveyed area of produc- tion forest and, as it provided a continuation of the habitat found within thecommunity forest,we did not consider it as a separate habitat in this study. Cameras were unbaited and operational continuously during August–November 2017. They took three photographs each time they were triggered, using low glow infrared flash set to medium, with a trigger speed of 0.14 s and a 1-s delay between triggers. Suitable places to position the cameras were chosen within 100 m of each grid point, close to frequently used animal trails (Amin et al., 2015) or possible feeding spots. Cameras were attached to trees c. 4 m from the trails. The cameras had high sensitivity and were placed 30–45 cm off the ground, angled horizontally. To avoid sunlight interfering with the cameras, they were set facing north or south (Bruce et al., 2018a). Tall grass and foliage that could have obstructed the field of view were cleared. The placement of two cameras close to the road had to be adjusted as they would have been within a hunting camp, but the 1 km spacing was not substantially compromised. The total survey area was c. 26 km2.


Species richness and composition


Species identification was aided by Kingdon (2015). For Herpestidae (mongoose) species, data were pooled because of the low numbers of records of individual species and


difficulties of identification.We excluded images of small ro- dents that could not be identified to species level as their small body size limited detectability, resulting in sampling error (Tobler et al., 2008;Bruce et al., 2018a).We generated a spe- cies accumulation curve using the package vegan in R 3.6.2 (Oksanen et al., 2019; R Core team, 2019) to examinewhether our sampling effort was sufficient to capture the majority of mammal species and to estimate mammal species richness. To infer whether hunting was sustainable or not, species composition was compared with the terrestrial mammal community that would be expected within our study area withminimal human disturbance. The expected community was based on species whose distributions coincided with our study area according to Kingdon (2015) and the IUCN Red List (IUCN, 2021), were likely to be detected by ground-level camera traps within continuous forest in this area based on species ecology and habitat preferences, and were detect- ed by camera-trap surveys in similar habitat within the Reserve (Bruce et al., 2018a,c)or in community forests to the north-east (Lhoest et al., 2020).


Occupancy analysis


We used occupancy analysis as it can be used to model spe- cies distributions while accounting for imperfect detectabil- ity (MacKenzie et al., 2002, 2006), and is being increasingly used as a monitoring tool (e.g. Ahumada et al., 2011; Rich et al., 2017). Species detection histories were created by re- cording the presence (1) or absence (0) of a species within 5-day windows at each camera trap, a compromise between having an adequate number of repeat visits and model sta- bility. Single-species, single-season occupancy models were run using the package unmarked in R (MacKenzie et al., 2002; Fiske & Chandler, 2011). As the home ranges of the


Oryx, 2022, 56(6), 947–955 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321000806


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