Living on the edge 233
TABLE 2 Coefficient estimates for the generalized linear mixed model with Gaussian distribution testing the effects of distance from the forest edge on hourly temperature and light intensity (N = 21,071) recorded over 49 days during August–October 2019 at Aras Napal, Indonesia (Fig. 2).
Distance from forest edge (m) Intercept
Random effects1 σ2
τ00 AIC
*P,0.1; **P,0.05; ***P,0.01. 1σ2, residual variance; τ00, random intercept variance.
1,079 sampling days (after accounting for days lost because of camera malfunctions), 1,384 images and 300 mammal detection events. We identified 16 mammal species across 14 families and six orders (Table 4). It was not possible to identify animals in the families Muridae (mice and rats) and Sciuridae (squirrels) to species level. The mean num- ber of detected species was lowest at the forest edge (μ = 3.00 ± SE 1.00) and highest at 1 km from the forest edge (μ = 7.00 ± SE 3.56). Three families had fewer than five detections, and five families had more than 20 detec- tions. The species accumulation curve (Fig. 3) shows that after c. 200 total sampling days, 12 out of 14 families had been detected, indicating that the sampling effort was adequate to capture all present and detectable families. The number of detection events of each mammal order
differed between distances from the forest edge (χ2 = 75.324, df = 20,P,0.01; Fig. 4). Primate detection rates were higher towards the National Park boundary and elephants were detected only within 1 km from the forest edge and not farther into the forest. Moonrats were only detected at distances .1 km from the forest edge and carnivores were not detected at the edge. Ungulates and rodents were detected at all distances but had a higher detection rate at 1 km from the forest edge than at any other distance (Fig. 4).
Environmental predictors of mammal abundance
All temperature and light intensity variables except for minimum temperature were highly correlated (r.0.7); accordingly, only maximum and minimum temperature were used in the models. We selected maximum temp- erature as the variable to be included in the analysis as it varied the most between locations and is likely to restrict the occurrence of diurnal terrestrial mammals more than mean temperature. Total tree height and bole height were also strongly correlated (r.0.7); consequently,we included only total tree height in the analysis.
Overall mammal detections The best performing model was that with the variables maximum and minimum tem- perature, tree height and diameter at breast height (Table 5). The deviance explained by this model was 28%. The number of detections decreased with increasing min- imum and maximum temperatures, and tree height (Table 5, Fig. 5a–c), and increased with increasing diameter at breast height (Table 5, Fig. 5d).
Detections by mammal order The mixed model with the best performance included maximum temperature, tree height and diameter at breast height (Table 6, Fig. 6). For all mammal orders, maximum temperature and tree height were negatively correlated with the number of detections (Table 6, Fig. 6a,b). Diameter at breast height was positively correlated with number of detections (Table 6, Fig. 6c).
Discussion
Edge effects on abiotic forest conditions Mean and maximum temperatures and light intensity were higher at the forest edge, whereas minimum temp- eratures increased towards the forest interior. Elevated temperatures occurred up to 0.5–1.0 km into the forest (Fig. 2d,e). Smaller forest fragments are subject to more extreme diurnal variation than larger fragments. Open- access climate datasets are usually only available at scales much larger than the body size of a species or even its mean home range. Many climate envelope models only in- corporate annual means and do not account for fine-scale temporal variations such as daily maximums, which can be much higher than the mean (Bennie et al., 2014). We re- corded daily maximum temperatures of up to 37.5 °C, which is considerably higher than the overall mean of 25.5 °C.
Oryx, 2024, 58(2), 228–239 © The Author(s), 2023. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605323000212
Dependent variable Temperature ± SE (°C) −0.0002*** ± 0.00001
25.80*** ± 0.41 1.23
0.36Day of year 3.58Hour
0.04Transect 64,557.59
Light intensity ± SE (lux) −0.91*** ± 0.02
2,025.94*** ± 392.20 5,881,034.02
22,637.55Day of year 2,015,972.65Hour 273,899.88Transect 388,437.70
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