Using population surveys and models 849
TABLE 1 The seven sites surveyed in the Madeira–Aripuanã interfluve and Ji-Paraná River for Prince Bernhard’s titi monkey Plecturocebus bernhardi (Fig. 1).
Site River A Low Manicoré
B Roosevelt–Aripuanã confluence
C Madeirinha Upper Ji-Paraná Year
2012–2015 2012–2015
2015
D Mid Roosevelt (west bank) 2015 E Mid Ji-Paraná (east bank) 2009 F
G Cautário
2014 2014
Legally protected land None
None
Parque Estadual Tucumã/Estação Ecológica do Rio Madeirinha
Estação Ecológica do Rio Roosevelt Reserva Biológica do Jaru None
Resex do Rio Cautário
We oriented the transects perpendicular to road or river, to account for any gradient of environmental factors or primate density from the start of the trail to the interior of the forest. The mean length of the transects was 3.07 ± SD 0.63 km (range 2.0–4.0 km) and we placed them at least 2 km apart to guarantee spatial independence. We surveyed the transects during 07.00–11.00 in one direction and during 14.00–17.00 in the reverse direction and considered each survey during these periods of the day as independent sam- pling occasions. Two observerswalked along the transects at a mean speed of 1.5 km/h and counted the number of indi- viduals in each detected P. bernhardi group. We measured the perpendicular distance between the centre line of the transect and the centre of each detected group, to facilitate density estimates using distance sampling (Buckland et al., 1993). Considering walks during different periods of the day as our sampling occasions, we surveyed each transect at least eight times (mean 10, range 8–12), with at least four surveys in both morning and afternoon. We implemented a 2-day break between subsequent surveys to reduce the impact of observers on the detection rate. In total we walked 271.6 km along the transects. We estimated the population density of P. bernhardi
using Distance 7.1 (Thomas et al., 2010). This analysis fits detection functions to perpendicular distances, providing the probability of detecting groups and estimating the number of individuals potentially missed by the observers. Following the method used by Silva et al. (2020), we used a χ2 test to determine the appropriate truncations and perpendicular distance intervals at P.0.6. We then com- pared the adjustments of detection functions using the Akaike information criteria (AIC), with the models with the smallest AIC values considered as best fitting the data. We selected the model for which the density estimate had the lowest coefficient of variation (CV) when more than one function yielded a difference in AIC value (ΔAIC) ,2. We then estimated mean abundance, A,using A=D× a, whereby D is density and a is the species potential area of oc- currence calculated using occurrence records (Supplementary Table 1).We calculated the 95%CIandtheCVfor all estimates.
Latitude
5°59′03″S 7°31′18″S
8°52′43″S 9°13′15″S
10°2′52″S 11°26′38″S 11°54′50″S
Assessment of conservation status
We calculated the total habitat loss within the potential area of occurrence of P. bernhardi up to 2019.We used predictive deforestation models to assess how much habitat the species could lose over the next 24 years, which is equivalent to three titi monkey generations. This time frame of three genera- tions is recommended for assessing population decline whether by direct observation, by measuring a decline in area of occupancy or extent of occurrence, or by measuring a decline in quality of habitat or other variables that can indicate ongoing population reduction (IUCN, 2012). We obtained data on current forest loss from MapBiomas (2020)for 1995–2019. For predicted forest loss we considered two scenarios (after Soares-Filho et al., 2006; see also Boubli et al., 2019;Silva et al., 2020): (1) A governance scenario (i.e. considering the current deforestation trends but with a 50% cap in forest loss through the current laws being effective at preventing farmers fromclearing.50%of the forest on their properties and assuming that protected areas are managed effectively). (2) A business-as-usual scenario (i.e. with the continuation of the current deforestation trends along with poor management of protected areas). To estimate the impact of habitat loss on the population
of P. bernhardi, we used the lower bound of the CI of the estimate of abundance, which is the recommended measure of abundance for conservation status assessments (IUCN, 2012). We then used the Red List criteria (IUCN, 2012)to assess whether P. bernhardi should remain categorized as Least Concern or requires recategorization.
Results
Geographical distribution We obtained 21 new locality re- cords of P. bernhardi through our surveys, and 54 records from the literature (Fig. 1, Supplementary Table 1). The majority of the distribution of this species is delimited by the Aripuanã, Madeira and Ji-Paraná Rivers, but we also recorded the species on the west bank of the upper Ji-Paraná River, where its range overlaps with that of
Oryx, 2022, 56(6), 846–853 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605322000655 Longitude
61°32′15″W 60°40′25″W
61°13′52″W 60°50′03″W
61°58′15″W 61°27′44″W 64°09′41″W
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