850 F. E. Silva et al.
protected areas and Indigenous lands would be 3.2 and 16.7% under the governance and business-as-usual scen- arios, respectively. Considering the lower bound of the CI of the population abundance (1,037,231 individuals), such levels of habitat loss under the business-as-usual scenario translate into a reduction of 831,859 P. bernhardi individuals from the population over this period. Under both scenarios considered, the projected population reduction of P. bernhardi qualifies the species for categorization under a threatened category on the IUCN Red List (44.5% habitat loss indicates a categorization as Vulnerable, and 80.2% a categorization as Critically Endangered; criteria A3c, IUCN, 2012).
FIG. 2 Distribution of perpendicular distances of observations of P. bernhardi from the centre of transects in the Madeira– Aripuanã interfluve. The trend line indicates the best detection function fitted to the distance classes.
Plecturocebus brunneus (Supplementary Fig. 1), although we did not record these species in syntopy during our surveys. In the headwaters of the Ji-Paraná and Roosevelt Rivers there is a contact zone between P. bernhardi, Plecturocebus parecis and Plecturocebus cinerascens (Gusmão et al., 2019) (Supplementary Fig. 1). We estimated that P. bernhardi potentially occurs in an area of 131,295 km2 (Fig. 1)of which 49.6%is legally protected.
Population estimate We obtained 57 observations of P. bernhardi groups along the transects, with 161 individuals detected. The encounter rate was 0.2 groups/km (CV = 11.9). The best grouping of perpendicular distances to fit the detection curve was obtained with five intervals of 10 m each. The best detection function was uniform with one cosine adjustment term (Goodness-of-fit χ2 = 0.67,df = 3, P=0.88, AIC = 163.19; Fig. 2). Mean group size was 2.8 individuals/group (95%CI = 2.5–3.2,CV= 6.5). We esti- mated density to be 10.8 individuals/km2 (95%CI = 7.9–14.9, CV= 15.3), and 3.8 groups/km2 (95%CI = 2.9–5.1,CV= 13.8), and mean abundance to be 1,365,468 individuals (95% CI = 1,037,231–1,956,296,CV= 15.3).
Reassessment of conservation status We estimated there was a loss of 36,903 km2 of forest cover within the species’ potential range during 1995–2019, 28.1% of the total original range of the species (Fig. 3). Only 0.5% of this deforestation occurred within protected areas or Indigenous lands. In our predictivemodels the habitat loss of the species over the next 24 years would amount to 58,365 km2 under the governance scenario and 105,289 km2 under the business-as-usual scen- ario (Fig. 3), 44.5 and 80.2% of the species’ potential range, respectively. We estimated predicted deforestation within
Discussion
Although we estimated that P. bernhardi has a minimum population size of 1,365,468 individuals within a large geo- graphical range, the current rate of deforestation in the region will probably result in considerable decline over the next 24 years. Protected areas and Indigenous lands have been effective at maintaining lowrates of deforestation with- in their borders, and these land categories are the only large forest fragments in the southern distribution of this species. Under the business-as-usual scenario, however, deforesta- tion rates would increase considerably. This region is a hot- spot of deforestation (Carrero et al., 2020) and the rate of deforestation predicted by 2050 in the Amazon rainforest (Soares-Filho et al., 2006; Nobre et al., 2016; Walker et al., 2019) could cause reductions in the populations of several primate species (Silva et al., 2018, 2020; Rabelo et al., 2020). Thus the large geographical ranges of some primates in southern Amazonia should not necessarily be used to cat- egorize a species as Least Concern, especially when most of the distribution range of a species is within an area with an actual or potential high rate of deforestation. There have been few studies of the ecology and
behaviour Amazonian titi monkeys (e.g. Palacios et al., 1997; Bicca-Marques & Heymann, 2013; Kulp & Heymann, 2015; Martinez & Wallace, 2016) and inferences regarding their habitat preferences are based mainly on data from species in the Atlantic Forest (but seeWagner et al., 2009;Chagas& Ferrari, 2010). Nonetheless, the ecological flexibility of many Amazonian titi monkeys and their preference for secondary forests (Wagner et al., 2009) have been used to support their
categorizationasLeastConcern.However,deforestationwith- in the species’ range, whether ongoing or predicted, is usually fromactivities that result in clear-cutting, leaving no continu- ous forests or trees that could be inhabited and used by any primate species. A similar situation was also found for the recently described Plecturocebus grovesi (Boubli et al., 2019) c. 230 km to the east of our study area. The species was included in the list of the 25 most threatened primates, being categorized as Critically Endangered on the IUCN
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
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