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Background The study of the cultural significance (CS) of biodiversity provides key information to develop conservation strategies consistent with traditions and perceptions of human communities. In Los Tuxtlas Biosphere Reserve (TBR) in Mexico, the mantled howler monkeys ( Alouatta palliata mexicana ) and the black-handed spider monkeys ( Ateles geoffroyi vellerosus ) have historically coexisted with Popoluca Indigenous Peoples. This study sought to determine how the presence of a natural protected area (TBR location) and a range of sociodemographic factors (gender, age, origin, language proficiency, education level, religion) relate to the CS held by the Popoluca Indigenous People in relation to these two endangered primate species. Methods The first Primate Cultural Significance Index (PCSI) was designed as a composed index of 11 cultural variables (sub-indices) and was applied randomly to a representative size sample of people over 15 years old in two Popolucas communities, one within the TBR (Piedra Labrada = 81 people) and another outside (Los Mangos = 91). U Mann–Whitney tests were used to compare the PCSI between communities and Generalized Linear Models (GLM) to evaluate the sociodemographic factors of participants that influenced the sub-indices in the PCSI. Results The cultural significance of spider monkeys held by the Popolucas was higher for the community within the TBR than for the community outside, while for howler monkeys it was higher outside. For both primate species across the two communities, the most relevant sub-indices were (1) interest in conservation and (2) touristic significance of primates. Sociodemographic factors of participants influenced nine sub-indices of cultural significance out of the possible 10 sub-indices applied for each primate species. The demographic factors that most influenced each sub-index for both species were location and gender . Conclusions The main differences found between communities may be linked to the conservation and sustainable development programs promoted by the reserve, as well as the greater persistence of Popolucan ancestral traditions within the boundaries of the reserve. We recommend that conservation efforts should focus on people less interested about primate conservation (women, non-natives and residents outside the reserve), and turn to the leadership of people more interested (native men who reside inside the reserve).

Environmental stressors impact physiology in many animal species. Accordingly, the monitoring of fecal glucocorticoid metabolites (fGCM) has been increasingly used to evaluate the physiological costs of habitat disturbance on wild animal populations, providing a powerful tool for conservation and management. Several studies have suggested that primates in forest fragments have higher fGCM levels than those in continuous forests, yet the proximate causes of fGCM variation remain to be identified. In previous studies of Mexican howlers ( Alouatta palliata mexicana ) in Los Tuxtlas, Mexico, we found that individuals living in a smaller and more disturbed forest fragment consumed significantly less fruit and had a significantly higher feeding effort than those living in a bigger, more conserved forest fragment. Here, we aimed to examine the effects of fruit consumption and travel time on fGCM levels in the same two groups of howlers, during three sampling sessions that differed markedly in fruit availability. We found that fGCM levels ( N  = 202 fecal samples) were higher in the howler group living in the smaller forest fragment and varied seasonally in both focal groups, being lowest when fruit consumption was highest. However, our results suggest that travel time is the main factor predicting fGCM levels in howlers, and that although fruit consumption may be negatively related to fGCM levels, this relationship is probably mediated by the strong effect that fruit consumption has on travel time. Our results provide important insight into the proximate causes of fGCM variation in primates in fragments and highlight the potential conservation significance of studies showing that habitat loss and transformation can lead to increases in travel time in wild primates.

The Mexican howler monkey ( Alouatta palliata mexicana ) is a critically endangered primate, which is paleoendemic to Mexico. However, despite the potential significance of genetic data for its management and conservation, there have been no population genetic studies of this subspecies. To examine genetic diversity in the key remaining forest refuge for A. p. mexicana , the Selva Zoque, we amplified full-length mitochondrial control region sequences (1,100 bp) from 45 individuals and found 7 very similar haplotypes. Haplotype diversity ( h  = 0.486) and nucleotide diversity ( π  = 0.0007) were extremely low compared to other Neotropical primates. Neutrality tests, used to evaluate demographic effects (Tajima’s D  = −1.48, p  = 0.05; Fu’s F s  = −3.33, p  = 0.02), and mismatch distribution (sum of squares deviation = 0.006, p  = 0.38; raggedness index = 0.12, p  = 0.33) were consistent with a recent and mild population expansion and genetic diversity appears to be historically low in this taxon. Future studies should use a combination of mitochondrial and nuclear markers to fully evaluate genetic diversity and to better understand demographic history in A. p. mexicana . These studies should be undertaken throughout its geographic range in order to evaluate population structure and identify management units for conservation. Due to the limited distribution and population size of A. p. mexicana , future conservation strategies may need to consider genetic management. However, a more detailed knowledge of the population genetics of the subspecies is urgently recommended to maximise the conservation impact of these strategies.

The populations of the Mexican mantled howler monkey (Alouatta palliata mexicana) in the Los Tuxtlas region, Mexico, have declined drastically due to habitat loss and fragmentation. Nevertheless, several troops still inhabit very small and isolated rain forest fragments. We identified the main vegetation attributes that can favor the presence of howlers within 18 small (< 10-ha) fragments that did not differ significantly in size, shape, and isolation (nine occupied and nine unoccupied by howlers). We found that habitat quality (i.e., food resources and vegetation structure) affected howler incidence in small fragments. Particularly, the occupied fragments showed greater density of big trees (dbh > 60 cm), greater total basal area, greater basal area of persistent tree species, and greater basal area of top food species than the unoccupied fragments; suggesting that even for small fragments the loss of big trees and particularly the decrease in size class of the top food species can negatively affect howler distribution in highly fragmented landscapes. These findings could be used to establish foreground conservation areas for this critically endangered subspecies in fragmented landscapes of Los Tuxtlas.

The activity patterns and diet of howler monkeys (Alouatta palliata mexicana) were studied in 3 forest fragments in south-eastern Mexico: Playa Escondida (PLA), Agaltepec Island (AGA) and Arroyo Liza (LIZ). Intersite differences offered the opportunity to investigate the foraging adaptations of howler monkeys in response to population and habitat size. In the largest fragment (PLA), the howlers’ diet was based on high-quality items (fruit and young leaves). In AGA, where the density of howlers was the highest, their diet was mostly folivorous with a marked exploitation of uncommon food items such as vines, lianas, shrubs and herbs. The dietary differences in AGA were accompanied by more time spent travelling and less time spent resting. Although LIZ was the smallest fragment and had a high howler density, the small group size and the use of energy-minimizing strategies (less time spent travelling and more time spent resting) probably allowed howlers to maintain a frugivorous diet.

Understanding the effect of landscape structure on biodiversity is critically needed to improve management strategies. To accurately evaluate such effect, landscape metrics need to be assessed at the correct scale, i.e. considering the spatial extent at which species–landscape relationship is strongest (scale of effect, SE). Although SE is highly variable, its drivers are poorly known, but of key relevance to understand the way species use the landscape. In this study, we evaluate whether and how species traits, biological responses, landscape variables and the regional context of the study drive SE in Mexican primates. We estimated the relative abundance and immature-to-female ratio (a proxy of reproductive success) of howler monkeys Alouatta palliata and A. pigra and spider monkeys Ateles geoffroyi in 48 forest patches from four rainforest regions (12 patches per region) with different land-use intensity. We then assessed the composition (forest cover, matrix functionality) and configuration (forest patch density, connectors’ density, forest edge density) of local landscapes considering 13 scales (100 to 1300-m radius) to identify the spatial extent at which each landscape variable best predict each response variable in each species and region. We found that SE did not differ significantly among the drivers evaluated. However, it tended to be lower for connectors’ density than for forest patch density and forest edge density, probably because connectors’ density is associated with local-scale processes such as supplementary dynamics. Surprisingly, SE also tended to be higher in the more disturbed region than in the rest of the regions, probably because primates in the more disturbed region used larger areas of the landscape. Our findings therefore suggest that SE depends more strongly on landscape variables and regional context than on species traits and biological responses, and hence, especial caution should be taken when attempting to generalize SE to different explanatory variables and regions.

Parental care strategies are adaptations shaped by evolutionary pressures to maximize offspring survival while balancing current and future reproductive investment. Maternal care styles, which are consistent patterns of behavior that vary among individuals, have been well-documented in catarrhines but remain poorly understood in platyrrhines. Furthermore, while previous studies have documented that maternal behaviors change as infants develop, whether individual maternal styles remain consistent or shift across infant developmental stages remains largely unexplored. This represents a critical gap, because understanding the interaction between maternal styles and infant age could reveal whether mothers maintain fixed behavioral phenotypes or demonstrate flexible responses to changing developmental needs. We investigated whether wild mantled howler monkeys (Alouatta palliata) show distinct maternal care styles that change across infant development. Using an age-specific analytical approach, we examined whether maternal behavior is organized into distinct styles during each of early, middle, and late infant development. We observed 16 mother-infant dyads in four groups at three sites in Los Tuxtlas, Mexico, collecting 743 hours of focal observations over 2 years. Using robust principal component analysis and bootstrap-validated cluster analysis, we identified three distinct maternal styles during early infancy (Minimal-investment, High investment, and Proximity-focused), three styles during middle infancy (Minimal-investment, High-support, and Mixed-investment), and two styles during late infancy (Minimal-investment and Selective-support). We found minimal consistency in individual maternal styles across infant development stages, with infant age significantly explaining behavioral variance whereas maternal identity did not. Our results offer preliminary evidence that mantled howler monkey mothers strategically adjust care patterns in response to infant developmental needs rather than maintaining consistent individual styles. If such dynamic adjustment allows for the successful balancing of the competing demands of ensuring current offspring survival and maintaining capacity for future reproduction, our results contribute to the understanding of the evolution of maternal investment strategies in primates.

Variation in tropical forest management directly affects biodiversity and provisioning of ecosystem services on a global scale, thus it is necessary to compare forests under different conservation approaches such as protected areas, payments for ecosystem services programs (PES), and ecotourism, as well as forests lacking any formal conservation plan. To examine the effectiveness of specific conservation approaches, we examined differences in forest structure and tree recruitment, including canopy cover; canopy height; seedling, sapling, and adult tree density; and average and total diameter at breast height (DBH) across 78 plots in 18 forests across Costa Rica representing protected areas, private forests utilizing PES and/or ecotourism, and private forests not utilizing these economic incentives. The effectiveness of conservation approaches in providing suitable primate habitat was assessed by conducting broad primate census surveys across a subset of eight forests to determine species richness and group encounter rate of three primate species: mantled howler monkey ( Alouatta palliata ), Central American spider monkey ( Ateles geoffroyi ), and the white-faced capuchin monkey ( Cebus imitator ). Only canopy height was significantly different across the three approaches, with protected areas conserving the tallest and likely oldest forests. Canopy height was also significantly associated with the group encounter rate for both mantled howler and spider monkeys, but not for capuchins. Total group encounter rate for all three monkey species combined was higher in incentivized forests than in protected areas, with capuchin and howler monkey group encounter rates driving the trend. Group encounter rate for spider monkeys was higher in protected areas than in incentivized forests. Incentivized conservation (PES and ecotourism) and protected areas are paragons of land management practices that can lead to variation in forest structure across a landscape, which not only protect primate communities, but support the dietary ecologies of sympatric primate species.

Many researchers have suggested that Australopithecus anamensis and Australopithecus afarensis were among the earliest hominins to have diets that included hard, brittle items. Here we examine dental microwear textures of these hominins for evidence of this. The molars of three Au. anamensis and 19 Au. afarensis specimens examined preserve unobscured antemortem microwear. Microwear textures of these individuals closely resemble those of Paranthropus boisei, having lower complexity values than Australopithecus africanus and especially Paranthropus robustus. The microwear texture complexity values for Au. anamensis and Au. afarensis are similar to those of the grass-eating Theropithecus gelada and folivorous Alouatta palliata and Trachypithecus cristatus. This implies that these Au. anamensis and Au. afarensis individuals did not have diets dominated by hard, brittle foods shortly before their deaths. On the other hand, microwear texture anisotropy values for these taxa are lower on average than those of Theropithecus, Alouatta or Trachypithecus. This suggests that the fossil taxa did not have diets dominated by tough foods either, or if they did that directions of tooth–tooth movement were less constrained than in higher cusped and sharper crested extant primate grass eaters and folivores.

Habitat loss due to deforestation is a primary threat to global biodiversity. Clearing tropical rainforests for agriculture or development leads to forest fragmentation. Forest fragments contain fewer large trees and provide lower food availability for primates compared to continuous forests. Mantled howler monkeys ( Alouatta palliata ) inhabit fragmented rainforests and may need to alter their activity budgets and spatial cohesion to mitigate competition and conserve energy in fragments where food quality is lower. We compared howler monkey activity and spatial cohesion across a small forest fragment (La Suerte Biological Research Station, LSBRS) and a large, continuous forest (La Selva Research Station) in Costa Rica. We predicted that monkeys at LSBRS would rest more, feed more, travel less, and be less spatially cohesive compared to La Selva to contend with fewer resources in the small fragment. Using instantaneous scan sampling at 2-min intervals during 30-min focal samples, we recorded activity and the number of individuals within 5 m of the focal animal. We collected 1505 h of data from 2017–2024. Monkey activity and spatial cohesion differed significantly across sites. As predicted, monkeys at LSBRS spent more time feeding than at La Selva, but contrary to our predictions, they rested less and traveled more. The mean number of individuals within 5 m was significantly lower at LSBRS compared to La Selva. The ability to modify their activity and spatial cohesion in response to fragmentation provides insight into how primates can contend with fewer resources and higher competition in changing ecosystems worldwide.