RESUMO
Callitrichids are small Neotropical primates and, due to their cooperative breeding system, infants are of particular interest in research on social dynamics. Although a few studies have investigated the role of helpers in this type of system, there is still a lack of research in field studies seeking to determine whether there is a relationship between the number of helpers (adults) in a social group and the motor development of infants. With that in mind, four groups of wild marmosets (Callithrix jacchus) were observed and the motor behaviors of 1 to 4 month-old infants were recorded. To investigate the influence of the adult:infant ratio on motor diversity, used as an indicator of motor development, we ran a GLMM with a Gaussian distribution and found that: (i) in groups with fewer adults, 2-month-old infants show earlier motor diversity; (ii) motor diversity increases with age regardless of the ratio of adult males per infant; (iii) in groups with more adult females per infant, the motor diversity of 2-month-old infants is significantly lower compared to 3-month-old infants. Although adult callitrichid males play an important role in the care of their offspring, the presence of females appears to be a key factor in motor development at this early stage in the study groups. In a cooperative breeding system, the lack of helpers seems to drive the development of independence in infants, resulting in earlier development.
Assuntos
Callithrix , Atividade Motora , Animais , Feminino , Masculino , Callithrix/crescimento & desenvolvimento , Fatores EtáriosRESUMO
We aimed to determine the conservation status of medium- and large-sized mammals and evaluate the impact of 500 years of forest fragmentation on this group of animals in the Pernambuco Endemism Center, in the biogeographical zone of the Atlantic forest north of the São Francisco River in northeastern Brazil. Line transect surveys were performed in 21 forest fragments, resulting in a checklist of the mammals of the entire Pernambuco Endemism Center area. We ran a generalized linear model (Factorial ANCOVA) to analyze to what extent the vegetation type, fragment area, isolation, sampling effort (as total kilometers walked), or higher-order interactions predicted (a) richness and (b) sighting rates. To determine if the distribution of the species within the forest fragments exhibited a nested pattern, we used the NODF metric. Subsequently, we performed a Binomial Logistic Regression to predict the probability of encountering each species according to fragment size. Out of 38 medium- and large-sized mammal species formerly occurring in the study area, only 53.8% (n = 21) were sighted. No fragment hosted the entire remaining mammal community, and only four species (19%) occurred in very small fragments (73.3% of the remaining forest fragments, with a mean size of 2.8 ha). The mammalian community was highly simplified, with all large mammals being regionally extinct. Neither the species richness nor sighting rate was controlled by the vegetation type, the area of the forest fragments, isolation or any higher-order interaction. Although a highly significant nested subset pattern was detected, it was not related to the ranking of the area of forest fragments or isolation. The probability of the occurrence of a mammal species in a given forest patch varied unpredictably, and the probability of detecting larger species was even observed to decrease with increasing patch size. In an ongoing process of mass extinction, half of the studied mammals have gone extinct. The remaining medium-sized mammal community is highly simplified and homogenized. The persistence of these species in a forest patch is determined by their ability to adapt to a novel simplified diet, the efficient use of the surrounding matrix without being engulfed by the sink effect, and escaping hunting. Our results suggest that the 21st century medium-sized mammalian fauna of this region will comprise only four species unless strict conservation measures are implemented immediately and every forest fragment is effectively protected.