Spider Monkeys of the Americas：美洲的蜘蛛猴

Spider Monkeys of the Americas：美洲的蜘蛛猴 Spider Monkeys of the Americas Ateles sp, There are 7 species of spider monkeys: Ateles belzebuth (long-haired spider monkey), Ateles chamek (Peruvian spider monkey), Ateles fusciceps (brown-headed spider monkey), Ateles geoffroyi (Geoffroy's spider monkey), Ateles hybridus (brown spider monkey), Ateles marginatus (white-cheeked spider monkey), Ateles paniscus (black spider monkey). They are called spider monkeys because they look like spiders when they suspended themselves by their tails. Features Spider monkeys are usually all black, but some have flesh coloured rings around their eyes and white chin whiskers. Their hair is generally coarse and stringy and, unlike some other monkey species, they lack underfur. Color of fur ranges from golden, red, buff, brown or black, with hands and feet generally black. These monkeys depend highly on their keen binocular vision. Male body length varies between 38 to 48 centimeters (14 to 16 inches), tail 63-82 cm, 9-10 kilograms. Female body length ranges between 42-57cm, with the tail 75-92cm in length. Body weight of adults ranges from 6 to 8 kilograms. Males and females look the same. The body structure and several other morphological characteristics of spider monkeys are adaptations to their completely arboreal lifestyle. First, they have slender bodies and limbs with long narrow hands. Their elongated arms allow them to move in a specialized manner through the trees using a hand-over-hand motion (a form of locomotion called brachiation, which is also seen in the lesser apes). In addition to their elongated arms, spider monkeys have especially hook-like hands with elongated fingers that allow them to swing from branch to branch with ease. Unlike most other primates, spider monkeys lack an external thumb, which is a specialized adaptation to their arboreal lifestyle. Their ancestors had an opposable thumb, but over time, it has shrunk in size relative to other bones of the hand due to selection for those animals that had smaller thumbs. Another morphological adaptation seen in spider monkeys is the presence of a long, prehensile tail, an adaptive trait seen only in some New World monkeys, and which allows arboreal animals to move through the canopy with additional ease, security, and efficiency. The prehensile tail is often called a ‘fifth hand' because it allows spider monkeys to grasp branches while moving through the canopy, preventing side-to-side swinging motion that could lead to inefficiency and increased effort in locomotion. On the underside of the very tip of the tail there is a patch of skin with distinct pattern of lines like a fingerprint. This patch of skin, or friction pad, at the tip is functionally important because it helps the tail grip onto surfaces, much like fingers on a hand. Additionally, the presence of a prehensile tail is important in suspensory (hanging below branches) feeding: the tail supports the entire weight of the monkey while both hands are free to forage. The prehensile tail seen in spider monkeys is relatively longer than the non-prehensile tail of other primates and has more vertebrae which are smaller relative to overall tail length than non-specialized tails seen in other primates. This anatomical feature is significant because the presence of additional, but smaller vertebrae allows for increased flexibility and extension in the prehensile tail compared to non-prehensile tails. In addition to brachiation, black spider monkeys move through the environment through quadrupedal walking and running along the tops of branches and through clambering movement that utilizes numerous supports in no particular order or pattern. Location Spider monkeys are restricted to arboreal habitats, mainly in the top of the tree canopy. Some species live at sea level while other species can be found in the high mountains. Irrespective of the elevation of their home territory, spider monkeys are forest dwellers, and are found in evergreen rainforests, semi deciduous and mangrove forests, lowland rainforests as well as mountain forests. In these forests they live mostly in the upper canopy, preferring undisturbed high forest, almost never coming to the ground. They prefer wet than dry forests. Species of spider monkeys can be found from Mexico to South America, along the coasts and the banks of the Amazon, south to Bolivia and the Matto Grosso in Brazil, and the mountain forest slopes of the Andes. Food Spider monkeys occupy the upper layers of the rainforest and forage in the high canopy (from 25 to 30 m [82.0 to 98.4 ft]) consuming primarily fruits (thus they are called frugivores), but also occasionally consuming young leaves, flowers, sometimes bark and decaying wood, as well as honey. A very small part of the diet consists of insects, insect larvae and birds’ eggs. The amount of fruit and supplemental foods such as flowers and leaves vary seasonally, as fruit production is linked to rainfall. During the long dry season, for example, fewer fruits are available, therefore fewer fruits are consumed and spider monkeys rely more heavily on other food sources. When feeding, they may hang by their tails and reach out for tidbits with 1 their hands. They can also pick up things with their tails. They eat large quantities of food over a relatively short period of time and they tend to feed by suspension while hanging, climbing or moving. They do not pick fruit and carry it to another location to be eaten. As large-bodied frugivores, spider monkeys are important seed dispersers within the rainforest ecosystem and play a crucial role in regenerating tropical forests. Because of their large body size, which has high caloric needs, and dependence on fruit, a geographically scattered resource found in small, widely dispersed patches, spider monkeys require large home range sizes as well as long daily travel lengths. The lead female is often observed determining the forage route for the group; however if food is scarce they tend to divide into smaller groups. The largest groups of monkeys, sometimes up to 100 monkeys, are found in a big tree loaded with fruits. When they feed in a large tree, spider monkeys continuously adjust their positions so they are not too close to one another. Latecomers wait until earlier arrivals leave before entering the tree. It seems that spider monkeys can be quarrelsome feeders if they are too close to one another, and this spacing out saves them all trouble. During those months of the year when they have to depend on small, scattered sources of fruit, such as from palm trees, lone individuals and smaller aggregations are found moving through the forest. Thus, they avoid quarrelling at food sources with only enough ripe fruit at any one time to feed a few monkeys. Social Spider monkeys live in medium-sized, loosely associated groups of about 30 individuals. Their social structure is of the type primatologists call fission-fusion, which is a form of social grouping pattern in which individuals form temporary small parties (also called subgroups) whose members belong to a larger community (or unit-group) of stable membership; there can be fluid movement between subgroups and unit-groups such that group composition and size changes frequently. The females have a more active leading role than males, so their social system is often said to be matrilineal. Within the group, adult males can coexist peacefully, although there is a clear hierarchy determined by age. The group is centered on the females and their young. Males are dominant over females, but it is the females that make the key decisions for the group. Males may forage in small groups. Females and offspring often forage alone. Every 2 – 3 years, a mother will give birth to one entirely black baby. No one else besides the mother looks after the baby. The baby is continuously carried by the mother, clinging to her and at about 5 months of age it will begin riding on her back, wrapping its tail around the mother's tail for additional security. It will be dependent on its mother's milk for 2 years. Juveniles at the age of 24 to 50 months old never ride on their mother's back but they will still stay close to her. They spend their time exploring, or chasing, grappling, and jumping on others. They will play with others their same age or with adults. The average lifespan in the wild is about 22 years. Movement Spider monkeys have been called "the supreme acrobat of the forest." In the wild, the spider monkeys rarely come down to the jungle floor. They travel in small bands in forest trees, moving swiftly by making tremendous leaps, sprawling out like spiders, and grasping tree limbs with their prehensile tail. Acrobatic and swift, they also move through the trees by brachiating, with one arm stride covering up to 40 feet. Their feet are greatly elongated and their big toe is prehensile (grasping), working like hands to grasp thinner branches, as well as for better grip as it walks upright on two legs on broad branches. Spider monkeys may even stand upright on a branch using the tail as a third limb in a tripod arrangement with its two legs! When the animal is on the lookout, it stands or walks on two feet, using the tail to hold on to a support. Their specialized prehensile tails may contribute to increased efficiency in travel, allowing them to cover larger distances using less energy. It also contributes to increased feeding efficiency after they have found a patch of fruit and are foraging. Thus, spider monkeys use several different types of locomotion: quadrupedal, using all four limbs for locomotion as seen while walking or running; brachiation (or suspensory locomotion) used when hanging, climbing or moving through the trees and bipedalism, using only two limbs when leaping. Quadrupedal locomotion is usually observed if the monkey is on a stable relatively substrate free of obstacles. When they are using suspensory locomotion they may be swinging with their arms from one branch to another while often maintaining a tail hold. On the rare occasions when they move on the ground, they may walk upright on two legs, their long tails held stiffly upright against the back. Territories Groups defend their ranges. Males will mark their territory with secretions from chest glands. Anyone stumbling into spider monkey territory receives an unpleasant ‘welcome’ of screams, barks, and rattling branches and thrown branches or feces. The interactions will often begin with males, often along with one or two females, calling, which will bring other group members into the area. 2 When males are within 100 meters of each other, they will mutually threaten with a great deal of bluster. They chase about in the trees, shaking branches and whoop and growl at each other. These noisy sessions can easily last for an hour or more but they seem to be strictly male affairs; females remain quietly in the background. But troops rarely come to blows. Sometimes a male will occasionally scent mark branches by smearing saliva and a secretion that comes from a gland on his chest onto the branches, presumably to deposit his scent in the area. Communication These monkeys have a variety of loud calls, audible for 800-1000m on the ground and 2,000m above the canopy. These "long" calls are used to help the groups space out in the forest and avoid unnecessary confrontations. These calls are also used to alert members of a group to a central feeding site. Juveniles develop their long call by trial and error. When threatened, they make barking noises, but if that doesn’t scare intruders away, they fragment into subgroups and run. They prefer retreat, so fights are rare. When they spot a predator on the ground, both males and females make a loud "ook-brak" bark, while throwing branches and shaking tree limbs by jumping up and down. Only males whoop. But when this fails to scare off the intruder, they scatter in smaller groups. The most frequently heard call resembles whinnying of a horse - probably a greeting or contact call. Like other primates, they have a wide range of facial gestures to express their moods. Both genders sniff and embrace when greeting. Habits The spider monkey travels in groups and the route they take through trees remain constant. During more abundant times of the year, the route shortens but does not change. Spider monkeys are diurnal (i.e., active during the day). They are most active in the early morning. Feeding bouts are 1-15 minutes long. At night they use sleeping trees that are usually tall enough so that the crown is free from the canopy beneath it having a broad open crown that has horizontally forked branches for prolonged resting postures. The sleeping trees are often chosen for their ability to provide a ready source of food. Sleeping high in a tree above the canopy also affords security from predators. Since the thumb is absent, the spider monkey's grooming is not as developed as in other primates. They scratch themselves with hands and feet, but most of their social grooming is mothers grooming their young. Status: Critically Endangered Their lifespan in the wild is about 27 years. Average 20 years in the wild, 33 years in captivity. The spider monkey is critically endangered, which means it is facing an extremely high risk of extinction in the wild in the immediate future. Considered good to eat and because of their large body size, spider monkeys have been severely hunted throughout their range. They are easy to locate because they are noisy and travel in big groups. So spider monkeys are often extinct in areas easily accessible to people. There is also a lucrative pet trade. They are also affected by habitat destruction, particularly logging, which removes the tall trees that they depend upon. They are also vulnerable because they have low maturation and reproduction rates. Three of the spider monkey species, the white-bellied spider monkey, brown-headed spider monkey, and white- whiskered spider monkey are listed as Endangered by either USESA or IUCN. This means that these species have at least a 20% chance of going extinct in the wild within 20 years or 5 of their generations. The black-handed and black spider monkeys are listed as Vulnerable by IUCN - there is at least a 10% probability of extinction within 100 years. Only the black-faced black spider monkey is considered at Lower Risk (CITES II.) 3