CONTINUING EDUCATION
Special Topic: Intern Lisa
Spider Monkeys, Behavior, Ecology, and Evolution of the Genus Ateles
Chapter 1 Introduction
Chapter 1 discusses how Spider monkeys (genus Ateles) have been largely unstudied in the wild, despite the fact that this genus is often seen as the “typical monkey”. Studying Spider Monkeys in the wild has been difficult due to the fact that they are fast moving, wide ranging, and live high in the canopy. So often, when being studied, only a few community members can be studied at one time. However, in the last decade the number of studies on spider monkeys has increased. Areas of study include Spider Monkey ecology (the study of the relationships between the organism and their environment), behavior, physiology (the functions of an animal’s parts), morphology (the study of the form or shape of an organism) and evolution.
Part 1: Taxonomy, phylogeny, and evolution
Chapter 2 Morphology and evolution of the spider monkey, genus Ateles
Spider monkeys are well suited for life in the upper canopy foraging for ripe fruit. This is seen throughout the spider monkeys skeletal morphology. Spider monkeys’ bodies are also the closest to a gibbon that has evolved in the Order Primates. Spider monkeys, like gibbons are brachiators, meaning they use their arms to move from tree branch to branch.
The general morphology of spider monkeys has enabled them to successfully adapt to their environment. The skeleton is designed to help suspend and hurl their body weight, which allows them to swing through the trees. Their energy rich diet had allowed them to have modestly enlarged brains. The brain of the genus Ateles typically weighs over 100 grams. The dentition (teeth) in the Ateles is functionally suited for a classically frugivore (fruit eating) diet. Incisor teeth (which are used to shear food sharply) are well developed. The canines (teeth used to firmly hold food in order to tear apart) differ in male and females. In males the upper canines are long, slender, and re-curved and in females they are slightly shorter, stouter, and less projecting. Studies are being conducted to understand why there is sexual dimorphism in canine teeth. Another interesting morphological features of the spider monkey is its missing thumb, or as it is also known the pollex. The fingers on a spider monkey hand are long and re-curved, almost hook-like, and the limbs tend to be long and spindly. The arms tend to be about 25% longer than the legs. Another interesting feature of the spider monkey is its prehensile tail. The tail is very strong and has a palm-like pad at the end. The tail acts almost as an extra limb. All these interesting morphological features have made the genus Ateles a very proficient animal for life high in the rainforest canopy.
-Campbell, Christina J. Spider Monkeys: The Biology, Behavior and Ecology of the Genus Ateles (Cambridge Studies in Biological and Evolutionary Anthropology). UK. Cambridge University Press. 2008
Special Topic: Intern Cheryl
The Complete Capuchin. The Biology of the Genus Cebus
Chapter 1: Taxonomy, Distribution and Conversation: Where and What Are They and How Did They Get There?
In this chapter, the authors describe the appearance of the Genus Cebus as well as the areas occupied by Capuchins and distribution of the species. The chapter also discusses the main causes of decreasing wild populations of Capuchins in Central and South America.
TAXONOMY: Capuchins are robustly built due to their arboreal (tree-dwelling) lifestyle and have arms and legs of nearly equal length. They also possess semi-prehensile tails that enable them to grasp with their tail like they do with their hands and feet. Although mainly arboreal, Capuchins are known to venture down to the ground to forage for food. They have large canine teeth and thickly enameled molars that are well adapted to crushing seeds and tearing open hard fruits.
Capuchins are known for the distinctive caps on their crowns that appear in various colors and shapes in different species. For example, White-fronted Capuchins (Cebus albifrons) have a brown cap, whereas the White-faced Capuchin (Cebus capucinus) typically has a black cap. The White-faced Capuchin is the only species with jet-black fur on their body, limbs and tail. White fur occurs around the black cap on the crown, as well as on the throat, shoulders, chest and upper arms. The facial skin is pink and the amount of white fur on the face tends to vary depending on sex, class and age.
Capuchins can find their closest phylogenetic affinities (evolutionary relations) in Squirrel monkeys. It has been suggested that Capuchins branched off from a common Cebid ancestor around 22-23 million years ago; compare that to marmosets and tamarins that are younger at 13-16 million years. More fossil samples are needed however to clarify the picture of Cebid evolution.
DISTRIBUTION: Capuchins have one of the widest distributions of any New World primate genus. Most species are found throughout South America from extreme northwestern Ecuador to parts of Argentina and Paraguay. Many species of Cebus will inhabit similar areas in South America. The White-faced Capuchin has been noted mostly in Ecuador, western Colombia, Panama, Costa Rica, Nicaragua and the Honduras and is the only species of Capuchin to occupy Central America starting in the Honduras, while still maintaining areas in South America along the Colombian Andes.
Capuchins tend to occupy humid and dry tropical forests, swamp forests and seasonally flooded forests as well as dry deciduous forests where rainfall is absent for 5-6 months a year. They are mostly seen in the middle layers of the forest, but use all levels from the canopy to the under storey and sometimes the ground to drink, forage and travel.
The numerous amounts of data collected from different habitat types suggests that they exhibit the ability to explore almost any type of Neotropical forest to the fullest extent.
CONSERVATION STATUS: It is well known that most species of Cebus are under threat from more than one source. Three main causes are listed here:
1) Many populations across central and South America are affected by humans altering the natural environment for economic development, in particular by the outright destruction of their forests. This is considered to be the most significant factor in the decline of wild populations of Capuchins. It is important to state that as tropical forests decline, so will the number of animals that depend on them.
2) Hunting is a highly significant stress on Capuchin populations. Monkeys are hunted for food as well as body parts (for ornamental purposes and medicinal). In South America as well as Africa, monkeys are often used for ‘bush meat’. Hunters would usually aim for the larger monkeys such as Spider monkeys, Woolley monkeys and Howler monkeys. Infant monkeys are usually raised as pets
3) Live capture for export and trade on the pet market, for biomedical research or for exhibition in zoos is also another big threat to Capuchin populations. Fortunately, this factor has been greatly reduced in recent years due to imposed legislations and introductions of animal welfare and changing missions in zoos. The want to protect and preserve has now overtaken the need to exhibit.
This chapter has educated the reader in identifying species of Cebus, identified where to find them and what in this world is threatening their existence. There is some argument when defining habitat usage for the genus, as many populations over large parts of South America have not been documented.
- Fragaszy, D.M., Visalberghi, E., Fedigan, L.M. (2004) The Complete Capuchin: The Biology of the Genus Cebus. UK. Cambridge University Press.
Special Topic: Intern Dana
Rylands Marmosets and Tamarins, Systematics, Behavior and Ecology
CHAPTER 8: Flexibility and Co-Operation as Unifying Themes in Saguinus Social Organization and Behavior
For most of the history of primatology, New World Monkeys have been considered poor candidates for behavioral research. It was believed that there was little to be gained from studying them, since they are farther removed from humans evolutionarily than Old World Monkeys and apes. The Callitrichidae have been the least studied, and it wasn’t until the late 1980’s when researchers began investigating the complexities of marmoset and tamarin mating systems. It was around the same time that the field of Primatology began investigating the issue of predation as an important pressure on primate social behavior. In this article, Caine discusses how the natural behavior of tamarins has been and continues to be shaped largely by predation.
The author argues that there are two fundamental principles in understanding tamarin social behavior. These are 1) The fundamental elements of tamarin social life are co-operation, tolerance, and adaptability, and 2) that predation is among the most important selection pressure influencing social behavior and group structure.
Until recently, monogamy was assumed to be the center of tamarin social organization. However, research has shown that they are more polyandrous (one female, multi-male) than originally assumed. In captivity, Cotton Top Tamarin (Saguinus oedipus) pairs act aggressively to new conspecifics (other animals of the same species) during intruder studies; interestingly, it is only the males who act with aggression, and only to other males.
A trait that characterizes all Saguinus species to date is co-operation, especially regarding infant care. All adult members carry infants, usually from within a few hours or a few days of birth. The infants go back to their mothers mainly to nurse. Adults also have been seen sharing food with infants. When traveling and foraging, group members move in a cohesive manner and even produce monitoring calls as they move through the jungle. Aggression is rarely observed in free-ranging groups. In captivity, adults are far more likely to tolerate each other when feeding; food calls are given when even a small amount of desirable food is found.
Tamarins are also very co-operative with respect to anti-predator behavior. Predators include birds, snakes, tayras (large weasels), and ocelots. Avoidance, alarm calling, and sometimes mobbing are their primary tactics. To avoid predators at night, tamarins retire before dusk, have increased vigilance, and carefully select sleeping sights. Caine argues that it is the tamarins’ vigilance for predators, rather than their response to them, that promotes cooperative social behavior. Individuals can spend more time eating and less time looking around when responsibility for vigilance is shared. In conclusion, predation pressures seem to play the most critical role in determining tamarin group size and social interactions.
-Rylands, A.B. Marmosets and Tamarins. Systematics, Behavior, and Ecology. Oxford, U.K.: Oxford University Press, 1993.
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