CONTINUING EDUCATION
Special Topic: Intern Caroline
Perceiving the world. Memory and Perception
How do capuchins perceive the world? Moreover, what do they think of us? Evidence has suggested that capuchins are able to recognize individual people and other monkeys with whom they’ve interacted after years of separation. Capuchins also have quite good memories for significant events, which might explain why they tend to be drawn to certain people or objects over others. In the case of Viola who was hand raised as an infant, it is evident she is the most comfortable of any of the capuchins around humans here at PPS.
In their natural habitat, capuchins have been found to be consistent with their ability to travel efficiently among multiple food sites by remembering the location of their food sources and not retracing their paths on the same day. They are also able to learn to search smaller spaces systematically much like Miranda has been trained to take her food out of her red food bucket and Viola, the food tray.
Did you know capuchins do not hear melodies? It is true. Field studies have shown capuchins appeared not to remember the patterned auditory stimuli (tunes), but rather relied on the local features (i.e. first or last note) to discriminate the sounds (D’Amato and Salmon 1984).
The next time you’re preparing the capuchins’ diet try ‘honey-dipped raisins’ which proved to be a favorite amongst capuchins in various field studies.
-Fragaszy, D.M., Visalberghi, E., Fedigan, L.M. (2004) The Complete Capuchin: The Biology of the Genus Cebus. UK. Cambridge University Press
Special Topic: Extern Dawn
Chapter 10 – Spider Monkey Reproduction and Sexual Behavior
Specific data pertaining to the reproductive biology and behaviour of spider monkeys continues to be underrepresented in literature and this is primarily due to the sheer difficulty of studying them in the wild.
Spider monkeys are monomorphic (males and females are the same) in body size and it is only the clitoris that clearly distinguishes females from males…
Sexual encounters are usually long and very private under the cover of darkness, with the male and female separating from the group to find an isolated tree location before copulating.
…Male spider monkeys are known to be aggressive toward females and aggression may be linked to conflicts of reproductive interests between males and females and, in turn mating strategies.
The actual mating system is extremely promiscuous and these encounters take place at times when conception is not likely or impossible, thus strengthening the conclusion that copulation is not strictly tied to ovulation in spider monkeys.
-Campbell, Christina J. Spider Monkeys: The Biology, Behaviour, and Ecology of the Genus Ateles (Cambridge Studies in Biological and Evolutionary Anthropology). UK. Cambridge University Press. 2008.
Special Topic: Intern Simon
Chapter 14: The Ecology of the Lion Tamarins, Leontopithecus;
by Anthony B. Rylands
Introduction
Callitrichids are made up of marmosets, tamarins, and lion tamarins. Weighing up to two pounds, llon tamarins are the largest, which helps illustrate just how small all callitrichids are.
There are four species of lion tamarins: the Golden lion tamarin, the Golden-headed lion tamarin, the Black lion tamarin, and the Black-faced lion tamarin. All four are found exclusively within the Atlantic coastal forest of Brazil. Lion tamarins differ from marmosets and other tamarins in various ways, but this chapter focuses on differences related to their ecology—specifically how the interrelationship between ecology and the behaviors of hunting, diet, and nesting affect these endangered species.
Hunting strategies
Hunting among lion tamarins is performed by rummaging through foliage with their hands and upturning concealed critters, rather than the stalk-and-pounce visual hunting of the marmosets and most other tamarins. By being more proactive in their hunting, lion tamarins are able to find hidden larger insect prey, which is necessary for them since they are bigger monkeys than marmosets.
Possibly because of these different hunting strategy preferences, Weid’s Marmoset and the Golden-headed lion tamarin are able to coexist in the same habitat. Not only do they employ different hunting strategies, the two also forage at different levels of the forest, with the Lion tamarin species looking in the upper levels and the marmoset species foraging more in the middle and lower levels. Interestingly, the other three Lion tamarin species forage at the lower forest levels, and though they are known to share forest space with marmosets they do not cohabitate (live together) with them. This is very likely due to the fact that they would be competing for the same foods if they did. The exploitation of different forest levels, therefore, allows Weid’s Marmoset and the Golden-headed Lion tamarin to live together in harmony.
Diet
Like the other callitrichids, lion tamarins eat insects and fruit. They may eat exudates (gums and saps) but only in the dry season when fruit is scarce. Since they lack the specialized dentition of marmosets to extract exudates they can only eat them when it has been made accessible by cracked branches or insect-bored holes. This inability to access tree gum for themselves has had ecological consequences for the lion tamarins. You see, because the White tufted-eared marmoset possess the ability to extract exudates from trees, they can comfortably live in seasonal forests subject to drought and can have small home ranges; they don’t have to travel to far away fruit trees because they can simply feast on gum and sap from nearby trees and vines. Lion tamarins, on the other hand, don’t have the luxury of subsisting on exudates. They rely more on fruit, and when fruit trees dry up they need to move on to the next one to survive. For this reason, lion tamarins have the largest ranging patterns of all the callitrichids.
Nesting habits
When it comes to nesting for the night, lion tamarins are very particular. All four lion tamarin species sleep in tree-hole shelters. In fact, they require them. This behavior limits lion tamarins to forests that have such holes. The kinds of trees that have these holes are typically found in primary forest, which means that lion tamarins require primary forest. This ecological limitation would explain why other tamarins and marmosets—who may use primary forest but thrive in damaged and fragmented forests—do not employ the same tactic of sleeping in tree-holes. It also explains why all four lion tamarin species are so endangered—they insist on a habitat that is, itself, endangered.
Conclusion
In summary, by using a different hunting strategy than marmosets, Lion tamarins have been able to avoid direct competition with their fellow callitrichids, with one species—the Golden-handed lion tamarin—even cohabitating with a species of marmoset. But due to an inability to exploit exudates or to adapt to severely degraded forests lacking tree-hole shelters, the majestic lion tamarins are in danger of extinction.
Chapter 15: Ecological differentiation in the Callitrichidae; by Stephen F. Ferrari
Introduction
As the title suggests, this chapter gives a general overview of the differences between the various callitrichids (marmosets and all tamarins), and the ecological implications of those differences. It covers their evolutionary history, explains their dwarfism, and focuses on how body size ecologically relates to their consumption of gums and foraging strategies.
Evolutionary history and dwarfism of callitrichids
A big difference between callitrichids and other monkeys is their small size. Their tiny stature is an evolutionary adaption allowing them to inhabit marginal and damaged forest habitats. But while all marmosets and tamarins are small compared to most other primates, there is actually relatively large difference between the smallest—the pygmy marmoset—and the largest—the Black Lion tamarin—with varying degrees amongst the species in between. These differences have likely played a critical role in their ecology, social structure, and evolutionary history.
The widely accepted hypothesis for the evolutionary history of the callitrichids is that their ancestor was most similar to the Lion tamarins, and that as time passed a trend towards shrinking (dwarfism) began. This trend is probably the result of competition between two groups sharing a common habitat, with one group having to adapt so as not to compete directly with the other. The more adaptable a species is, the more successful it becomes. For the callitrichids, shrinking meant adapting. This may explain why the larger Lion tamarins are endangered and the most successful callitrichid species—White-tufted eared marmosets and Saddleback tamarins—are smaller. Saddleback tamarins are the smallest of all tamarins. White-tufted eared marmosets are as small as can be before shrinking begins to become unfavorable.
When dwarfism becomes too extreme (below 250 grams), the disadvantages begin to outweigh the benefits. Pygmy marmosets are an exception to this rule, however they do underscore problems associated with excessive smallness. For one, Pygmy marmosets are extremely prone to predation. Additionally, reproduction is a monumentally large burden on them—their litters can weigh up to nearly a quarter the weight of the birth mother. That’s like a 140-pound human mother giving birth to a 35-pound baby! Also, like other marmosets and tamarins, Pygmy marmosets carry their infants with them throughout the day. This is clearly inconvenient for such tiny monkeys. But the Pygmy marmosets are a special case. Remember, competition is the driving force for dwarfism among the callitrichids. Since the Pygmy marmosets share a habitat with two other tamarins, their dwarfism was likely a way for them to occupy a different niche so as not to compete with the tamarins. Though their tiny size may not be ideal, they have made it work in their favor.
The benefits of dwarfism on foraging and hunting
So we have heard the disadvantages of extreme dwarfism. What are the advantages of non-extreme dwarfism? Well, the small size of marmosets and tamarins gives them an advantage when it comes to food. They can rely on trees that produce tiny fruits over long periods of time. It’s not worth the energetic expenditure for larger monkeys sharing the habitat to forage for such tiny fruit, but it sustains marmosets and tamarins due to their tiny body size. This reduces competition. Likewise, marmosets and tamarins get more bang for their buck when they eat insects than the larger monkeys—such as capuchins and squirrel monkeys—would get.
Since marmosets and tamarins are small, the longer they spend hunting for insects to eat, the higher their chances are of being eaten themselves by predators. But because they are so small they don’t have to hunt for very long. Whereas a larger monkey would have to eat many insects to get a meal’s worth, these little guys can fill up on one or two insects and call it a day, limiting their vulnerability.
Small size has also allowed the callitrichids to get more nutritional mileage out of gums and saps. However, as we saw in preceding chapters, there is some disparity between the marmosets and tamarins regarding their ability to exploit exudates (gums and saps). Most marmosets have specially adapted lower front teeth for the purpose of extracting exudates. This specialization allows them to live in damaged forests and forests that are susceptible to drought—eating exudates and hunting insects throughout the year when fruit is absent. They are also adapted to digest exudates in a way that maximizes nutritional extraction.
Tamarins, by contrast, do not have these advantages. They eat exudates opportunistically, but cannot extract it themselves. This difference between marmoset and tamarin gummivory has an intricate influence on their behavior, ecology, and social organization—which has been discussed in previous chapters. Even their physiology has been morphed to better capitalize on the available exudates around them.
In addition to the specialized marmoset teeth, the claw-like nails that both marmosets and tamarins have are not a primitive trait. They are actually an evolutionary adaptation, which likely developed as a means to cling to the trunks and branches where gum deposits are often found. While all callitrichids consume gums to some extent, the difference of just how reliant on this nourishing ooze they are has resulted in large distinctions between the various callitrichid genera. But regardless, their small size has allowed them to really reap the benefits of high calorie exudates.
Conclusion
Ecological flexibility is critical for a species’ success. Dwarfism has given the callitrichids advantages that have allowed them to flourish in their niches. Being small allows them to make a complete meal out of insects, exudates, and small fruits. But environments change, and if species do not change with it, they face extinction. The difference between the Lion tamarins and the Saddleback tamarin helps demonstrate this point.
As we just saw in the last chapter, since the Lion tamarins sleep in habitats that contain the sorts of trees where tree-holes are found, they are limited to select forests. While other tamarins and marmosets can thrive in severely damaged forests, Lion tamarins cannot. They are considered ecologically inflexible and, as a result, are highly endangered. Saddleback tamarins, in contrast, hunt for prey and forage in very similar ways to the Lion tamarin but do not require the tree-holes and thus are not as limited. And their small size—recall that that are the smallest tamarin—affords them more options for finding sleeping spots. Because they aren’t as picky about their habitat as Lion tamarins, and because they have evolutionarily adapted via dwarfism, saddlebacks are one of the most widespread of all the callitrichids, while the large, ecologically particular Lion tamarins are among the most endangered.
-Rylands, A.B. Marmosets and Tamarins. Systematics, Behavior, and Ecology. Oxford, U.K.: Oxford University Press, 1993.
I am not interested to know whether vivisection produces results that are profitable to the human race or doesn't. The pain which it inflicts upon unconsenting animals is the basis of my enmity toward it, and it is to me sufficient justification of the enmity without looking further. -Mark Twain
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