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Why are the Golden Lion Tamarins endangered?
Golden Lion Tamarins (GLTs) are marmosets native to the Atlantic Forest of Brazil. Their original habitat was located from the southern part of the state of Rio de Janeiro to the southern part of the state of Espirito Santo. Unfortunately, deforestation of the Amazon Rainforest for commercial purposes, predation, and capture of the GLTs for animal trade and sale as pets has limited their population to about five municipalities across Rio de Janeiro. Most of the population is now found in the Poco des Antas Biological Reserve in Rio de Janeiro.
Golden lion tamarins are characterized by using manipulative foraging in places such as tree barks and epiphytic bromeliads. Their sites of foraging are usually distributed around their home ranges, which are large territories (averaging 123 hecta acres) in which multiple foraging sites are located, to find sufficient resources over long periods of time. These areas are sufficient enough in size so that even if there is overlap in between the home range of two different groups, the interactions are minimal due to the distribution of the foraging sites (they spend 50% of their time in approximately 11% of their home range). However, due to the deforestation and fragmentation of the Amazon forest, their home ranges have decreased in size. The decrease in size has been reported in terms of fragmentation, and today the forest consists of thousands of fragments equaling only 8% of its former size. This directly affects their areas of foraging and subsequently, the amount of resources available. Therefore, it can be concluded that decreasing the size of their home range can potentially increase competitive interactions between different groups.
A study conducted by Hankerson and Franklin shows that increased predation has caused significant decreases in the population numbers. A survey conducted in 1992 found the number of wild population of GLTs to be 562 individuals in 109 groups. Currently, the average group size includes 3.6 to 5.7 individuals and densities from 0.39 groups/km to 2.35 groups/km. These predatory attacks occur at the GLT sleeping sites. The predators make those sleeping sites, which are mainly tree holes (about 63.6%), larger in order to attack the GLTs, sometimes wiping out the entire family. The preferred sleeping sites of most GLTs are tree holes in living trees next to other larger trees with a small percentage of canopy cover. These sleeping sites not only provide a place for sleep, but also offer protection and easy access to foraging sites. Most of the tree holes are lower to the ground, so they are easier to enter. Tree holes that are located in living trees are drier, warmer, and have a lower number of insects and therefore a decreased percentage of transmitted diseases. A smaller percentage of canopy coverage allows the GLTs to detect the predators faster, and being surrounded by other large trees allows them access to escape routes. Due to degradation of their habitats, there are fewer trees that can support entire social groups and some have to resort to using bamboos (17.5%), vine tangles (9.6%), and bromeliads (4.7%) as a sleeping site, making them more susceptible to predators. GLTs are known to use different den sites, but do not change sites often. They are more likely to reuse secure sites that will offer protection. However, the disadvantage of doing so is that predators are able to learn where these sites are located. GLTs also scent mark their den holes, so they can quickly return to them in the afternoon time when predators are most active. Scent marking is also a method of claiming their territory from competitors. Scent marking increases in wet seasons, because the scent is more likely to be washed away by the rain. While excessive scent makes it easier for GLTs to find their sleeping sites, it also helps predators locate their prey. Moreover, increased deforestation has decreased habitat space, providing predators easy access to their prey, causing a decline in the GLT population.
The habitat of the tamarins also has an impact on their behavior and social interactions. For example, the type of trees present has a significant effect on the behavior of juvenile GLTs.. Their juvenile behavior is characterized by social play between individuals of different ages and species. This is a key aspect of their social, cognitive and motor skill development, and it influences their behavior when facing competition and predators; how they play mirrors the way they act when facing predatory or competitive interactions. Social play is observed more in large branches (>10cm) and vine tangles (4m above ground), which is considered safe for them, as they are less vulnerable to predators, compared to play in the dangerous areas including canopy branches and the forest floor. Therefore, deforestation affects the diversity in the forest and decreases the “safe” areas for play for the juvenile tamarins. As a result, play decreases and therefore the development of learned survivorship behaviors does as well. Also, if play is observed in the dangerous areas, the individuals are more exposed to predators, leading to a population decline; which resembles the effect of predation on their sleeping sites. The exposure to predation not only affects the juvenile tamarins but the adults as well, since it has been observed that play happens in the center of the group for protection of the young.
Additionally, this deforestation and fragmentation also leads to demographic instabilities, and an increased probability of inbreeding, consequently leading to inbreeding depression and a population decline. In the case of inbreeding, the problem lies in the increase of the isolated fragments where GLTs live. Inbreeding leads to low levels of genetic diversity and has a negative effect on survivorship; inbred offspring have a lower survivorship than non-bred offspring. Fragmentation leads to a decline in dispersal and as a result, a decline in breeding with individuals of other groups. Consequently, inbreeding depression is observed in these populations. With delay breeding, the decrease and shortage of territory puts pressure on GLTs to disperse in order to find necessary resources and areas suitable for their survival. However, dispersal is risky and requires a lot of energy that could have been used for reproduction instead.
Importance of Golden Lion Tamarins to their Ecosystem
Furthermore, the conservation of this species is significant as they play a key role in the Amazonian ecosystem. They have a mutualistic interaction with 96 species of plants found in this forest. This interaction is based on seed dispersal and food sources for the tamarins. The tamarins show repeat visits to those plants with abundant resources. They tend to move around their territories, and therefore, seeds are dispersed to areas far from the parent shadow, which is perfect for germination. Their seed distribution is important to forest regeneration, and genetic variability and survival of endangered plant species.
Because of the importance of GLTs to their habitats, it is necessary that we conserve this species. Therefore, two programs, reintroduction and translocation, have been established to assist in stabilizing the GLT populations.
Conservation Efforts for the Golden Lion Tamarin
Unfortunately, because of the extensive habitat loss of the golden lion tamarin, the wild population reached endangered status in the early 1980’s . Beginning in 1983, there has been a huge effort on behalf of scientists and conservationists to reintroduce captive born golden lion tamarins back into the wild. With the help of the Brazilian government, conservationists established the Poço das Antas Biological Reserve and the Unaio Biological Reserve as sites for reintroduction. The goals of the reintroduction process include increasing the size as well as the genetic diversity of the wild population, increasing the available range to better encompass the historic range of the tamarins in Brazil, and widening the scope of public awareness and education programs.
The first step of reintroduction begins with zoo free ranging programs, where tamarins have access to explore the entire zoo. However, they are kept on zoo grounds by the presence of a nest box, an ice box like container where their food is kept. When the tamarins are reintroduced in Poço das Antas, they require a large amount of post-release training and veterinary care. For the first 6-18 months, a salaried Brazilian team keeps watch over the reintroduced groups. Additionally, 1-2 tamarins from each group are radio collared to allow careful monitoring, and all reintroduced tamarins are tattooed and dye marked for easy identification.
Secondly, in an effort to save the GLTs from extinction, some of the GLTs have been removed from small, isolated unsafe forests and placed into a larger, protected forest; specifically they were moved to União Biological Reserve and Poco das Antas reserve. This effort to move the GLTs into União Biological Reserve in Brazil began in 1991. The GLTs faced the potential of getting new diseases that they had not been previously exposed to. Many were exposed to callitrichid hepatitis, and contracted the disease.This disease was not fetal for all the GLTs as the 42 GLTs have increased in population size to 200 GLTs.
Despite the challenge of illness it wasn’t fetal for all GLTs; the forty-two translocated golden lion tamarins population grew to over 200 in União Biological Reserve. And the number of wild Golden Lion Tamarins is now up in the 1700s in all reserves and ranches combined in Brazil.These populations were once down in the 200’s in 1991. By 2025, the populations of GLTs that are protected are projected to be greater than 2000.
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