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Symbiosis Spring 2011
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Brazil Nut Tree - Animal Symbiosis
Brazil-Nut Tree Symbiosis's
By Gregory Cello
Rainforests are characterized by a unique vegetative structure consisting of several vertical layers including the overstory, canopy, understory, shrub layer, and ground level. One of the largest trees in the rainforest that makes up a large portion of the canopy is the Brazil nut tree (
). These trees are dependent on several animal species for their survival such as the agouti, a ground-dwelling rodent, for a key part of their life cycle. The agouti is the only animal with teeth strong enough to open their grapefruit-sized seed pods. While the agouti eats some of the Brazil nut's seeds, it also scatters the seeds across the forest by burying caches far away from the parent tree. These seeds then germinate and form the next generation of trees. For pollination, Brazil nut trees are dependent on Euglossine orchid bees. Without these large-bodied bees, Brazil nut reproduction is not possible. For this reason, there has been little success growing Brazil nut trees in plantations as they only appear to grow in primary rainforest.
Brazil-nut tree - Overview
A particularly distinctive species because of its towering height, the Brazil-nut tree is widely considered to be one of the most economically important plants of the Amazon. Its valuable seeds are harvested and the oil, in particular, is extracted and used in a wide variety of products. The Brazil-nut tree is also the only widely traded commodity that is still harvested from the wild, rather than plantations and is possibly the most significant non-timber forest product besides rubber.
The seeds of the Brazil-nut tree are long and angular, and have a hard, thin outer shell, a white kernel (the edible part of the seed), and a nutty texture. Between 12 and 25 seeds are enclosed inside the large, round fruits (‘pyxidia’), which are typically around 10 centimeters in diameter, and weigh up to 2.2 kilograms. The outer layer of the fruit is tough and woody, giving it a heavily armored, bark-like appearance. The flowers of the Brazil-nut tree are, with six fleshy, oblong, yellow-cream or yellow petals and pale green.
The Brazil-nut tree is native to South America and naturally occurs throughout the Amazonian rainforest, in Brazil, Bolivia, Columbia, Ecuador, Peru, Suriname and Venezuela.
The Brazil-nut tree grows in non-flooding areas, commonly known as
, in the lowland rainforests of the Amazon.
The Brazil-nut tree occurs in stands (groups of trees) that usually contain between 50 and 100 individuals, with each tree capable of producing around 60 to 100 fruits each season. The tree will usually begin fruiting after 12 years of age, and the development of the fruit takes around 15 months, with mature fruits dropping to the ground during the rainy season. The fruits are indehiscent, meaning that the woody capsules do not break open and disperse the seeds when they hit the forest floor. Instead, the Brazil-nut tree relies upon agouti (rodents in the genus
) to gnaw through the tough outer wall of the fruit, releasing the seeds. Some of these seeds will be eaten by the agouti, whilst others will be hoarded and buried intact. Seeds that are not subsequently destroyed or eaten by the agouti or another seed predator will remain in these scattered caches and may germinate after 12 to 18 months.
Flowering generally occurs through the dry season, with a peak in flowering between October and December. Pollination of the Brazil-nut tree is limited to a specific group of insects, the large-bodied bees, and some bats, because of its unusual flower structure. An arched ‘hood’ is formed by several elongated staminodes (stamens that do not produce pollen), creating a chamber that encloses the reproductive organs. Only bats and those insects which have the necessary size and strength to lift the hood are able to gain entry into the flower to obtain the nectar.
The seeds of the Brazil-nut tree are some of the most economically valuable non-timber forest products produced within the Amazon region, and the Brazil-nut has long been harvested from the wild. However, research has indicated that juvenile trees of the Brazil-nut are missing from populations where nuts have been persistently harvested over many generations, causing concern that the current level of exploitation may not be sustainable.
Evidence also suggests that people involved in the harvest of Brazil-nuts are often involved in other activities which may negatively affect the biodiversity of the forest, such as slash-and-burn agriculture, timber extraction, hunting and mining. Deforestation in particular is thought to be having an increasingly negative effect on the Brazil-nut tree, usually as a result of clearing land for agriculture
Here is a video showing an overview of the Brazil Nut Tree:
Agouti – Overview
Eastern South America
50 cm (20 inches)
2.5 cm (1 inch)
3 Kgs (6.5 lbs)
Up to 20 Yrs (in Captivity)
Azara's Agoutis are large rodents. They have a body length of approximately 50 cm (20 inches), a short tail measuring approximately 2.5 cm (1 inch) and they weigh approximately 3 kg (6.5 lbs). Their fur is speckled and colored pale to mid brown with a paler underside. They have prominent ears and short legs. Their distinctive feet have five toes on the front feet but only three toes on the hind feet. They have very sharp teeth and when feeding they sit on their hind legs and hold food in their front paws. They are active during the day and in the wild they are shy animals, fleeing from humans if they approach. They have an active, graceful gait which is either a trot or a series of springing movements and they are good swimmers. If they are alarmed they will let out a bark.
Azara's Agoutis are found in the rainforests and savannahs of Brazil, Paraguay and Argentina. They are solitary animals and they live in burrows or tree hollows.
Azara's Agouti Range Map (Eastern South America)
Azara's Agoutis diet mainly consists of seeds, nuts, fallen fruit and other plant material. They are known as the only animal that can open a brazil nut due to their strength and exceptionally sharp teeth.
After a gestation period of approximately 90 days, 2 - 4 young are born in a burrow. When they are born they have their eyes open and they are covered in fur. They remain with their mother until they are able to fend for themselves then they leave to begin a solitary lifestyle.
Across much of its range people hunt Azara's Agoutis for meat.
Agouti's are known as jungle gardeners as they often bury nuts and seeds and forget where they put them, therefore helping new plants to grow.
The Agouti and the Brazil Nut Tree Symbiosis
Naturally occurring Brazil nut trees heavily depend on a large rodent, the agouti, to disperse the seeds once they drop. The agouti is a small mammal bearing large teeth, the only teeth in the entire Amazon capable of opening the seed pods. These creatures have incredibly strong jaw muscles, a large head, long legs, and little ears. Depending on which classification approach, there are four or five species with the black agouti and red-rumped agouti as the two most prevalent. Hiding in the brush, the agouti adapts to a variety of habitats including the preferred virgin forest as well as developed locations such as roadsides and plantations, however, these creatures are most frequent in undisturbed locations. Hey are often hunted by locals for food in developed areas and castaneros for stealing their seed pods. The agouti is commonly spotted during dawn and dusk when its vision is poor. They are typically independent of other agoutis, but exceptions in terms of life mates have been noted. Newly born agoutis live in a hidden den area for protection. The mother will not enter the den, but require that her young come out to meet her.
A diet of fruits and nuts provides the agouti with plenty of food falling from the canopy. The special and influential characteristic of these rodents is that they typically open their food and hide it in the ground to save for later when times get tough. In turn, this gives the Brazil nut tree the extra help it needs to reproduce by planting the seeds in the rain season. In an attempt to better understand the symbiosis between the agouti and Bertholletia excelsa, researchers use magnets to locate caches of seed deposits.
The empty seed pods are useless to the agouti, but very beneficial to many animals and microscopic plants. The pod is in effect a water reservoir perfect for many animals to breed. Some species of amphibians reproduce in the empty pods and nowhere else. Amphibians and insects compete for the location, typically a "first come, first serve" situation in which the first to hatch has an abundant food source. If the insects hatch first then their larvae will eat other larvae and juvenile amphibians. If the amphibians hatch first then they have an extensive food supply as well. The empty Brazil nut seed pod serves as an "all you can eat buffet" for the first to hatch which has driven evolution of the species to reproduce there. The most efficient species will be able to produce several offspring that do not require excessive time for embryonic development.
Here is a video showing an Agouti breaking into a Brazil-nut fruit before feeding on and burying the nuts:
Orchid Bees and the Brazil Nut Tree Symbiosis
Naturally occurring Brazil nut trees are only found in areas that have not been flooded (terra firma) and have a three to five month dry season. Coincidentally, the only natural pollinators of the Brazil nut blossoms also occur in these areas. Metallic colored orchid bees of the family Euglossinni are highly specialized to penetrate the defenses of the small yellow blossoms. The flowers have a structure designed to prevent insects' passage to the pollen and nutrients (with an exception to euglossines, large flying insects bearing a long tongue). This symbiotic relationship provides the buds with a specialized pollinator and the bees receive a consistent carbohydrate energy source. The euglossine dependence of the Brazil nut flower continues further than energy requirements. Male orchid bees require a scent found in the orchids of the canopy to court female bees. These orchids are abundant in the emergent tree habitat such as that of Bertholletia excelsa.
Establishing a colony of orchid bees on a plantation seems like a quick fix to pollination issues, however the results prove otherwise. In contrast to honey bees, euglossines are basically nonsocial beings. There is no hive to transport to a growing plantation. Therefore, plantations should be located near natural high density Brazil nut stands, called manchales (Peru, castanhais in Brazil), so the bees will be required to migrate very short distances. Other pollinators have been found on plantation grounds occurring outside of the natural range for euglossines, although their ability to efficiently pollinate the plantations has been indeterminable as of yet.
Here is a very interesting article written by freelance writer, David Taylor, who went to the Amazon to explore all about this symbiosis:
The Agouti's Nutty Friend - inter-dependence of the Brazil nut trees and the reclusive animals called agoutis
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