|THE ECOLOGY OF THE SIBUN RIVER|
The headwaters of the Sibun River drain densely forested areas of the Maya Mountains. These headwaters receive tremendous amounts of forest debris in the form of leaves, flowers, seeds and branches along with rain runoff. This detritus is then partially broken down and decomposed by many different organisms living within the river. That which is not processed is carried further downstream and eventually to the mangrove systems along the coastline of Belize where further biological breakdown takes place.
This energy that is released all along the river, provides a food source for many creatures. One of the main objectives of this expedition was to gather baseline data on the many different creatures which live in and around the river. The following section will introduce the concept and importance of river watersheds - including structure of foodchains - and highlight some of the more interesting creatures encountered on the expedition.
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|...surface water is the runoff draining from the highest points through springs, lakes, streams, and rivers to the lowest points, at sea level, where it feeds into the oceans, the whole area being drained is called a watershed... |
A watershed is a living river system which transforms and transports food from the headwaters to the mouth. Headwaters may comprise over 80% of all stream miles within any watershed system. In the case of the Sibun, the watershed system is an intricate network of feeder streams that drain the northeastern part of the Maya Mountains. These feeder streams not only funnel rainwater into the Sibun River, but also carry nutrients to biological communities downstream.
These headwaters drain densely forested areas of the Maya Mountains. Here the water is clear, cold and fresh. Special communities of animals use the small amounts of detritus in the water as food, transforming leaves, soil and wood into animal bodies which in turn become food for animals downstream.
Further downstream, gallery or riverside forests form canopies over the river, dropping more leaves and branches into the water. Rainwater runoff carries soil and minerals into the water. When the river floods, nutrient rich waters spill out over the banks of the river, depositing the nutrients onto the land, making them available to river side plants and eventually animals. That is why the vegetation along tropical rivers is so lush and thick.
The watershed forests are extremely important in maintaining the health of tropical river ecosystems. Any sudden or large scale disruption of the flow of nutrients not only effect the organisms in and around the river, but also the coastal marine systems that feed off of the river nutrients flowing in to the sea.
Disturbances such as land clearing, road construction, and farming can increase the flow of water into the river. This can result in loss of topsoil in the forest, increased amounts of soil in the water turning the water dark and dirty, and the increase in the amounts of nutrients in the water which can unbalance the system. Communities downstream often rely on these rivers and watershed for drinking water. So disturbance to watersheds not only disrupt the ecology, but can also have grave consequences for people which live along the river.
River or watershed systems essentially function as filters, trapping and transforming nutrients that flow through the tropical ecosystem. These watershed systems are one directional, moving water and nutrients from the higher elevations to the lower ones. Many creatures feed off the nutrients, further filtering and transforming. So watersheds act as the basis of the FOOD CHAIN for tropical ecosystems.Top |Watershed | Foodchain | Animals
|...the sequence of stages by which food is used by organisms in an ecosystem... |
A simple foodchain begins when a plant, or part of a plant is eaten by an animal, then that animal is eaten by another. The food itself - the plants - are created from nonliving material like minerals, water, and the sun's energy in the form of light. Therefore, plants are the base of the food chain.
Base of Sibun Foodchain
In the Sibun River, the base of the food chain would contain algae which grows on e rocks and stream sides, fruits which fall from trees in the river, and from the leaves, branches and other material called detritus which falls into the river.
Primary Consumers of the Sibun River
Bacteria and other microbes then feed on the detritus in the river, while insects feed on the algae, fruits and bacteria ladened detritus. Invertebrates such as crabs and shrimps also feed on the foodchain base components. Small fish will feed on clumps of bacteria, graze on the algae and pick at the fruit which falls into the river. In each case though, the number of organism, or biomass is less on the second level of the foodchain then the amount of food on the base.
Secondary Consumers of the Sibun River
The insects, crustaceans and smaller fish become prey for the larger fish in the river. Within in the deep holes along side rapids or under fallen logs lie a singular or small school of fish which feed on the insects washed to them by the river. Again, the number of large fish is much smaller then the number of organisms in the previous layer.
Top of the Foodchain of the Sibun River
Finally, the top of the foodchain is normally a large creature such as an Osprey or a river otter. But these levels of the food chain are not fixed. The river otter could be caught by a jaguar, putting the jaguar at the top of the foodchain. The Osprey could fall prey to a wildcat also. This is just an example of how a specific foodchain might be constructed.
As you can see, the foodchain might better be called a food pyramid, for the base is occupied by large numbers of small organisms, while at each higher level the number of organisms gets smaller as their size gets larger. It is also important to realize that a foodchain is only a specific flow of food, and that other food chains may differ. For example, the large fish may directly eat the algae, instead of eating the insects that eat the algae.
When we look at all the possible routes that food may take within a river system, we end up something that looks like a spider web. In fact, the pattern of food and therefore energy that flows through a river system would better be described as a food web.Top |Watershed | Foodchain | Animals
|...limited information on the abundance and distribution of wildlife in the upper Sibun River is available. But two species of primates and six species of carnivores... |
The Sibun River Watershed supports a wide variety of wildlife. Though limited numbers of birds and mammals were sighted during the expedition, the Maya Mountains in general have healthy populations of mammals and birds, including two species of monkey, all six species of wildcats, and over 500 species of birds. The following six animals represent some of the more endangered and spectacular animals of the Sibun River Watershed and the Maya Mountains in general.Margay | Otter | Howler Monkey | Tapir | Scarlet Macaw |Boat-billed Heron
The margay is a small, slender cat with a tail over half the length of its body. Because of the small size of its pelt, the margay has not been hunted as heavily as the other cats in Belize. But due to habitat destruction, the margay is becoming more rare as it prefers deep vegetation of primary forests.
The "Tiger Cat" as it is known to Belizeans, is the most nocturnal and arboreal of all cats in Belize. The large eyes and extremely bright eyeshine attest to the highly developed night vision. The superlative balance, great leaping ability and proportionately longer claws than other species of cat make the Margay ideally suited for life in he forest canopy. In fact, the ankle joints of this cat can rotate 180 degrees to allow the rear claws to grasp the tree trunk with enough force to control a descent upside down.
The margay eats small mammals, birds, reptiles and amphibians and forages almost solely through the top of the forest trees. The margay is thus tied ecologically to forested watershed areas and especially to deep tropical rainforests.Margay | Otter | Howler Monkey | Tapir | Scarlet Macaw |Boat-billed Heron
The Southern River Otter, known as the "water dog" in Belize, is active both during the day and night. These are semi-aquatic creatures that feed mainly on fish and crustaceans, putting them near the top of the food chain. River otters are extremely graceful in the water, swimming and diving with ease.
These otters like the clear fresh waters of the upper reaches of most Belizean Rivers. They like fast flowing water and streams, and tend to stay away from the more muddied lowland rivers, though they are found along the coast of Belize. They are therefore found mainly along the upper reaches of riverine habitats. Otters are known to be plentiful in the upper reaches of most of the rivers in the Maya Mountains.
Otters are well known for their playfulness. They often slide down mud banks or tumble in the water with mates or siblings. This play is thought to help reinforce social bonds between family members as well as teach hunting and fighting skills.Margay | Otter | Howler Monkey | Tapir | Scarlet Macaw |Boat-billed Heron
The Black Howler Monkey, known as "baboon" in Belize, has the largest distribution and uses the widest range of habitats of any mammal in Belize. Howlers prefer forests along river banks, but they will utilize all ages of forests as long as food is available.
Howlers are thought to travel only about 200 meters (about 650 feet) each day for food. Howlers tend to favor the leaves of trees, especially of the following species - bread fruit, chicle, gumbo limbo, trumpet, bri-bri and fig trees.
Howlers live in small troops of 4 to 8 members. Each troop will usually consist of an adult male, and several females with young This entire troop will usually eat, sleep and travel together.
The howler monkey is very territorial, and will defend its territory by using their incredible strong voice. The howling is so loud that it is often mistaken for a jaguar. The roars can be heard from as far away as a mile. You can usually hear the howlers at the start and end of the day as well as when it starts to rain.Margay | Otter | Howler Monkey | Tapir | Scarlet Macaw |Boat-billed Heron
The Tapir, known as the "mountain cow" in Belize, is the largest terrestrial mammal in .Belize, growing to 200-300 kg. This creature has inhabited the region for some 70-100 million years. Though common in Belize, Tapirs are listed as endangered through its range in Central and South America.
Because Tapirs are so large and require a large home range to feed, they are very susceptible to habitat destruction. The upper watersheds of many of Belize rivers provide a good home for the tapir. Seasonal flooding causes rich and thick secondary growth along most river banks. This type of vegetation is preferred by the tapir for food.
Though active mainly at night, tapirs do move about during the day. They are mainly solitary creatures, but the mothers are often accompanied by offspring. They are excellent swimmers and are often encountered in or along the upper reaches of rivers in Belize.Margay | Otter | Howler Monkey | Tapir | Scarlet Macaw |Boat-billed Heron
The Scarlet Macaw, known as "Guacamaya" in Belize, prefers the higher elevations and the dense forests along the rivers and streams of the Maya Mountains. Because of its size and bright colorful plumage, the Scarlet Macaw has been trapped and hunted almost to extinction. The scarlet macaw does not make a good pet. The large bill can often cause serious wounds, and the bird is known to be vicious at times. In the more remote areas of the Maya Mountains, flocks of 10-15 can still be seen in the tops of tall trees.
With the large strong bill, the scarlet macaw eats mostly vegetable foods such as forest fruits and seeds. The macaw will often hold the food with a single foot while tearing the fruit or cracking the nut. The short, flat muscular tongue helps to manipulate the food.
Scarlet macaws nest in the hole in tall trees. The adult macaw can be seen at the entrance to the hole, and receives food from the other mate without it having to enter the nest. These nesting sites are often well above ground.Margay | Otter | Howler Monkey | Tapir | Scarlet Macaw |Boat-billed Heron
The Boat-billed Heron is a large bird with a vary large, flat bill. The bill is thought to be used as a scoop while feeding along the shores of rivers and ponds. Not much is known of the bird other then nesting in the lower branches of trees which hang over water and rivers.
The heron has a distinctive behavior while guarding its nest. When danger approaches, or the birds mate lands nearby the nest, the boat-billed heron will raise the feathers on its crown, increasing the size of its head substantially. This makes the bird look much larger then it is. It will also clack its bill in alarm.
The boat-billed heron is a nocturnal bird, and prefers the company of others of its species like most herons do. The Belizean name for this bird is "cooper". The origin of this name is unknown.Margay | Otter | Howler Monkey | Tapir | Scarlet Macaw |Boat-billed Heron
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