Tropical Rainforests and their Biological Communities.
Tropical Rainforests are characterised by warm temperatures and year-round rainfall. This hot, moist biome is found near the equator, with the largest of tropical rainforests found in South America, Africa and South-East Asia (Fig.2). Tropical rainforest have trees growing to large sizes, which are supported by a strong base that helps to keep the trees stabilized in the shallow soils of the forest. It occupies a huge variety of different trees compared to any other forests, which include mahoganies, teaks and rosewood trees. Tropical rainforests consist of four levels (Fig.2); the emergent, canopy, understory and the ground layer. Certain factors contribute to the different communities inhabiting the different levels of the rainforest. This will be discussed further below.
Fig.ure 1. Tropical Rainforests Across the World. Source: http://www.thewildclassroom.com/biomes/rainforest.html
The Emergent Layer is the few tallest trees that protrude into the open in stalks above the canopy of the tropical rainforest. These trees are tall, have few branches, are umbrella shaped and have evolved tough little leaves with thick waxy cuticles in order to withstand the harsh weather conditions. The waxy cuticle reduces evaporation and water loss which adapted them to endure the long-time direct sunlight, high winds, heavy rain downpours and extreme hot and cold temperature fluctuations. The tree tops spread out to as much as 10 meters wide and each emergent tree is spaced far apart from each other. The tallest trees provide shelter for many insects and birds, mostly birds of prey, that habitat in the emergent layer. The animals need to be able to fly or glide because the branches wouldn’t be strong enough to carry heavy animals. Birds’ wings are short to enable them to navigate the dense forest vegetation and sight and hearing needs to be good in order to survive. The trees depend on insects and some birds for pollination. Even though there aren’t many flowers, high winds also help spread winged seeds and pollen across the tropical rain forest away from the forest floor directly below.
The canopy is the main layer of a Tropical Rainforest, and may reach over 30m from the ground. It is extremely dense and made up of overlapping branches and leaves. The canopy occupies majority of life in the rainforest, because it protects the forest below from the sunlight and heavy rainfall. The huge diversity of food sources contribute to the wide variety of animal species, although, the lack of visibility also contribute to the species living there. Since the canopy of the rainforest is so dense, the animals need to rely on sound signals which warn other animals entering their territory. Thus, animals living in the canopy are very loud; primates howl and birds sing to let animals know when they are intruding. Most animals living in the canopy never go down to the forest floor as all their needs are supported in the canopy. This keeps them protected from predators on the forest floor, such as snakes and jaguars. The species which occupies the canopy of a tropical rainforest include; sloths, howler monkeys and Woolley monkey’s. While the colourful bird community include the Macaw, Cockatoo and the Toucan’s.
The Understory Layer is made up of young trees and herbaceous low-level light plants. This layer only receives about 2 – 15 % light and therefore is dark compared to the canopy and higher. The leaves of the plants are generally large and wide in order to capture the maximum of the little amount of sunlight available. This layer is very hot and humid due to little air movement because the wind is blocked by the canopy and emergent layer. This type of climate is perfect for many mosquitos and other insect species. Geckos, lizards, snakes, monkeys and bats are some common animals that inhabit the understory and mostly feed off insects or each other. They live amongst the branches of the trees and camouflage is vitally important for survival. Most animals are prey and competition for food is high, so camouflage may provide an advantage. The trunks of trees are often covered in moss and fungi and frogs do well in this climate because of the abundance of moisture. Plants need insects to pollinate them, so often the flowers of the plants are pale in colour so that the contrast is easier to see in low light, or they have a strong smell to attract pollinators.
The floor of a rain forest is characterized by little sunlight, very high humidity and heat. The flora and fauna adapted to these conditions. Since only 1 to 2% of the sunlight that passes through the canopy reaches the ground, it is mostly shaded and thus only plants that don’t need much sunlight grow there. The vegetation is composed of some small bushes and shrubs such as the lianas. Since most plants require more sunlight, it isn’t very crowded on the floor (Fig.3). This favours the bigger animals that live on the forest floor such as anteaters, tapirs, jaguars and humans, but also reptiles like snakes, lizards and caimans. But the smaller animals, mainly insects, spiders, scorpions etc. make up the larger amount of the forest floor community. The topsoil forms a very important part of the forest floor, because there all the decomposers are found, which are needed to break down the leave litter and dead animals. The decomposers are mainly bacteria, termites, fungi and earthworms. The high humidity and heat help with the breakdown. This thin layer is very nutrient poor, because the shallow roots of the trees take up the released nutrients immediately. Therefore the nutrients are mainly found in the living organisms. Water bodies like rivers and lakes form part of the forest floor. There are plants found like the giant water lily, which have leaves growing up to 3m in diameter. Fishes such as the piranha live in those waters, but also the caiman. The forest floor community is very different from the other communities and is well adapted to the extreme conditions.
Figure 2. Rainforest Layers. Source: http://rainforestheroes.com/about-rainforests/what-is-a-rainforest-2/
Figure 3. Blue Mountains Rainforest, Australia. Source: Adam. J. W. C
By : Janine Greuel, Simone Louw & Timia Sanchez