Unit 6: The diversity of the ecosystems                                      1   2   3

2.3. Biomes of torrid zones

a) Desert

A desert climate is characterised by great variations in daytime and nighttime temperatures (they can vary by up to 40 ºC) and by little rainfall.

Desert animals are adapted to survive the extreme lack of water there. Reptiles, for example, have scales which cover their skin and prevent water loss; many insects are covered with chitin which also prevents water loss; and camels and dromedaries transform the fat they store in their humps into water.

The vegetation in deserts is either very poor or non-existent. Desert plants are also adapted to this climate and have small leaves (often thorns), and thick external layers to prevent water loss, for example, cacti, prickly pears and agaves. Some plants also store water inside their leaves and stems.

b) Savannah

Savannah develops in tropical regions, especially in Africa. The typical climate of this region consists of long, hot, dry summers and short, warm rainy seasons.

The main vegetation consists of grasses. There are a few trees and shrubs, such as the acacia and the baobab.

The fauna of the savannah includes large carnivores, such as lions, leopards, cheetahs, hyenas and vultures and large herbivores, such as the elephants, hippopotamus, rhinoceros, giraffes, antelope, gazelles, zebras, etc.

c) The tropical rainforest

This biome is found in the rainiest regions of the planet, from the equator to the two tropics.

The climate of the tropical rainforest is characterised by abundant rainfall. Temperatures are also constantly high during the whole year.

Due to the climatic conditions of these regions, the rock that forms the rainforest floor, and on which the ecosystem develops, undergoes an intense process of disintegration and chemical change, which forms a thick layer of weathered rock particles. However, the layer of humus is very thin. This is because organic remains decompose very quickly in this warm, wet atmosphere and are transformed into mineral matter, which is quickly absorbed by the exuberant vegetation.

The flora (jungle) is very dense and formed by large trees. There are a lot of climbing plants (vines or lianas), and also plants that live on tree branches (e.g. orchids). The forest floor does not receive very much sunlight, so vegetation is relatively scarce here. Ferns, mosses, and palm trees are the most representative species.

The fauna is extremely diverse and abundant. The typical species are snakes, monkeys, parrots, frogs, tigers, alligators, jaguars, toucans and an enormous variety of insects

2.8.  Name some adaptations to lack of water of desert animals.

2.9.  Look at the trophic web of the savannah and write three food chains.

2.10. The jungle soil is very poor in mineral matter and humus.

           However the vegetation is  exuberant. How can we explain this?