8.1 3.1.2 biomes

Biomes

Key concepts

In this session we will focus on summarising what you need to know about:

• Terrestrial and aquatic biomes of Southern Africa.
• How climate, soil and vegetation influence the organisms found in each.
• Location of the different biomes in South Africa.

Terminology&Definitions

Biomes can be defined as the major climatic regions of the world, classified according to their predominant vegetation and characterised by adaptations of organismsto that particular environment.

Content

The biosphere can be divided into relatively large regions called biomes. A biome has a distinct climate and certain living organisms (especiallyvegetation) characteristic to the region and may contain many ecosystems. The key factors determining climate are average annual precipitation andtemperature. These factors, in turn, depend on the geography of the region, such as the latitude and altitude of the region, and mountainous barriers. Themajor types of biomes include: aquatic , desert , forest , grassland and tundra . Biomes have no distinct boundaries. Instead, there is a transition zone called an ecotone, which contains a variety of plants and animals. For example, anecotone might be a transition region between a grassland and a desert, with species from both.

You will be required to learn about terrestrial and aquatic biomes.

Aquatic biomes

Water covers a major portion of the earth's surface, so aquatic biomes contain a rich diversity of plants and animals. Aquatic biomes can be subdivided into two basic types: freshwater and marine .

A freshwater region has a low salt concentration, usually less than 1 percent, and occurs in several types of regions: ponds and lakes, streams and rivers, and wetlands.

• Ponds and lakes range in size, and small ponds may be seasonal. They sometimes have limited species diversity due to isolation from other water environments. They can gettheir water from precipitation, surface runoff, rivers, and springs.
• Streams and rivers are bodies of flowing water moving in one general direction (i.e., towards the sea). Streams and rivers start at their upstream headwaters, which could besprings, snowmelt or even lakes. They continue downstream to their mouths, which may be another stream, river, lake or ocean. The environment of a streamor river may change along its length, ranging from clear, cool water near the head, to warm, sediment-rich water near the mouth. The greatest diversity ofliving organisms usually occurs in the middle region.
• Wetlands are places of still water that support aquatic plants, such as cattails, pond lilies and cypress trees. Types of wetlands include marshes, swamps and bogs. Wetlands have the highest diversity of species with many species of birds, mammals, amphibians and reptiles. Some wetlands, such as salt marshes, are notfreshwater regions.

Marine regions cover nearly three-fourths of the earth's surface. Marine bodies are salty, having approximately 35 grams of dissolved salt per litre of water (3.5percent). Oceans are very large marine bodies that dominate the earth's surface and hold the largest ecosystems. They contain a rich diversity of living organisms. Oceanregions can be separated into four major zones: intertidal, pelagic, benthic and abyssal .