Biomes (SL IB Biology)

Biomes

• The term biome can be defined as follows:

A large community of plants and animals that has developed as a result of environmental factors

• Abiotic environmental factors, such as rainfall and temperature patterns determine which biome develops in a particular location
• Regions of the world that experience similar abiotic factors will contain the same biome, e.g. desert occurs in parts of Africa, North and South America, and Australia

Biomes map

Regions of the world that experience similar abiotic factors will contain the same biome

• Biomes contain many ecosystems
• The ecosystems found in equivalent biomes in different parts of the world contain similar communities, even if the species are not exactly the same
  • E.g. the ecosystems in the deserts of South America will contain similar communities to those in the deserts of Africa
• These similarities exist due to shared abiotic factors and resultant convergent evolution
  • Species face similar selection pressures, so similar features provide a survival advantage
  • These advantageous features become more common in the population due to natural selection
• This means that these communities are similar not because they have all evolved from a recent common ancestor, but because they have independently adapted to have similar features
  • Species that are adapted to survive in the deserts of South America will not be close genetic relatives of those found in the deserts of Africa, though they may have similar morphology

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CC BY-SA 3.0, via Wikimedia Commons

The cacti of the South American deserts (left) and the euphorbias of the African deserts (right) share spines and succulent stems as adaptations to their desert biome environments, but the two plant groups are not closely related

Climate conditions of major biomes table

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Public domain, via Pix4free	CC BY-SA 3.0, via Wikimedia Commons
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Tropical forest (top left), temperate forest (top right), taiga (middle left), grassland (middle right), tundra (bottom left) and hot desert (bottom right) are all examples of biomes

Adaptations

• Adaptations are traits, or characteristics, that increase survival chances in a specific environment
• Adaptations come about by the process of natural selection
• Species are adapted to the abiotic and biotic features of the biome in which they live, e.g.
  • Species living in hot desert biomes have adaptations to hot, dry conditions
  • Species living in tropic rainforests are adapted to deal with competition and predation

Hot desert adaptations

Saguaro cactus

• The saguaro cactus (Carnegia gigantea) is native to the hot deserts of North America, and is adapted for survival in dry conditions
  • Its stem has a thick waxy cuticle to reduce water loss by evaporation
  • It has spines instead of leaves; this reduces the surface area from which water can be lost by adaptation, and reduces grazing
  • Cells in the stem can expand to take on and store water
  • A deep tap root enables access to water deep under the ground, and shallow surface roots allow fast absorption of any water from rainfall

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Kangaroo rat

• Kangaroo rats (Dipodomys sp.) are small rodents found in the hot deserts of North America
• They spend daylight hours in underground burrows, a behavioural adaptation that allows them to avoid the high daytime temperatures
• Kangaroo rats are able to extract enough water to survive from their diet, and can produce highly concentrated urine, so can go without drinking water for extended periods

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Tropical rainforest adaptations

Kapok tree

• Kapok trees (Ceiba pentandra) form parts of the upper canopy in the tropical rainforests of Central and South America
• Rapid growth allows Kapok trees to outcompete other species by growing tall very quickly; this height allows them to absorb enough sunlight in a densely forested habitat
• Wide buttress roots provide a sturdy base to support the trees during their rapid growth

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Kapok trees have wide buttress roots to provide stability

Orchid mantis

• The orchid mantis (Hymenopus coronatus) is an insect found in the tropical rainforests of southeast Asia
• The adult female mantis looks very similar to an orchid flower, enabling it to attract insect pollinators which then become its prey; this is an example of mimicry
  • Scientists believe that orchid mantis are 'aggressive mimics', meaning that they are more attractive to insects than the surrounding orchid flowers
• The male orchid mantis is much smaller and plainer in appearance, allowing it to camouflage in amongst the stems and branches of plants

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The orchid mantis is camouflaged on the surface of the orchid