NCERT & CBSE Class 12 Biology PATTERNS OF BIODIVERSITY
Biodiversity is the variety in organisms found at every level of biological organization. The ecologists studied biodiversity in the environment and observed a regular pattern in which diversity was distributed over the entire area of the planet.
Darwin* noticed three distinctive patterns of biological diversity: (1) Species vary globally, (2) species vary locally, and (3) species vary over time. Darwin noticed that different, yet ecologically similar, animal species inhabited separated, but ecologically similar, habitats around the globe.
Species Vary GloballySpecies living in similar habitats but in different parts of the world, making them distantly related, looked and acted in a similar way. Emus found in Australia; Rheas found in S. America; Ostriches found in Africa. They are flightless birds.
Some areas such as islands had endemic species. Endemic species are species of plants and animals that exist only in one geographic region. Species may be endemic to a particular continent, some to part of a continent, and others to a single island.
Species Vary Locally: the Galapagos Islands are a group of islands relatively close to each other but have different climates. Isabela mountains are more mountainous with higher rainfall. Espanola island has lower elevations with dry climate. Each island has its own finch species and tortoise species. Each is adapted to conditions on that particular island.
Species Vary over Time: Through the studies of fossils, it was found that– some were enormous versions of modern-day species. For Example, modern-day armadillo(50 cm long) and the fossil remains of glyptodont(3 m long)resemble each other.
* Charles Robert Darwin, was an English naturalist, geologist, and biologist, and he was best known for his contributions to the science of evolution.
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PATTERNS OF SPECIES BIODIVERSITY
Ecologists have studied various patterns of species biodiversity. The various patterns of biodiversity can also be explained in terms of space and time. They are discussed below.
PATTERNS ACCORDING TO SPACE
Till date, it is the most well defined and well-known pattern of biodiversity that has been studied. According to this pattern, the species diversity shows a systematic pattern as one moves from the equator to the polar regions. Scientists have observed that species diversity tapers at the poles, either north or south. The tropics are very rich in species diversity. This pattern is an ancient pattern that has existed for thousands of years, across many taxa, from trees to fossil foraminifera.
Like the variety of the habitat increases, greater is the species diversity within it. This pattern explains, why there are more species in a bigger area. The big area covers a greater variety of habitat.
PATTERNS ACCORDING TO TIME
The diversity of species can be seen during different seasons of the year. According to different seasons, the population of one particular species fluctuates. For example, some terrestrial beetles have larval stages that are underground and they only emerge to the surface as adults. The birds also show seasonal patterns, because many are migratory and the bird diversity of an area may be affected by the absence of seasonal breeders and the presence of migrants passing through. These seasonal patterns are mostly seen in temperate areas but are also reported in tropical areas. In both terrestrial and aquatic habitats, the diversity of species can be seen during different seasons.
After a disturbance (such as fire or harvesting in agriculture), the plants and animals’ species begin to reoccupy the habitat, grow, and get replaced or out-competed by other species. This pattern of a gradual time-based shift in the species composition of a community is called succession. It may result from a variety of processes including migration, dispersal, growth, competition and environmental change. For plants, diversity increases with succession until woody species (trees and brushes) begin to flourish, whereby diversity then decreases. For animals, diversity generally increases with succession, for example, this has been observed for birds and insects.
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