Distribution of life on Earth
According to some biologists, the distribution of life on Earth has three aspects, two of which deals with the distribution of life in space and one in time. The two stages of spatial distribution are very closely related to each other however are typically studied separately as Bathymetric and Geographic distribution.
The distribution of life with respect to time, present and past, is called Geologic or Durational distribution.
Bathymetric distribution deals with the vertical distribution of organisms in space, i.e., from the high Himalayan-Alpine peaks to the abyssal depth of the sea. Bathymetric distribution concerns itself with the vertical range of organisms in space, and indicates much more than simple altitude, for in passing from the highest alpine peak to the abyssal depths of the sea one would find a series of contrasting conditions which of necessity exceptionally affect the organism.
From a bathymetric viewpoint, three major realms may be acknowledged as
It deals with the vertical distribution of animals in freshwater sources.
The vertical distribution of animals in the sea or marine environments.
It describes the distribution of life on land. This extends from the highest tidemark along the shores of all continents to the summit of the greatest mountains. The progressive changes in temperature level, light, rains, and other climatic elements from the equator towards poles and from lowlands to the mountain peaks control the distribution of specific significant plant life types and these, in turn, are accompanied by particular sets of animal species.
The continental life zones are formed by the approximately latitudinal plans of specific the primary biotic formations or Biomes. Each biome has its unique set of conditions and each supports a particular kind of animal and flora. Some of the important terrestrial biomes recognized by ecologists are the tundra biome, alpine biome, forest biome, grassland biome, desert biome.
Geographical or Horizontal Distribution
The distribution of animals on land and fresh water in different continents and on different islands is called geographical or horizontal distribution.
Zoogeography is the study of the distribution of animals and plants on our planet, which occur in various regions of the world in a unique pattern. The distribution of some animal species is so peculiar that it is challenging to explain their occurrence in a particular region.
Zoogeography efforts to understand the complexities along with the simpleness in the distribution of animals in the light of evolutionary and environmental impacts.
Phytogeography deals with the distribution of plants only, more particularly the vascular plants i.e., the plants that have vessels or vascular bundles for transport of water and food.
The distribution of animals in the past of Earth’s history is called the distribution in time. This can be studied by fossil evidence only. The description of this type of distribution can be made on the Geological time scale.
The geological distribution is extremely important for understanding the process of evolution. The branch of geology which concerns the study of ancient life from fossils is called paleontology.