The nature around us is rich in various types of organisms. Many species are so similar to each other that only a specialist can distinguish them. Nevertheless, these are precisely different species, since they do not give common offspring. How could such a large number of species on Earth have formed? There are several million of them on the planet.
Two main pathways of speciation
According to the theory of evolution, all kinds of living organisms descended from one common ancestor: a microscopic living clot. This organism not only evolved, but also gave rise to new species, which, according to scientists, happened in two main ways:
- Geographic (alopatric).
- Ecological (sympatric).
As a result, various types of microorganisms appeared, as well as arthropods, fish, birds, mammals and many other representatives of the biosphere.
Geographic speciation is the process of formation of new species onareas isolated from each other. As such, there may not be isolation in the form of mountains and rivers, however, environmental conditions in biotopes differ so much that organisms do not move to neighboring territory.
Ecological speciation is the process of formation of new species in overlapping or overlapping ranges. In this case, it is the ecological features of the species that do not allow them to interbreed. Populations occupy different ecological niches. The newly formed species in this case will be called sympatric.
Types of geographic speciation
Examples of geographic speciation are associated with two reasons for the separation of populations from each other:
- An obstacle has arisen in the habitat of the species that organisms cannot overcome. These may be mountains that have arisen as a result of the movement of lithospheric plates. Thus, the Ural Mountains divided Eurasia into Europe and Asia. These parts of the world differ significantly in species composition. This is an example of geographic speciation.
- Expansion of the species range so that populations have little contact with each other. This example of geographic (alopatric) speciation becomes especially striking if the number of individuals of the species subsequently decreases. In this case, the populations are further separated by distance. Having chosen the most favorable habitat areas, they leave less favorable territories uninhabited, which in this case become an obstacle for communication and interbreeding of individuals.
Formation of species under different environmental conditions
When expanding habitatspecies also increases the number of diverse biotopes available on the territory. For example, the African elephant occupied two types of biotopes: forest and savannah. Thus, two subspecies were formed.
An example of geographic speciation is the formation of species in different climatic conditions. For example, the common fox is very different from the northern fox - arctic fox. The fennec fox lives in desert areas. It has a small body size, but large auricles for better heat transfer from the body.
Finches of the Galapagos Islands
There is a special example of geographic speciation in biology. This is the formation of various types of finches in the Galapagos Islands. It is believed that the birds were brought to the islands from the continent by accident, by the wind. Living for a long time on the islands, the resulting populations evolved separately, since there is a significant distance between the ranges. At the same time, birds from different islands chose different food: plant seeds, cactus pulp or insects. Some species of birds collect insects from the surface of the leaves (a beak bent down is required); while others get it from under the bark (these representatives have a long, narrow and straight beak, like a woodpecker). This example of geographic speciation shows how different beak shapes have evolved over the course of evolution. On one island the beak is thick and short, on the other it is narrower and longer, on the third it is curved. In total, 14 species of finches from 4 genera were formed from one species that came to islands remote from the mainland. On the nearbyCoconut Island has its own species - the coconut finch - endemic to the island.
Example of geographic speciation: squirrel
Our big planet shows different climatic conditions. They cause the formation of new subspecies, and then species of plants and animals when settling over large areas. Belka is a vivid example of geographic speciation. Animals of this genus settled in Eurasia, North and South America. In total, there are about 30 species of squirrels of the genus Sciurus in the world. Squirrels living on the American continent are not found in Eurasia. However, on the territory of Russia, the common squirrel has formed more than 40 subspecies. This is a prerequisite for the formation of new species. Subspecies of the common squirrel live in Europe and the temperate zone of Asia and differ from each other in the size and color of the fur.
Endemics of Lake Baikal
Endemics of Lake Baikal are a striking example of geographic speciation. Baikal has been separated from other water bodies for several million years. Surprisingly, there are more endemics in the waters of Lake Baikal than other species. For example, the crustacean epishura, which purifies the waters of the largest lake in the world, makes up 80% of the zooplankton biomass of Baikal. Epishura is an endemic of Baikal. Baikal omul, transparent golomyanka fish, Baikal seal are famous representatives of the lake.
Baikal is appreciated by specialists from all over the world for its huge reserves of clean fresh water and the endemic species composition of its inhabitants.
African and Indian elephants are an example of geographic speciation
Easy differentfrom a friend African and Indian elephants, which once descended from a common ancestor. The African elephant is larger, has a large ear area, as well as a lower lip on the trunk. Moreover, the nature of the African elephant is such that this species cannot be trained and domesticated.
Australia - Territory of Ancient Mammals
The entire territory of Australia serves as an example of geographic speciation. The continent broke away from Asia many millions of years ago. Representatives of the ancient fauna are best preserved here.
Marsupials are an intermediate link between monotremes and placental mammals. They give birth to cubs 2 to 3 centimeters in size, and then carry them in a bag or among the folds of skin on their belly, because the placenta connecting mother and offspring is poorly developed. On the rest of the continents, placental representatives almost replaced the marsupials. In Australia, the ancient representatives of the animal world are very diverse. And they occupied all habitats. Herds of kangaroos graze in the meadows, the marsupial mole digs the ground, koalas eat eucalyptus leaves in the forests and marsupial martens (otherwise they are called marsupial cats) jump through the trees.
Marsupial mice scurry about under the canopy of the forest. There are marsupial opossum, marsupial marmot wombat, fox kuzu in Australia, and marsupial anteater eats ants.
The marsupial wolf was recently exterminated by man and dog dingo. The names of marsupials coincide with the names of representatives of placental mammals. However, they gave themnames only for a distant external resemblance. For example, the relationship between the marsupial and the house mouse is more distant than between the mouse and the cat.
There are many placental mammals in Australia, but they are represented by only two orders: rodents and bats. Precisely because many other larger representatives of higher mammals did not enter the territory, the fauna of marsupials was preserved.
Egg-laying mammals - an example of geographic speciation - are endemic to Australia. The platypus and echidna are even older mammals, still laying eggs, but already feeding their young with milk. The continent is home to one species of platypus and five species of echidnas.
There are many examples of geographic and ecological speciation. Because all kinds of organisms appeared geographically or ecologically. Examples of geographic speciation are especially common.
The table below shows the sequence of stages in the formation of animal species.
Thus, the wide variety of environmental conditions and the vast surface area of our planet lead to the richness of the wildlife world.
