The nature around us is rich in various species of organisms. Many species are so similar to each other that only a specialist can distinguish between them. Nevertheless, these are precisely different species, since they do not produce common offspring. How could such a large number of species form on Earth? There are several million of them on the planet.
Two main ways of speciation
According to the theory of evolution, all types of living organisms evolved from one common ancestor: a microscopic living clot. This organism not only evolved, but also gave new species, which, according to scientists, happened in two main ways:
- Geographical (allopathic).
- Ecological (sympatric).
As a result, various types of microorganisms appeared, as well as arthropods, fish, birds, mammals and many other representatives of the biosphere.
Geographical speciation is the process of the formation of new species in isolated territories. As such, isolation in the form of mountains and rivers may not exist, however, environmental conditions on biotopes differ so much that organisms do not move to the neighboring territory.
Ecological speciation is the process of the formation of new species on overlapping or coincident habitats. In this case, it is the ecological characteristics of the species that prevent them from interbreeding. Populations occupy different ecological niches. The newly formed species in this case will be called sympatric.
Types of geographical speciation
Examples of geographic speciation are associated with two reasons for the separation of populations from each other:
- In the habitat of the species, an obstacle arose that organisms do not overcome. These may be mountains resulting from the movement of lithospheric plates. So, 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.
- The expansion of the habitat of the species is such that the populations have little contact with each other. This example of geographic (allopathic) speciation becomes especially vivid if in the future the number of individuals of the species decreases. In this case, the populations are further separated by distance. Having chosen the most favorable habitats, they leave less favorable territories unpopulated, which in this case become an obstacle for communication and crossing individuals.
Species formation under different environmental conditions
With the expansion of the species habitat, the number of various biotopes available on the territory also increases. For example, an 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, an ordinary fox is very different from a northern fox - a polar fox. Fenech fox lives in desert areas. It has small body sizes, but large auricles for better heat transfer from the body.
Galapagos reels
There is a particular example of geographic speciation in biology. This is the formation of various species of finches in the Galapagos Islands. It is believed that birds were brought to the islands from the continent by chance, by the wind. Inhabited for a long time on the islands, the formed populations evolved separately, since there is a considerable distance between the ranges. At the same time, birds from different islands chose a different food: plant seeds, cactus pulp or insects. Some species of birds insects gather from the surface of the leaves (beak bent down is necessary); and others get out from under the bark (for these representatives, the beak is long, narrow and straight, like a woodpecker). This example of geographic speciation shows how various forms of beak arose during evolution. On one island, the beak is thick and short, on the other - narrower and longer, on the third - bent. Only 14 species of finches from 4 genera were formed from one species that fell on islands remote from the mainland. On the nearby island of Cocos, its kind - coconut finch - endemic to the island.
Geographic speciation example: protein
Our large planet shows various climatic conditions. They cause the formation of new subspecies, and then species of plants and animals when moving to large areas. Squirrel is a prime example of geographic speciation. Animals of this genus settled in Eurasia, North and South America. There are about 30 species of Sciurus squirrels in the world. Squirrels that live on the American continent are not found in Eurasia. However, in Russia, the common squirrel 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.
Endemic to Lake Baikal
A striking example of geographic speciation are endemic to Lake Baikal. Baikal is separated from the rest of the water bodies for several million years. It is surprising that there are more endemic species in the waters of Lake Baikal than other species. For example, epishura crustacean, which cleans the waters of the world's largest lake, accounts for 80% of the biomass of Baikal's zooplankton. Epishura is an endemic of Lake Baikal. Baikal omul, transparent golomyanka, Baikal seal are famous representatives of the lake.
Experts from all over the world appreciate Baikal for its huge reserves of clean fresh water and the endemic species composition of its inhabitants.
African and Indian elephants - an example of geographic speciation
The African and Indian elephants that once descended from a common ancestor are easily distinguished from each other. 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 it cannot be trained and domesticated.
Australia - Territory of Ancient Mammals
An example of geographic speciation is Australia. The continent broke away from Asia many millions of years ago. Here, representatives of the ancient fauna are best preserved.
Marsupials are an intermediate between monotreme mammals and placental. They give birth to 2–3 cm cubs, and then carry them in a bag or among the folds of skin on their belly, because the placenta connecting the mother and offspring is poorly developed. On other continents, placental representatives almost replaced the marsupials. In Australia, the ancient representatives of the animal world are very diverse. Moreover, they occupied all habitats. Herds of kangaroos graze in the meadows, marsupial mole digs in the ground , koala eucalyptus leaves eat in the forests and marsupial martens jump on trees (they are called marsupial cats in other words).
Marsupial mice scurry under the forest canopy. There is a marsupial possum in Australia, a marsupial wombat marmot, a fox body, and an anteater anteater eats ants.
Recently exterminated by the human and dog dingo marsupial wolf. The names of marsupials animals coincide with the names of representatives of placental mammals. However, they were given such names only for 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 marsupial animals was preserved.
Oviparous mammals - an example of geographic speciation - are endemic to Australia. The platypus and echidna are even more ancient mammals, which still lay their eggs, but are already feeding their young with milk. On the continent there is one species of platypus and five species of echidna.
Many examples of geographic and ecological speciation can be cited. Because all kinds of organisms appeared geographically or ecologically. Particularly common are examples of geographic speciation.
The table below shows the sequence of stages in the formation of animal species.
Thus, a wide variety of environmental conditions and the huge surface area of our planet lead to the richness of the wildlife world.