Biological diversity includes all organisms, species and populations living on earth or in a particular area. In other words, biodiversity reflects full diversity and variety of life on Earth. Biodiversity shows how healthy an ecosystem is – the healthier an ecosystem, the larger its biodiversity.
Biodiversity has three levels – genetic, species and ecosystem diversity.
A species is a group of plants or animals that are similar and able to breed and produce offspring under natural conditions. Species diversity is the number of different species of living things living in a particular area and all the differences within and between populations of species, as well as between different species.
Ecosystems change all the time – some of them faster, and some of them slower. Ecological succession is the changing cycle of communities or species that live in an ecosystem during a particular time period. There any minor changes even in relatively stable ecosystems. At any point of time, any ecosystem can become a subject to external forces, which can restart succession process.
First,
pioneer species come to places, where there were no living beings before them. In such cases, it is
called primary succession. Pioneer species are usually autotrophs, photosynthetic bacteria and
lichen and they can find, for example, bare rocks to occupy. Primary succession can also occur in
the places after volcano eruption, glacier retreat, fire or flood. Pioneer species should be able to
continue to exist under tough conditions. For example, lichen are able to overcome nearly drying
out. Pioneer species change their microenvironment, which allows new species to come. After lichen,
mosses usually come next. As primitive species colonize the area, they increase the fertility of the
soil, become decaying matter and leave minerals. Afterwards, ferns can appear, followed by flowers
and grass. Grasses prevent water from running off, keeping it trapped in the soil. As a next stage,
trees and bushes come. Larger trees bring shade and hide smaller tries from sunlight. Consequently,
some smaller plants die out.
Succession can also occur, when one community comes instead of another one. Such successions are much more common. For example, when plants occupy a field, where crop used to grow, or a wood, where trees were cut down. This is called secondary ecological succession and usually occurs faster than primary succession. When large trees are cut down, more light appears and smaller plants benefit from it. When secondary succession occurs same or different species can occupy the land as a result.
Biodiversity usually grows as the succession evolves and does not undergo significant changes during the climax period. The climax phase is when ecosystem becomes stable and very few changes occur. It is the highest stage of ecological development. Every stage of succession has its own plants and animals which change the environment and in this way allow new community do develop. As plants biodiversity increases (they play a role of producers), so does diversity of animals (they play a role of consumers).
After volcano eruptions or retreat of glaciers, soil is destroyed and there are no living beings, so succession occurs very slowly. When secondary succession occurs, soil is present and seeds of previous species may remain in the soil and quickly occupy the land again. Some patters of succession are easy to predict, while others are more unpredictable. There have been developed mathematical models to predict shifts in plants and animals.
Human activities influence ecosystems and cause human-induced succession. Humans can change ecosystems to serve their needs or cause unintended changes. Activities such as sea pollution, excessive fishing or cattle grazing can change a biological community so much that it is replaced by another community. Cattle overgrazing can lead to pasture degradation. Such activities as cutting down forests, clearing land for agriculture or abandoning it also lead to human-induced succession. Humans have learned to change directions of rivers and to irrigate their land, which also changes affected ecosystems. Mining, dam building and urbanization are also among human activities, which trigger changes in ecosystems.
Global warning, which is seen by many experts as human-induced phenomenon, is causing unintended changes in many ecosystems. Ecosystems adapt to environmental changes. They are sensitive to changes in temperature and precipitation changes. People do not necessarily damage or destroy ecosystems. When people manage landscapes sustainably, have proper forest fire management systems, they only support ecosystems.
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