Everything is connected on earth- states the first law of ecology. Meaning that we cant even make one step without disruption the environment. Even a usual step on the lawn is tens of ruined microorganisms and scared insects that might be changing their migration paths and reducing their natural efficiency. During the last century humans have gotten to be alarmed about the destiny of the planet, however, when we stepped into this century, we have stepped into the ecological crisis that we ourselves created.
Environmental contamination, exhaustion of natural resources and infringements of ecological communications in ecosystems became global problems. And if the mankind will continue to continue obusing environment, its death is inevitable.
Now, during an approaching ecological crisis on the planet, it is necessary for us to cooperate and preserve nature.
By consuming natural resources more intensively human beings have progressed and improved conditions of development and the growth of Homo sapiens as a biological species. However, by "winning" the nature, we have created almost crisis situation in interaction between the person and the nature, fraught with greater dangers to the future of our civilization. It could be clearly seen in the problems with natural resources, power, quality of an environment in its communication with the further industrial development in the world and growth of the population. Interdependent changes have led to occurrence of new communications between global economy and global ecology. In the past we were alarmed about the consequences of an economic growth for an environment. Now we can not simply ignore the consequences of " ecological stress " – the deterioration of grounds, a water polution, a condition of an atmosphere and forests.
Now becomes more clear, that sources and the reasons of pollution are much more various, complex and interconnected, and consequences of pollution carry wider, cumulative and chronic character, than it was considered earlier. Science has already given a definition of anthropogenous environmental contamination. It is physical, chemical and biological change of the quality of an environment (atmospheric air, waters, ground) as a result of the economic or other activity, exceeding the established specifications of harmful influence on an environment and creating threat to health of the person and to the conditions of flora and fauna.
The practical output of ecology can be first seen in making the decisions in the questions of wildlife management; it should create a scientific basis of operation of natural resources. We can ascertain, that neglect of the laws underlying natural processes has led to the serious conflict between the person and the nature.
CONCEPT OF THE POPULATION
Population ecology is defined as group of organisms of one kind (inside of which individual can exchange the genetic information), occupying concrete space and functioning as a part biotic community.
The population is a set of individuals of one kind living in certain territory, freely crossed among themselves and it is partially or completely isolated from other populations.
The population has its own characteristics: number, its density, spatial distribution of individuals. It could be distinguished by age, sexual and dimensional structure.
Structure. It is possible to allocate three ecological
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age groups: prereproductive - group of individuals, which age has not reached ability of reproduction; reproductive - the group reproducing new individual; postreproductive - the individuals who have lost ability to participate in reproduction of new generations. Duration of these ages in relation to the general life expectancy strongly varies between different organisms.
Number and density express quantitative characteristics of a population as the whole. Number of a population is expressed by number of individuals of the given kind living on the unit of the area borrowed by it. Dynamics of the population numbers in time is defined by a parity of parameters of birth rate, death rate, survival rate which in turn are defined by conditions of life.
The density of a population is the size of population dependant upon the space taken by it: number of individuals, or biomass, of the population per unit of an area or volume. The density depends on a trophic level on which there is a population. The lower a trophic level, the higher the density.
Many species under those conditions are able to only have males or females, or sometimes unable to reproduce at all. In plant louses, for example, generations consisting from one females replace each other in the summer. Under adverse conditions only males are born. In some molluscs, worms, fishes and crustations changes in sex occur with age.
FEATURES OF POPULATIONS
So, what are the conditions of birth and death ratios depend upon? They are dependant upon many factors from the outside, and also from its own properties. An objective parameter of an ability of organisms to increase the number is the maximal speed of a population gain. This parameter is inversely proportional to the life expectancies of organisms. It is easy to be convinced of it, having addressed to the hyperbolic dependence between congenital speed of increase in number of a population and the average time of generation expressed in days (fig. 1). Smaller organisms have higher values rтах, than larger ones, that explains shorter time of generation. The reason of this correlation is clear, because it takes more time for a larger organism to grow. The delay in reproduction also inevitably leads to the reduction of rтах.
Nevertheless the advantages in having a larger sizes of a body, should exceed the lacks that have to do with reduction of rтах, otherwise large organisms would never appear in evolution. The tendency to increase the body size with the flow of the geological time, tracked on fossils, has formed the basis for introduction of the phyletic size concept.
Larger body sizes give abundantly clear advantages: larger organism should attract less potential predators and, hence, it has more chances to not become a prey and should differ with the best survival rate; smaller organisms are in close dependence on the physical environment, and even little changes can appear to be deadly to them. It is easier for larger organisms to adapt to the surroundings and therefore they are better protected. However larger organisms require more food and energy per one individual in unit of time, than smaller ones. Besides less safer places exist for them.
There are three periods in the life of an organism: prereproductive, reproductive and postreproductive. Relative duration of each varies. The first period is the longest in many animals. A very good example of this are mayflies, which