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32 | IL. Biocoenosis and zoocoenosis various biomes have visually recognisable differences, and they also differ in their species composition. These differences emerge from the effects of factors outside the biome, the abiotic factors; an example of a biome is the tundra. The biogeocoenosis is a concept above that of the biome that also includes all the abiotic factors that are outside the biome but are influencing factors, and are responsible for its appearance. The various biogeocoenoses differ from each other in their physiognomy and species composition that emerge due to the differences in climatic, edaphic, geographical and geological conditions. A biogeocoenosis, for example, is the tundra and the totality of the conditions that lead to its formation and the ones that sustain it. The biocoenosis is a particular association of species that includes living beings connected by biotic links. The various biocoenoses differ not only in species composition but are also spatiallyseparated. The alpine meadow, as a biome, is the same in the Pyrenees and Carpathians but the two biocoenoses, in reality, are totally different entities that have no interaction with each other, and, possibly, even have different species compositions. All subalpine meadows, as a geographical formation, belong to the same biome, and can also be classified into the same biogeocoenosis and, as such, differ from the needleleaved forest biome and biogeocoenosis. The biome is immutable and, if a certain biome is transformed, for example, a needle-leaved forest develops on the site formerly occupied by a subalpine meadow, then the relevant biome would no longer exist, because it has disappeared as a geographical formation. However, the biocoenosis is under constant change, yet remains a biocoenosis, because its core is not a certain formation or species complex, but the biotic connections between its plant and animal species. A biocoenosis is always a particular assemblage that is encountered at a given location, at a given time. The ecosystem is a concept that is wider than the biocoenosis, and includes the abiotic factors that generate or sustain the biocoenosis. Therefore, an ecosystem is a product of the organisms associated with each other, and the factors generating this association, that are effective in a space at a particular time, that then function and coexist in that space and time. The ecosystem changes - as does the biocoenosis — because, with changing abiotic conditions (that may be caused by the biocoenosis itself), the biocoenosis will change and, with it,the ecosystem will also change. At the highest level, the ecosystem is under the influence of macroclimatic factors, within which edaphic factors are influential and, finally, it is also under the influence of the biocoenosis formed within its boundaries. Therefore, all existing ecosystems are different, but all of them are existing realities. The oak forests of the Buda Hills are ecosystems that are different from oak forests in the Matra Mountains, because they exist in different geographical locations. As a biogeographical concept, they belong to the same biome and the same biogeocoenosis but, as an outcome of the effects of factors influential at a particular location, and through associations emerging through their activity, they are different ecosystems and different biocoenoses.
