Each ecosystem has functional living elements which maintain homeostasis. The quality and quantity of these elements are important factors when considering disturbed ecosystems. Species diversity and the diversity of their functions are decisive. Species diversity has been discussed in many publications on plant and animal communities, whereas functional diversity has received little attention. Species diversity and function diversity are, however, interconnected, since they determine the multi-channel connexions at different levels of ecosystem organization. These connexions have been termed consortive, biogeocoenotic and trans-biogeocoenotic. Multi-channel connexions enable high levels of material and energy exchange in an ecosystem, and provide for inter-substitution of living elements in particular and general functions. The more complex the system, the more stable it is against human pressure. Along with complexity of system organization, an increase of species diversity and an intensification of its functional significance in the biosphere can occur. In the ecosystem sequence of desert - steppe - temperate forest - tropical forest biodiversity is increased tenfold. Simplified ecosystems are therefore the most sensitive. Consistent human pressure, though, makes impoverishes biodiversity, and causes changes in different ecosystems. Strong pollution in the steppe and forest ecosystems of industrial Prydniprovia resulted in destruction of the former, but only moderate change to the latter. Poor animal diversity in steppes leads to a decline of reduction processes, such as digging and excretion, with a simultaneous intensification of the heterotrophic functions of plant-eating organisms. The result is a reduction of productive processes, and the ecosystem's ability to purify itself from pollution is disturbed. In forest ecosystems, the same level of disturbance causes a similar loss in biodiversity, but multi-channel consortive and biocoenotic connexions repair the loss of functional diversity by inter-substitution of living organisms. The ecological stability of the system is thereby increased. Biodiversity is thus an essential factor providing stability in ecosystems under human pressure.