MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedonyuk 2010

BIOLOGY

CHAPTER 2. BIOCOENOTIC LEVEL OF ORGANIZATION OF LIFE AND HUMAN PLACE IN IT

2.1. BASICS OF HUMAN ECOLOGY

Environment as an Ecological Concept

The environment is an essential component of all living systems. An Organism and its environment are in close interaction and function as a single entity; an organism cannot exist outside its environment. The environment is defined as the totality of all external elements acting upon a living organism within its habitat. The MAIN TYPES OF environments include terrestrial-air, aquatic, soil, and living organisms themselves as a specific habitat. Environmental elements that exert a certain influence on organisms are called ecological factors. These are traditionally classified into abiotic, biotic, and anthropic factors. Abiotic factors are elements of non-living nature (humidity, Temperature, light, soil, relief); biotic factors represent the influences of living nature; and anthropic (anthropogenic) factors are associated with human impact. Although multiple factors act upon an organism simultaneously, only some of them are vital. Such factors are called limiting factors; their absence, or their presence below or above critical levels, makes the existence of the organism impossible. Each ecological factor is characterized by its intensity of action. The intensity most favorable for vital activity is called the optimum. The threshold values of factor intensity beyond which the organism cannot survive are referred to as the lower and upper limits of tolerance (critical minimum and maximum points). The range of a species' adaptability to environmental conditions is known as ecological valence. Species with a high ecological valence can withstand significant fluctuations in external conditions, whereas those with a low valence exist only within narrow limits. The former are termed eurytopic (from Greek eurus - wide), and the latter stenotopic (from Greek stenos - narrow). The same species may be eurytopic with respect to certain factors and stenotopic with respect to others.