Chapter 2 

 Ecology 



WITH regard to their habitats, the Protozoa may be divided 

 into free-Uving forms and those Hving on (epizoic) or in 

 (cndozoic) other organisms. 



The free-living Protozoa 



The vegetative or trophic stage of free-hving Protozoa have 

 been found in every type of fresh and salt water, soil and decay- 

 ing organic matter. In the circumpolar regions or at extremely 

 high altitudes, certain Protozoa occur at times in fairly large 

 numbers. The factors, which influence their distribution in a giv- 

 en body of water, are temperature, light, chemical composition, 

 acidity, kind and amount of food, and degree of adaptabihty of 

 the individual protozoans to various environmental changes. 

 Their early appearance as living organisms, their adaptability to 

 various habitats and their capacity to remain viable in encysted 

 condition possibly account for the wide distribution of the Pro- 

 tozoa throughout the world. The common free-living amoebae, 

 numerous testaceans and others, to mention a few, of fresh wa- 

 ters, have been observed in innumerable parts of the world. 



Temperature. The majority of Protozoa are able to live only 

 within a small range of temperature variation, although in the 

 encysted state they can withstand a far greater temperature 

 fluctuation. The lower Hmit of the temperature is marked by the 

 freezing of the protoplasm, and the upper limit by the destructive 

 chemical change within the body. The temperature toleration 

 seems to vary among different species of Protozoa; and even in 

 the same species under different conditions. For example. Chalk- 

 ley (1930) placed Paramecium caudatum in 4 culture media (bal- 

 anced saline, saline with potassium excess, saline with calcium 

 excess, and saline with sodium excess), all with pH from 5.8 or 6 

 to 8.4 or 8.6, at 40°C. for 2-16 minutes and found that 1) the re- 

 sistance varies with the hydrogen-ion concentration, maxima ap- 

 pearing in the alkaline and acid ranges, and a minimum at or near 

 about 7.0; 2) in a balanced saline, and in saline with an excess of 

 sodium or potassium, the alkaline maximum is the higher, while 



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