Protozoan Ecology

Abstract

Protozoan ecology is the interaction in space and time of protozoa (flagellates, amoeboid organisms and ciliates) with other living organisms and the physical environment. It encompasses, among other factors, sources of food and energy used to sustain life, food web dynamics, the role of protozoa in maintaining fertility of ecosystems and adaptive strategies for survival in varying habitats. Among the physical environmental (abiotic) factors, temperature, salinity, nutrients and levels of pollutants, when present, are major sources of influence. A complex set of interactions exists among microbial biota, including the role of nutrient regeneration during protozoan predation on bacteria resulting in release of nutrients due to digestion and disruption of the bacteria during feeding. These nutrients, in turn, are reutilised by algae during photosynthesis. This process of cyclical nutrient uptake by algae and subsequent release by protozoan predation is known as ‘the microbial loop’. The use of molecular genetic analyses has substantially improved our identification of protozoan species and their role in ecology including the microbial loop.

Key Concepts

  • Characteristics of the physical environment (including temperature, available nutrients and salinity) set the boundary conditions for the abundance and diversity of protozoa within a given habitat.
  • Algae and other photosynthetic organisms are primary producers that fix carbon into organic compounds through photosynthesis and thus provide food sources for all other organisms, including protozoa, within a food web.
  • Heterotrophic (nonphotosynthetic) microorganisms, particularly the protozoa, prey on algae and other microbes, including bacteria, and are consumers within food webs.
  • A complex set of interactions exist in microbial communities, including predator–prey relationships, that determine the flow of matter and energy through the food webs.
  • Competition within and among species partially accounts for the abundance and diversity of species in a microbial community.
  • The stability of microbial communities depends in part on the diversity of species and available resources needed to support life.
  • Protozoa, as predators and also as prey for larger organisms, are often key members of microbial communities and sustain the flow of energy and matter through food webs, including the regeneration of nutrients through their significant role in the microbial loop.

Keywords: abiotic factors; biotic factors; ecosystem dynamics; food webs; microbial loop; molecular genetics; predator–prey relations; soil fertility

Figure 1. Protozoa: (a) flagellate, Polytoma uvella (15 μm); (b) naked amoeba, Metachaos discoides (400 μm) and (c) ciliate, Phacodinium metchnikoffi (100 μm). (From Lee JJ, Hutner SH and Bovee EC (eds) (1985) Illustrated Guide to the Protozoa. Lawrence, KS: Society of Protozoologists © 1985 International Society of Protistologists.)
Figure 2. The effect of temperature on the population density of Tetrahymena pyriformis. Growth is best at 25 °C, with a minimum temperature of 10 °C. (Adapted from Sleigh M (1989) Protozoa and Other Protists, p. 260. London: Edward Arnold.)
Figure 3. A photosynthesis‐based protozoan food web. Green arrows show dissolved nutrient flow and orange and blue arrows indicate prey and predator relations. Feeding activity of protozoa mineralises nutrients that are available for primary production (recursive arrows).
Figure 4. A terrestrial protozoan, bacterial‐based food chain showing predator–prey relations. (Adapted from Griffiths BS (1994) Soil nutrient flow. In: Darbyshire JF (ed.) Soil Protozoa, p. 80. Wallingford, UK: CAB International.)
close

References

Adl SM (2003) The Ecology of Soil Decomposition. CAB International: Cambridge.

Adl SM, Simpson AGB, Lane CE, et al. (2012) The revised classification of Eukaryotes. Journal of Eukaryotic Microbiology 59: 429–493.

Adl SM and Gupta VVSR (2006) Protists in soil ecology and forest nutrient cycling. Canadian Journal of Forest Research 36: 1805–1817.

Albouvette C, Couteaux MM, Old KM, et al. (1981) Le protozoaires du sol: aspects écologiques et méthodologiques. Annals of Biology 20: 255–303.

Anderson OR (1988) Comparative Protozoology: Ecology, Physiology, Life History. Springer: Heidelberg.

Anderson OR and Rogerson A (1995) Annual abundances and growth potential of gymnamoebae in the Hudson Estuary with comparative data from the Firth of Clyde. European Journal of Protistology 31: 223–233.

Anderson OR (2007) A seasonal study of the carbon content of planktonic naked amoebae in the Hudson Estuary and in a productive freshwater pond with comparative data for ciliates. Journal of Eukaryotic Microbiology 54: 388–391.

Anderson OR (2010a) The reciprocal relationships between high latitude climate changes and the ecology of terrestrial microbiota: emerging theories, models, and empirical evidence, especially related to global warming. Chapter 2. In: Tundras: Vegetation, Wildlife and Climate Trends, pp 47–79. Nova Science Publishers, Inc.: New York.

Anderson OR (2010b) Field and laboratory studies of encysted and trophic stages of naked amoebae: including a perspective on population life cycle dynamics. Acta Protozoologica 49: 1–8.

Aquilera A, Zettler E, Gomez F, et al. (2007) Distribution and seasonal variability in the benthic eukaryotic community of Rio Tinto (SW Spain), an acidic, high metal extreme environment. Systematic and Applied Microbiology 30: 531–546.

Baumgartner M, Yapi A, Gröbner‐Ferreira R and Stetter KO (2003) Cultivation and properties of Echinamoeba thermarum n. sp., an extremely thermophilic amoeba thriving in hot springs. Extremophiles 7: 267–274.

Buskey EJ (2008) How does eutrophication affect the role of grazers in harmful algal bloom dynamics? Harmful Algae 8: 152–157.

Caron DA and Countway PD (2009) Hypotheses on the role of the protistan rare biosphere in a changing world. Aquatic Microbial Ecology 57: 227–238.

Corliss JO (2004) Why the world needs protists. Journal of Eukaryotic Microbiology 51: 8–22.

Darbyshire JF (1976) Effect of water suctions on the growth in soil of the ciliate Colpda steini and the bacterium Azotobacter chroococcum. Journal of Soil Science 27: 369–376.

Darbyshire JF (ed.) (1994) Soil Protozoa. CAB International: Wallingford, UK.

Darbyshire JF, Anderson OR and Rogerson A (1996) Protozoa. In: Hall GS (ed.) Methods for the Examination of Organismal Diversity in Soils and Sediments, pp 79–90. CAB International: Wallingford, UK.

Fenchel T (1987) Ecology of Protozoa: The Biology of Free‐Living Phagotrophic Protists. Science Tech: Madison, WI.

Fenchel T (2008) The microbial loop – 25 years later. Journal of Experimental Marine Biology and Ecology 366: 99–103.

Finlay BJ, Berninger U‐G, Clarke KJ, et al. (1988) On the abundance and distribution of protozoa and their food in a productive freshwater pond. European Journal of Protistology 23: 205–217.

Finlay BJ and Fenchel T (2004) Cosmopolitan metapopulations of free‐living microbial eukaryotes. Protist 155: 237–244.

Foissner W (1987) Soil protozoa: fundamental problems, ecological significance, adaptations in ciliates and testaceans, bioindicators and guide to the literature. In: Corliss JO and Patterson DJ (eds) Progress in Protistology, vol. 2, pp 69–212. Biopress: Bristol.

Foissner W (2008) Protist diversity and distribution: some basic considerations. Biodiversity and Conservation 17: 235–242.

Geisen S, Tveit AT, Clark IM, et al. (2015) Metatransscriptomic census of active protists in soils. ISME Journal 9: 2178–2190.

Grossmann L, Jensen M, Heider D, et al. (2016) Protistan community analysis: key findings of a large‐scale molecular sampling. ISME Journal 10: 2269–2279.

Hauer G and Rogerson A (2005) Remarkable salt tolerance of naked amoebae from the salton sea and beyond. Journal of Eukaryotic Microbiology 52: 15S.

Hausman LA (1917) Observations on the ecology of protozoa. American Naturalist 51: 157–172.

Jones H, Cockell CS, Goodson C, et al. (2009) Experiments on mixotrophic protists and catastrophic darkness. Astrobiology 9: 563–571.

Kyle DE and Noblet GP (1986) Seasonal distribution of thermotolerant free‐living amoebae I. Willard's Pond. Journal of Protozoology 33: 422–434.

Laybourn‐Parry J (1992) Protozoan Plankton Ecology. Chapman and Hall: London.

Lesen AE, Juhl AR and Anderson OR (2010) Abundance and biomass of heterotrophic microplankton in the lower Hudson River Estuary, USA: potential importance of naked, planktonic amebas for bacterivory and carbon flux. Aquatic Microbial Ecology 61: 45–56.

Muylaert K, Van Mieghem R, Sabbe K, Tackx M and Vyverman W (2000) Dynamics and trophic roles of heterotrophic protists in the plankton of a freshwater tidal estuary. Hydrobiologia 432: 25–36.

Park JS, Kim H, Choi DH and Cho BC (2003) Active flagellates grazing on prokaryotes in high salinity waters of a solar saltern. Aquatic Microbial Ecology 33: 173–179.

Park JS, Simpson AGB, Brown S and Cho BC (2009) Ultrastructure and molecular phylogeny of two heterolobosean amoebae, Euplaesiobystra hypersalinica gen. et sp. nov. and Tulamoeba peronaphora gen. et sp. nov., isolated from an extremely hypersaline habitat. Protist 160: 265–283.

Patterson DJ, Larsen J and Corliss JO (1989) The ecology of heterotrophic flagellates and ciliates living in marine sediments. In: Patterson DJ and Corliss JO (eds) Progress in Protistology, vol. 3, pp 185–277. Biopress: Bristol.

Stoecker DK, Johnson MD, de Vargas C and Not F (2009) Acquired phototrophy in aquatic protists. Aquatic Microbial Ecology 57: 279–310.

Tilman U (2004) Interactions between planktonic microalgae and protozoan grazers. Journal of Eukaryotic Microbiology 51: 156–168.

Weisse T (2002) The significance of inter‐ and intraspecific variation in bacterivorous and herbivorous protists. Antonie van Leeuwenhoek 81: 327–341.

Zou S, Zhang Q and Gong J (2020) Comparative transcriptomics reveals distinct gene expressions of a model ciliated protozoan feeding on bacteria‐free medium, digestible, and digestion‐resistant bacteria. Microorganisms 8: 559. DOI: 10.3390/microorganisms8040559.

Further Reading

Anderson OR (1983) Radiolaria. Springer: New York.

Archibald JM, Simpson A and Slamovits C (eds) (2017) Handbook of the Protists, 2nd edn. Springer International Publishing AG: Cham, Switzerland.

Beebee TJC and Rowe G (2017) An Introducrtion to Molecular Ecology, 3rd edn. Oxford University Press: Oxford.

Capriulo GM (ed.) (1990) Ecology of Marine Protozoa. Oxford University Press: New York.

Goff LJ (ed.) (1983) Algal Symbiosis: A Continuum of Interaction Strategies. Cambridge University Press: Cambridge.

Hemleben CH, Spindler M and Anderson OR (1989) Modern Planktonic Foraminifera. Springer: New York.

Röttger R (ed.) (2009) Courses in Protozoology. Shaker Verlag: Aachen.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Anderson, O Roger(Dec 2020) Protozoan Ecology. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0029234]