Theory question 103
Population Ecology(a) Write short notes on each of the following:
(i) ecological niche; (ii) population density; (iii) climax community.
(b) Describe briefly the interactions between abiotic and biotic components of an ecosystem.
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(a)(i) Ecological niche: the role or functional position of a species in its habitat — where it lives, what it feeds on, what feeds on it and how it affects other organisms.
(ii) Population density: the number of individuals of a species per unit area (or volume) of habitat, e.g. 20 plants per m²; = total population ÷ area.
(iii) Climax community: the final, stable community reached at the end of a succession, in balance with the climate, e.g. tropical rainforest; it changes little unless disturbed.
(b) Abiotic factors affect organisms: light controls photosynthesis and distribution; temperature and rainfall determine which plants and animals live there; soil type and pH affect plant growth; wind disperses seeds. Organisms affect abiotic factors: plants add humus and bind soil; transpiration raises humidity; shade lowers temperature and light; decomposers return minerals to the soil; organisms take in and give out O2 and CO2; earthworms aerate soil.
For (b) give examples in both directions: environment on organisms and organisms on environment.