Theory question 107
Population Ecology(a)(i) Define ecological succession (ii) List four characteristics of ecological succession of plants
(b) Explain four factors which affect population size
(c) State the adaptation of tapeworm (Taenia Solium) to its habitat in the gut of human.
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(a)(i) Ecological succession is the gradual, orderly change in the kinds of organisms (communities) living in an area over time, until a stable climax community is formed.
(ii) Any four: it starts on bare or disturbed land with pioneer species such as lichens, mosses or grasses; each community changes the habitat (e.g. builds soil) and makes it suitable for the next; species number and variety increase over time; plants become larger and more complex; it is slow at first then speeds up; it ends in a stable climax community.
(b) Any four, explained: food supply – plenty of food raises the population, shortage lowers it; predators – more predators lower prey numbers; disease – epidemics cause many deaths; birth (natality) and death (mortality) rates – more births than deaths raise the population; immigration and emigration add or remove individuals; space/shelter and competition – overcrowding leads to competition and fewer survivors; climate/natural disasters such as floods or drought kill many.
(c) Thick cuticle resists digestion by the host's enzymes; scolex with hooks and suckers holds it to the gut wall; absorbs digested food over its whole body surface (no gut); flat, thin body gives a large surface for absorption; can respire anaerobically in the low-oxygen gut; hermaphrodite and produces very many eggs; ripe proglottids pass out with faeces to reach a new host; secretes anti-enzymes.
In (b) explain how each factor raises or lowers the population, not just its name.