The population structure of a species (continued)
The species composition of a biocenosis is the number and proportions of species in the biotope (species richness). Tropical forests hold thousands of species, while tundra, desert and conifer forest hold tens to hundreds; a community with high species diversity is stable. The most numerous species that shape the habitat are dominants (pine in a pine wood), the next are subdominants, and there are scarce and rare species; rare ones are protected (Red Data Book). The vertical structure is layering: in a forest tiers of tall trees, lower trees, shrubs, herbs and mosses; it allows full use of light and reduces competition, and animals also settle by tiers. The horizontal structure is a mosaic: individuals are spaced evenly (trees in a dense forest), randomly or in groups (the commonest: colonies, packs, patches of herbs); grouping helps in defence and finding food. Animals have an ethological structure: solitary life, family (lion pride), pack (wolves), herd (zebras), colony (penguins, ants, bees – with division of tasks). These structures ensure fuller use of resources.
Mark a 10×10 m plot in the schoolyard, count plant species and find which is dominant. Write which are spread evenly and which in groups. If you have dust or pollen allergy, wear a mask; do not pick or taste plants that may be poisonous.