Species richness varies between different areas at both regional and global scales. Outline three explanations for variation in species richness between different communities.. Ecology

  1. Evolutionary Speed: more time and more rapid evolution permits the evolution of new species. There is higher species diversity in the tropics because speciation has gone on longer in this area or because speciation is faster in the tropics.
  2. Geographical Area: Larger areas and physically or biologically complex habitats provide more niches. For example the tropics support more species than temperate because they have larger land area.
  3. Interspecific Interactions: competition affects niche partitioning and predation retards competitive exclusion. In more physically stressful environments such as Polar Regions physical factors affect diversity whereas in tropical areas biological competition becomes more important.
  4. Ambient Energy: fewer species can tolerate climatically unfavourable conditions. Climate determines energy availability, which determines diversity. For example, more solar radiation, temperature and water in the tropics leads to higher diversity.
  5. Productivity: richness is limited by the partitioning of production or energy among species. Tropical habitats are more productive and have a higher diversity.
  6. Disturbance: moderate disturbance retards competitive exclusion. Example Littorina littorea (periwinkle snail) on rocky intertidal zones. The snail is the most common grazer. In tide pools the snail feeds on algae that are competitively dominant. Moderate grazing by the snails allows competitively inferior algae to survive.
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