Competition What are limiting factors What do organisms

Competition • What are limiting factors? • What do organisms compete for? • What is the difference between interspecific and intra specific competition?

What is competition? When two or more individuals share any resource (e. g. light, food, space) that is insufficient to satisfy all of their requirements fully, then competition results.

Types of competition Intraspecific Interspecific • Individuals competing for resources who are the same species. • Availability of the resources will determine the size of that population. • The larger the availability of resources, the larger the population. • Individuals competing for resources who are different species. • If individuals of different species occupy the same niche, one will have a competitive advantage over the other.

Competitive exclusion principle Where populations of two species initially occupy same niche, one normally has competitive advantage: Known as competitive exclusion principle – where two species competing for limited resources, one uses resources most effectively and ultimately eliminates the other.

Evidence for Competition Intraspecific competition In the lab… Interspecific competition leading to exclusion of p caudatum

Evidence of Interspecific Competition Remember lots of factors affect population size. This is not proof of a causal relationship.

Looking at data… Look at the data on the sheets and annotate it: • Describe the data • Explain/suggest explanations for what the data shows • What could you be asked about this data?

a) p. caudatum stealdy growth up to 8 days then levels off; p. Aurelia slower growth at first/up to 4 days; p. Aurelia reaches higher population size b) p. caudatum reaches lower peak at 6 days then population declines, p. Aurelia reaches lower peak c) Interspecific competition for resources e. g. food, oxygen; p. Aurelia more successful competitor; but competition means less energy available for reproduction; more deaths of p. caudatum

The effect of competition on population size • To show a factor influences the size of a population it is necessary to link it to birth rate and death rate. • Example: More food means that individuals are more likely to survive so increased chance of reproduction = population increases. • Not enough food means individuals more likely to die = population decrease.