Population

• Birth and immigration rates increase a population
• Death and Emigration rates decrease a population

The max size a population can support under particular conditions is the carrying capacity.

• Environmental resistance factors reduce growth rate: available food; parasitism; toxic waste; competition 
• Factors that may cause a population crash include a sudden/violent change: freezing; flood; fire

Population Size

• Different strategies for growth are used by different species
• fugitive species - poor at competition so rely on large capacity for reproduction and dispersal to increase numbers. They invade a new environment rapidly.
• Equilibrium species - control population by competing with stable habitiat, rather than by reproduction and dispersal. Usual pattern of growth is sigmoid 'S' curve called one step growth curve. 

Population growth curves

• Obtained by plotting change in population size against time.
• calculation of…