Populations Topic 5.3

Assessment Statements Outline how population size is affected by natality, immigration, mortality and emigration Draw and label a graph showing a sigmoid (S- shaped) population growth curve Explain the reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases List three factors that set limits to population increase.

Outline how population size is affected by natality, immigration, mortality and emigration. Natality – # of new members of the species due to reproduction Mortality - # of deaths Immigration – members arriving from different places Emigration – members leaving the population

Mount Saint Helens 1980 How is/was the sizes of populations affected by: –Natality? –Mortality? –Immigration? –Emigration?

Draw and label a graph showing a sigmoid (S-shaped) population growth curve.

Population dynamics simulation model

Sigmoid (S-shaped) curve of the graph shows three stages in population growth 1.Exponential growth phase – a.k.a. logarithmic phase, in which the # of individuals increases at a faster and faster rate 2.Transitional phase – growth rate slows down considerably 3.Plateau phase – stationary phase, in which the # of individuals has stabilized

Causes of exponential phase Plentiful resources Little or no competition from other inhabitants Favorable abiotic factors Little or no predation or disease

Causes of the transitional phase Increasing competition for resources among individuals of population Predators, attracted by a growing food supply, move into the area b/c of large numbers of individuals living together in a limited space, opportunities for disease to spread within the population increase

Causes of the plateau phase Less and less space Limited supply of food, animals tend to have smaller numbers of offspring Predators and disease increase mortality and the growth curve tends to level off # of births plus the # of immigrants is balanced with the # of deaths plus the # of emigrants

List three factors that set limits to population increase. The maximum number of individuals that a particular habitat can support is called the carrying capacity and it is represented by the letter K. Limiting factors: –Availability of resources –Build-up of waste –Predation –Disease