Population Dynamics – Growth Rates Chapter 4

Learning Targets I can… 1. Explain the concept of carrying capacity 2. Model how limiting factors and organism interactions affect carrying capacity 3. Describe the growth of populations using logistic and exponential growth models

Limiting Factors All species have limiting factors Limiting Factors: an abiotic or biotic factor that restricts the number, distribution, or reproduction of a population of organisms Examples:  Food  Shelter  Space  Water

Limiting Factors Density - Independent Factors: any factor in an organisms’ environment that does not depend on the number of individuals in the population Usually abiotic and include natural phenomena such as weather events Ex: rain, drought, tornado, fire, etc.

Limiting Factors Density-Dependent Factors: any factor in the environment that depend on the number of individuals in a population Often biotic factors Ex: predation, disease, parasites, and competition

Carrying Capacity Carrying Capacity – the maximum number of individuals an environment can support long term The carrying capacity of organisms is limited by the amount of resources available to the population

Population Growth Rates Population Growth Rate – explains how fast a given population grows Natality – birth rate (# of births each year) Mortality – death rate (# of deaths each year)

Population Growth Rates Population growth rates include info about individuals who enter or leave Emigration – describes the number of individuals moving away from a population Immigration – describes the number of individuals moving into a population

Population Growth Rates In order to notice trends of population growth over multiple years, ecologists look at mathematical models Exponential Growth Model Logistic Growth Model

Exponential Growth Model Exponential Growth Model – occurs when the growth rate is proportional to the size of the population All populations grow exponentially until some limiting factors slows the population’s growth

Exponential Growth Model The graph begins with a lag period Reproduction of the population occurs slowly The rate of population growth increases rapidly because the total number of organisms that can reproduce has increased Called Exponential growth period The graph is recognizable by the J-shape it creates

Logistic Growth Model Logistic Growth occurs when the population’s growth slows or stops following exponential growth Occurs after reaching the carrying capacity Many populations grow more like this model than the exponential model Number of births is less than the number of deaths Recognized by the S-shape on graph

Logistic Growth Model