Populations and Population Growth

Populations Population - a group of interbreeding organisms of the same species that live together at the same time in the same place

Population size - number of members in a population 2 ways to estimate population size: Random sampling – used mainly for plants; samples and counts organisms in random plots Mark & recapture – used mainly for animals; captures, marks, and releases animals, then samples the population again

Population growth – an increase in the size of a population 2 kinds of population growth: Exponential Logistic Why do populations grow???

Population Growth Exponential – “J” curve - population growth is slow at first then increases rapidly - more members = more reproduction - continues as long as there are unlimited resources

Why is exponential unrealistic? Resources (food, space, etc.) are limited in nature! There are other limiting factors. Things that limits the survival of an organism Ex. Predators, diseases, natural disasters

Populations cannot grow indefinitely. They will reach their carrying capacity The maximum number of individuals in a population that an area can support

Population Growth Logistic – “S” curve Shows a population growing with limits such as food and space Levels off at carrying capacity Carrying capacity can be raised or lowered depending on the amount of available resources

Even more realistic…

Human Population Growth

Human Population Graph

Human Population Human population remained stable for many years Human population has grown exponentially since the time of the industrial revolution Humans have not reached their carrying capacity yet because we can: Plant/raise food Build for shelter Control/treat diseases

Growth Rate Growth Rate = Birth – death Birth rate - # of births per year Factors affecting birth rate: religious/social beliefs, use of birth controls Death rate - # of deaths per year Factors affecting death rate: diseases/medicines, nutrition, homicides

If birth rate is greater than death rate… Population increases If birth rate is less than death rate... Population decreases

Age Structure Distribution of various age groups in an area