Section 1: How Populations Change (ranking order) Chapter 8 Section 1: How Populations Change

What Is a Population? -A group of organisms of the same species that live in a specific geographical area and breed with each other -Usually breed with members of their own population (won’t go to another population to find a mate)

Properties of Populations -Used to describe populations and to predict changes within them. - Size is the number of individuals in the area -Density is the number of individuals of the same species in that live in a specific area. -Dispersion is the how the organism are dispersed or arrange in the population - can be even, clumped, or random.

How Does a Population Grow? - A population gains individuals with each new offspring or birth and loses them with each death. - The resulting population change over time can be represented by the equation below.

How Does a Population Grow? - Growth rate has 2 meanings: - the increase in the size of an organism - increase in population over a given period of time. - birth rate minus the death rate. -Overtime, the growth rates of populations change because birth rates and death rates increase or decrease. -SO growth rates can be positive, negative, or zero.

How Does a Population Grow? - Zero Growth Rate  births = deaths - Positive Growth Rate  births > deaths - Negative Growth Rate  deaths > births

How Fast Can a Population Grow? - Populations usually stay about the same size from year to year -various factors kill individuals before they can reproduce. - These factors control the sizes of populations. - The factors also determine how the population evolves over a long period of time.

Biotic Potential The Fastest Rate a population can grow - Limited by reproductive potential.

Reproductive Potential - Reproductive potential is the maximum number of offspring that a given organism can produce. - Some species have much higher reproductive potentials than others. -This affects how quickly a population can grow.

Reproductive Potential - Increases when individuals: -produce more offspring at a time - reproduce more often -reproduce earlier in life. - Reproducing earlier in life has the greatest effect on reproductive potential Also shortens generation time - Time it takes an organism to reach reproductive age

Reproductive Potential - Small organisms (bacteria and insects) can reproduce when they are only a few hours or a few days old. -Their populations can grow quickly -Large organisms (elephants and humans, etc.) become sexually mature after a number of years have a much lower reproductive potential than insects.

Exponential Growth Population keeps growing faster and faster Growth in which numbers increase by a certain factor in each successive time period. - Occurs in nature only when populations: -have plenty of food and space -have no competition or predators. - For example, population explosions occur when bacteria or molds grow on a new source of food.

Exponential Growth -A large number of individuals is added to the population in each succeeding time period.

What Limits Population Growth? -Natural conditions are neither ideal nor constant SO populations cannot grow forever. -Resources are used up -The environment changes -Deaths increase or births decrease. Natural Selection has only some members of any population survive and reproduce. - Properties of a population may change over time.

Carrying Capacity -The largest population that an environment can support at any given time. -A population may increase beyond this number but it cannot stay at this increased size.

Carrying Capacity - Ecosystems change so carrying capacity is difficult to predict or calculate exactly, but can be estimated by looking at average population size.

Resource Limits on Populations - Only so much to go around A species reaches carrying capacity when it consumes a particular natural resource at the same rate that the ecosystem produces the resource. -called a limiting resource. -The supply of the most limited resources determines the carrying capacity of an environment for a particular species at a particular time. Examples: water, safe shelter, etc.

Competition Within a Population - Limits Populations Direct The members of a population use the same resources in the same ways - They will compete for those resources (example – food) Competition is part of natural selection

Competition Within a Population In Direct- -Members of a species may compete indirectly for social dominance or for a territory. - Wolf packs have an alpha male and female who get first dibs A territory is an area defended by one or more individuals against other individuals. - The territory is of value not only for the space but for the shelter, food, or breeding sites it contains.

Two Types of Population Regulation Population size can be limited in ways that may or may not depend on the density of the population. Causes of death in a population may be: -density dependent – more deaths occur in a crowded population - caused by limited resources, predation and disease -density independent – affects all populations in a general way - caused by severe weather and natural disasters

Population Regulation Density Dependent Density Independent Limited Resources Natural Disaster