Population Graphs See p. 40 – 42 of your textbook.

What is a population? A population is a group of members of the same species that live in the same area. The number of individuals in a population often changes. Factors such as natality, mortality, immigration and emigration change the number of individuals.

Population Changes To calculate a change in a population: New population # = (original population + natality + immigration) (factors that increase populations) – (mortality + emigration) (factors that decrease populations)

Population Changes Natality is the number of live births in a population over a period of time. Mortality is the number of deaths that occur in a population over a period of time.

Population Changes Immigration is the number of individuals that move into a population over a period of time. Emigration is the number of individuals that move out of a population over a period of time.

Population Changes In an existing population of Canada Geese there are 21 individuals. Over a period of time, 12 goslings are born, 10 geese die, 4 geese join the flock from a different population and 3 are lost from the population. How many geese will be in this flock now?

New Population = (original pop + natality + immigration) – (mortality + emigration) = (21 + 12 + 4) – (10 + 3) = 24

Factors Affecting Population Size Populations would grow and grow and grow if there were unlimited amounts of food, water and space. Therefore, population size is determined by the forces of: a) biotic potential b) limiting factors

What things allow for a population size to grow? An organisms ability to make many more of itself (through reproduction) is called biotic potential. Biotic potential is the maximum number of offspring that a species can produce with unlimited resources.

Factors that Determine Biotic Potential a) Birth potential = the maximum number of offspring per birth (e.g. a whooping crane will lay 2 eggs per year, but only one survives). b) Capacity for survival = the number of offspring that reach reproductive age (e.g. sea turtles lay many eggs (150-200), but very few reach maturity (about 0.01%)).

Factors that Determine Biotic Potential Procreation = The number of times the organism reproduces per year (e.g. elk reproduce once per year). Length of reproductive life = The amount of time the individual can reproduce (e.g. elephants can reproduce from about age 15 to 90 (75 years)).

Limiting Factors There are factors in an ecosystem that prevent populations from becoming too large. These are known as limiting factors. Limiting factor is a factor that prevent increases in the number of organisms or prevents them from moving into a new population.

Limiting Factors There are 2 types of limiting factors: Abiotic – factors such as availability of light, temperature, and chemicals. Increase Decrease Much light Warm temperatures fertilizers Low light Cold temperatures pesticides

Limiting Factors b) Biotic factors – factors such as the availability of food, predators, diseases parasites, competition for resources Increase Decrease Lots of food Few predators Few diseases Few parasites Little competition Little food Many predators Many diseases Many parasites Much competition

Population Graphs Population graphs show the growth of a population in an area, and can often be used to determine the carrying capacity of the population for that environment. Carrying capacity is the maximum number of individuals of a species that can be supported by an ecosystem.

Population Graphs Population number A B C Time

Section A Section A represents an area of slow growth. Growth of a population is often slow because the initial number of organisms in that population is low. There may also be other factors in the environment that are limiting growth of the population, such as: Lack of resources, predators, competition, disease

Section B Section B represent an area of rapid growth. In this type of growth, there are few limiting factors restricting the reproduction of species. The rate of growth can be exponential.

Section C Section C represents an area where carrying capacity has been met. The abiotic and biotic factors in an environment will regulate the number of organisms of a species that can survive in an environment. The population will fluctuate (temporarily rise and fall repeatedly) slightly around that number, but at this point the population is said to be in equilibrium – the number of individuals remains relatively the same.

In a sustainable ecosystem, none of the populations in a community can exceed their carrying capacities for very long. Why?

A population that exceeds its carrying capacity will soon run out of resources and will strain the environment in which they live. When this happens, competition will cause the population to decrease.