Growth of PopulationsCHAPTER 22

How Many Organisms Live in a Particular Environment, and Why?

• Population ecology is the study of the number of organisms in a particular place

• Population ecology is essential for solving real-world problems, such as protecting endangered species or controlling pest species

What Is a Population?• A population is a group of

interacting individuals of a single species located within a particular area

• Population size: total number of individuals in the population

• Population density: the number of individuals per unit of area.

Ex: 200 humans/square mile

There are three populations in this picture

Changes in Population Size

• Whether a population increases or decreases in size depends on the birth and death rates and immigration and emigration rates

• Birth and death rates and immigration and emigration rates are all affected by environmental factors

Calculating Changes in Population Size

ΔP = [N+I] – [M+E]

N=natality I = immigration

M=mortalityE = emigration

Density= # or organisms/ unit of area

Exponential Growth: J-Shaped Growth

Patterns • Endless exponential

growth of a population is limited by the availability of resources and is not seen under natural conditions

• Doubling time: The time it takes a population to double in size

Erosion of a gully in South Australia caused by rabbits

The No. 1 rabbit-fence in Western Australia (1926)

Rabbits around a waterhole in the myxomatosis trial site on Wardang Island in 1938

"The introduction of a few rabbits could do little harm and might provide a touch of home, in addition to a spot of hunting.” -Thomas Austin

Population Growth Has its Limits

• Growth is limited by essential resources and other environmental factors

• Populations cannot increase in size indefinitely—limits exist

Limiting Factors

• A Limiting Factor is any living or non-living factor that restricts the existence, numbers, reproduction, or distribution of organisms.

• Factors that limit one population will affect other populations (Remember all living things in a committee are part of a whole).

• Water, space, food, temperature, soil, etc.

Population Growth Has its Limits

• Space and nutrients are important limiting factors in the population growth of an organism

• Habitat is the type of environment in which an organism lives and is an environmental factor that limits population growth

Abiotic Factors: Physical and

Chemical Characteristics of the

environment (Non-living)

Ex: Solar Energy, Oxygen, CO2,

Water, Temperature, Humidity,

pH, Nitrogen, Phosphorus

Abiotic Factors

Biotic Factors: living aspects of the

environment. Plants, animals, etc.

Biotic Factors

Logistic Population Growth:S-Shaped Growth Pattern

• Logistic growth: – What we see in nature most of

the time– Represented by an S-shaped

curve– Consideration that growth rates

change as resources become limited

• Carrying capacity: – The maximum population size

that can be sustained in an environment

– At the carrying capacity, the population growth rate is zero

Density-Dependent Factors

• Birth rates and death rates are density-dependent because they change as the density of the population changes

• Density-Dependent Factors include disease, competition, and parasites

• Biotic factors

Density-Independent Factors

• Density-Independent Factors affect all populations regardless of their density

• Abiotic factors

• Temperature, storms, flood, drought, or other natural habitat disruptions

Population Cycles

• In a population cycle, the population sizes of two or more species change together because at least one of the two is influenced by the other

Predator Prey relationships

encourage the health of an ecosystem:• Usually, in prey populations, the weak,

young, old, or injured members are caught • Keeps population size within the limits of

available resources• Improves the genetic make up of the

surviving members of that population

Patterns of Population Growth: Irregular Fluctuations

• Populations of the same species may experience different patterns of growth depending on the environment

• In1800 estimated 100,000 breeding pairs present

• By the early 1960s, population counts indicated that only 417 breeding pairs of eagles remained in the lower 48 states

Patterns of Population Growth: Irregular Fluctuations

• Which will we experience? The jury is still out.

• How are we different that the rest of the animal Kingdom

Human Population Growth