Population Population DynamicsDynamics

Exponential Growth and Doubling Times Exponential Growth: Growth at a constant

rate of increase per unit of time Geometric Growth: Same as exponential

growth– Sequence of growth follows a geometric pattern

of increase Arithmetic Growth: Growth increases at a

constant amount per unit of time 6.4

J curve: Growth curve produced by a constant rate of growth– Represents theoretical unlimited growth– It represents the biotic potential

Biotic Potential

The maximum reproductive rate of an organism having no limiting factors.

If all the individuals in the population survived and reproduced at the maximum rate.

It is a reference value allowing one to determine if the observed growth rate is close to the biotic potential.

Population Oscillations and Irruptive Growth Dieback: When death rates begin to surpass

birth rates Overshoot: The extent to which a

population exceeds the carrying capacity of its environment

Malthusian (Irruptive) Growth: Pattern of population explosion followed by a population crash

Growth to a Stable Population

Logistic Growth: Constantly changing rate– When growth slows as populations approach

the carrying capacity of the environment Environmental Resistance: Factors that

tend to reduce population growth rates 6.7 S curve: Population growth and

stabilization in response to environmental resistance

Carrying capacity

The maximum number of individuals of a certain species that an environment can support.

It reflects the limits imposed on population growth by finite space and finite resources.

Lifestyle greatly affects carrying capacity

It is estimated that 10-15 acres are necessary to sustain one person with an affluent lifestyle

To support the 5.6 billion humans at such a lifestyle would require 3 times as much productive land

In these terms, the earth can support only 1.8 billion people

Environmental resistance can include any of the following.

food runs out waste accumulates and becomes toxic living space runs out over-crowding makes the population an

easy target for parasites and predators disease predation

Calculating % Growth Rates (GR)

Population Growth for a Specific Location% GR= (birth +immigration)- (deaths+emmigration)

100

% Global Population Growth Rate

% growth rate = (birth rate %-death rate percent)

i.e. 6 births/100 people each year

4 deaths/100 people each year

this is a rate of increase of 2%

Calculating Doubling Time

DT = _____70_____

% growth rate

70 is a demographic constant

Factors that Increase or Decrease Populations

Natality , Fecundity and Fertility Immigration and Emigration Mortality and Survivorship Age Structure

Natality, Fecundity, and Fertility Natality: Production of new individuals by

birth, hatching, germination, or cloning– Main source of addition to most biological

populations Fecundity: Physical ability to reproduce

“Potential” Fertility: Measure of actual number of

offspring produced “Actual or Realized”

Migration

Immigration: movement of organisms into a new ecosystem

Emigration: movement of organisms out of an ecosystem

**Migration is not a factor when determining Global Population Growth Rates

Mortality and Survivorship

Mortality: Death rate– Determined by dividing number of organisms

that die in a certain time period by the number alive at the beginning of the period 6.9

Survivorship: Percentage of a cohort that survives to a certain age

Life Span vs Life Expectancy

Life Span: Longest period of life reached by a given type of organism 6.10

Life Expectancy: The probable # of years of survival for an individual of a given age

Age Structure

Population Momentum: Large number of prereproductive individuals – Rapid increase in natality once youngsters

reach reproductive age 6.11

Factors That Regulate Population Growth

Density-Dependent: Effects are stronger or a higher proportion of the population is affected as population density increases

Density-Independent: The effect is the same or a constant proportion of the population is affected regardless of population density

More…..

Intrinsic: Factors operating within individual organisms or between organisms in the same species

Extrinsic: Imposed from outside the population

Biotic: Caused by living organisms Abiotic: Caused by nonliving components of

the environment

Characteristics of contrasting reproductive strategies

Extrinsically Controlled Growth Intrinsically Controlled GrowthShort Life Long Life

Rapid growth Slower growth

Early maturity Late maturity

Little parental care or protection High parental care and protection

Little investment in individual offspring High investment in individual offspring

Adapted to unstable environment Adapted to stable environment

Pioneers, colonizers Later Stages of succession

Niche generalists Niche specialist

Prey Predators

Regulated mainly by extrinsic factors Regulated mainly by intrinsic factors

Low trophic levels High trophic levels

Density-Independent Factors

Factors that affect natality of mortality independently of populations density

abiotic

Density-Dependent Factors

Factors that reduce population size by decreasing natality or increasing mortality– Tend to be biotic

Interspecific Interactions: Two species compete for the same environmental resources in an ecosystem 6.12– May be beneficial or neutral, such as mutualism

Intraspecific Interactions – Individuals within a population compete for

resources– Territoriality is an example

Stress and Crowding – Stress Shock: A loose set of physical,

psychological, and/or behavioral changes thought to result from the stress of excess competition and extreme closeness to other members of the same species