Population Dynamics. Exponential Growth and Doubling Times nEnExponential Growth: Growth at a...
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Transcript of Population Dynamics. Exponential Growth and Doubling Times nEnExponential Growth: Growth at a...
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%
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