Transcript Unit II Section I Ecology: Population Ecology

Learning Goal 1
Populations
The Science of Ecology
Definition –
Levels of Organization in Nature –
Features of Populations
Population Characteristics –
Population Dispersion –
Survivorship Curves –
Life History Patterns
Consist Of –
Fecundity vs Parental Care –
Reproductive Episodes –
Early vs Late Reproduction –
R and K Selected Species –
Models of Population Growth
Growth Rate –
Exponential Models –
Logistic Models –
Population Regulation
Density Dependent Factors –
Density Independent Factors –
Human Population Growth
Increased Carrying Capacity –
Population Growth and Age Structure –
Demographic Transition Model -
Ecology
Learning Goal One
Analyze aspects of populations in terms of
life history patterns, growth models,
limiting factors, and human population
trends.
What’s Wrong with This Picture?
The Science of Ecology
• Definition
Ecology is the study of
interactions between
organisms and their
environment.
The environment consists of
both abiotic and biotic factors.
Abiotic components consist
of nonbiological factors such
as temperature, water, soil
chemistry.
Biotic componenents consist
of biological factors such as
plants, microorganisms, and
animals.
Levels of Organization in Nature
• Organisms
Individuals within a population.
• Populations
Made up of individuals of the
same species.
• Community
Made up of all populations in
an area.
• Ecosystems
Includes the community as
well as the physical
environment.
• Biosphere
Refers collectively to all
ecosystems on earth.
Features of Populations
• Population
Characteristics
Population size
refers to the total
number of individuals
in any given
population.
Density refers to the
number of individuals
per unit area of
habitat.
Population Dispersion
•
•
•
Clumped
Individuals are grouped together.
Uniform
Organisms are evenly spaced in their habitat because they repel each
other.
Random
Organisms are distributed unpredictably. Used when the other two
dispersion patterns don’t apply.
Survivorship Curves
Depict changes in survival rate.
Type I
High survivorship until late in life.
Type II
Relatively constant rate of mortality at all ages.
Type III
High juvenile mortality followed by low mortality once a certain age or size is
reached.
Life History Patterns
• Consist of:
Growth
Increase in cell number from birth to
maximum size for that species.
Maturation
Usually refers to the point where sexual
maturity is reached.
Reproduction
Offspring is produced to ensure the
survival of the species.
Fecundity vs Parental Care
• Passive Parental Care
Energy is invested in offspring
before birth. ie., egg yolks,
endosperm in seeds, nutrients
that cross placenta
• Active Parental Care
Continued parental care after
birth.
• Fecundity refers to the
number of offspring produced
during a female’s lifetime.
Organisms that produce large
numbers of offspring are
generally passive parents
whereas low numbers of
offspring receive active care.
Reproductive Episodes
• One Episode
All energy is devoted to
one reproductive event,
like the salmon and most
insects.
• Several Episodes
Other species devote
only some of their energy
budget to reproduction so
spread it out over many
episodes with the rest
allocated to maintenance
and growth.
Early vs Late Reproduction
• Early Reproduction
Favored by natural
selection if adult survival
rates are low as in a prey
species, or adults do not
increase in size as they
age (they’re small).
• Late Reproduction
Favored by natural
selection if sexually
mature individuals have a
good chance of surviving
to produce more
offspring.
R and K Selected Species
R-Selected Species
Function well in rapidly changing environments.
Usually small and produce numerous offspring often in a single reproductive
event.
Little or no active parental care.
Most die before reaching sexual maturity so success depends on producing
so many that a few are likely to survive.
• K-selected Species
Thrive in more stable environments.
Larger with longer generation times.
Produce offspring repeatedly throughout their life time.
Offspring receive substantial parental care.
Small number of offspring.
Models of Population Growth
• Growth Rate Change in population size =
number of births (B) – number of deaths (D)
Normally expressed in births (b) and deaths (d)
per capita (individual) during a specified time
period.
B/N = b and D/N = d (N = population size)
Growth rate r= b-d
Exponential Models
Occurs when populations are
exhibiting unlimited growth.
Assumes unlimited resources
and no build up of toxic waste
products.
Population size increases by a
constant ratio.
Graphs of exponential growth
are known a J curves
because of their characteristic
shape.
Logistic Model
•Most populations exhibit a
logistic model of growth.
•Growth increases rapidly
at first then slows down as
the population gets larger.
•As resources run out fewer
offspring are produced
and a population reaches
its carrying capacity, the
maximum number of
individuals that an
environment can support.
•Logistic models exhibit an
S-shaped curve.
Population Regulation
• Density Dependent Factors
Factors that have more impact as population
density increases.
Intraspecific Competition
• Competition between members of the same species.
• Leads to decrease in reproduction, slower growth, and
smaller adult size.
• May stimulate behavioral and developmental changes as
with locusts. Some will become migratory with longer
wings and more body fat so they can fly great distances.
Other Examples of
Density-Dependent Factors
• Interspecific
Competition
• Competition between
different populations.
• Disease
Microorganisms
spread quickly in
denser populations.
Density-Independent Factors
• Factors that reduce population size regardless of its density.
• Climate, fires, earthquakes, storms are some examples.
• Density-Independent factors do not cause a population to fluctuate
around its carrying capacity the way density dependent factors do.
• They reduce, but do not regulate populations.
Cycles in Population Size
Intrinsic Control:
As population grows,
individuals undergo hormonal
changes that may cause
aggressive behavior, or
reduced reproduction, or lead
to migrating to other areas.
Extrinsic Control:
Population cycles in response
to food and/or predators.
Human Population Growth
• Ways Humans Increased
carrying capacity:
11,000 years ago humans
shifted from hunter/gather
cultures to agriculture. They
cultivated plants and
domesticated animals and
significantly alter their
environment by diverting water
for irrigation and building
settlements.
Once the energy from fossil
fuels was harnessed in the mid
eighteenth century food supply
increased further.
• Advances in Public
Health:
Reduced malnutrition,
contagious diseases,
and improved
sanitation all reduced
death rates sharply.
Population Growth and Age
Structure
• Zero Growth:
Equal number of people
in prereproductive and
reproductive age groups.
• Slow Growth:
Slightly more
prereproductive than
reproductive population
• Rapid Growth:
Broad base of
prereproductive
population. One third of
the world’s population.
• Negative Growth:
Fewer
prereproductive
individuals that any
other age group.
Demographic Transition Model
• Preindustrial Stage-Birth and death rates are high and population
grows slowly.
• Transitional Stage-Food production rises, health and sanitation
improve leading to decreasing deaths.
• Industrial Stage –Birth rate declines as more people move to cities.
• Postindustrial Stage – Birth rate equals or falls below death rate
leading to ZPG or declining population growth.
Options for Limiting Population
Growth
• Family planning
programs that limit
human population
growth.
• Wait until the
environment does it
for us.
LG 1 Terms
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Abiotic/Biotic Components
Levels of Organization in Nature
Population Size vs Density
R – Selected Species
K – Selected Species
Exponential vs Logistic Growth Model
Carrying Capacity
Density Dependent Factors
Density Independent Factors
Demographic Transition Model