Download All Ecology Chapters PPT 52-55

Chapter 52-55 Ecology
Characteristics of a Population
• A population is a group of individuals of a single
species that simultaneously occupy the same
general area.
Populations may increase in
either of these 2 ways
• Population Density: # of individuals per unit
(ex: # people/square miles)
• Population Dispersion: how individuals are
arranged or dispersed (even, clumped,
random)
• Mark and recapture: used to estimate
population size .
– Individuals are trapped in an area and captured,
marked with a tag, recorded, and then released.
– After a period of time has elapsed, traps are set
again, and individuals are captured and
identified.
*Why do we care about estimating a population
size?
• Additions occur through birth, and subtractions
occur through death.
– Demography studies the vital statistics that affect
population size.
– A graphic way of representing the data is a
survivorship curve.
• This is a plot of the number of individuals in a
cohort still alive at each age.
–A Type I curve shows a low death rate early
in life (humans).
–The Type II curve shows constant mortality
(squirrels).
–Type III curve shows a high death rate early
in life (oysters).
Fig. 52.3
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Factors that effect reproductive
potential
• Reproducing earlier in life
• Generation time (average age of reproduction)
• Gestation Period: the time in which a fetus
develops (mammals)
(elephants – 22 months!)
Population Growth
• Population Growth Rate:
Birth rate – death rate
 Biotic Potential: the fastest rate at which a
population can grow
 Reproductive Potential: the maximum number of
offspring an individual can produce (in lifetime)
Who has a bigger reproductive potential: Bacteria or elephants?
Exponential Growth
• Exponential Growth:
 Population significantly increases with each
generation
 Occurs with unlimited resources and no
competitors/predators
 R-selection: growth that occurs when birth
rates are high
Fig. 52.9
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Carrying Capacity
• Carrying Capacity: the maximum population
an ecosystem can support.
• Logistical Growth: in a population, the initial
growth is exponential, then the growth slows
and eventually stops
• K-selection: growth that incorporates the effect
of population density on rate of increase
Fig. 52.11
Population Growth Models
• Exponential model (red)
• idealized population in an
unlimited environment (Jcurve); r-selected species
(r=per capita growth rate)
• Logistic model (blue)
•carrying capacity (K):
maximum population size that a
particular environment can support
(S-curve); K-selected species
• The logistic population growth model and life
histories.
– This model predicts different growth rates for
different populations, relative to carrying capacity.
• Resource availability depends on the situation.
• The life history traits that natural selection favors may
vary with population density and environmental
conditions.
• In K-selection, organisms live and reproduce around K,
and are sensitive to population density.
• In r-selection, organisms exhibit high rates of
reproduction and occur in variable environments in
which population densities fluctuate well below K.
Population life history “strategies”
• r-selected (opportunistic)
• K-selected (equilibrial)
• Short maturation &
lifespan
• Many (small) offspring;
usually 1 (early)
reproduction; no
parental care
• High death rate
• Long maturation &
lifespan
• Few (large) offspring;
usually several (late)
reproductions; extensive
parental care
• Low death rate
Some questions…
• Why do all populations eventually stop growing?
• What environmental factors stop a population
from growing?
• The first step to answering these questions is to
examine the effects of increased population
density.
Two Types of Population
Regulation
• Density Dependent: A more crowded population
causes more deaths (ex: starvation, predation,
disease)
• Density Independent: A certain percent of a
population dies regardless of the population density
(ex: severe weather, natural disaster)
http://www.youtube.com/watch?
v=BSVbdaubxxg&NR=1
• The Demographic Transition.
– A regional human population can exist in one of
2 configurations.
• Zero population growth = high birth rates –
high death rates – where?
• Zero population growth = low birth rates –
low death rates- where?
– The movement from the first toward the second
state is called the demographic transition.
Fig. 52.21
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Fig. 52.22
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Earth’s Carrying Capacity?
• Predictions of the human population vary from
7.3 to 10.7 billion people by the year 2050.
– Will the earth be overpopulated by this time?
• Wide range of estimates for carrying capacity.
– What is the carrying capacity of Earth for
humans?
– This question is difficult to answer.
• Estimates are usually based on food, but
human agriculture limits assumptions on
available amounts.
• Ecological footprint.
– Humans have multiple constraints besides food.
– The concept an of ecological footprint uses the
idea of multiple constraints.
• For each nation, we can calculate the aggregate
land and water area in various ecosystem
categories.
• Six types of ecologically productive areas are
distinguished in calculating the ecological
footprint:
–
–
–
–
–
–
Land suitable for crops.
Pasture.
Forest.
Ocean.
Built-up land.
Fossil energy land.
Community structure
• Community~ an assemblage of
populations living close enough together for
potential interaction
Interactions
• Interspecific (interactions
between populations of different
species within a community):
The Niche
• Ecological niche~ the sum total of
an organism’s use of biotic and abiotic
resources in its environment; its “ecological
role”
√ fundamental~ the set of
resources a population is theoretically
capable of using under ideal conditions
√ realized~ the resources a
population actually uses
• Thus, 2 species cannot coexist in
a community if their niches are
identical
Ex: Barnacle sp. on the coast of Scotland
• Resource partitioning~
sympatric species consume slightly
different foods or use other
resources in slightly different ways
Ex: Anolis lizard sp. perching sites in the
Dominican Republic
Relationships
• Trophic structure / levels~ feeding
relationships in an ecosystem
• Primary producers~ the trophic level
that supports all others; autotrophs
• Primary consumers~ herbivores
• Secondary and tertiary consumers~
carnivores
• Detrivores/detritus~ special consumers
that derive nutrition from non-living organic
matter
• Food chain~ trophic level food pathway
Food Chains
This is a food chain
Grass
Insect
Bird
Fox
Where does the initial energy come from?
How does each organism obtain their energy?
A food chain is a sequence in which energy is
transferred from one organism to the next as each
organism eats another organism
Food Webs
• Food webs are interconnected food chain
that show many feeding relationships
hawk
Bird
snake
mouse
seeds
insect
pine tree
- The arrows show the FLOW OF
ENERGY
Energy Pyramid
• Review 10% law
Dominant species and keystone
species exert strong controls on
community structure
• Dominant species are those in a community that
have the highest abundance or highest biomass
(the sum weight of all individuals in a
population).
– If we remove a dominant species from a
community, it can change the entire community
structure. (often plants)
Keystone Species
• Keystone species: a species that has a major
impact and role within an ecosystem. Without
them the ecosystem will fall apart.
– Sea otter
(Decrease Sea Otter  Increase sea urchinDecrease Kelp- Decrease Fish spawning
Most communities are in a state of
nonequilibrium owing to disturbances
• Disturbances are events like fire, weather, or
human activities that can alter communities.
– Some are routine.
Fig. 53.16
• We usually think that disturbances have a
negative impact on communities, but in many
cases they are necessary for community
development and survival.
Fig. 53.18
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Humans are the most widespread
agents of disturbance
• Human activities cause more disturbance than
natural events and usually reduce species
diversity in communities.
Give examples
Succession
• Ecological succession~
changes to an ecosystem over time
• Primary~ begun in lifeless area; no
soil, perhaps volcanic activity or
retreating glacier
• Secondary~ an existing community
has been cleared by some disturbance that
leaves the soil intact (fire)
Primary Succession In I Am Legend
Secondary Succesion
Ecosystems
• All of the biotic and abiotic factors in an
area
Trophic Relationships
• The autotrophs are the primary producers, and
are usually photosynthetic (plants or algae).
– They use light energy to synthesize sugars and other
organic compounds.
• Heterotrophs
are
at trophic levels
above the
primary
producers and
depend on their
photosynthetic
output.
Fig. 54.1
– Herbivores that eat primary producers are called
primary consumers.
– Carnivores that eat herbivores are called
secondary consumers.
– Carnivores that eat secondary producers are called
tertiary consumers.
– Another important group of heterotrophs is the
detritivores, or decomposers.
• They get energy from detritus, nonliving
organic material and play an important role in
material cycling.
Primary Production
• The amount of light energy converted to chemical
energy by an ecosystem’s autotrophs in a given
time period is called primary production. (very
important to an ecosystem)
In aquatic ecosystems, light and
nutrients limit primary production
• Production in Marine ecosystems.
– Light is the first
variable to control
primary production
in oceans, since
solar radiation
can only penetrate
to a certain depth
(photic zone).
Fig. 50.22
–In the open ocean, nitrogen and phosphorous
levels are very low in the photic zone, but
high in deeper water where light does not
penetrate.
Fig. 54.5
• Nitrogen is the one nutrient that limits
phytoplankton growth in many parts of the ocean.
Fig. 54.6
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• Production in Freshwater Ecosystems.
– Solar radiation and temperature are closely linked
to primary production in freshwater lakes.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
– During the 1970s,
sewage and fertilizer
pollution added
nutrients to lakes,
which shifted many
lakes from having
phytoplankton
communities to those
dominated by diatoms
and green algae.
• This process is called
eutrophication,
and has undesirable
impacts from a human
perspective.
Impacts of Eutrophication
• Algal blooms block light available to other
plants
• When algae die, decompose and deplete
dissolved oxygen creating dead zones
• Controlling pollution may help control
eutrophication.
–Experiments are being done to study this
process.
Fig. 54.8
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Chemical Cycling
•
•
•
•
•
Biogeochemical cycles: the various nutrient circuits, which involve both abiotic and
biotic components of an ecosystem
Water
Carbon
Nitrogen
Phosphorus
Human Impact
• Biological magnification: trophic process
in which retained substances become more
concentrated at higher levels
• Greenhouse effect and climate change
: warming of planet due to atmospheric
accumulation of carbon dioxide
• Ozone depletion: effect of
chlorofluorocarbons (CFC’s) released into the
atmosphere, deplete ozone
• Rainforest destruction
• Cause: Overpopulation?
Conservation Biology
• Conservation biology is a goal-oriented science
that seeks to counter the biodiversity crisis, the
current rapid decrease in Earth’s variety of life.
• Extinction is a natural phenomenon that has been
occurring since life evolved on earth.
– The current rate of extinction is what underlies the
biodiversity crisis.
– A high rate of species extinction is being caused
by humans.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
What is biodiversity?
• Biodiversity: the total of genetically different
organisms in an area
A lot of biodiversity: Rainforest
Levels of Diversity
• Species diversity: # of different species in an area
• Ecosystem diversity: the variety of habitats,
communities within an ecosystem
• Genetic Diversity: different genes within a population
• Loss of genetic diversity.
– If a local population becomes extinct, then the
entire population of that species has lost some
genetic diversity.
• The loss of this diversity is detrimental to the
overall adaptive prospects of the species.
• Loss of species diversity.
– The U.S. Endangered Species Act (ESA) defines
an endangered species as one in danger of
extinction throughout its range, and a threatened
species as those likely to become endangered in
the foreseeable future.
• Loss of ecosystem diversity.
– The local extinction of one species, like a
keystone predator, can affect an entire community.
– Some ecosystems are being erased from the Earth
at an unbelievable pace.
• For example, an area the size of the state of
West Virginia is lost from tropical forests each
year.
Biodiversity: Human welfare
• 25% of all medical
prescriptions
• Genetic variability
• Aesthetic and ethical
reasons
• Species survival
Biodiversity crisis- 4 major
threats
Major Threats:
1. Habitat destruction ~
single greatest threat; cause
of 73% of species
designation as extinct,
endangered, vulnerable, rare;
93% of coral reefs
Biodiversity crisis- 4 major
threats
Major Threats:
2.Competition by exotic
(non-native) or invasive
species – species that
humans move from
native locations to new
geographic locations
- What are the problems
associated with this?
Biodiversity crisis- 4 major
threats
Major Threats:
3. Overexploitation ~
commercial harvest or
sport fishing; illegal
trade, hunting.
• The African elephant has been overhunted and
the populations have declined dramatically.
• The bluefin tuna is another example of an overharvested species.
Fig. 55.9
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Disruption of food chains.
– The extinction of one species can doom its
predators, but only if the predator feeds
exclusively on this prey.
Conservation biology focus
• Preservationism: setting side select
areas as natural and underdeveloped
Nature Reserves
Population & species level conservation
• Biodiversity hot spot: small area
with an exceptional concentration of
species
• Endemic species: species found
nowhere else
• Endangered species: organism
“in danger of extinction”
• Threatened species: likely to
become endangered in the foreseeable
future
• Bioremediation: use of living
organisms to detoxify polluted systems