Transcript video slide - Phoenix College

•
Aquatic biomes account for the largest part of the biosphere in terms
of area
•
They can contain fresh water or salt water (marine)
•
Oceans cover about 75% of Earth’s surface and have an enormous
impact on the biosphere
Stratification of Aquatic Biomes
• Many aquatic biomes are stratified into zones or layers
defined by light penetration, temperature, and depth
•
The upper photic zone has
sufficient light for
photosynthesis while the
lower aphotic zone receives
little light
•
The organic and inorganic
sediment at the bottom of all
aquatic zones is called the
benthic zone
•
The communities of
organisms in the benthic
zone are collectively called
the benthos
•
Detritus, dead organic
matter, falls from the
productive surface water and
is an important source of
food
In which zone are the
photosynthesizers
going to live?
Light penetration &
attenuation in water
• In oceans and most lakes, a temperature boundary called
the thermocline separates the warm upper layer from the
cold deeper water
• Many lakes undergo a semiannual mixing of their waters
called turnover
• Turnover mixes oxygenated water from the surface with
nutrient-rich water from the bottom
Seasonal Changes in Lakes
• Oxygen depletion!
• How does this happen?
Oligotrophic lakes are nutrientpoor and generally oxygen-rich
Eutrophic lakes are nutrient-rich and
often depleted of oxygen at depth
Population Ecology
Counting Sheep
• A small population
of Soay sheep
were introduced to
isolated Hirta
Island (Scotland) in
1932
• They provide an
ideal opportunity to
study changes in
population size on
an isolated island
with abundant food
and no predators
Soay Sheep population fluctuations
1955- 2003
• Population ecology is the study of populations in relation
to environment, including environmental influences on
density and distribution, age structure, and population size
• A population
is a group of
individuals of
a single
species living
in the same
general area
• Population Density, the number of individuals per unit
area or volume, is the result of an interplay between
processes that add individuals to a population, and those
that remove individuals
Patterns of Dispersion
•
Environmental and social factors
influence spacing of individuals in a
population
•
In a clumped dispersion, individuals
aggregate in patches
•
A clumped dispersion may be
influenced by resource availability and
behavior
•
A uniform dispersion is one in which
individuals are evenly distributed
•
It may be influenced by social
interactions such as territoriality
•
In a random dispersion, the position of
each individual is independent of other
individuals
•
It occurs in the absence of strong
attractions or repulsions; relatively
uncommon in nature!
Demographics
•
Demography is the study of the vital statistics of a population and how
they change over time
•
Death rates and birth rates are of particular interest to demographers
•
A survivorship curve is
a graphic way of
summarizing the survival
pattern of a population
based by age
•
The survivorship curve for
Belding’s ground squirrels
shows a relatively
constant death rate
• Survivorship curves can be classified into three general types:
–
Type I: low death rates during early and middle life, then an increase
among older age groups
–
Type II: the death rate is constant over the organism’s life span
–
Type III: high death rates for the young, then a slower death rate for
survivors
Life history traits are products of natural selection
• An organism’s life history comprises the traits that affect
its schedule of reproduction and survival:
– The age at which reproduction begins
– How often the organism reproduces
– How many offspring are produced during each
reproductive cycle
• Organisms have
finite resources,
which may lead to
trade-offs between
survival and
reproduction
The males of many bird species provide no parental care. If this were true
for the European kestrel, how would the experimental results differ from
those shown above?
Per Capita Rate of Increase – A Little Math
• If immigration and emigration are ignored, a population’s
growth rate (per capita increase) equals birth rate minus
death rate
B=
N, population size
D=
• Most ecologists use differential calculus to
express population growth as growth rate at a
particular instant in time:
N 
t rN
Where:
N = population size,
t = time, and
r = per capita rate of increase = birth – death
Exponential Growth – “J”-shaped growth curves
• Exponential population growth is population increase
under idealized conditions
• Under these conditions, the rate of reproduction is at its
maximum, called the intrinsic rate of increase
dN 
rmaxN
dt
• Different species
have different rmax’s!
• The J-shaped curve of exponential growth
characterizes some rebounding populations
The logistic model describes how a population
grows more slowly as it nears its carrying capacity
• Exponential growth
cannot be sustained
indefinately in any
population
• A more realistic
population model
limits growth by
incorporating carrying
capacity
The Logistic Growth – “S”-shaped growth curves
• Carrying capacity (K) is the maximum population size the
environment can support
• In the logistic population growth model, the per capita
rate of increase declines as carrying capacity is reached
• We construct the logistic
model by starting with the
exponential model and
adding an expression that
reduces per capita rate of
increase as N
approaches K
(K  N)
dN
 rmax N
dt
K
Table 53-3
The Logistic Model and Real Populations
• The growth of laboratory
populations of paramecia
fits an S-shaped curve
• These organisms are
grown in a constant
environment lacking
predators and competitors
(K  N)
dN
 rmax N
dt
K
• Some populations
overshoot K before
settling down to a
relatively stable density
• Some populations
fluctuate greatly and
make it difficult to
define K
(K  N)
dN
 rmax N
dt
K
Population Change and Population Density
• In density-independent populations, birth rate
and death rate do not change with population
density
• In density-dependent populations, birth rates
fall and death rates rise with population density
The Logistic Model and Life History Strategies
• K-selection, or
density-dependent
selection, selects for
life history traits that
are sensitive to
population density
• r-selection, or
density-independent
selection, selects for
life history traits that
maximize reproduction
Competition for Resources
• In crowded populations, increasing population
density intensifies competition for resources
and results in a lower birth rate
Many factors that regulate population growth are
density dependent
• There are two general questions about
regulation of population growth:
– What environmental factors stop a population
from growing indefinitely?
– Why do some populations show radical
fluctuations in size over time, while others
remain stable?
Explaining Population Dynamics: Hudson
Bay Trading Company
• Bought animal furs from
traders.
• Distributed them to
Eastern seaboard and
Europe.
• Kept records of pelts
bought each year.
• One fur they bought was
the snowshoe hare.
• Let’s see how the number
of furs varied…
Why the fluctuations in abundance?
• Hypothesis 1: Hare
populations fluctuate with
their food supply.
• Hypothesis 2: Hare
populations are kept down
by their predators.
• Prediction 1: Hare food
supply should increase
and decrease along with
hare densities.
• Prediction 2: Their
predator, the lynx, should
increase as the hare
increases, and decrease
following the decline of the
hare.
• We cannot test prediction
1, because we have no
record of past food
supplies.
Conclusion?
• Lynx may indeed
control hare
populations.
• But…
What would the graph look like if hare populations
were not controlled by lynx (hyp. 2), but were in
fact controlled only by food availability (hyp. 1)?
Problems with the lynx/hare data
• Lynx/hare graph would look the same, whether the hare
population densities were controlled by lynx predation, or
by food availability.
• In fact, maybe the cycling was more tied to fashion trends
in Paris, than to biological reasons. (When hare furs are
popular, the trappers catch more hare because they are
worth more.)
• The main problem here: the lynx/hare data are
correlational, and therefore may not be
causal. (Maybe the trends are caused by a third
unknown factor.)
Be wary of correlations!
• Correlations indicate
relationships, but do not
guarantee cause and
effect!
• Often, both variables
are affected by a third
variable you aren’t
considering.
• Frogs and wine
Ice cream and suicide
• Suicide is highest in
areas where ice cream
consumption is lowest.
• What is the third
variable affecting the
other two?
• Weather!
Fig. 53-22
6
5
4
3
2
The Plague
1
0
8000
B.C.E.
4000 3000
2000 1000
B.C.E. B.C.E. B.C.E. B.C.E.
0
1000
C.E.
2000
C.E.
Human population (billions)
7
• Though the global population is still growing,
the rate of growth began to slow during the
1960s
Regional Patterns of Population Change
• To maintain population stability, a regional
human population can exist in one of two
configurations:
– Zero population growth =
High birth rate – High death rate
– Zero population growth =
Low birth rate – Low death rate
• The demographic transition is the move from
the first state toward the second state
Most of the current global population growth is concentrated in developing
nations
The demographic transition is associated with an increase in the quality of
health care and improved access to education, especially for women
• The demographic transition is associated with
an increase in the quality of health care and
improved access to education, especially for
women
• Most of the current global population growth is
concentrated in developing countries
Age Structure
•
Age structure is the relative number of individuals at each age
•
Age structure diagrams can predict a population’s growth trends,
illuminate social conditions, and help to plan for the future
Global Carrying Capacity
• How many humans can the biosphere support?
• The carrying capacity of Earth for humans is uncertain
• The average current estimate is 10–15 billion
Limits on Human Population Size
• The ecological footprint concept summarizes
the aggregate land and water area needed to
sustain the people of a given nation
• It is one general measure of how close we are
to the carrying capacity of Earth
• Countries vary greatly in footprint size and
available ecological capacity
All possessions of
an average household
in India
(population: 1,166,000,000)
All possessions of
an average household in
the United States
(population: 305,000,000)
Ecological demand (hectares per person)
ECOLOGICAL FOOTPRINTS
16
14
12
New Zealand
10
USA
Germany
Netherlands
Japan
Norway
8
6
Australia
Canada
Sweden
UK
Spain
4
World
China
India
2
0
0
2
6
4
10
12
8
Available ecological capacity
(hectares per person)
14
16
Fig. 53-27
The amount of photosynthetic products
that humans use around the world
Log (g carbon/year)
13.4
9.8
5.8
Not analyzed
Factors that affect human population growth
• Culture and Attitude
• Poorest nations have the highest growth
rates.
• Why?
• Poorly educated women.
• Rich people have fewer children than poorer
people.
• This trend extends between countries, or
within the US despite any ethnic differences.
• Some religions advocate for large families.