Transcript Week 5 Lecture - Environmental Studies Program

Announcements
•
•
•
Check your syllabus with the one online to
make sure it is the right one!
No reading assignment for section this
week
Focus on your textbook
Two-minute Quiz
Imagine that you are a wetland ecologist. It is early
summer, and you and your limnologist best friend are
mapping a system of streams, rivers, and wetlands
near the coast in northern Siberia.
You ford a small, rocky, fast moving stream. True or false:
Most of the litter in this stream is likely to be highly processed.
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You follow the water downstream until it slows and pools in
an area filled with sedges and accumulated organic matter.
Are there many trees in this biome?
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You hike overland to a large river that empties into the sea.
You taste the water and it is brackish. The birding is great.
Where are you now? (multiple answers possible for this one)
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Summary from Wednesday
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aquatic ecosystems
differences between low & high order streams
production vs. biomass pyramids
lakes
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light penetration
thermal stratification and O2 content
phytoplankton and abiotic factors over the year
oligotrophic vs. eutrophic
wetlands
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biogeochemistry
Wetland Biogeochemistry
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When land is flooded, O2 gets used up by
decomposers and the soil becomes anaerobic
Demand for O2 is still high
Other minerals containing oxygen get reduced
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Reduction is when a compound gains an electron- in
this case by giving up an O2 atom
Some molecules release O2 more easily than others
O2  NO3-  Fe(OH)3  MnO2  SO42-  CO2
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If the water level drops, O2 enters the soil again,
and the reduced substances can get oxidized
Saltwater vs. Freshwater Systems
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Salt marshes
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sulfur cycling important
CO2
organic
matter
H2S
SO42-
SO42-
Saltwater vs. Freshwater Systems
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Freshwater systems
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decomposition is slow
organic matter accumulates
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storage of carbon
reduction of CO2 produces methane (CH4)
O2  NO3-  Fe(OH)3  MnO2  SO42-  CO2
Environmental Concerns in Wetlands
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Drainage
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either for agriculture and development, or to
use the available water
Pollution
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wetlands are in low-lying areas
The open ocean is most like…
A) a temperate rain forest
B) the chaparral
C) the desert
D) a Mediterranean grassland
…with regard to productivity.
Where is the ocean most productive?
Where nutrients are
available:
• near the coast
• rivers bring nutrients
• in upwelling zones
Coastal Upwelling
Coastal Upwelling
Off-shore winds blow southward.
Coastal Upwelling
Friction and the effects of the
Earth's rotation cause the
surface layer of the ocean to
move away from the coast.
Coastal Upwelling
As the surface water moves
offshore, cold, nutrient-rich
water comes up from below,
replacing it.
Why are nutrients down deep?
Why are surface waters low in nutrients?
Euphotic zone
Aphotic zone
Sediment
Dead material
sinks to the
bottom, where it
is dark and
photosynthesis is
not taking place
Coral reefs
• Coral reefs are extremely
•
•
productive
Visibility is great!
But we know that
nutrient-rich water is
murky
How is this possible?
Where are the nutrients?
Coral reefs
• Efficient cycling of nutrients
• Complex relationships
between organisms
• zooxanthellae in coral
• intricate food webs
Ecology subfields:
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Population Ecology:
• the study of individuals of a certain species
occupying a defined area during a specific time
Population Ecology
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Population density
• # of individuals of a certain species in a given area
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Population demography
• a way of assessing well-being
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proportion of males to females
birth rates
death rates
replacement of parents by next generation (fitness)
life expectancy
The Tools of Population Ecology
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Modeling
Creation of Life Tables
Why are models powerful?
You can use them to:
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synthesize information
look at a system quantitatively
test your understanding
predict system dynamics
make management decisions
Population Growth
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t = time
N = population size (number of individuals)
dN = change in population size
dt = change in time
dN/dt = rate in change of population size
r = growth constant; maximum rate of
population increase
K = carrying capacity; maximum population size
Population Growth
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Assume a fixed rate of reproduction per
individual
• for starters, let’s assume no limits on growth
• change in number of individuals over time
would be equal to the number of individuals
multiplied by a growth constant
dN
=r*N
dt
• exponential growth
Time (t)
Population size (N)
Population size (N)
Can the population really
grow forever?
Time (t)
Population size (N)
Can the population really
grow forever?
What should this curve look
like to be more realistic?
Time (t)
Population Growth
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logistic growth
• assume that as a population increases, it
becomes limited by resources
• growth rate should decline when the
population size gets large
• symmetrical S-shaped curve with an upper
asymptote
Announcements
•
Women in Science and Engineering
• “Applying to Graduate School in Sciences”
workshop and lunch Oct. 27th
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•
•
•
Check your syllabus with the one online to
make sure it is the right one!
No additional reading assignment for
section this week
Focus on your textbook reading
Bring your calculator to section
Summary from Monday
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Wetland biogeochemistry
• H2S production in brackish wetlands
• Methane (CH4) production in freshwater wetlands
Open oceans vs. coastal areas
• Population ecology
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• The power of modeling
• Modeling exponential growth
dN
=r*N
dt
• Logitstic growth
• Resources limit population growth
N
t
Population Growth
 How do you model logistic growth?
 How do you write an equation to fit that S-shaped
curve?
 Start with exponential growth
dN
=r*N
dt
Population Growth
 How do you model logistic growth?
 How do you write an equation to fit that S-shaped
curve?
 Start with exponential growth
dN
= r * N (1 –
dt
N
)
K
Population Growth

logistic growth
dN
= r * N (1 –
dt
N
)
K
Population Growth
dN
= r * N (1 –
dt

logistic growth

so, when N is much smaller than K
N
≈0
K
N
)
K
dN
= r * N (1 – 0) exponential growth
dt
Population Growth
dN
= r * N (1 –
dt

logistic growth

so, when N is much smaller than K
N
)
K
N
dN
≈0
= r * N (1 – 0) exponential growth
K
dt
 when N is equal to K
N
dN
≈1
= r * N (1 – 1) no growth
K
dt
Population Growth
dN
= r * N (1 –
dt

logistic growth

so, when N is much smaller than K
N
)
K
N
dN
≈0
= r * N (1 – 0) exponential growth
K
dt
 when N is equal to K
N
dN
≈1
= r * N (1 – 1) no growth
K
dt
 when N is much larger than K
N
dN
>1
= r * N (1 – 2) population shrinks
K
dt
What is carrying capacity?
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where births = deaths
number of individuals an area can support
through the most unfavorable time of year
population an area can support without
degradation of the habitat
What limits populations?
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Density-dependent factors:
• intra-specific competition
• food
• space
• contagious disease
• waste production
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Density-independent factors:
• disturbance, environmental conditions
• fire
• flood
• colder than normal winter
Species interactions
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How do we model them?
• Start with logistic growth
dN
= r * N (1 –
dt
dN
K
=r*N(
dt
K
N
)
K
-
dN
K-N
=r*N(
)
dt
K
N
)
K
Use this
equation for
2 different
species
Species interactions
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Population 1  N1
dN1
K1-N1
= r1 * N1 (
)
dt
K1
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Population 2  N2
dN2
K2-N2
= r2 * N2 (
)
dt
K2
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But the growth of one population should have
an effect the size of the other population
Species interactions
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New term for interactions
a12  effect of population 2 on population 1
a21  effect of population 1 on population 2
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Multiply new term by population size
the larger population 2 is, the larger its effect
on population 1 (and vice versa)
a12 * N2
a21 * N1
Species interactions

If two species are competing, the growth of one
population should reduce the size of the other

Population 1  N1
dN1
K1 - N1 - a12 N2
dt = r1 * N1
K1

Population 2  N2
dN2
K2 - N2 - a21 N1
dt = r2 * N2
K2
Species interactions

If two species are competing, the growth of one
population should reduce the size of the other
Because this is a negative term, K
is reduced

Population 1  N1
dN1
K1 - N1 - a12 N2
dt = r1 * N1
K1

Population 2  N2
dN2
K2 - N2 - a21 N1
dt = r2 * N2
K2
Species interactions
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If it is a predator-prey relationship, then the two
populations have opposite effects on one another
Because this is a negative term, K
is reduced
Prey (N1)
dN1
K1 - N1 - a12 N2
dt = r1 * N1
K1
Predator (N2)
Because this is a positive term, K
is increased
dN2
K2 - N2 + a21 N1
dt = r2 * N2
K2
Species interactions



If it is a mutually beneficial relationship, then the
two populations increase each other’s size
Because this is a positive term, K
is increased
Population 1  N1
dN1
K1 - N1 + a12 N2
dt = r1 * N1
K1
Population 2  N2
Because this is a positive term, K
is increased
dN2
K2 - N2 + a21 N1
dt = r2 * N2
K2
Problems with simple logistic growth
•
births and deaths not separated
• you might want to look at these processes
separately
• predation may have no effect on birth rate
•
no age structure
• when is a fish just a fish?
Announcements
•
•
Check your syllabus with the one online to
make sure it is the right one!
Bring your calculator to section
Summary from Wednesday
•
•
•
Modeling Logistic Growth
dN
= r * N (1 –
dt
N
)
K
Limits on populations
• Density-dependent
• Density-independent
Modeling Population Interactions
dN1
K1 - N1 - a12 N2
= r1 * N1
dt
K1
dN2
K2 - N2 + a21 N1
dt = r2 * N2
K2
Summary from Wednesday
•
•
•
Modeling Logistic Growth
dN
= r * N (1 –
dt
N
)
K
Limits on populations
• Density-dependent
• Density-independent
Modeling Population Interactions
dN1
K1 - N1 - a12 N2
= r1 * N1
dt
K1
Prey
dN2
K2 - N2 + a21 N1
dt = r2 * N2
K2
Predator
Births and Deaths
Births:
As a population increases:
• # of births will go up
• with more individuals, more
young will be born
# births = birth rate * N
•
birth rate can go down
• resources become limiting
• each mother gives birth to
fewer young
Deaths:
Background level of mortality
• mortality due to old age
fundamental death rate = f(N)
(df)
Density-dependent mortality
• mortality due to crowdedness
• competition for resources
death rate = df * (
deaths = df * (
N
K
N
K
)
)*N
Problems with simple logistic growth
•
births and deaths not separated
• you might want to look at these processes
separately
•
no age structure
• age matters for reproduction
% of Total Population
Different populations can have
different age structures
Age
% of Total Population
Age structure affects reproduction
growing rapidly
not replacing itself- population is
likely in decline
window of reproduction
Age
The Tools of Population Ecology
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•
Modeling
Creation of Life Tables
Life Tables
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Way of looking at age structure of
population
Trends and dynamics
Provides quantitative information about:
• life expectancy
• proportion living
• reproductive output
Static vs. Cohort-based Life Tables
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Static
• analyze age structure of current population
• assumes that one generation is similar to the
next in terms of dynamics
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Cohort-based (cohort= group)
• follow a single generation through its entire
lifespan
• accurately describes the experience of that
generation only
Grasshopper Life Table
Life
stage
# at
start
(nx)
Proportion
surviving at
start
(lx)
Proportion
dying in
stage
(dx)
Mortality
rate in
stage
(qx)
Proportion
alive in
stage
(Lx)
Life
expectancy
(Ex)
Egg
44,000
1.00
0.92
0.92
0.54
0.74
Inst. 1
3,513
0.08
0.02
0.28
0.07
2.55
Inst. 2
2,529
0.06
0.01
0.24
0.05
2.35
Inst. 3
1,922
0.04
0.01
0.24
0.04
1.94
Inst. 4
1,461
0.03
0.00
0.11
0.03
1.39
Adult
1,300
0.03
0.03
1.00
0.01
0.50
Opportunists vs. Competitors
Do well in variable or
unpredictable climate
• High mortality
• Population boom and
bust cycles
• Not very competitive
• Rapid development
• Early reproduction
• Small body size
• Single reproductive effort
• Short lifespan
•
Do well with constant or
predictable climate
• Lower mortality
• Population in equilibrium
near carrying capacity
• Very competitive
• Slow development
• Late reproduction
• Large body size
• Repeated reproduction
• Longer lifespan
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Survivorship Curves
Competitors (K-selected)
Large mammals,
some plants
Invertebrates, fish
Opportunists (r-selected)
(Life stage)
Seasonal variation in life history
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Daphnia retrocurva
Spring morphology:
Summer morphology:
Round body, more eggs
protective spikes,
fewer eggs
To avoid predation, natural selection favors a protective
summer morphology that reduces egg production
Why different life strategies?
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More ways to live in an environment and
use its resources
Another way to say this: filling niches
What is a niche?
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A niche is the total of all biotic and abiotic
factors that determine how an organism
fits into its environment.
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Where and how does an organism live and
function?
• habitat
• role in community