Transcript Week 6 Lecture - Environmental Studies Program

Announcements
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Midterm Exam: Wednesday, Nov 3rd
Review this week in section:
• Bring questions to section
Summary from Friday
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Building a model to show population
interactions
Age structure affects population
Life tables
• static vs. cohort-based
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Life strategies
• opportunists vs. competitors
• seasonal variation in life strategy within a
species
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Niche
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
Success
potential
survival, but
stressed
intolerant
potential
survival, but
stressed
optimum
intolerant
Environmental variable (Temperature, for example)
Niche in n-variable hyperspace
Fundamental vs. Realized Niche
Fundamental niche: where a
species could live
Realized niche: with competition
from other species, where a
species does live
Niche Partitioning in Animals
• Species divide up an apparent niche
perennial grasses
annual grasses
Convergent Evolution
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Organisms adapt to fill open niches
Organisms in two different environments
that are not closely related may have the
same “job” and similar anatomy
Selection minimizes
competition
Two species living
separately.
Two species living
together.
Species interactions
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Competition
Mutualism
• both species benefit
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Commensalism
• one benefits, other is unaffected
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Parasitism
• one benefits, one loses
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Predator-Prey
Parasitism
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microparasites vs. macroparasites
Biotropic
• thrive on live hosts only
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Necrotropic
• can benefit even if host dies
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Parasitoids
• always kill their host
Predator-Prey Relationships
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Prey defenses
• coevolution
• as predator evolves, prey evolves to evade it
Predator-Prey Relationships
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Prey defenses
• coevolution
• as predator evolves, prey evolves to evade it
• warning coloration and mimicry
• aposematic “away signal” = bright red and yellow
• some mimics very toxic, others harmless
Predator-Prey Relationships
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Prey defenses
• coevolution
• as predator evolves, prey evolves to evade it
• warning coloration and mimicry
• aposematic “away signal” = bright red and yellow
• some mimics very toxic, others harmless
• camouflage
• blending in
Predator-Prey Relationships
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Prey defenses
• coevolution
• as predator evolves, prey evolves to evade it
• warning coloration and mimicry
• aposematic “away signal” = bright red and yellow
• some mimics very toxic, others harmless
• camouflage
• blending in
• moment-of-truth defenses
• large or startling displays
Predator-Prey Relationships
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Optimal Foraging Theory- describes how
prey are chosen
• small prey provide little food, but they are
easy to hunt
• large prey provide a lot of food, but they are
more difficult to hunt
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Trophic Cascades
Food webs can be complex
Prey Selection
Trophic Cascade
predator/
tertiary consumer
Eagles
4th trophic level
predator/
secondary consumer
Foxes
3rd trophic level
herbivore/
primary consumer
Mice
2nd trophic level
autotroph/
primary producer
Plants
1st trophic level
Trophic Cascade
if eagles go
extinct, what
could happen
to…
foxes?
mice?
plants?
Eagles
4th trophic level
Foxes
3rd trophic level
Mice
2nd trophic level
Plants
1st trophic level
Trophic Cascade
If a new predator
on mice is
introduced, what
could happen to…
mice?
foxes?
plants?
eagles?
Eagles
4th trophic level
Foxes
3rd trophic level
Mice
2nd trophic level
Plants
1st trophic level
Trophic Cascade
If drought caused
a dip in plant
production, what
would happen to…
mice?
foxes?
eagles?
Eagles
4th trophic level
Foxes
3rd trophic level
Mice
2nd trophic level
Plants
1st trophic level
Simplified Temperate Forest Food Web
To which trophic level do these organisms belong?
Eagle
Wolf
Deer
Oak seedling
Fox
Shrews
Rabbit
Caterpillars
Grasses
Herbs
Optimal Foraging
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Predators tend to target dominant prey
• enhancement of diversity
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What about herbivores?
• don’t necessarily eat dominant plants
• plants have secondary compounds and
chemical toxins that taste bad
herbivores
may target
tasty rare
plants
Community Ecology
A community is a group of living organisms
that occupy a certain area and interact
with one another.
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Niche partitioning
Species interactions
Food web dynamics
Environmental variation/disturbance
• driver of diversity
Do communities change?
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What we see now wasn’t always here
• communities do change
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Spatial scale is important
• global vs. local change
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Time scale is important
• long term change
• measured in 10’s of thousands of years or more
• short term change
• measure on a decadal time scale
Announcements
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Look at course webpage for study guide
Read Enserink et al. articles “Biological Invasions
Sweep In…” for section next week (after
midterm)
Please let know today if you have special needs
for the exam
Note on syllabus: problem set will be handed out
Nov. 10th
Office hours: Monday after class
Summary from Wednesday
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Niche partitioning
Convergent evolution
Community ecology
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Species interactions
Optimal foraging theory and prey selection
Herbivory and plant selection
Trophic cascades and food web dynamics
Change over time
How do we detect long-term change?
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Sediment cores
Ice cores
Pollen records
Fossil records
Packrat middens
Tree rings
Isotopes
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Isotope: element where atoms have a different # of
neutrons
O16
Lighter and common
= proton
= neutron
O18
Heavy and rare
Isotopes
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Isotope: element where atoms have a different # of
neutrons
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Can be used to detect global-scale long-term change
Isotopes
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Isotope: element where atoms have a different # of
neutrons
Can be used to detect global-scale long-term change
• Total oxygen pool is composed of:
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• Mix of O16 and O18
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Fractionation during seawater evaporation
• O16 evaporates easily
• O18 gets left behind
Isotopes in Sediment Cores
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Sediment contains foraminiferans
• microscopic sea creatures
• O16/O18 in tests reflects that of seawater
• live on sediment or sink to bottom when dead
Isotopes in Sediment Cores
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Sediment contains foraminiferans
• microscopic sea creatures
• O16/O18 in tests reflects that of seawater
• live on sediment or sink to bottom when dead
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If the climate cools…
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ice sheets will expand
ice comes from rain from evaporated seawater
evaporated seawater is high in O16
seawater left behind high in O18
therefore, high O18 in ocean = cold conditions
Variation in Ocean O18
more negative values: less O18 and warmer conditions
less negative values: more O18 and colder conditions
Ice core measurements:
• thickness of layers
• physical properties
• dust and silt
• conductivity
• trapped air (CO2,
NOx, and O2)
• ions (K+, Ca2+, NO3-)
• isotopes
Pollen records
can be used to
detect long term
change on a
regional scale.
Trees can
migrate 200-300
miles in 1000
years.
Fossil Pollen – Silver Lake, OH
J. G. Ogden III, 1966.
Dendrochronology:
• exact calendar dating
using annual growth rings
in wood
Dendroclimatology:
• using tree rings to look at
past climate
• very old trees can be
used to get the longest
history
• Bristlecone pine
(Pinus longaeva)
White Mountains, CA
~5000 years old
Soil
development
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Weathering of
primary minerals
• nutrients become
more available
• in old soils, the
nutrients get
leached out
Formation of clays
• Accumulation of
organic matter
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Long-Term Change
Shifts in climate
Change in
vegetation
Change in animal
populations
Change in soil
development
Long-Term Change
Shifts in climate
Change in
vegetation
Change in animal
populations
Change in soil
development
Community
change
Short-Term Change
Succession
Textbook definition:
“a change in species that occupy a given area,
with some species invading and becoming
more numerous while others decline in
population and disappear”
Can be thought of as the replacement of
one community by another
Primary vs. Secondary Succession
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Primary:
• Community gets established on a new surface
• Lava flow
• River sandbar
• Glacial moraine
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Secondary:
• Recovery following disturbance
• Fire
• Flood
• Post-agriculture
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Primary Succession
• Can take hundreds
to thousands of
years
• Soil must develop
• New species must
come from
somewhere else
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Secondary Succession
• Faster
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Primary Succession
• Can take hundreds
to thousands of
years
• Soil must develop
• New species must
come from
somewhere else
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Secondary Succession
• Faster
Early vs. Late Succession Species
Early
• shade intolerant
• nutrient
demanding
• short-lived
• poor competitors
Late
• shade tolerant
• adapted to lower
nutrient conditions
• long-lived
• good competitors
Classic Succession
Clements’ idea of “climax community”
• eventually, a given system reaches a
predictable steady-state
• independent of the early succession
community
Mixed Beech-Maple Forest
Oak-Hickory
Oak woodland
Oak forest
Willow shrub
Sumac-Pine
Pine forest
Cattail marsh
Broomsedge
Poplars
Aquatic plants
Aster-Goldenrod
Dune grass
Annual weeds
Swamp
Old field
Sand dune
Bird succession