ecosystem

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Transcript ecosystem

Ecology
Richard LLopis-Garcia
Ecosystem Ecology
Ecosystem Ecology
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Goals for the day
Why is this field important?
What is a ecosystem?
Trophic Structure
Nutrient cycles and food webs
Ecosystem Processes
Ecosystem engineers
Biomes
Global Changes
Population Growth Exercise
– Describe the curves – what was happening when?
– When would you get population oscillations in the
Logistic Model?
– Approximate K for humans?
What is a Population?
• Components?
• Definition :
– One species
– One area
– Isolated from other
areas
– Able to interbreed
• Example:
Only minimal genetic
flow, at most
Characteristics of a Population
• What features can we measure of a population?
• Features:
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Size
Age structure
Sex ratios
Effective population size
Birth rate
Death rate
Immigration
Emigration
Why Does Population Size
Change?
• Density Independent Forces
– Forces that are at work irrespective of the
population density
• Density Dependent Forces
– Forces that vacillate depending on the population
density
Density Independent Forces
• Types?
• Examples
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Climate
Topography
Latitude
Altitude
Rainfall
Sunlight
• In Sum: Abiotic factors
– Exceptions do exist!
Density Dependent Forces
• Types?
• Examples
– Within species
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Breeding spaces
Food
Mates
Foraging spots
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Predation
Parasitism
Pollinators
Competition
– Between species
• In Sum: Biotic factors
– Exceptions do exist!
Indeterminate Factors
• Most influences are pretty constant and
Deterministic
• Opposite of deterministic factors is
Stochastic forces
• Examples
– Environmental: Droughts, floods, asteroids,
volcanoes, fires, etc.
– Demographic: Crash in effective population
size, series of single sex born, etc.
Small Populations
• Usually at great risk
• Why?
-Small population size
-Small genetic diversity
-Highly susceptible to
stochastic forces
-Poor competitors with resident
biota
•Severely limited adaptability
Types of Population Growth
• Exponential
– Unlimited, rapid growth
– Often called Malthusian
– Growth without bounds
• Logistic
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Growth within natural limits
What sets that limit?
What is the limit?
More in a moment…
Exponential Population
Growth
• Examples of this?
– Think close to home
• Often an unnatural
occurrence
• Conditions under which this
occurs naturally
– Introduced species
– Nutritionally enriched
environments
– Cultural innovations?
Exponential Population
Growth Equation Derivation
• Which measured population
growth components can
change?
• They are:
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Birth
Death
Immigration
Emigration
• Relationship between these?
Community Definition
• “an association of
interacting populations,
usually defined by the
nature of their
associations or the habitat
they use”
• Key features:
– Several species
– One area
What Structures a
Community?
• Abiotic
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Climate
Latitude
Proximity to Ocean
Disturbances (abiotic)
• Biotic
– Interspecific Interactions
• Keystone Species
– Disturbances (biotic)
– (Intraspecific Interactions?)
Niches
• Definition
• 1. The ecological
role played by a
species in a
community
– sharp boundaries
– abrupt ecotones
– distinct associations
between species
• Open
– boundaries are vague,
gradual
– little or no association
between species
abundance
• Closed
abundance
General Types of
Communities
Abundance of
a single species
geographic range
geographic range
Keystone Species
• The most important species
– Structures the community
– What is the origin of the term?
• Contributes greatest amount to ecosystem
functioning
– Controlling herbivores
• Terminal Predators are most commonly thought of here
– Decomposition
– Produces greatest amount of biomass?
Keystone Species
• Usually thought of as Strong interactors
– Tightly woven into the fabric of the food web
– The species that is the very strongest
interactor
• Definition #2:
– The species that, when removed, leads to a
total breakdown of the food web
Succession Definitions
• Chronological
distribution of
organisms within an
area
• The sequence of
species within a
habitat or community
through time
• Shared:
– Time
– Single area
Succession Types – by Habitat
• Primary
– New habitat from
barren ground
•Secondary
–Modified habitat in already
areas with biotic growth
Measuring Biodiversity
• Aspects of biodiversity to
measure?
• Possibilities
–Richness
–Abundance
–Diversity (interaction of
richness & abundance)
–Trophic Levels
–Feeding Guilds
–Taxonomic Diversity
Diversity Indices
• Used to compare sites or evaluate a single one
through time
• Many many many types
• Main ones:
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Shannon (diversity)
Simpson (diversity)
Rarefaction (richness)
Sorenson (comparative diversity)
Relationship Between Community
Diversity and Stability
• Stability components
– Resistance
– Resilience
– Recovery speed
• Biodiversity has been
thought to influence
Stability
– Croplands – Unstable
– Tropics – Stable
• Jury still out
– preliminary work seems to
support this
Global Distribution of
Biodiversity
• Greatest in areas where NPP is greatest
– Terrestrial: toward Equator - Why?
– Aquatic: near shore, marine upwellings – Why?
Ecosystem Ecology
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Why is this field important?
What is a ecosystem?
Trophic Structure
Nutrient cycles and food webs
Ecosystem Processes
Ecosystem engineers
Biomes
Global Changes
Definition of an Ecosystem
• Properties?
• A system where populations of species group
together into communities and interact with each
other and the abiotic environment.
• The entire biological & physical content of a
biotope
– the smallest geographical unit that can be delimited by
convenient boundaries
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Trophic Structure
• Definition:
– Feeding relationships among the species
– Within a food web/chain
– Within a single ecosystem
food web
food chain
Trophic Structure
• Influenced by resource availability
– Both biotic and abiotic
• More productive areas tend to have greater trophic
diversity (as well as species diversity – NPP example)
• Connectivity
– Degree and number of associations between species
– What type of species is likely to have the greatest level of
connectivity in the community?
Bottom Up vs. Top Down
Control
• What biotic factor determines organismal
abundance at each trophic level?
Top Down?
Answer:
Depends on
ecosystem &
species
composition
Bottom Up?
Trophic Structure
• Influenced by resource availability
– Both biotic and abiotic
• More productive areas tend to have greater trophic
diversity (as well as species diversity – NPP example)
• Connectivity
– Degree and number of associations between species
– What type of species is likely to have the greatest level of
connectivity in the community?
Nutrient Cycles
• How would nutrient cycles tie in with food
webs?
– Is there anything that is being recycled here?
Stages in Nutrient Cycles
Unassimilated
Biomass
Biomass
Biomass
Biomass
Necromass
Materials Cycled
• Nutrients
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Carbon
Hydrogen
Nitrogen
Oxygen
Phosphorus
Sulfur
• Energy?
– Is energy cycled?
Energy
• Does energy
cycle?
• What defines a
cycle?
• Is energy lost /
gained in an
ecosystem?
– How is it lost?
– How is it gained?
Predator
Herbivore
Producers
Energy vs. Nutrients
• Nutrients cycle
– Conservation of material
– A lot of new material does not
generally enter an ecosystem
• Energy flows
– A one-way movement of energy
through an ecosystem
– Energy originates by gathering
solar energy
– Energy lost through growth and
metabolism
Predator
Herbivore
Producers
Ecosystem Processes
• Types?
• Examples:
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Water purification
Decomposition
Biomass production
Nutrient cycling
Carbon sequestration
• An emergent property at the
level of ecosystem
Biodiversity and
Ecosystem Processes
•  Biodiversity   ecosystem processes
– Why so?
• Trophic redundancy
– Have multiple species at the same trophic level
– Performing similar ecological roles
– Could lose a few species without major changes
Ecosystem Engineers
• Species that create novel ecosystems and habitats
• Examples?
• Anything that significantly modifies the environment
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Pigs in Hawaii
Peccaries in Brazil
Beavers in Northeast
Humans everywhere
Prominent successional species?
Engineering Questions
• Can we substitute species as ecosystem
engineers?
– Are cows good bison substitutes?
– Argument for introducing cattle on Midwest rangeland
• Are these just keystone species?
– What do you think?
Biomes
• Definition:
• From Dictionary.com:
– A major regional or global biotic
community
– Chiefly characterized by the dominant
forms of plant life and the prevailing
climate
• Examples:
– Eastern Deciduous Forest, Arctic
Tundra, Grasslands, etc.
Ecological Pyramid
• Trends down pyramid:
– Increase in geographic scale
– From single species to multiple
species
– Increasing number of ecological
factors that may be influential
– Decreasing certainty in results
Population
Community
Ecosystem
Biome
Biosphere
Global Changes
• What processes are at work at present in the
planet?
• Examples
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Global Climate Change
Acid Rain
Spread of Pollution and Toxins
Spread of Biotic Pollution
• How are these occurring?
– What is the generative force behind them?
Global Change Cause
• What is the Generative
Force behind these
changes?
US!
Human Impact
• We have altered nearly all of the Earth that it is
profitable for us to do so