EcologyEcology

Richard LLopis-Garcia

Ecosystem Ecology

Ecosystem EcologyEcosystem Ecology

• Why is this field important?• What is a ecosystem?• Trophic Structure • Nutrient cycles and food webs • Ecosystem Processes • Ecosystem engineers• Biomes • Global Changes

Goals for the day

Population Growth Population Growth ExerciseExercise

– 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?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 Characteristics of a PopulationPopulation

• What features can we measure of a population?

• Features:– Size– Age structure– Sex ratios– Effective population size– Birth rate– Death rate– Immigration– Emigration

Why Does Population Why Does Population Size Change?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 Density Independent ForcesForces

• Types?• Examples

– Climate– Topography– Latitude– Altitude– Rainfall– Sunlight

• In Sum: Abiotic factors– Exceptions do exist!

Density Dependent Density Dependent ForcesForces

• Types?• Examples

– Within species• Breeding spaces• Food• Mates• Foraging spots

– Between species• Predation• Parasitism• Pollinators• Competition

• In Sum: Biotic factors– Exceptions do exist!

Indeterminate FactorsIndeterminate 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 PopulationsSmall 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 Types of Population GrowthGrowth

• Exponential– Unlimited, rapid growth– Often called Malthusian– Growth without bounds

• Logistic– Growth within natural

limits– What sets that limit?– What is the limit?– More in a moment…

Exponential Population Exponential Population GrowthGrowth

• 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 Exponential Population Growth Equation Growth Equation

DerivationDerivation• Which measured

population growth components can change?

• They are:– Birth– Death– Immigration– Emigration

• Relationship between these?

Community DefinitionCommunity 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 What Structures a Community?Community?

• Abiotic– Climate– Latitude– Proximity to Ocean– Disturbances (abiotic)

• Biotic– Interspecific Interactions

• Keystone Species

– Disturbances (biotic)– (Intraspecific

Interactions?)

NichesNiches

• Definition• 1. The ecological

role played by a species in a community

General Types of General Types of CommunitiesCommunities

• Closed– sharp boundaries– abrupt ecotones– distinct associations

between species

• Open– boundaries are

vague, gradual– little or no

association between species

ab

un

dan

ce

geographic range

Abundance of a single species

ab

un

dan

ce

geographic range

Keystone SpeciesKeystone 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 SpeciesKeystone 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 DefinitionsSuccession 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 Succession Types – by HabitatHabitat

• Primary– New habitat from

barren ground

•Secondary

–Modified habitat in already areas with biotic growth

Measuring BiodiversityMeasuring Biodiversity

• Aspects of biodiversity to measure?

• Possibilities

–Richness

–Abundance

–Diversity (interaction of richness & abundance)

–Trophic Levels

–Feeding Guilds

–Taxonomic Diversity

Diversity IndicesDiversity Indices

• Used to compare sites or evaluate a single one through time

• Many many many types

• Main ones:– Shannon (diversity)– Simpson (diversity)– Rarefaction (richness)– Sorenson (comparative diversity)

Relationship Between Relationship Between Community Diversity and Community Diversity and

StabilityStability• 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 Global Distribution of BiodiversityBiodiversity

• Greatest in areas where NPP is greatest– Terrestrial: toward Equator - Why?– Aquatic: near shore, marine upwellings – Why?

Ecosystem EcologyEcosystem Ecology

• 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 Definition of an EcosystemEcosystem

• 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

= +

Trophic StructureTrophic Structure

• Definition:– Feeding relationships among the

species – Within a food web/chain– Within a single ecosystem

food chain

food web

Trophic StructureTrophic 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 Bottom Up vs. Top Down ControlDown Control

• What biotic factor determines organismal abundance at each trophic level?

Top Down?

Bottom Up?

Answer: Depends on ecosystem & species composition

Trophic StructureTrophic 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 CyclesNutrient Cycles

• How would nutrient cycles tie in with food webs?– Is there anything that is being recycled

here?

Stages in Nutrient Stages in Nutrient CyclesCycles

Unassimilated

Biomass

Biomass

Biomass

Biomass

Necromass

Materials CycledMaterials Cycled

• Nutrients– Carbon– Hydrogen– Nitrogen– Oxygen– Phosphorus– Sulfur

• Energy?– Is energy cycled?

EnergyEnergy

• 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. NutrientsEnergy 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 ProcessesEcosystem Processes

• Types?• Examples:

– Water purification– Decomposition– Biomass production– Nutrient cycling– Carbon sequestration

• An emergent property at the level of ecosystem

Biodiversity and Biodiversity and Ecosystem Processes 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 EngineersEcosystem Engineers

• Species that create novel ecosystems and habitats

• Examples?• Anything that significantly modifies the

environment– Pigs in Hawaii– Peccaries in Brazil– Beavers in Northeast– Humans everywhere– Prominent successional species?

Engineering QuestionsEngineering 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?

BiomesBiomes

• 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 PyramidEcological 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

Biome

Biosphere

Population

Community

Ecosystem

Where do Biomes

Fit?

Global ChangesGlobal Changes

• What processes are at work at present in the planet?

• Examples– 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 CauseGlobal Change Cause

• What is the Generative Force behind these changes?

US!US!

Human ImpactHuman Impact

• We have altered nearly all of the Earth that it is profitable for us to do so