Ecology Ecology Richard LLopis-Garcia Ecosystem 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 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: –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 –Climate –Topography –Latitude –Altitude –Rainfall –Sunlight In Sum: Abiotic factors –Exceptions do exist!

Density Dependent Forces Types? Examples –Within species Breeding spaces Food Mates Foraging spots –Between species Predation Parasitism Pollinators Competition 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 –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: –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 –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

General Types of Communities Closed –sharp boundaries –abrupt ecotones –distinct associations between species Open –boundaries are vague, gradual –little or no association between species abundance geographic range Abundance of a single species abundance 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: –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 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 = +

Trophic Structure Definition: –Feeding relationships among the species –Within a food web/chain –Within a single ecosystem food chain food web

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? Bottom Up? Answer: Depends on ecosystem & species composition

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 Necromass

Materials Cycled Nutrients –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: –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 –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 BiomeBiosphere Population Community Ecosystem Where do Biomes Fit?

Global 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 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