Transcript ecosystem
Ecology Richard LLopis-Garcia Ecosystem Ecology Ecosystem Ecology • • • • • • • • 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: – – – – – – – – 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 • • • • 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 – – – – 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 – 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: – – – – 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 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 – – – – – – 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 Population Community Ecosystem Biome Biosphere 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