ENVS 202 1st EditionFinal Study Guide: 2/3 New Concepts, 1/3 from before Midterm (*)Concepts and Causal maps* Independent and dependent variables, causation Ex. In general, how do zooplankton affect the abundance of fish? The more zooplankton, the more fishSo, fish abundance is the dependent variable, zooplankton abundance is the independent variableThe abundance of fish must depend on the abundance of zooplanktonWhat effect do fish have on the abundance of zooplankton? The more fish, the fewer zooplanktonHere, zooplankton is the dependent variable, fish abundance is the independent variableThe abundance of zooplankton must depend on the abundance of fishPositive and negative feedback loopsNegative feedback loops are self-regulating, promotes stability rather than exponential growth (like positive loops)Most predator/prey relationships are negative feedback loops- the more predators, the less prey; themore prey, the more predators – the two population sizes keep each other in checkPositive feedback loops are self-reinforcing – an increase in one variable leads to a further increase in that variable (and decrease leads to further decrease as well)The “self-reinforcing” quality has nothing to do with whether it’s beneficialEx. Snow is produced -> snows high albedo reflects a lot of sunlight -> the Earth cools -> more snow is producedMany feedback loops are interconnected or affecting others – domino effectResidence times and steady stateThe residence time is the average time a unit of something remains in a reservoirResidence time is found by dividing the volume of your reservoir by the flow rate (flux)  = V / FThe residence time is in time (days, hours, minutes, etc.)The volume is in length3 (cubic meters, cubic feet, etc.)The volume flux AKA discharge is in volume per time (m3/ s, etc.)Steady state vs Dynamic systemI = O +/-  S inputs = outputs plus or minus a change in the systemDynamic equilibriumLyme Disease story Forests in suburban areas increase the contact between bacteria, ticks, and humansMice are a natural reservoir for Lyme disease; ticks that bite them get infectedAs species richness increased, Lyme frequency decreasedEmergence of Lyme is a direct result of biodiversity lossWho were the “players” in this case?Spirochete bacterium (Borreliaburgdorferi), causative agent of Lyme diseaseTicks, which harbor and transmit the bacteriumMice, deer, raccoons, humans, squirrels, shrews, etc. are hosts to the ticksOther variables to Lyme:Number of ticks and tick hosts presentPercent of the ticks infectedHabitat destruction and fragmentation on vertebrate speciesMice feed ~800 tick larvae per acreThe percentage of tick larvae on mice that become infected is very high compared to any other hostCausal map of this system – How do ticks affect the abundance of the bacterium? The more ticks, the more bacteriaHow do ticks affect the abundance of mice? The more ticks, the fewer miceHow do mice affect the abundance of ticks? The more mice, the more ticksFeedback loop of this system – Biodiversity/Ecosystem health* Biodiversity can be measured by genetic diversity (within a species), species diversity (within communities) and community/ecosystem level diversityBiodiversity keeps up resilience and work together with ecosystem servicesTwo ways to measure biodiversity are species richness and the effective number of speciesSpecies richness and evennessSpecies richness is the number of species represented in a given area or communityIt is simply a count of species, and does not take into account the abundances of each or their relative abundancesSpecies evenness is a diversity index, and measures how close in absolute numbers different species areEffective species number and Simpson’s index Effective species number is the number of equally abundant species necessary to produce the observed value of diversityEx. There a 5 species in a given forest, 50 foxes, 2 squirrels, 2 mice, 2 frogs, and 2 snakes; even though the species richness is 5, the species evenness is so low that the effective number of species is ~1Simpson’s Index is a measure of diversity; measures the number of species present and the abundance of each speciesInvasive species, indicator speciesInvasive species are alien species which are introduced to an area outside their original homeThey have no natural enemies and spread rampantly, usually causing harm and diminishing biodiversityIndicator species are organisms that, by their presence, abundance, or chemical composition, demonstrate some distinctive aspect of the character or quality of the environmentEx. Northern Spotted Owls are indicator species because they rely upon so many other organisms and traits of Douglas-fir forests Ecosystem services“Benefits attained from nature that are critical to human health and well being”Four categories of servicesProvisioning: farming, water serviceRegulating: installing riparian zones, flood controlSupporting: nutrient cycling, soil developmentCultural: spiritual enrichment, recreationLyme disease case study In the Lyme disease study above, forests of different fragmentation levels were studiedIn fragmented forests, much of the area becomes an edge, species become more concentrated, and biodiversity typically diminishesThe smaller the forest area, the larger the density of infected ticks“Dilution effect” – larger area, larger species richness; less infected nymphsAtmosphere Greenhouse effect and greenhouse gases The major gases that make up the atmosphere are oxygen, nitrogen, carbon dioxide, and methaneGases increasing due to anthropogenic causes are carbon dioxide, methane, ozone, carbon monoxide, and nitrous oxideThe major greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and ozoneGreenhouse gases absorb longwave radiation and reradiate it into the atmosphere, warming the earth’s surfaceThe greenhouse effect is when the greenhouse gases in the atmosphere form a sort of atmospheric blanket around the earth, allowing incoming radiation to enter the atmosphere but not allowing all of it to reradiateCarbon cycle: stores, fluxes, sources of carbon Global carbon stores from highest to lowest: intermediate/deep ocean, fossil fuels, vegetation/soil/detritus, surface ocean, atmosphereCarbon fluxes, in amount gained or lost in the last year Intermediate and deep ocean: 37,100ppm + 100ppmFossil fuels: 3700ppm – 244ppmVegetation, soil, and detritus: 2300ppm +101ppm