Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
An introduction to Ecosystems Lecture 11 Principles of Ecology College of Forestry, Guangxi University Eben Goodale Primary reading for this class • Jackson et al. 2001. Questions: – What kind of scientists wrote this article? What do they study and what kind of data did they collect. – What kind of marine habitats do they review? – What’s their conclusion as to what has been the most important human activity that has harmed these ecosystems? Primary reading for this class • Groups of 4. – Talk about for 10 minutes (title, abstract, figures). Circle words in abstract that are difficult and translate them in phone. – Each person write by themselves answers to questions for 10 minutes. – Switch papers with someone else in your group. Read what they wrote and criticize their paper. 10 minutes. Moving up a Layer: Definition of an Ecosystem Ecosystem Characteristics of the community: Number of species Species relative abundances Species diversity (1 + 2) Last lecture, we finished communities asking why different communities have different species diversities. Definition of an Ecosystem Arthur Tansley Ecosystem: Biological community with all the abiotic factors influencing that community ECOSYSTEM Flow of Energy through the Ecosystem; Cycling of Chemical Nutrients Biological realm high energy organic compounds Light Photosynthesis Respiration Heat Energy required energy released Motion Physical realm low energy inorganic compounds Notice similarities To a machine(机器) Moving up a Layer: Definition of an Ecosystem Ecosystem Characteristics of the ecosystem That we’ll talk about: - Productivity (biomass) - Energy flow - Nutrient flow Today’s lecture • Productivity – Gross and Net Primary Productivity • What is it? • How to measure it? • How does it vary across the globe • Food web and Energy transfer – Efficiencies of Transfer – Biomass Pyramids – Food webs and Toxins Productivity(生产力) • Productivity of an ecosystem = accumulation of carbon/biomass(生物量)/energy over time (flow) – Produced by the autotrophs, in most cases the photoautotrophs: plants or plankton. – Gross primary productivity 总初级生产力(GPP): total carbon fixed by plants. Never > 4% available sunlight. – Net primary productivity 净初级生产力(NPP): fixation – plant respiration. Usually ~ 1% available sunlight. Primary Production • Measured by: A) biomass (gr.) B) energy (kcal) Convert biomass to Energy through caliometry (热量) Bomb caliometer: burn it and see how much temp raised Ways of estimating NPP Satellite(卫星) imagery makes use of different vegetation types having different reflectance(反射率) patterns Ways of estimating NPP Most common index called NDVI: normalized difference vegetation index. Available for 1km2 for whole world ( NIR red ) NDVI ( NIR red ) Ways of estimating NPP • More local techniques include measuring amount of CO2 given off by forest. • “Eddy(涡度) covariance technique” Productivity of ecosystems Limits to productivity: abiotic factors AET Actual evapotranspiration Limits to Primary Production: Terrestrial ecosystems - Soil Moisture and Evapotranspiration rate - Length of Growing Season (depends on average temperature) - Nutrient Limitation Must be in correct chemical form and must be soluble Nitrogen (as NO3, NH4) Phosphorous (as PO4) Limits to Primary Production: Terrestrial ecosystems • Soil moisture and evapotranspiration rate also greatly effects decomposition (分解)rate. • Decomposition rates very low in cold climates. • Very high in tropics -> tropical soils tend to have very little top soil(表土); once disturbed, tropical forests more difficult to grow back. Limits to Primary Production: Marine Ecosystems -- Light - Penetrates less in turbid waters -- Nutrients Much of the sea only as productive as a desert Enriched w/ Phosphorus, Carbon and Nitrogen Nitrogen very important Upwellings bring nutrients to the surface near coasts, and highly influence fish stocks in marine ecosystems Enriched w/ Carbon and Nitrogen And iron can be, too. Limits to Primary Production: Freshwater Ecosystems -- Light -- Temperature – Can be important in small bodies of water -- Nutrients Enriched w/ Phosphorus, Carbon and Nitrogen Phosphorus strongly effects primary production Enriched w/ Carbon and Nitrogen of freshwater bodies: famous lake study by Schindler and colleagues. Eutrophication(富营养化) of lakes may be brought on by the addition of phosphate-detergents Eutrophication Nutrient inputs -> Algae, bacterial bloom -> Oxygen depletion -> Die-off of animals A freshwater example.. Where have you seen something like this? Eutrophication also a problem for marine systems Dead zones problems For more than 400 rivers A “dead zone” (light blue) at mouth of Mississippi River Before we go on…. Case study of Chapter 20: Deep sea trenches • The majority of life supported by the photoautotrophs • But in deep sea vents, no light. Chemical plumes coming up from ocean floor. • First explored in 1976…amazing discovery: so much life! • Most of these large organisms filled with chemosynthetic bacteria. Today’s lecture • Productivity – Gross and Net Primary Productivity • What is it? • How to measure it? • How does it vary across the globe • Food web and Energy transfer – Efficiencies of Transfer – Biomass Pyramids – Food webs and toxins Food webs An early foodweb by Raymond Lindeman (1942) Food webs Animals not just grouped by size or relatedness. Grasshoppers and deer at same level. Food webs Reality is complex and many species are not really just on one level (“omnivores(杂食动物)”). A food web determined by stable isotope data Food webs have some repeated patterns There are fewer species on top than there are on bottom There are fewer individuals of each species on top than on bottom This is called the trophic pyramid. Why does this happen? Energy Transfer Energy transfer is not efficient (有效率的) Secondary production • Detritus(碎屑) feeders + Herbivores • Gross assimilation(同化作用) (amount of plant/algal material eaten) reduced by the amount of energy used for maintenance (respiration etc.) = net assimilation (biomass of detritus + herbivores) = 1% of net production. Energy transfer is not efficient • Energy dissipation: energy is “wasted” with each trophic transfer • Ecological efficiency is typically only 10%, ranges from 5-20% • Ecol. efficiency depends on: metabolic efficiency, energy spent in other activities (e.g. endothermy) Much of not primary production is not consumed…. Energy transfer is not efficient • …and what is consumed is then lost into excreta (feces/urine) or respiration. • Only what is “assimilated” (turned to body tissue) is not lost. • At each transfer step, only ~5-20% of the energy left; the rest lost. Energy pyramids • Basic problem with energy dissipation(损耗): not enough energy left to go around at the top levels • Biomass/energy content vs. numbers: energy available gets smaller and energy/individual tends to get larger as we go up the chain Biomass pyramids • Biomass (dry weight), carbon, energy, number are all correlated (approximately). • Why is the English Channel biomass pyramid inverted(倒金字塔型)? High turnover… plankton(浮游生物) small and die soon, But very high rate of reproduction Question: Is the food web controlled by the top or bottom? What’s an example of “top-down” control that we’ve already talked about? Question: Are there limits to the number of trophic levels? Number of levels rarely goes beyond 4. Limited by: •Total amount of energy •Amount of disturbance •Size of the ecosystem Question: Are more complex food webs more stable? The experiments of Tilman et al. In Minnesota Top predators increase Specialist herbivores decrease, but Total # herbivores increase Plant biodiversity increases Not just plants. In same system have looked at insects Food webs and toxins • Some toxins such as heavy metals and persistent organic pollutants (POPs) are not metabolized (broken down) or excreted. • These pollutants build up in higher trophic level organisms. Food webs and toxins • Well-known example of a POP is DDT, an insecticide. Made eggshells birds thin, and many high trophic species like hawks became rare. • Major influence of Rachel Carson’s Silent Spring. Food webs and toxins • Well-known example of a POP is DDT, an insecticide. Made eggshells birds thin, and many high trophic species like hawks became rare. • Major influence of Rachel Carson’s Silent Spring. 1962 Food webs and toxins • Well-known example of a POP is DDT, an insecticide. Made eggshells birds thin, and many high trophic species like hawks became rare. • Major influence of Rachel Carson’s Silent Spring. The power of one scientist’s voice … Can it be you? Rachel Carson Food webs and toxins • Mercury is a heavy metal than bioaccumulates. • It is a neurotoxin, and affects the behavior and reproduction of high trophic organims. Food webs and toxins • It is put into air by any kind of industrial process. • Could be problem for large Asian countries like China and India Mercury emissions in 2005 From Pacyna et al. 2010 Homework • Chapter 22, 23 summaries • Myers et al. 2000 “Biodiversity hotspots of conservation priorities” Questions: - How do the authors define a hotspot? - Are there any in China and where? - How do the authors want their hotspot list to be used? Key concepts • An ecosystem is a biological community with all the abiotic factors influencing that community. • Net primary productivity (NPP) is the energy fixed minus energy used = amt of biomass per year. • NPP varies with temperature and rainfall in terrestrial ecosystems. • At each step on a food web, energy is lost. The efficiency of the transfer of energy is low. • Trophic pyramids show there are fewer species and animals at higher trophic levels.