Grading so far….
• Midterm (n= 67 exams)– highest= 96, median = 79
– A, A-: 16 exams >= 87
– B+, B & B-: 23 exams 74-86
– C+, C & C-: 25 exams 53-73
• Essay #1
The Flux of Energy & Matter through Ecosystems
• These fluxes tie biological communities to the abiotic environment; both together are called ecosystems
• Biomass is the standing crop of living organisms and is expressed as dry matter (kg) per unit area (or energy (joules)/area in case of energy flow)
• Primary productivity (PP): rate at which biomass is produced
• Net primary productivity (NPP): energy produced by plants minus energy lost as as community respiratory heat
• Secondary productivity: rate of biomass production by heterotrophs (non-autotrophs or non-plants)
Total NPP summed for each of the Earth’s biomes- tropical rain forests & savannas highest- marine & terrestrial totals similar
Net PP from the biomass of different ecosystems- higher productivity for aquatic & non-forest for given biomass
Ultimately, the functioning and nature of biological communities depends on plant productivity
Plant net productivity varies with latitude- forests:boreal: 1025 gC/m2/yr temperate: 1400 gC/m2/yr tropical: >3000 gC/m2/yr
a) grasslands & tundra b) cultivated crops c) lakes
These relationships suggest that temperature & radiation limit NPP
What limits Primary Productivity?- for terrestrial communities, 4 possible resources and a condition (temperature)
1) Radiation from the sun …. not usually a limiting factor
Photosynthetic efficiency maxes out at only 1-3% of available radiation
…..although under optimal conditions, crop plants may achieve 3-10%
2) Carbon dioxide Some communities respond
to global increases in CO2) …..but concentration similar around earth, so can’t explain differences
….
3) Rainfall & 4) Temperature are critical factors that commonly limit primary productivitya) savannas (global sample) b) all ecosystems (Tibetan plateau)
5) Mineral nutrients (N & P especially, sometimes micronutrients) are often limiting factors where rainfall abundant
--- fertilization works!
-*limiting factors change seasonally in most ecosystems
- length of growing season & temp/water
NA broadleaf forests: Sandy soils are water- & N-limited
Aquatic systems
Mineral nutrients commonly limit production in aquatic ecosystems phytoplankton in Canadian lakes
upwelling zone (nutrient-rich)-shading effect
nutrient-poor marine area
b&c: Namibia ocean phytoplankton
Net PP rises, then declines during succession
- early successional pine vs. late successional fir
Managing a forest forCarbon sequestration?
Not surprisingly, secondary productivity is positively related to primary productivitya) zooplankton in lakes b) bacteria in water
c) Caterpillars on Daphne Island, Galapagos
Transfer efficiencies- only 10% of PP is converted in aquatic & terrestrial systems
1) Much primary productivity is not consumed by grazers and supports the decomposer community
CE= consumption efficiency
2) Not all consumed biomass is assimilated into consumer biomass
AE= assimilation efficiency
3) Some assimilated biomass is converted and lost as respiratory heat
PE= production efficiency
Trophic transfer efficiency (=CE x AE x PE) varies tremendously between trophic levels and communities (e.g., variation in 48 studies of TTE in aquatic communities)
General patterns of energy flow for different communities: - note major distinctions in % NPP flows to consumers vs. decomposers- plankton: “live consumer community”; terrestrial: low consumption
The Process of Decomposition
• release of energy and the mineralization of chemical nutrients
• gradual disintegration of dead bodies & other organic matter through biological and physical agents
• finally, breakdown into CO2, H2O & inorganic nutrients by consumers of dead organic matter
• These consumers are:– Decomposers (bacteria & fungi)– Microbivores (tiny animals feeding on detritus, bacteria & fungi– Detritivores (larger generalized feeders)
Organisms of the Terrestrial Decomposer Food Web:
- Classification by Size
- Invertebrate decomposers are very diverse
Plant decomposition depends on mutualisms for cellulose digestion with either gut microflora
(bacteria) or microfauna (protozoa in termite guts)
- Interactions between species are important and increase overall levels of decomposition, indicating some “facilitation”
(e.g., Alder leaf loss increased as more stonefly species participated)
Stoneflies are bioindicators of stream health
Consuming carrion & feces
- Carnivores scavenge & digest animal bodies with high efficiency (80%)
- Herbivore feces is less digestible but specialists recycle
isopods speed breakdown & recycling of caterpillar feces
African dung beetles were deliberated imported into Australia in 1963 to solve problem of massive accumulations of bovine feces or “cow pies”
- 300 million pies/day generated with loss of 2.5 million ha/yr under dung!
- now 20 spp introduced
Flux of matter through ecosystems: Pools of chemical elements in atmosphere, lithosphere (rocks) & hydrosphere (water)
Biogeochemistry: Study of fluxes of elements between these three compartments Components of nutrient budgets of a terrestrial & aquatic system linked by streamflow
Annual carbon budget for a ponderosa pine (Oregon)
tree rootslitter
soil carbon
Respiratory heat loss From herbivores
Units: gC/m2 & gC/m2/yr
Pathways of carbon in the ocean
All water bodies receive inputs from land, so human activities critical
- vast amounts of methane ice trapped in continental shelf sediments (19x damaging re CO2 greenhouse gas)
- small & large phytoplankton most important
Global Biogeochemical Cycles: nutrients move
around globe by winds and water -the hydrological cycle showing fluxes & reservoirs of water
Lowlights of Pollution
• Pollution: contamination of environment by human waste and by unwanted products of human activities
• Homo sapiens unique in:– using fire, fossil fuels and nuclear fission to do work & transform
landscapes– mine, smelt & transform metals– create new chemicals– alter atmosphere and climate on large scale
• We will focus on pollution of natural systems• Note that other courses in the Environmental Management
program deal with these issues in detail
Effect of 1947 DDT pesticide introduction on wild bird eggshell thicknesssome peregrine falcon populations dropped to 10% of former size; others went extinct
-Sparrowhawk eggshell thickness index -Correlated with DDT use
Environmental Economics: valuation of ecosystem services and of net loss from human activities
1) Provisioning services
Wild foods, fibers, timber, water
2) Regulating services
Regulation of climate, floods, filtering of pollutants
3) Supporting services
Primary production, nutrient cycling, soil formation
4) Cultural services
Spiritual, esthetic fulfillment, scientific, recreational
Valuation of lost services: Indonesian forest fires of 1997: 50,000 km2 burned
1) Replacement cost
Lost forest and agricultural products, clean water, tourism income, health care from smoke pollution
Increased greenhouse gas emissions 2) Contingent valuation
Public willingness to pay for different forest use scenarios
Total estimated loss of 4.5 billion $$
Agricultural Pollution: runoff of nitrates, insecticides and herbicides (ex.: nitrate leaching from soils and fertilizer; Germany)
Agricultural Pollution: managing agricultural runoff by restoring wetlands
148 wetlands under construction in Sweden to capture 40% of N before entering Baltic Sea
Managing eutrophication through biomanipulation
Objective: reduce plankton bloom due to N & P runoff in Lake Mendota, Wisconsin
- 1987: introduced two piscivorous fish spp
- zooplankton increase as predatory fish reduced by piscivores
- Larger zooplankton species bedame dominant, efficiently grazing on phytoplankton and improving water clarity
Pesticide Pollution
Biomagnification of two classes of pesticides in the Barents Sea:chlordanes & PCBs
- transport to the Arctic is from river runoff, and oceanic and atmospheric circulation
- chlordanes are biomagnified
less than PCBs
The Mauna Loa Observatory data tracking CO2 & the earth’s seasonal respiration
(from 280 ppm to 380 today, to 700 by 2100?)
Fossil Fuels & the Atmosphere
Net change- Earth’s surface temperature: - extremes in temp & rainfall to increase- map of 1951 to 1997 changes in temp
Predicted changes in the distribution of the Argentine ant by 2050
Red= improved conditions, blue = worse
CO2 emissions are from fossil fuels in the temperate developed world, but more from deforestation & burning in the tropical/underdeveloped world
Dubious US leadership in per capita carbon emissions & easy policy solutions in the transportation sector
Acid rain: pollution by sulfur dioxide & nitrogen oxides
Diatom changes in Irish lake > 1900
If pH --> 4.0-4.5, thenAl, Fe & Mn increase & toxic to organisms
Spruce forest damage…. US EPA: “allowance trading”- some success
Pollution causing thinning of ozone layer over the Antarctic: - but now a successful example of effective international policy
-Sept 24, 2006 image--blue: thinnest layer--avg size Sept 7 - Oct 6 each yr
The Montreal Protocol has led to reductions in production of damaging chemicals…. But the Kyoto Protocol lacks similar legal sanctions