Lecture 1 Ecosystems: Summary of Readings

Summary of Beyond Global Warming: Ecology and Global Change by Peter M. Vitousek 1993

Global Anthropogenic Environmental Changes caused due to the increasing size and resource use of human population.

  1. Present Major Global Changes
  2. Increasing concentrations of CO2 in atmosphere
  3. Alterations in biogeochemistry of global Nitrogen Cycle
  4. Decreasing natural land cover

Other Documented Global Changes

  1. Widespread distribution of synthetic organic compounds (DDT,CFC,PCB)
  2. Alterations in biogeochemistry of global element(Sulfur, Phosphorous) Cycle
  3. Harvesting of populations of species by humans.
  4. Biological invasions of non-native species.

Dominant Long Term Global Changes

  1. Climate Change
  2. Loss in biodiversity

These ecological changes are global and every ecosystem on earth has been affected (as all ecosystems are interlinked interconnected interdependent).
The general public thinks these changes and their causes are not certain.
There is some uncertainty because of high level of complexity of the interaction and feedbacks of the “earth system”.
There is a consensus in the scientific community that there is enough data and evidence to prove that these global changes are happening and are due to human activities.
Climate change (Global warming) is not the most significant anthropogenic environmental change. It is growth in human population and use of resources.

To handle the various components of global environmental change, ecologists must

  1. Get active: communicate the problem and its cause to the public
  2. Get connected: Collaborate with people from outside the natural sciences and academia to change human-environment interactions
  3. Get real: Work with environmental change and simultaneously reduce consequences
  4. Get involved with The Ecological Society: to make public policy and communicate knowledge about anthropogenic environmental change.
  5. Don’t get down: We cannot stop global change but we can still make a difference individually and collectively.

Increasing concentrations of CO2 in atmosphere
[CO2] increased by 26% after 1800 primarily due to combustion of fossil fuels causes climate change affecting all biota on earth.
The rate of increase in [CO2] is 5 to 10 times more than that in the last 160,000 yrs.
We know this by measuring the [CO2] in air bubbles trapped in Greenland and Antarctic ice which were formed 160,000 years ago.

Major Cause of increasing [CO2]

  1. Combustion of fossil fuels
  2. Deforestation

Increase in [CO2] comes from fossil fuel combustion and not deforestation.
How do we know that the increasing [CO2] comes from burning fossil fuels?
We release 5.6 X1015 g (5.6 Giga Tons) of CO2-C into the atmosphere annually from combusting fossil fuels. Annual increase in [CO2] in the atmosphere is 3.5X1015g (5.6 Giga Tons) of CO2-C. (The rest and that released from deforestation is absorbed by oceans* Confirm with Prof Currie)

The atmosphere has a particular amount of C14. C14 has a half life of ≈6000 years. Fossil fuels are millions of years old and hence have no C14, and so their combustion releases CO2 without C14. There by diluting the existing concentration of CO2 with C14 in the atmosphere. The concentration of CO2 with C14 has been measured to decrease over the last decades.

Effects of Increasing [CO2] in atmosphere

  1. Melting of polar Ice Caps and flooding of low lying areas.
  2. Increases the growth rate of C3 plants more than C4 plants if H20 and nutrients are not limiting changing the structure and function of ecosystems.
  3. Plants produce nutrient poor tissue which will affect heterotrophs (species, populations and communities of herbivores, carnivores and decomposers).
  4. Changes the amount of Aragonite (CaCO3) being formed causing changes to coral reefs.

Alterations in biogeochemistry of global Nitrogen Cycle
Natural annual N2 fixation
Terrestrial Ecosystems 100Tg
Marine Ecosystems 5-20Tg
Lightning Fixation 10Tg

Alterations in biogeochemistry of global Nitrogen Cycle caused by

  1. Annual anthropogenic N2 fixation
  2. Nitrogen fertilizers 80Tg
  3. Cultivation of legumes 30Tg
  4. Combustion of fossil fuel 25Tg

Anthropogenic Nitrogen mobilization from long term storage pools

  1. Biomass burning
  2. Draining wetlands
  3. Land use

More annual anthropogenic Nitrogen fixation than annual natural nitrogen fixation

Consequences of alterations in biogeochemistry of global Nitrogen Cycle
1.Changes in the chemistry of atmosphere
Increasing concentration Nitrous Oxide in atmosphere leading to climate change because N2O is stable green house gas.
Production of reactive nitrogen oxides cause formation of ozone in troposphere and make NH3 volatile

2.Changes in the chemistry of aquatic ecosystems
Reduction in water quality and Eutrophication
Higher rates of de-nitrification to N2 which is harmless

3.Changes in chemistry of terrestrial ecosystems
Increase in Carbon storage
Increase in Nitrogen deposition
Increase in Nitrate leaching
Nitrogen containing trace gas emission

4.Changes in biodiversity
In many ecosystems Nitrogen is a limiting nutrient. Increasing its concentration may favour the dominance of a few plant species which are not adapted to infertile soils causing increase in NPP and Biomass and decrease in species richness.
Plants produce nutrient rich tissue which will affect Nitrogen fixing microbial symbionts and heterotrophs (species, populations and communities of herbivores, carnivores and decomposers).

Decreasing natural land cover
33% to 50% of natural land cover modified by human land use
Hard to quantify by direct measurements but tools exist(satellite imagery)
Single most important component of global environmental change on ecosystems
Consequences

  1. Increase in [CO2] in atmosphere
  2. Increase in [N2O] and [CH4] in atmosphere
  3. Forest fires add CO and Nitric Oxide changing the reactive chemistry of atmosphere
  4. Fires produce aerosols that affect climate
  5. Conversion of forests to pasture and desertification reduces humidity and precipitation, increases temperature, affects atmospheric circulation
  6. Fragmentation and loss of entire ecosystems
  7. Extinction and extirpation of species
  8. Aquatic and marine ecosystems affected by nutrient runoff, siltation and overexploitation

Nitrogen fixation: process of converting atmospheric nitrogen (N2) to ammonia or oxides of nitrogen
Biota: the total collection of organisms of a geographic region or a time period
Biogeochemistry: scientific study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment
Legumes: Members of a plant family have the ability to fix atmospheric nitrogen, thanks to a symbiotic relationship with certain microbes found in the root nodules of these plants eg peas, beans, peanuts, clover.
Eutrophication: increase in the concentration of chemical nutrients in an ecosystem to an extent that increases in the primary productivity of the ecosystem.
Land Cover: the physical material at the surface of the earth e.g. grass, asphalt, trees, bare ground, water, etc.
Land Use: human modification of natural environment or wilderness into built environment such as fields, pastures, and settlements
Land cover change: Alteration of physical and biotic nature of a site
Land use change: Alteration of the way humans use land
What is CO2-C?


Terrestrial Ecosystems in changing environments by H.H. Shugart

Summary: 3- Temporal scale and spatial scale and ecosystem
Roots of Ecosystem Concept
Community: Assemblage of interacting and interdependent plant and animal populations.
Ecosystem: Basic unit of nature consisting of communities of populations of various species of organisms and their physical environment.
System consisting of physical-chemical-biological processes active within a space time unit of any magnitude (biotic community + abiotic environment)

The Trophic Dynamic-Concept
Trophic dynamics of ecosystems = ecoenergetics = structure of exchange of energy and matter in ecosystem; core of ecosystem analysis

Trophic Level: an animal's place in the food chain (producer, primary consumer, secondary consumer)
Trophic function (definition?)
Trophic Relation(definition?)
Trophic Structure(definition?)
Trophic Pyramid: The decrease in overall energy transferred towards production in each trophic level (consumers of a certain organism only use a small portion of the energy obtained from consuming that organism—the rest is either transpired or excreted)

Energetics: Thermodynamic study of progressive removal of energy through the various steps of a food chain

Two Views on the Cause of trophic structure

  1. Darwinian/Evolutionary view of population dynamics: Organisms have an intrinsic property to produce excessive number of offspring allowing predation to occur because of excess of prey population in natural systems.
  2. Spencerian/Holistic view of system dynamics: Evolution produces organized configurations with increased internal organization and mutual interdependencies. Organisms produce excessive number of offspring because they evolved in a system in which these additional offspring will be eaten by predators.

Food Chain, food webs and element cycles
Food Chain: Depiction of simple feeding relationships among biota in an ecosystem
Food Web: Depiction of feeding relationship with multiple pathways among biota of an ecosystem
10% law: On average in terrestrial ecosystems, only 10% of biomass is transferred from one trophic level to the next higher trophic level.

Ecological Sucession
After a disturbance that changes the system, regular and predictable replacement of one community by another until the development of a final community (climax community) that perpetuates itself.
Whole System Theories: view succession as a ecosystem level property
Individual Organism oriented theories: view succession as caused by characteristics and interactions of individual organisms.

Biogeocoenosis and ecosystem
Ecosystem of a particular size or fixed area which is determined by the homogeneity of air, water, soil and organisms.

Recent interpretation of ecosystem
Original definition did not mention boundary or limits newer definitions talk about size and dimensions.

Ecosystem as a System of definition
Abstract: size according to the objectives of the study, analogous to system concept from physics. Explicit assumptions.
Modern usage: Idiom for what should be held as the objective of stud. Implicit assumptions based on context.

Temporal scale and spatial scale and ecosystem
Time and space scales are important because they give us an idea on how an ecosystem will respond to a large scale environmental change and if we ignore then the chances of failure in modeling ecosystems increases. Necessary to understand system dynamics.

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