Lecture 02 - The Biosphere

Chapter 3

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Unit Organization:

• The Earth
• The Biosphere
• Populations
• Communities
• Ecosystems
• Biogeochemical Cycling
• Energy Flow
• Normal Approximation of the Binomial

Reading:

Textbook: Chapter 3

Ancillary Reading:

The Earth

• Earth is a flattened (at the poles) sphere (due to rotation) - 43 km difference with an average diameter of 12,742 km (7918 mi) and circumference = 40,030 km or 24,874 mi)
  • From highest mountain peak (Everest, 8.848 km [5.5 mi]) to deepest oceanic trench (Marianas Trench, western Pacific, 10,91 km [6.78 mi] deep) is 19.76 km (12.28 mi)
    • The surface roughness is only 0.16% of diameter (a very smooth almost round ball!)
  • 32% Iron, 30% Oxygen, 15% Silicon, 14% Magnesium, 3% Sulfur and the other 6% composed of the remaining elements
• Regions of the Earth
  • Core - innermost region of the Earth is more dense than crust
  • Inner Core - solid, may spin a bit faster than the rest of the Earth, may be mostly iron and nickel due to the Iron Catastrophe (when forming Earth got hot enough to melt and denser material, mostly iron, sank to center of forming Earth)
    • May be composed of huge crystals of iron (mixed with other elements) with a north-south orientation
  • Outer Core - liquid and mostly iron
    • Spinning iron in outer core may be source of Magnetosphere (Dynamo Theory)- the magnetic field around the Earth that protects it from harmful effects of the Solar Wind (inner core is too hot to produce the magnetic field)
  • Mantle - a viscous solid, not a liquid  At the temperature and pressure of the mantle (1.4 million atmospheres at the inner edge), solids flow
    • mostly Silicate rock with other minerals that is ductile, allowing motion over long periods of time - motion that moves the plates that compose the crust
    • The upper regions of the mantle are complex
    • The outermost layer of the Mantle is part of the Tectonic Plates that form the Lithosphere (see below)
    • Below the outermost layer is the Asthenosphere, the region of ductile, slowly moving rock moves the tectonic plates
      • It is a convective flow and brings heat from the inner Earth closer to the surface
  • Crust - rock is 6 km thick under oceans and 40 km thick on continents, mostly oxides (47% of crust is oxygen and CO2 is 1.2%) -and we will divide it into three regions
    • Hydrosphere - only about 0.023% of Earth's mass
      • Major components are Ocean (97.4%), Snow and Ice (1.98%), Groundwater (0.059%), and all Rivers, lakes, and Plants (0.014%)
    • Atmosphere - very complex boundary between the surface of the Earth and space and its presence is vital to creating the conditions suitable for life at the surface
      • All the water in the atmosphere is only 0.0014% of total water
      • Troposphere - surface to 8 km at the poles and to 17 km at equator. The air cools as you go up at a rate of about 6.5°C per kilometer for 12 km but then stops cooling (this is called the
        Tropopause and it the boundary layer between the troposphere and
        the stratosphere)
        • This is the layer of most clouds and precipitation.  The average temperature of the surface of the Earth is about 15°C and the tropopause is about -60°C.
      • Stratosphere - from tropopause to Stratopause at about 50 km up.  The stratosphere warms as you go up because oxygen is absorbing the sun's energy and heating the layer (from -60°C to about -10°C).
        • The stratosphere is where airliners fly and there are two important climatic factors in
          this layer.
        • Ozone Layer - as Oxygen absorbs sunlight the energy of the photons can either cause the molecules to speed up (increasing their temperature) or be absorbed by electrons, including those involved in the O2 bond
          • This addition of energy makes the oxygen molecules reactive and some break apart. The singlet oxygens are highly reactive and, if they happen to bump into oxygen molecules, ozone (O3) molecules are formed. Ozone is important because it absorbs ultraviolet radiation and the layer in the Stratosphere greatly reduces the amount of UV that reaches organisms at the surface.
        • Jet Streams - occur at the lower areas of the stratosphere and are currents of air that move very fast (some over 300 kmph).
          • The jet streams cause movement in the troposphere of the high and low pressure areas of the troposphere we follow on the weather forecasts.
      • Mesosphere - from stratopause to the Mesopause at about 100 km.  This is an area of cooling gasses and it drops from -10° to -100°C.  However, at the mesopause, the upper boundary of the mesosphere, the temperature begins to rise again.
      • Thermosphere - from mesopause until the atmosphere becomes too thin to measure, over 3000 km up. It heats because nitrogen and oxygen are maximally exposed to the sun and they can heat up to temperatures over 2000°C. However, the atmosphere is so thin here that the amount of energy involved is not very great
      • Ionosphere - mesosphere to 600 km. Here, the gas molecules are broken apart by the absorption of sunlight and they become ionized as they leave behind or take up electrons. The ions have a strong effect on long wave radiation and the can cause reflection or disruption of radio waves.
      • Exosphere - 600 to end of atmosphere.
    • Lithosphere - (actually, uppermost portion of mantle is part of the lithosphere) rock that has broken into the Tectonic Plates and there are two general regions of rock:
      • Continental - less dense granitic rocks than oceanic
        • Silicon Dioxide (60%), Aluminum Oxide (15%), Calcium Oxide (5.5%, CaO, not a carbonate), Magnesium Oxide (3%), Iron Oxide (4%), and rest (12.5%)
      • Oceanic - line the bottom of the oceans, mostly denser basaltic rock
        • Silicon Dioxide (49%), Aluminum Oxide (16.5%), Calcium Oxide (12%, CaO), Magnesium Oxide (7%), Iron Oxide (6%), and rest (9.5%)

The Biosphere

The region of the Earth occupied by life is the Biosphere

• There is a hierarchy based on size in the Biosphere
• From micrometers (bacteria) to thousands of kilometers (biosphere), a span of 11 powers of 10

Ecology

Study of the abundance and distribution of organisms

• both factors are set by Interactions between organisms and both the physical and biotic environments
• Ecological principles underlie our understanding of the relation of humans to our environment and to our impact on the natural environment

Populations

Populations are groups of interacting individuals of the same species

• They are not eternal, so they have a beginning, often small, grow to a mature size that may be stable for a time and eventually they decline and go extinct (the population, not the species)
• Growth rate depends on birth and death rates, on the age of first reproduction, and on age structure
• Population stability is linked to the carrying capacity of the environment for that organism

Abundance (and Distribution) is affected by

• Physical Tolerances of the organisms in the population to physical factors (pH, temperature, salinity, moisture, chemistry, etc.)
• Resource Availability
  • Law of the Minimum - that resource in least supply will limit population growth
• Biotic Interactions
  • Competition
    • Competitive Exclusion Principle - two species can't occupy the same niche in the same place
    • Niche - role of a organism (population) in an ecosystem - sum total of its interactions with the environment
  • Mutualism
  • Parasitism
  • Predation
• Two Complications
• These interactions are not mutually exclusive
• Species interact directly and indirectly

Human Impacts on Populations

• Positive
  • Increase resource availability
  • Predator Release
  • Competitive Release
  • Transport and introduction to new regions
  • Domestication
• Negative
  • Habitat reduction and disruption (alteration)
  • Introduction of new competitors, parasites or predators
  • Over Exploitation - hunting, gathering from the wild, fishing, etc.
• Humans often affect populations through indirect interactions (as the introductions of predators, etc.)

Communities

Populations that inhabit the same habitat and interact with one another form Communities

• Associations are populations in the same habitat that do not necessarily interact
• Community Structure is often of interest
  • the distribution of the species in both space and time
  • patterns of co-occurrence
• Ecosystems are composed of the communities in a specific area plus their physical environment
  • Ecosystem Dynamics is often of interest
  • Flow of materials and energy into the system, as it moves among the parts of the system, and as it exits the system

Community Structure

Patterns of species distributions:

• Ecotones - sharp changes where many populations drop out or are gained all at once
• Gradients - gradual changes in community composition as some specie drop out and some are gained

Community Succession

• Sequential replacement of one community by another
  • After a disturbance that removes communities, pioneer species may arrive
  • These are later replaced by other species
  • The replacements don't prefer the pioneering conditions but prefer the conditions after the influence of the pioneers
• Thus one community replaces another because each community alters the habitat and the alterations allow a successor community to invade
  • When a community alters the habitat to make it most preferable for itself, succession stops and we call this last community the Climax Community
• As Succession proceeds, each successive community is:
  • Less Productive (new biomass per year per square meter)
  • More Diverse - more species and more evenness
  • Larger Standing Biomass

Ecosystems

Basic process in ecosystems are

• Matter Cycling
• Energy Flow

All ecosystems are Open, not Closed

• matter and energy are exchanged with the non-living environment
• Human impact can be measured as changes to these flows in natural systems due to human influence

Food Webs

• Energy and material flows dictated by feeding relationships

Trophic Biomass Pyramids

• biomass is the mass of living organisms
• First Trophic (feeding) Level - Primary Producers (autotrophs that capture energy from the environment and use it to build organic compounds)
• Second Trophic Level - Primary Consumers who eat primary producers
• Third Tropic Level - Secondary Consumers who eat primary consumers
• Forms a pyramid (really a ziggurat) because each successive level only captures a rather small portion of the biomass (and the energy it represents) from the lower level, so the pyramid gets ever smaller
• Law of the tenth - each level only gets about a tenth of the preceding level

Ecosystem Productivity - varies with the ecosystem

• Net Primary Productivity - rate of production of new biomass by primary producers
  • Terrestrial NPP is highest in moist tropical forests and lowest in deserts
  • Marine NPP is highest on coral reefs and lowest in clear, open waters

Biogeochemical Cycles

We can consider any quantity, be it energy, biomass, a particular element such as carbon, or compound, such as water and model it as a Biogeochemical Cycle

• first identify the reservoirs (storage compartments) and measure how much in each
  • can be both living and non-living
• then measure the flow between the reservoirs as well as out of and into the system (remember, ecosystems are open systems)
• many times, flows can form a circular pattern
  • when this happens, material or energy is being recycled between reservoir in the system
  • mature ecosystems often have many potential cycling pathways so that material or energy travels a long way within the system before leaving it
• net change in a reservoir or the system itself depends on the difference between inflow and outflow
  • inflow greater than outflow, reservoir or system is growing
  • outflow greater than inflow, reservoir or system is declining
• rates of change can vary greatly for any one material (carbon in and out of trees vs carbon in and out of limestone)

Hydrologic Cycle

• Water moves by bulk flow, precipitation and evaporation between the major reservoirs
• Ice represents longer term storage for water

Carbon Cycle

• Carbon is an important component of living things but has large pools outside of living biomass
• Carbon in rocks (as limestone, etc.) and in oil
• Carbon in atmosphere (and dissolved in water), mostly as CO2 and CH4
• Photosynthesis and respiration are important carbon cycling processes

Nitrogen Cycle

• Nitrogen vital for production of nucleic acids and proteins
• Atmospheric nitrogen not directly available to most organisms
• Must be fixed into nitrate, nitrite or ammonia by some bacteria
• Decay releases nitrogen as N2

Phosphorous Cycle

• Phosphorus is not found in its elemental state but almost always as phosphate
• Phosphate necessary for nucleic acids
• Often the limiting nutrient in fresh water aquatic systems
• Source is phosphates in rocks
• Cycles through organisms until it is re-"lithified" (made into rock again)

Residence time

• Time an atom or molecule (or erg!) spends in the system before leaving it
• Varies greatly between reservoirs

Cycling time

• Time an atom or molecule spends before it returns to the same point in a biogeochemical cycle
• Varies greatly between different types of molecules or elements

Human Impact on Cycles

• Humans can only recently impact world-wide cycles
• Carbon cycle is impacted by burning of fossil fuels
• Hydrologic cycle is being affected by land clearing, dam construction, and surface alteration

Energy Flow

• Thermodynamic Law 1 - energy cannot be created or destroyed but can be transformed from one kind to another
• Thermodynamic Law 2 - when energy is transformed, some useful energy (energy that can be used as work) is lost
• Energy transformation occurs when light (electromagnetic energy) is converted into heat or stored in a chemical bond. or used to ionize an atom

Last updated September 9, 2012