Ecosystems

1
Chapter 4

• Ecosystems

2

• The creature at your feet dismissed
• as a bug or a weed is a creation in and of
  itself.
• It has a name, a million year history, and a
  place in the world. Its genome adapts it to a
  special niche
• in an ecosystem. The ethical value substantiated
  
• by close examination of its biology is that life
  forms around us are too old and too complex to be
  carelessly disregarded.
• Edward O. Wilson, The Future of Life, 2002

3
Ecology

• The study of the interactions between organisms
  and the abiotic and biotic components of their
  environment limit the distribution of species
• The abiotic components of an environment are the
  nonliving, chemical and physical components
  (temperature, water, sunlight, wind, rocks and
  soil composition)
• The biotic components are the living members
  (parasites and pathogens, as well as predators
  and prey organisms)

4
Ecosystems

• Refers to the collection of components and
  processes that comprise some defined subset of
  the part of the planet where life occurs
  (biosphere). An ecosystem includes all biotic and
  abiotic components, and their interactions with
  each other, in some defined area, with no
  conceptual restrictions on how large or small
  that area can be

5
Ecosystems

• Components of ecosystems life, energy, matter
• Biological components producers consumers
• Producers are autotrophs, photosynthesize for
  food
• Primary productivity is the rate at which solar
  energy is converted into chemical energy via
  photosynthesis
• Net primary productivity is the rate of
  photosynthesis minus the rate of respiration
  (chemical energy is used)
• Consumers are heterotrophs, ingest or absorb food
  
• May be herbivores, carnivores, omnivores,
  scavengers, detritus feeders, or decomposers
• Trophic levels useful energy is 1 from
  sunlight through photosynthesis, at every other
  step 10

6
Components of Ecosystems
7
Trophic Levels
8
Law of the Conservation of Matter

• Law of Conservation of Matter In a chemical or
  physical change, no atoms are created or
  destroyed. This law is the premise for the
  statements matter cycles through an ecosystem
  because the Earth is a closed system for matter
  and there is no away.

9
Laws of Thermodynamics

• First Law of Thermodynamics Energy can neither
  be created nor destroyed, it simply changes form.
  Energy transformations are very important in
  living systems.
• Second Law of Thermodynamics Systems naturally
  move towards maximum disorder (entropy). It takes
  a lot of energy to maintain organization (like
  that found in a living creature). All energy
  ultimately ends up as the very disordered entity
  we call heat. This law is the premise for the
  statement energy flows through ecosystems
  because the Earth is an open system to energy.

10
The two laws of thermodynamics
11
Matter Energy

• Earth is an open system for energy energy flows
  through an ecosystem
• All energy is ultimately in the form of heat
• Organisms transform energy they do not create
  energy
• Earth is a closed system for matter matter is
  recycled in an ecosystem
• Organisms recycle matter

12
Biogeochemical Cycles

• Water/hydrologic
• Driven primarily by solar energy (evaporation)
  gravity (precipitation)
• Water accessibility use
• Personal water use
• Sulfur
• Phosphorous (never stored in the atmosphere)
• Oxygen
• Nitrogen (five-step cycle)
• Carbon (primarily photosynthesis and respiration)

13
The Nitrogen Cycle

• The most complex of the biogeochemical cycles
• N2 78 of the troposphere, chemically
  unreactive, cannot be used/absorbed directly in
  this form by multicellular plants or animals.
• Even though N2 is a large source of nitrogen,
  must be converted before it can be of use to
  living organisms.
• Nitrogen cycle steps nitrogen fixation,
  nitrification, assimilation, ammonification and
  denitrification

14
The Nitrogen Cycle

• Nitrogen Fixation N2 converted to ammonia (NH3)
• By cyanobacteria in soil/water and bacterium
  Rhizobium in root nodules of legumes (peas,
  clover, beans, etc.)
• Nitrification Ammonia converted to nitrite
  (NO2-)and then nitrate (NO3-), the most usable
  formsof nitrogen
• Both reactions carried out by bacteria
• Assimilation These usable forms are taken in by
  plants and animals. Plant roots absorb nitrates
  that are then converted into organic compounds
  like proteins and DNA. And of course, animals eat
  plants.
• Ammonification These organic compounds, wastes,
  caste-off particles, dead bodies, etc., are
  converted into simpler compounds (e.g., ammonia
  NH3)
• By decomposer bacteria
• Denitrification Ammonia (NH3) is converted back
  to N2
• Mostly by anaerobic bacteria in waterlogged soil,
  bottom sediments of lakes, swamps, bogs and
  oceans

15
Significant Human Interventions

• Internal combustion engine exhaust (i.e., fossil
  fuel burning)
• Results in O2 being added to the atmosphere
• Combining O2 with atmospheric nitrogen results
  in nitric acid, a significant component of acid
  rain
• Farming, agriculture and cities
• Nitrogen-rich fertilizers from farms and sewage
  from municipalities runs off into bodies of water
• This stimulates the growth of algae and aquatic
  plants which then die and are broken down by
  aerobic decomposers
• This aerobic decomposition reduces the dissolved
  oxygen (DO) content in the water, killing fish
  and other aquatic animals

16
More Human Interventions

• Mining for nitrogen-rich minerals from the
  earths crust and soil
• Nitrogen can be depleted from topsoil when we
  over-harvest or over-graze plants and then burn
  or clear grasslands and forests
• Cattle waste and inorganic nitrogen-containing
  fertilizers are broken down by bacteria into
  nitrous oxide, which is a heat-trapping gas and
  can contribute to the warming of the atmosphere.

17
The Carbon Cycle

• Cycles closely with hydrogen and oxygen,
  especially as an essential component of organic
  molecules (e.g., carbohydrates) and inorganic
  molecules (e.g., CO2)
• Aerobic respiration C6H12O6 6O2 gt 6 CO2 6H2O
  38 ATP
• Photosynthesis 6CO2 6H2O light energy gt
  C6H12O6 6O2
• CO2 0.036 of the troposphere (lowest part of
  atmosphere) gases, is also easily dissolved in
  H2O
• CO2 enters the atmosphere by burning fossil
  fuels, aerobic respiration and volcanic activity
• CO2 is a heat-trapping gas, and an important
  component of the earths thermostat
• More CO2 higher temperatures with the
  greenhouse effect

18
The Carbon Cycle

• The oceans help regulate the CO2 in the
  atmosphere
• When oceans take in CO2, there is a cooling
  effect due to the heat-trapping ability of CO2
• Some CO2 stays dissolved in sea water
• Some is removed by photosynthesis (aquatic
  plants, algae and phytoplankton)
• Some reacts with sea water to form CaCO3
• CaCO3 is used by marine organisms for shells and
  skeletons
• These organisms live, die, sink, are buried for
  many years, and over time, under pressure, the
  CaCO3 turns into limestone on the ocean floor

19
The Carbon Cycle

• The long term carbon storage units sequester CO2
  for thousands or millions of years
• The ocean floor (limestone)
• Limestone and other sedimentary rocks and soils
  on the continents
• The short term carbon storage units are the
  atmosphere oceans
• Atmosphere (3 years)
• Soils (25-30 years)
• Oceans (1500 years )
• CO2 is released from the oceans as H2O
  temperature increases
• Warm waters cannot absorb as much CO2 as cooler
  waters
• There is a positive feedback loop between CO2
  levels and atmospheric temperatures future
  implications for global climate change

20
Carbon and the Oceans

• Data shows that overall, there are increasing
  amounts of CO2 in the oceans, which causes
  acidification of the oceans through this
  reaction H2O CO2 gt H2CO3 (carbonic acid)
• Because of ocean currents and upwellings, the
  dissolved CO2 that is now rising to the surface
  waters dissolved out of the atmosphere about 50
  years ago
• Therefore, this trend of acidification would
  continue for the next 50 years even if we stopped
  increasing the levels of CO2 today
• Acidification negatively impacts corals, mussels,
  and other marine organisms by slowing the rate of
  calcification

21
Significant Human Interventions

• There are two major interventions that lead to
  increasing levels of CO2 in the atmosphere
• Vegetation removal/deforestation
• Fossil fuel and wood burning
• Reasons for concern
• Enhanced/magnified natural greenhouse effect
• Altered global food production due to shifting
  climate belts
• Altered wildlife habitat due to changes in
  temperature and precipitation
• Altered species interactions
• Rise in sea levels due to thermal expansion of
  water as troposphere temperature increases