Ecosystems

1
Ecosystems

• Reading Freeman Chapter 54

2

• An ecosystem is the unit composed of all the
  living things in a single place at a given time,
  in addition to, the important non-living
  components of the system.
• Nonliving components include sunlight, rainfall,
  silica and clay particles in the soil, the air,
  the water in the soil, etc.
• Thus, an ecosystem encompasses all aspects of a
  biological community, in addition to factors such
  as rates of CO2 uptake, rates of nitrogen
  fixation from the atmosphere, precipitation,
  seasonal flooding and its effects on nutrients,
  etc.

3

• Ecosystems vary in size. Like communities, small
  ecosystems are stacked within larger ones, and
  the boundaries are sometimes diffuse.
• The biosphere the largest and most encompassing
  ecosystem we know-it encompasses all the plants
  and animals on Earth.

4
Energy and Biomass

• Much of ecosystems ecology concerns itself with
  the flow of energy and biomass.
• Nutrient cycling and energy flow are common to
  all biological communities.
• These phenomena are both a consequence, and a
  function of biological communities.
• The complex matrix of interactions among members
  of a community expends energy, as well as passing
  it from one member to the next through trophic
  interactions.
• Likewise, biomass is constantly recycled through
  production, predation, herbivory, and
  decomposition.

5
Energy

• The sun is the ultimate energy source for almost
  every ecosystem on earth.
• Hydothermal vent communities are a partial
  exception-(they rely on geothermal energy, but
  still depend upon oxygen fixed by photosynthetic
  organisms).
• Energy enters ecosystems via photosynthesis (or,
  in a few exotic excosystems, chemosynthesis).
• Organisms that bring energy into an ecosystem are
  called producers.
• Producers include green plants, algae,
  cyanobacteria, etc..anything that can make its
  own energy from nonliving components of the
  environment.

6

• Organisms continuously use energy.
• All metabolic processes consume energy in some
  way, and in each reaction, much of it is
  effectively wasted
• ..this is one reason why rapid metabolism makes
  us homeothermic-the waste heat from metabolic
  processes, mostly as molecular motion, warms our
  bodies.
• Ultimately, all biological energy radiates into
  the environment as infrared light (a by-product
  of respiration).
• Much energy is lost every time it passes from one
  trophic level to the next.
• Energy does not recycle.
• it must be continually replenished from the sun.

7

• Autotrophs fix their own energy from inorganic
  sources.
• Autotrophs are the producers in an ecosystem.
• Heterotrophs depend upon energy and carbon fixed
  by some other organism
• they are consumers, detritivores, or
  decomposers.
• (A mixotroph is gets its energy from inorganic
  sources, but relies of organic sources of carbon.)

8

• A food web is a schematic diagram that describes
  the patterns of energy flow in an ecosystem
• Every instance of predation, herbivory, and
  parasitism is a trophic interaction that moves
  energy from one organism to another.
• Decomposition is also a trophic interaction that
  uses up the energy left over in dead bodies of
  organisms.
• A food chain is one path through a food web,
  from bottom to top.
• Because energy is lost at each step, food chains
  have a limited number of links.

9
Matter

• Unlike energy, matter recycles through
  ecosystems.
• Atoms of every biologically important element
  constantly recycle through ecosystems, into the
  abiotic component of the biosphere, and back into
  living systems.
• Elements are passed from one organism to another
  via trophic interactions, or are taken directly
  from the environment.
• Via the process of decomposition, each element
  ultimately becomes nonliving, and has the
  potential to re-enter the biosphere again.
• Thus, each element has its own biogeochemical
  cycle-these can take days, years, or eons,
  depending upon the element and the circumstances.

10
(No Transcript)
11
Biomass

• Biomass can be defined as the weight of living
  matter (usually measured in dry weight per unit
  area).
• A pyramid of biomass is a figure that quantifies
  the relative amounts of living biomass found at
  each trophic level.
• In most ecosystems, the amount of biomass found
  in each trophic level decreases progressively as
  one moves from the bottom to the top of the food
  chain.

12
Pyramid of biomass for a pond. (Source Data from
Whittaker, R.H. 1961. Experiments with
radiophosphorus tracer in aquarium microcosms.
Ecological Monographs 31157-188).
13
(No Transcript)
14

• Primary consumers eat producers.
• They generally possess significantly less biomass
  than producers.
• Plants have evolved numerous mechanisms to
  protect their tissues from consumption by
  herbivores and pathogens
• In most ecosystems only a small amount of
  producer biomass is eaten.
• Significant losses of biomass occur because of
  digestive inefficiencies, and return of CO2 to
  the atmosphere via respiration.
• Assimilation efficiencies for most terrestrial
  herbivores range from 20 to 60 percent. Some
  invertebrates do better than that..some do not.
• A very large proportion of the assimilated
  biomass is lost through the process of
  respiration, so only a small amount of the
  biomass is available to the next level.

15

• Secondary consumers consume primary consumers.
• Tertiary consumers consume secondary consumers,
  and so forth.
• Not all organisms at one level are eaten, because
  of defensive mechanisms-and predation is only one
  way to die.
• Defensive adaptations include the ability to fly
  and run, body armor, quills and protective
  spines, and camouflage.
• In general, carnivores have higher assimilation
  efficiencies than herbivores. These range from 50
  to 90 percent.
• Only a small fraction of the assimilated energy
  becomes carnivore biomass because of the
  metabolic energy needs of body maintenance,
  growth, reproduction, and locomotion.

16

• Most food chains have at most four or five
  trophic levels.
• The amount of biomass found at each trophic level
  is small relative to amount found at the next
  lowest level.
• This is because less energy is available to
  successive consumers.

http//www.bioquip.com
17
(No Transcript)
18

• Decomposers, scavengers, saprophytes, and
  detritivores are organisms that eat dead organic
  matter.
• Detritivores eat the dead bodies of living
  things, such as carrion, leaf litter, etc..
• Scavengers are animals that eat dead animals.
• Decomposers are microscopic organisms that break
  down organic compounds into nonliving, inorganic
  precursors.
• Saprophytes are organisms that feed on dead
  organic matter, this term is usually applied to
  fungi or bacteria, but there are plant
  saprophytes as well

19
Primary Productivity

• Primary productivity is the amount of biomass
  produced through photosynthesis per unit area and
  time by producers.
• It is usually expressed in units of energy (e.g.,
  joules /m2 day) or in units of dry organic matter
  (e.g., kg /m2 year).
• Globally, primary production amounts to 243
  billion metric tons of dry plant biomass per
  year.
• The total energy fixed by plants in a community
  through photosynthesis is referred to as gross
  primary productivity (GPP).

20
Net vs. Gross Primary Productivity

• Most gross primary productivity is used via
  respiration by the producers themselves.
• Subtracting respiration from gross primary
  production gives net primary productivity (NPP)
• NPP represents the rate of production of biomass
  that is available for consumption (herbivory) by
  heterotrophic organisms (bacteria, fungi, and
  animals). It is also easier to measure, because
  it tends to accumulate over time.

21

• Problem
• A plot of Panicum sp. grass has a gross
  primary productivity of 10,700 kcal/m2year. The
  grass respire approximately 9,100 kcal/m2year.
• What is the net primary productivity?

22

• Answer
• 10,700kcal/m2year - 9,100 kcal/m2year1600kcal/m2y
  ear.
• Problem
• The field is 10m x 10m. Over the course of
  one year, what is the total net primary
  productivity for the field?

23

• Answer
• 100m2 x 1600kcal/m2year1.6x105kcal/year.
• Problem
• If Panicum grass has an energy value of
  6kcal/gram, and all of the primary productivity
  were to accumulate as biomass, how much biomass
  (expressed as dry weight) will have accumulated
  in the field over the course of 1 year?

24

• Answer
• (1.6x105kcal/year x 1 year)/(6kcal/gram)2.67x104
  grams or 267kilograms.
• Problem
• Suppose herbivores (wild mules) eat ALL this
  biomass, and assimilate 10. The respiration of
  the mule is 15kcal/kilogram day.
• Would this field be sufficient to support a 150
  kilogram mule?

25

• Answer
• The mule would assimilate (1.6x105kcal/year x
  10)1.6x104kcal/year.
• Over the course of the year, the mule would
  require 15kcal/kilogram day x 365 days x 150
  kilograms8.21x105kcal.
• The field is not nearly enough. This is why
  large herbivores move around so much.

26
Communities Differ in their Productivity

• Globally, patterns of primary productivity vary
  both spatially and temporally.
• The least productive ecosystems are limited by
  heat energy, nutrients and water like the deserts
  and the polar tundra.
• The most productive ecosystems have high
  temperatures, plenty of water and lots of
  available soil nitrogen.

27
(No Transcript)
28
Productivity is high in areas of oceanic
upwelling-oceanic producers, which include
diatoms, dinoflagellates, cryptomonads, and other
algae-require nutrients
29
Nutrient Cycling

• Each biologically important element has nutrient
  cycle.
• A nutrient cycle is the path of an element from
  one organism to another, and from organisms into
  the nonliving part of the biosphere and back.
• Nutrient cycles are sometimes referred to as
  biogeochemical cycles, reflecting the fact that
  chemicals are cycled between biological
  organisms, and between organisms and the geologic
  (physical) environment.

30
C, H, O, N

• Carbon, hydrogen, oxygen, and nitrogen make up
  most of the biological molecules found in living
  organisms. These elements are passed from
  organism to organism by chemical conversion
  processes, which occur in food webs.
• They are also converted from non-living forms to
  living forms by photosynthesis and nitrogen
  fixation, and from living forms to non-living
  forms through cellular respiration.

31
Reservoirs

• The non-living forms of carbon, hydrogen, oxygen,
  and nitrogen form huge reservoirs in the physical
  environment. For instance, nitrogen makes up 78
  of the atmosphere as N2, and hydrogen comes from
  water.
• In ecosystems ecology, a reservoir is a supply of
  a biologically meaningful element that is not
  easily obtainable by living organisms.
• Elements can have multiple reservoirs

32
(No Transcript)
33
Carbon

• Most of the material substances that make up
  living organisms consist of organic compounds of
  carbon. In contrast, carbon is relatively scarce
  in the nonliving part of the Earth.
• Carbon exists in the non-living environment as
  carbon dioxide in the atmosphere, dissolved
  carbon dioxide (HCO3-, etc.) in the ocean, and as
  carbonates in the Earths crust.
• It is also locked in fossil deposits, and
  embedded in the ocean floor as deposits of
  methane anhydride.

34

• Carbon cycles between the living and nonliving
  components of the biosphere.
• The most important reservoir for carbon is the
  atmosphere
• Although CO2 makes up less than one percent of
  the atmosphere, it is very important to the
  biosphere.
• Much of the carbon in your body was part of the
  atmosphere, some of it relatively recently.
• When you decompose, it will return to the
  atmosphere.

35
Carbon Fixation

• Fixation, in this sense, means capture and
  conversion to a biologically useful form.
• Eg., water does not need to be fixed, neither
  does sodium, but carbon and nitrogen do.
• CO2 is fixed by plants during photosynthesis.
• Photosynthesis converts atmospheric CO2 into
  organic carbohydrates by combining them with
  water, also from the nonliving part of the
  biosphere.
• This process requires the input of specific light
  photons, which plants capture with the pigment
  chlorophyll.
• Once fixed by plants, CO2 is passed up the food
  chain by trophic interactions such as herbivory
  and predation.

36
Respiration

• Most organisms, including plants, respire.
• Respiration liberates carbon back into the
  atmosphere and provides energy to the organism.
• CO2 enters the atmospheric reservoir.
• If it is not eaten and respired, or decomposed,
  organic carbon may become buried and enter a
  carbon reservoir in the soil, or ultimately
  fossilize.

37

• Carbon that is "fixed" can also return to the
  atmosphere if the plant material is burned,
  either naturally, or through human activities.
• Even ancient plant and animal material that
  contains carbon that was fixed millions of years
  ago can be returned to the atmosphere by burning
  fossil fuels.
• Carbon can also be recycled back into the
  atmosphere through volcanic activity.
• As a tectonic plate goes underneath a continent,
  superheated oceanic material upgasses through
  geological vents and reenters the atmosphere.

38
Carbon, Global Warming, Anthropogenic Climate
Change

• CO2 has a crucial role in the climate of the
  Earth because it is quite transparent to light at
  the visible wavelengths, and relatively opaque to
  infrared light.
• Gasses with this property are called greenhouse
  gasses, because they tend to trap heat, forcing a
  higher equilibrium temperature.
• Methane, and CFCs are also greenhouse gasses,
  but CO2 is the most important because it occurs
  at higher concentrations.
• Geological periods of low CO2 concentration (such
  as the present) are strongly correlated with low
  global temperatures, higher CO2 is strongly
  correlated with higher global temperatures.
• Additionally, sudden increases in CO2 can be
  linked to a sudden warming of the climate.
• Such an event occurred in the Miocene, 15 million
  years ago.

39
(No Transcript)
40

• There is very solid evidence that CO2
  concentrations have increased significantly over
  the course of the last 150 years.
• This is partially due to the burning of fossil
  fuels, and partially due to deforestation.
• By cutting and burning of forests, the carbon
  that once was locked in the trees is released
  into the atmosphere.
• Huge stores of fossilized carbon are present
  within the Earths crust, much of it buried and
  fossilized during the Carboniferous period,
  200million years ago.
• Liberation of these stores into the atmosphere
  has the potential to dramatically change the
  climate of the Earth.
• Evidence is mounting that these higher CO2 levels
  have already affected the climate of the Earth.

41

• Some possible effects
• Higher temps, especially in the high latitudes
• Drier continental interiors
• More unpredictable weather patterns, with more
  extreme storms, and extreme heat events
• The potential for tropical diseases to enter
  higher latitudes and higher elevations
• The potential for currently farmable areas to
  become too dry to farm
• The potential to interfere with oceanic
  thermohaline circulation, and cause conditions in
  Europe and Eastern North America to become very
  cold.
• The potential to interfere with oceanic
  productivity through changes in Ph
• The potential for increases in sea level.

42
(No Transcript)
43
N

• N is one of the most common elements that form
  biological molecules.
• It is a major component of amino acids, also a
  primary constituent of nucleic acids.

44
The major reservoir for nitrogen is the atmosphere

• N2 makes up 78 of the Earth's atmosphere.
• The majority of living organisms are not able to
  use it in that form.
• N2 contains a triple bond between the atoms, it
  is a very stable molecule and therefore,
  biologically inert.
• A large amount of energy is required to break the
  triple bond.
• lightning is responsible for converting some of
  the atmospheric nitrogen into forms that
  organisms can use.
• The process of converting atmospheric nitrogen
  into forms that organisms can use is called
  nitrogen fixation.

45

• Although most organisms are not able to convert
  nitrogen, there are a few that are able to "fix"
  atmospheric nitrogen.
• Some free-living soil bacteria as well as some
  blue-green bacteria have the ability to convert
  nitrogen into ammonia.
• Nitrogen is also fixed by symbiotic bacteria that
  live in and among the root cells of several types
  of plants, most notably, the legume plants such
  as beans, peanuts, and peas. Other plants such as
  alfalfa, locust, and alders also have root
  nodules.

46

• There are a few that are able to "fix"
  atmospheric nitrogen.
• These include bacteria in the genus Rhizobium and
  Bradyrhyzobium, and also some cyanobacteria, such
  as Anabaena and Nostoc,
• This process, which is energetically expensive,
  converts nitrogen into ammonia.
• Other bacteria convert ammonia to nitrates
  through nitrification.
• Most plants use nitrogen in the form of nitrates,
  though ammonia is also useful.
• Nitrogen fixing bacteria frequently live in
  mutualistic symbiosis with plants, notably
  legumes.
• Thus, legumes can be disproportionately important
  to the ecology of a plant community.

47

• Once nitrogen is absorbed by plants and built
  into the plant molecules, the nitrogen can be
  passed to consumers and to decomposer organisms
  through the food chain.
• Nitrogen can be mineralized and converted to
  organic compounds that enter the soil or water
  upon their death, or enter as waste through their
  digestive tracts.
• These decomposed nitrogen compounds - ammonia,
  nitrite, and nitrates, then become available for
  other plants to absorb and recycle. This process
  is called ammonification.
• Alternatively, other bacteria, known as
  "denitrifiers," convert nitrites and nitrates in
  the soil to N2O and N2, which returns to the
  reservoir in the atmosphere. This process, which
  completes the nitrogen cycle, is called
  denitrification.

48

• Certain bacteria convert ammonia to nitrates
  through nitrification. Most plants use nitrogen
  in the form of nitrates.
• Once nitrogen is absorbed by plants and built
  into the plant molecules, the nitrogen can be
  passed to consumers and to decomposer organisms
  through the food chain.

49
Water

• The water cycle is one of the most important
  processes to living organisms on Earth.
• Water that has evaporated into the atmosphere
  condenses and falls as precipitation.
• This precipitation will either run off as surface
  water and collect as streams or rivers, or it can
  seep into the ground and collect in huge
  underground rock formations called aquifers, that
  act much like sponges.
• The water eventually flows from lakes or streams
  down into the oceans, where it can reside for
  long periods of time, or get evaporated back up
  into the atmosphere as water vapor, which
  collects as clouds.

50

• A portion of the water absorbed into the ground
  is taken up by plants, which use the water to
  transport minerals internally as well as to take
  part in the photosynthetic process.
• Some of this water is transferred to animals that
  feed on plants from there, water can cycle
  within the food web of an ecosystem.
• Water can be given off to the atmosphere by plant
  leaves through transpiration, or by animals
  through respiration, perspiration, or excretion.

51
(No Transcript)