Connecting Links

1
Connecting Links

• Chapter 1 Unit 1 Sustainability of Ecosystems

2
Key concepts

• The ultimate source of energy for most ecosystems
• Conversion of radiant energy to chemical energy
• Channeling of energy through ecosystems
• Position of an organism in the food chain may
  determine mass and population size
• Human consumption of large part of all radiant
  energy converted into living material

3

• Eating food is one of the main activities of all
  animals
• What are some examples
• Eating food is really about material and energy
  transfer from one organism to another
• This transfer is the basis of a food chain
• Energy flows through living systems by being
  transferred from one organism to another

4

• The original source of the energy for food is the
  Sun
• Radiant energy is captured by green plants,
  algae, and some bacteria through photosynthesis
  and is used to make food
• Many of our environmental problems are caused by
  disrupting the energy flow among organisms e.g.

5
Capturing Energy from the Sun

• Energy is the common denominator for growth,
  reproduction, and sustaining life
• Ecology is the study of all the interactions that
  occur within the biosphere
• An ecosystem is all the interacting parts of a
  biological community and its environment a group
  of living organisms and their abiotic
  environment, forming a self-regulating system
  through which energy and materials flow
• Some ecosystems are forest, lake, pond, ocean,
  desert

6
Capturing Energy from the Sun

• Photosynthesis involves the capture of sunlight
  by green plants and the fixation of atmospheric
  carbon into carbohydrate molecules i.e chemical
  energy
• Energy flows through an ecosystem from one
  species to the next as herbivores eat plants and
  carnivores eat the herbivores

7
Capturing Energy from the Sun

• Chemosynthesis is a process of energy transfer in
  the absence of sunlight whereby bacteria living
  around hot thermal vents on the sea floor use
  chemical compounds to produce sugars. The
  bacteria then use the sugars as energy
• Since green plants convert radiant energy into
  chemical energy for ecosystems, they are called
  producers and represent the first feeding level
  in the ecosystem

8
Capturing Energy from the Sun

• Rabbits, deer, some mice , and herbivorous
  insects that all eat plants are called primary
  consumers
• Animals that feed on the plant eaters are called
  secondary consumers
• Ecosystems require a continual input of energy
  from the Sun
• Green plants produce more energy per unit land
  area than animals so in an agricultural ecosystem
  such as a field of corn or wheat, only a fraction
  of the energy produced is transferred when the
  crops are eaten
• This is analogous to when gasoline is combusted,
  all the energy in the chemical bonds is not
  transferred to the wheels of the car.

9
Feeding or Trophic levels

• Eosystems are made up of several trophic levels.
  Trophic means nourishment
• Producers?Primary Consumers?Secondary
  Consumers?Tertiary Consumers
• 1st tl ?2nd tl ? 3rd tl ?4th tl where tl means
  trophic level

10
Trophic Levels

• Most of the energy at each trophic level is used
  by the organism simply to stay alive
• Energy is required to feed itself, to grow, to
  move, to reproduce, etc
• Only a small fraction of the energy is stored by
  the organism as body tissues.
• It is this fraction that is available as
  potential food for consumers at the next trophic
  level
• Scientists estimate that between 5 and 20 of the
  energy at one trophic level is available for the
  subsequent level. As a rough average, 10 is
  considered a reasonable estimate

11
Trophic Levels

• Consider the following example
• 100 kJ------------------10kJ---------------------
  1kJ-------------------0.1kJ
• Producers------Prim Con--------2nd
  Con----------3rd Con

12
Trophic Levels

• The remaining 90 goes into thermal energy and
  waste.
• Organisms that die without being eaten still
  maintain energy in their tissues.
• Scavengers such as vultures, bald eagles, ravens,
  hyenas, certain species of ants and beetles are
  consumers which feed on the bodies of dead larger
  animals.
• Detritivores are organisms such as crabs,
  earthworms, wood beetles, carpenter ants, which
  feed on the dead bodies of smaller dead animals,
  dead plant materials, and animal dung. They
  include decomposers such as bacteria and fungi
  which consume any remaining dead plant and animal
  matter.
• Decomposers break down the cells and extract any
  remaining energy

13
Trophic levels

• Detritivores feed at every trophic level and
  comprise their own food chains.
• Earthworms and beetles feeding on cow dung become
  part of the food chain for birds and other
  organisms

14
Pyramid of Numbers

• Generally speaking, the higher up the food chain
  you go, the smaller the total numbers of each
  species e.g. hawks eat snakes which in turn eat
  mice. There are more mice than snakes and more
  snakes than hawks. Why might this be so?
• Consider availability of energy
• This leads to the formation of a pyramid of
  numbers

15
Pyramid of numbers
16
Trophic Levels

• There are cases where for example a thousand pine
  bark beetles can feed on one tree. So some
  smaller organisms can feed on larger ones.
  Pyramids of numbers have limitations- they do not
  account for the sizes of the individual
  organisms.
• Another way of measuring energy flow in an
  ecosystem combines the number with the size.
  Biomass refers to the total dry mass of a given
  population of organisms

17
Pyramid of Biomass

• This pyramid graphically represents the decrease
  in biomass while moving up the trophic levels.
  See text p.16

18
Trophic levels

• Exceptions to this upright pyramid do exist. One
  example is a larger biomass of zooplankton
  (microscopic animals) feeding on a smaller
  biomass of phytoplankton (microscopic algae-plant
  organisms) in an ocean ecosystem. See text p.16
• The ecosystem does not crash because of the
  faster growth and reproductive rate of the algae.
  This enables sustainability of the larger biomass
  of zooplankton.
• Another example involves fish and the zooplankton
  they feed on.

19
Trophic Levels

• In addition to the pyramid of numbers and the
  pyramid of biomass, a pyramid of energy flow can
  also be used to represent energy flow in an
  ecosystem. It represent the total chemical energy
  flowing through each trophic level. Since energy
  flow diminishes moving up a food chain, these
  pyramids are always oriented in an upright
  position.

20
Trophic Levels
21
Trophic Levels

• If ,as scientists estimate, only 10 of the
  energy is transferred to the next trophic level,
  then, less and less energy is available to the
  organisms higher up in the food chain. For this
  reason, food chains rarely have more than four
  links.

22
Populations

• Refer to text example p. 18 Killer whales and sea
  otters
• This example illustrates how population changes
  in one part of a food web impact populations in
  other parts of the web.
• A food web is a set of interactions and
  interconnections among different food chains

23
Carrying Capacity

• This refers to the largest population of a
  species than an environment can support.
• Factors determining carrying capacity
• Materials and energy
• Food chains
• Competition
• Density

24
Carrying Capacity

• Materials and energy refer to the supply of
  water, carbon, and other essential materials as
  well as energy from the Sun
• Food Chains refer to the limitations placed on a
  population by the available food supply and by
  predation
• Competition refers to the competing demands for
  resources such as food, water, mates, and space
  among individual organisms. Two types of
  competition are intraspecific within species and
  interspecific or among different species
• Density refers to the need for space. Population
  density means how many individuals can live in an
  area at one time. Overcrowding may lead to
  stress, disease, aggression, neglect of offspring
  etc.
• Factors which increase in significance as the
  population grows are density dependent.
• Other factors can limit a population regardless
  of size they are density independent e.g floods,
  forest fires

25
Feeding People

• Different ecosystems have differing levels of
  productivity. A tropical rainforest ecosystem is
  considerable more productive than desert scrub
  or extreme desert.
• Productivity refers to the average amount of new
  plant biomass produced annually per unit area.

26
Feeding People

• Plants need water and carbon dioxide to make food
  and to grow.
• They also need nutrients like nitrogen and
  phosphorus to grow. The rate of growth is
  affected by temperature. Warmer conditions enable
  faster growth and greater biomass.
• Using irrigation, fertilizers, and
  genetically-modified (gm) crops can improve
  productivity of some ecosystems but they have
  downside risk. What might be some examples of
  this risk?

27
Feeding People

• Clearing tropical rainforest for agriculture and
  cattle ranching has adverse consequences. What
  might some of these be?
• Think in terms of erosion, loss of habitat,
  biodiversity
• When trees are cut in a tropical rainforest, thin
  poor soil remains since most of the biomass is in
  the trees. Detritivores quickly consume most of
  the dead and waste materials on the forest floor.
  The soil washes away by heavy rainfall.

28

• Refer to figure 1.23 in your text. Note that the
  longer the food chain, the smaller the amount of
  energy available to humans at the top of the
  chain. Also most of the worlds population have a
  diet consisting of mostly grain.
• Agriculture aims to produce short, simple food
  chains with usually no more than two links i.e
  plants to humans. Single crops such as wheat,
  corn, or rice are grown on huge tracts of land.
  This is referred to as monoculture.
• Natural ecosystems tend to have hundreds of
  species interconnected in complex food webs.
• When we grow food, insects, birds, and other
  organisms feed on the crops. We consider them
  pests and we impact their population by providing
  a food supply or by chemicals to control insects.
• Pesticides are poisonous chemicals farmers use to
  minimize crop damage. Although they target
  insects, they often have unintended consequences

29

• Referring to the graph on p. 33, note that the
  human population has surpassed 6 billion and
  continues to grow. The population growth has been
  attributed to a decline in the mortality rate due
  to improved health care, sanitation, water supply
  and increased food production. As the population
  grows, energy flow in ecosystems is impacted.
  Burning forests, draining wetlands, paving over
  land for highways, building golf courses and
  residential subdivisions on fertile land, damming
  rivers for energy mega projects, overgrazing land
  with livestock collectively reduce plant biomass
  and energy flow. It has been estimated that
  humans either use, convert, or divert more than
  20 of the Earths biomass.