Transcript Connecting Links Ecology

Connecting Links
Chapter 1 Unit 1 Sustainability of
Ecosystems
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
• 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
• 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. …
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
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
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
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.
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
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
Trophic Levels
• Consider the following example
• 100 kJ------------------10kJ---------------------1kJ-------------------0.1kJ
• Producers------Prim Con--------2nd Con---------3rd Con
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
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
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
Pyramid of numbers
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
Pyramid of Biomass
• This pyramid graphically
represents the decrease in
biomass while moving up the
trophic levels. See text p.16
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 algaeplant 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.
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.
Trophic Levels
Secondary
Consumers
Primary Consumers
Producers
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.
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
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
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
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.
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?
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.
• 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 world’s 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
• 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
Earth’s biomass.