Ecology and the Environment

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Chapter 22

• Ecology and the Environment

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Environment
Ecology study of relationships between
organisms and environment.
Factors Biotic living Abiotic nonliving
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The Organization of Ecological Systems

• The smallest living unit is the individual
  organism.
• Populations are groups of organisms of the same
  species.
• Communities are interacting groups of populations
  of different species.
• An ecosystem consists of all the interacting
  organisms in an area and their interaction with
  their abiotic surroundings.

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Ecological systems
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Ecosystems

• Those organisms that trap sunlight for
  photosynthesis are called producers, since they
  produce organic material from inorganic material.
  They include green plants, algae, and
  cyanobacteria. They convert sunlight energy into
  the energy contained within the chemical bonds
  organic compounds.
• The organisms that obtain energy in the form of
  organic matter are called consumers. All animals
  are consumers. They either eat plants directly or
  eat other sources of organic matter derived from
  plants.
• Each time the energy enters a different organism
  it is said to enter a different trophic level. It
  is a step or stage in the flow of energy through
  an ecosystem.

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Trophic Levels

• Plants are producers and occupy the first trophic
  level.
• Animals that are herbivores are primary consumers
  and occupy the second trophic level.
• Animals that eat other animals are secondary
  consumers or carnivores. They can be subdivided
  into trophic levels depending on what animals
  they eat.
• Animals that eat herbivores occupy the third
  trophic level and are primary carnivores.
• Animals that feed on the primary carnivores are
  known as secondary carnivores and occupy the
  fourth trophic level.
• A human can eat a fish that ate a frog that ate a
  spider that ate an insect that consumed plants
  for food.
• The sequence of organisms feeding on one another
  is known as a food chain.
• Omnivores are animals that are both carnivores
  and herbivores.

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Trophic Levels

• If an organism dies the energy in the organic
  compounds of its body is released to the
  environment as heat by organisms that decompose
  the dead body into carbon dioxide, ammonia, and
  other simple organic molecules. These organisms
  are called decomposers.
• Decomposers include bacteria and fungi.
• The simple inorganic compounds can now be used by
  producers to trap energy again.

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Ecosystems
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Ecological systems
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Ecological systems
The food chain
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Energy Flow in Ecosystems

• There is about a 90 loss of available energy as
  we proceed from one trophic level to the next
  higher level. When the energy in producers is
  converted to the energy of herbivores much of the
  energy is lost as heat to the surroundings. The
  same is true for all the other levels.

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Energy flow in Ecosystems
Sun is primary source of energy for most living
things. Higher trophic levels lose 90 of
energy to space due to 2nd law of thermodynamics.
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Community Interactions

• Food chains are interwoven into a food web.
• In a community the interacting food chains
  usually result in a relatively stable combination
  of populations.
• Most ecosystems are not constant. As one
  population increases another decreases. This can
  occur because the there are differences in
  rainfall throughout the year or changes in the
  amount of sunlight and in the average
  temperature.
• Some communities, like tropical rainforests, have
  large numbers of different kinds of organisms
  present. Such communities have high biodiversity.
  Others, like tundra communities, have low
  biodiversity. If a specific kind of organism is
  eliminated form a region there is a loss of
  biodiversity.

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Terrestrial Communities

• Terrestrial communities are determined primarily
  by climatic factors of precipitation patterns and
  temperature ranges. They are called biomes.
• Biomes include
• Temperate Deciduous Forest-found in parts of the
  world that have a lot of rainfall and cold
  weather for a significant part of the year.
  Predominant plants lose their leaves more or less
  completely during the year. In much of this
  region the natural vegetation has been removed to
  allow for agriculture.
• Grasslands or Prairie-Common in western North
  America and parts of Eurasia, Africa, Australia
  and South America. The dominant vegetation is
  various species of grasses. The rainfall is not
  adequate to support the growth of dense forests.
  Most have been converted to agricultural uses.
• Savanna-Found in tropical regions that have
  pronounced rainy and dry seasons. Fires during
  the dry seasons prevent the establishment of
  forests. Found in Central Africa and parts of
  South America. Consist of grasses with scattered
  trees.

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Deciduous Forest
Grasslands
Savannah
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Terrestrial Communities

• Desert-Very dry areas and are found throughout
  the world wherever rainfall is low and irregular.
  Some are extremely hot and others can be quite
  cold during the year. Animals avoid the hottest
  part of the day by staying in burrows or other
  shaded, cooler areas. Almost no vegetation.
• Boreal Forest-Also known as taiga-Found in parts
  of southern Canada and northern US and much of
  northern Asia. Evergreen trees are the
  predominant vegetation like spruces and firs.
  Long, cold winters, abundant rainfall.
• Temperate Rainforest-The coastal areas of
  northern California, Oregon, Washington, British
  Columbia and Alaska. Ample precipitation, fertile
  soil and mild temperatures result in lush growth
  of plants like spruce and fir which are
  evergreens. There are trees as old as 800 years.

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Desert
Boreal Forest or Taiga
Temperate Rainforest
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Terrestrial Communities

• Tundra-North of the temperate rainforest.
  Extremely long, severe winters and short, cool
  summers. The deeper layers of the soil are
  permanently frozen-permafrost. Very few plants
  and animals and no trees survive.
• Tropical Rainforests-Primarily in the equator in
  Central and South America, Africa, parts of
  southern Asia and some Pacific Islands. High
  temperatures, daily rain, and many species of
  plants.

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Tundra
Tropical Rainforest
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Carbon cycle essential for the organic compounds
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Nitrogen cycle essential for formation of amino
acids. Often the limiting factor in terrestrial
ecosystems.
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Population Characteristics

• A population is a group of organisms of the same
  species located in the same place at the same
  time, like the rat population in the sewers of
  your city, the number of people of New York City,
  etc..
• The people of the world constitute the human
  population. A species is the largest population
  of a particular kind of organism.
• A population usually implies a place and a time.

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Populations

• A local population is a small portion of a
  species and local populations of the same species
  will show some differences.
• Gene frequency is a difference that populations
  could show. For example, the genes for tallness
  in humans is greater in certain African tribes.
• Another difference in population is its age
  distribution. If the majority of a population is
  prereproductive then a baby boom should be
  anticipated in the future. If it is reproductive
  then the population should be growing rapidly. If
  it is post reproductive then a population decline
  should be anticipated.
• Populations can also differ in their sex ratios.
  (female male). The larger this ratio is the
  faster the population grows.

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Population Growth
Kenya-large prereproductive population will grow
rapidly in the future. US-large reproductive
population, low prereproductive. Will continue to
grow for a time but will Stabilize in the
future. Germany-large post reproductive.
Population is beginning to fall.
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The Population Growth Curve

• There is a tendency for populations to grow if
  environmental conditions permit.
• The change in in population size over time is
  known as a population growth curve.
• The change in the size of a population depends on
  the rate at which new organisms enter the
  population compared to the rate at which they
  leave.
• The number of new individuals added to the
  populations by reproduction per thousand
  individuals is called natality. The number of
  individuals leaving the population by death per
  thousand individuals is called mortality.
• When a small number of organisms, e.g., two mice,
  first invade an area there is a period of time
  before reproduction takes place when the
  population remains small and relatively constant.
  This is called the lag phase.
• The exponential growth phase is when active
  reproduction is occurring and the mortality rate
  is low because the population is young.
• Eventually conditions such as food, water, or
  nesting sites will be in short supply, or
  predators or disease may kill many individuals.
  Then the number of individuals entering the
  population by reproduction or immigration will
  come to equal the number of individuals leaving
  it by death or migration and the population size
  becomes stable
• During the stable equilibrium phase there is a
  decrease in natality and an increase in mortality.

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Population growth curve
Natality added to population by
reproduction Mortality leaving population by
death.
First introduced Natality and mortality low.
Natality equals mortality
High natality
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Limiting Factors to Human Population Growth

• The curve of population growth over the past
  several thousand years for humans shows that the
  human population remained low and constant for
  thousands of years but has increased rapidly in
  the past few hundred years.
• When Columbus discovered America the native
  American population was about 1 million and was
  at near the carrying capacity, the maximum that
  the area could support.
• Today the population of the US and Canada is
  about 300 million people. This tremendous
  increase in the carrying capacity is due to
  technological changes and the displacement of
  other species. Much of it is due to the removal
  of diseases, improvement in agricultural methods,
  and replacement of natural ecosystems with
  artificial agricultural ecosystems.
• However, there are limits, since we cannot
  increase beyond our ability to get raw materials
  and energy or our ability to dispose of waste
  products or the other organisms with which we
  interact.

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Exponential growth
Presently the human population is growing at 75
million people per year. All animals reach a
carrying capacity.
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Practice Exercises

• P. 508-509 Applying the Concepts
• 1, 3, 4, 6, 7, 9, 10, 11, 12

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Summary

• Ecology study of relationships between
  organisms and environment. Biotic-living,
  abiotic-nonliving.
• The smallest living unit is the individual
  organism. Populations are groups of organisms of
  the same species. Communities are interacting
  groups of populations of different species. An
  ecosystem is all the interacting organisms in an
  area and their interaction with their abiotic
  surroundings.
• Those organisms that trap sunlight from inorganic
  material for photosynthesis are called
  producers, the first trophic level, like green
  plants, algae, and cyanobacteria. They convert
  sunlight energy into the energy contained within
  the chemical bonds organic compounds. Consumers
  obtain energy in the form of organic matter.
• All animals are consumers. Each time the energy
  enters a different organism it is said to enter a
  different trophic level. Animals that are
  herbivores are primary consumers and occupy the
  second trophic level. Animals that eat other
  animals are secondary consumers or carnivores.
  Animals that eat herbivores occupy the third
  trophic level and are primary carnivores. Animals
  that feed on the primary carnivores are known as
  secondary carnivores and occupy the fourth
  trophic level. The sequence of organisms feeding
  on one another is known as a food chain.
  Omnivores are animals that are both carnivores
  and herbivores.
• The energy in the organic compounds of dead
  organisms is released to the environment as heat
  by decomposers that turn them into carbon
  dioxide, ammonia, and other simple organic
  molecules and include bacteria and fungi. These
  can now be used by producers to trap energy again.

• There is about a 90 loss of available energy as
  we proceed from one trophic level to the next
  higher.
• Biomes temperate deciduous forest-cold, rainy
  Grasslands-medium rain, vegetation mostly grass
  savannah-rainy and dry seasons, little
  vegetation desert-very dry, almost no
  vegetation taiga or boreal forest-long cold
  winters, rainfall temperate rainforest-mild T,
  rain, evergreen trees tundra-very cold, little
  vegetation tropical rainforest-warm, rainy, many
  plants.
• Carbon cycle-CO2 from atmosphere intake by
  plants, photosynthesis converts it to organic
  materials and O2. Organic materials are taken in
  by herbivores and use it for energy and to grow
  through respiration, and this produces CO2 which
  It is returned to the atmosphere.
• Nitrogen cycle-N2 Bacteria convert it to
  compounds that plants can use and animals obtain
  it from plants. It is later returned to
  atmosphere after decomposition of living matter
  or taken up by plants again.
• Population growth based on age distribution and
  sex. More females-more reproduction. More
  reproductive age-positive current growth, more
  post reproductive age-negative growth. More
  prereproductive age-future positive growth.
• Initial lag phase, then natality greater than
  mortality- exponential growth phase. Later
  natality equals mortality stable equilibrium
  phase.
• Carrying capacity-the maximum population an area
  can hold. Can be increased by technological
  advances. The world as a whole is now in an
  exponential growth phase.