Transcript Chapter 23* Ecology and the Environment The Organization of Ecological Systems • The smallest living unit is the individual organism. • Populations are groups of.

Chapter 23*
Ecology and the Environment
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.
Environment
Ecology – study of
relationships between
organisms and
environment.
Factors:
Biotic – living
Abiotic – nonliving
Ecological
systems
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.
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.
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.
Ecosystems
Ecological systems
Ecological systems
The food chain
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.
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.
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.
Terrestrial Communities
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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.
Deciduous Forest
Grasslands
Savannah
Terrestrial Communities
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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.
Desert
Boreal Forest
or Taiga
Temperate
Rainforest
Terrestrial Communities
• Tundra-North of the boreal forest. 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.
Tundra
Tropical Rainforest
Carbon cycle – essential for the organic compounds
Figure 23.18
Nitrogen cycle – essential for formation of amino acids.
Often the limiting factor in terrestrial ecosystems.
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.
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.
The allele for type B blood is not evenly distributed in the world. This map shows
that the type B allele is most common in parts of Asia and has been dispersed to
the Middle East and parts of Europe and Africa. There has been very little flow
of the allele to the Americas.
Age Distributions
• 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.
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.
The Population Growth Curve
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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.
Population growth curve
Natality – added to
population by reproduction
Mortality – leaving
population by death.
First introduced
Natality and
mortality low.
High natality
Natality equals
mortality
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.
A number of factors in the environment, such as food, oxygen supply, diseases,
predators, and space, determine the number of organisms that can survive in a
given area-the carrying capacity of that area. The environmental factors that limit
populations
Presently the human population is growing at ~75 million people
per year. All animals reach a carrying capacity.
The Plague
The number of humans doubled from A.D. 1800 to 1930 (from 1-2 billion)
It is projected to double again by the year 2025.
Exponential
growth
Practice Exercises
• P. 508-509 Applying the Concepts:
# 1, 3, 4, 6, 7, 9, 10, 11, 12
New Book:
p. 578-579 # 1, 2, 3, 4, 6, 9, 10, 12
Summary
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Ecology – study of relationships between
organisms and environment. Biotic-living, abioticnonliving.
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.
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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,
many trees, loss of leaves, marked seasons;
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; tundravery cold, little vegetation; tropical rainforestwarm, 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.