Download Analyzing Communities

Ecology, Evolution and Biodiversity
Very important for students
In the study of ecology, we will be looking at organisms and their interactions. Most of
this you have done before, but now we will take it to the next level.
In this unit it is important to know the key terms and the meanings. You will need to
distinguish between terms that refer to similar, but not identical, concepts. You will also
have to give specific examples where appropriate.
Try to watch as many nature documentaries as you can, as they will often illustrate the
issues discussed in class.
Diagrams and interpretation of graphs become very important here, so make sure you
keep up with the assignments given.
Most of this can be done on your own, and pieces of work will be given every day for
homework.
KEEP UP, please.
Communities and Ecosystems
Assessment Statement
5.1.1
Define species, habitat, population, community, ecosystem and ecology
Understanding the relationships between organisms and their environment is just as
important as knowing about the structure and physiology of animals and plants. Ecology
is an essential part of modern biology.
Ecology –
One of the ideas that ecologists have introduced is that of the ecosystem.
Ecosystem –
The ecosystem is a basic functional unit of ecology since the organisms that make up a
community cannot realistically be considered apart from their physical environment.
Ecosystems are variable in size and content, depending on where it is located and the
organisms that inhabit the area.
Examples of ecosystems are ponds, lakes, woods, forests, sea shores, salt marshes,
grasslands, savannah or tundra.
A lake or woodlands illustrate two important features of an ecosystem:

a largely self-contained unit, since most organisms of the ecosystem spend their
entire lives there and their essential nutrients will be endlessly recycled around
and through them

an interactive system, in that the kinds of organisms that live there are largely
decided by the physical environment, and the physical environment is constantly
altered by the organisms.

the organisms (community) of an ecosystem are called the biotic component

the physical environment is known as the abiotic component
More Ecology Terms you need to know:
Habitat –
Population –
Community –
Species –
Environment is a term we commonly use to mean ‘surroundings’. In biology, we talk
about the environment of cells in an organism, or the environment of organisms in a
habitat. It is a very general term.
Question
Suggest why the dominant plant species of a habitat may more or less determine the types
of animal life present.
The Biosphere
The biosphere is defined as
It is a narrow zone around the earth that harbours all life. Energy enters the biosphere
and each of the ecosystems, often in the form of sunlight. Energy is lost from the
biosphere in the form of heat. Matter remains within the biosphere so it needs to be
recycled continuously, often beyond the limits of one ecosystem. For example, the
destruction of the tropical rainforest is one of the factors contributing to the increase of
carbon dioxide in the atmosphere, which, is thought, to be linked to global warming.
This illustrates that even ecosystems that seem far away from each other, may be
interconnected and interrelated.
Key Points
1.
2.
3.
4.
5.
The biosphere is composed of smaller parts called ecosystems
The biosphere has biotic and abiotic components
Ecosystems have boundaries that are sometimes hard to distinguish, and
organisms can move between two ecosystems in the course of a life or day
There is a cycling of matter between the biotic and abiotic portions
Energy drives the ecosystem, but it cannot be recycled and the amount of energy
in decreasing.
DO THE SHEET ON BIOMES.
Energy and the Ecosystem
Assessment Statement
5.1.2
5.1.3
Distinguish between autotrophy and heterotroph
Distinguish between consumers, detritivores and saprotrophs
Feeding relationships – Producers, Consumers and Decomposers
The essence of survival of organisms is their activity. To carry out these activityes,
organisms need energy. The immediate source of energy in cells is the molecule
_____________________, which is produced by respiration. We will learn more about it
later and its production.
The only input of energy on Earth is sunlight, which is absorbed by plants and converted
into sugar. The energy ATP represents has been transferred from sugar and other organic
molecules, the respiratory substrates. These organic molecules are obtained from
nutrients as a result of the organism’s mode of nutrition.
Some organisms can use chemicals to produce energy. This is called chemosynthesis.
Movement of Energy
There are two main types of organisms. They are autotrophs and heterotrophs.
Autotrophs are organisms that
Heterotrophs are organisms that
There are three types of consumers:
1.
Herbivores – feed exclusively and directly on plants and plant material.
Herbivores are primary consumers.
2.
Carnivores – feed exclusively on other animals. Carnivores that feed on
primary consumers (herbivores) are called secondary consumers. Carnivores
that feed on secondary consumers are called tertiary consumers, and so on.
3.
Omnivores – feed on both plant and animal matter. Therefore, they are a
blending of a consumer. An example would be a black bear.
Eventually, al producers and consumers die and decay. Organisms that feed on dead
plants and animals, and on the waste matter of animals are called saprotrophs (meaning
‘putrid feeding’). In ecology, these feeders are known as detritivores and decomposers.
Detritivore –
Decomposer –
Feeding by saprotrophs releases inorganic nutrients from the dead organic matter,
including carbon dioxide, water, ammonia, and ions, such as nitrates and phosphates.
The inorganic nutrients are absorbed by green plants and re-used.
DO PAGES, COMPONENTS OF AN ECOSYSTEM, HABITATS, DINGO
HABITATS AND PHYSICAL FACTORS AND GRADIENTS.
Apply one or more of the terms below to describe each of the listed features of a
freshwater lake.
population ecosystem habitat abiotic factor community biomass
1. The whole lake
2. All the frogs in the lake
3. The flow of water through the lake
4. All the plants and animals present
5. The total mass of vegetation growing in the lake
6. The mud of the lake
7. The temperature variations of the lake
Trophic Levels, the Food Chain and Food Webs
Assessment Statement
5.1.4
5.1.5
5.1.6
5.1.7
5.1.8
Describe what is meant by a food chain, giving three examples, each
with at least three linkages (four organisms)
Describe what is meant by a food web
Define trophic level
Deduce the trophic level of organisms in a food chain and a food web
Construct a food web containing up to 10 organisms, using appropriate
information
The feeding relationship in which a carnivore eats a herbivore, which itself has eaten
plant matter, is called a _____________.
Energy from the sun is the initial energy source. The arrows go from producers to
consumers to represent the energy flow. Depending on the ecosystem, the food chains
are different.
There are two types of food chains:
Grazer food chain – a producer that is fed on by a herbivore, who is in turn eaten by a
carnivore.
Detritus food chain – food for decomposers come from plant and animal waste and
remains. This is where scavengers are located.
In an ecosystem, food chains are not isolated. They interconnect with one another, as a
predator may have several species of prey, or a primary consumer that eats several
species of plants. This is called a ___________.
Food webs are advantageous as they allow predators and prey alternative food choices
when one source becomes scarce. It also allows the consumers to take full advantage of
some food sources when they become plentiful as well.
Trophic Levels refer to
For example, if it is a producer, it is the first trophic level. Plants are said to belong to the
first trophic level since the chemical energy they store and use is one step from the
original energy source, the sun. When an organism eats another, it is one step further
removed, or one trophic level up.
For example:
What trophic level do humans occupy?
Note that there is not a fixed number of trophic levels to a food chain, but there are
usually three to five levels only.
Also important, is that food chains tell us about the feeding relationships of organisms in
an ecosystem, but they are entirely qualitative relationships rather than providing
quantitative data (numbers of organisms).
Using the information on the food webs, identify the trophic levels for each of the
organisms. Then construct two individual food chains from each ecosystem, each
with at least three linkages (four organisms). Identify each organism with its
common name and state whether each is a producer, primary consumer, secondary
consumer, etc.
Construct a food web containing up to 10 organisms. Identify all the food chains
present, identify the trophic levels and the producers, primary consumers,
secondary consumers, etc.
Problems with Food Webs – The Flow of Energy
Assessment Statement
5.1.9
5.1.10
State that light is the initial energy source for almost all communities
State that energy transformations are never 100%
Light is the initial source for almost all communities. While materials cycle through the
ecosystem, energy enters with autotrophs and is used or changed into other forms of
energy and leave the ecosystem again.
The problem is that every time energy is transferred from one level to another, some is
lost, mostly as heat.
Much of the light energy is not retained in a green leaf. Some is reflected, some
transmitted, and some lost as heat energy. Heat is also a waste product of the reactions of
respiration and of the plant’s metabolism, as sugar is converted into lipids and amino
acids. Some of the metabolites are used in the growth and development of the plant, and
by these reactions energy is locked up in the organic molecules of the plant body. When
the plant is eaten, the stored energy is passed on to the consumer. When the plant dies,
the remaining energy passes on to the detritivores and decomposers. When the consumer
eats the producer, the energy is passed on. The consumer transfers some of the energy
into muscular movements and to maintain its metabolism. Some remains undigested and
goes through the consumer unchanged. If the consumer is caught and eaten by another
consumer, the energy is again transferred.
In general, the higher the trophic level, the more food you must consume to maintain a
desired level of energy. Only 10% - 20% of what is eaten by a consumer is built into the
body of an organism to be potentially available for a predator or browsing. There are two
consequences of this:
1.
2.
The energy loss at transfer between trophic levels is the reason why food chains
are short. Few transfers can be sustained when so little of what is eaten by one
consumer is potentially available to the next step in the food chain. That is why
most food chains have 5 levels at the most.
Feeding relationships of a food chain may be structured like a pyramid. At the
start of the chain is a very large amount of living matter (biomass) of green
plants. This supports a smaller biomass of primary consumers, which in turn
supports and even smaller biomass of primary consumer, which in turn supports
and even smaller biomass of secondary consumers.
In other words, there is a huge loss of energy at each stage and an ecosystem can only
support a limited number of higher trophic level organisms.
For example:
Only 1.2% of sunlight is used for photosynthesis, a loss of 98.8%. Of the 1.2 %, a deer
only will get 16.2 % of the energy out of plants. Of this energy, a wolf only gets 11.4%
of useful energy from the deer.
Ecological Pyramids
Assessment Statement
5.1.11
Explain reasons for the shape of pyramids of energy
Ecological pyramids are practical means of analysing ecosystems. They can be used to
express seasonal changes in one ecosystem or to compare different ecosystems at
comparable times.
Initially, pyramids of numbers were produced. All the organisms at each trophic level
were counted. The results were presented as rectangular blocks, stacked on top of each
other, representing the numbers of organisms at each trophic level in a bar diagram. The
organisms can be observed and not damaged with this approach.
The problem with this approach was that it did not allow for differences in size of
organisms. Also, some organisms are so numerous it was hard to make the levels of the
pyramid. A giant oak tree and single green algae are counted the same. Consequently,
the pyramids of numbers created strange shapes of limited meaning.
To overcome this, is to produce pyramids of biomass. To find biomass, the numbers of
organisms or each type in a trophic level are estimated and then the dry weight of the
organisms is found by using a sample of a representative size. A pyramid of biomass will
have a shape close to the ideal model. Based upon seasonal changes or the amount of
nutrients available at each trophic level, the pyramid can change shape. The problem
with a pyramid of biomass is the organism is destroyed to find its dry mass. More mass
is on the bottom due to the amount of flow of nutrients.
One of the problems with pyramids of biomass is they measure the matter in different
organisms at that point. It does not allow for matter being added (births, growth) or for
matter consumed. The preferred pyramid is a pyramid of energy that looks at the inflow
of energy in each trophic level.
A pyramid of energy will never be inverted since it looks at figures of the amount of
energy per unit area (or volume) that flows through the trophic level in a given period of
time. There are a few examples of the pyramid, but they destroy the observed organism
and the data is hard to obtain. They still provide the most accurate tool to analyze an
ecosystem based upon the populations of organisms.
Pyramids of biomass can be converted to pyramids of energy. The amounts of energy are
converted into kJ (kilojoules) and are measured in square meters or area occupied by the
community per year. (kJ m-2 year-1).
Interfering with Pyramids
Most ecosystems can adapt to small changes, for example, the changing of the seasons.
Large changes can permanently alter the types and size of a population found in the
ecosystem.
Factors are:

Hunting and fishing

Monocultures – where diversity becomes limited and ecosystems become less
stable. An example would be our reliance on only certain species of plants
(softwood) has a negative impact.

Pesticides – by wiping out a member of a food chain, we may disrupt the entire
ecosystem. Another issue is biological amplification, where pesticides go through
a food chain and build up in the top of the food chain with tertiary consumers.
Due to the need for more biomass, the toxic build up in top predators is great.
(Peregrine Falcon)
Analyzing Communities
After looking at a community, we can see the very intricate ways in which animals relate
to one another. Every animal has its own habitat, or physical space to live, as well as a
niche, or a role to play in that community.
As a community ages, the organisms and the niches they occupy tend to change. This is
called succession.
In a new community, pioneer organisms (weeds, grasses, etc.) move in first, helping to
regenerate the soil, lowering the soil temperature and the amount of moisture
evaporation. These plants are sun tolerant and resist fluctuations in soil temperatures.
The pioneer community is pushed out by a seral community whose species are similar
to the pioneers but have a longer life cycle. These plants stabilize and enrich the soil, but
crowd out the annual and biennial plants.
A second seral community then follows. These are tree that grow rapidly and require
more nutrients and water than shrubs from the previous community. The shade caused
by these trees cause shrubs to die and prevents the growth of saplings.
Finally a climax community forms. These are trees that tolerate shade and have a high
rate of sapling survival. They work to stabilize the environment, and stay in place until a
major event takes place, bringing the community back to pioneer status.
Give an example of succession after a major event.
The majority of communities described so far are climax communities. However,
change is very important for the maintenance of diversity. In the pioneer community,
diversity is the largest and in the climax community where biodiversity is in decline.
Generalizations about succession:




Species composition changes more rapidly during the earlier stages of succession
The total number of species increases dramatically during the early stages of
succession, begins to level off during intermediary phases, and usually declines as
the climax community becomes established.
Food webs become more complex and the relationships more clearly defined as
succession proceeds.
Total biomass and non-living organic matter increase during succession and begin
to level off during the establishment of the climax community.
LOOK AT THE SUCCESSION STUDY AND THE HANDOUT. ANSWER THE
QUESTIONS PROVIDED.