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Worksheet 18.1
Chapter 18: Ecology and conservation – fifteen summary
facts
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Plants are distributed according to abiotic factors such as temperature (e.g. grasses on the beach
can survive hot temperatures because they have deep root systems), water (e.g. grasses can find
water in dry sand because they have a long root systems), soil pH (e.g. grasses can live on a sand
dune where the pH is 7.5), salinity (e.g. beach grasses are resistant to dryness caused by salt spray)
and mineral nutrients (e.g. in the forest, a more diverse group of plants is found because there are
more mineral nutrients available). In order to study the distribution of plants living on the beach, in
the foredune and in the forest, a sampling technique called the transect method can be used (page
557).
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Animals are distributed according to abiotic factors such as temperature (e.g. rabbits can withstand
high temperatures of the foredune by building deep burrows), water (e.g. blue herons need
interdunal ponds for nesting), breeding sites (e.g. blue herons breed in interdunal wetlands), food
supply (e.g. rabbits eats the grasses which grow where their burrows are) and territory (coyotes
stay within the territory that they mark, usually in the forest). In order to study the distribution of
animals, the quadrat sample method can be used (Figure 18.2, page 556)
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The niche is the particular role an organism has in an ecosystem. The niche includes where an
organism lives, spatial habitat (e.g. frogs live in mud burrows at edge of a pond), feeding activities
(e.g. green frogs eat aquatic larva of mosquitoes) and interactions with other species. These
interactions can be competitive (e.g. frogs and small fish compete for aquatic larva), herbivory
(e.g. rabbits eat the grasses of the dunes), predation (e.g. blue herons eat the green frogs),
parasitism (e.g. leeches suck the blood of a fish) or mutualism (e.g. lichens are a cooperative
relationship between alga and fungus). A niche can be fundamental (the perfect situation). For
example, the heron eats frogs and lays its eggs in the grasses of the pond. A niche can be realized.
The realized niche is the reality that the organism must live with. For example, if the pond has
dried up due to drought, the heron is in direct competition with the other birds for food and space.
If competition is severe, the principle of competitive exclusion may apply. This states that no two
species in a community can occupy the same niche (Figure 18.3, page 560).
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Biomass is measured as dry mass of organic matter of living organisms. To obtain the dry mass of
an animal, trap and weigh the animal. Use a chart to determine the biomass based on its size or
weight. To obtain the dry mass of plants, choose one plot to sample. Measure the size of each plant
species, then cut them down. Dry the plants in an oven at 90 °C. Use a chart to show the
relationship between height and biomass. Sample other plots in the area and use this information to
determine biomass of the plants.
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A pyramid of energy shows movement of energy through an ecosystem (Figure 18.6, page 564).
Gross production is the total amount of energy trapped in organic matter produced by plants per
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area per time in kilojoules. Net production is the gross production minus the energy lost through
respiration. Biomass is the dry weight of an organism measured in grams per square metre per
year. The formula for calculation of net production is:
gross production minus respiration
GP
–
R
equals
=
net production
NP
A pyramid of biomass has the same shape as the pyramid of energy because higher trophic levels
have lower biomass per unit area. Each successive level of the ecosystem loses more and more
biomass. A pyramid of numbers has a similar shape because the total biomass of food available at
the top trophic level is small. Communities of organisms do not fit perfectly into these pyramids.
For example, Grizzly bears eat plants and insects and some mammals so they do not fit easily in
one trophic level. An eagle is a tertiary consumer when it eats rattlesnakes but a secondary
consumer when it eats rabbits. A food web gives a true picture of what is being eaten in an
ecosystem.
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Primary succession begins when plants slowly begin growing on a previously barren and lifeless
area such as a volcanic island. Secondary succession is more rapid and takes place following an
upheaval of the primary succession such as a recolonization after a forest fire (table, page 568).
During primary succession, the plants affect the soil development by building humus, recycling
mineral nutrients as they decay, and reducing erosion as their roots stabilize the soil. Soon larger
and more diverse organisms can populate the area as soil structure improves.
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The biosphere is all the living parts of the Earth where organisms live. Biomes are divisions of the
biosphere defined by their vegetation and community structure. Biomes are distributed according
to weather patterns, altitude and latitude. A single mountain may have alpine tundra at the top,
coniferous forest next, deciduous forest below, and at the lowest altitude maybe a tropical forest
(Figure 18.9, page 570). A climograph plots the temperature and rainfall in particular regions
(Figure 18.10, page 570). Rainfall and temperature determine the different characteristics of seven
major biomes of our biosphere (chart on page 571)
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Using the Simpson diversity index, the diversity of two different communities can be compared.
This index takes into account the number of individuals of each species present and the number of
species. If one species is dominant in an ecosystem, it is less diverse than an ecosystem with more
evenly distributed organisms. The formula for the index and some practice calculations are found
on pages 573–4.
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The introduction of alien species into an ecosystem can be deliberate, accidental or specifically
intended for biological control. Kudzu was deliberately introduced to the US from Japan in 1876
to prevent soil erosion. Unfortunately, kudzu’s thick growth crushes many other plants as it grows
over them and significantly reduces diversity. Zebra mussels were accidentally released into North
America in the 1980s. They were carried into the Great Lakes in the ballast waters of ships from
Europe. These mussels have done significant damage by clogging up pipes and attaching
themselves to ships. A successful example of biological control is the introduction of a moth,
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Cactoblastic cactorum, from the US into Australia. The moth was introduced to control the spread
of the prickly pear cactus. The prickly pear cactus is under control and a balance exists between
the two populations.
10 Biomagnification is a process by which a chemical substance becomes more concentrated at each
trophic level. DDT is a pesticide that was introduced into the environment to kill insect pests. It
was not known at the time that DDT would not break down and would persist for decades in the
environment. It entered the water supply and was ingested by microscopic organisms. These were
eaten by small fish, which in turn were ingested by larger fish. DDT was magnified in the fatty
tissue of the fish. As the fish were eaten by birds, the magnification increased. The decline of
predator birds was caused by DDT interfering with the production of the hard shells on the bird’s
eggs.
Other serious problems affecting the biosphere include excess UV radiation and the presence of
CFCs (chlorofluorocarbons). CFCs, released from propellants in aerosol sprays and refrigerants,
have been recognized as a cause of depletion of the ozone layer since 1985. CFCs destroy ozone
molecules. The destruction of the ozone layer in the stratosphere allows more damaging UV
radiation to reach the earth. Excess UV radiation causes damage to living tissues (e.g. skin cancer,
mutation of DNA, sunburn and cataracts). Excess UV radiation also causes reduced biological
productivity. Floating microscopic plants are especially susceptible.
11 Environmental changes can be monitored by indicator species. These are species that are very
sensitive to environmental change. Lichens are very sensitive to pollution in the atmosphere.
Macroinvertebrates found in rivers and streams can be used to judge water quality. The number of
organisms of each group is multiplied by a factor which is determined by how sensitive the
organism is to pollution. The higher the biotic index, the higher the quality of the water. Extreme
environmental change can cause a species of organism to become extinct. The extinction of the
Carolina parakeet was caused by several factors – one was the introduction of the honey bee from
Europe which displaced the birds from their nesting areas; another was the clearing of trees for
farm land and fuel; a third was the use of their feathers in women’s hats.
12 Nature reserves can be planned to have certain biogeographical features that promote conservation
of diversity: the size of the reserve, the amount of edge and the use of corridors. Nature reserves
must be actively managed to restore areas and protect native species. Techniques employed are:




restoration (UK is restoring the heathlands)
recovery of threatened species (Florida is restoring habitat for the recovery of gopher
tortoises)
removal of introduced species (US is removing kudzu)
legal protections (posting signs to prevent harmful human activities).
Some conservation is in situ, such as maintaining habitat, removing invasive species and assuring
a large enough population to maintain genetic diversity. Other conservation is ex situ, such as
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captive breeding, botanical gardens where plants are kept in captivity and seed banks where
samples of seed can be kept for decades.
13 Most invertebrates are r-strategists: they reproduce only once, producing many offspring as
quickly as possible. They have a short life span and early maturity in order to survive in an
unstable environment. This is why ecological disruption (e.g. farms) favours pathogens and pests.
Pests tend to be invertebrates (e.g. cockroach, mosquito). On the other hand, K-strategists flourish
in a stable environment (e.g. forest); they invest more resources in development and long-term
survival. They have longer life spans, late maturity, fewer offspring, more than one reproduction in
a lifetime and likelihood of some parental care. Large mammals are excellent K-strategists (table
page 590).
14 Capture–mark–release–recapture method is a sampling technique to estimate the number of
animals in an ecosystem. Capture some animals in a population and mark them. Release the
animals back into the ecosystem to mix with the others in the population. Recapture a second set.
The proportion of marked to unmarked in the second sample will be the same proportion as the
marked to unmarked in the population as a whole (page 591).
15 How do we predict the size of a population of fish? Some of the methods used are: gathering
information from fishers, using research vessels to cast nets, monitoring fish populations with
sound devices, calculating the age of fish in a population by studying the rings on their ear bones
and tagging the fish so that when they are recaptured the total population can be estimated. The
goal is to educate fishers about the maximum sustainable yield (MSY). This is the highest
proportion of fish that can be removed from a total population without jeopardizing the future of
the fish in that area. To maintain the MSY, enough fish stock must be left to spawn a new
population of healthy fish. The following measures could be put in place by an international
commission to promote the conservation of fish: regulation of bottom trawling, awareness of
MSY, elimination of by-catch, enactment of fishing quotas, development of less damaging fishing
gear, and establishment of marine reserves and no-catch zones. International cooperation is needed
but many impediments exist. Governments may be under political pressure not to limit fish
catches.
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