Download chapter 37 - Aurora City Schools

CHAPTER 37
COMMUNITIES AND
ECOSYSTEMS
I. KEY TERMS
http://www.radiolab.org/popup_player/# at 49 min.
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Community – includes the populations of all
organisms that live close enough to each other
for potential interaction.
Ecosystem – all the organisms in a given area,
along with the nonliving (abiotic) factors with
which they interact.
Species – A group of organisms which can
interbreed with each other and able to produce a
fertile offspring.
Habitat – the environment in which a species
normally lives or the location of a living
II. Characteristic Features of
Communities
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Species diversity – The variety of different
organisms that make a community up.
Includes:
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species richness (the total number of different
species)
abundance – the density of living organisms.
Do you think these two communities have equal
species diversity? Why? Why not?
Which one would be a more stable community?
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High species diversity makes the
populations healthier, because:
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Can resist various natural disasters and fires
better
Viral, bacterial or fungal infections can be
less harmful
Can also resist extreme weather conditions
better
Diverse community of plants can give rise a
more diverse community of animals,
microbes, fungi etc.
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Scientists are very concerned today, because
most of the earth’s humans use only 3 main
species of grains as food sources. Why can
this be a major danger to the food supply of
the planet? How can we decrease the risks?
III. Interspecific Interactions –
Feeding Relationships
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Interspecific interactions – interactions
between organisms of different species.
These interactions can be beneficial or
harmful for both or one of the organisms
involved.
During feeding relationships one organism
benefits, however, the other is harmed.
A. Predation – Predator kills the prey for
feeding purposes.
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Predators have acute senses to locate and
identify prey, many also have structures such
as teeth, claws, stingers, fangs and poison to
catch the prey.
Prey uses passive defenses, such as hiding
and mimicry or active ones such as escaping
and defending themselves.
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Examples of prey capturing strategies:
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Concealment – camouflage themselves
Infrared senses – especially for night animals
(snakes, mosquitoes)
Traps – spider webs
Lures – angler fish, glow worms, some spiders
Examples of predator avoidance:
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Mimicry
Unpleasant chemicals and poisons (skunk,
monarch butterfly)
Visual deception (owl butterfly)
B. Herbivory – animals eating plants, however,
they usually do not kill the plant.
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Herbivores – animals that eat plants or
algae.
Herbivore adaptations:
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Chemical sensors
Specialized teeth or mouth structures
Specialized digestive track
Coevolution of herbivores with plants can
also occur – ants and acacia trees
IV. Interspecific Interactions -Symbiosis
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Symbiotic relationships: permanent
interaction between organisms.
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http://www.youtube.com/watch?v=uxVMeLWzB_o
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Three types of symbiosis:
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Parasitism – a form of exploitation, where one
organism lives on or in an other organism and benefits
for growth or reproduction from the other organism
while it harms the other.
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Mutualism – both species benefit from the
association.
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Commensalism – The presence of one species has a
beneficial effect on the other, but is not itself affected
by the association.
IV. Interspecific Relationship:
Competition
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Intense competition exist within individuals of
the same population because they compete
for the exact same habitat and resources –
intraspecific competition.
Competition exist between different species.
These species usually adopted through
evolution to slightly different environments or
the same resources but at different times –
interspecific competition
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Ecological niche – the functional position of
an organism in its environment, comprising
its habitat, resources and the periods of time
during which it is active. The following are
included in a niche:
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Physical conditions – Ex. Humidity, sunlight,
temperature, salinity, pH, exposure, depth
Resources offered by the habitat – Ex. Food
sources, shelter, mating sites, nesting sites,
predator avoidance.
Adaptations for – locomotion, biorhythms,
tolerance of physical conditions, defence,
predator avoidance, reproduction, feeding.
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Gause’s Competitive Exclusion Principle:
Organisms occupying exactly the same niche
cannot coexist because they will compete for
the same resources. Frequently results in
resource partitioning.
Gray squirrel
Red squirrel
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Look at your picture of an owl. What is
included in his niche?
What other animal would this owl compete
with?
How would they resolve the competition
VII. Ecological Succession
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Ecological succession is the process by
which communities in a particular area
change over time. This takes place as a
result of complex interactions between biotic
and abiotic factors.
The succession proceeds in stages until the
formation of a climax community – the most
stable community in the given environment
until some disturbance occurs.
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Primary succession (colonization of regions
with no preexisting community):
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Bare rock → Lichens, bryophytes, annual herbs→
Grasses, small shrubs → Fast growing trees (ash)
→ slower growing broadleaf species (oak)
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Secondary succession – takes place after a
land clearance, tend to be faster than primary
succession. The time scale depends on the
type of species, climatic and soil factors:
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Primary bare earth → open pioneer community
(annual grasses) → grasses and low growing
perennials → shrubs and small trees → young
broadleaved trees → mature woodland.
VIII. Food chains and food
webs
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Food chains – linear sequences that link the
various trophic levels (feeding levels) to each
other. Its composition usually involves a
producer
primary consumer
secondary consumer
tertiary consumer
(occasionally even a quaternary consumer)
and decomposers can be included after every
level.
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Food webs – a more branched arrangement
of feeding relationships. Includes the same
levels that are included in a food chain.
http://teacher.scholastic.com/activities/explorer/ecosystems/be_an_explorer/map/foodweb_play.htm