Transcript seral communities

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Ecology – Community Interactions
As populations interact with one another
and influence each other’s survival and
reproduction, they serve as agents of
natural selection – leads to Coevolution
Biotic Interactions:
1. Predator-prey – very close relationship
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Results in coevolution because each exerts
intensive environmental pressure on the other
Generally fewer predators than prey
Most predators are larger than prey or hunt
collectively (wolf pack)
 Includes herbivores eating plants (coevolve also)
 Produce a “saw-tooth” curve
2. Symbiosis – means “living together”, close
interaction between organisms of different
species for extended period of time
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Mutualism – both benefit – ex. Plants and
pollinators, cows and intestinal bacteria
Commensalism – one benefits, the other is
unaffected – ex. Barnacles riding on a whale
Parasitism – parasite benefits, host is harmed
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Parasite harms and weakens host but does not kill it
immediately
In parasitism and mutualism, both species
coevolve since they exert very intense natural
selection pressures on each other
3. Keystone species – some communities have
certain key species that play a major role in
determining community structure
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Role is out of proportion to its abundance in community
Removal drastically alters community
•Ex. Starfish (Pisaster) in rocky
intertidal (overgrowth of
mussels eliminates other
species)
•otters along Calif. coast
(prevent overgrowth of urchins
and destruction of kelp forests)
•elephants in the savanna
prevent encroachment of
forest in grasslands
Succession
• Structural change in a community and it’s
nonliving environment over time
• Occurs because successional communities
tend to alter the area in which they occur in
such a way as to make it less favorable for
themselves and more favorable for other
communities
• Two types: Primary and Secondary
Succession
Primary Succession
• Community gradually colonizes bare rock, sand,
or clear glacial pool where there is no trace of a
previous community (“from scratch”)
 Typically requires thousands or tens of thousands of
years
 First species to arrive are the pioneers – very hardy,
lichens, mosses – change the environment
(breakdown bare rock) so new life can enter
 Pioneer community replaced by seral communities –
intermediate communities such as woody shrubs, trees
(that need sunlight)
 Shade-tolerant, faster growing tree seedlings replace
seral communities leading to climax community
 Climax community – most diverse and stable
community, permanent
Primary Succession
Secondary Succession
• New community develops after an existing
ecosystem is disturbed (forest fire, volcano
eruption, abandoned farm field)
 Occurs much more rapidly (only a few hundred
years)
 Pioneer species are typically grasses, weeds,
wildflowers
• Succession occurs in lakes and ponds
• Start as clear, clean pools of water –
oligotrophic
• Sediments and nutrients begin to
accumulate and fill water – eutrophication
• Eventually water fills and becomes a marsh,
then a meadow, then a forest
Lake Succession
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Common trends in succession:
1. Species composition changes continuously but more rapid
in earlier stages
2. Total number of species represented increases initially,
declines slightly, and finally stabilizes in older stages
3. Net primary productivity increases and is highest in climax
community
4. Store of inorganic nutrients in organisms and plants
increase with older stages
5. Total biomass and amount of nonliving organic matter
increases with older stages
6. Height and massiveness of plants increases
7. Food webs become more complex
• Climax communities found in similar climates
are somewhat alike
• Factors such as annual temperature and
precipitation along with wind, humidity,
latitude, altitude, and topography result in
biotic regions called biomes
• Biomes are characterized by different
climates, plants and animals
• Read about different biomes in textbook