Transcript EK 4.A.5 Communities are composed of populations of organisms

Data Analysis and Mathematical Models
 The structure of a community is described in terms of
species composition and diversity
 Communities are comprised of different populations
of organisms that interact with each other in negative
or positive ways
 The physical structure of a community is affected by
abiotic factors and also the spatial distribution of
organisms
 The mix of species in terms of both the number of
individuals and the diversity of the species defines the
structure of the community
 Predator/prey
relationships: Snowshoe
Hare and Lynx
 Changes in hare pop. is
followed by similar changes
in lynx pop. – predation
limits hare pop. and food
supply limits lynx pop.
 Fluctuation cycles are
commonly observed
between predator and prey
 Symbiotic Relationships
 Mutualism (+,+)
 Acacia trees provide food
& housing for ants; in
exchange, resident ants
kill any insects or fungi
found on the tree and crop
veg to increase sun
exposure for tree
 Lichen – algae provide
sugar from
photosynthesis; fungi
provide minerals, water,
attachment and protection
 Commensalism (+,0)
 Birds build nests in tree
(benefit from protection)
the tree gets no benefit
or harm
 Egrets gather around
cattle; birds get to eat
insects that swarm
around cattle; cattle are
neither helped or
harmed
 Parasitism (+,-)
 Tapeworm live in the
digestive tract of
animals, stealing
nutrients from the host
 http://youtu.be/rLtUkW5Gpk
 Introduction of Species
 Competitive Exclusion
occurs when two species
compete for exactly the
same resources (they
occupy the same niche),
one is likely to be more
successful. One species
outcompetes the other and
eventually the second
species is eliminated from
the area
 http://youtu.be/rZ_up40F
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 Resource Partitioning
occurs when species
coexist in spite of
apparent competition for
the same resources
 Species do this by
occupying slightly
different niches
 Which species of
paramecia outcompetes
the other?
 Paramecium aurelia
 Physical and biological conditions influence the pace of
succession – in both cases, the conditions which make a
habitat attractive to resident species may no longer exist,
making the habitat more favorable to a new species.
Changes include:
 Substrate texture – change from solid rock, to sand, to fertile

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
soil
Soil pH – decrease due to the decomposition of organic
matter
Soil water potential – ability to retain water varies based on
substrate
Light availability – full sunlight to partly shady to total shade
Crowding – increases with population growth
Primary Succession
Occurs on
substrates that
never previously
supported living
things.
Occurs on volcanic
islands, on lava
flows, on rock left
behind by
retreating glaciers
The first organisms
to colonize a newly
exposed habitat are
called pioneer
species
 Rock & Lava
 1st pioneer species is
typically lichens; hyphae
of fungal component holds
onto rock and absorbs
moisture; lichen secretes
acid which breaks down
rock into soil; as soil
accumulates more and
more species can move in
 R-selected species will be
replaced by K-selected
species
 Sand Dunes – begins
with the appearance of
grasses adapted to taking
root in shifting sands;
grasses stabilize sand to
allow for new species to
follow
 Dunes of Lake Michigan
are an example
Process begins in habitats where communities were entirely of
partially destroyed by some kind of damaging event – this event
does not destroy the soil which allows secondary succession to
proceed at a faster rate.
 Succession on abandoned cropland – begins with the
germination of r-selected species from seeds already in
the soil; trees follow
 Secondary succession of
lakes and ponds – begins
with a body of water,
progresses to a marshlike state, then a meadow
and finally to a climax
community of native
vegetation.