Transcript E7 Within communities different species use different

E7 Within communities different species use
different reproductive strategies
E7.1 KNOW THAT SPECIES WITH HIGH
REPRODUCTIVE EFFORT, SHORT LIFE, AND
MANY OFFSPRING, ARE MORE COMMON IN
EARLY SUCCESSION OR DISTURBED
COMMUNITIES (R-SELECTED)
species
 Not all species have the same capacity for
reproduction
 Microorganisms in the optimum conditions can
breed exponentially- average generation time of 20
minutes
 Exponential growth is not sustained however, or they
would take over the earth: there is limiting factors to
growth, such as nutrients/resources and
accumulation of wastes that can be toxic
 Temperature, predators and disturbances like fire
can limit populations of organisms
R- Selected (reproductive strategists)
 Short germination or gestation period
 Large numbers of offspring
 Little care of the offspring
 Short life span
 Rapid time to maturity and reproduction
 OPPORTUNISITIC- on a continuum
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Sea stars and oysters
Cockroaches
Grasses
Weeds
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All have lots of reproductive effort and right conditions means
millions of offspring quickly
Opportunists or the r-selected organisms:
 First to appear in damaged communities or new
communities like sand dunes or lava flows
 Reproduce rapidly with little competition
E7.2 Know that species with low reproductive effort, long life
and few offspring are more common in stable communities
(k- selected)
 As a community stabilises and organisms are more
established
 Shift in what is in the community
 More of the K selected organisms
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They have fewer offspring
Look after the young
Slow to maturity and reproductive age
Bigger in general
Lizards
 Kangaroos
 Koalas
 Eucalyptus
 Acacia trees
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E7 .3 Understand that r and k strategies are
extremes on a continuum
 The r selected are rapid reproducers but this does depend
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on favourable conditions being available
They will tend to boom in an environment or “bust”
The K selected- refers to those that move into a
community that has begun to be established…has
resources etc …the k standing for carrying capacity- or
maximum population density that the environment can
sustain indefinitely
Involves resources/ food/and species interactions(predators etc.) of all the species of an environment.
generally have adaptations in order to survive that area
The S curve
 The growth of K selected organisms tends to be in an s
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curve
Numbers increase slowly…as the population increases,
then number stabilise around the carrying capacity.
Numbers can fluctuate or cycle around the values of K
In reality most populations lie on a continuum: r and k
selected being the extremes
Some species typically r- locusts
Some typically k –humans
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nimation_-_r_and_k_strategies.html