Transcript ECOSYSTEMS ARE ALWAYS CHANGNING

ECOSYSTEMS ARE ALWAYS
CHANGING
• POPULATIONS CHANGE OVER TIME
– POPULATION GROWTH & DECLINE
– MAINTAINING A BALANCE
• ECOSYSTEMS CHANGE OVER TIME
– SUCCESSION: gradual change in an
ecosystem in which one biological community
is replaced by another (fieldforest).
• PRIMARY SUCCESSION
• SECONDARY SUCCESSION
– PATTERNS OF CHANGE
Population Growth & Decline
• Birth rate is 1 factor affecting population (unstable
ecosystem-lack of food-may delay reproduction)
• Predator-Prey interactions affect population size.
• Limiting Factor = any factor/condition that limits
the growth of a population in an ecosystem. A large
# of predators will limit # of prey. Lack of nutrients
for soil limits plant population; large population of
algae in lake can use up oxygen & limit # of fish.
Maintaining a Balance
• Living things have certain minimum
requirements for food, water & living space.
• CARRYING CAPACITY = when a population
reaches a state where it can no longer grow (the
maximum number of individuals that an
ecosystem can support).
• An ecosystem’s carrying capacity is different for
each population (a meadow can support more
ants & bees than bluebirds; Isle Royale supports
more moose (1o consumer eating plants) than
wolves (2o consumer).
• Biotic factors can be limiting factors; interactions
between populations (competition, predation,
parasitism). Abiotic factors (temp., water,
minerals, wind exposure) are limiting too.
PRIMARY SUCCESION
• Primary succession: establishment of a new biological
community (plants starting to grow where a glacier retreated
& left a barren area)
• Pioneer Species: the first living things to move into a barren
environment (moss & lichen are common when no topsoil is
available- have tiny rootlike anchors)
• As pioneers grow, they weaken rock, it breaks down & mixes
with decaying plant matter to form soil. Now, new plants can
move in & take root, eventually supporting small animals
which in turn support larger ones.
•
Secondary
Succession
Takes place after a major disturbance to biological
community in a stable ecosystem. (Soil remains after
flood/fire/human activity)
• Seeds & plant roots survive, so after time grasses &
small shrubs grow up among decaying remains.
• Birds, insects, rodents return. Alder trees (put
nutrients into soil) take root and biological
community grows & develops.
PATTERNS OF CHANGE
• Succession can establish forest, wetland,
coastal or an ocean community. May
happen over tens or hundreds of years.
Pattern is same: community of producers
forms first, then decomposers &
consumers, then more producers and even
more decomposers & consumers, leading
to a stable biological community.
Patterns of Change con’t.
• Pioneer species can help other species
grow or prevent others from establishing.
– Alder trees have nitrogen-fixing bacteria
on roots to improve nutrient content in
soil-allowing other trees to grow. So
pioneering species may stabilize soil,
shade soil or add nutrients to soil when
they die/decompose.
– Plants may release chemicals to keep
other plants from taking root. Or a new
species may outcompete other species
by using up resources or resisting dz.