Download Influences on Ecosystems

Biotic & Abiotic Influences on
Ecosystems
Population Change and Stability
Populations
• Recall that a population is the amount of species in
an ecosystem
• What would cause the human population on Earth
to change?
– Births and Deaths
• What would causes the human population of
Milton to change?
– Births, Deaths, Immigration, Emigration
• Earth is a closed population since organisms
cannot enter or leave
• Milton is an open population since they can
Limits on Populations
• There are natural limits to the size of populations
in an ecosystem
• For example, Milpond might have a population of
a few hundred fish, but Lake Ontario would have
many thousands - Why?
• Limiting Factors!
– A factor that puts an upper limit on the size of a
population
– Amount of food, space, access to water, …
Abiotic Factors
• Every species can survive within a certain range of
abiotic factors – tolerance range
– Example: A pike needs water between 4oC and 25oC –
outside of that range, they cannot survive
• Within a tolerance range is an optimal range – the
range in which the species is best adapted to
survive
• Each species has a tolerance and optimal range for
each abiotic factor
• Species with a large tolerance range tend to be
widespread
Tolerance and Optimum Range
• See Also Figure 1, Pg 52
Key Abiotic Factors in Terrestrial
Ecosystems
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Light availability
Water availability
Nutrient availability
Temperature
Key Abiotic Factors in Aquatic
Ecosystems
• Light availability
• Nutrient availability
• Acidity
– Some species prefer acidic environments,
others basic
• Temperature
• Salinity
– The amount of salt in the water
Biotic Factors
• While abiotic factors determine where an
organism can live, the biotic factors
determine how well it can survive
(population size)
• Organisms in the same ecosystem affect
each other greatly
• They affect each other in 5 main ways
Competition
• Two species compete for access to the same
resource
• Foxes and coyotes feed on the same prey
• Humans and wolves feed on the same
livestock
Predation
• One species feeds on another
• In general,
– If prey goes up, predator will go up soon after
– If predator goes up, prey will soon go down
• If no or few predators exist, the population
will grow out of control (Deer in New York
State)
Mutualism
• Two species working together and both
benefiting
• Nitrogen-Fixing bacteria (recall yesterday!)
• Studying with a friend for a test
Parasitism
• One species lives on (or in) another and
feeds on it (the host)
• Tapeworms live in the digestive tract of
animals and absorb much of the nutrients
• Ticks burrow under the skin of animals
Commensalism
• One species benefits while the other is
neither helped nor harmed
• Barnacles live on large whales but don’t
hurt them
• Birds nest it trees
Carrying Capacity
• The population of a species naturally varies over
time
– If the weather is unseasonably warm, the population of
mice may increase, but as their food supply is used up,
the population will decline again
• But, communities tend towards stability
– When they are stable, they are said to be in equilibrium
• The maximum number of individuals of a species
that can be supported indefinitely by an ecosystem
is called its carrying capacity
Carrying Capacity Con’t
• The carrying capacity is determined by the
limiting factors in an ecosystem
• An organism can exceed its carrying
capacity temporarily, but will eventually
return to it
Homework
• Study for Friday’s Quiz
– Everything up to and including tomorrow
– (Chapter 2)
• Pg 55 #1 – 4, 8