Download 1.7.populationsandresources_review

Determining a Population size
 How many fish can live in a pond?
 How many deer can live in a forest?
 What factors can you think of might change this
number?
???????
What is a population?
Population vs. Community?
What is Exponential Growth?
Fig. 1: Number of Bacteria Cells Present Over
Time on an Agar Plate.
Factors affecting Population Size
1. Births number of surviving offspring (natality)
2. Deaths number dying from all causes (mortality)
3. Immigration
 Number entering an area
4. Emigration
 Number leaving an area
What is Exponential Growth?
Fig. 1: Number of Bacteria Cells Present Over
Time on an Agar Plate.
Exponential Growth
Population growth =
(births+ immigration) – (deaths + emigration)
Exponential Growth: accelerated growth that produces a
J-shaped curve when population is graphed over time
 happens when populations reproduce faster and have
immigration of individuals greater than the rate at
which individuals emigrate from the area or die off
Can exponential growth be
sustained?
 NO!
 Usually happens when an organism comes
into a new habitat that has a lot of resources
and little competition or when other
pressures on a population are removed ex.
A predator is removed/eliminated from a
food chain
 Example- pg. 49 textbook protected
elephants in Kruger National Park
Example
 The turkey population in Durham Ontario has seen a
massive spike in the number of wild turkey populating the
area.
 Question: The number of new births is estimated at 200
young making the total population close to 2000 birds. If
only 50 have been hunted and 50 die from natural causes
how many birds can we expect in the next year if no
immigration or emigration occurs?
 Answer:
 Births= 200; deaths= 100; no immigration or emigration
 Population growth = 200 – 100 = 100 individual
 Next year approximately 2100 birds
Human Population change over timeexponential growth
Limiting Factors- prevent exponential
growth
Abiotic Limiting Factors
 Limiting factors (also known as a "constraining" factors)
limits the growth or development of an organism,
population, or process.
 Population growth has a limit that is determined by;
 Abiotic factors –water/precipitation, space
(habitat), temperature, acidity, salinity (salt
concentration), oxygen (in aquatic ecosystems
only), nutrients (e.g. nitrogen), sunlight
 Humans are often a limiting factor in
ecosystems
Key Limiting Biotic Factors
 Can be between individuals of the same species or
between species
 Competition within or between species
 Predator-Prey relationships – one feeds off another
 Symbiotic relationships (parasitic, mutualistic,
commensalism)
 Disease
Biotic Potential
 No ecosystem has an unlimited supply
of resources
 Limits on the population of species are imposed by the
species itself, called biotic potential
 Biotic potential is defined as the maximum number of
offspring that a species could produce if resources
were unlimited
Tolerance Range
 The abiotic conditions
within which a species
can survive
 Some have a wide range
others have a narrow
range
 Optimal range is where
the organism grows
best.
Carrying capacity
 The maximum number of individuals (the largest
population of a species) that the environment can
support in a given area and this is determined by
specific limiting factors
 http://www.youtube.com/watch?v=8FPMP41LYJ8
Carrying Capacity
 Depends on the sustainability of an ecosystem
 Can be altered through natural or human activity
Equilibrium and Carrying Capacity
Fig. 2: Changes in the size of a fish population over time.
CARRYING CAPACTITY
B
A
• In this graph, the fish population has achieved equilibrium, and the
population remains constantly below the ecosystem’s carrying
capacity
• However, populations in ecosystems often goes in cycles.
Carrying Capacity
 Look at the lynx





population
Which number seems to
be the most common
peak?
About 4000
Therefore, 4000 is their
carrying capacity.
If they go over 4000, there
is too much competition
and they run out of food.
Their population
consequently dips below
the carrying capacity
Factors affecting carrying capacity
 Materials:
 the amount of food, nutrients, water, shelter.


If a population continues to grow it will soon out grow its food
supply
Death or starvation may occur *********
Urban Sprawl!!!!
 Food Chains:
 Populations are limited by predator and prey
sustainability, competition
 Hunting, Disease, Parasites, Habitat loss, Pollution
Population Density
 The number of organisms living in a given space
 Think about the population density of wolves in
Ontario compared to the population density of
Canadian geese.
 What differences exist between these two animals that
account for different densities?
 Different Animals need different amounts of space to
roam, forage, hunt and find mates and both require
different amounts of food to live
Limiting Factors that Affect
Carrying Capacity
 Disease
 Pollution
 Density
 Starvation
 Habitat/space
 Food/ water
 Competition
 Hunting
 Climate