Download Biodiversity

Biodiversity
• Biodiversity refers to the number and
variety of species on Earth
• The number of known species is about 1.6
million, most of which are insects.
• However, the estimated number is around
13 million species.
How are Humans Causing
Extinctions?
1. Population increasing at a rate of
220,000 people each day! More space is
required for homes and cropland to feed
them.
Requiring more space means taking away
the habitats of other species.
THE MOST COMMON CAUSE OF
EXTINCTION TODAY IS THE
DESTRUCTION OF HABITATS
2. Unregulated Hunting leads to
extinction. For ex., the American buffalo
once numbered over 60 million; however,
after Europeans settled in America the
numbers were reduced to only 300.
3. Exotic species threaten native species
because they do not have natural
defenses against them.
Ch 5 “Populations”
• Population density is the number of
individuals in an area
Population Growth
• Three factors that affect population size:
(1) number of births
(2) number of deaths
(3) number of individuals that enter or
leave the population
• Immigration- movement of individuals into
an area
• Emigration- movement of individuals out of
an area
Exponential Growth
• If a population has
enough space, food
and is protected from
predators and
disease, then the
population will
increase.
• A J-shaped curve
indicates that a
population is
undergoing
exponential growth.
Under ideal conditions with unlimited
Resources, a population will grow
Exponentially.
Logistic Growth
• As resources become
less available, the
growth of a population
slows or stops.
• S-shaped curve of
this growth pattern is
called logistic growth.
• How does population
growth slow or stop?
Carrying Capacity
• The carrying capacity is the largest
number of individuals that an environment
can support.
Limits To Growth
•
Limiting factors cause population growth
to decrease.
Density-Dependent Factors
When SIZE matters!
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•
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1.
2.
3.
4.
Density-Dependent Factors is a limiting factor
that depends on population size.
When a population reaches a certain size,
especially large, dense populations
Density-dependent factors that limit a
population include:
Competition
Predation
Parasitism
disease
Density-Independent Factors
Size DOES NOT matter!
•
Density-independent factors affect ALL
populations in similar ways, regardless of
the size of population
• Examples include:
1. Unusual weather
2. Natural disasters
3. Human activities like
damming rivers & clear-cutting forests