Transcript Populations - jfindlay.ca

Populations
What influences how
populations flourish or
die out?
Biotic Potential
The maximum number of offspring that a species could
reproduce in a life time, if resources were unlimited.
Biotic Potential is determined by:
1. Birth potential: max # of offspring per birth
2. Capacity for survival: # of offspring that reach
reproductive age
3. Procreation: # of times a species reproduces
each year
4. Length of reproductive life: # of years species
can reproduce
Limiting Factors
A limiting factor is any factor that places an upper limit
on the size of a population
Limiting factors can be biotic or abiotic
Human influences often act as limiting factors
What are the limiting factors that might affect a
population of penguins? How about a suburban human
population?
Tolerance Range
The abiotic conditions within which a species can survive
Species can be successful over a range of
abiotic conditions
A population will become stressed and die out if
conditions exceed their tolerance limits
See Figure 1, Nelson, p. 52
Tolerance Range
Use Figure 2, p. 53 (Nelson) to fill in the following chart
Cacti
Waterlillies
Bunchberries
- water levels
minimize exposure
of roots to air
-full
exposure
to sun
- shade
abiotic
conditions
that keep
species
within
tolerance
range
- long
periods of
Drought
-full
exposure
to sun
abiotic conditions
that put species
outside of tolerance
range
- long
- if water level
- too much light
periods of
drops
rain (roots
exposing roots to
cannot
air
survive
-low light availability
damp conditions
-low light availability
Carrying Capacity
The population remains within the limits that the
environment can support
This is the largest population size of a species that an
ecosystem can support or sustain
There are several factors that can influence the Carrying
Capacity of a species:
 food (think also food chains, webs)
 water
 shelter
 space
 climate
 susceptibility to disease
 predation
 competition for many of the above
Carrying Capacity
Carrying capacity can be altered through natural or human
Think-Pair-Share: Consider a species we
have discussed or you know about from your previous
personal experience. How was the carrying capacity of this species
affected by either a natural or human action? (can be positive or negative)
Example 1: Irrigation systems in African deserts increases the carrying
capacity of organisms living in a desert ecosystem (increased water
availability)
Example 2: the removal of wolves by human hunters will increase the
carrying capacity of moose in this ecosystem (more space, less predators)
Example 3: clear-cutting trees will decrease the carrying capacity of
certain bird species that rely on these trees for habitat and to maintain
their nests
Population Density
Is the number of organisms living in a given space
Use a diagram to show a high population density
vs. low population density and provide a specific real
example in nature
Population Density
Densityindependent factors
 factors that do not
depend on the population
size
 weather (storms, cold,
drought, floods, early
freezing, heavy snow)
 forest fires
 comets
 affect
population size
 can lead to
species aggression
and/or panic
can lead to
extinction
can help
populations flourish
 density-independent
diseases (DDT poisoning)
 environmental pollution
Density-dependent
factors
 factors that do depend
on the population size
 food availability
 space (shelter, territories
denning sites, nest cavities
 density-dependent
diseases (rabies, SARS)
 competition
(intraspecific. vs.
interspecific)
Intraspecific vs. Interspecific
Intraspecific: when two organisms from the same
species are after the same resources or food
THINK/PAIR/SHARE: Give a specific example of intraspecific competition.
Interspecific competition: when two organisms from
different species are after the same resources or food
THINK/PAIR/SHARE: Give a specific example of interspecific competition.
Reaching the Carrying Capacity
In the 1800s, the fur trade led to a
Drastic decline in the fur seal population
In 1911 a treaty was signed to protect the
fur seal population
Exponential Growth
Carrying capacity
reached (population
size has reached
equilibrium or is in
balance)
Humans and Carrying Capacity
What actions have humans taken to increase the carrying capacity of our species?
- Early on: using fire, making simple tools/weapons
- Improvements in public health, education, agriculture,
medicine, technology
- Exploiting huge amounts of energy and resources to
run complex, modern societies
What paths might the curve take after this century? Which path do you think is most
likely? Why?
What next?
Invasive species
An invasive species is one that can be
either native and non-native that heavily
colonize a particular habitat.
Natural, wild species can be threatened
with extinction.
The good ones
Asian Oysters- are better
at filtering out water
pollutants than native
oysters.
Garlic Mustardintroduced as a means of
erosion control
Characteristics of Good Invaders
High rate of reproduction (short generation time)
Long-lived
High dispersal rates (produces a lot of seeds)
Single-parent reproduction
Tolerant of wide range of conditions
Habitat generalist
Broad diet
Opportunistic (aggressive, out competes)
Difficult to control and resistant to eradication
Characteristics of the Community
(that make it susceptible to invaders)
Invading nonindigenous species tend to be more
successful when native species do not occupy similar
ecological niches
Species that inhabit disturbed environments and those
with a history of close association with humans tend to
be successful in invading human-modified habitats
Successful invasion is enhanced by similarity in the
physical environment between the source and target
areas
Absence of predators on invading species
Absence of native species morphologically (form or
structure) or ecologically similar to the invader