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Ecology
Examine factors such as carrying capacity, fecundity,
density and predation that can cause fluctuations in
populations.
Determine through computer simulations the characteristics
of population growth of two different populations (looking at
the predator prey cycles.
REVIEW
Population Limiting Factors
3. Population growth rate
– How fast a given population grows
– Factors that influence this are:
•
•
•
birth rate)
Natality (____
death rate)
Mortality (_____
Emigration (the number of individuals moving
_________
away
from a population)
moving to a
• Immigration (the number of individuals _________
population)
Population Limiting Factors
• Density-independent factors
– Factors that limit population size, regardless of
population density.
– These are usually abiotic factors
– They include natural phenomena, such as weather
events
• Drought, flooding, extreme
heat or cold, tornadoes,
hurricanes, fires, etc.
Population Ecology: Density-dependent factors
Population Limiting Factors
• Density-dependent factors
– Any factor in the environment that depends on
the number of members in a population per unit
area
– Usually biotic factors
– These include
•
•
•
•
Predation
Disease
Parasites
Competition
Determine whether the following are density independent or density
dependent factors:
A flash flood destroys a field of corn
Density Independent
A puffin cannot find a nesting site because of nesting seagulls
Density Dependent
A tomato plant is killed by an early frost
Density Independent
A deer population is prey for a wolf family
Density Dependent
West Nile Virus spread faster in the crows in Southern Ontario
Density Dependent
Passenger pigeons are extinct because their numbers dropped
below 50,000 birds
Density Dependent
Painted turtles often dig up the nests of other painted turtles.
Density Dependent
Density dependent factors:
A: Competition – Interspecific vs intraspecific
Interspecific = Between different species
Intra specific= Between the same species
As the population density increases, there is more competition
so that growth rate slows.
B: Predation
Keeps the population numbers down since predators often select the:
Weaker
Slower
Younger
Survival of the fittest
Density dependent factors:
C. Disease
Pathogens spread more easily when populations are overcrowded
D. The Allee Effect (named after Warder Allee)
When populations are below a critical level they cannot bounce back
• Because limited reproductive potential
• Usually with low fecundity (reproductive potential)
Population Ecology: Population Growth Rate
Understanding Exponentials
• Put your pens down for a minute & think about
this:
– An employer offers you two equal jobs for one hour
each day for fourteen days.
– The first pays $10 an hour.
– The second pays only 1 cent a day, but the rate
doubles each day.
– Which job will you accept?
Population Ecology: Population Growth Rate
Understanding Exponentials
Job 1
90
80
70
60
50
40
30
20
10
0
Job 2
Now, how much would
your employer owe you
if you stayed at this job
for another 2 weeks?
Job 2 lags for a long
time before
exponential growth
kicks in!
1
2
3
4
5
What would happen if this
type of growth took place
within a population?
6
7
8
9
10 11 12 13 14
Population Ecology: Population Growth Rate
Population Limiting Factors
• Population growth models
– Exponential growth model
• Also called geometric growth or J-shaped growth.
• First growth phase is slow and called the lag phase
• Second growth phase is rapid and called the exponential
growth phase
• Bacteria can grow at this rate, so why aren’t we up to our
ears in bacterial cells?
Population Ecology: Population Growth Rate
Population Limiting Factors
• Population growth models
– Limits to exponential growth
• Population Density (the number of individuals per unit of
land area or water volume) increases as well
• Competition follows as nutrients and resources are used
up
• The limit to population size that a particular environment
can support is called carrying capacity (k)
Population Ecology: Population Growth Rate
What population do you think this is?
So, what do you think is going to
happen to the human population?
• We will probably reach our carrying capacity.
• Our growth rate will start to look like most
organisms, which is the Logistic Growth Model
Carrying Capacity (k)
What letter does this curve
kind of look like?
Population Ecology: Population Growth Models
Population Limiting Factors
• Population growth models
– Logistic Growth Model
• Often called the S-shaped growth curve
• Occurs when a population’s growth slows or stops
following exponential growth.
• Growth stops at the population’s carrying capacity
• Populations stop increasing when:
– Birth rate is less than death rate
(Birth rate < Death rate)
– Emigration exceeds Immigration
(Emigration > Immigration)
Population Ecology: Population Growth Models
Population Limiting Factors
•
Population growth models
– Logistic Growth Model
The S-curve is not as pretty as the image looks
1. Carrying capacity can be raised or lowered. How?
Example 1: Artificial fertilizers have raised k
Example 2: Decreased habitat can lower k
2. Populations don’t reach k as smoothly as in the logistic
graph.
•
•
Boom-and-Bust Cycles
Predator-Prey Cycles
Sinusoidal patter can result from seasonal changes or
predator /prey relationships also
Predator prey relationships
Introduction – what does a typical predator-prey cycle
look like?
What factors does it depend on?
http://www.sims.scienceinstruction.org/predprey/index.html
(start around 5,1,8)
In our first model the following factors were important:
Predator birth rate
Predator aggression
Predator dependency.
In this model carrying capacity could be reached for both
populations. “Predator dependency” reflected alternative
resourses for the predator in the ecosystem.
Predator aggression, birthrate and dependency could be
directly affected by…..
Competition in the ecosystem. Both intra and interspecies
competition.
http://www.leinweb.com/snackbar/wator/
Ecosystem size would also be relevant to the dynamics
of predator/prey cycles.
http://www.xjtek.com/anylogic/demo_models/12/
Ecosystem health and distribution of resources can
also be directly affected by
A single species….
Summary from our simulations on predator/prey
relationships
Predator prey relationships can result in cyclic populations.
The nature of these are dependent upon:
•
•
•
•
•
.
Birth rate (of predator and prey)
Predator aggression
Predator dependency (availability of other resources)
Intra and interspecies competition
Habitat size
The elephant simulation demonstrated that :
An individual species can have an large overall effect
on the distribution of resources for other species.
Who is the elephant in the room??
Community Ecology: Communities
Communities
• Review:
– A community is a group of interacting populations
that occupy the same area at the same time.
Community Ecology: Communities
Communities
• Limiting Factors
– Any abiotic or biotic factor that restricts the
numbers, reproduction, or distribution of
organisms.
Community Ecology: Communities
Communities
• Range of Tolerance
– The limits within which an organism can exist.
Community Ecology: Ecological Succession
Ecological Succession
• Ecological Succession
– The change in an ecosystem that happens when
one community replaces another as a result of
changing biotic and abiotic factors
Community Ecology: Ecological Succession
Ecological Succession
• Ecological Succession
– Consists of 2 types:
• Primary Succession
• Secondary Succession
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– The establishment of a community in an area of
exposed rock that does not have topsoil is called
Primary Succession.
• It occurs very slowly at first
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– The first organisms to arrive are usually lichens or
mosses, which are called pioneer species.
• They secrete acids that can break down rock
• Their dead, decaying organic materials, along with bits
of sediment from the rock make up soil.
Why did the fungus marry
the Algae?
They took a Lichen to
each other!!
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– Small weedy plants and other organisms become
established.
– As these organisms die, additional soil is created
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– Seeds brought in by animals, water and wind
begin to grow in the soil.
– Eventually enough soil is present for shrubs and
trees to grow.
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– The stable, mature community that eventually
develops from bare rock
is called a
climax community.
Community Ecology: Ecological Succession: Secondary Succession
Ecological Succession
• Ecological Succession: Secondary
– Disturbances (fire, flood, windstorms) can disrupt
a community.
– After a disturbance,
new species of plants
and animals might
occupy the habitat.
Community Ecology: Ecological Succession: Secondary Succession
Ecological Succession
• Ecological Succession: Secondary
– Pioneer species in secondary succession are
usually plants that begin to grow in the disturbed
area.
– This is much faster
than primary
succession
Community Ecology: Ecological Succession
Ecological Succession
• Ecological Succession: End point?
– Cannot be predicted
– Different rates of growth &
human involvement
make it impossible to
know if a true climax
community has been
reached.
Biodiversity and Conservation: Introduction
FOOD WEB
• What would happen if all of the jackrabbits in
a food web died suddenly?
• Is the disappearance of one species from
Earth important, or will another species fill its
niche?
Biodiversity and Conservation: What is biodiversity?
Biodiversity
• What is Biodiversity?
The variety of life in an area that is
determined by the number of different
species in that area.
• There are 2 main types:
Genetic Diversity
Species Diversity
Biodiversity and Conservation: Why is biodiversity important?
Biodiversity
Penicillin: Derived from
bread mold
Teosinte: A
distant relative
of corn
Domestic corn
plant
Madagascar Periwinkle: Used to
treat childhood forms of leukemia
Biodiversity and Conservation: Extinctions
Extinction Rates
• The gradual process of becoming extinct is
known as background extinction.
• Mass extinctions: When a large percentage of
all living species become extinct in a relatively
short period of time.
• 250 MYA: Over
90% of species
died
Biodiversity and Conservation: Extinctions
Estimated number of Extinctions since
1600
Group
Mainland
Island
Ocean
Total
Approximate
Number of
Species
Percent of
Group
Extinct
Mammals
30
51
4
85
4000
2.1
Birds
21
92
0
113
9000
1.3
Reptiles
1
20
0
21
6300
0.3
Amphibians
2
0
0
2
4200
0.05
Fish
22
1
0
23
19,100
0.1
Invertebrates
49
48
1
98
1,000,000+
0.01
Flowering
Plants
245
139
0
384
250,000
0.2
Biodiversity and Conservation: Extinctions
Five Most Recent Mass Extinctions
Cretaceous Period (65 MYA)
Triassic Period (200 MYA)
Permian Period (250 MYA)
Devonian Period (360 MYA)
Ordovician Period (444 MYA)