Ecology2

Ecology
Populations, Communities
Biodiversity and Conservation
B.Sc.IIyear,Paper-II
Dr. Pinky Dwivedi

Population Characteristics
1. Population Density:
– The number of organisms per unit area
2. Spatial Distribution:
– Dispersion: The pattern of spacing a population
within an area
– 3 main types of dispersion
• Clumped
• Uniform
• Random
– The primary cause of
dispersion is resource
availability
Population Ecology: Population Characteristics

Population Limiting Factors
3. Population growth rate
– How fast a given population grows
– Factors that influence this are:
• Natality (____ rate)
• Mortality (_____ rate)
• Emigration (the number of individuals moving
_________ a population)
• Immigration (the number of individuals _________ a
population)
Population Ecology: Population Characteristics
birth
death
away from
moving to

• 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-independent 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
Population Ecology: Density-dependent factors

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
0
10
20
30
40
50
60
70
80
90
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Job 1 Job 2
Job 2 lags for a long
time before
exponential growth
kicks in!
Now, how much would
your employer owe you
if you stayed at this job
for another 2 weeks?
What would happen if this
type of growth took place
within a population?

• 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?

– 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)
– When you’re done writing, put your pens down…

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?

– 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

– 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
Population Ecology: Population Growth Models

Communities
• Review:
– A community is a group of interacting populations
that occupy the same area at the same time.
Community Ecology: Communities

Communities
• Range of Tolerance
– The limits within which an organism can exist.
Community Ecology: Communities

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
– Consists of 2 types:
• Primary Succession
• Secondary 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

– 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.

– Small weedy plants and other organisms become
established.
– As these organisms die, additional soil is created

– 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.

– The stable, mature community that eventually
develops from bare rock
is called a
climax community.

Community Ecology: Ecological Succession: Secondary 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: Secondary
– Pioneer species in secondary succession are
usually plants that begin to grow in the disturbed
area.
– This is much faster
than primary
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.

On the left side of your IntNB,
address the following:
• 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: Introduction

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:
Biodiversity and Conservation: What is biodiversity?
Genetic Diversity Species Diversity

Biodiversity
Biodiversity and Conservation: Why is biodiversity important?
Teosinte: A
distant relative
of corn
Domestic corn
plant
Penicillin: Derived from
bread mold
Madagascar Periwinkle: Used to
treat childhood forms of leukemia

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 Main-
land
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

Five Most Recent Mass Extinctions
Ordovician Period (444 MYA)
Devonian Period (360 MYA)
Permian Period (250 MYA)
Triassic Period (200 MYA)
Cretaceous Period (65 MYA)

Activity: Understanding Geological
Time
• Working in your groups, you will get the
following supplies:
– A meter stick
– A roll of 5 meters of paper
– Colored pencils
• Using the worksheet, plot out the dates.
– 1 million years is a millimeter
– 1 billion years is a meter

Ecology2

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