Species Interactions &
Population Control
Five Major Interactions
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•
•
•
•
Interspecific Competition
Predation
Parasitism
Mutualism
Commensalism
Interspecific Competition
Different species competing for the same resources
• Niche overlap
– Greater overlap = more intense competition
• Outcomes:
– Resource partitioning
• Evolution/speciation
– Competitive exclusion
• Local Extinction
Resource Partitioning
When species divide a niche to avoid competition
for resources
Competitive Exclusion
two species competing for the same resource cannot coexist at constant
population values, if other ecological factors remain constant
Predation
Symbiosis
Close long term associations between two or more species
* Three types:
1. Mutualism
2. Commensalism
3. Parasitism
Brood Parasitism
The manipulation and use of a host to raise the young
of the brood parasite
*Nest hypothesis
*Mafia hypothesis
Population
A group of interbreeding individuals of the
same species
Population Characteristics
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•
•
•
Size
Density
Dispersion
Age distribution
Population Size
Four variables determine population size:
1. Births
2. Deaths
3. Immigration
4. Emigration
Population
Change
=(Births + Immigration) - (Deaths + Emigration)
Dispersion
Dispersion
Clumps -most popular
1. Cluster near resources
2. Groups increase chance
of finding resources
3. Protection
4. Hunting
Dispersal Examples
Clumped
(elephants)
Uniform
(creosote bush)
Territorial
Random
(dandelions)
Solitary
Age Structure
• Distribution of individuals among various ages
• Dictates how rapidly a population
• Three groups:
1. Pre-reproductive stage
not mature enough to reproduce
2. Reproductive stage
capable of reproduction
3. Post-reproductive stage
too old to reproduce
A
B
C
D
Life Tables
 Shows life expectancies for age groups
 Demography: Study of a populations vital statistics and how
they change over time
Life table
females
males
What adaptations have
led to this difference
in male vs. female
mortality?
Survivorship curves
Generalized life strategies
Survival per thousand
1000
Human
(type I)
I. High death rate in
post-reproductive
years
Hydra
(type II)
100
II. Constant mortality
rate throughout life
span
Oyster
(type III)
10
1
0
25
What do these graphs
tell about survival &
strategy of a species?
50
75
Percent of maximum life span
100
III. Very high early
mortality but the few
survivors then live
long (stay
reproductive)
Reproductive strategies
 K-selected
late reproduction
few offspring
invest a lot in raising offspring
 primates
 coconut
 r-selected
K-selected
early reproduction
many offspring
little parental care
 insects
 many plants
r-selected
Exponential Growth
• Constant growth of a population
–Birth rate exceeds the death rate
• J shaped curve
Conditions for Exponential
Growth
• Unlimited resources
–Abundant space
–Abundant food
–Shelter
–Decrease in predators
–Decrease in disease
–Reproduction
Rule of 70
• How long does it take to double?
– Resource use
– Population size
– Money in a savings account
• Rule of 70
– 70 divided by the percentage growth rate =
doubling time in years
– 70 / 7% means it takes ten years to double
Human Population
Logistic Growth
• Growth of a population slows or stops
as resources become less available
• S curve
Carrying Capacity
The largest number of individuals that a given
environment can support at a given time
Regulation of population size
 Limiting factors
marking territory
= competition
density dependent
 competition: food, mates, nesting
sites
 predators, parasites, pathogens
density independent
 abiotic factors
 sunlight (energy)
 temperature
 rainfall
competition for nesting sites
St. Matthew’s Island
Ecological Succession
Predictable changes that occur in a community
over time
• Two types:
– Primary
– Secondary
Primary Succession
Begins in a place without any soil
• Examples:
– Volcanos
– Glacier retreats
• Process begins with pioneer species
– lichens or cyanobacteria
Primary Succession
• Moss move in bringing insects
• Ferns & grasses
• Shrubs & Trees
Secondary Succession
Organisms evades an ecosystem that already
existed before
• Usually a result of disturbance
–Human disturbance
–Natural catastrophes
Steps in Secondary Succession
• Major disturbance – weeds
come in
• Grasses
• Pines begin to grow
–Grasses are shaded
out
• Old pines die – hardwoods
begin to replace
Secondary Succession
Climax Community
A stable group of plants and/or animals that
colonize an area after a succession event
Ex: Old Growth Forest
Climax Community
• Climax communities are not always BIG trees!
– Grasses in prairies
– Cacti in deserts
Aquatic Succession
Transition of aquatic habitats (mainly
ponds) filling with sediments & the
eventually becoming a terrestrial
ecosystem