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Species Interactions & Population Control
Five Major Interactions• 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 Exclusiontwo species competing for the same resource cannot
coexist at constant population values, if other ecological factors remain constant
Predation
SymbiosisClose long term associations between
two or more species
* Three types:1.Mutualism2.Commensalism3.Parasitism
Brood ParasitismThe manipulation and use of a host to raise the young of the brood parasite
*Nest hypothesis *Mafia hypothesis
PopulationA group of interbreeding individuals of
the same species
Population Characteristics
• Size• Density• Dispersion• Age distribution
Population SizeFour variables determine population size:
1. Births2. Deaths3. Immigration4. Emigration
=(Births + Immigration) - (Deaths + Emigration)
Population
Change
DispersionClumps -most popular
1. Cluster near resources2. Groups increase chance
of finding resources3. Protection4. Hunting
Dispersal Examples
Clumped(elephants)
Uniform(creosote bush)
Random(dandelions)
Territorial Solitary
Age Structure• Distribution of individuals among
various ages• Dictates how rapidly a population • Three groups:1. Pre-reproductive stage
not mature enough to reproduce2. Reproductive stage
capable of reproduction3. Post-reproductive stage
too old to reproduce
Life table
Life Tables Shows life expectancies for age
groups Demography: Study of a populations vital
statistics and how they change over time
females males
What adaptations have led to this difference in male vs. femalemortality?
Survivorship curvesGeneralized life strategies
What do these graphs tell about survival & strategy of a species?
0 25
1000
100
Human(type I)
Hydra(type II)
Oyster(type III)10
150
Percent of maximum life span
10075
Su
rviv
al p
er th
ousa
nd
I. High death rate in post-reproductive years
II. Constant mortality rate throughout life span
III. Very high early mortality but the few survivors then live long (stay reproductive)
Reproductive strategies K-selected
late reproductionfew offspringinvest a lot in raising
offspring primates coconut
r-selectedearly reproductionmany offspringlittle parental care
insects many plants
K-selected
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
marking territory= competition
competition for nesting sites
Limiting factorsdensity dependent
competition: food, mates, nesting sites
predators, parasites, pathogensdensity independent
abiotic factors sunlight (energy) temperature rainfall
Ecological SuccessionPredictable changes that occur in a
community over time• Two types:
– Primary– Secondary
Primary SuccessionBegins 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 SuccessionOrganisms 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
Climax CommunityA 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 SuccessionTransition of aquatic habitats
(mainly ponds) filling with sediments & the eventually
becoming a terrestrial ecosystem
