Transcript Population cycles

Population Ecology
Biotic potential:
-maximum possible growth rate for a species
-depends on:
-age at maturity
-clutch size
-how often and
how long can
reproduce
-how well and how
many offspring survive
-never attained in nature!
Why?
Limiting Factors:
-space, light, water, food, nutrients, etc.
Density-dependent factors
-have an increasing effect as population density
rises
Density-independent factors
-population size does not influence effect
Growth Rate:
r = births-death
N
Patterns of Growth
Exponential -rapid growth
-frequent doubling
-results in J curve
*Occurs when: new habitat, new food source,
decrease in predators, etc.
Stabilization phase - # deaths = # births
-S (sigmoid) curve
*Carrying capacity: max. # of individuals a habitat can
sustain
Population cycles
-lynx and snowshoe hare
-gypsy moths
r strategists
-many offspring  small, mature quickly
-little or no parental care
-often in unpredictable environments
- “opportunists”
k strategists
-small # of large, slow maturing offspring
-lengthy parental care
-adapted to stable environments
Interactions between species
(community ecology)
Competition
“Interspecific competition” – between members of
different species; for limited resources
Competitive Exclusion Principle
-when 2 species compete for 1 limited resource 
1 wins, the other is eliminated
-only 1 species per niche
Realized niche
-actual niche
Fundamental niche
-theoretical
-larger
-could be occupied by a species if no
competitors present
Predator-Prey
Complex, dynamic interactions
Co-evolution: 2 species evolve in response to each other
1. Plant structural defenses
-thorns, spines, hairs, silica, sticky substances
2. Secondary compounds in plants
-toxic to herbivores
-therefore, plants are avoided
eg. mustard oils, tannins,
nicotine, poison ivy toxin
3. Cryptic coloration
4. Aposematic (warning) coloration
-conspicuous coloration
-predators learn to avoid
5. Mimicry
-1 or more species evolves to
resemble another
Batesian mimicry- unprotected
species mimics protected species
Muellerian mimicry- many
protected species share a color pattern
Symbiosis
-Parasitism
botfly video
-Commensalism
which is this?
-Mutualism
Ecosystem Dynamics
Energy – does it cycle?
NO! it flows through ecosystems, gradually lost as heat
Matter – (nutrients) do not leave ecosystem, they cycle
Biogeochemical cycles:
-water cycle
-carbon cycle – CO2 based
-phosphorous cycle
-nitrogen cycle
-78% of air is N2
but most organisms can not use N2
Biogeochemical cycles (Nitrogen)
3 sources of useable N in ecosystems:
1. lightning - N2  NO32. Decomposition in soil
3. N-fixing bacteria - N2  NH4+
Nitrogen fixation – without it there would be virtually no life!
*free living bacteria – in soil
*symbiotic bacteria - in root nodules of
legumes
Nitrification – bacteria in soil
NH4 + 
NO2 –
NO2 -NO 3- (nitrate)
(plants take in through
roots and use)
Dentrification – bacteria
NO3 - N2
*N is often THE limiting factor in ecosystems
Where does each get its N from? (and in what form?)
Animals
Plants
Bacteria
Atmosphere
500 bushels of wheat
1 cow
What should they do to survive the longest?
A. Eat the cow and then the wheat
B. Drink the cow’s milk, then eat the wheat
C. Don’t feed the cow but drink the milk, eat the
cow when the milk stops, then eat the wheat
D. Feed the wheat to the cow and drink the milk
E. Feed the wheat to the cow, drink the milk, then
eat the cow
F. Eat the wheat, then the cow