population ecology
DESCRIPTION
Population EcologyTRANSCRIPT
Ecology I
Population Ecology
Why is it important? •assessing health of population•determining endangered or threatened status•predicting population dynamics
Population size… is the number of individuals present at a given time.
The passenger pigeon was once North America’s most numerous bird, but it is now extinct.
Population density… is the number of individuals per unit area.
In the 19th century, the flocks of passenger pigeons showed high population density.
Population distribution…is the spatial arrangement of
individuals.
a) Randomb) Uniformc) Clumped
Population growthPopulations grow, shrink, or remain stable, depending on rates of birth, death, immigration, and emigration.
(crude birth rate + immigration rate) –(crude death rate + emigration rate)
= growth rate
Two Modes of Population Growth1. Exponential growth2. Logistic growth
Represent two different growth patterns or Strategies of populations
Exponential Growth
Also known as a J-curveGrowth is a fixed
percentage of the whole (e.g., 10% per day or year)
Population is growing at its full biotic potential
Exponential growth in a growth curve
Population growth curves show change in population size over time.
Scots pine shows exponential growth
Biotic PotentialMaximum possible growth rate of a
population.Absence of limitations to growth
Example:2 cats plus all their kittens make how
many cats in 10 years? 2 litters/year 2.8 surviving kittens per litter Breeds for 10 years (“breeding life”)
(Drum roll…)(Drum roll…)
ANSWER:80,399,780 cats!!!
Do you need a cat?
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
BioticPotential
J curve
Time
Popu
latio
n
Carrying Capacity
Carrying Capacity: MAXIMUM number of individuals that can be supported
• in a given AREA.• FOREVER.
Can Populations Grow Forever?
OscillationsOscillations::•Populations Populations overshootovershoot the the carrying capacity carrying capacity and and experience a experience a dieback dieback •Can be regular or irregularCan be regular or irregular
•Overshoot Overshoot When a population When a population surpasses the carrying surpasses the carrying capacity of its environment or capacity of its environment or population explosionpopulation explosion
•Dieback Dieback Population crashPopulation crash
Population growth: OscillationsSome populations fluctuate continually above and below carrying capacity, as with this mite.
Population growth: Dampening oscillationsIn some populations, oscillations dampen, as population size settles toward carrying capacity, as with this beetle.
r-Selected Species
r = Growth rateReproduce youngHigh reproductive
ratesMany small
offspringShort-livedFound in unstable
or unpredictable environments
Examples of r-Selected SpeciesWeeds, bacteria, insects, algae, small
mammals
Logistic GrowthAlso known as S-curveGrowth slows as the
population approaches Carrying Capacity
Populations stabilize at carrying capacity
K-Selected SpeciesK = Carrying Capacity
Reproduce later in lifeLow reproductive ratesFewer large offspringLong-livedStable or predictable
environments
Examples of K-Selected Species
Elephants, great apes, hippopotamus, whales, humans (?)
What Determines Population Size or Carrying Capacity?
Environmental ResistanceEnvironmental Resistance All the limiting factors that tend
to reduce population growth rates
BalanceBalance between biotic between biotic potential & environmental potential & environmental resistance determines growth resistance determines growth raterate
Environmentalresistance
Carryingcapacity
Stabilizedpopulation
size
Expo
nent
ial g
rowth
Limiting factors:WaterSpaceFoodPredatorsDisease
LE 4-11
Predator–prey cyclesPopulation dynamics of predator–prey systems sometimes show paired cycles: ups and downs in one drive ups and downs in the other.
QUESTION: ReviewWhich is a K-selected species?
a. A dragonfly that lays 300 eggs and flies away
b. An oak tree that drops its acorns each year
c. A bamboo plant that flowers only once every 20 years
d. A human who raises three children
e. A fish on the second trophic level
QUESTION: ReviewHow can you tell that this population growth curve shows exponential growth?
a. Population is increasing.
b. Data points match curve closely.
c. Population is rising by the same number during each interval.
d. Population is rising by the same percentage during each interval.
QUESTION: ReviewThis shows growth ending at a(n) .
a. exponential… carrying capacity
b. intrinsic… equilibrium
c. logistic… carrying capacity
d. runaway… equilibrium
e. logistic… extinction