Population Population Growth Cycles Growth Cycles and Stresses and Stresses
Chapter 35Section 2
Population GrowthPopulation Growth
No Population Can Grow No Population Can Grow
Indefinitely: Indefinitely:
J-Curves and S-CurvesJ-Curves and S-Curves
Biotic potential – capacity for population growth under ideal conditions
o Larger organisms tend to have low potential
Intrinsic rate of increase (r) – rate the population of a species would grow if it had unlimited resources
J-CurvesJ-CurvesIndividuals in populations with high r
o Reproduce early in lifeo Have short generation timeso Can reproduce many timeso Have many offspring each time they
reproduce
Population StressesPopulation StressesAny population growing exponentially goes through a “J” shaped growth, but most of the time environmental influences create an “S” shaped pattern in growth
S-Curves S-Curves Environmental resistance – combination of all factors that act to limit the growth of a population Carrying capacity (K) – maximum population of a given species that a habitat can sustain indefinitely without being degraded
Carrying Capacity and J shaped growth
This shows exponential growth leading to overshoot and population dieback of a species
Phases of Logistic Phases of Logistic Growth CurveGrowth Curve
1. Lag Phase – little initial growth.2. Rapid Growth Phase3. Stable Phase – stabilizing factors limit
growth
Species Reproductive Species Reproductive PatternsPatterns
• r-Selected species, opportunists – species with a capacity for a high rate of population increaseo Many small offspringo Little to no parental care or protectiono Reproductive opportunists
• K-selected species, competitors – reproduce later in life and have a small number of offspring with fairly long life spanso Few large offspringo High parental care
r- and K- selected Organisms
r Unstable environment,
density independent
K Stable environment, density
dependent interactions
small size of organism large size of organism
energy used to make each individual is low
energy used to make each individual is high
many offspring are produced few offspring are produced
early maturity late maturity, often after a prolonged period of parental
care
short life expectancy long life expectancy
each individual reproduces only once
individuals can reproduce more than once in their lifetime
most of the individuals die within a short time but a few live much
longer
most individuals live to near the maximum life span
Courtesy of www.bio.indiana.edu
Positions of r- and K-Selected Species on Positions of r- and K-Selected Species on
the S-Shaped Population Growth Curvethe S-Shaped Population Growth Curve
Types of Population Types of Population ChangeChange
• Stable – population fluctuates slightly above and below its carrying capacityo Characteristic of undisturbed rain
forestso Late loss curve
• Irruptive – short-lived rapidly reproducing specieso Linked to seasonal changes in weather
or nutrient availabilityo Algal Bloomso Early loss curves
S-Curve FluctuationsS-Curve Fluctuations
Types of Population Types of Population ChangeChange
• Cyclic fluctuations, boom-and-bust cycleso Top-down population regulation
• Controlled by predationo Bottom-up population regulation
• Controlled by scarcity of one or more resources
• Irregular – changes in population size with no recurring patterno chaos
r-Curve Fluctuationsr-Curve Fluctuations
Top-down RegulationTop-down Regulation
Survivorship CurvesSurvivorship CurvesThese curves demonstrate
o Type I: Late Loss Populations (K – strategists)
o Type II: Constant Loss Populations (K – strategists)
o Type III: Early Loss Populations (usually r-strategists)
Video for ReviewVideo for Review