Population Growth Cycles and Stresses Chapter 35 Section 2.

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)

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