Population Growth Cycles and Stresses

1. Population Growth Cycles and Stresses Chapter 35 Section 2

2. Population Growth

3. No Population Can Grow Indefinitely: J-Curves and S-Curves Biotic potential – capacity for population growth under ideal conditions • 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

4. J-Curves Individuals in populations with high r • Reproduce early in life • Have short generation times • Can reproduce many times • Have many offspring each time they reproduce

5. Population Stresses Any population growing exponentially goes through a “J” shaped growth, but most of the time environmental influences create an “S” shaped pattern in growth

6. 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

8. Carrying Capacity and J shaped growth

9. This shows exponential growth leading to overshoot and population dieback of a species

10. Phases of Logistic Growth Curve • Lag Phase– little initial growth. • Rapid Growth Phase • Stable Phase– stabilizing factors limit growth

11. Species Reproductive Patterns • r-Selected species, opportunists – species with a capacity for a high rate of population increase • Many small offspring • Little to no parental care or protection • Reproductive opportunists • K-selected species, competitors – reproduce later in life and have a small number of offspring with fairly long life spans • Few large offspring • High parental care

12. r- and K- selected Organisms Courtesy of www.bio.indiana.edu

13. Positions of r- and K-Selected Species on the S-Shaped Population Growth Curve

14. Types of Population Change • Stable – population fluctuates slightly above and below its carrying capacity • Characteristic of undisturbed rain forests • Late loss curve • Irruptive – short-lived rapidly reproducing species • Linked to seasonal changes in weather or nutrient availability • Algal Blooms • Early loss curves

15. S-Curve Fluctuations

16. Types of Population Change • Cyclic fluctuations, boom-and-bust cycles • Top-down population regulation • Controlled by predation • Bottom-up population regulation • Controlled by scarcity of one or more resources • Irregular – changes in population size with no recurring pattern • chaos

17. r-Curve Fluctuations

18. Top-down Regulation

19. Survivorship Curves These curves demonstrate • Type I: Late Loss Populations (K – strategists) • Type II: Constant Loss Populations (K – strategists) • Type III: Early Loss Populations (usually r-strategists)

20. Video for Review