r and K selected species

1. r and K selected species

2. 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

3. Population Growth • Exponential growth – population that increases at a fixed rate • J-Curve • Logistic growth – rapid exponential population growth followed by a steady decrease in population growth • S-Curve

4. Population Growth

5. J-Curves • Intrinsic rate of increase (r) – rate the population of a species would grow if it had unlimited resources

6. 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

7. 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. S-Curves

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

10. 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

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

12. Transitioning between J and S curves… • Carry capacity isn’t fixed • Varies depending on climate and season • Unpredictable changes can be devastating to the speciesAND the habitat • Reproductive time lag – period needed for the birth rate to fall and the death rate to rise in response to resource overconsumption • May lead to overshoot • Dieback (crash)

13. r-Curve Fluctuations

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. Top-down Regulation

18. Your Turn! • Make a K selected  r selected continuum on your desk • Organize your cards ON YOUR OWN • Discuss with partner

19. Survival Strategies • Which organisms were difficult to classify? Why?

20. Survival Strategies • K selected • r selected • Red-tailed hawk • Coyote • Western rattlesnake • Roadrunner • Kangaroo Mouse • Whiptail lizard

21. Your Turn! • Live for Today Life Table • Review: • What does late loss look like? • What does early loss look like? • What does constant-loss look like? • Remember to include a key (molting species)