r and K selected species

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

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

Population Growth

J-Curves• Intrinsic rate of

increase (r) – rate the population of a species would grow if it had unlimited resources

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

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

S-Curves

Phases of Logistic Growth Curve

1. Lag Phase – little initial growth.2. Rapid Growth Phase3. Stable Phase – stabilizing factors limit

growth

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

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

• Carry capacity isn’t fixed– Varies depending on climate and season– Unpredictable changes can be devastating to the

species AND 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)

Transitioning between J and S curves…

r-Curve Fluctuations

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

S-Curve Fluctuations

• 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

Types of Population Change

Top-down Regulation

Your Turn!• Make a K selected r selected

continuum on your desk

• Organize your cards ON YOUR OWN

• Discuss with partner

Survival Strategies• Which organisms were difficult to

classify? Why?

Survival Strategies• K selected

• r selected

• Red-tailed hawk• Coyote• Western

rattlesnake• Roadrunner• Kangaroo Mouse• Whiptail lizard

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)