APES Agenda: Review Pop. Probs. HW Ppt. Lecture on Growth Curves Homework: Read “Women: Critical Link” Announcments: Exam: Thur. & Fri. All work for Q2 due Friday

r and K selected species Growth Curves

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 Lag Phase – little initial growth. Rapid Growth Phase 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

Transitioning between J and S curves… 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)

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

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

Top-down Regulation

Survivorship Curves

Survivorship Curves

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