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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)