Unit 3.2: K-Selected vs. R-Selected Species

Overview

This lecture covers K-selected and R-selected species, focusing on their reproductive strategies, population dynamics, and ecological implications.

Selection theory explains species' reproductive strategies based on quality (K) or quantity (R) of offspring.
K-selected species focus on quality, producing fewer, well-cared-for offspring.
R-selected species focus on quantity, producing many offspring with little to no parental care.

Larger body size, long lifespan, late sexual maturity.
Produce few offspring with high parental investment.
Populations remain near carrying capacity (K) in stable environments.
High competition for limited resources.
Recover slowly after disturbances and are more affected by environmental change.
Example organisms: elephants, humans, whales, bears, whitetail deer.

Smaller body size, short lifespan, early maturity.
Produce many offspring with minimal parental care.
Populations fluctuate widely (boom and bust cycles) and do not stay near carrying capacity.
Low competition, rapid colonization.
Recover quickly after disturbances; less affected by invasive species.
Example organisms: mice, mosquitoes, dandelions, annual plants, zebra mussels.

K-selected: logistic (S-curve) growth, population limited by carrying capacity.
R-selected: exponential (J-curve) growth, rapid increases without population limits.

Biotic potential is the maximum reproductive rate under ideal conditions.
R-selected species have higher biotic potential than K-selected species.
Many species fall on a continuum and may not fit neatly into either type (e.g., sea turtles, corals).

Invasive R-selected species (e.g., zebra mussels) can outcompete native K-selected species.
K-selected species like whitetail deer recover slowly, requiring population management.

K-selected species — Species with traits favoring stable populations near carrying capacity, few offspring, and high parental care.
R-selected species — Species with traits allowing rapid population growth, many offspring, and little parental care.
Carrying capacity (K) — Maximum population size an environment can sustain.
Biotic potential — Maximum reproductive rate of a population under ideal conditions.
Logistic growth (S-curve) — Population growth that levels off near carrying capacity.
Exponential growth (J-curve) — Rapid population increase without limiting factors.