Module 8 Lesson 6 - 2

Life Strategies

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Read pages 712 to 713

Two general types of life strategies allow species to thrive in varying types of environment: r-selected strategy and K-selected strategy.

K-selected Strategy

What happens to a population that is nearing its carrying capacity? Strong competition occurs for limited resources within the population. This may lead to a reduction in reproductive rate to ensure that limited resources are utilized effectively. A population that adopts this type of strategy is said to be K-selected because that population does better when it is near its carrying capacity. Some examples of K-selected species include humans, coconut palms, tawny owls, and wood bison.

The K-selected species produce a small number of offspring, and the offspring require much time to reach reproductive age. The parents must invest more time and energy to rear the offspring successfully into their maturity. These individuals tend to have larger bodies and to live for longer periods.

r-selected Strategy

On the other hand, a population that adopts an r-selected strategy is suited better in an environment that is far below its carrying capacity. Resources are abundant and competition is less. The population does not need to invest so much energy into reproduction. Instead, individuals try to take advantage of the favourable conditions and reproduce as many offspring as possible. Examples of r-selected species include dandelions, mice, algae, and fruit flies.

The r-selected species have a short lifespan and reach their reproductive age quickly. Their reproduction rate is fast and the offspring do not receive parental care.

Very few species on Earth are completely r-selected or K-selected. Sometimes, they show only some of the characteristics listed on the table below. Many species in their natural habitats demonstrate a life strategy that ranges along a continuum between r- and K-selected strategies.

Use the table below for a comparison of r-selected and K-selected species. To help you remember these two life strategies, use the following mnemonics: r stands for 'rate' and K stands for 'capacity' (Kapazität in German).

Characteristics of r- and K- selected species

Variables	r-selected species	K-selected species
Life span	Short	Long
Reproductive age	Early	Late
Number of offspring	Many	Few
Growth rate is close to biotic potential (r) or to carrying capacity (K)?	Close to biotic potential	Close to carrying capacity
Nurturing of offspring	No	Yes, often extended
Size of organism	Small	Large
Stability of environment	Unstable - high potential of disruption from density independent factors	Stable
Show logistic growth (S-curve) or exponential growth (J-curve)?	Exponential growth pattern (J-curve)	Logistic growth pattern (S-curve)
Examples	Insects and bacteria	Mammals (such as elephants, whales)