IB Environmental systems and societies Topic 2.1N R- and K Strategists Revision Notes (HL)

IB Environmental systems and societies Topic 2.1N R- and K Strategists Revision Notes (HL) | RevisionDojo

Written by official IB examiners

Life-Cycle Strategies: Fast and Many vs Slow and Few

Every organism has a life cycle of birth, growth, reproduction, and death, but species differ hugely in how they run it.
The two key differences are reproductive behaviour (how often and how many young a species produces) and lifespan.
These traits are evolutionary responses to the stability of the environment and the availability of resources.
Species in unstable habitats tend to breed fast and in large numbers, while species in stable habitats breed slowly and invest heavily in a few offspring.
This pattern is explained by r/K-selection theory.

r/K-Selection Theory: Two Reproductive Bets

The r/K-selection theory explains how species tune their reproductive strategy to environmental conditions.
It was proposed by MacArthur and Wilson (1967).
1. The symbol r is the rate of population increase, which is high for fast-reproducing species.
2. The symbol K is the carrying capacity, the largest population the resources can support.

r-Strategists: The Opportunists

Definition

r-strategists

Species that reproduce rapidly, producing many offspring with little parental care.

r-strategists reproduce quickly to exploit short-lived or disturbed environments.
They rely on producing large numbers of offspring rather than protecting each one.

Note

High reproductive rate: many offspring so that some survive.
Minimal parental care: young are left to fend for themselves.
Short lifespan: individuals mature fast and die young.
Small body size: little energy invested per individual.
Unstable populations: numbers swing widely with resources.
Rapid colonisation: they quickly occupy new or disturbed habitats.

Example: Fruit Flies and Rodents

Example

Insects such as fruit flies (Drosophila) and rodents are classic r-strategists.
They breed rapidly and have many young, but face high mortality from limited resources and predation.

How r-Strategists Grow

Note

r-strategists show exponential (J-curve) growth, rising fast when resources are plentiful.
Growth has little density regulation, so numbers can crash in a boom-and-bust cycle.

Thinking About r-Strategists

Analogy

r-strategists are the entrepreneurs of nature, taking high risks for high rewards in fast-changing conditions.

K-Strategists: The Competitors

Definition

K-strategists

Species that reproduce slowly, producing few offspring but investing heavily in their survival.

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Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
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Life-Cycle Strategies: Fast and Many vs Slow and Few

Every organism has a life cycle of birth, growth, reproduction, and death, but species differ hugely in how they run it.
The two key differences are reproductive behaviour (how often and how many young a species produces) and lifespan.
These traits are evolutionary responses to the stability of the environment and the availability of resources.
Species in unstable habitats tend to breed fast and in large numbers, while species in stable habitats breed slowly and invest heavily in a few offspring.
This pattern is explained by r/K-selection theory.

r/K-Selection Theory: Two Reproductive Bets

The r/K-selection theory explains how species tune their reproductive strategy to environmental conditions.
It was proposed by MacArthur and Wilson (1967).
1. The symbol r is the rate of population increase, which is high for fast-reproducing species.
2. The symbol K is the carrying capacity, the largest population the resources can support.

r-Strategists: The Opportunists

Definition

r-strategists

Species that reproduce rapidly, producing many offspring with little parental care.

r-strategists reproduce quickly to exploit short-lived or disturbed environments.
They rely on producing large numbers of offspring rather than protecting each one.

Note

High reproductive rate: many offspring so that some survive.
Minimal parental care: young are left to fend for themselves.
Short lifespan: individuals mature fast and die young.
Small body size: little energy invested per individual.
Unstable populations: numbers swing widely with resources.
Rapid colonisation: they quickly occupy new or disturbed habitats.

Example: Fruit Flies and Rodents

Example

Insects such as fruit flies (Drosophila) and rodents are classic r-strategists.
They breed rapidly and have many young, but face high mortality from limited resources and predation.

How r-Strategists Grow

Note

r-strategists show exponential (J-curve) growth, rising fast when resources are plentiful.
Growth has little density regulation, so numbers can crash in a boom-and-bust cycle.

Thinking About r-Strategists

Analogy

r-strategists are the entrepreneurs of nature, taking high risks for high rewards in fast-changing conditions.

K-Strategists: The Competitors

Definition

K-strategists

Species that reproduce slowly, producing few offspring but investing heavily in their survival.

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Note

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Excepteur sint occaecat cupidatat non proident

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

Topic 1: Foundation 3 subtopics

Topic 2: Ecology5 subtopics

Topic 3: Conservation and biodiversity3 subtopics

Topic 4: Water4 subtopics

Topic 5: Land2 subtopics

Topic 6: Atmosphere and climate change4 subtopics

Topic 7: Natural resources3 subtopics

Topic 8: Human populations and urban systems3 subtopics

HL lenses 3 subtopics

IB Environmental systems and societies 2.1N R- and K Strategists Notes

Topic 1: Foundation 3 subtopics

Topic 2: Ecology5 subtopics

Topic 3: Conservation and biodiversity3 subtopics

Topic 4: Water4 subtopics

Topic 5: Land2 subtopics

Topic 6: Atmosphere and climate change4 subtopics

Topic 7: Natural resources3 subtopics

Topic 8: Human populations and urban systems3 subtopics

HL lenses 3 subtopics

Life-Cycle Strategies: Fast and Many vs Slow and Few

r/K-Selection Theory: Two Reproductive Bets

r-Strategists: The Opportunists

Example: Fruit Flies and Rodents

How r-Strategists Grow

Thinking About r-Strategists

K-Strategists: The Competitors

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Life-Cycle Strategies: Fast and Many vs Slow and Few

r/K-Selection Theory: Two Reproductive Bets

r-Strategists: The Opportunists

Example: Fruit Flies and Rodents

How r-Strategists Grow

Thinking About r-Strategists

K-Strategists: The Competitors

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account