r and K Selection Calculator

In ecology, species are classified by whether they prioritize rapid reproduction (r-selection) or stable, resource-efficient survival (K-selection) — and the r and K Selection Calculator determines which strategy best describes a population based on its life history traits. Enter your Reproductive Rate (r), Carrying Capacity (K), Initial Population, Time Period, Offspring per Reproduction Event, Generation Time, Juvenile Survival Rate, and Adult Survival Rate to get the Selection Strategy Type. Secondary outputs include Final Population Size, Population Growth Rate, Reproductive Effort Index, and both r-Strategy and K-Strategy scores.

Intrinsic rate of population increase

individuals

Maximum sustainable population size

individuals
generations

Number of offspring produced per breeding event

years

Time from birth to reproductive maturity

%

Proportion of juveniles surviving to adulthood

%

Annual adult survival probability

Results

Selection Strategy Type

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Final Population Size

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Population Growth Rate

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Reproductive Effort Index

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K-Strategy Score

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r-Strategy Score

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Results Table

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Frequently Asked Questions

What is the difference between r-selection and K-selection?

r-selection favors high reproductive rates and rapid population growth in unstable environments, while K-selection favors competitive ability and stable populations near carrying capacity. r-strategists produce many offspring with low survival rates, while K-strategists produce fewer offspring with higher survival rates.

How do I interpret the r/K selection scores?

Higher r-strategy scores indicate organisms that reproduce quickly with many offspring, typical in unstable environments. Higher K-strategy scores suggest organisms with longer lifespans, fewer offspring, and greater parental investment, typical in stable, competitive environments.

What are typical examples of r-selected and K-selected species?

r-selected species include bacteria, weeds like dandelions, insects, and small mammals like mice. K-selected species include elephants, primates, large trees, and humans - species with long lifespans and extensive parental care.

How does carrying capacity affect population growth?

Carrying capacity (K) represents the maximum population size an environment can sustain. As populations approach K, growth rates slow due to increased competition for resources, following the logistic growth model.

What environmental factors influence r/K selection strategies?

Unstable, unpredictable environments with frequent disturbances favor r-selection, while stable, predictable environments with intense competition favor K-selection. Climate variability, resource availability, and predation pressure all influence these strategies.

Can species exhibit both r and K characteristics?

Yes, most species fall somewhere on a continuum between pure r and K strategies. Many organisms can shift their reproductive strategies based on environmental conditions, displaying phenotypic plasticity in their life history traits.

How does generation time relate to r/K selection?

r-selected species typically have short generation times, reaching reproductive maturity quickly. K-selected species have longer generation times, investing more time in growth and development before reproducing.

What is the reproductive effort index in this calculator?

The reproductive effort index measures the proportion of an organism's resources allocated to reproduction versus survival and growth. Higher values indicate greater investment in reproduction (r-strategy), while lower values suggest more investment in survival (K-strategy).