r/K Selection: Videos & Practice Problems

R and K selection are two contrasting life history strategies shaped by natural selection. K-selected species thrive in stable environments near carrying capacity (K), exhibiting low fecundity and high parental investment, as seen in orcas. In contrast, r-selected species, like monarch butterflies, flourish in unstable conditions, maximizing reproduction (r) with high fecundity and minimal parental care. This results in type 3 survivorship curves for r-selected species and type 1 for K-selected species, highlighting the trade-off between fecundity and survivorship in ecological dynamics.

r/K Selection

In the study of ecology, understanding the life history strategies of different species is crucial. These strategies, shaped by natural selection, can be categorized into two main types: r-selection and k-selection. These concepts represent opposite ends of a spectrum regarding how species allocate their time, energy, and resources for survival, growth, and reproduction.

K-selection refers to species that thrive in stable environments where population densities are near the carrying capacity (denoted as K). These species are characterized by intense competition and stable populations. K-selected organisms typically invest significant resources in raising fewer offspring, resulting in high survivorship rates. For example, species like orcas exemplify k-selection, as they produce few young but provide substantial parental care, leading to a type I survivorship curve. This curve indicates low mortality rates early in life, with most individuals surviving to adulthood, followed by increased mortality in later stages.

Conversely, r-selection is associated with species that flourish in unstable environments where population densities are low and not near carrying capacity. These species maximize their reproductive output, often producing a large number of offspring with minimal investment in each, resulting in low survivorship rates. Monarch butterflies serve as a prime example of r-selected species, exhibiting high fecundity and low parental care. They typically follow a type III survivorship curve, characterized by high mortality rates early in life, with only a few individuals surviving to adulthood.

Overall, the r and k selection strategies illustrate the trade-off between fecundity and survivorship. While r-selected species focus on rapid population growth and high offspring numbers, k-selected species prioritize the survival and quality of fewer offspring. Understanding these strategies is essential for predicting population dynamics and the ecological roles of various species.

r/K Selection Example 1

Survivorship curves are essential tools in understanding the life history strategies of different organisms, particularly in relation to their reproductive strategies. These curves illustrate the number of survivors at each age, providing insights into mortality rates and survivorship patterns across different species.

There are three primary types of survivorship curves: Type I, Type II, and Type III. Type I survivorship curves are typically associated with K-selected organisms. These organisms produce few offspring but invest significantly in their care, resulting in high survivorship and low mortality rates during early life stages. As individuals age, mortality rates increase, leading to a decline in survivorship. This pattern is often seen in larger mammals, such as elephants and humans, where the majority of offspring survive to adulthood due to parental investment.

In contrast, R-selected organisms exhibit a Type III survivorship curve. These species produce a large number of offspring, often numbering in the hundreds or thousands, but provide minimal parental care. Consequently, there is a high mortality rate among the young, resulting in low survivorship early in life. However, those few individuals that do survive to adulthood tend to experience lower mortality rates. This strategy is common in species like fish and insects, where the sheer number of offspring increases the likelihood that some will survive despite high early mortality.

Understanding these survivorship curves is crucial for studying population dynamics and the ecological strategies that different species employ to survive and reproduce in their environments.

Which of the following statements about r & K selection is true?

• A. K-selected organisms tend to exhibit iteroparity so they can better care for their offspring.
• B. r-selected organisms tend to exhibit iteroparity so they can care for their offspring.
• C. K-selected organisms often exhibit semelparity as they invest all their resources towards producing offspring.
• D. r-selected organisms usually exhibit semelparity as they can’t continuously reproduce throughout life.

Answer: (A)

Which type of survivorship curve would you expect K-selected organisms to follow & why?

• A. Type I, because many resources are allocated to the survival of few offspring.
• B. Type II, because the probability of death remains constant even if offspring are well cared for.
• C. Type III, because many offspring are produced in K-selection.
• D. Could be anywhere on the spectrum of survivorship curves, as it’s too difficult to predict.

Answer: (A)

Here’s what students ask on this topic:

What is the difference between r-selected and K-selected species?

r-selected species and K-selected species represent two ends of a spectrum of life history strategies shaped by natural selection. r-selected species, like monarch butterflies, thrive in unstable environments and maximize reproduction (r). They have high fecundity, producing many offspring with minimal parental care, resulting in type 3 survivorship curves characterized by high mortality rates early in life. In contrast, K-selected species, such as orcas, are adapted to stable environments near carrying capacity (K). They exhibit low fecundity, producing few offspring with high parental investment, leading to type 1 survivorship curves with low mortality rates early in life and higher mortality rates later. This trade-off highlights the balance between fecundity and survivorship in ecological dynamics.

What are the characteristics of r-selected species?

r-selected species are adapted to unstable environments and focus on maximizing reproduction. Key characteristics include high fecundity, producing many offspring, and minimal parental care. These species often experience boom and bust cycles, with rapid population growth followed by crashes. r-selected species typically exhibit type 3 survivorship curves, where most offspring have high mortality rates early in life, but those that survive to adulthood have lower mortality rates. Examples of r-selected species include insects like monarch butterflies, which produce hundreds or thousands of offspring with little investment in each individual.

What are the characteristics of K-selected species?

K-selected species are adapted to stable environments near the carrying capacity (K) and focus on optimizing fitness at high population densities. Key characteristics include low fecundity, producing few offspring, and high parental investment. These species tend to have stable populations and intense competition for resources. K-selected species typically exhibit type 1 survivorship curves, characterized by low mortality rates early in life and higher mortality rates later. Examples of K-selected species include large mammals like orcas, which invest significant resources into the care and survival of their few offspring.

How do r-selected and K-selected species differ in their survivorship curves?

r-selected and K-selected species exhibit different survivorship curves due to their contrasting life history strategies. r-selected species typically have type 3 survivorship curves, characterized by high mortality rates early in life, with most offspring not surviving to adulthood. However, those that do reach adulthood tend to have lower mortality rates. In contrast, K-selected species exhibit type 1 survivorship curves, characterized by low mortality rates early in life, with most offspring surviving to adulthood. Mortality rates increase later in life for K-selected species. These differences reflect the trade-off between high fecundity and low parental investment in r-selected species versus low fecundity and high parental investment in K-selected species.

What is the significance of the carrying capacity (K) in K-selected species?

The carrying capacity (K) is a crucial concept in understanding K-selected species. It represents the maximum population size that an environment can sustainably support. K-selected species are adapted to stable environments where population densities are near the carrying capacity. These species optimize their fitness by producing fewer offspring with high parental investment, ensuring that each offspring has a higher chance of survival in a competitive environment. The carrying capacity influences the population dynamics of K-selected species, leading to stable populations with intense competition for limited resources. This strategy contrasts with r-selected species, which thrive in environments far from carrying capacity.