R-Selected Species

NEET'22 Crash Course

Introduction to R-Selected Species

According to the Darwin theory of evolution, the fitness of species or an organism is based on the number of the offsprings that are left behind that survive and are then capable of reproduction. This helps in furthering the genes and assists with the continuation of the species and their survival as a whole. Based on this, the species or organisms can be classified in two extreme categories in evolutionary terms - r-selected species and k-selected species.  

What are R-Selected Species?

The r-selected species are those species that tend to produce a higher number of offspring or protogenies but they offer less parental care. This means less individual investment in terms of parenting, while the K-selected species produce less number of progenies or offspring but they provide more parental care or investment for each individual. Many of the species fall between these two extremes. 

The r-selected species exhibit and display some specific characteristics. These characteristics are as follows.

  • The R-selected species are prominently involved in the high growth rates.

  • These species usually exploit ecological niches and less crowded areas, and thus each of them produces numerous offspring. Less crowding helps in providing lesser competition for the resources. 

  • The offspring have considerably less probability of survival to adulthood due to various environmental conditions. 

  • The characteristics of the r-selected species make them the dominant species, in the unstable or unpredictable environment due to their ability to fast reproduction. 

  • Even though high in the numbers, the r-selected species are less likely to make the adaptation to the changing environment and hence the survival is based on the number of the offspring. 

  • The traits which are important for the r-selected species’ characteristics include the ability of high reproduction which is the high fertility rate, early onset of maturity, small body size, short generation time, and ability to disperse offspring widely. 

  • R strategists tend to be primary colonisers, especially in the region of ecological disruption like those surrounding volcanic eruptions. These are followed by the succession of incredibly competitive flora and fauna.

Examples of R-Selected Species

There are various examples of the r-selected species and the most common instances include rats or rodents. They are the most relatable and common species which can be used to explain the concept related to r-selected species. The rats produce various progenies and after tending to them for a few days, the offspring are dispersed. They also have the qualitative traits which define characteristics of the r-selected species like high ability to reproduce, small body size, shorter generation time, and early maturity in comparison to other species like humans. 

According to Darwinian evolutionary theory, the fitness of an organism or the species as a whole depends on the number of offspring that are left behind by themselves that survive and are capable of reproduction thus furthering their genes and continuing the survival of the species population as a whole. 

With respect to that, organisms or species used to be classified in between two extreme types of species in evolutionary terms - the r selected species and the K-selected species. The r-selected species are the species that produce a higher number of progenies or offsprings but offer less parental care i.e. less individual parental investment, whereas the K-selected species produced less offspring or number of progenies but providing more parental care or parental investment to each individual. 

Many species lie in-between the two extremes. But this theory in recent years has been replaced by the life-history paradigm which seeks to explain these factors of quality vs quantity based on several factors such as surroundings, etc., although it derives several important themes from the r/K selection theory. 

A Brief Explanation of R-Selected Species

In the r selected species, the r can be said to be a reference to reproduction. The r strategist species are the ones that are said to be dependent on quantity over quality for the propagation of their genes over generations. In the evolutionary processes, the r strategist finds an advantage in the survival factor because of sheer numbers. If the numbers are more, then even under adverse conditions that can lead to the deaths of many offspring, some of them will survive and thus being capable to reproduce, they will pass on the genes to the next generation. Thus, this concept is completely based on the advantage of the quantity of offspring that an organism can produce for the survival of the species even while facing high mortality rates. 

But in this process, there is a significant impact on the parental investment in the offspring of the r selected population. Here, parental investment means, parental care and protection, nurturing and providing nutrition to the offspring for a longer period of time, teaching to the offspring the methods of survival like hunting in wild animals, etc. Since in r strategist species there are a large number of children it is difficult for the parent or parents to invest and focus on each individual. Hence, because of this, the offsprings or progenies in an r selected population even mature early as compared to the K selected population. In some of the r selected species examples, it is observed that after the birth of progenies or laying of eggs, the parent usually leaves them off and goes on to live their lives accordingly. These are the cases that lie towards the r selection extreme of the spectrum of selection regime or quantity of population vs the quality of the population. 

These are the two important characteristics of r selected species that provides the explanation of the concept. Other characteristics of r selected species are given as follows:

R selected species are the ones that are prominently involved in high growth rates.

They usually exploit less-crowded areas and ecological niches, each producing many offspring. Less crowding provides less competition for the resources. 

The offspring have less probability of surviving to adulthood owing to several environmental conditions. 

The characteristics of r selected species prove them dominant species in the unpredictable or unstable environment because of their ability for rapid reproduction. 

Although high in number, the r selected population are less likely to adapt rapidly to the changing environment and hence their survival depends on the number of offspring. 

The traits that are important for the characteristics of r selected species include high ability to reproduce i.e. high fertility rate, small body size, early onset of maturity, short time of generation, and the capability to disperse off the progeny widely. 

R strategists are usually the primary colonisers, especially in areas of major ecological disruption such as regions surrounding volcanic eruptions. They are followed by a succession of increasingly competitive flora and fauna.

R Selected Species Examples

There are many r selected species examples among which the most common ones are the rodents or rats. They are the most common and relatable species that is best to explain the concept of r selected species. Rats produce a number of progenies and then after tending them for a few days they disperse off their offspring. Also, they have the qualitative traits that define the characteristics of r selected species such as small body size, high ability to reproduce, early maturity and shorter time of generation as compared to any other species such as humans. This example also demonstrates the variation in the spectrum observed among a particular phylogeny as both rats and humans are mammals. 

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Other R Selected Species Examples Include the Following

The most common species of organisms that can be found almost anywhere on Earth is bacteria. A bacterial species is the best example of the r selected species.

Diatoms are a group of algae or more specifically microalgae, and are found in oceans, waterways, and soils of the world. They are also r selected species. 

In arthropods, insects are one of the best examples of r strategists. They lay eggs in huge numbers and this is the biggest reason for the survival of these species. Even with the development of modern pest control methods such as insecticides, they are able to survive because they lay huge numbers of eggs around a potential nutrient source. 

Amongst, the plants of the different species of grasses are r selected. Even though they are trampled by and destroyed by large mammals such as elephants, they tend to survive because of their number. Also, they prove a basis for the development of more competitive species of exclusive plants, trees and other vegetation, which mostly are found in a particular region, unlike grass.

FAQs (Frequently Asked Questions)

1. Do humans fall under the R-Selected species?

No, humans don’t fall under the R-selected species. The R-Selected species are categorised by their massive amount of progeny and small size. Due to large offspring numbers, they can’t invest high levels of parental care for each individual and hence the early outset of maturity is needed in r-selected species. The k-selected species on the other hand are classified by the complex biology and less number of progeny. Because of fewer offspring, they can invest in high levels of parental care. Humans are one of the examples of the k-selected species. 

2. What are the major differences between the R-Selected species and the K-Selected species?

The major difference between the k-selected species and the r-selected species can be observed in progeny number, lifespan, and early mortality amongst others. The progeny number for r-selected species is high and parental care is low. Whereas in the K-Selected species, the progeny number is low and the levels of parental care is high. The early mortality for r-selected species is high and it is low for the k-selected species. The lifespan for r-selected species is low and high for k-selected species. 

3. What are the different factors that impact r-selected species?

The different factors that have an impact on the r-selected species are as follows. High reproductive rate, rapid development, small body size, early reproductive age, short life span, one reproductive cycle, high mortality of the offspring, good offspring dispersal and poor competitive ability amongst a host of others. The r-selected species are not as biologically complex as the r-selected species and they also don’t provide high levels of parental care.

4. How do I study from the Vedantu notes on “R-Selected species?

If you want to study from the Vedantu notes on “R-Selected species” then it is available for download at the Vedantu app or the website. These notes are provided in the PDF file and are available for free. All you have to do is visit the Vedanu website or app, browse to the specific category and then click on the “Download PDF” button for downloading the file.

5. What are the salient features of the Vedantu notes on “R-Selected species”?

The Vedantu notes on the R-Selected species provide in-depth coverage of the concept and give a comprehensive description of the different aspects associated with the chapter. It includes various sub-sections including definition, brief explanation, examples, characteristics, and common queries. The notes are well structured and presented in an easy to understand format to help the students with their studies and help them prepare for their exams.  

6. Are Humans R Selected Species?

R selected species are characterised by their small size and a huge amount of progeny. Because of the large numbers of offspring, they are unable to invest high amounts of parental care to each individual and therefore, early onset of maturity is required in the r selected species. Examples of these kinds of species include mosquitos, rats, and bacterias. On the other hand, k selected species are characterised by complex biology, medium to large size, and less number of progeny. Hence, because of the fewer offspring, they are able to invest high amounts in parental care. Examples of these species are elephants, humans, bison, etc. 

7. What are Three Differences Between R Selected Species and K Selected Species?

The common differences between the r and k selected species can be seen in terms of progeny number, care obtained from the parents, early mortality, lifespan, etc. The progeny number in case of r selected species is high whereas K selected species, parental care is low in r selected species and high in K selected species, and the early mortality is high in r selected species as compared to K selected species. Also, the lifespan is short for r selected species and long for K selected species.