The term "species evenness" describes how numerous each species is in an environment. It is described mathematically as a diversity index, which is a type of biodiversity index that measures how numerically equal a community is. Therefore, if there are 40 foxes and 1000 dogs in a community then the community is not really even. When every species in a sample has the same abundance, species evenness is at its maximum level. With varying relative abundances, evenness approaches zero. This article will explain to you about Species Evenness which will be helpful in preparing the Environment Syllabus for the UPSC Civil Service exam.

What is Species Evenness?

• Species evenness is a measurement of the relative abundance of various species in a given area.
• Greater species evenness can be seen in areas where all species are present in roughly equal numbers.
• For example, Areas 1 and 2 both include four different species of trees.
  • However, one species actually dominates Area 2, and one of those species is quite rare (only one individual)
  • Despite the exact same species richness in both areas, Area 1 has a better species evenness than Area 2, which results in a higher overall species diversity.

An illustration of Species Evenness

What is Species Richness? The degree of diversity found within a specific ecological system is known as biodiversity. The total number of species found on Earth is frequently used to quantify the biodiversity of the planet. Thus, the species richness of an ecosystem is taken into account as one of the most popular methods for estimating biodiversity. Species richness is the measurement of all the species that are present in a given area. The ecosystem will be more stable if there are more species since more species mean more species richness. Increased species diversity will eventually boost biodiversity, which is a crucial component of preserving biodiversity.

Number of Species on Earth

• Despite many efforts, there is little known about the species that live on the planet.
• There have been about 1.5 million species described, however, there are still many unknown species.
• There are an estimated 3 million to 100 million species on Earth, with more recent estimates often falling between 8 and 11 million species.
• According to a 2011 survey, just 13% of eukaryotic species—which include plants, animals, fungus, and algae—have been named.
• Although bacterial species numbers are primarily speculative, biologists agree that science has just recently started to document their variety.
• There are actually between 1 and 6 billion species on Earth, with at least 70% of them being bacteria, according to a 2017 study by Brendan Larsen and colleagues.

Measurement of Species Evenness

• For species evenness, ecologists must be aware of the relative abundance of each species in a given community.
• Area-based counts, distance methods, and mark-recapture studies are some of the techniques used to measure abundance.
• Area-based Counts: Area-based counts are used to determine the total population size by counting the number of organisms in a number of quadrants, which are used to measure the abundance of immobile organisms.
• Distance Methods: In distance methods, the number of people per unit of area is calculated from the distance of individuals from a random point.
• Mark-recapture Studies: It is possible to estimate the number of mobile creatures using mark-recapture techniques. Ecologists take a sample of the population, mark it, and then release it.
  • Following a period of time during which the marked individuals are allowed to circulate among the population, individuals are once more collected.
  • The percentage of marked people discovered during recapture is used to calculate the population size.

What Happens If There is No Species Evenness?

• Lumbering is challenging in tropical evergreen forests because there is very little evenness, in contrast to temperate regions of the planet.
• Lack of evenness causes species to inbreed, and the resulting infants will have several abnormalities.
• In today's world, no species' evenness may hasten extinction.
• No evenness increases the financial load on the government because it becomes necessary to strictly defend this smaller group.

Conclusion

When the number of individuals in each species is evenly distributed, evenness must be maximized. Less research has been done so far in ecology on the effects of species evenness than on the effects of species richness. However, a rising body of work has concentrated on the social equivalent of species evenness.

FAQs

MCQs

1. What is species evenness a measure of?

A) The total number of species in a community
B) The relative abundance of species in a community
C) The genetic diversity within a species
D) The physical size of species

2. How can low species evenness affect an ecosystem?

A) It can make the ecosystem more resilient to disturbances.
B) It can lead to the domination of one species, disrupting ecosystem balance.
C) It increases the biodiversity of the ecosystem.
D) It promotes the coexistence of different species.

3. Which of the following is a characteristic of an ecosystem with high species evenness?

A) One species is much more abundant than others.
B) All species have a roughly equal number of individuals.
C) There are very few species present.
D) There is a complete lack of species diversity.

4. Which index is commonly used to measure species evenness?

A) Shannon-Wiener Index
B) Jaccard Index
C) Simpson's Diversity Index
D) Both A and C

5. What happens when species evenness is low in a community?

A) It leads to higher ecosystem stability.
B) It can cause a collapse of biodiversity.
C) It results in increased competition between species.
D) It promotes a greater variety of ecological niches.

GS Mains Questions and Model Answers

Q1: Discuss the importance of species evenness in maintaining biodiversity. How does it affect ecosystem services?

Answer: Species evenness plays a crucial role in maintaining biodiversity by ensuring that no single species dominates the ecosystem. High species evenness supports a more stable and resilient ecosystem, which is better equipped to handle disturbances such as climate change, pollution, and habitat destruction. Moreover, ecosystems with high evenness provide essential services, such as pollination, water purification, and nutrient cycling, which depend on a diverse range of species working together. Maintaining evenness is key to preserving ecosystem health and the benefits it provides to humans.

Q2: Explain how species evenness is measured in ecological studies. What are some of the methods used?

Answer: Species evenness is measured using indices like the Shannon-Wiener Index and Simpson's Index, which assess both species richness (the number of species) and the distribution of individuals among those species. Ecologists use various sampling methods, including area-based counts, distance methods, and mark-recapture techniques, to estimate species abundance. These methods help determine the relative abundance of each species and allow for the calculation of evenness. By comparing different ecosystems or time periods, researchers can track changes in species evenness and make informed conservation decisions.

Q3: How does a decrease in species evenness impact ecosystem functioning and human well-being?

Answer: A decrease in species evenness can lead to the dominance of a few species, disrupting ecosystem processes such as nutrient cycling and pollination. This can reduce biodiversity, making ecosystems less resilient to environmental stresses and increasing the risk of ecosystem collapse. The loss of species evenness can also affect human well-being by impairing the ecosystem services that people rely on, such as food production, clean water, and climate regulation. Sustainable management of ecosystems to maintain species evenness is critical for ensuring long-term ecological and human health.

Previous Year Questions on Species Evenness

1. UPSC CSE Prelims 2020:

Question: Which of the following is used to measure species evenness?

A) Simpson’s Index
B) Jaccard’s Index
C) Shannon-Wiener Index
D) Both A and C

Answer: (D)

Explanation: Both Simpson’s Index and the Shannon-Wiener Index are commonly used to measure species evenness in ecological studies.

2. UPSC CSE Mains 2019 (GS Paper 3):

Question: "How does species evenness contribute to the stability of ecosystems? Discuss its role in biodiversity conservation."

Answer: Species evenness contributes to ecosystem stability by ensuring that no single species overwhelms others. High evenness promotes the coexistence of diverse species, which supports ecosystem resilience. In biodiversity conservation, maintaining species evenness helps preserve the integrity of ecosystems, ensuring they continue to provide essential services such as clean air, water, and food security.