3.1C Species diversity Notes

1. Species diversity is a key measure of biodiversity in an ecosystem, influenced by species richness and species evenness.
2. These two factors together determine how balanced and functionally stable a community is.

Components of Species Diversity

Species Richness

1. It provides a simple count of how many different types of organisms are present.
2. Although it gives an overview of biodiversity, it does not reveal how evenly individuals are distributed across species.
3. Higher species richness means greater variety in an ecosystem, leading to more ecological roles and interactions.

Species Evenness

1. Describes how uniformly individuals are distributed among the different species in a community.
2. High evenness means that species have similar population sizes, suggesting a stable and balanced ecosystem.
3. Low evenness occurs when one or a few species dominate, indicating lower stability and resilience.

Significance of Richness and Evenness for Biodiversity

1. High Richness, Low Evenness (Unstable Ecosystem)
   1. A large number of species exist, but a few species dominate.
   2. Low evenness can lead to imbalances where dominant species outcompete others, reducing overall biodiversity.
2. Low Richness, High Evenness (Limited Diversity, More Stability)
   1. Fewer species present, but they exist in similar proportions, meaning no single species outcompetes the rest.
   2. More stable than a low-evenness system, but still vulnerable to disturbances due to low species variety.
3. High Richness, High Evenness (Most Stable and Resilient Ecosystem)
   1. Diverse species and balanced populations create a strong, resilient ecosystem.
   2. Supports high productivity, efficient resource use, and greater resistance to environmental changes.

Importance for Ecosystem Stability and Functioning

1. Higher richness provides functional redundancy: multiple species can perform the same ecological role, preventing collapse if one species declines.
2. Higher evenness prevents dominance: ensures no single species takes over, keeping the ecosystem balanced.
3. Diverse and even communities are more resilient: ecosystems with both high richness and evenness recover faster from disturbances like climate change, fires, or disease.

Simpson’s Reciprocal Index

1. Biodiversity can be quantified using mathematical indices that combine richness and evenness.
2. The most widely used is Simpson’s Reciprocal Index (D), which provides a single value to compare ecosystems or track changes over time.
3. Simpson’s reciprocal index provides:
   1. A quantitative measure of biodiversity.
   2. A way to compare ecosystems with similar species types.
   3. A method to monitor biodiversity changes in a single ecosystem over time.

The formula for Simpson’s Reciprocal Index

$$D = \frac{N(N - 1)}{\sum n(n - 1)}$$

Where:

1. D is Diversity index (higher values = greater diversity).
2. N is Total number of individuals in the sample (sum of all species counted).
3. n is Number of individuals of a single species.
4. Σ is Summation symbol (sum of all species calculations).

Sampling Procedures for Calculating Simpson’s Index

1. Choose an appropriate sampling area
   1. Select two or more sites for comparison (e.g., forest vs. grassland).
   2. Ensure sites are similar in size and environmental conditions.
2. Use a standardized sampling method
   1. Quadrats (e.g., 1m² for plants, 10m² for trees).
   2. Transects (line or belt transects for zonation studies).
   3. Pitfall traps or sweep nets (for insects and small animals).
3. Record species abundance
   1. Count the number of individuals per species.
   2. Repeat for multiple quadrats to improve accuracy.

Example Calculation of Simpson’s Reciprocal Index

Collected Data from Two Sample Sites (Same Ecosystem, Different Areas)

Step 1: Calculate $N(N−1)$

1. Site A: 36(36−1)=1260
2. Site B: 60(60−1)=3540

Step 2: Calculate $∑n(n−1)$

1. For Site A: (12(11)+8(7)+10(9)+6(5)) = (132+56+90+30)= 308
2. For Site B: (20(19)+25(24)+5(4)+10(9)) = (380+600+20+90)=1090

Step 3: Calculate $D$

1. For Site A: D = 1260/308 = 4.09
2. For Site B: D = 3540/1090 = 3.25

Interpretation

1. Site A has higher diversity ($D = 4.09$), meaning species are more evenly distributed.
2. Site B has lower diversity ($D = 3.25$), suggesting one species may be more dominant.

Global and Regional Biodiversity Knowledge

1. Conserving biodiversity requires comprehensive data collection at global, regional, and local levels.
2. This knowledge guides management strategies and helps identify conservation priorities.

Global Data Collection

1. International agencies such as the IUCN and WWF maintain global biodiversity databases.
   1. The IUCN Red List classifies species by extinction risk (e.g., Least Concern, Endangered, Critically Endangered).
   2. The WWF identifies and monitors biodiversity hotspots worldwide.
2. These databases help governments and NGOs coordinate conservation actions and set priorities.

Regional and Local Data Collection

1. Government agencies (e.g., Natural England, Forest Survey of India).
2. NGOs and voluntary organizations (e.g., Wildlife Trusts, BirdLife International).
3. Citizen science projects, where volunteers record species observations (e.g., eBird, Big Butterfly Count).
4. Indigenous and local communities, trained as parabiologists, contribute traditional ecological knowledge for monitoring and conservation.

Conservation Applications of Biodiversity Data

1. Protected Areas: Identify biodiversity hotspots for national parks or reserves.
2. Restoration: Track changes after reforestation or pollution mitigation.
3. Policy Decisions: Support national biodiversity strategies aligned with the UN Sustainable Development Goals (SDG 14 & 15).
4. Sustainable Use: Inform community-based resource management (fisheries, forestry).