18.13 Assessing Species Diversity

Definition

• Species diversity: The variety of species in a community, considering both species richness (number of species) and species evenness (distribution of individuals among species).

Purpose

• Understanding biodiversity requires assessing the number of species, their relative abundance, and how they interact within their ecosystem.
• The first step in assessing diversity is to identify, catalogue, and list species present in the ecosystem.

Steps for Assessing Species Diversity

1. Identifying Species

• Begin by identifying the most visible organisms (e.g., trees, birds, large animals).
• Tools for Identification:
  • Identification keys:
    • Help name species through systematic observations.
    • Types:
    • Dichotomous key: Series of yes/no questions to narrow down species identity.
    • Photographic/illustrated keys: Visual guides for field use.
  • Observation Skills:
    • Essential for accurate identification.
    • Look for distinguishing features such as color, shape, and size.
  • Fieldwork Practice:
    • Conduct a timed search to systematically explore the study area.
    • Record all observed species and assign placeholder names (e.g., Species A, B) for unidentified ones.
    • Use photographs for later analysis and comparison.

2. Collecting Hard-to-Find Species

• Small, elusive animals (e.g., beetles, ants) may require specialized tools for collection.
• Collection Tools:
  • Pooter:
    • Apparatus for safely collecting small animals by suction.
    • Collected organisms are examined using a hand lens and released back into their habitat.
  • Sweep nets:
    • For flying insects or organisms in tall vegetation.
  • Pitfall traps:
    • Used for capturing ground-dwelling insects.
  • Quadrats:
    • Sampling frames used for estimating species abundance in plants and immobile organisms.

3. Cataloguing Species

• Organize findings into a species list, grouping organisms by taxonomic categories (plants, animals, fungi).
• Focus on Target Groups:
  • Full cataloguing is rare due to practical constraints.
  • Biologists typically study specific groups:
    • Grassland/Woodland: Focus on flowering plants and insects.
    • Rocky Shore: Concentrate on seaweeds and mollusks.
    • Forest Ecosystems: Observe dominant trees and birds.

4. Example Process

• Forest Ecosystem Study:
  • Identify large organisms first, such as trees and birds.
  • Use a pooter for collecting smaller species like beetles.
  • Catalog all species into a comprehensive list.

Fieldwork Tools and Methods

Identification Keys

• Help classify organisms during fieldwork.
• Types:

1. Dichotomous key:
   • Sequential yes/no questions based on physical traits.
2. Photographic/illustrated key:
   • Visual aids for identifying organisms in the field.

• Accuracy relies on keen observation and attention to detail.

Collection Tools

• Pooter:
  • Simple suction-based tool for collecting small animals.
  • Useful for studying tree canopies or ground-level organisms.
• Hand Lens:
  • For examining minute features of collected specimens.
• Photographs:
  • Ideal for recording species that are difficult to collect or observe closely.

Challenges in Species Diversity Assessment

1. Elusive Species:

• Small or nocturnal animals are harder to locate.
• Behavioral adaptations like camouflage can hinder detection.

1. Time and Resource Constraints:

• Comprehensive cataloguing of all species in an ecosystem is impractical.
• Focused studies on key groups mitigate this challenge.

FIGURE

• Figure A: Example of a forest ecosystem where species diversity is assessed by studying trees, birds, and smaller organisms.
• Figure B: An ecologist using a pooter to collect small animals from the canopy of a Yungas forest in Argentina.

Summary

• Assessing species diversity involves identifying and cataloguing species using tools like identification keys and pooters.
• Fieldwork focuses on target groups of organisms, employing efficient collection methods like timed searches, quadrats, and photographic records.
• Accurate assessment of species diversity helps understand ecosystem health, interactions, and biodiversity.