ENVR101 Species Distribution, Biodiversity, and Quantification

Global Species Distributions

Temperature and rainfall are major determinants of species distributions. The latitudinal diversity gradient shows that species richness is highest near the Equator and decreases towards the poles. Possible reasons include stable warm temperatures, high primary productivity, older age of tropical systems allowing more time for speciation and complex habitats.

Niche Partitioning

Niche partitioning allows similar species to coexist by utilizing different resources or habitats.

  • Spatial Partitioning: Species occupy different areas within a habitat.

  • Temporal Partitioning: Species use the same resources at different times.

  • Dietary Partitioning: Species eat different things.

  • Morphological/Behavioral Partitioning: Differences in physical abilities or behavior lead to resource partitioning.

Factors Affecting Species Distribution

Besides biotic and abiotic factors, distribution and abundance are also affected by: biogeography, dispersal, and behavior.

Range of Tolerance

Organisms thrive within an optimal range of each environmental factor. Beyond this range, stress increases, and survival and reproduction are affected. Population density is greatest where all conditions are optimal.

Importance of Biodiversity

Biodiversity is important due to ecosystem services and its inherent value:

  • Regulating Services: Air purification, pollination, climate stabilization, disease control.

  • Provisioning Services: Food, water, medicines, wood, fiber.

  • Cultural Services: Tourism, cultural identity.

  • Supporting Services: Photosynthesis, nutrient cycling.

  • Inherent Value: Biodiversity is valuable regardless of its usefulness to humans.

Quantifying Species Diversity

  • Species Richness: The number of species in an area.

  • Species Evenness: The relative abundance of each species.

  • Species Diversity: Accounts for both richness and evenness.

To calculate Shannon diversity index (HH):

  1. Calculate the proportion (p<em>ip<em>i) of each species: p</em>i=number of individuals of species itotal number of individualsp</em>i = \frac{\text{number of individuals of species } i}{\text{total number of individuals}}

  2. Calculate the natural log of each proportion: ln⁡(pi)\ln(p_i)

  3. Multiply the proportion by the natural log: p<em>i×ln⁡(p</em>i)p<em>i \times \ln(p</em>i)

  4. Sum these values and multiply by -1: H=−∑(p<em>i×ln⁡(p</em>i))H = -\sum(p<em>i \times \ln(p</em>i))

To calculate Evenness (EE):

  1. Calculate the maximum diversity: Hmax=ln⁡(S)H_{max} = \ln(S) , where SS is the number of species (richness).

  2. Calculate evenness E=HHmaxE = \frac{H}{H_{max}}

An evenness index closer to 1 indicates a more even community, while closer to 0 indicates dominance by one species.