Biodiversity and Ecosystem Services: Comprehensive Study Notes

Introduction to Biodiversity and Ecosystem Services

Biodiversity Basics

Biodiversity is defined as the diversity of life forms in an ecosystem. It is measured on three distinct levels:

Genetic diversity: This refers to how different the genes are among individuals within a population (a group of the same species).
Species diversity: This encompasses two aspects: the total number of different species present in an ecosystem and the balance or evenness of the population sizes of all species within that ecosystem.
Ecosystem diversity: This measures the number of different habitats available in a given area.

A general rule is that higher biodiversity correlates with higher ecosystem and population health.

Species Richness & Evenness

These are two key components of species diversity:

Richness (r): This is simply the total number of different species found in an ecosystem. A high species richness is generally considered a good indicator of ecosystem health, as more species often imply the presence of more quality resources like water and soil.
Evenness: This is a measure of how balanced the individual organisms are across the different species in an ecosystem. Evenness helps to determine if there are one or two dominant species, or if the population sizes are relatively well-balanced among all species.

Benefits of Genetic Diversity

Genetic diversity is the measure of how different the genomes (the complete set of genes) are among individuals within a population of a given species. It is inherently present in all populations due to:

Random mutations during DNA copying.
Recombination of chromosomes in the sex cells of parents, leading to new gene combinations and traits in offspring.

Advantages of High Genetic Diversity

Enhanced Response to Environmental Stressors: Populations with greater genetic diversity are better equipped to respond to environmental stressors such as drought, disease, or famine. This is because a larger gene pool increases the chance that some individuals will possess traits that enable them to survive the stressor.
Increased Survival Rate: More genetic diversity means a higher probability that some individuals in a population will have the necessary adaptations to endure and reproduce even when conditions become challenging.

Bottleneck Events

A bottleneck event is an environmental disturbance, such as a natural disaster or human-caused habitat destruction, that dramatically reduces the size of a population. Organisms are killed indiscriminately, regardless of their genetic makeup.

Consequences of Bottleneck Events

Reduced Genetic Diversity: The surviving population is smaller and, because individuals died randomly, it often does not represent the original population's full genetic diversity. Many unique genes can be lost.
Increased Vulnerability: The smaller, less genetically diverse population becomes even more susceptible to future environmental disturbances, as it has a diminished capacity to adapt.

Inbreeding Depression

Inbreeding occurs when organisms mate with closely related individuals. This results in the offspring having a higher chance of inheriting two copies of a deleterious (harmful) recessive gene from both parents.

Consequences of Inbreeding

Reduced Genetic Diversity: Similar to bottleneck events, inbreeding reduces the overall genetic diversity within a population.
Increased Expression of Harmful Recessive Traits: Closely related individuals share more similar genes, increasing the probability of offspring inheriting two copies of recessive alleles that can lead to genetic disorders, reduced fertility, or lower survival rates. This reduces the fitness of the population and makes it more vulnerable to environmental changes.

Importance of Species Diversity

Ecosystem Resilience: Ecosystems with a larger number of different species (high species richness) tend to be more resilient and stable. They are better able to recover from environmental disruptions, natural disasters, or human-caused disturbances because alternative species can take over the roles of those that are negatively affected.

Ecosystem Services

Ecosystem services are the many and varied benefits that humans freely gain from the natural environment and from properly functioning ecosystems. They are essential for human well-being and economic stability. These services can be categorized into four main types:

Provisioning Services:
- These are products obtained from ecosystems.
- Examples: Food (crops, livestock, fisheries), fresh water, timber, fiber (cotton, hemp), medicinal plants, and genetic resources.
Regulating Services:
- These are benefits obtained from the regulation of ecosystem processes.
- Examples:
  - Climate Regulation: Forests absorb CO_2.
  - Air Quality Regulation: Plants remove pollutants from the air.
  - Water Purification: Wetlands filter pollutants from water.
  - Disease Regulation: Biodiversity can help control disease vectors.
  - Pollination: Insects and other animals pollinate crops.
  - Pest Control: Predators and parasites control crop pests.
Cultural Services:
- These are non-material benefits people obtain from ecosystems through spiritual enrichment, cognitive development, recreation, and aesthetic experiences.
- Examples: Recreational activities (hiking, bird watching), aesthetic appreciation, spiritual inspiration, educational opportunities, and cultural heritage.
Supporting Services:
- These are services necessary for the production of all other ecosystem services. They differ from provisioning, regulating, and cultural services in that their impacts on people are indirect or occur over a very long time.
- Examples:
  - Nutrient Cycling: e.g., carbon, nitrogen, and phosphorus cycles.
  - Soil Formation: Weathering of rock and accumulation of organic matter create fertile soil.
  - Primary Production: Photosynthesis by plants forms the base of food webs.
  - Habitat Provision: Providing living spaces for species.