Biodiversity and Conservation Notes

3.1 Biodiversity and Evolution

Biodiversity

  • A combination of "biological" and "diversity."

  • The diversity of life forms in an environment.

Types of Biodiversity

  • Habitat Diversity: The range of different habitats per unit area in a particular ecosystem.

  • Species Diversity: In communities, it is a product of two variables: the number of species (richness) and their relative proportions (evenness).

  • Genetic Diversity: The range of genetic material present in a gene pool or population of a species.

Species Richness and Evenness

  • Species richness and species evenness are two different measures of species diversity.

  • Community 1 (more even distribution of species) is more diverse than Community 2 (less even distribution).

Ecosystem Health

  • Biodiversity is very important for the resilience of ecosystems.

  • Biodiversity allows ecosystems to resist changes in the environment and avoid ecological tipping points.

  • Several indices can be used to measure diversity, with Simpson’s index being the best known.

Simpson’s Reciprocal Diversity Index

  • A numerical value used to measure species richness and species evenness.

  • The higher the number, the greater the species diversity.

  • Allows for comparison of similar ecosystems or tracking changes in ecosystems over time.

Biodiversity Hotspots

  • A region with a high level of biodiversity that is under threat from human activities.

  • Species are not evenly distributed around the planet.

  • Certain areas have large numbers of endemic species (those found nowhere else).

  • Many biodiversity hotspots are heavily threatened by habitat loss and other human activities.

Evolution

  • Evolution is cumulative change in the heritable characteristics of a population or species.

Natural Selection

  • Variation: Every species exhibits genetic variation, meaning individuals have slightly different traits.

    • Example: Some moths may be lighter in color than others due to genetic differences.

  • Competition: In crowded environments, individuals must compete for limited resources.

    • Example: A lighter-colored moth blending into tree bark may offer a survival advantage by making them harder to spot by predators.

  • Adaptations: Traits that improve survival are examples of adaptations.

    • Example: Camouflage in moths.

    • These traits help individuals avoid predators and increase their chances of survival in a competitive environment.

  • Selection: Individuals with advantageous traits are more likely to survive, reproduce, and pass these traits to the next generation.

    • Over time, these beneficial traits become more common in the population as they are inherited by offspring.

Speciation

  • Speciation is the formation of new species when populations of a species become isolated geographically or behaviorally, and evolve differently from other populations.

How Plate Activity Influences Biodiversity

  • Where tectonic plates meet, they may:

    • Slide past each other (e.g., the San Andreas fault line, California).

    • Diverge (e.g., the mid-Atlantic ridge).

    • Converge:

      • Collide and both be forced up as mountains (e.g., formation of the Himalayas and Alps).

      • Collide and the heavier oceanic plate sinks underneath the lighter continental plate (e.g., where the Nazca plate under the Pacific meets the west coast of South America and the Andes form).

Fossil Evidence

  • Fossil evidence supports the idea of continents being joined in the past.

    • Fossils of the fern Glossopteris found in all of the southern continents.

    • Fossil remains of Cynognathus, a Triassic land reptile approximately 3m long.

    • Fossil remains of the freshwater reptile Mesosaurus.

    • Fossil evidence of the Triassic land reptile Lystrosaurus.

Biodiversity Over Time

  • Biodiversity has increased steadily over Earth's 4.5 billion year history, driven by evolutionary processes like speciation and extinction.

  • The balance between these two processes shapes the overall level of biodiversity at any given time.

Background Extinction Rate

  • The background extinction rate is very slow: about one species in a million every year. \frac{1}{1,000,000} per year.

  • Some scientists estimate that more than 1,000 species are currently going extinct each year, which is about 500 times the background rate of extinction.

Mass Extinction

  • A mass extinction is an event in which 75% of the species on Earth disappear within a geologically short time period, usually between a few hundred thousand to a few million years.

The Sixth Mass Extinction

  • Humans are the direct cause of ecosystem stress:

    • Transform the environment with cities, roads, industry, agriculture.

    • Overexploit other species in fishing, hunting, and harvesting.

    • Introduce alien species, which may not have natural predators.

    • Pollute the environment, which may kill species directly or indirectly.

The Living Planet Index

  • Measures trends in the Earth’s biological diversity.

  • It follows populations of 2,500 vertebrate species (fish, amphibians, reptiles, birds, mammals) from all around the world and so gives a numerical index of changes in biodiversity.