Biodiversity and Phylogenetic Tree Construction

Reminders and Announcements

  • Exam grading will be completed by the end of the week.
  • Not everyone has taken the exam yet.
  • Lab: Ensure the platypus paper has been read.

Constructing a Phylogenetic Tree: Practice Problem

  • Trait Table:

    • Species X: Vertebrae (yes), Wings (no), Exoskeleton (no), Eyes (yes), Endothermy (yes)
    • Species Y: Vertebrae (yes), Wings (yes), Exoskeleton (no), Eyes (yes), Endothermy (yes)
    • Species Z: Vertebrae (yes), Wings (no), Exoskeleton (yes), Eyes (yes), Endothermy (no)
    • Species W: Vertebrae (no), Wings (no), Exoskeleton (yes), Eyes (yes), Endothermy (no)

  • Steps for Construction:

    1. Identify the outgroup: The outgroup is the species least related to the others (Species W).
    2. Identify the most commonly shared trait among remaining taxa: Vertebrae presence is shared by Species X, Y, and Z.
    3. Map this trait onto the tree.
    4. Add any taxa that match existing traits on the tree: Add species X, Y, and Z which possess the vertebrae trait.
    5. Continue until all traits and taxa are added.

Biodiversity (Chapter 26)

  • Biological Diversity: Approximately 1.7 million species have been identified, with new species being discovered annually.
  • Changes Over Time: The number of species on Earth has varied over time; environmental conditions influence both speciation and extinction rates.

Biodiversity Over Time

  • Mass Extinctions: These are not evenly spaced throughout time.
  • General Trend: Biodiversity has generally increased over time.
  • Association with Climate Change: Mass extinctions are often linked to significant changes in climate.

Biological Diversity Across the Globe

  • Species Richness: This refers to the total number of species present in a given area.
  • Latitudinal Gradient: Species diversity tends to decline as you move away from the equator.
  • Variation Among Taxa: The pattern of diversity relative to the equator varies among different groups of organisms.

Exceptions to the Latitudinal Gradient

  • Example: Cactacae exhibit varying species richness across different regions.

Latitudinal Patterns: Proposed Explanations

  • There are over 25 proposed explanations for why the latitudinal diversity pattern exists.
    • Glacial Limitations: Presence of glaciers may have limited northward expansions of species.
    • Spatial Area: Polar areas are smaller in area compared to the area around the equator.
    • Evolutionary History: Historical evolutionary events may play a key role.
    • Climate Stability: Environmental stability can enhance biodiversity.

Environmental Energy Hypothesis

  • Thermal Energy and Evaporation Rate: Measured by Potential Evapotranspiration (PET) rate.
  • Positive Relationship: Evidence shows a positive correlation between PET and species richness, particularly for vascular plants.
  • PET Increase: PET increases as you approach the equator.

Species Richness and Primary Productivity

  • Autotroph-Heterotroph Link: Autotrophs (primary producers) provide both food and habitat for heterotrophs (consumers).
  • Plant-Animal Diversity Link: Increased plant diversity leads to increased animal diversity.
  • Primary Productivity Defined: It is the rate of photosynthesis (NPP = net primary productivity).
  • Solar Radiation Impact: Solar radiation determines mean surface temperature and potential evapotranspiration (PET).
  • Decline from Equator to Poles: Both temperature and PET decline from the equator towards the poles.