Biodiversity and Ecological Communities

Biodiversity and Ecological Communities

Introduction

  • Lecture by Dr. Amy Greer, BSc, MSc, PhD, Associate Professor, Department of Biology.
  • Date: Week 6 – Lecture 1, October 7, 2025.

Course Reminders

1020-A Reminders for the Week of October 6, 2025

  • Lab Attendance: Attend Lab 3 this week (Thursday or Friday).
  • Presentations: Group presentations for Lab 2; no preparation needed, presentations completed during lab.
  • Paper Preparation: Prepare to write a full scientific paper on lichen data; outline will be returned on October 14.

1020-A Midterm Examination

  • Dates: October 30/31.
  • Locations and Times:
    • A-F01: October 30, 9:00 – 10:15, DNA D106
    • A-F02: October 30, 9:00 – 10:15, DNA D108
    • A-F03: October 30, 1:00 – 2:15, DNA D106
    • A-F04: October 30, 1:00 – 2:15, DNA D108
    • A-F05: October 30, 4:00 – 5:15, DNA D106
    • A-F06: October 30, 4:00 – 5:15, DNA D108
    • A-F07: October 31, 9:00 – 10:15, DNA D106
    • A-F08: October 31, 9:00 – 10:15, DNA D108
    • A-F09: October 31, 1:00 – 2:15, DNA D106
    • A-F10: October 31, 1:00 – 2:15, DNA D108
  • Attendance is mandatory: Must arrive on time and write in the correct room.

1020-B Reminders for the Week of October 6, 2025

  • No Lab Attendance: No lab scheduled for this week.
  • Lab 2 Paper Outline: Due Friday, October 10, by 4 PM.
  • Submission Format: Fill in ‘Lichen ASSIGNMENT – BLANK 2025 – FINAL.docx’ on Blackboard and convert to PDF for submission via Crowdmark.

1020-B Midterm Examination

  • Dates: October 30/31.
  • Locations and Times:
    • B-F01: October 30, 10:30 – 11:45, DNA D106
    • B-F02: October 30, 10:30 – 11:45, DNA D108
    • B-F03: October 30, 2:30 – 3:45, DNA D106
    • B-F04: October 30, 2:30 – 3:45, DNA D108
    • B-F05: October 30, 5:30 – 6:45, DNA D106
    • B-F06: October 30, 5:30 – 6:45, DNA D108
    • B-F07: October 31, 10:30 – 11:45, DNA D106
    • B-F08: October 31, 10:30 – 11:45, DNA D108
  • Attendance is mandatory: Must arrive at the scheduled time for your section; arriving early will require waiting until the scheduled time.

Midterm Logistics

  • Waiting Protocol: Wait outside until called in by exam invigilators.
  • Entry Requirements: Enter quietly with items secured except for a pen/pencil/eraser/calculator/student card; NO PHONES or Smart Watches allowed.
  • Exam Conditions:
    • Place bags at the front before taking a seat.
    • Write name and student number on the front page.
    • Begin only when instructed.
    • Maintain silence and focus on own paper (different versions of the exam are provided).

Midterm Structure

  • Format: In-person test (specific details already provided).
  • Valuation: Worth 18 points (14% of total grade).
  • Components:
    • 10 multiple-choice questions (10 points total), to be answered on a bubble sheet.
    • 3 short answer questions (choose 2 to answer, each worth 4 points = 8 points total).
  • Duration: 60 minutes to complete; expected to finish in 45-50 minutes.
  • Scope: Questions will encompass all lecture material, not restricted to weekly quizzes.
  • Review Session: To be conducted next week.

Midterm Review Preparation

  • Question Submission: Students can submit one question/topic for review consideration; it is optional, aimed to address areas needing clarification.
  • Submission Timeline: Available from October 7th at noon until October 10th at 4 PM.
  • Priority Consideration: Questions submitted through the form will receive priority, but coverage of all questions may not be possible due to time constraints.

Key Concepts in Biodiversity and Ecological Communities

Biological Community

  • Definition: A biological community refers to the collection of species that exist together within the same habitat.
  • Connections: Species within the community are linked through both their interactions and geographic co-location.

Biodiversity

  • Definition: Biodiversity serves as a metric for the number of species present in a given area.
  • Measuring Scales: Biodiversity can be measured at different scales, with a primary focus on the ecosystem or habitat scale in the context of community ecology.
  • Community Ecology: The study of biodiversity, including species count, community structure, and interaction relationships, falls under the sub-field known as community ecology.

Measuring Biodiversity

  • Basic Measures:
    • The simplest and most comprehensible approach to measure biodiversity is through species richness.
  • Counting Species: Counting species becomes easier in well-known or thoroughly studied communities.

Examples and Case Studies

  • Species Area Curve:
    • Figure 2.3 illustrates the species area curve with nested square plots sampling perennial plants in the Sonoran Desert in Arizona (2007). When the plot area increases from 1 to 10 m² (Point A), the captured species double. By 20 m² (Point B), additional area provides only one more species, indicating diminishing returns on species capture as area increases.
    • Efficient Sampling Area: The example suggests that an effective plot area might be 20 m².

Factors Affecting Species Richness and Diversity

Community Structure Metrics
  • Comparison of Community Structures: Species richness should not be evaluated in isolation, as two communities may have identical species richness but different species abundance distributions.
  • Example of Communities:
    • Community 1:
    • Species A: 25%
    • Species B: 25%
    • Species C: 25%
    • Species D: 25%
    • Community 2:
    • Species A: 80%
    • Species B: 5%
    • Species C: 5%
    • Species D: 10%
    • Species abundance affects the interaction strengths, meaning Community 2 has higher dominance of Species A, affecting overall interactions in the community.
Species Diversity Metrics
  • Shannon-Weiner Diversity Index:
    • Defined by the equation:
      H = -(pA imes ext{ln} pA) + (pB imes ext{ln} pB) + (pC imes ext{ln} pC) + ext{…}
      where A, B, C, etc. are the species in the community, and $p$ is the relative abundance of each species, with ln denoting the natural logarithm.
  • Example Calculations:
    • For Forest 1:
    • H = -(0.25 imes ext{ln} 0.25) + (0.25 imes ext{ln} 0.25) + (0.25 imes ext{ln} 0.25) + (0.25 imes ext{ln} 0.25) = 1.39
    • For Forest 2:
    • H = -(0.8 imes ext{ln} 0.8) + (0.05 imes ext{ln} 0.05) + (0.05 imes ext{ln} 0.05) + (0.1 imes ext{ln} 0.1) = 0.71
    • Comparison Result:
    • H( ext{Forest 1}) > H( ext{Forest 2})
  • Interpretation of H: Higher values of H indicate habitats with greater species variety and more even distribution of species, as rare species contribute less to the ecosystem functionality.

Geographic Distribution of Species

  • Tropical Regions vs. Polar Regions:
    • Tropical locales exhibit high mammal diversity, encompassing all major groups, while polar regions host minimal species, typically rodents, their predators, seals, and whales.

Island Biogeography

  • Effect of Island Size on Biodiversity:
    • Relationship established by R. H. MacArthur and E. O. Wilson in 1967, suggesting biodiversity increases with island area.
  • Applications: The principle can inform reserve design and conservation strategies.

Factors Influencing Biodiversity

  1. Energy and nutrients from primary productivity.
  2. Availability of water.
  3. Occurrence of disturbances.
  4. Presence of invasive species.
  5. Predation dynamics.
  6. Ecological succession processes.
  7. Biogeographic features.

Energy Flow in Ecosystems

  • Forms of Energy Acquisition: Living organisms obtain energy in several ways:
    • Photosynthesis
    • Chemosynthesis
    • Consumption and digestion of other organisms by heterotrophs.
  • Food Web Dynamics: Food webs demonstrate the directional flow of energy and nutrients throughout ecosystems, highlighting the efficiencies of energy acquisition and distribution.
  • Examples of Trophic Levels:
    • Figure 16.1: Shows trophic levels within Lake Ontario, beginning with photosynthetic green algae as the primary producers feeding into higher trophic levels (e.g., Chinook salmon).
    • Figure 16.3: Illustrates food web interactions, where arrows designate the consumer-contributed energy flow, with decomposers terminating the cycle.

Ecological Succession

  • Types of Succession:
    1. Primary Succession: Starts from bare rock post-disturbance. Initial colonizers are pioneer species such as lichens. The sequence progresses from small annual plants to grasses and eventually to perennial plants.
    2. Secondary Succession: Occurs following a disturbance in an established habitat where soil is still intact. Transition phases may include grasses, shrubs, and eventually leading to climax communities of shade-tolerant species.
  • Timeline Dynamics:
    • Primary succession may stretch over hundreds of years. Secondary succession demonstrates predictable colonization patterns transitioning from r-strategists to K-strategists as the ecosystem stabilizes.

Keystone Species

  • Definition: A keystone species is one whose impact on its ecosystem is disproportionately large relative to its abundance.
  • Case Study: Pisaster as a Keystone Species:
    • Research by Paine (1974) analyzed the removal of the starfish Pisaster from intertidal zones in Washington state, yielding insights into its role in maintaining biodiversity by predation.
    • Results: Demonstrated the presence of significantly more species with Pisaster (control) than without it (experimental), confirming that predators create space for additional niches occupied by other invertebrates.