Ecology and Ecosystem Dynamics

Size of the Great Pacific Garbage Patch

  • Size Comparison:

    • Great Pacific Garbage Patch: 1.6 million km²

    • Equivalent to 4.5 times the size of Germany (357,386 km²).

Microplastics

  • Sources of Microplastics:

    • Small manufactured plastics.

    • Microbeads.

    • Breakdown of larger plastic items due to:

    • Weathering

    • Photodegradation

    • Mechanical abrasion

  • Environmental Presence:

    • Found in caves, clouds, Arctic, and Antarctic regions.

    • Present inside animals’ stomachs and bloodstreams (e.g., seabirds, deep sea fish, sharks).

Exam Announcements

  • Topic Test 1:

    • Date: Saturday, October 4th at noon.

    • Duration: 60 minutes.

    • Locations will be announced soon.

    • Students registered with SAS should book ASAP for SAS Exam Centre.

  • Student Drop-In Hours:

    • Wednesdays, 3:30 to 5 PM, SSC 2315.

Ecological Interactions

Niche Partitioning Experiment

  • Setup: 20 octopuses and 20 clownfish placed in 3 aquariums with open water and rock piles.

  • Evidence of Niche Partitioning:

    • Example Locations:

    • A: Octopuses: 10, Clownfish: 0 (Open Water)

    • B: Octopuses: 10, Clownfish: 10 (Balanced)

    • C: Octopuses: 4, Clownfish: 6 (Competing)

    • D: Octopuses: 12, Clownfish: 0 (Dominance)

Importance of Plant Species

  • Plants' Roles in Ecosystems:

    • Primary producers (autotrophs).

    • They provide:

    • Oxygen in aquatic environments and atmosphere.

    • Carbon storage in plant tissues.

  • Habitat Creation: Trees create distinct habitats.

Foundation Species

  • Definition: Provide ecological foundation; often highly abundant, do not necessarily benefit from interactions.

  • Examples: Trees, corals, kelp.

Keystone Species

  • Definition: Disproportionately large impact relative to abundance or biomass.

  • Ecological Roles: Can include predators and mutualists.

  • Examples: Wolves, otters, starfish (e.g., Pisaster).

    • Pisaster (Purple Sea Star):

    • Top predator in intertidal zones, lives 4-20 years, captures prey with tube feet, eats mussels.

Consequences of Removing Keystone Species

  • Removal of Pisaster resulted in:

    • Drastic increase in mussel populations.

    • Loss of biodiversity as community shifted from diverse species to dense mussel beds.

Species Interactions

  • Direct vs Indirect Interactions:

    • Direct: One species directly affects another (e.g., predation).

    • Indirect: Relationships mediated by additional species (e.g., trophic cascades).

Food Webs

  • Definition: Illustrates who eats whom in an ecosystem.

  • Complexity: Real food webs can have numerous species and interactions (e.g., 100 species leading to ~10,000 possible interactions).

  • Imaginary Island Food Web:

    • Statements based on food webs can include impacts of species removals or increases.

Energy and Matter Flow in Ecosystems

  • NPP vs GPP:

    • Gross Primary Productivity (GPP): Rate of energy capture by producers.

    • Net Primary Productivity (NPP): Rate of energy converted into biomass.

    • Formula: NPP=GPP−extrespirationNPP = GPP - ext{respiration}

  • Limiting Factors: Defined as ecological factors restricting growth, distribution, or abundance of organisms (light, nutrient availability).

    • Liebig's Barrel: Growth is limited by the scarcest resource, emphasizing that adding more of a non-limiting factor won't help.

Exam Preparation Tips

  • Reading Questions:

    • Highlight keywords (e.g., must, could).

    • Beware of absolutes and qualifiers.

    • Look for causality in statements.

    • Assess parts of statements for accuracy (if one part is false, the whole is false).