week 5

Course Information

• Course name: SC253: Ecology and Environmental Problems
• Date: September 30, 2024
• Instructor: Prof. Amy L. Frick

Housekeeping

• Midterm: October 14, 2024. The midterm will cover multiple choice and short answer questions from class discussions (September 16 - October 7), readings referenced in class, and in-class activities/assignments.
• Ecological Footprint Essay: Deadline extended to October 21, 2024. Find updated details in the (/Content/Case Study of One) folder.
• Reading assignments: Check the updated (/Course information/schedule) folder for reading assignments for the following week.

Ecosystem Organization

• Ecosystems are organized in a hierarchical structure: Organism → Population → Community → Ecosystem → Biome
• Shows the relationships between living things and their environment.

Ecological Stability

• A stable ecosystem has a low variability, resisting shifts in environmental conditions. Stability is maintained by negative feedback loops.
• Action → Effect → Action (negative feedback loop)

Stability Domain

• Stability domain: the range within which a system, or group of organisms, can withstand stress before collapsing to a new stability domain.
• Environmental stress can push a system from one stability domain to another.

Resilience

• Resilience: an ecosystem's ability to maintain balance after stress.
• Factors influencing resilience include compensatory dynamics, plant diversity, temporal mean of ANPP, soil mutualists/high soil biodiversity, and free-living soil biota.

Stability Domain Shift

• As ecosystems are pushed beyond their stability domain, they can shift to a new one.
• Feedback loops can either reinforce the shift or bring the system back to its original state.

"Switch"

• Complex adaptive systems can remain relatively stable over long periods.
• However, high levels of stress can lead to sudden changes in stability domain.

Example of Stability Domain Switching: Sea Otters and Kelp

• The disruption of an ecosystem, like the removal of predators (otters), can result in major changes: Maintenance → Crisis → Dissolution → Reorganization

Trophic Cascade

• A trophic cascade is a significant indirect interaction within an ecosystem, affecting the entire food chain.
• Removal of sea otters can lead to increases in sea urchin populations, resulting in the decimation of kelp forest communities.

Stability Domain Switching (Example: Marine Forests and Sea Urchins)

• Climate change impacts and overfishing are examples of factors that can cause stability domain switching.

Complex Adaptive Systems

• Developed through community assembly.
• Exist in stability domains.
• High stress can cause a "switch" to a new stability domain.

Ecological Succession

• A process of progressive change in community structure over time, often leading to a climax community.
• Bare rock → Lichens → Small annual plants/lichens → Grasses and perennials → Grasses, shrubs, and shade-intolerant trees → Shade-tolerant trees.

What Makes a Community Stable?

• Species diversity is a key factor. This includes both species richness (number of species) and species composition (identity of species).
• High biodiversity vs. Low biodiversity
• A diverse community is often more stable than a less diverse one.

Ecological Niches

• Autotrophs (producers), heterotrophs (consumers), and decomposers play distinct roles within ecosystems.
• Defining roles within the food web.

Trophic Levels

• Organisms within an ecosystem can be categorized into trophic levels.
• Plant → Herbivore → Carnivore → Apex predator (primary producer - primary consumer - secondary consumer - tertiary consumer)

Ecosystem = Flow of Energy

• An ecosystem's structure is defined by the flow of nutrients and energy through its communities.
• Communities and organisms in an ecosystem form a food web.

Food Web

• Represents the complex interconnected paths of energy and nutrients within an ecosystem.
• A food web differs from a food chain because it represents all possible connections in the overall ecosystem. Multiple food chains are interconnected within a food web.

Vocabulary

• Urchin
• Sea otter
• Kelp
• Killer Whale

Keystone Species

• Keystone species have crucial roles in an ecosystem.
• Their removal or disruption can cause significant changes in the overall community structure.
• Sea otters are an example.

Relationships Between Species

• Relationships between species in ecosystems, including:
  • Competitive relationships
  • Predator-prey relationships
  • Symbiotic relationships:
    • Mutualism
    • Commensalism
    • Parasitism

Competition

• Competition (at any trophic level) occurs when species compete for resources such as food, water, and habitat.
• Competitive exclusion: two species competing for the same resources cannot coexist.

Invasive Species

• Invasive species may outcompete native species for resources

Group Activity

• Students will research and present on specific examples of interrelationships between species. Examples include Aphids/ants, Oxpeckers/mammals; e.coli in rodents; mycorrhizae/vascular plants and allelopathy in plants

Additional Details

• The midterm date is October 14, 2024, covering material from September 16-October 7, including class discussions, readings, and in-class activities/assignments.
• The deadline for the Ecological Footprint Essay is October 21, 2024 and further details can be found in the designated folder.
• Students are expected to have researched the subject matter, and present their findings with a diagram that explains their findings.