Unit 4: Ecosystems

By Violet Voon, 8/12/2025

Introduction to Ecosystems

• Ecology: The study of ecosystems, which encompass networks of interactions between all living organisms and non-living components in their environment.
• Ecosystem: A complex network of interactions that includes all living organisms (plants, animals, microorganisms) and their non-living environment, functioning together as a unit.
• Food Web: A type of interaction among living organisms where plants use energy from the sun to produce food through photosynthesis, making energy available to other organisms in the food web.
    - Chemical Energy Transfer: Represented by arrows in the food web that show the flow of energy from one organism to another.

Interactions in Ecosystems

• Living and Non-Living Interactions: These interactions define the ecosystem and include various factors:
    - Sunlight: Essential for photosynthesis.
    - Temperature: Influences the behavior of organisms; many become nocturnal to avoid heat.
    - Soils and Rocks: Provide minerals necessary for plant growth and building materials for ground-nesting birds.
    - Water: Vital for all life forms.
    - Air: Organisms can alter air composition through respiration.

Habitat vs. Ecosystem

• Habitat:
    - Definition: The specific physical area where an organism resides, such as forests or ponds.
    - Characteristics: It is a physical unit that can be defined by specific boundaries.
    - Example: Different species have unique habitats (e.g., a forest, pond).

• Ecosystem:
    - Definition: The interrelationships between living organisms and their non-living environment.
    - Components: Includes various habitats and species within a larger context.
    - Characteristics:
      1. An ecosystem can encompass many habitats.
      2. Ecosystems are generally larger than singular habitats.
      3. A habitat may support a few species, while an ecosystem hosts a wide variety of species.

Desert Ecosystem

• Habitat Examples:
    - Cactus: Open desert.
    - Rattlesnake: Underneath rocks.
    - Gila Woodpecker: Saguaro cactus.
    - Hawk: In trees.
    - Desert Ant: Under rocks and on the soil surface.
    - Termites: At the base of saguaro stems.
    - Sap Beetles: Inside saguaro flowers.

• Adaptations:
    - Defined as special characteristics that enable organisms to survive and reproduce in their environments.
    - Example: The roots of saguaro cacti spread widely to absorb rainfall quickly.
    - Example: Teddy bear cholla cacti, which are spiky, protecting the cactus wren's eggs from predators.

Adaptations in Desert Plants and Animals

• Waxy covering on leaves to minimize water loss.
• Long vertical roots extend deep into the soil to reach water tables.
• Prickles and spikes on stems protect against thirsty animals.
• Some plants may have no leaves to prevent water loss through transpiration.
• Horizontal roots collect surface water efficiently.

Ecosystem in Mangrove Forests

• Various organisms interact in mangrove ecosystems:
    - Young Fish: Utilize mangrove roots as shelter.
    - Decomposition: Bacteria decompose fallen leaves, while crabs and prawns consume the decomposing material.
    - Wildlife: Various seabirds and animals feed on crustaceans present.
    - Mudskippers: Can emerge from mud during low tide; a unique adaptation to their habitat.

Arctic Ocean Ecosystem

• Key organisms include:
    - Phytoplankton: The foundation of marine food webs and essential for energy transfer.
    - Fish, Seals, Walrus, Polar Bears, Ice Algae, and Zooplankton: All play vital roles in this ecosystem, displaying adaptations to cold environments.

Native and Introduced Species

• Native Species: Found naturally in an ecosystem due to their historical distribution.
• Introduced Species: Species brought into an ecosystem intentionally or accidentally.
    - Example: Stoats in New Zealand, introduced for rabbit control, have negatively impacted native species such as the kiwi. Control efforts face challenges due to the widespread and cherished nature of introduced species.

Bioaccumulation and Biomagnification

• Bioaccumulation: Gradual accumulation of substances, such as pesticides, in organisms. It occurs when substances cannot be broken down within the organism.
    - Example: DDT, an insecticide that, once ingested, remains in the organism's body and accumulates over time.

• DDT Effects: Slow degradation leads to weak eggshells in birds, which decreases populations due to broken eggs.

• Biomagnification: The increase in concentration of toxic substances as one moves up the food chain.
    - Example of DDT concentrations:
      - Producers: $0.04 ext{ ppm}$
      - Primary Consumers: $0.23 ext{ ppm}$
      - Secondary Consumers: $2.07 ext{ ppm}$
      - Tertiary Consumers: $13.8 ext{ ppm}$
    - Concentration increases at each trophic level due to the accumulation in prey organisms, leading to significant health impacts at higher levels of the food chain (e.g., gulls can accumulate DDT at up to 400 times the concentration in their food).

Summary of Definitions: Bioaccumulation vs. Biomagnification

• Bioaccumulation: Increase of a toxic substance within an individual organism.
• Biomagnification: Increase of a toxic substance as it moves between trophic levels in a food chain.
• Occurrence:
    - Bioaccumulation occurs within an organism.
    - Biomagnification occurs between different trophic levels.