Ecology and Biogeochemical Cycles: Key Concepts and Processes

What is the difference between predation and parasitism?

Predation: One organism kills and consumes another; Parasitism: One organism benefits while harming the host.

What is the difference between detritivores and decomposers? Give examples.

Detritivores: Physically ingest organic matter (e.g., earthworms, millipedes); Decomposers: Use chemical/enzymatic processes (e.g., fungi, bacteria).

List the 5 stages of decomposition in order.

Fragmentation, Leaching, Catabolism, Mineralization, Humification.

Explain fragmentation and leaching in decomposition.

Fragmentation: Physical breaking apart of material into smaller pieces; Leaching: Water-soluble materials wash away.

Explain catabolism and mineralization in decomposition.

Catabolism: Chemical decomposition by fungi and bacteria; Mineralization: Release of nutrients from organic matter.

What is humification?

Remaining material that can't be broken down becomes soil/humus (final stage of decomposition).

What is the Hadley cell and what biomes does it create?

Warm air rises at equator → high rainfall; Air descends at ~30° latitude → dry conditions; Creates: Tropical rainforests at equator, deserts at 30° latitude.

What is a trophic cascade? Use wolves as an example.

Top predators control lower trophic levels. Wolf example: Wolves removed → elk increase → vegetation overgrazed → erosion; Wolf reintroduction → elk behavior changes → vegetation recovers.

Why is nitrogen fixation essential for ecosystems?

Most organisms can't use atmospheric N₂; Must be 'fixed' into NH₃/NH₄⁺ by bacteria; Necessary for protein synthesis and plant growth.

What are the three types of assisted migration/reintroduction?

Reintroduction: Moving species to historical range where locally extinct; Captive breeding: Using zoo-bred offspring to repopulate; De-extinction: Using ancient DNA to genetically recreate extinct species.

Give an example of successful reintroduction and what it restored.

Wolves to Yellowstone: Restored trophic cascade, changed elk behavior, allowed vegetation recovery, improved stream health.

What is carbon use efficiency?

Proportion of carbon taken up that's converted to growth vs respiration; Higher efficiency = more carbon stored in biomass = better growth.

Why is water considered a polar molecule?

Charges not distributed equally: Oxygen end is more negative; Hydrogen ends are more positive.

What is the 10% rule in ecology?

Only ~10% of energy transfers from one trophic level to the next; 90% lost as heat, waste, metabolism; Limits food chain length and number of top predators.

Define cohesion and adhesion. How do they work together in plants?

Cohesion: Water molecules stick together; Adhesion: Water molecules stick to other surfaces; Together = capillary action: Adhesion binds water to xylem, cohesion pulls rest up.

What is phylosymbiosis?

Microbes associated with host species mirror the evolutionary relationships of the host; More closely related hosts have more similar microbiomes.

What is the Redfield ratio and why is it important?

C:N:P = 106:16:1; Describes constant chemical requirements of phytoplankton; Variations suggest decomposability.

What is specific heat and why is water's specific heat important?

Amount of energy to raise 1g by 1°C; Water has HIGH specific heat = resists temperature change; Influences local and continental climates.

What is an ecosystem engineer? Give two examples.

Species that physically modify environment affecting other species; Examples: Beavers build dams → create wetlands; Prairie dogs dig burrows → aerate soil, create habitat.

Define blue carbon ecosystems and list the three major types.

Coastal ecosystems that capture and store carbon in sediments at high rates; Types: Salt marshes, Seagrass beds, Mangroves.

List the 5 largest water pools on Earth (largest to smallest).

Ocean, Ice sheets/glaciers, Groundwater, Permafrost, Lakes.

What are the two most important water fluxes?

Precipitation: Water falling from atmosphere; Evaporation: Water entering atmosphere from surfaces.

What was the Gulf of Mexico Dead Zone and what caused it?

Large area of oxygen-depleted water where marine life can't survive; Caused by: Excess nutrients from agriculture → algal blooms → decomposition consumes oxygen.

How does nutrient pollution lead to hypoxia? (Steps)

Excess nutrients (N, P) enter water; Algal bloom occurs; Algae die and sink; Decomposition consumes oxygen; Oxygen depletion creates hypoxic zones.

What does it mean for a compound to be reduced? Give an example.

Reduced = gains electrons (more energy-rich); Examples: Methane (CH₄), Ammonium (NH₄⁺).

What does it mean for a compound to be oxidized? Give an example.

Oxidized = loses electrons (less energy-rich); Examples: Carbon dioxide (CO₂), Nitrate (NO₃⁻).

How does acid rain form?

SO₂ and NOₓ from fossil fuel combustion → react with water vapor → form H₂SO₄ and HNO₃ → fall as acid precipitation.

Why is acid rain considered a success story?

Clean Air Act regulations reduced SO₂ and NOₓ emissions; Significant improvement in rainfall pH; Ecosystem recovery in affected areas; Shows environmental policy can work.

What were the conditions of early Earth?

Water vapor, ammonia, hydrogen, CO₂, methane; Lightning provided energy; No free oxygen; High UV radiation.

What is the endosymbiotic theory?

Small aerobic prokaryote engulfed by larger anaerobic prokaryote → not digested → provides energy → becomes mitochondria; Explains evolution from prokaryotes to eukaryotes.

Why did endosymbiosis increase evolutionary rates?

Aerobic metabolism much more efficient; More energy for growth and reproduction; Enabled larger, more complex organisms; Faster reproduction and adaptation.

What is ecological restoration and why is it needed?

Process of assisting recovery of degraded ecosystems. Needed because of habitat loss, pollution, climate change, invasive species, human development.

What is a challenge in choosing restoration targets?

Must decide between historical conditions, pre-disturbance conditions, future conditions (climate change), and novel ecosystems. Consider feasibility, stakeholder values, climate, resources.

How do you measure restoration success?

Absence of threats, restored physical conditions, native species present, structural diversity, functioning ecosystem processes, self-sustaining with less intervention, resilience to disturbance.

Name three ecological consequences of dams on Klamath River.

Blocked salmon migration to spawning grounds, altered water temperature and quality, trapped sediment preventing downstream transport.

Who were stakeholders in Klamath River restoration and their interests?

Native tribes: Cultural/subsistence fishing, restoration; Farmers: Water for irrigation; Fishermen: Healthy salmon populations; Hydropower companies: Energy generation; Environmentalists: Ecosystem restoration.

What are the four types of ecosystem services? Give examples from salt marshes.

Supporting: Nutrient cycling, fish nursery habitat; Provisioning: Shellfish, raw materials; Regulating: Coastal protection, water purification; Cultural: Birdwatching, recreation, education.

What is phytoremediation?

Using plants to remove, stabilize, or break down contaminants from soil or water.

List three mechanisms of phytoremediation.

Phytoextraction: Plants absorb contaminants into tissues; Phytostabilization: Plants immobilize contaminants in soil; Phytodegradation: Plants break down contaminants.

What does the Eddy Covariance Tower measure and tell us?

Measures CO₂ exchange, water vapor flux, energy exchange. Tells us net ecosystem production, if ecosystem is carbon sink/source, how ecosystems respond to conditions.

What does 'microbes are engines of biogeochemical cycles' mean?

Microbes drive all major biogeochemical cycles, diverse metabolic capabilities transform elements, core genes responsible for global processes, global interconnectedness of pathways.

Why does oxygen disappear first in deep sediments?

Microbes use oxygen first for respiration (most efficient). As oxygen depletes, switch to anaerobic processes, creating layered zones with different metabolic processes.

What is top-down vs bottom-up forcing?

Top-down: Ecosystems controlled by top predators (best for odd # trophic links). Bottom-up: Nutrients and primary production dictate biomass (best for even # trophic links).

What is nutrient limitation?

When ecosystem productivity is limited by availability of specific nutrients. Common: Nitrogen (terrestrial), Phosphorus (aquatic). Based on Liebig's Law of the Minimum.

How does anthropogenic nitrogen alter ecosystems?

Fertilizers and fossil fuels add excess nitrogen, leading to eutrophication, algal blooms, dead zones, altered species composition, changed ecosystem structure and function.

What properties does water have because of polarity?

Cohesion (water sticks to itself), adhesion (water sticks to other surfaces), high specific heat, universal solvent, capillary action.

Describe Land as Capital vs Land as Community.

Capital: Commodity to exploit, no obligation to restore, extraction focus. Community: Part of cultural/spiritual practice, reciprocal responsibilities, humans part of ecosystem.

How is fire an example of reciprocity?

Give-and-take relationship: Indigenous peoples use fire to care for ecosystems; land provides healthier forests, wildlife habitat, renewed growth.

Why might more production go to detritus than herbivory?

Not all plant material palatable/accessible to herbivores; plants have defenses; seasonal die-off creates large detrital inputs.

What is the Coriolis Effect?

Earth's rotation deflects moving air masses: Right in Northern Hemisphere, left in Southern Hemisphere, creates prevailing wind patterns.

What are two mitigation strategies for the Gulf Dead Zone?

Create wetland buffer zones (denitrifying bacteria remove nitrate); reduce fertilizer application, improve timing to match crop needs.

What are the primary sources of phosphorus for fertilizers?

Sources: Rock phosphate mining, guano deposits. Yes, we should be concerned: finite resource, limited reserves, no substitute, essential for food.

Describe seagrass and oyster carbon interactions.

Seagrass fixes CO₂, exports POC (feeds oysters), increases alkalinity; oysters filter POC (increases light for seagrass), calcification reduces alkalinity.

Why are blue carbon ecosystems important for climate change?

Sequester carbon at very high rates, store carbon long-term in sediments, co-benefits include coastal protection, water filtration, habitat.

What is a scavenger and give an example?

Organisms that feed on dead animals (don't kill them). Examples: Vultures, hyenas, crabs.

How do different stakeholders influence restoration projects?

Provide funding and resources, determine goals and priorities, can support or oppose projects, bring different values and knowledge systems.

What is a strategy to combat 'beyond repair' perceptions in restoration?

Show successful restoration examples, emphasize ecological resilience, engage community in process, demonstrate incremental improvements.

Describe two ways human water use impacts the environment.

Agriculture: Irrigation depletes groundwater, alters river flows; Dams: Block sediment, disrupt migration, change downstream ecosystems.