Environmental Science: Ecosystems & Ecology

Distinguish between biotic and abiotic factors in an ecosystem and provide examples of each.

Biotic factors are the living components of an ecosystem, such as plants, animals, and fungi. Abiotic factors are the non-living physical and chemical elements, such as sunlight, temperature, soil pH, and water availability.

Explain the 10% Rule of energy transfer between trophic levels.

The 10% Rule states that only approximately 10% of the energy stored as biomass in one trophic level is passed to the next level; the remaining 90% is lost primarily as heat through metabolic processes or remains unconsumed.

What is the primary difference between primary and secondary succession?

Primary succession occurs on bare substrate where no soil or previous life exists (e.g., volcanic rock), whereas secondary succession occurs in areas where a disturbance has cleared the vegetation but the soil remains intact (e.g., after a forest fire).

Define a keystone species and its impact on an ecosystem's structure.

A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. Its removal often leads to a significant shift in ecosystem structure or a loss of biodiversity.

Identify the biome characterized by permafrost, extremely low temperatures, and very short growing seasons.

The Tundra biome is characterized by permafrost (permanently frozen subsoil), low precipitation, and vegetation consisting mainly of mosses, lichens, and short grasses.

Why is the phosphorus cycle unique compared to the nitrogen or carbon cycles regarding its reservoir?

The phosphorus cycle is unique because it does not include a significant gaseous or atmospheric phase; phosphorus primarily cycles through sedimentary rocks, soil, and water.

Define Net Primary Productivity (NPP) and provide the formula relating it to Gross Primary Productivity (GPP).

NPP is the energy captured by producers through photosynthesis minus the energy they use for cellular respiration. The formula is NPP = GPP - R, where R is respiration.

Describe the process of nitrogen fixation and identify the primary biological agents responsible.

Nitrogen fixation is the conversion of atmospheric nitrogen (N2) into ammonia (NH3) or nitrates. This is primarily performed by specialized bacteria, such as Rhizobium, often found in the root nodules of legumes.

Explain the sequence of events in cultural eutrophication that leads to a 'dead zone.'

Nutrient runoff (N or P) triggers algal blooms; as algae die, aerobic bacteria decompose them, consuming dissolved oxygen in the process. This leads to hypoxia (low oxygen), which kills fish and other aquatic life.

What is a top-down trophic cascade, and how does it affect lower trophic levels?

A top-down trophic cascade occurs when a change in the population of a top predator triggers alternating increases and decreases in the populations of lower trophic levels (e.g., more predators lead to fewer herbivores and more producers).