AP Environmental Science Quiz: Natural Disruptions To Ecosystems

What this quiz covers

This quiz focuses on Natural Disruptions To Ecosystems, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Environmental Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Warmer water holds less dissolved oxygen, and increased respiration can outpace oxygen supply, stressing fish and causing mortality. (correct answer)
2. Warmer water holds more dissolved oxygen, but fish suffocate because oxygen becomes too concentrated in gills.
3. Heat waves eliminate sunlight penetration, stopping photosynthesis permanently and causing oxygen to rise to toxic levels.
4. Fish die because heat waves increase salinity in freshwater ponds to ocean levels within hours, causing osmotic shock universally.

Explanation: Heat waves warm pond water, reducing dissolved oxygen capacity while increasing metabolic demands. This leads to hypoxia, stressing and killing fish. Warmer conditions favor respiration over oxygenation. Die-offs occur when oxygen supply fails. Mitigation includes shading or aeration. Such events highlight thermal disruptions in aquatics.

Question 2

1. Increase soil salinity to limit plant growth, thereby reducing competition and promoting longleaf pine regeneration.
2. Mimic natural fire regimes to reduce fuel loads, recycle nutrients, and maintain fire-adapted species composition. (correct answer)
3. Eliminate all insects permanently, preventing any future herbivory and increasing ecosystem stability indefinitely.
4. Convert the ecosystem to primary succession by removing soil organic matter and exposing bedrock for lichens.

Explanation: Prescribed burns in pine savannas mimic natural fires, reducing fuels and recycling nutrients. This maintains fire-adapted species and prevents intense wildfires. Goals include preserving biodiversity and ecosystem structure. Fires promote understory diversity by limiting woody encroachment. Without them, succession shifts habitats. Such management sustains disturbance-dependent ecosystems.

Question 3

1. Increasing dominance of fast-growing sun-loving annuals and decreasing woody biomass, indicating early succession persists.
2. Rising structural complexity (multiple canopy layers) and increasing shade-tolerant tree seedlings, indicating later successional stages. (correct answer)
3. Complete absence of decomposers and fungi, indicating nutrient cycling has stopped and a climax community has formed.
4. Declining soil organic matter and increasing erosion rates, indicating stable late-successional equilibrium has been reached.

Explanation: Post-clear-cutting, progression to late succession shows increased structural complexity and shade-tolerant species. Canopy layers develop as pioneers give way. Indicators include rising woody biomass and understory changes. Succession rebuilds ecosystem functions over decades. Monitoring helps assess recovery. Disturbances like logging reset but allow regrowth.

Question 4

1. Lower turbidity and lower nutrient levels because ash settles instantly and removes phosphorus from the water column.
2. Higher turbidity and increased nutrients (especially phosphorus), potentially increasing algal growth and reducing oxygen later. (correct answer)
3. Higher dissolved oxygen because ash adds oxygen directly, preventing any changes in biological oxygen demand.
4. Lower pH to near 1 because ash is strongly acidic, dissolving all carbonate buffers immediately.

Explanation: Wildfire ash enters lakes via runoff, increasing turbidity and nutrient levels like phosphorus. This can spur algal growth, potentially leading to oxygen depletion as blooms decompose. Short-term water quality declines, affecting aquatic organisms. Ash also alters pH slightly but mainly impacts clarity and productivity. Recovery occurs as sediments settle and vegetation regrows. Such disruptions show fire's cascading effects on nearby water bodies.

Question 5

1. Corals increase zooxanthellae density to absorb more heat, turning white as pigments become more concentrated.
2. Corals expel symbiotic algae (zooxanthellae) under stress, losing photosynthetic pigments and reducing energy supply. (correct answer)
3. Bleaching occurs when corals ingest plastic, which dyes their tissues white and prevents any future reproduction.
4. Bleaching is caused by low salinity from upwelling, which always occurs during heat waves in tropical oceans.

Explanation: Heat stress causes corals to expel zooxanthellae, leading to bleaching and loss of color. These algae provide energy via photosynthesis, so expulsion reduces coral health. Bleaching increases mortality if prolonged. Recovery depends on stress alleviation and algal return. Climate change exacerbates such disturbances. Understanding symbiosis is key to reef conservation.

Question 6

1. Secondary succession, because the seed bank and soil nutrients remain intact under the bedrock surface after sliding.
2. Primary succession, because soil is largely removed and pioneer species must create new soil before later plants establish. (correct answer)
3. No succession occurs because bedrock cannot support any organisms, so the slope remains barren indefinitely.
4. Climax community develops immediately because disturbance resets competition, allowing late-successional trees to dominate instantly.

Explanation: Landslides stripping to bedrock initiate primary succession, as soil must reform. Pioneer species like lichens start the process by weathering rock. Soil absence distinguishes it from secondary succession. Recovery is slow, building complexity over time. Vegetation stabilizes slopes eventually. Such events reset ecosystems dramatically.

Question 7

1. Obligate aquatic amphibian larvae that require standing water for development, leading to reduced recruitment in dry years. (correct answer)
2. Upland cacti that rely on frequent flooding to store water in tissues, causing immediate mortality when wetlands dry.
3. Deep-rooted mature trees that only use groundwater, so they die first when surface water declines slightly.
4. Apex predators in the region because they cannot hunt without wetland water, regardless of prey availability.

Explanation: Droughts shorten wetland hydroperiods, directly threatening species needing prolonged water like amphibian larvae. These obligate aquatics fail to develop without standing water, reducing populations. Other species with adaptations may persist longer. This illustrates how hydrological changes cascade to dependent organisms. Wetland ecosystems rely on water regimes for biodiversity. Management focuses on water conservation to mitigate impacts.

Question 8

1. Lower water temperature from increased shading, raising dissolved oxygen and boosting trout populations in newly shaded channels.
2. Higher sediment input from reduced root stabilization, increasing turbidity and potentially reducing benthic macroinvertebrate diversity. (correct answer)
3. Immediate increase in stream pH because drought adds carbonate ions, causing long‑term alkalinization of all watersheds.
4. Permanent elimination of decomposition because drought kills all bacteria, preventing leaf litter breakdown for centuries.

Explanation: Droughts kill trees, reducing root stabilization along streams and increasing sediment erosion into water. This raises turbidity, which can harm aquatic life like macroinvertebrates by blocking light and clogging habitats. Short-term changes include decreased biodiversity in benthic communities. Riparian vegetation normally filters sediments, so its loss exacerbates impacts. Recovery depends on regrowth and rainfall patterns. Such disruptions illustrate linkages between terrestrial and aquatic ecosystems.

Question 9

1. Negative feedback: more grass reduces fire probability by increasing soil moisture and decreasing fine fuels.
2. Positive feedback: invasive grass promotes more frequent fires, which further favors the grass over native shrubs. (correct answer)
3. Neutral feedback: fire frequency is unaffected by vegetation changes because ignition is controlled only by lightning rates.
4. Abiotic buffering: grass converts $CO_2$ to oxygen, preventing combustion and stabilizing climate at the site.

Explanation: Invasive grasses creating fine fuels promote more fires, which further advantage the grass in a positive feedback loop. This alters native shrub communities negatively. Feedbacks amplify changes in disturbance regimes. Native systems may shift irreversibly. Management aims to break such cycles. This illustrates invasion-disturbance interactions.

Question 10

1. Thin bark and shallow roots, increasing water uptake and ensuring rapid mortality that opens space for competitors.
2. Thick bark and high canopy, protecting cambium from heat and allowing survival through frequent surface fires. (correct answer)
3. Complete dependence on animal pollination only, because fire eliminates wind and prevents airborne pollen transfer.
4. Low seed production, because fires reduce competition and guarantee survival of every seed that is produced.

Explanation: In fire-prone forests, traits like thick bark protect trees from heat damage during low-intensity fires. High canopies elevate vulnerable parts above flames. These adaptations favor survival in repeated disturbances. Fire regimes select for such species over time. Thin-barked trees are outcompeted. Ecosystem dynamics depend on these traits.

Question 11

1. Hardening all shorelines with seawalls, eliminating wetlands and dunes to maximize developable land and shorten evacuation routes.
2. Maintaining natural buffers like wetlands and dunes, limiting building in flood-prone zones, and using setback regulations to reduce exposure. (correct answer)
3. Increasing groundwater extraction to lower sea level locally, preventing storm surge and improving freshwater availability simultaneously.
4. Replacing native coastal vegetation with lawns, which absorb wave energy better and require fewer nutrients than natural plants.

Explanation: Resilient coastal planning emphasizes preserving natural buffers like wetlands and dunes, which absorb storm energy and reduce flooding. Setback regulations prevent building in high-risk zones, minimizing human and ecological damage. This approach integrates ecosystem services for long-term sustainability. Hardening shorelines can exacerbate erosion elsewhere. Choice A is counterproductive as it eliminates protective features. Options C, D, and E are misguided: extraction does not lower sea levels, lawns are less effective than natives, and mangroves reduce surge, not increase it.

Question 12

1. High genetic and species diversity, providing varied tolerances and regeneration strategies that increase resilience after disturbance. (correct answer)
2. Eliminating decomposers so fallen wood remains, preventing nutrient release that could favor early successional species.
3. Removing all understory plants to reduce competition, ensuring no new seedlings establish until mature trees return.
4. Increasing soil compaction with heavy machinery to stabilize roots, which increases infiltration and seedling survival.

Explanation: Ice storms break branches, creating openings that diverse species can exploit for recovery. High genetic and species diversity provides varied strategies, speeding regeneration. Resilient ecosystems bounce back faster with multiple tolerances. Decomposers aid nutrient recycling from debris. Factors like soil compaction hinder recovery. Biodiversity acts as insurance against disturbances.

Question 13

1. Introduced predators may become invasive and prey on non-target species, disrupting food webs beyond the intended pest control. (correct answer)
2. Biocontrol always reduces biodiversity to zero because predators eliminate all organisms in the ecosystem indiscriminately.
3. Predators cannot survive in new habitats, so biocontrol guarantees no ecological side effects under any conditions.
4. Biocontrol increases atmospheric methane directly through predator respiration, causing immediate climate change at global scale.

Explanation: Biocontrol involves introducing natural predators to manage pest populations, but it carries risks if the predator becomes invasive. Introduced species may prey on non-target native species, disrupting food webs and potentially causing unintended declines in biodiversity. This can lead to cascading effects throughout the ecosystem, altering community structures. Careful assessment is needed to ensure the predator targets only the pest and does not thrive excessively in the new environment. Choice B exaggerates by claiming biodiversity drops to zero, which is unrealistic. Options C, D, and E are incorrect as biocontrol can have side effects, does not directly cause climate change via methane, and predators do not evolve into decomposers.

Question 14

1. Mixing redistributes oxygen and nutrients through the water column, often increasing oxygen in deeper layers temporarily. (correct answer)
2. Turnover eliminates oxygen entirely by forcing it into the atmosphere, leaving the lake anoxic for the rest of the year.
3. Turnover occurs only in tropical lakes, so a cold front cannot influence dissolved oxygen distribution in temperate systems.
4. Mixing permanently stratifies the lake, locking oxygen at the surface and preventing nutrient movement for decades.

Explanation: Lake turnover, triggered by cold fronts, mixes stratified layers, redistributing oxygen from surface to deeper waters. This can temporarily alleviate hypoxia in bottom layers, benefiting aquatic organisms. Nutrients are also circulated, potentially boosting productivity. Temperate lakes commonly experience this seasonal mixing. Choice B is false as turnover increases oxygen in depths, not eliminates it. Options C, D, and E are incorrect: turnover happens in temperate lakes, it destratifies rather than stratifies, and it does not directly affect salinity.

Question 15

1. Net primary productivity typically increases from near zero as pioneers establish, then may peak and later stabilize as forests mature. (correct answer)
2. Net primary productivity remains permanently zero because only mature trees can photosynthesize, and pioneers cannot fix carbon.
3. Net primary productivity decreases steadily from the first day after fire and never recovers, regardless of colonization.
4. Net primary productivity is highest immediately after fire because ash alone performs photosynthesis until plants return.

Explanation: Post-fire, net primary productivity (NPP) starts low but increases as pioneer species colonize and exploit increased sunlight. NPP often peaks during mid-succession with fast-growing plants, then stabilizes in mature forests. This pattern reflects resource availability and community development. Sunlight is a key driver in early stages. Choice B is wrong as pioneers do fix carbon. Options C, D, and E are inaccurate: NPP increases then stabilizes, ash does not photosynthesize, and it's not controlled by lunar or geomagnetic factors.

Question 16

1. Reduced sediment transport, creating clearer water and eliminating floodplain deposition that supports riparian vegetation.
2. Restored sediment and nutrient delivery to floodplains, supporting riparian succession and increasing habitat heterogeneity. (correct answer)
3. Permanent elimination of disturbance, stabilizing the river channel and preventing any changes in species composition.
4. Immediate shift to primary succession because riverbeds become bare rock and cannot support any aquatic organisms.

Explanation: Dam removal restores natural flood regimes, delivering sediments and nutrients to floodplains. This supports riparian vegetation succession and habitat diversity. Floods create heterogeneous environments, benefiting multiple species. Previously, dams reduced such dynamics, simplifying ecosystems. Restoration enhances biodiversity and resilience. Understanding hydrological disturbances informs river management.

Question 17

1. Net ecosystem carbon storage increases because dead wood instantly becomes stable soil organic matter without decomposition.
2. Photosynthetic carbon uptake decreases while decomposition of dead biomass increases $CO_2$ release, reducing net carbon sequestration. (correct answer)
3. Atmospheric $CO_2$ decreases because insects fix carbon during respiration and convert it into long-lived minerals.
4. Carbon cycling stops because decomposers require living trees; dead trees cannot be broken down by fungi or bacteria.

Explanation: Insect outbreaks like beetles killing trees disrupt carbon cycling by reducing photosynthetic uptake from living biomass. Dead wood decomposes, releasing CO2 and decreasing net carbon storage. This shifts the ecosystem from a carbon sink to a source temporarily. Forests normally sequester carbon through growth, but mass mortality reverses this. Recovery involves new vegetation regrowth over time. Such events highlight vulnerability in monoculture-like stands.

Question 18

1. Increased plant uptake from rapid growth, which removes nitrate from soils and prevents any leaching during storms.
2. Reduced vegetation uptake and increased runoff/leaching, moving nitrate from soils into streams during and after disturbance. (correct answer)
3. Immediate conversion of nitrate to atmospheric oxygen, which reduces nutrient export and increases dissolved oxygen in streams.
4. Increased denitrification in dry, oxygen-rich soils, which always accelerates after storms and removes all nitrate.

Explanation: Severe storms in forested watersheds can damage vegetation, reducing plant uptake of nutrients like nitrate. This leads to increased nitrate in soils, which can leach into streams via runoff during and after the storm. The disturbance also increases erosion and overland flow, facilitating nutrient export to aquatic systems. This can contribute to downstream eutrophication if nitrate levels rise significantly. Choice A is opposite, as reduced uptake increases leaching, not prevents it. Options C, D, and E are wrong because storms do not convert nitrate to oxygen, denitrification prefers wet anaerobic soils, and storms often enhance groundwater connectivity.

Question 19

1. Increased permafrost stability, reducing erosion and preventing thermokarst formation because warming strengthens frozen soils.
2. Permafrost thaw can create thermokarst and release greenhouse gases, altering hydrology and vegetation patterns across landscapes. (correct answer)
3. Immediate formation of deep tropical soils, enabling rainforest succession within a few seasons after mild winters.
4. Complete elimination of microbial activity, because warmer temperatures inhibit decomposition and stop carbon cycling.

Explanation: Unusually warm winters in tundra can cause permafrost thaw, leading to thermokarst formation where ground subsides into ponds or lakes. This alters hydrology by changing drainage patterns and can release stored greenhouse gases like methane from decomposing organic matter. Vegetation shifts may occur as wetter conditions favor different plant species, impacting the entire ecosystem. These changes represent a significant disturbance amplified by climate change. Choice A is incorrect as warming destabilizes permafrost, increasing erosion. Options C, D, and E are inaccurate: tundra does not become rainforest, microbes increase with warmth, and ocean upwelling is unrelated to land.

Question 20

1. More frequent, low-intensity fires that reduce fuels gradually, increasing resilience and preventing crown fires in conifer forests.
2. Less severe fires because fuel accumulates moisture; suppression increases humidity and reduces ignition probability permanently.
3. Infrequent but high-intensity crown fires that kill mature trees, alter species composition, and increase erosion risk afterward. (correct answer)
4. Immediate conversion to primary succession because suppression removes soil microbes needed for decomposition and nutrient cycling.

Explanation: Fire suppression policies allow fuel loads to accumulate, altering natural disturbance regimes in forests. This leads to infrequent but intense crown fires that can kill mature trees and change species composition. Such fires increase erosion by removing vegetation cover. Natural low-intensity fires historically prevent this buildup, maintaining ecosystem balance. Suppression disrupts this, reducing resilience to large disturbances. Understanding fuel dynamics is key to forest management.