Ecology Exam 4

Not best work - not exactly copied off of study guide.

Carbon moves through photosynthesis, respiration, decomposition, and fossil fuel combustion.

What are the main pathways of the carbon cycle

Photosynthesis removes CO₂ from the atmosphere and stores it in organic matter.

How does carbon enter the biosphere

Respiration by plants, animals, and microbes releases CO₂ back to the atmosphere.

How does carbon return to the atmosphere biologically

Atmospheric CO₂ is ~425 ppm, a value explicitly required to be memorized.

What is the current atmospheric concentration of CO₂

Terrestrial ecosystems fix ~120 gigatons of carbon annually via photosynthesis.

How much carbon is fixed by land vegetation each year

Plant respiration and soil microbial respiration each return ~60 gigatons of carbon annually.

Why is there no net biological change in atmospheric CO₂ from terrestrial systems

Fossil fuel combustion adds ~5–6 gigatons of carbon per year to the atmosphere.

What is the primary driver of rising atmospheric CO₂ since the Industrial Revolution

Nitrogen fixation converts atmospheric N₂ into biologically available forms.

What process allows inert atmospheric nitrogen to enter ecosystems

Nitrogen fixation is performed by bacteria, cyanobacteria, and lightning.

What organisms or processes can fix N₂

Ammonification converts organic nitrogen into ammonium (NH₄⁺).

What is ammonification

Nitrification converts NH₄⁺

NO₂⁻

Denitrification converts nitrate into N₂ gas under anaerobic conditions.

What is denitrification

Wetlands promote denitrification due to oxygen-poor soils.

Why are wetlands important in nitrogen cycling

Denitrification reduces nitrate pollution but releases N₂O, a greenhouse gas.

What is the ecological significance of denitrification

Human nitrogen pollution comes from fertilizers, sewage, and fossil fuel burning.

What are the major causes of nitrogen pollution

Atmospheric O₂ is produced primarily by photosynthesis.

What is the main source of atmospheric oxygen

Most ozone is located in the stratosphere and protects Earth from UV radiation.

Where is “good ozone” found

Tropospheric ozone is a pollutant harmful to plants and animals.

What is “bad ozone” and where is it found

Ozone concentration is measured in nanobars (Nb) and Dobson units.

What units are used to measure ozone concentration

UV radiation splits O₂, allowing free oxygen atoms to form O₃.

How is ozone produced naturally

CFCs release chlorine radicals that catalytically destroy ozone molecules.

How do CFCs destroy stratospheric ozone

The Antarctic ozone hole is caused by CFCs interacting with polar stratospheric clouds.

Why does ozone depletion peak over Antarctica

A biome is a large ecological region defined by climate and dominant vegetation.

What is a biome

Temperature and precipitation are the primary determinants of biome distribution.

What factors control global biome patterns

Latitudinal zonation mirrors altitudinal zonation due to temperature gradients.

How are altitudinal and latitudinal zonation similar

Species richness increases toward the equator.

How does latitude affect biodiversity

Endemism is highest in regions with long-term climate stability and isolation.

What factors increase species endemism

Grasslands require fire to prevent forest encroachment.

Why is fire essential for maintaining grasslands

Grasslands have greater below-ground biomass than above-ground biomass.

Where is most grassland biomass located

Grassland NPP decreases as temperature rises due to drought stress.

How does grassland productivity respond to increasing temperature

Representative grassland animals include bison, prairie dogs, and black-footed ferrets.

What are characteristic grassland animals

A savanna is a tropical grassland with scattered trees.

What defines a savanna

Savannas are found in Africa, South America, Australia, and South Asia.

Where are savannas located globally

Savannas have poor soils and strong wet–dry seasonality.

What are key characteristics of savannas

Most deserts occur at ~30° latitude due to descending dry air.

Where are most deserts located

Hot deserts and cold deserts differ mainly in temperature, not precipitation.

What are the two major types of deserts

Desert plants use drought evasion and drought resistance strategies.

How do desert plants survive extreme aridity

Deep roots indicate drought resistance; shallow roots indicate drought evasion.

How does root depth reflect desert adaptation mechanisms

Tundra is characterized by permafrost and short growing seasons.

What defines tundra ecosystems

Arctic tundra and alpine tundra differ by latitude and elevation.

What are the two types of tundra

Krummholz refers to wind-stunted, deformed trees near treeline.

What is krummholz

The three forest types are boreal, temperate deciduous, and tropical rainforest.

What are the three major forest types

Forests play a major role in global carbon sequestration.

Why are forests important in the global carbon cycle

Conifers have needle leaves, thick cuticles, and are evergreen.

What are general characteristics of conifers

Major conifer genera include Pinus, Picea, Abies, Larix, Tsuga, and Juniperus.

What are the six important conifer genera

Temperate deciduous forests occur in eastern North America, Europe, and East Asia.

Where are temperate deciduous forests found

American beech and sugar maple are late-successional species.

Which deciduous trees are late successional

Late-successional species have lower light saturation points.

How do late-successional trees respond to light

Birch is the common deciduous tree in boreal forests.

What deciduous tree is common in boreal forests

Thin, smooth bark reduces epiphyte growth and water-loss protection is unnecessary.

Why do tropical rainforest trees have thin, smooth bark

Lianas allow plants to reach light without investing in thick trunks.

What is the adaptive advantage of lianas

Lentic ecosystems are standing waters like lakes and ponds.

What are lentic ecosystems

Oligotrophic lakes are deep, clear, and nutrient-poor.

What characterizes oligotrophic lakes

Eutrophic lakes are shallow, nutrient-rich, and oxygen-poor.

What characterizes eutrophic lakes

Phosphorus is usually the limiting nutrient in freshwater eutrophication.

What nutrient limits eutrophication in lakes

Lotic ecosystems are flowing waters like rivers and streams.

What are lotic ecosystems

Headwater streams are typically heterotrophic.

Why are small streams heterotrophic

Tropical rainforests are being destroyed at extremely rapid rates.

How fast are tropical rainforests being lost

Deforestation alters weather patterns and releases stored carbon.

How does rainforest destruction affect climate

Industrial smog forms from coal combustion; photochemical smog forms from NOx + sunlight.

What is the difference between industrial and photochemical smog

Biological pollutants include pathogens and invasive species.

What is biological pollution

DDT is persistent, bioaccumulative, and biomagnifies in food webs.

Why is DDT environmentally dangerous

DDT caused eggshell thinning in birds of prey.

What was the major ecological effect of DDT

Rachel Carson’s Silent Spring catalyzed the modern environmental movement.

Who was Rachel Carson and why is she important

Pesticide resistance leads to resurgence and secondary pest outbreaks.

What problems arise from pesticide use

The best long-term pest control strategy is integrated pest management (IPM).

What is the best long-term solution to insect problems

Atmospheric CO₂ has increased sharply since the Industrial Revolution.

What is the historical trend of atmospheric CO₂

CO₂ is measured directly at Mauna Loa and inferred from ice cores.

How is atmospheric CO₂ measured historically and currently

Elevated CO₂ increases photosynthesis by ~44% on average.

What is the CO₂ fertilization effect

C3 plants respond more strongly to elevated CO₂ than C4 plants.

Which plants benefit more from rising CO₂ and why

Elevated CO₂ improves water-use efficiency (WUE).

How does CO₂ affect plant water use

Low soil nutrients limit the CO₂ fertilization effect.

Why doesn’t elevated CO₂ always increase plant growth

Elevated CO₂ can partially offset ozone damage to roots.

How do CO₂ and ozone interact in plant physiology

Respiration generally increases with temperature regardless of CO₂ concentration.

How does rising temperature affect plant respiration

Net primary production depends on the balance between photosynthesis and respiration.

Why can higher temperatures reduce NPP even if photosynthesis increases

Elevated CO₂ often decreases leaf nitrogen concentration.

How does elevated CO₂ affect leaf chemistry

Lower leaf nitrogen reduces plant nutritional quality for herbivores.

How does elevated CO₂ indirectly affect herbivores

C4 plants already concentrate CO₂ internally using PEP carboxylase.

Why do C4 plants respond less to elevated atmospheric CO₂

IRGA measures CO₂ differences between incoming and outgoing air.

What is the principle behind photosynthesis measurement using IRGA

FACE experiments enrich CO₂ without enclosing vegetation.

What advantage do FACE facilities have over growth chambers

Growth chambers may exaggerate CO₂ effects due to artificial conditions.

Why must CO₂ experiment results be interpreted cautiously

Elevated CO₂ can increase biomass but reduce grain protein content.

How does higher CO₂ affect crop quality

CO₂ fertilization effects are strongest in early successional species.

Which plants benefit most from elevated CO₂ and why

An ecological pyramid represents trophic structure.

What does an ecological pyramid describe

Primary producers always form the base of an ecological pyramid.

Which organisms form the foundation of all food webs

Energy flows upward but decreases at each trophic level.

Why are food chains short

Only ~10% of energy transfers between trophic levels.

What is the ecological efficiency rule

Pyramids of numbers can be inverted.

When can an ecological pyramid appear upside down

Pyramids of biomass are rarely inverted in terrestrial ecosystems.

Why are terrestrial biomass pyramids usually upright

Aquatic systems may show inverted biomass pyramids.

Why can aquatic biomass pyramids be inverted

Instantaneous biomass does not reflect long-term productivity.

Why can phytoplankton support more biomass than they contain

Consumers are always dependent on producers for energy.

Why does energy flow never reverse in ecosystems

Food webs better represent ecosystem complexity than food chains.

Why are food webs more realistic than linear food chains

GPP is total photosynthetic production.

What is gross primary productivity

NPP = GPP − respiration.

How is net primary productivity calculated

NPP determines energy availability to higher trophic levels.

Why is NPP ecologically important

Forests have high NPP but lower turnover rates.

Why do forests store large amounts of carbon

Grasslands have lower NPP but faster nutrient cycling.

Why are grasslands resilient to disturbance

Temperature limits NPP in cold ecosystems.

What limits productivity in tundra and boreal forests

Water limits NPP in deserts and grasslands.

What limits productivity in arid ecosystems