# Ecology, Population & Environmental Change

> Review selected concepts in ecosystem productivity, nutrient cycles, biodiversity, population dynamics and environmental management. Apply formulas with consistent units, explain mechanisms and distinguish useful models from universal rules. This focused recall unit supports study; it does not cover a complete environmental-science or geography examination.

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- **Level:** basic
- **Languages:** en → en
- **Total Cards:** 32

## Flashcards (32 Cards)

| # | Front (Term / Prompt) | Back (Definition / Answer) | Example | Multiple-Choice Options |
| :--- | :--- | :--- | :--- | :--- |
| 1 | How should population growth and doubling time be calculated without mixing units? | For one period, ΔN = B − D + I − E, using counts of births, deaths, immigrants and emigrants for the same population and interval. Percentage growth is 100ΔN/N₀, where N₀ is the initial population. Under constant positive annual percentage growth g, the rule of 70 gives an approximate doubling time of 70/g years. Exact discrete doubling time is ln(2)/ln(1 + g/100); do not combine rates per thousand with raw migration counts. |  |  |
| 2 | Why should forest harvesting and prescribed fire be evaluated in ecological context? | Clearcutting removes a stand's trees over an area and can create suitable conditions for some regeneration goals while increasing risks such as erosion or habitat disruption. Selection systems retain some cover but can still damage soils or remaining trees. Prescribed fire is planned under specified conditions and may reduce certain fuels or restore fire-adapted habitats. Effects depend on site, species, severity and follow-up; no treatment universally prevents severe wildfire. |  |  |
| 3 | What does total fertility rate mean, and why is replacement fertility not universally exactly 2.1? | Period TFR is the number of births a hypothetical woman would have if she experienced the period's age-specific fertility rates throughout reproductive life. It is not the observed completed family size of a real cohort. Replacement fertility also depends on survival to reproductive ages and the sex ratio at birth. About 2.1 is a low-mortality benchmark, not a universal threshold or a guarantee of immediate population stability. |  |  |
| 4 | Why can forest climate help explain soils without uniquely determining their soil type? | Warm, wet conditions can accelerate weathering and nutrient leaching; litter decomposition and nutrient return differ between tropical, temperate and boreal forests. Cold conditions can slow decomposition, and many boreal soils are acidic. But soil formation also depends on parent material, organisms, drainage and topography, and time. A biome cannot be assigned one soil order everywhere: tropical rainforest does not automatically mean Oxisol, for example. |  |  |
| 5 | How does the logistic growth model modify exponential population growth? | Exponential growth uses dN/dt = rN with constant per-capita rate r. The simple logistic model uses dN/dt = rN(1 − N/K), with r > 0 and K > 0, so growth slows as N approaches carrying capacity K. It assumes a particular form of density dependence and fixed parameters; real carrying capacity can change. Density dependence concerns how per-capita effects change with density, not an infallible list of named environmental factors. |  |  |
| 6 | What transformations connect nitrogen fixation, ammonification, nitrification, assimilation and denitrification? | Biological fixation converts N₂ into ammonia, present mainly as ammonium in many soils. Ammonification releases ammonium from organic nitrogen. Nitrification oxidizes ammonia/ammonium to nitrite and then nitrate; both bacteria and archaea participate in ammonia oxidation. Assimilation incorporates available nitrogen into organic molecules. Denitrification reduces nitrate through intermediates to gaseous nitrogen products, especially under oxygen-limited conditions. Lightning provides another route to reactive nitrogen, principally through nitrogen oxides, not biological ammonia production. |  |  |
| 7 | How can excess nutrients lead to aquatic hypoxia? | Additional nitrogen or phosphorus can stimulate algal and plant production. Respiration and microbial decomposition of the resulting organic matter consume dissolved oxygen; limited mixing can prevent replenishment. Human-accelerated enrichment is called cultural eutrophication. Oxygen below about 2 mg/L is a commonly used hypoxia threshold in coastal studies, but biological responses vary among organisms and conditions. A 'dead zone' is not necessarily devoid of all life. |  |  |
| 8 | What does net primary productivity measure, and how is it calculated from gross primary productivity? | NPP = GPP − Rₐ, where Rₐ is respiration by the primary producers themselves. NPP is the rate at which producers retain newly fixed energy or carbon in organic matter; it can support growth, consumers and decomposers. Compare values using the same area, time and energy or carbon units. A highly productive ecosystem per square metre need not have the greatest total production worldwide. |  |  |
| 9 | How can aquatic invertebrates indicate environmental stress without proving its cause on their own? | Species differ in tolerance to oxygen conditions, temperature, sediments and pollutants. Assessors examine the abundance and composition of the whole assemblage, ideally against suitable reference conditions, alongside chemical and physical evidence. Many stonefly larvae are sensitive, while some worms tolerate low oxygen, but one organism's presence is not a definitive pollution test. Habitat, season and life stage can also affect observations. |  |  |
| 10 | What are genetic, species and ecosystem diversity, and why does a population bottleneck matter? | Genetic diversity is variation within populations or species; species diversity concerns the species present and their relative abundances; ecosystem diversity concerns different ecological systems and habitats. A severe population reduction can randomly remove genetic variants and increase subsequent inbreeding risk. High initial diversity is useful, but it does not prevent a bottleneck from eliminating variants or guarantee adaptation to every environmental change. |  |  |
| 11 | How can urbanization and excessive groundwater pumping alter the water cycle? | Impervious surfaces often reduce local infiltration and increase rapid runoff. Pumping can lower groundwater levels and reduce discharge to streams. Subsidence occurs where susceptible sediments compact; saltwater intrusion is a particular concern in coastal aquifers. These effects depend on local geology and water flows. The Ogallala is generally an unconfined aquifer, so it should not be used as a blanket example of a confined aquifer. |  |  |
| 12 | Why is the phosphorus cycle often called a sedimentary cycle? | Its major reservoirs are rocks and sediments, with no large gaseous atmospheric reservoir comparable to nitrogen or carbon. Weathering releases phosphate, organisms take it up, decomposition recycles it, and sediment burial and uplift connect shorter and longer pathways. Dust and aerosols can still transport phosphorus through the atmosphere. Phosphorus often limits freshwater productivity, but nitrogen or several nutrients together may also limit growth. |  |  |
| 13 | What does the demographic transition model describe, and what does it leave out? | The conventional four-stage model describes a shift from high birth and death rates to low birth and death rates, with rapid natural increase when mortality falls before fertility. Later low rates need not be exactly equal. A proposed fifth stage describes sustained births below deaths in some populations. The model is a broad historical framework, not a compulsory national timetable; migration can change total population even when natural increase is near zero or negative. |  |  |
| 14 | Why can population momentum sustain growth after fertility falls to replacement level? | A population with many people entering reproductive ages can have more births than deaths even when fertility per woman has fallen. Conversely, an older age structure can contribute to continued decline. A population pyramid shows age and sex composition, not a complete forecast: future fertility, mortality and migration also matter. A broad base indicates many young children relative to older groups; it does not alone establish a future growth rate. |  |  |
| 15 | How does integrated pest management reduce reliance on repeated broad-spectrum pesticide use? | IPM combines correct identification, monitoring, action thresholds, prevention and evaluation of control options. It favors effective approaches with lower risks and checks their results; chemical controls can be part of the strategy when justified. Repeated use of the same pesticide mode of action can select resistant pests, and broad-spectrum treatments can harm natural enemies. 'Pesticides only as a last resort' is too broad: EPA specifically treats non-specific broadcast spraying as a last resort. |  |  |
| 16 | What benefits can wetlands provide, and why are those benefits site-dependent? | Wetlands can provide habitat, store floodwater, retain or transform some pollutants, and store carbon. Their performance depends on hydrology, vegetation, soils, loading and landscape position. Some receive groundwater discharge, some recharge groundwater, and some do both at different times. Pollutant retention has limits, and not every wetland removes every contaminant or protects every coast equally. Drainage or altered water flows can impair these functions. |  |  |
| 17 | How do fast and slow carbon-cycle processes differ? | Photosynthesis, respiration, decomposition and air–sea exchange move carbon through relatively fast biological and surface reservoirs. Weathering, sediment burial, rock formation and tectonic recycling operate over much longer timescales. Carbonate rocks and other sediments are major long-term stores in the crust. Burning fossil fuels rapidly transfers carbon from long-lived geological stores into the active atmosphere–ocean–biosphere system. |  |  |
| 18 | What distinguishes primary succession from secondary succession? | Primary succession begins on newly exposed substrate with little or no developed soil, such as a new lava surface. Secondary succession follows disturbance where soil and some biological legacies remain. Surviving roots, organisms or seeds can speed recovery, but a seed bank is not guaranteed. Colonists and later changes depend on local conditions; succession need not follow one fixed sequence ending in a single inevitable community. |  |  |
| 19 | How does bioaccumulation differ from biomagnification? | Bioaccumulation is the build-up of a substance within an organism from its exposure routes over time. Biomagnification is an increase in concentration across successive trophic levels through feeding. A substance may bioaccumulate without biomagnifying. Persistence, uptake, metabolism and food-web structure matter; neither process requires a fixed or exponential increase. Methylmercury is an important example of a substance that can biomagnify in aquatic food webs. |  |  |
| 20 | How do the U.S. Endangered Species Act and CITES protect species in different ways? | The ESA is U.S. legislation addressing listed species through measures such as prohibitions, recovery planning and federal-agency duties. Protections vary with listing status, species, applicable rules and exceptions; animal 'take' rules are not a blanket rule for every listed plant. CITES regulates international trade in listed specimens through different appendix-based controls and permits, rather than banning all trade. As of November 2026, U.S. threatened-species protections must be checked against the applicable rules, including 2026 revisions. |  |  |
| 21 | Why should r/K life-history tendencies not be equated with fixed survivorship curves? | The r/K framework describes contrasting tendencies, such as rapid reproduction versus investment in survival and competitive ability; real species can mix traits. Survivorship curves describe age-specific mortality: Type I has relatively low early mortality and higher late mortality; Type II has roughly constant mortality risk with age; Type III has high early mortality among young individuals. Long-lived trees can produce many seeds with Type III survivorship, so longevity alone does not imply Type I. |  |  |
| 22 | Why should aquatic light zones and dissolved-oxygen profiles be considered separately? | The photic zone receives enough light for substantial photosynthesis; the aphotic zone does not. Depth alone does not determine oxygen concentration: mixing, ventilation, respiration, temperature and salinity also matter. A stratified lake may lose oxygen near the bottom, whereas deep ocean water can contain more oxygen than an intermediate oxygen-minimum zone. 'Warm deep water always has the least oxygen' is not a general rule. |  |  |
| 23 | What are the four ecosystem-service categories in the Millennium Ecosystem Assessment framework? | Provisioning services supply products such as food and timber. Regulating services include pollination, water-quality regulation and flood moderation. Cultural services include recreation and spiritual or aesthetic benefits. Supporting services, such as nutrient cycling and soil formation, underpin other services. These are categories in the 2005 assessment framework; actual benefits depend on ecological and social context, and other classification systems may organize them differently. |  |  |
| 24 | How do species richness and evenness contribute to Shannon diversity? | Richness is the number of species; evenness describes how similarly abundant they are. Shannon diversity is H′ = −Σpᵢ ln(pᵢ), summing over the species present, where pᵢ is each species' proportion of individuals and the proportions sum to 1. For a fixed richness, equal proportions maximize H′. Two equally abundant species give H′ = ln(2) ≈ 0.693. This index summarizes composition; it does not by itself measure ecosystem stability over time. |  |  |
| 25 | Why can the lowest dissolved oxygen occur downstream from an organic-waste discharge? | Microorganisms consume oxygen while decomposing the added organic matter. As water travels downstream, this oxygen demand competes with replenishment, especially reaeration from the atmosphere. The greatest oxygen deficit can therefore occur after the discharge point. An oxygen-sag curve is a simplified profile, not a promise of automatic recovery; flow, temperature, continuing inputs, photosynthesis and other oxygen demands affect the outcome. |  |  |
| 26 | How do keystone and foundation species differ from generalists and specialists? | A keystone species has an ecological effect large relative to its abundance. A foundation species helps create or maintain habitat, often through its abundance or physical structure, as kelp does in kelp forests. Generalist and specialist instead describe niche breadth: broad versus narrow resource or habitat use. These categories are not mutually exclusive, and specialization alone does not prove that a species will become extinct. |  |  |
| 27 | Why is the '10% rule' for energy transfer between trophic levels only an approximation? | Trophic transfer efficiency compares production at one trophic level with production at the level below over compatible areas and periods. It varies among organisms and ecosystems; thermodynamics does not prescribe exactly 10%. Some biomass is uneaten or unassimilated and enters detrital pathways, while respiration dissipates usable energy as heat. Energy is conserved, but progressively less remains available for biological work. |  |  |
| 28 | Why is a non-native species not automatically invasive, and what can favor invasion? | Non-native describes origin outside the relevant natural range; invasive additionally implies harmful spread or impacts under the definition being used. Establishment can be helped by repeated introductions, disturbance, resource availability or release from some natural enemies. Outcomes depend on both the species and the receiving ecosystem. Invasive species are not invariably fast-breeding generalists, and it is inaccurate to claim that every introduced species has no predators or diseases. |  |  |
| 29 | How can the HIPPCO mnemonic help organize biodiversity pressures without becoming a universal ranking? | It groups habitat loss, invasive species, pollution, human population pressure, climate change and overexploitation. These pressures interact, and population effects also depend on consumption and institutions. Their relative importance varies by ecosystem and period. For example, the IPBES 2019 assessment identified land-use change as the largest direct driver in terrestrial and freshwater systems, and direct exploitation in marine systems. A mnemonic should not replace such context. |  |  |
| 30 | How do coral bleaching and ocean acidification differ? | Bleaching is the loss of symbiotic algae or their pigments under stress, often from excessive heat; a bleached coral is not necessarily dead and may recover. Ocean acidification is declining seawater pH, chiefly from absorbed CO₂, which shifts carbonate chemistry and can hinder calcification. One net reaction is CO₂ + H₂O + CO₃²⁻ ⇌ 2HCO₃⁻. Acidification does not require seawater to become acidic below pH 7. |  |  |
| 31 | Why is overuse of a shared resource a risk rather than an inevitable 'tragedy of the commons'? | When each user gains from extraction while sharing depletion costs with others, unregulated access can encourage overuse. But common ownership is not identical to unrestricted access. Users can create institutions with defined access rights, monitoring, proportionate sanctions and conflict-resolution procedures. Ostrom's research documents such governance possibilities; neither privatization nor state control is the only possible response, and no arrangement is guaranteed to succeed everywhere. |  |  |
| 32 | How does classical island biogeography relate island size and isolation to species richness? | The model balances immigration of new species against local extinction. Less isolated islands generally receive more immigrants, while larger islands generally support lower extinction rates, so large, nearby islands tend to have greater equilibrium richness. Species can continue turning over at equilibrium. Real islands also differ in habitat, history and speciation; the model is a useful simplification, not a claim that area and distance alone explain every community. |  |  |

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