Flashcards · IB Diploma Programme Environmental Systems and Societies · Topic 2

Ecology flashcards

29 cards on Topic 2, subtopics 2.1 to 2.5. Pick a subtopic or study them all.

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2.1 Individuals, populations, communities and ecosystems

Define population, community and ecosystem: Population: organisms of the same species in the same area at the same time. Community: populations of different species living and interacting in one area. Ecosystem: a community plus its abiotic environment, interacting.
Fundamental niche versus realised niche: Fundamental niche: everything a species could occupy. Realised niche: what it actually occupies, reduced by competition and other interactions.
J-curve versus S-curve population growth: J-curve: exponential growth with no limit reached yet, often followed by a crash. S-curve: lag → exponential → transitional → plateau at carrying capacity (K), held there by negative feedback.
How do you estimate a population with the Lincoln index?: Mark M individuals and release them; after mixing, catch C and count R marked. N = (M × C) ÷ R. Example: 30 marked, 45 caught, 9 marked → N = 150. Assumes a closed population, marks stay on and do not affect survival, full mixing.
How do you estimate a plant population with quadrats?: Place quadrats at random; count individuals in each. Mean per quadrat ÷ quadrat area = density per m²; density × total area = population. Example: mean 5 in 0.25 m² quadrats → 20 per m² → 12,000 in a 600 m² lawn.
What is carrying capacity (K)?: The maximum population an environment can support sustainably. A limiting factor is the factor in shortest supply relative to need, which restricts growth.

2.2 Energy and biomass in ecosystems

How do you calculate net primary productivity?: NPP = GPP − R, in kJ m⁻² yr⁻¹ or g m⁻² yr⁻¹. Example: GPP 12,000 and R 7,800 → NPP = 4,200 kJ m⁻² yr⁻¹.
How do you calculate GSP and NSP for consumers?: GSP = food eaten − faecal loss. NSP = GSP − R. Example: eats 900, faeces 540, respiration 250 → GSP 360, NSP 110 kJ m⁻² yr⁻¹. Remove faecal loss before subtracting respiration.
How do you calculate ecological efficiency?: (energy into new biomass at a level ÷ energy at the level below) × 100. About 10% is typical but values vary. Example: 270 ÷ 3,000 × 100 = 9.0%. A value over 100% means you divided the wrong way up.
Why is energy lost between trophic levels?: Not all biomass is eaten (roots, bones, bark); not all eaten material is digested (lost as faeces); most assimilated energy is respired and lost as heat (second law of thermodynamics). Energy flows one way; matter cycles.
Which ecological pyramids can be inverted?: Numbers: yes (one tree, many insects). Biomass: yes (phytoplankton and zooplankton at one moment). Productivity: never, because each level receives only part of the energy flowing into the level below.
What is biomagnification?: Persistent substances such as some pesticides and mercury become more concentrated at each higher trophic level.

2.3 Biogeochemical cycles

Carbon cycle: main storages: Atmosphere, oceans, biomass, soil, fossil fuels and sedimentary rock.
Carbon store versus carbon sink versus source: A store holds carbon. A sink takes in more carbon than it releases. A source releases more than it takes in.
How does more atmospheric CO₂ cause ocean acidification?: More CO₂ dissolves in the ocean → carbonic acid → lower pH → less carbonate available for shells and coral.
Nitrification versus denitrification: Nitrification: NH₄⁺ → NO₂⁻ → NO₃⁻ by Nitrosomonas and Nitrobacter; needs oxygen (aerobic). Denitrification: NO₃⁻ → N₂ by anaerobic bacteria, for example in waterlogged soil.
What is nitrogen fixation and what carries it out?: Conversion of N₂ gas into usable compounds (NH₄⁺, or nitrate via nitrogen oxides from lightning). Done by free-living bacteria, Rhizobium in legume root nodules, the Haber process and lightning.
How do you convert a mass of carbon to a mass of CO₂?: Multiply by 44/12 (1 t C ≈ 3.67 t CO₂). Example: 2 t C per hectare per year → 2 × 44/12 = 7.33 t CO₂.

2.4 Climate and biomes

What is a biome?: A collection of ecosystems with similar climate and so similar communities, found in different parts of the world.
Why is insolation per m² lower at high latitudes?: Rays hit at a low angle, so the energy spreads over a larger area; and they pass through more atmosphere, so more is absorbed, scattered or reflected.
Tricellular model: what happens at 0°, 30°, 60° and 90°?: 0°: rising air, low pressure, heavy rain (ITCZ) → rainforest. 30°: sinking air warms and dries, high pressure → hot deserts. 60°: rising air at the polar front → temperate forest. 90°: sinking cold air, high pressure, very dry → polar desert.
How do you identify a biome from a climate graph?: Total the monthly precipitation; find the annual temperature range (warmest − coldest month); check for a dry season or months below 0 °C; match to a biome quoting at least two figures; link the pattern to its cause (ITCZ, sinking air, latitude).
How is climate change expected to affect biomes?: Biomes shift poleward and upslope; tundra and mountain-top habitats shrink; thawing permafrost releases CO₂ and CH₄, which causes more warming (positive feedback).

2.5 Zonation, succession and change in ecosystems

Zonation versus succession: Zonation: change in community along an environmental gradient in space. Succession: change in community at one place over time. A dune transect shows zonation that reflects succession, because inland dunes are older.
Primary versus secondary succession: Primary: starts on bare substrate with no soil (a lava flow). Secondary: starts where soil is already present (an abandoned field), so it is faster.
What are pioneer species?: The first colonisers of bare ground. They tolerate harsh conditions, grow fast, produce many small well-dispersed seeds or spores (r-strategists) and add organic matter that helps build soil.
What does the P:R ratio show during succession?: P:R = GPP ÷ R. Above 1: biomass is accumulating. About 1: steady state (climax). Below 1: biomass is falling. Example: GPP 12,000 and R 7,500 → P:R = 1.6, still accumulating.
When is NPP highest in a succession?: Mid-succession. GPP keeps rising towards climax, but respiration by the large standing biomass rises to nearly match it, so NPP falls towards zero at climax.
Climax community versus plagioclimax: Climax: a relatively stable end community in balance with climate and soil. Plagioclimax: a community held below climax by human activity, such as grazed pasture, a mown lawn or moorland burned in rotation.