PSC Chronicles Team

A.G. Tansley coined the term ‘Ecosystem’ in 1935

• Tansley defined an ecosystem as the whole system of organisms plus physical factors forming a stable interacting unit
• In his 1935 paper, Tansley introduced “ecosystem” to replace the “superorganism” concept, shifting the focus from mystical plant “lives” to scientific, integrated systems

Ernst Haeckel coined the word ‘Ecology’ in 1866

Eugene Odum popularised the ecosystem concept through ‘Fundamentals of Ecology’ (1953)

Abiotic Components: These are the non-living physical and chemical parts of an ecosystem, such as temperature, light, humidity, water, and soil.

Producers (Biotic): Green plants that create their own food through photosynthesis and form the base of the food chain.

Consumers (Biotic): Animals that must eat other organisms to get the nutrition they need.

Decomposers (Biotic): Organisms like bacteria and fungi that recycle nutrients by breaking down dead matter.

System Regulation: Abiotic factors control where organisms live, how many there are, and how their bodies function (metabolism).

• Producers (autotrophs — green plants, algae) form the first trophic level as they synthesize organic matter from sunlight and CO₂ via photosynthesis
• Herbivores are primary consumers at the second trophic level — they depend on producers
• Carnivores occupy the third or higher trophic levels as secondary/tertiary consumers
• Decomposers (bacteria, fungi) break down dead matter and are not assigned a specific trophic level in the grazing chainEnergy flows unidirectionally:

Producers → Herbivores → Carnivores → Decomposers 

Sunlight is the primary energy source — green plants capture solar energy through photosynthesis and convert it into chemical energy stored in organic molecules

• Wind energy plays no direct role in ecosystem energy flow through food chains
• Geothermal energy supports chemosynthetic ecosystems at deep-sea hydrothermal vents — a rare exception, not the norm
• Chemical energy in soil is not a primary energy source for ecosystem productivity

Solar energy drives approximately 99% of Earth’s biological productivity directly or indirectly through the process of photosynthesis

A natural ecosystem develops without human intervention — forests, ponds, oceans, and grasslands are all natural ecosystems with self-regulating mechanisms | Aquarium is an artificial (man-made) ecosystem maintained by human effort and external inputs | Garden is an artificial ecosystem — human intervention determines plant composition, irrigation, and pest control | Paddy field (rice field) is an agro-ecosystem, a type of artificial ecosystem created and managed for agriculture | Natural ecosystems have greater species diversity, complex food webs, and greater resilience than artificial systems

Ernst Haeckel coined the term ‘Oekologie’ (Ecology) in 1866, derived from Greek ‘oikos’ (house/dwelling place) and ‘logos’ (study) | Charles Darwin is celebrated for the Theory of Natural Selection in ‘On the Origin of Species’ (1859) — not for coining ecological terms | A.G. Tansley coined the term ‘Ecosystem’ in 1935 — a distinct and related but separate concept from Ecology | Eugene Odum popularised ecosystem ecology through his textbook ‘Fundamentals of Ecology’ (1953) but did not coin the term | Ecology is defined as the scientific study of the relationships between organisms and their environment

• Fungi are decomposers (saprotrophic organisms) that secrete extracellular enzymes to break down dead organic matter (detritus) into simpler inorganic substances
• Grass is a producer (autotroph) at the first trophic level — it synthesises food using sunlight
• Deer is a primary consumer (herbivore) at the second trophic level — it feeds on grass
• Tiger is a tertiary/apex carnivore — the top predator at the highest trophic level

Decomposers mineralise nutrients and return them to the soil, completing biogeochemical cycles — they are indispensable for ecosystem functioning

• Pyramid of Energy is always upright because energy decreases at each successive trophic level — governed by Lindeman’s 10% law and the Second Law of Thermodynamics
• Pyramid of Numbers can be inverted — e.g., in a forest ecosystem, one large tree (producer) supports thousands of insects (consumers)
• Pyramid of Biomass can be inverted — e.g., in aquatic ecosystems, phytoplankton standing biomass is less than zooplankton at any given time

Energy is always lost as heat during metabolic processes, making the energy pyramid non-invertible

Plants fix less than 1% (approximately 0.1–1%) of the total solar radiation incident on Earth’s surface through photosynthesis.

• Large portions of the spectrum (like infrared) can’t be used.
• Leaves reflect or transmit much of the light.
• Energy is lost as heat during the chemical conversion process.

GPP is the TOTAL rate of photosynthesis including the organic matter subsequently used by plants in their own respiration — it is the total energy fixed by autotrophs

NPP (Net Primary Productivity) = GPP minus Autotrophic Respiration — this is the energy available to consumers. NPP is the only part of the energy that can actually move up the food chain to herbivores and predators.

Raymond Lindeman proposed the 10% law in 1942 — only about 10% of energy at one trophic level is transferred to the next, rest is lost as heat via respiration.

Because 90% of the energy is “burned” off just to keep the organism alive—moving, breathing, and staying warm—the energy supply physically runs out after 4 or 5 levels.

The 10% law implies: if 1000 kJ is fixed by producers, only 100 kJ reaches herbivores, 10 kJ reaches secondary consumers — explaining the scarcity of top predators

Nitrogen Cycle

Nitrogen Fixation: Nitrogen gas (N₂) is converted into Ammonia (NH₃) or Ammonium (NH₄⁺) by bacteria like Rhizobium.

Nitrification:  Ammonia (NH₃) / Ammonium (NH₄⁺) is oxidized into Nitrites (NO₂⁻) by Nitrosomonas, then into Nitrates (NO₃⁻) by Nitrobacter.

Assimilation:  Plants absorb these nitrates (NO₃⁻) from the soil to build proteins and DNA.

Ammonification:  Decomposers break down organic nitrogen from dead matter back into Ammonia (NH₃) / Ammonium (NH₄⁺).

Denitrification:  Pseudomonas bacteria convert Nitrates (NO₃⁻) back into Nitrogen gas (N₂), releasing it into the atmosphere.

Fix → Nitrify → Assimilate → Ammonify → Denitrify
N₂ → NH₃/NH₄⁺ → NO₂⁻ → NO₃⁻ → Plants → NH₃ → N₂

• Phosphorus cycle is a purely sedimentary cycle — phosphorus moves from rocks → soil → water → organisms → sediments, with no gaseous atmospheric phase
• Carbon cycle has a prominent gaseous phase — CO₂ is exchanged between the atmosphere, organisms, and oceans continuously
• Nitrogen cycle is dominated by its gaseous phase — N₂ constitutes 78% of the atmosphere and is central to the entire cycle
• Sulphur cycle has both gaseous (SO₂, H₂S, DMS) and sedimentary phases — making it a combined cycle

Phosphorus scarcity is often a limiting factor in aquatic ecosystems precisely because there is no atmospheric reservoir to replenish it quickly

Dead leaves → Earthworm → Robin is a classic detritus food chain — it begins with dead organic matter (detritus) and involves detritivores (earthworms) | Grass → Grasshopper → Frog → Snake is a grazing food chain — it begins with living plant material | Phytoplankton → Zooplankton → Fish is an aquatic grazing food chain beginning with living algae | Plant → Caterpillar → Bird is also a terrestrial grazing food chain | In many terrestrial ecosystems (especially forests), more energy flows through the detritus food chain than the grazing food chain — a key ecological insight

Charles Elton introduced the concept of ecological niche in ‘Animal Ecology’ (1927) — describing the functional role, position, and relationships of a species in its community | Eugene Odum is known for energy flow studies and ecosystem ecology — not for originating the niche concept | A.G. Tansley coined the term ‘ecosystem’ in 1935 — distinct from niche theory | G.E. Hutchinson later formalised the niche as an ‘n-dimensional hypervolume’ (1957) — refining Elton’s concept into its modern form | Ecological niche encompasses an organism’s habitat, food, time of activity, and all biotic/abiotic interactions — often called ‘the profession of an organism’

Ecotone is the transitional or boundary zone between two different adjacent ecosystems — e.g., the grassland-forest margin, mangroves between land and sea, or estuaries between rivers and ocean | The climax stage of succession is the final stable community (climax community) — not called an ecotone | Ecotones tend to have HIGHER species diversity than either adjacent ecosystem (Edge Effect), but the term itself means the transition zone, not the zone of highest diversity | Maximum primary productivity occurs in tropical rainforests, not specifically in ecotones | Examples of ecotones: mangroves, river banks, alpine meadows bordering forests, wetland-upland boundaries

Xerarch succession on bare rock begins with Lichens as pioneer species — they physically and chemically weather rock, creating thin soil | Mosses colonise next as soil deepens slightly, retaining more moisture and nutrients | Herbs/Grasses establish as soil becomes richer, increasing organic matter further | Shrubs follow, modifying the microclimate and soil further | Trees (climax community) finally establish — typically a deciduous or coniferous forest depending on climate | Primary succession on bare rock takes hundreds to thousands of years due to the need to build soil from scratch

Denitrification converts nitrates (NO₃⁻) back to free atmospheric nitrogen (N₂) — performed by anaerobic bacteria like Pseudomonas denitrificans and Thiobacillus under waterlogged/anaerobic conditions | N₂ to NH₃ is Nitrogen Fixation — performed by Rhizobium, Azotobacter, Clostridium, and cyanobacteria | NH₃ to NO₃⁻ is Nitrification (in two steps: NH₃→NO₂ by Nitrosomonas; NO₂→NO₃ by Nitrobacter) | NO₃⁻ to NH₃ is Dissimilatory Nitrate Reduction (DNRA), distinct from denitrification | Denitrification is the primary mechanism returning fixed nitrogen to the atmosphere, maintaining the balance of the nitrogen cycle

Edge Effect is the tendency for greater species diversity to occur at the boundary (ecotone) between two different ecosystems — species from BOTH adjacent ecosystems plus edge-specialist species are all present | Edge Effect does NOT decrease diversity — the correct pattern is increased diversity at ecotones | Temperature’s effect on species distribution is the concept of thermal tolerance (Shelford’s Law), not edge effect | Predator-prey dynamics at edges is a separate concept studied in landscape ecology | The edge effect is why forest edges, riverbanks, and wetland margins are biodiversity hotspots within landscapes

NPP = GPP minus Autotrophic Respiration (Ra) — it represents the net organic matter available after plants use energy for their own metabolic processes | GPP minus Heterotrophic Respiration gives Net Ecosystem Productivity (NEP), not NPP | GPP plus respiration is mathematically incorrect and has no ecological meaning | Total biomass of producers at a given time is ‘Standing Crop’ — a different concept from productivity (which is a rate) | NPP is the energy available to all heterotrophic consumers and represents the actual production that supports the entire animal kingdom and decomposers

Extraction of fossil fuels is NOT an ecosystem service — it is a human economic extractive activity that depletes natural capital and often damages ecosystems | Pollination by bees is a regulating ecosystem service crucial for agricultural productivity and plant reproduction | Water purification by wetlands is a regulating service — wetlands filter pollutants and excess nutrients from water bodies | Soil formation by decomposers is a supporting ecosystem service — the foundation for all terrestrial productivity | The MEA (2005) identified 4 categories: Provisioning, Regulating, Cultural, and Supporting services — fossil fuel extraction belongs to none

Hydrarch succession begins in a water body: Phytoplankton (pioneer in open water) → Submerged rooted hydrophytes (e.g., Vallisneria) → Floating hydrophytes → Reed swamp (Typha, bulrushes) → Marsh meadow → Shrubs → Climax Forest | Phytoplankton colonise first as they need only open water and sunlight | As sediment accumulates, rooted hydrophytes establish, then emergent vegetation like reeds | Marsh meadow develops as the pond becomes shallower with organic matter accumulation | The climax is a terrestrial forest — hydrarch succession leads from aquatic to terrestrial ecosystem over geological time

Phytoplankton (producers) have an extremely HIGH turnover rate — they reproduce rapidly (days) so their standing biomass at any point is low, despite high productivity | Phytoplankton are NOT heavier than zooplankton — the opposite is true; zooplankton accumulate more biomass per unit time | Fish biomass is LESS than zooplankton in typical aquatic systems — making the pyramid inverted even higher up | Aquatic decomposers are important but do not invert the pyramid of biomass | This is a critical exam point: aquatic biomass pyramid is inverted because of RAPID TURNOVER of phytoplankton, not because they are unproductive — they are highly productive

Carrying capacity (K) is the maximum population size that an environment can sustain indefinitely given available food, water, space, and other resources | Intrinsic rate of natural increase is ‘r’ in population ecology — it measures the maximum potential rate of population growth | Total number of species in an ecosystem is ‘species richness’ — a measure of biodiversity, not carrying capacity | Minimum Viable Population (MVP) is the smallest population size below which extinction risk increases sharply — a different concept | In the logistic growth equation: dN/dt = rN[(K-N)/K] — as N approaches K, growth rate approaches zero

Mycorrhizae are mutualistic associations between soil fungi and plant roots — fungi dramatically increase the absorptive surface area, helping plants take up water and minerals, especially phosphorus which is relatively immobile in soil | Mycorrhizal fungi do NOT cause plant diseases — they are beneficial and found in over 80% of all plant species | Nitrogen fixation is performed by Rhizobium (in legumes), Azotobacter (free-living), and cyanobacteria — not mycorrhizal fungi | Decomposition of dead matter is performed by saprotrophic fungi — mycorrhizal fungi are living in symbiosis with plant roots, not breaking down dead matter | Mycorrhizal networks (‘Wood Wide Web’) also allow nutrient transfer between trees in a forest community

The National Biodiversity Authority (NBA) was established in 2003 under the Biological Diversity Act, 2002 — to regulate access to biological resources and ensure benefit sharing | Wildlife Protection Act, 1972 established the framework for wildlife sanctuaries, national parks, and protected species — not NBA | Forest Conservation Act, 1980 regulates diversion of forest land for non-forest purposes and requires central government approval | Environment Protection Act, 1986 is the umbrella environmental legislation empowering the central government to protect the environment | NBA is headquartered in Chennai and implements the Convention on Biological Diversity (CBD) at national level

Biomagnification is the progressive INCREASE in concentration of persistent toxic substances (DDT, mercury, PCBs) at each successive trophic level — organisms at higher levels accumulate more toxins | Biomass decreases at higher trophic levels due to the 10% law — this is NOT biomagnification | Toxins accumulate increasingly in HIGHER trophic levels, not lower ones — top predators suffer most | Toxin concentrations INCREASE up the food chain — the opposite of option D | Classic example: DDT — plankton (0.025 ppm) → small fish (0.5 ppm) → large fish (2 ppm) → osprey/human (25+ ppm) — explains eggshell thinning in raptors

Tropical rainforests have the highest species diversity — covering less than 7% of Earth’s land surface but harbouring over 50% of all known species due to stable warm temperatures, high rainfall, and year-round sunlight | Temperate deciduous forests have moderate diversity — seasonal temperature extremes limit the range of species | Boreal forest (Taiga) has very low diversity — harsh subarctic climate with long winters supports limited species | Tropical savanna has moderate diversity — seasonal drought restricts which species can survive | Three key reasons for tropical rainforest diversity: high energy input (sunlight), high moisture, long evolutionary history without major extinction events

Mutualism is a symbiotic interaction where BOTH species benefit (+/+) — e.g., lichens (algae provides food, fungi provides shelter/moisture), mycorrhizae, Rhizobium in legume nodules, clownfish and sea anemone | Commensalism (+/0) is where one species benefits while the other is neither helped nor harmed — e.g., epiphytic orchids on trees | Parasitism (+/-) is where the parasite benefits but the host is harmed — e.g., Cuscuta on host plants, lice on mammals | Amensalism (0/-) is where one is unaffected while the other is inhibited — e.g., Penicillium releasing penicillin that kills bacteria | Mutualism is evolutionarily stable when both partners gain more than they would alone

The Ramsar Convention is an international treaty for conservation and wise use of WETLAND ecosystems — named after Ramsar city in Iran where it was signed | Biodiversity Hotspots are a concept developed by Conservation International (Norman Myers) — not covered by Ramsar | Forest conservation is governed by separate national laws and UNFCCC-related REDD+ mechanisms | Marine ecosystems are protected under UNCLOS, London Protocol, and regional marine agreements | India (as of 2024) has the highest number of Ramsar sites among South Asian countries — 82 sites including Chilika Lake (Odisha) and Pulicat Lake (Andhra Pradesh)

Secondary succession occurs in areas WHERE AN ECOSYSTEM PREVIOUSLY EXISTED but was disturbed or destroyed — soil, seeds, and organic matter already present allow faster recovery | Primary succession starts on BARE SUBSTRATE (rock, sand, lava) with no previous life and no soil | Secondary succession is FASTER than primary succession because soil with nutrients and seed banks already exist | Pioneer species in secondary succession are typically grasses and herbs — NOT lichens (lichens pioneer primary succession on bare rock) | Examples of secondary succession: abandoned agricultural fields, logged forests, areas recovering from wildfires

Stratification is the VERTICAL LAYERING of vegetation at different heights — Emergent trees → Canopy → Understory → Shrub layer → Herb/ground layer → Forest floor | Horizontal distribution of species across a landscape is ‘zonation’ — a different spatial pattern | Seasonal variation in species composition is ‘temporal dynamics’ or ‘phenology’ — not stratification | Underground root distribution patterns are studied as part of soil ecology, separate from above-ground stratification | Each forest layer intercepts different light intensities creating distinct microclimates and microhabitats — maximising resource use and supporting high biodiversity

Biodiversity Hotspots (Norman Myers concept, refined by Conservation International) are defined by TWO criteria: ≥1,500 endemic vascular plant species AND having lost ≥70% of original habitat | Western Ghats has exceptional endemism — over 5,000 flowering plant species, 139 mammal species, 508 bird species, many endemic | Introduced (invasive) species are NOT a criterion for hotspot designation — high endemism is the key | Presence of wildlife sanctuaries alone does not make an area a hotspot — habitat loss combined with endemism is the defining feature | India has 4 Biodiversity Hotspots: Western Ghats-Sri Lanka, Indo-Burma, Eastern Himalayas, and Sundaland

NEP = GPP − Total Ecosystem Respiration = GPP − (Autotrophic Respiration + Heterotrophic Respiration) — it measures whether the ecosystem is a net carbon sink or source | GPP minus Autotrophic Respiration alone gives NPP (Net Primary Productivity), not NEP | NPP plus Heterotrophic Respiration arithmetically equals GPP — not NEP | In mature climax ecosystems, NEP approaches ZERO (not equal to NPP) because all NPP is consumed by decomposers and heterotrophs | A positive NEP means the ecosystem sequesters carbon (carbon sink); negative NEP means it releases carbon (carbon source)

Oceans (particularly the deep ocean and marine sediments) act as the largest carbon reservoir on Earth — storing approximately 38,000 GtC compared to ~800 GtC in the atmosphere | Healthy undisturbed forests are net CARBON SINKS — they absorb more CO₂ through photosynthesis than they release through respiration | Photosynthesis is a CENTRAL process in the carbon cycle — it is how CO₂ is removed from the atmosphere and fixed into organic compounds | Carbonate rocks (limestone, chalk) store enormous amounts of carbon over geological timescales — they are a major long-term carbon reservoir | The carbon cycle links the atmosphere, biosphere, hydrosphere, and lithosphere through photosynthesis, respiration, decomposition, and geological processes

Standing State refers to the amount of inorganic nutrients (N, P, K, Ca etc.) present in the SOIL and WATER of an ecosystem at any given time — the abiotic pool available to organisms | Standing Crop refers to the total biomass (living organic matter) present at a trophic level at a given time — distinct from standing state | Dead organic matter in soil is ‘detritus’ or ‘humus’ — separate from the standing state of inorganic nutrients | Total biomass across all trophic levels is ‘total biomass’ — not the standing state | Standing State + Standing Crop together represent the total nutrient pool of an ecosystem

Food webs provide ecosystem STABILITY by offering alternate energy pathways — if one species is lost, energy can be rerouted through other species maintaining ecosystem function | Food webs are NOT linear — they are complex interconnected networks of multiple overlapping food chains | Energy always flows from lower to higher trophic levels (producers to consumers) — maintaining thermodynamic directionality | Food webs have MORE connections and pathways than individual food chains — increased complexity, not fewer connections | The more complex the food web, the greater the ecosystem’s ability to absorb perturbations — a central concept in conservation ecology

Liebig’s Law (1840) states that the yield or growth of an organism is determined by the essential nutrient available in the SMALLEST quantity relative to the organism’s requirement — the limiting factor concept | The most ABUNDANT nutrient does NOT limit growth — abundance of other nutrients is irrelevant if one is scarce | Growth does NOT indefinitely increase with each additional nutrient — Liebig’s law identifies which single factor is the bottleneck | Shelford’s Law of Tolerance (not Liebig’s) describes the range of conditions organisms can tolerate | The barrel analogy illustrates Liebig’s Law: the water level (productivity) equals the height of the SHORTEST stave (scarcest nutrient) — adding more water above the shortest stave is wasted

Phytoplankton are microscopic photosynthetic organisms (algae, cyanobacteria) — they are PRODUCERS (autotrophs) forming the base of aquatic food chains | Phytoplankton do NOT consume other organisms — they use sunlight and dissolved nutrients to produce organic matter | Decomposers in aquatic systems are bacteria and fungi that break down dead organic matter — not phytoplankton | Detritivores feed on dead organic particles — phytoplankton are living and photosynthetically active | Phytoplankton contribute approximately 50% of Earth’s total oxygen production and form the foundation of marine food webs

Tropical rainforests have the highest Net Primary Productivity (800–3500 g C/m²/year) due to year-round high solar radiation, warm temperatures, and abundant rainfall | Deserts have the lowest NPP due to water limitation — often less than 200 g C/m²/year | Tundra has very low NPP due to extremely cold temperatures and short growing seasons — permanently frozen subsoil (permafrost) further limits productivity | Temperate grasslands have moderate NPP (200–600 g C/m²/year) — seasonal temperature and rainfall limitations apply | Estuaries and coral reefs rival tropical rainforests in productivity among aquatic ecosystems

Joseph Connell proposed the Intermediate Disturbance Hypothesis in 1978 — based on studies of coral reefs and tropical rainforests showing maximum diversity at intermediate disturbance levels | Robert Paine is known for the keystone species concept from intertidal starfish experiments (1966) — not IDH | Charles Elton introduced food chains, food webs, and ecological niche concepts — not IDH | Joseph Grinnell defined the Grinnellian niche based on physical constraints on species distribution | IDH predicts: low disturbance → competitive exclusion reduces diversity; high disturbance → only disturbance-tolerant species persist; intermediate → coexistence of many species maximises diversity

Ecological Stoichiometry (Sterner & Elser, 2002) studies the balance of energy and multiple chemical elements (especially C:N:P ratios) in organisms and their ecological consequences for nutrient cycling and food web dynamics | Energy flow efficiency studies belong to trophic ecology — related to Lindeman’s 10% law, not stoichiometry | Population growth models (logistic, exponential, Lotka-Volterra) are part of population ecology — not stoichiometry | Seasonal productivity changes are studied under ecosystem phenology and climate-ecosystem interactions | Stoichiometric imbalances between consumer nutrient demands and food quality can limit growth and alter nutrient cycling rates in ecosystems

Resistance = the ability of an ecosystem to WITHSTAND disturbance without being substantially altered (e.g., an old-growth forest resisting moderate wind storms) | Resilience = the ability to RECOVER and return to its original state after being disturbed (e.g., grassland recovering quickly after fire) | Options that reverse these definitions are a common exam trick — resistance is ‘withstand,’ resilience is ‘recover’ | Generally, highly diverse and complex ecosystems have higher resistance; simpler ecosystems (like grasslands) have higher resilience | Conservation implications: a highly resistant ecosystem may still be vulnerable if pushed past a threshold — both properties are needed for long-term stability

Trophic cascade is the INDIRECT effect where a change in the abundance of a top predator propagates down through the food web, affecting multiple trophic levels below it | Direct sequential feeding from one trophic level to the next simply describes a food chain — not a cascade | Energy loss at each trophic level is Lindeman’s 10% law — a different concept | Nutrient transfer via decomposers is part of biogeochemical cycling — not trophic cascade | Classic example: Wolf reintroduction in Yellowstone reduced elk overgrazing → vegetation recovered → rivers changed course — demonstrating a top-down trophic cascade across the entire ecosystem

Gause’s Principle (1934) states that two species competing for exactly the SAME limiting resources in the same niche CANNOT stably coexist indefinitely — one will competitively exclude the other | Species CAN coexist if they partition their niche (resource partitioning) or occupy different niches — the key word is ‘identical’ niche | Competition rarely leads to extinction of BOTH species — the competitively inferior species is excluded or adapts | Migration is not the primary mechanism of competitive resolution — niche differentiation and character displacement are | This principle drives niche differentiation in nature: closely related species living together often evolve to use slightly different resources

IPBES was formally established in April 2012 at an intergovernmental meeting in Panama City — it serves as the ‘IPCC for biodiversity’ providing scientific assessments to policymakers | 2005 is the year the Millennium Ecosystem Assessment (MEA) was published — not IPBES establishment | 2010 was the year of CBD COP10 in Nagoya, Japan, where Aichi Biodiversity Targets were adopted — not IPBES founding | 2015 was the year of SDG adoption in New York — not IPBES founding | IPBES publishes global and regional assessments on biodiversity, ecosystem services, pollinators, land degradation, and invasive species — informing international policy

Robert MacArthur and E.O. Wilson introduced r-selection and K-selection theory in ‘The Theory of Island Biogeography’ (1967) — relating life history strategies to environmental stability | Darwin and Wallace independently developed the Theory of Natural Selection — not life history r/K strategy theory | Odum contributed to ecosystem ecology; Menge to intertidal ecology — neither introduced r/K theory | Hutchinson developed niche theory; Gause the competitive exclusion principle — not r/K selection | r-strategists: fast reproduction, short lifespan, high mortality, unstable environments (e.g., weeds, rodents) | K-strategists: slow reproduction, long lifespan, low mortality, stable environments near K (e.g., elephants, whales)

Functional redundancy is the property where multiple different species can perform the same ecological function — if one species is lost, others can maintain the same ecosystem process | Functional redundancy ENHANCES (not reduces) ecosystem stability by providing insurance against species loss | Ecosystems with many DIFFERENT roles (functional diversity) are distinct from redundancy — redundancy specifically means overlapping functions | Redundancy is NOT about having the same species perform different roles — it is about different species performing the same role | High functional redundancy means an ecosystem can lose some species without losing key functions — an important concept for conservation biology and ecosystem services maintenance

Regime shifts are abrupt, large-scale, and often difficult-to-reverse changes in ecosystem structure and function — the ecosystem transitions from one stable state to another | Regime shifts are NOT gradual — they are characterised by ABRUPT transitions once a tipping point (threshold) is crossed | After a regime shift, the ecosystem does NOT easily revert to its original state — this hysteresis makes regime shifts especially concerning | Regime shifts are NOT restricted to marine ecosystems — they occur in all ecosystem types including lakes (algal blooms), savannas, and coral reefs | Classic example: shallow lakes switching from clear-water (macrophyte-dominated) to turbid (algae-dominated) states when nutrient loading crosses a threshold

Extensive experimental evidence (Tilman’s Minnesota grassland experiments, Hooper et al. syntheses) shows that greater biodiversity generally enhances ecosystem stability and productivity through functional redundancy and complementarity | Simpler ecosystems (monocultures) are MORE vulnerable to perturbations — monoculture crops are devastated by single pests or disease outbreaks | The diversity-stability relationship is well-supported empirically — multiple meta-analyses confirm the positive correlation | Maximum stability occurs at HIGHER species richness — not at minimal species richness | Functional redundancy means multiple species can perform similar roles, buffering the ecosystem against the loss of any single species — providing ‘ecological insurance’