#ecosystem function

BIODIVERSITY

Which hypothesis explains function with increasing species richness in unpredictable ways?

The idiosyncratic hypothesis treats ecosystem performance as dependent on which species are present and how they interact, not as a smooth function of species number. Adding a species may increase productivity through complementarity, reduce it through competition, or produce little change if its role overlaps with existing organisms. Consequently, function can rise, fall, or fluctuate as richness changes, generating an unpredictable relationship. This contrasts with the redundancy model, in which several species share functional roles and initial losses have little effect; the rivet model, in which each loss progressively weakens function; and the keystone model, in which one species has a disproportionately large effect. “Unpredictable” does not mean ecologically uncaused. The response can result from species identity, trophic links, facilitation, inhibitory effects, environmental conditions, and the order in which species enter or disappear. Once these mechanisms are known, particular outcomes may be explained, but richness alone is insufficient to forecast them. The idiosyncratic framework therefore warns against assuming that every added species contributes equally or that all communities with the same richness provide the same ecosystem function.

Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation

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SPECIES HYPOTHESIS

A graph showing steep decline in function after initial loss indicates:

A steep functional decline after the first species loss is consistent with a keystone pattern when that initial removal eliminates a disproportionately influential species. The response reflects species identity rather than the number of species removed, distinguishing it from gradual rivet loss or buffered redundancy. Biodiversity–function hypotheses differ in how they assign ecological importance among species. Complementarity emphasizes distinct contributions, redundancy emphasizes overlap and compensation, rivet theory emphasizes cumulative weakening, keystone theory emphasizes particular influential species, and idiosyncrasy emphasizes context dependence. Real communities can display several patterns because functions differ and environmental conditions alter interactions. Richness alone therefore cannot identify mechanism; species traits, relative abundance, functional groups, and the order of species loss must also be considered. In this context, the keyed term, Keystone, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation

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SPECIES HYPOTHESIS

Which hypothesis suggests unpredictable functional effects?

The idiosyncratic hypothesis treats functional consequences of diversity change as contingent on species identity and interactions. Because different combinations produce different outcomes, adding or removing species yields irregular and unpredictable changes rather than a common linear, threshold, or stepwise curve. Species richness counts taxa but does not show their abundance, traits, or interaction strengths. Dominant species may control bulk process rates, rare species may provide specialized functions or future insurance, and predators can restructure whole food webs through indirect effects. Functional groups summarize role overlap, while keystone effects identify unusually strong influence. Separating these dimensions explains why equal losses of richness can have very different ecological consequences and why conservation cannot rely solely on the number of species remaining. In this context, the keyed term, Idiosyncratic, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation

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ECOLOGICAL SUCCESSION

Redundancy hypothesis implies function is maintained until:

The redundancy hypothesis groups species with overlapping ecological roles. Loss of one member may have little immediate effect because another can compensate, but function declines after losses remove enough members—or a uniquely important member—to cross the system's effective functional threshold. Biodiversity–function hypotheses differ in how they assign ecological importance among species. Complementarity emphasizes distinct contributions, redundancy emphasizes overlap and compensation, rivet theory emphasizes cumulative weakening, keystone theory emphasizes particular influential species, and idiosyncrasy emphasizes context dependence. Real communities can display several patterns because functions differ and environmental conditions alter interactions. Richness alone therefore cannot identify mechanism; species traits, relative abundance, functional groups, and the order of species loss must also be considered. In this context, the keyed term, Critical species are lost, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20

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Ecosystem Ecology & PRODUCTIVITY

Which is NOT a function of an ecosystem?

Ecosystem functions are processes that operate at the level of interacting organisms and their environment. They include primary production, transfer and dissipation of energy, decomposition, nutrient cycling, soil formation, and regulation arising from ecological interactions. DNA replication, in contrast, is a cellular molecular process by which an organism copies its genetic material before cell division or reproduction. It is essential to organisms and ultimately underlies population continuity, but it is not normally classified as an ecosystem-level function. Energy flow connects trophic levels, while nutrient cycling returns elements from organisms to air, water, and soil. Regulation can involve predation, competition, mutualism, disturbance, and feedback between biotic and abiotic components. The difference is one of biological scale, not importance: a process can be indispensable to life without being an emergent function of an ecosystem. Therefore, DNA replication is the outlier among the listed processes because its immediate mechanism and unit of operation are molecular and cellular rather than community-environmental.

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 17

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