In a grassland experiment, two-species mixtures produce more biomass than the monoculture of either component species. This "transgressive overyielding" is best explained by

complementarity — the species use resources differently or facilitate each other

the selection effect — the more productive species dominates the mixture

competitive exclusion of one species by the other

Which are correctly classified as regulating ecosystem services?

Pollination of crops by wild bees

Flood protection by coastal mangroves

Pollination of crops by wild bees

Flood protection by coastal mangroves

Timber harvested from a plantation

Which statements about global conservation initiatives are correct?

CITES regulates international trade through three appendices, and Appendix I species are generally barred from commercial trade

The three objectives of the CBD are conservation, sustainable use and fair and equitable sharing of benefits from genetic resources

The Nagoya Protocol under the CBD concerns access to genetic resources and benefit-sharing

CITES regulates international trade through three appendices, and Appendix I species are generally barred from commercial trade

The three objectives of the CBD are conservation, sustainable use and fair and equitable sharing of benefits from genetic resources

The Nagoya Protocol under the CBD concerns access to genetic resources and benefit-sharing

The IUCN Red List is a treaty that obliges governments to protect listed species

Inbreeding depression arises mainly because inbreeding

increases homozygosity, exposing rare recessive deleterious alleles

changes allele frequencies towards deleterious alleles

increases heterozygosity at every locus

The standard DNA barcode region for identifying most animal species is

the mitochondrial cytochrome c oxidase subunit I (COI) gene

the nuclear ribosomal ITS region

hypervariable minisatellite loci

Which statements about conservation genetics are correct?

Genetic rescue introduces unrelated individuals to reduce inbreeding in a small population

Outbreeding depression can follow crosses between populations adapted to different conditions

Microsatellite genotypes from scat can be used to count individual animals

Genetic rescue introduces unrelated individuals to reduce inbreeding in a small population

Outbreeding depression can follow crosses between populations adapted to different conditions

Microsatellite genotypes from scat can be used to count individual animals

A population of 1000 animals always has an effective size of 1000

Applied Ecology and Evolution I: Biodiversity and Ecosystem Function, Ecosystem Services, Conservation and Conservation Genetics

Section 5 of the GATE Ecology and Evolution paper, Applied Ecology & Evolution, first half. Section 5 joins two subjects: conservation biology, which is this chapter, and the ecology and evolution of disease together with global change, which is the next. This chapter covers the relationship between biodiversity and ecosystem function; ecosystem services; conservation through endemism, biodiversity hotspots and protected areas; the global conservation initiatives the syllabus names — the Conferences of the Parties, the IUCN, the Convention on Biological Diversity and CITES; and conservation genetics — genetic diversity, inbreeding and inbreeding depression, and the DNA fingerprinting and DNA barcoding used to identify individuals and species. Dates and counts are given only where they are fixed facts.

1. Biodiversity and ecosystem function

Does losing species change how ecosystems work? Grassland experiments that sow plots with different numbers of species — Tilman’s at Cedar Creek in Minnesota and the Jena experiment in Germany — found that productivity and nutrient retention generally rise with plant species richness, steeply at first and then levelling off, and that diverse plots vary less from year to year. Two mechanisms explain the rise. Complementarity (niche partitioning and facilitation): species use different resources, depths, seasons or partners (nitrogen-fixing legumes), so a mixture captures more of the available resources than any single species. The selection (sampling) effect: a richer mixture is more likely to contain a highly productive species that then dominates. The two are separated statistically by comparing mixtures with the monocultures of their component species.

Insurance hypothesis (portfolio effect): species respond differently to fluctuations, so their declines and increases partly cancel and aggregate function is more stable in diverse communities.
Redundancy hypothesis: several species perform each function, so some can be lost with little effect until the last of a functional group goes.
Rivet hypothesis (Ehrlich): each species, like a rivet in an aircraft wing, contributes, and losses weaken the system until it fails suddenly.
Idiosyncratic effects: the identity of the species lost matters more than their number — losing a keystone predator or a dominant tree is not the same as losing a rare herb.

2. Ecosystem services

Ecosystem services are the benefits people obtain from ecosystems. The Millennium Ecosystem Assessment (2005) grouped them into four categories, a scheme still widely used in teaching; later frameworks such as IPBES’s "nature’s contributions to people" regroup them but keep the ideas.

The four categories of the Millennium Ecosystem Assessment
Category	What it provides	Examples
Provisioning	products obtained directly	food, timber, fibre, fresh water, medicinal plants, genetic resources
Regulating	benefits from the regulation of ecosystem processes	pollination, climate regulation and carbon storage, water purification, flood control by wetlands and mangroves, pest control
Supporting	processes needed for all other services	soil formation, nutrient cycling, primary production
Cultural	non-material benefits	recreation, tourism, spiritual values of sacred groves, education, aesthetic value

Services are valued by market prices (timber), replacement or avoided costs (the cost of a water-treatment plant a forested catchment makes unnecessary), travel costs (what visitors pay to reach a park) and stated preferences (willingness to pay). Payments for ecosystem services reward landholders for maintaining services others enjoy — upstream farmers paid by downstream water users to keep forest cover. Because many services are public goods that nobody pays for, markets tend to under-supply them, which is the economic argument for conservation policy.

3. Conservation: endemism, hotspots and protected areas

An endemic species is found naturally in one region and nowhere else; islands, isolated mountains and old, stable landscapes are rich in endemics, and range-restricted species are at greatest risk because a single threat can end them. Myers (1988) proposed biodiversity hotspots to target conservation where much is at stake and much is being lost. Under the criteria used by Conservation International a region qualifies if it holds at least 1500 endemic vascular plant species (more than 0.5 % of the world total) and has lost at least 70 % of its original habitat. There are 36 hotspots, covering a small fraction of the land surface but holding a large share of endemic plants and vertebrates. India includes parts of four: the Himalaya, Indo-Burma, the Western Ghats and Sri Lanka, and Sundaland (through the Nicobar Islands).

Protected areas are the core of in situ conservation. The IUCN classifies them from Ia (strict nature reserve) and Ib (wilderness area) through II (national park), III (natural monument), IV (habitat or species management area) and V (protected landscape) to VI (protected area with sustainable use of resources). In India, the Wildlife (Protection) Act, 1972 provides for national parks and wildlife sanctuaries, and its 2002 amendment added conservation reserves and community reserves; biosphere reserves follow UNESCO’s Man and the Biosphere programme, with a protected core, a buffer zone and a transition zone where people live and work. Ex situ conservation — zoos, botanic gardens, seed banks, gene banks and captive breeding — supports but cannot replace protection in the wild.

Reserve design draws on island biogeography and metapopulation theory: larger reserves, reserves close together or linked by corridors, and compact shapes that reduce edge effects (the altered light, wind, temperature and predation at habitat edges) generally hold more species. The SLOSS debate — a single large or several small reserves of the same total area — has no general answer: one large reserve suits wide-ranging species with large area needs, several small ones spread the risk of a single catastrophe and may capture more habitat types. The species–area relation predicts losses from habitat loss: with S = cA^z and z = 0.25, destroying 90 % of a habitat leaves S_new/S_old = 0.1^0.25 = 0.562, so about 43.8 % of its species are eventually expected to be lost — fewer than 90 %, but not immediately visible, because extinctions lag behind habitat loss (the extinction debt).

ℹ️ Flagship, umbrella and keystone are different ideas

A flagship species is chosen for public appeal to raise support (the tiger, the snow leopard). An umbrella species needs so much habitat that protecting it protects many others (the tiger again, or the Asian elephant). A keystone species has an ecological effect out of proportion to its abundance (sea otters, figs as a year-round food for frugivores). One species can play several roles, but the reasons are distinct.

4. Global conservation initiatives: COP, IUCN, CBD and CITES

The initiatives the syllabus names
Initiative	What it is	Key points
IUCN	International Union for Conservation of Nature, founded in 1948: a union of governments and NGOs	publishes the Red List of Threatened Species: EX, EW, CR, EN, VU, NT, LC, DD, NE — only CR, EN and VU count as "threatened"; defines protected-area categories
CBD	Convention on Biological Diversity, opened for signature at the Rio Earth Summit in 1992, in force from December 1993	three objectives: conservation of biodiversity, sustainable use of its components, and fair and equitable sharing of benefits from genetic resources; Cartagena Protocol on biosafety (2000) and Nagoya Protocol on access and benefit-sharing (2010)
CITES	Convention on International Trade in Endangered Species of Wild Fauna and Flora, signed in Washington in 1973, in force from 1975	regulates trade, not habitat; Appendix I — threatened with extinction, commercial trade generally prohibited; Appendix II — trade controlled by permits to avoid overuse; Appendix III — listed by one party seeking others’ cooperation
COP	Conference of the Parties: the governing body of a convention, of all the states that have ratified it	CBD COP15 adopted the Kunming–Montreal Global Biodiversity Framework in 2022, including the target to conserve 30 % of land and sea by 2030; UNFCCC COP21 adopted the Paris Agreement in 2015

⚠️ The Red List assesses risk; CITES regulates trade

A species can be Critically Endangered on the IUCN Red List and not listed by CITES, if it is not threatened by international trade, and a CITES Appendix II species need not be threatened at all. The IUCN is not a treaty and has no enforcement power; CITES is a treaty whose parties must enforce it through national permits.

5. Conservation genetics: diversity, inbreeding, fingerprinting and barcoding

Small populations lose genetic diversity — measured as heterozygosity, allelic richness and the proportion of polymorphic loci — through drift at 1/(2Nₑ) per generation. A captive population kept at Nₑ = 50 retains (1 − 1/100)²⁰ = 0.99²⁰ = 0.818 of its heterozygosity after 20 generations; zoo programmes commonly aim to keep 90 % of the founders’ diversity over a hundred years, which requires large Nₑ and equalised family sizes. Nₑ is lowered by an unequal sex ratio — 4 males and 16 females give Nₑ = 4 × 4 × 16/20 = 12.8 — and by variance in family size. Franklin’s rough 50/500 rule suggested Nₑ ≥ 50 to avoid serious short-term inbreeding depression and Nₑ ≥ 500 to retain adaptive variation in the long term; later work argued for larger numbers.

Inbreeding — mating between relatives — raises homozygosity. The inbreeding coefficient F is the probability that the two alleles at a locus are identical by descent: F = 1/4 for the offspring of full siblings, 1/8 for half siblings and 1/16 = 0.0625 for first cousins. Heterozygosity falls to H = 2pq(1 − F), so at p = 0.5 and F = 0.25 it is 0.5 × 0.75 = 0.375 instead of 0.5. Inbreeding depression, the reduced fitness of inbred offspring, arises mainly because inbreeding exposes rare, recessive deleterious alleles in homozygotes, and secondarily through loss of heterozygote advantage. Small, isolated populations can enter an extinction vortex, in which low numbers cause inbreeding and demographic chance, which lower numbers further. Genetic rescue introduces unrelated individuals: eight female pumas from Texas released into the inbred Florida panther population in 1995 led to higher survival and population growth. Too distant a source risks outbreeding depression, the break-up of locally adapted gene combinations.

DNA methods in conservation
Method	Markers	Question answered
DNA fingerprinting (Jeffreys, mid-1980s)	hypervariable minisatellites (VNTRs), now mostly microsatellites (STRs) and SNP panels	which individual? — parentage, relatedness, counting tigers from scat or hair, tracing poached ivory and skins to source populations
DNA barcoding (Hebert and colleagues, 2003)	a short standard gene region: mitochondrial COI for animals, the plastid rbcL and matK for plants, the nuclear ITS for fungi	which species? — identifying larvae, fragments and traded products, revealing cryptic species
Environmental DNA (eDNA) and metabarcoding	barcode regions sequenced from water or soil samples	which species are present? — detecting rare or invasive species without seeing them

Key takeaways

Diverse plant communities are more productive and more stable, through complementarity and the selection effect; insurance, redundancy and rivet hypotheses describe how function responds to loss.
Ecosystem services are provisioning, regulating, supporting and cultural; a hotspot needs 1500 endemic vascular plants and 70 % habitat loss, and India has parts of four of the 36.
With S = cA^z, losing a fraction f of habitat leaves (1 − f)^z of the species, lost slowly as an extinction debt.
IUCN (1948) keeps the Red List; the CBD (1992) has three objectives and the Cartagena and Nagoya Protocols; CITES (1973) regulates trade in three appendices; a COP is a convention’s governing body.
F = 1/4, 1/8 and 1/16 for offspring of full sibs, half sibs and first cousins; H = 2pq(1 − F); fingerprinting identifies individuals, barcoding (COI, rbcL + matK, ITS) identifies species.

Practice questions (14)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

In a grassland experiment, two-species mixtures produce more biomass than the monoculture of either component species. This "transgressive overyielding" is best explained by
1. complementarity — the species use resources differently or facilitate each other
2. the selection effect — the more productive species dominates the mixture
3. the redundancy hypothesis
4. competitive exclusion of one species by the other
Show answer
Answer: A — complementarity — the species use resources differently or facilitate each other
A mixture dominated by its best species can at most match that species’ monoculture, so the selection effect cannot explain yield above the best monoculture. Exceeding it requires the species together to capture more resources than either alone — complementarity. Competitive exclusion would reduce the mixture to one species.
Which are correctly classified as regulating ecosystem services?
1. Pollination of crops by wild bees
2. Flood protection by coastal mangroves
3. Carbon storage in forests
4. Timber harvested from a plantation
Show answer
Answer: A — Pollination of crops by wild bees; B — Flood protection by coastal mangroves; C — Carbon storage in forests
Pollination, flood buffering and climate regulation through carbon storage are benefits of regulating ecosystem processes. Timber is a product taken directly from the ecosystem, which is a provisioning service.
To qualify as a biodiversity hotspot under the criteria used by Conservation International, a region must have at least 1500 endemic vascular plant species and must have lost at least what fraction of its original habitat?
1. 70 %
2. 50 %
3. 30 %
4. 90 %
Show answer
Answer: A — 70 %
The two criteria are irreplaceability (at least 1500 endemic vascular plants) and threat (at least 70 % of original habitat lost). A species-rich region that is still largely intact is not a hotspot, because the concept targets imminent loss.
A forest region loses 90 % of its area. Assuming the species–area relation S = cA^z with z = 0.25, the percentage of its species eventually expected to be lost, to one decimal place, is ____.
Numerical answer — type the value.
Show answer
Answer: 43.8
S_new/S_old = (0.1)^0.25 = 0.562, so 1 − 0.562 = 0.438, a loss of 43.8 %. Assuming loss proportional to area gives 90 %, and 0.1 × 0.25 confuses the exponent with a multiplier. The losses unfold slowly as an extinction debt.
Which global biodiversity hotspots include parts of Indian territory?
1. Himalaya
2. Indo-Burma
3. Western Ghats and Sri Lanka
4. Mountains of Central Asia
Show answer
Answer: A — Himalaya; B — Indo-Burma; C — Western Ghats and Sri Lanka
India includes parts of the Himalaya, Indo-Burma (the north-east and the Andamans), the Western Ghats and Sri Lanka, and Sundaland (through the Nicobar Islands). The Mountains of Central Asia hotspot lies in the Central Asian republics, China and Afghanistan.
Which statements about global conservation initiatives are correct?
1. CITES regulates international trade through three appendices, and Appendix I species are generally barred from commercial trade
2. The three objectives of the CBD are conservation, sustainable use and fair and equitable sharing of benefits from genetic resources
3. The Nagoya Protocol under the CBD concerns access to genetic resources and benefit-sharing
4. The IUCN Red List is a treaty that obliges governments to protect listed species
Show answer
Answer: A — CITES regulates international trade through three appendices, and Appendix I species are generally barred from commercial trade; B — The three objectives of the CBD are conservation, sustainable use and fair and equitable sharing of benefits from genetic resources; C — The Nagoya Protocol under the CBD concerns access to genetic resources and benefit-sharing
CITES works through Appendices I–III, with commercial trade in Appendix I species generally prohibited. The CBD’s three objectives and its Nagoya Protocol on access and benefit-sharing are as stated. The Red List is a scientific assessment of extinction risk by the IUCN, which is not a treaty body and cannot oblige governments.
A large carnivore needs so much habitat that protecting enough land for a viable population of it also protects most other species of the region. In conservation planning it is described as
1. an umbrella species
2. a keystone species
3. an indicator species
4. an endemic species
Show answer
Answer: A — an umbrella species
An umbrella species is defined by its large area requirement, whose protection shelters many others. A keystone species is defined by its outsized ecological effect, an indicator by what its presence reveals about environmental conditions, and an endemic by a restricted native range.
The inbreeding coefficient F of an individual whose parents are first cousins, to four decimal places, is ____.
Numerical answer — type the value.
Show answer
Answer: 0.0625
Tracing the two paths through the shared grandparents, each of six steps, gives F = 2 × (1/2)⁶ = 1/16 = 0.0625. 0.125 is the coefficient of relatedness between first cousins themselves; the offspring of full siblings have F = 0.25.
At a locus with allele frequencies p = q = 0.5, a population has an inbreeding coefficient F = 0.25. Its expected heterozygosity, to three decimal places, is ____.
Numerical answer — type the value.
Show answer
Answer: 0.375
H = 2pq(1 − F) = 2 × 0.5 × 0.5 × 0.75 = 0.375. Inbreeding does not change allele frequencies; it moves genotypes from the heterozygous class into the two homozygous classes. 0.5 is the random-mating value.
A captive population is maintained at a constant effective size Nₑ = 50. The fraction of its initial heterozygosity retained after 20 generations, to three decimal places, is ____.
Numerical answer — type the value.
Show answer
Answer: 0.818
H_t/H₀ = (1 − 1/(2Nₑ))^t = (1 − 1/100)²⁰ = 0.99²⁰ = 0.818. Using 1/Nₑ gives 0.98²⁰ = 0.668, and subtracting 20 × 0.01 gives 0.8, which ignores compounding.
A breeding group in a zoo has 4 males and 16 females, all breeding. Its effective population size, to one decimal place, is ____.
Numerical answer — type the value.
Show answer
Answer: 12.8
Nₑ = 4N_mN_f/(N_m + N_f) = 4 × 4 × 16/20 = 256/20 = 12.8, well below the 20 animals present. Using equal numbers of each sex (10 and 10) would raise Nₑ to 20.
Inbreeding depression arises mainly because inbreeding
1. increases homozygosity, exposing rare recessive deleterious alleles
2. changes allele frequencies towards deleterious alleles
3. raises the mutation rate
4. increases heterozygosity at every locus
Show answer
Answer: A — increases homozygosity, exposing rare recessive deleterious alleles
Inbreeding redistributes genotypes towards homozygotes without by itself changing allele frequencies, so recessive harmful alleles hidden in heterozygotes are expressed. It does not alter mutation rates, and it reduces rather than increases heterozygosity.
The standard DNA barcode region for identifying most animal species is
1. the mitochondrial cytochrome c oxidase subunit I (COI) gene
2. the plastid rbcL gene
3. the nuclear ribosomal ITS region
4. hypervariable minisatellite loci
Show answer
Answer: A — the mitochondrial cytochrome c oxidase subunit I (COI) gene
COI is the animal barcode. rbcL (with matK) is the plant barcode and ITS the fungal one. Minisatellites are hypervariable markers used to fingerprint individuals, not to identify species.
Which statements about conservation genetics are correct?
1. Genetic rescue introduces unrelated individuals to reduce inbreeding in a small population
2. Outbreeding depression can follow crosses between populations adapted to different conditions
3. Microsatellite genotypes from scat can be used to count individual animals
4. A population of 1000 animals always has an effective size of 1000
Show answer
Answer: A — Genetic rescue introduces unrelated individuals to reduce inbreeding in a small population; B — Outbreeding depression can follow crosses between populations adapted to different conditions; C — Microsatellite genotypes from scat can be used to count individual animals
Genetic rescue (the Florida panther) and outbreeding depression are the two sides of moving animals between populations. Individual genotypes from non-invasive samples allow capture–recapture counts. Nₑ is usually far below the census size because of unequal sex ratios, variance in family size and fluctuations in numbers.