IB Biology A4.2: Conservation of biodiversity worked solutions

The variety of alleles within one species is genetic diversity (A). Species richness counts species, ecosystem diversity compares habitats, and evenness compares the shares of species.

Draining a mangrove swamp removes the habitat of many species (A). Replanting, removing an invader and banning collecting all protect or restore biodiversity.

Hunting and destruction of habitat after humans arrived removed the moa (B). Climate change alone, an introduced disease or survival in zoos are not the evidence for this case.

Fewer large dead trees means fewer nest holes (1), so fewer pairs can breed and fewer chicks survive (1). Alternatively: the insects living in dead wood are lost (1), so adult survival falls (1).

Seeds in a bank are kept outside the habitat (B). A logging ban, reintroducing a species to a catchment and controlling invasive rats all protect or restore organisms within their habitat.

Fossil evidence suggests more species now than at any past time, and many living species are still undescribed, so the named total is incomplete (B). A crisis concerns the present rate of loss, not the total.

(a) Richness is the number of species present: P has 3 (the newt has no individuals) and Q has 4 (1). (b) In P the individuals are shared equally, but in Q the beetle supplies 20 of 28, so P has the greater evenness (1).

EDGE favours species that are both evolutionarily distinct and globally endangered: the only living member of its family and critically endangered (B).

Seeds (germ plasm) are kept alive outside the habitat, so the species is not lost if the wild plants die (1); they can be germinated later to restore or reintroduce populations when the habitat is suitable (1).

Fish counts fell at sites 1 and 2 (from 120 to 45 and from 95 to 80) (1) and rose slightly at site 3 (from 60 to 66) (1). The decrease was greatest at site 1, a fall of 75, or 63\% (1).

Any two pairs: clearing removes the trees that provide food and shelter (1), so species that depend on them decline or disappear (1); the road splits the forest into fragments (1), so populations become small and isolated and are more likely to die out (1); the road gives hunters access, so animals are over-exploited (1) and numbers fall below the level at which they recover (1).

(a) A named species, such as the giant moa (1), with the activity: hunting and habitat destruction after human arrival (1). Alternatively the Caribbean monk seal, with hunting and overfishing. (b) Hunting killed adults faster than the population could reproduce (1); the numbers kept falling until no breeding individuals were left (1).

(a) Each fragment is too small for a territory, so fewer individuals can live there (1); the populations become small and isolated, so mates are harder to find and the population is more likely to die out (1). (b) Plant or protect a corridor of forest between the fragments (1) so animals can move between them, find mates and recolonise a fragment if the local population dies out (1).

(a) Ex situ, because the frogs are kept outside their natural habitat (1). (b) Any two: the breeding stock survives even if the wild population is lost (1); offspring can be released when a suitable habitat is restored (1); the zoo can maintain genetic diversity by choosing mates (1). (c) One limitation: the drainage that endangered the frog is not stopped, or the captive population has a small gene pool (1). Maximum 4.

Reserve (in situ): protects the whole habitat, including pollinators and soil fungi, so the orchid keeps its interactions (1); the orchid can keep evolving with changing conditions (1); needs money, staff and enforcement against poaching or clearing (1). Seed bank (ex situ): stores many seeds in little space at a low cost (1); the seeds are safe from habitat destruction and can be sown later (1); it does not protect the habitat or interactions, so plants grown later need a suitable site (1). A balanced conclusion that uses both can replace one point. Maximum 6.

(a) Threat 1: ranger patrols and penalties (1); threat 2: remove the shrub and monitor for regrowth (1); threat 3: corridors between patches or a buffer zone (1). (b) The action must say why it works, for example: a corridor lets individuals move between patches, so populations are connected and can breed and recolonise (1).

(a) Richness is 5 in both plots (1). (b) N=30 in each plot, so N(N-1)=870. Plot 1: \sum n(n-1)=132+56+20+6+2=216, so D=870/216=4.0 (1). Plot 2: \sum n(n-1)=552+6+0+0+0=558, so D=870/558=1.6 (1). (c) Richness is the same (1), but plot 1 has the higher D because its individuals are shared more evenly, while one species dominates plot 2 (1).

(a) (150-380)/380\times100=-61\% (1). (b) The protected wetland gained birds (410 to 455, about +11\%) and kept its richness at 13 species (1); the drained wetland lost birds and species (from 14 to 9) (1); the fall in the drained site is much larger, which is consistent with loss of habitat (1).

(a) 71-40=31 percentage points, or 31/40\times100=78\% (1). (b) The unlinked patches are a control (1): they show what happens without a corridor, so changes caused by weather or a region-wide trend would appear in both sets (1). (c) Occupancy rose in linked patches and stayed near 42\% in the unlinked ones, which supports the claim that the corridor helped (1). Limits: only one species and ten patches each, and the other differences between patches are not known, so repeat the study in other regions (1).

Ecological: the wetland supports food webs, stores flood water and filters pollutants, services that a built site loses (1) plus a biological consequence, for example fewer species or nursery habitat (1). Economic and human: fishing, tourism or education provide income and livelihoods (1) and a named benefit to the residents (1). Ethical or cultural: species have a right to exist and the site has value for future generations (1). A cost is acknowledged, such as the need for housing, and a reasoned choice is made, for example building on degraded land instead (1).

(a) Species number rises as distance increases (1), from 2 at 50 m to 6 at 600 m, and does not change between 600 and 900 m (1). (b) The pattern is consistent with the hypothesis (1) but it is a correlation, and it does not show noise is the cause (1). (c) Other factors may differ, such as pond area, water quality or surrounding vegetation, so compare ponds of the same size and water quality (1) or compare the same ponds before and after the road opened, with measurements of noise (1).

(a) Species A should be first (1): it is the most distinct, so the loss of its lineage would remove the most unique evolutionary history (1), and it is also at the highest risk of extinction (1). (b) B has the same risk as A but 39 close relatives, so its loss removes much less unique evolutionary history (1). (c) One practical or ethical point, for example the cost per species, or whether the same habitat protection also saves other species (1).

(a) 120/15=8 records per volunteer in 2012 (1) and 960/300=3.2 in 2022 (1). (b) The total rose eightfold, but the number of volunteers rose twentyfold, so the effort changed and the rise does not show more butterflies (1). Records per volunteer fell, which could mean the butterfly became rarer (1), although volunteers may also visit different, easier sites; a standard survey with the same routes and times is needed (1).

(a) Collection Y (1), because it contains seeds from many parent trees and from different populations, so it holds more of the alleles of the species (1). (b) A more diverse stock lets reintroduced populations adapt to changing conditions (1). (c) The seeds do not save the habitat, so reintroduction needs a suitable site (1); stored seeds lose viability over time, so they must be germinated and replaced (1).

(a) (21-3)/(12-2)=1.8 species per year (1). (b) The reclaimed site rose from 3 to 21 species, while the unreclaimed quarry reached 4, so reclamation increased richness (1); it reached 21/29=72\% of the natural woodland, so recovery is incomplete (1) but still rising (1). (c) Any two: count evenness or the abundance of each species (1); record animals and not only plants (1); check that the species are native and not invasive, or monitor for longer (1). Maximum 6.

(a) In a small population, chance changes in allele frequency (genetic drift) are large (1); some alleles are lost (1); related animals mate, so harmful recessive alleles are expressed and survival falls (1). (b) The fragments have no gene flow (1); if conditions differ, selection favours different alleles in each (1); after long isolation the populations may become unable to interbreed, so a new species forms (1). (c) A corridor, or moving animals between fragments (translocation), restores gene flow and raises genetic diversity (1); the cost is that the two populations are no longer separate (1).

(a) N=35\times28/7=140 (1) skinks (1). (b) Any two: marked individuals mix at random with the rest (1); no births, deaths or movement in or out between the samples (1); the marks stay visible and do not change survival (1). (c) (98-140)/140\times100=-30\% (1). A fall of this size could show that the population is declining, but the same method and effort must be used each time (1), and two estimates cannot show a trend, so repeated surveys are needed (1). Maximum 7.

(a) (9-18)/18\times100=-50\% (1). (b) The predator kills deer (1); fewer deer browse saplings, so more saplings survive and grow (1); the extra trees provide food and habitat for other species, which raises biodiversity (1). (c) This is rewilding, because a lost species is restored (1) which brings back a feeding interaction that regulates the community and helps it to return to stability after disturbance (1).