Question 1
Define the term population.
[2]
State the level of ecological organization formed by interacting populations and their physical environment.
[1]
Question 2
A population of freshwater otters rests in dense vegetation beside rivers and feeds mainly on fish and crustaceans.
Distinguish between the habitat and niche of the otter population.
[2]
Outline one abiotic and one biotic parameter of this population's niche.
[2]
Question 3
Students investigated the distribution of a non-mobile woodland plant along a transect extending away from a footpath. At each distance, they placed several equal-sized quadrats and counted the number of plants, while measuring soil moisture and canopy cover. Mean values were calculated for each distance.
Figure 1 shows the results.
Measurements along a transect extending away from a footpath.
| Distance from footpath / m | Mean number of plants per quadrat | Mean soil moisture / % | Canopy cover / % |
|---|---|---|---|
| 0 | 2 | 9 | 8 |
| 5 | 5 | 13 | 18 |
| 10 | 11 | 18 | 35 |
| 15 | 18 | 24 | 52 |
| 20 | 14 | 27 | 76 |
| 25 | 6 | 29 | 91 |
Calculate the population density of the plant at 15 m from the footpath.
[2]
Describe the distribution of the plant along the transect.
[2]
Explain how the measured environmental factors may account for the distribution of the plant.
[3]
Question 4
Ecologists used capture–mark–release–recapture to estimate the abundance of a lizard population in an isolated grassland reserve. Figure 2 summarizes the procedure and results.
Using the Lincoln index, calculate the estimated size of the lizard population.
[2]
Outline two assumptions of the population estimate.
[2]
Explain how loss of marks before the second capture would affect the population estimate.
[2]
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Question 5
The model shows the growth of a mammal population after it colonized a protected grassland.
Identify the population-growth pattern shown.
[1]
Explain why the population fluctuates around carrying capacity.
[3]
Question 6
Eight randomly positioned quadrats, each measuring , were used to sample a plant population in a meadow. A total of 46 plants was counted, and the species occurred in six of the eight quadrats.
Calculate the estimated population density of the plant.
[2]
Calculate the percentage frequency of the plant.
[1]
State one reason for selecting quadrat positions randomly.
[1]
Question 7
In a capture–mark–release–recapture study of a lizard population, 60 lizards were captured, marked and released. In a second sample, 45 lizards were captured, of which 15 were marked.
Calculate the population size using the Lincoln index. Show your working.
[2]
Outline how loss of marks before the second capture would affect the estimate.
[2]
Question 8
The systems diagram represents a mature wetland ecosystem.
Outline why the wetland is an open system.
[2]
Describe how persistent removal of plant biomass at a rate greater than regeneration would affect the wetland's steady state.
[2]
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Question 9
The cladogram represents a hypothesis about the evolutionary relationships of five taxa.
Identify the taxon most closely related to taxon D.
[1]
State why taxa C, D and E form a clade.
[1]
Outline one advantage of classification using clades.
[1]
Question 10
Species X is an annual plant that rapidly colonizes disturbed ground and produces thousands of small seeds. Species Y is a large mammal that matures after several years and usually produces one offspring following prolonged parental care.
Identify the reproductive strategy represented by each species.
[2]
Outline why Species Y is likely to recover more slowly than Species X after a population decline.
[2]
Question 11
Ecologists investigated the distribution of a freshwater shrimp in the tidal reach of the fictional Luma River. Samples were taken at six sites during the same morning. Figure 1 shows mean shrimp abundance, salinity and dissolved oxygen along the river.
Identify the distance upstream at which the greatest mean shrimp abundance was recorded.
[1]
Calculate the percentage decrease in mean shrimp abundance between 8 km and 10 km upstream.
[2]
Explain how the data suggest that abiotic factors influence the distribution of the shrimp.
[3]
Evaluate the conclusion that dissolved oxygen is the main factor determining the distribution of the shrimp in the Luma River.
[4]
Question 12
Figure 3 shows changes in the populations of a herbivorous rodent and its main predator in a protected grassland.
Determine the time lag between each rodent population peak and the following predator population peak.
[1]
Describe the relationship between the two populations.
[2]
Explain how predation may act as a negative feedback mechanism in this system.
[3]
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Question 13
Four wetland vertebrates were traditionally classified using external morphology. A DNA survey was later used to construct the cladogram shown below.
Based on the stated DNA sequence similarities, identify the two taxa that are most closely related.
[1]
Outline why group X is a valid clade.
[2]
Explain why the DNA evidence may justify revising the traditional classification of taxa B and C.
[3]
Question 14
Two unrelated desert plant taxa were traditionally placed in the same group because both have thick, water-storing stems. DNA evidence indicates that the taxa do not share a recent common ancestor.
Outline three difficulties with using the traditional hierarchy of taxa to represent evolutionary relationships.
[3]
Question 15
Researchers investigated the vertical distribution of a shore species when a competing species was absent and when it was present.
Identify the fundamental niche and the realized niche of the study species in terms of shore height.
[2]
Explain why the realized niche is narrower than the fundamental niche.
[2]
Question 16
A conservation group investigated a 400 meadow containing a non-mobile orchid and a mobile ground beetle. Ten random quadrats, each of area 0.25 , were used for the orchid. Capture–mark–release–recapture was used for the beetle.
Figure 2 shows the sampling design and results.
Orchid quadrat counts and ground beetle capture–mark–release–recapture results.
| Sampling result | Count / individuals |
|---|---|
| Orchid quadrat | 4 |
| Orchid quadrat | 7 |
| Orchid quadrat | 0 |
| Orchid quadrat | 9 |
| Orchid quadrat | 6 |
| Orchid quadrat | 8 |
| Orchid quadrat | 5 |
| Orchid quadrat | 10 |
| Orchid quadrat | 0 |
| Orchid quadrat | 11 |
| Beetles, first capture | 60 |
| Beetles, second capture | 50 |
| Marked beetle recaptures | 15 |
Calculate the percentage frequency of the orchid in the ten quadrats.
[1]
Calculate the estimated orchid population in the whole meadow. Show your working.
[3]
Use the Lincoln index to estimate the ground beetle population.
[2]
Outline why different sampling methods were appropriate for the orchid and the beetle.
[2]
Evaluate the reliability of the two population estimates.
[4]
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Question 17
Figure 3 shows changes in a grassland rodent population, its owl predator and annual rainfall over 12 years. A severe wildfire occurred at the end of year 8.
Figure 3. Annual grassland surveys; a severe wildfire occurred after year 8.
| Year | Rodent population / individuals | Breeding owl population / pairs | Annual rainfall / mm | Event |
|---|---|---|---|---|
| 1 | 120 | 8 | 520 | |
| 2 | 210 | 9 | 545 | |
| 3 | 360 | 12 | 510 | |
| 4 | 510 | 18 | 535 | |
| 5 | 300 | 23 | 500 | |
| 6 | 170 | 17 | 550 | |
| 7 | 280 | 11 | 525 | |
| 8 | 470 | 15 | 515 | Wildfire after survey |
| 9 | 90 | 19 | 505 | |
| 10 | 130 | 6 | 530 | |
| 11 | 240 | 7 | 540 | |
| 12 | 390 | 11 | 520 |
State the year in which the greatest rodent population was recorded.
[1]
Describe the relationship between rodent and owl populations during years 1–8.
[2]
Explain how negative feedback could produce the population pattern during years 1–8.
[3]
Distinguish the effect of the wildfire from density-dependent regulation of the rodent population.
[2]
Evaluate the usefulness of this predator–prey model for predicting future rodent abundance.
[4]
Question 18
Researchers investigated the classification of six fictional island lizards. Figure 5(a) is a cladogram based on DNA sequences. Figure 5(b) compares selected visible characteristics and DNA differences.
Figure 5(b): visible characteristics and selected mean pairwise DNA differences for six fictional island lizards.
| Lizard | Habitat | Toe pads | Dorsal stripe | Selected DNA differences / % |
|---|---|---|---|---|
| A | Rocky shore | Absent | Present | : 2.1; : 6.8; : 13.2 |
| B | Rocky shore | Absent | Present | : 6.5 |
| C | Forest floor | Absent | Absent | — |
| D | Forest canopy | Present | Present | : 1.7; : 7.4 |
| E | Forest canopy | Present | Present | : 7.1 |
| F | Open scrub | Absent | Present | — |
Identify the two pairs of most closely related lizards shown by the cladogram.
[2]
State the labelled common ancestor of Lizards A, B and C.
[1]
Analyse how the DNA and visible-characteristic data support or challenge the relationships shown in the cladogram.
[3]
Explain two advantages of classifying these lizards using clades rather than visible similarity alone.
[2]
Evaluate the reliability of the cladogram as a model of the lizards’ evolutionary relationships.
[4]
Question 19
A shallow lake received increasing inputs of phosphorus from agricultural runoff. Figure 4 shows selected indicators of lake condition after five years at each phosphorus-loading rate.
Selected indicators of lake condition after five years at each phosphorus-loading rate.
| Phosphorus loading / | Submerged-plant cover / | Mean summer dissolved oxygen / | Algal biomass / |
|---|---|---|---|
| 10 | 82 | 9.0 | 8 |
| 20 | 78 | 8.7 | 11 |
| 30 | 70 | 8.0 | 17 |
| 35 | 28 | 5.0 | 48 |
| 40 | 9 | 3.0 | 82 |
| 50 | 3 | 2.2 | 96 |
Identify the interval of phosphorus loading within which the lake appears to cross a tipping point.
[1]
Calculate the percentage decrease in mean summer dissolved oxygen as phosphorus loading increases from to .
[2]
Explain how the changes shown could move the lake into a new algae-dominated equilibrium.
[4]
Suggest why reducing phosphorus loading to just below the transition zone may not immediately restore the original clear-water ecosystem.
[1]
Question 20
Researchers investigated the salinity niche of a native estuarine snail. Laboratory survival and reproduction were measured without competitors. Field occupancy was measured where an introduced snail was present and again two years after the introduced snail was removed.
Figure 6 shows the results.
State the salinity range representing the native snail's fundamental niche in this investigation.
[1]
Compare the native snail's field distribution before and after removal of the introduced competitor.
[2]
Explain how the results distinguish between the fundamental and realized niches of the native snail.
[4]
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Question 21
A severe storm removed most vegetation from an island. Ecologists compared two terrestrial vertebrate species that recolonized the disturbed area. Figure 7 presents life-cycle information and population recovery five years after the storm.
Life-cycle traits and population recovery of two vertebrate species after a severe storm.
| Characteristic | Species X | Species Y |
|---|---|---|
| Age at first reproduction | 6 weeks | 8 years |
| Offspring per reproductive event | 400 | 1 |
| Parental care | None | Prolonged |
| Mean lifespan | 8 months | 45 years |
| Population after 5 years | 90% of pre-storm abundance | 8% of pre-storm abundance |
Identify the reproductive strategy most closely represented by each species.
[2]
Using the data, explain the difference in population recovery between the two species.
[4]
Suggest why classifying species as either -strategists or -strategists may oversimplify their vulnerability to disturbance.
[2]
Question 22
Warmer springs cause a woodland plant to flower three weeks earlier than in the past. The emergence date of its main insect pollinator changes very little.
Explain how this change could affect the populations of both species.
[4]
Question 23
A threatened stream frog has the characteristics shown in the fact file.
Explain how knowledge of the frog's classification, niche and life cycle can be used to predict the effects of road construction on its population.
[4]
Question 24
Lake Merin is a shallow lake surrounded by farmland. From years 1–5 it had clear water and extensive submerged vegetation. Fertilizer runoff then increased. Figure 4(a) models the lake as an open system. Figure 4(b) shows changes in nutrient input, summer dissolved oxygen and submerged-plant cover.
Figure 4(b): annual nutrient input, summer dissolved oxygen and submerged-plant cover in Lake Merin. Years 9–12 represent the turbid-state period; the transition occurs between years 8 and 9.
| Year | Nutrient input / tonnes per year | Summer dissolved oxygen / | Submerged-plant cover / |
|---|---|---|---|
| 1 | 18 | 8.2 | 72 |
| 2 | 20 | 8.0 | 74 |
| 3 | 19 | 8.1 | 71 |
| 4 | 21 | 7.9 | 70 |
| 5 | 22 | 7.8 | 68 |
| 6 | 28 | 7.4 | 65 |
| 7 | 34 | 6.8 | 58 |
| 8 | 43 | 5.9 | 46 |
| 9 | 48 | 3.1 | 17 |
| 10 | 50 | 2.0 | 8 |
| 11 | 49 | 2.3 | 9 |
| 12 | 47 | 2.5 | 10 |
Using Figure 4(a), state one input of matter and one output of energy from the lake ecosystem.
[2]
Calculate the percentage decrease in summer dissolved oxygen from year 1 to year 10.
[2]
Explain how increased nutrient input could have caused the lake to cross a tipping point between years 8 and 9.
[4]
Evaluate whether reducing external fertilizer runoff alone is likely to restore the clear-water ecosystem.
[4]
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Question 25
The silver cushion plant is native to a mountain system. Laboratory trials tested its survival across a temperature gradient in the absence of competitors. Field surveys recorded its abundance with and without a dominant grass competitor. Figure 6 presents the results.
Determine the operational fundamental temperature niche across the tested temperatures, using the mean-survival criterion shown in Figure 6.
[1]
Distinguish between the fundamental niche and the realized niche of the plant.
[2]
Analyse the effect of the grass competitor on the realized niche of the silver cushion plant.
[4]
Evaluate the use of these results to predict the plant’s distribution under future climate warming.
[5]
Question 26
A coastal wetland was restored after drainage channels were blocked in year 0. Three animal species colonized the wetland. Their life-cycle characteristics and population changes are shown in Figure 7.
Figure 7(a). Life-cycle characteristics of three wetland species and the disturbance during restoration.
| Species | Maturity / days or years | Eggs per event / number | Parental care / extent | Adult lifespan / days or years |
|---|---|---|---|---|
| Marsh midge | 12 days | 600 | None | 18 days |
| Reed frog | 1 year | 180 | Eggs guarded for 3 days | 4 years |
| Bog turtle | 9 years | 5 | Nest guarding and repeated juvenile care | 45 years |
| Main disturbance | Flood in year 4 | of exposed individuals removed | All three species | — |
Identify which species is closest to an -strategist and which is closest to a -strategist.
[2]
Calculate the percentage increase in the marsh midge population index from year 4 to year 5.
[2]
Explain how the life-cycle data account for differences in recovery after the flood.
[3]
Evaluate a proposal to use the marsh midge population alone as an indicator that wetland restoration has produced a stable community.
[5]
Question 27
Researchers monitored a spring-flowering woodland plant and its main insect pollinator between 2000 and 2025. Day 1 represents 1 January. Figure 8 shows changes in flowering date, pollinator emergence and seed production.
Changes in seasonal timing and seed set of a woodland plant, 2000–2025.
| Year | Peak flowering / day of year | Peak pollinator emergence / day of year | Successful seed set / % |
|---|---|---|---|
| 2000 | 130 | 128 | 72 |
| 2005 | 126 | 127 | 67 |
| 2010 | 122 | 125 | 61 |
| 2015 | 118 | 124 | 55 |
| 2020 | 114 | 122 | 49 |
| 2025 | 110 | 121 | 44 |
Calculate the difference between peak flowering and peak pollinator emergence in 2025.
[1]
Calculate the percentage decrease in successful seed set between 2000 and 2025.
[2]
Explain how the changes shown may affect the realized niches and life cycles of both species.
[4]
Suggest one reason why the data do not prove that the timing mismatch caused the decrease in seed set.
[1]
Question 28
Distinguish between density-dependent and density-independent factors affecting population size.
[4]
Explain why technological advances make the carrying capacity of human populations difficult to assess.
[7]
Using named examples, evaluate the usefulness of population-growth and carrying-capacity models for predicting the environmental impacts of human populations.
[9]
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Question 29
Explain why the niche of a species is more than its habitat.
[3]
Explain how the removal of a keystone predator may affect the sustainability of an ecosystem.
[8]
Using named examples, evaluate the claim that protecting keystone species is the most effective way to maintain ecosystem sustainability.
[9]
Question 30
Cladograms provide hypotheses about evolutionary relationships and common ancestry. Answer all parts.
Outline how a cladogram represents evolutionary relationships.
[4]
Explain why classification based on clades may differ from classification using the traditional taxonomic hierarchy.
[7]
Using named examples, evaluate the importance of evolutionary classification when deciding conservation priorities.
[9]
Question 31
Contrast the typical life-cycle characteristics of -strategists and -strategists.
[4]
Explain how reproductive strategy may influence population recovery and community change following a severe disturbance.
[7]
Using named examples, evaluate the usefulness of - and -strategist models for predicting species vulnerability to human disturbance.
[9]
Question 32
A long-term study investigated a spring-flowering woodland plant and its main solitary-bee pollinator. The plant flowers after accumulated spring warmth reaches a threshold. Bee emergence also responds to temperature, but less strongly. For this question, timing mismatch is defined as the signed difference between the day of bee emergence and the day of first flowering: bee-emergence day minus flowering day. Figure 8(a) shows the timing of both events, and Figure 8(b) shows the relationship between their timing mismatch and seed production.
Figure 8(a): spring warming, flowering, bee emergence, and signed timing mismatch.
| Year | Spring temperature anomaly / | Mean first flowering / day of year | Mean bee emergence / day of year | Timing mismatch / days (bee − flowering) |
|---|---|---|---|---|
| 1990 | 0.0 | 126 | 124 | −2 |
| 1995 | 0.2 | 124 | 123 | −1 |
| 2000 | 0.4 | 121 | 121 | 0 |
| 2005 | 0.6 | 119 | 120 | 1 |
| 2010 | 0.9 | 116 | 119 | 3 |
| 2015 | 1.1 | 113 | 117 | 4 |
| 2020 | 1.4 | 109 | 115 | 6 |
| 2025 | 1.7 | 106 | 113 | 7 |
Calculate the increase in timing mismatch between flowering and bee emergence from 1990 to 2025.
[2]
Analyse the relationship between spring warming, event timing and plant seed production.
[4]
Explain how the timing mismatch could alter the realized niches and life cycles of both species.
[3]
Evaluate the use of this study to predict the long-term effect of climate change on the woodland community.
[4]
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Question 33
Outline how an ecosystem may maintain a steady state while remaining an open system.
[4]
Explain how human disturbance can cause an ecosystem to cross a tipping point and enter a new equilibrium.
[7]
Using named examples, to what extent can protecting ecosystem integrity reverse the loss of biosphere integrity at the planetary scale?
[9]
Question 34
Distinguish between the fundamental niche and the realized niche of a species.
[3]
Explain how human disturbance may alter both the fundamental and realized niches of a species.
[8]
Using named examples, evaluate the usefulness of niche models for predicting the effects of climate change on species distributions.
[9]
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