“Organisms and Populations” is central to understanding population growth, life-table parameters, dispersal/metapopulation dynamics, and sustainable harvesting—topics that commonly appear in CBSE Class 12 board exams and also form the conceptual base for higher-level questions in competitive exams. This set focuses on key quantitative models (exponential, logistic, Allee effect, age-structured growth, mark–recapture, and metapopulation/harvest models) to build strong problem-solving accuracy and interpretation.
20
Minutes
15
Questions
1 / -0
Marking
Q1. A population grows exponentially with intrinsic rate of increase and initial size . Using , after approximately how many days will the population reach individuals?
30 days
40 days
34.7 days
17.3 days
Q2. A life table for a species gives number alive at start of age 0 = 100, at start of age 1 = 40, and at start of age 2 = 20. Fecundity (daughters per female) is at age 1 and at age 2. Using with as proportion surviving to start of age (take ), what is the net reproductive rate ?
1.1
0.96
1.6
2.1
Q3. Consider a population with net reproductive rate . Evaluate the statements:
(I) The total population size will necessarily decrease in the next few years.
(II) If the current age structure is heavily weighted toward reproductive-age individuals, the total population may still increase in the short term despite .
Which option is correct?
Both (I) and (II) are true, and (II) explains (I)
Both (I) and (II) are true, but (II) does not explain (I)
Only (I) is true
Only (II) is true
Q4. A species exhibits a strong Allee effect; its deterministic dynamics can be approximated by
with and critical threshold . Two identical reserves are stocked with founders: Reserve A with individuals and Reserve B with individuals. Assuming no immigration and deterministic dynamics, which outcome is most likely?
Reserve A (40 individuals) will decline toward extinction, while Reserve B (60 individuals) will decrease toward the critical threshold .
Reserve A (40 individuals) will decline toward extinction (below ) while Reserve B (60 individuals) will increase toward the carrying capacity.
Both reserves' populations will decline toward extinction because for both reserves.
Both reserves' populations will approach because at .
Q5. In a local population per capita birth rate is , death rate , immigration per capita and emigration per capita . For initial population and ignoring density dependence, what is the expected population size after one year? (Use where .)
1120
1200
1000
1080
Q6. A 2000 m grassland is sampled using five 1 m quadrats. Counts of a plant species in the quadrats are 7, 9, 8, 6 and 10. Using the quadrat estimator (where is mean count per quadrat, total area and quadrat area), estimate the total number of individuals in the grassland.
8000 individuals
16000 individuals
2000 individuals
40000 individuals
Q7. A population follows logistic growth given by . For and , calculate the instantaneous growth rate when and state the immediate trend.
Population will decrease at a rate of 192 individuals per year.
Population will increase at a rate of 48 individuals per year.
Population will increase at a rate of 768 individuals per year.
Population will increase at a rate of 192 individuals per year.
Q8. A wetland is surveyed using the Lincoln–Petersen mark–recapture method. In the first visit frogs were captured, marked and released. After mixing, a second visit captured frogs, among which were marked. Using , estimate the population size and state how loss of marks (some marked frogs losing their marks before recapture) would bias the estimate.
; mark loss would cause an overestimate of true population size.
; mark loss would cause an underestimate of true population size.
; mark loss would cause an overestimate of true population size.
; mark loss would not affect the estimate.
Q9. For a population with age classes the survivorship and fecundity are: Compute , and approximate intrinsic rate . Which choice best represents and the population trend?
— population increasing rapidly
— population declining
— population slowly increasing
— population increasing very rapidly
Q10. A model with a strong Allee effect has per-capita growth rate , so . Let , , . If the initial population is , what is the most likely fate of the population?
Population will increase slowly and approach carrying capacity .
Population will decline toward extinction because is below the Allee threshold .
Population will overshoot and exhibit sustained oscillations around .
Population will increase initially and then stabilize at the Allee threshold .
Q11. In a grassland study, 30 individuals of a beetle species were captured, uniquely marked and released. A week later 45 individuals were captured, of which 15 were marked. Using the Lincoln–Petersen estimator , estimate the population size.
60
90
75
120
Q12. A population follows discrete geometric growth . If and , compute and predict (round to nearest integer).
225
257
320
293
Q13. For a species the life table values are: age ; survivorship ; fecundity . Using , and , which statement is correct?
Net reproductive rate , mean generation time time‑units, intrinsic rate — population increasing.
Net reproductive rate , mean generation time , intrinsic rate — population marginally increasing.
Net reproductive rate , so and population is declining.
Net reproductive rate but so the population is decreasing.
Q14. In the Levins metapopulation model the equilibrium fraction of occupied patches is where is colonization rate and extinction rate. If initially and , and fragmentation reduces to while remains unchanged, which of the following is correct?
Initially ; after fragmentation so occupancy halves.
Initially ; after fragmentation leading to slow decline.
Initially ; after fragmentation — the model predicts global extinction of the metapopulation.
is unaffected by colonization changes if extinction is constant.
Q15. A fish stock follows , where is constant harvest. Maximum sustainable yield is obtained at . For and , calculate MSY and state the likely outcome if managers set a constant annual harvest .
individuals/yr; since there is no sustainable positive equilibrium and the population will decline toward extinction if harvesting continues.
individuals/yr; because only slightly exceeds MSY the population will settle at a lower but stable equilibrium above zero.
individuals/yr; therefore equals MSY and the population will be sustainably harvested.
individuals/yr; the system will oscillate around but remain sustainable despite .