8 public questions tagged with this topic.
An age pyramid represents the proportion of individuals in different age groups within a population, providing insights into its growth trend.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Attributes - Birth Death Sex Ratio Age Distribution
Population density is influenced by natality (birth rate), mortality (death rate), immigration (arrival), and emigration (departure).
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Attributes - Birth Death Sex Ratio Age Distribution
A bell-shaped age pyramid represents a stable population with nearly equal birth and death rates.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Attributes - Birth Death Sex Ratio Age Distribution
The simplest two-sample Lincoln–Petersen mark–recapture model assumes demographic and geographic closure between sampling occasions. No births, deaths, immigration, or emigration should change the population or alter the proportion of marked individuals. Under closure, the marked fraction after thorough mixing remains interpretable, allowing M/N ≈ R/C and N ≈ MC/R. Quadrat and transect methods sample spatial units and do not inherently require a closed population in the same formal sense, although movement during counting can still create error. Satellite methods track individuals and may explicitly measure movement rather than assume its absence. Closure is an approximation whose plausibility depends on study duration and boundary design; investigators can shorten intervals or choose natural boundaries to improve it. Open-population capture–recapture models, such as Cormack–Jolly–Seber approaches, relax closure and estimate survival or recruitment from multiple occasions. Other assumptions remain important even in a closed study: marks must persist, capture probabilities should be comparable, marking must not affect organisms, and individuals must mix before recapture.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 9
In the standard continuous population-growth notation, b denotes the per-capita birth rate: the expected number of births contributed per individual per unit time. Multiplying b by population size gives the total birth input B = bN under a homogeneous model. Similarly, d is the per-capita death rate and D = dN. Their difference gives the instantaneous per-capita growth rate r = b − d, leading to dN/dt = (b − d)N for a closed population. A raw birth number is an absolute count and is usually written B, so distinguishing uppercase totals from lowercase per-capita rates prevents dimensional errors. Body mass and biomass are unrelated ecological quantities despite sharing the initial letter. Per-capita rates allow comparison among populations of different sizes: 100 births in a population of 1,000 is a higher birth rate than 100 births in a population of 10,000. The notation is conventional rather than universal, so any analysis should define symbols and time units explicitly, especially when age-specific birth schedules replace a single average b.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 11
“Rectangular” for which age structure has equal width for all age groups. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Selection favors the schedule that increases lifetime reproductive success under local mortality and resource conditions. Body size, development time, fecundity, parental investment, and generation length consequently tend to covary. The remaining alternatives—“Pyramid”, “Bell-shaped”, “Urn-shaped”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Life-history traits reflect allocation among growth, maintenance, survival, and reproduction. Energy invested in many offspring cannot simultaneously be invested in large offspring, prolonged care, or future breeding, creating measurable trade-offs. The cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit. Linking the wording to measurable consequences for fitness, abundance, or flux gives the conclusion its scientific meaning and prevents a purely mnemonic interpretation.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 10
“qx” for which of the following is a measure of age-specific death rate. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Life-history traits reflect allocation among growth, maintenance, survival, and reproduction. Energy invested in many offspring cannot simultaneously be invested in large offspring, prolonged care, or future breeding, creating measurable trade-offs. The remaining alternatives—“lx”, “dx”, “mx”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Survivorship curves summarize age-specific mortality: Type I concentrates loss late in life, Type II approximates a constant hazard, and Type III concentrates loss early. They are empirical patterns, not rigid taxonomic rules. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors. This distinction matters because similar surface patterns can arise through different mechanisms, whereas ecological prediction depends on identifying the mechanism that actually changes rates.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 10
“Group of individuals of the same age” for a cohort refers to. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Survivorship curves summarize age-specific mortality: Type I concentrates loss late in life, Type II approximates a constant hazard, and Type III concentrates loss early. They are empirical patterns, not rigid taxonomic rules. The remaining alternatives—“Entire population”, “A single individual”, “Randomly selected population”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Selection favors the schedule that increases lifetime reproductive success under local mortality and resource conditions. Body size, development time, fecundity, parental investment, and generation length consequently tend to covary. Linking the wording to measurable consequences for fitness, abundance, or flux gives the conclusion its scientific meaning and prevents a purely mnemonic interpretation. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 10
