9 public questions tagged with this topic.
Body mass is a characteristic of an individual, while population attributes include age distribution, sex ratio, and density.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Attributes - Birth Death Sex Ratio Age Distribution
High birth rates contribute to population growth, whereas emigration, mortality, and lack of resources lead to population decline.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Attributes - Birth Death Sex Ratio Age Distribution
If birth rate and immigration exceed death rate and emigration, the population size will increase.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Attributes - Birth Death Sex Ratio Age Distribution
Birth rate and death rate are key factors that regulate population growth and size.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Attributes - Birth Death Sex Ratio Age Distribution
Carrying capacity is not constant; it varies based on environmental conditions and resource availability.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Attributes - Birth Death Sex Ratio Age Distribution
Age distribution helps predict future population growth by showing the proportion of individuals in reproductive and pre-reproductive stages.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Attributes - Birth Death Sex Ratio Age Distribution
In the cited dune-fescue example, drought stress is identified as the main source of mortality. Limited soil moisture can prevent seedlings from establishing and can kill established plants through loss of turgor, reduced photosynthesis, and hydraulic failure. Because weather-driven moisture deficits may strike across densities, this case illustrates how an abiotic event can dominate mortality without providing reliable population-regulating feedback. Demographic mechanisms are linked by the balance dN/dt = births + immigration - deaths - emigration. Density-dependent changes in any of these terms can alter net growth. To infer regulation, ecologists compare per-capita rates across densities and distinguish causal feedback from coincidental correlations produced by weather, age structure, or habitat quality. This reasoning also explains why field observations may be approximate even when the underlying textbook classification is useful. This interpretation connects individual-level processes with measurable changes in survival, reproduction, recruitment, or abundance across the population. Field evidence should therefore be compared with the model assumptions before extending the conclusion to every species, habitat, or time period.
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 5
“Type II” for which survivorship curve is linear. 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—“Type I”, “Type III”, “None”—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. 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. 12
“Density-independent” for in r-selected species, mortality is. 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—“Density-dependent”, “Late-life driven”, “Genetically fixed”—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. 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. 12
