#r-strategists

Survivorship and rK Strategies

CSIR-NET: Which trait is NOT typical of r-strategists?

Density-dependent mortality is not part of the classic r-selected syndrome emphasized for organisms in ephemeral habitats. r strategists are expected to encounter substantial density-independent mortality from disturbance, weather, or temporary resource loss, often before crowding becomes decisive. Rapid development, strong dispersal, and effective colonization help them exploit newly available sites where competition is initially weak. Survivorship and reproductive schedules are connected through allocation. An organism has finite energy for growth, maintenance, defense, and reproduction; investment in one function constrains the others. Natural selection does not pursue a universal ideal. It favors combinations that leave more surviving descendants under the mortality risks and resource patterns experienced by a population. The decisive distinction is therefore between a descriptive label and the demographic mechanism that generates it. Interpreting the example at the appropriate population scale keeps the causal mechanism distinct from a simple correlation or an absolute rule. Ecological predictions remain conditional on the stated environment, because changing resources, mortality, or interactions can alter the observed demographic pattern.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 12

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Survivorship and rK Strategies

Which trait is NOT typical of r-strategists?

High parental investment is inconsistent with the usual r-selected syndrome. Early reproduction, short generation time, many small offspring, effective dispersal, and use of disturbed habitats all promote rapid colonization. Extensive care consumes time and energy per offspring, reduces the number produced, and is more characteristic of the K-selected end, where competition is intense and survival of each juvenile has high value. Life-history traits should be interpreted as correlated tendencies rather than rigid packages. Adult survival, juvenile mortality, body size, development time, fecundity, and parental investment interact. The central reasoning is evolutionary allocation: selection favors the schedule that maximizes lifetime reproductive success within a particular environment, even when that schedule reduces survival or reproduction at another stage. This causal chain is what makes the keyed content ecologically meaningful rather than merely definitional. 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: Concepts and Applications, Molles, 9th Ed., Ch. 12

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Survivorship and rK Strategies

In r-strategists, population size is usually:

Populations described as r-selected often fluctuate widely. Their rapid reproduction permits abrupt increases after rain, disturbance, or release from enemies, but short-lived resources and density-independent events can cause equally abrupt declines. Such populations need not cycle regularly; variable captures their tendency to track unpredictable opportunities rather than remain close to a stable carrying capacity. A survivorship curve is built from a cohort life table by plotting the proportion alive at each age. Type I concentrates mortality late, Type II approximates a constant hazard, and Type III concentrates mortality early. These are descriptive models, so a species may shift between them when predators, care, climate, or habitat quality changes. Reading the terms biologically, rather than memorizing labels, shows how individual survival and reproduction scale up to population change. Ecological predictions remain conditional on the stated environment, because changing resources, mortality, or interactions can alter the observed demographic pattern. This interpretation connects individual-level processes with measurable changes in survival, reproduction, recruitment, or abundance across the population.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 12

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Survivorship and rK Strategies

Which of these is NOT a trait of r-strategists?

The keyed exception is “High parental care.” In the context of which of these is not a trait of r-strategists, that statement differs from the governing ecological pattern and must be evaluated against the mechanism rather than accepted from wording alone. 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—“High dispersal ability”, “High reproductive rate”, “Small body size”—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. 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. 12

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Survivorship and rK Strategies

The r in r-selection stands for:

“Growth rate” for the r in r-selection stands for. 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—“Reproductive energy”, “Resource richness”, “Resistance”—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. This distinction matters because similar surface patterns can arise through different mechanisms, whereas ecological prediction depends on identifying the mechanism that actually changes rates. The cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 12

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