Read the passage and answer the following questions:
Organisms evolve in their respective habitats to maximise their reproductive fitness, also known as Darwinian fitness, which is often measured by a high "r" value. They adapt to the specific selection pressures present in their environment by developing the most efficient reproductive strategies. This includes variations in breeding frequency and the number and size of offspring produced. Some organisms, such as Pacific salmon fish and bamboo, exhibit a strategy known as semelparity, where they breed only once in their lifetime. In contrast, most birds and mammals follow an iteroparous strategy, breeding multiple times throughout their lives. Additionally, some species, like oysters and pelagic fishes, produce a large number of small-sized offspring, while others, such as birds and mammals, produce a small number of large-sized offspring. The desirable reproductive strategy for maximising fitness depends on the specific conditions and selection pressures within the habitat. Ecologists emphasise that the evolution of life history traits is influenced by the constraints imposed by the abiotic and biotic components of the environment. Factors such as resource availability, competition, predation, and other ecological interactions shape the evolution of these traits. Thus, populations evolve to maximise reproductive fitness in their habitats, and the specific reproductive strategies and traits they adopt depend on the selection pressures and constraints present in their environment. Ecologists investigate these relationships to uncover the mechanisms behind the evolution of life history traits and their ecological significance.
The intrinsic rate of natural increase (r) of a population is a measure of:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → the inherent potential of the population to grow
Population growth is written as dN/dt = rN, where N is the population size and r = b – d (per capita birth rate minus per capita death rate). This r is the intrinsic rate of natural increase. It shows how fast a population can grow by itself, so a high r value is used to measure Darwinian fitness.
Option (1) the inherent potential of the population to grow — Correct. r is a measure of the inherent potential of a population to grow. When resources are unlimited, a population grows exponentially at this rate.
Option (2) the carrying capacity of the habitat — Incorrect. The carrying capacity is written K. It is the largest population a habitat can support with its resources, so it belongs to the habitat, not to the growth potential of the population.
Option (3) the number of individuals per unit area (population density) — Incorrect. Population density (N) is the size of the population at a given time. r is not the size but the rate at which that size can change.
Option (4) the number of offspring produced in one breeding event — Incorrect. The number of offspring in one breeding event is a life history trait (as in oysters against birds). r combines births and deaths per individual over time, not offspring per breeding event.
NCERT Extract:
Population Growth – “… The r in this equation is called the ‘intrinsic rate of natural increase’ and is a very important parameter chosen for assessing impacts of any biotic or abiotic factor on population growth.”
Summary – “… When resources are unlimited, the growth is usually exponential but when resources become progressively limiting, the growth pattern turns logistic. In either case, growth is ultimately limited by the carrying capacity of the environment. The intrinsic rate of natural increase (r) is a measure of the inherent potential of a population to grow.”