Population and Population Attributes - Life History Variation

Populations evolve to maximise reproductive fitness or Darwinian fitness in their habitat. Reproductive fitness means the successful contribution of an organism to the next generation.
Under different selection pressures, organisms evolve the most suitable reproductive strategy.

• Life history traits include growth, reproduction, survival, lifespan, number of offspring, and offspring size.
• Different species show different life history patterns depending on the abiotic and biotic conditions of the habitat.
• This variation helps organisms survive and reproduce more successfully.

Types of strategies:

• Some organisms reproduce only once in their lifetime; these are called semelparous organisms.
• Examples: Pacific salmon fish and bamboo.
• Some organisms reproduce many times in their lifetime; these are called iteroparous organisms.
• Examples: most birds and mammals.

Offspring pattern:

• Some organisms produce a large number of small-sized offspring.
• Examples: oysters and pelagic fishes.
• Some organisms produce a small number of large-sized offspring.
• Examples: birds and mammals.

Why it happens:

• Life history traits evolve according to selection pressures in the environment.
• Both abiotic factors and biotic factors influence these strategies.
• Therefore, no single reproductive strategy is best for all organisms.

• Organisms evolve life history strategies to maximise reproductive (Darwinian) fitness in their environment.
• Different species adopt different strategies based on selection pressures.
• Some organisms reproduce once in a lifetime (e.g., salmon, bamboo), while others reproduce multiple times (e.g., birds, mammals).
• Species may produce many small offspring (e.g., oysters) or few large offspring (e.g., mammals), depending on survival needs.
• These variations are shaped by biotic and abiotic factors, and studying them is an important area in ecology.