Fitness and Selection

 Fitness and Selection

Within biology, absolute fitness is the overall reproductive success of an organism throughout their lifetime, not compared to any other organisms in their population. Relative fitness, on the other hand, takes into account the fitness of the organisms around them within the population. A species of snail with no patterns on its shell could produce 100 offspring throughout its lifetime. Although this is a fairly fit snail because it was able to produce many offspring, another snail in the same area has blue spots on it and produces 130 offspring in its lifetime. This shows that the absolute fitness of the plain snail is different than its relative fitness, because relative to the snail with spots, it is not as fit. 

Relative fitness of plain snail:
Relative fitness of spotted snail:

Initial population dynamics:
Plain snails: 100 Offspring
Spotted snails: 130 Offspring

An increase of blue flowers in their ecosystem allows the blue spotted snails to camouflage better and therefore, survive longer. This causes the plain snails to have increased predation, and struggle to survive. The plain snails are still alive, but over the next 5-10 years their population has decreased dramatically compared to the spotted snails. Because the population is starting to favor the phenotype of snail that produces more offspring, the amount of snails with spots will increase exponentially over the next decade, compared to the plain snails. For the next 10-20 years the population will continue to stabilize and favor the more profitable and successful trait. The spotted snails will contribute to roughly 90% of the snail population. 

Possible final population dynamics:
Plain snails: 27 Offspring
Spotted snails: 207 Offspring

In this example, some of the driving forces included environmental changes, increased predation. and snails increased mating preferences. Within 30-50 years, the spotted snails have exhibited positive selection, as the beneficial trait of having spots increased in frequency.

Comments

  1. GeminiSeptember 29, 2024 at 9:07 PM

    I think you've done a great job of explaining absolute fitness, but I did have a suggestion about the relative fitness. When we just look at the reproductive success and we don't take into account how many of the offspring have made it to adulthood, you would just divide each reproductive rate by the highest reproductive rate in the population. I think your explanation on how environmental factors influences positive selection was thorough :)!

    ReplyDelete
  2. LaylaOctober 6, 2024 at 12:56 PM

    Absolutely love how you broke it down mathematically, however this blog could’ve benefitted from an image.

    ReplyDelete

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