8: Ecology

Ecology

• Now that we’ve learned about non-human primate and human origins, we will go into the modern synthesis of evolution in more detail

• Modern synthesis of evolution:

  • Darwinian evolution + Mendelian genetics

Ecology Terms

• Environment – forces that an organism interacts with

• Population – group of individuals of the same species that occupy the same area and interbreed

• Habitat – where population lives

• Niche – how population interacts with resources and survives in its environment (kind of like a “profession”)

• Adaptation – genetic traits that facilitate survival and reproductive success

• Ecosystem – community of interacting organisms

Lamarck

• Jean Baptiste de Lamarck (1744-1829)

  • Restated Hippocrates’ inheritance of acquired characteristics

  • Argued that individuals could adapt themselves to improve their survival, and offspring would inherit these traits

• Example: If you go to the gym regularly and build muscle mass, you would have a child that is born muscular…

  • Individual -> modifies themselves -> child is born with improved trait

  • Not exactly correct, but contributed to early understandings of evolutionary theory

Charles Darwin and Alfred Russel Wallace

• You can learn more about Darwin and Wallace in Evolution 101!

• Darwin is famous for his examination of finches, tortoises, and iguanas on the Galapagos islands

  • Ancestral finch species migrated to different island on the Galapagos

    • Lead to adaptive radiation of several different varieties with different beaks, based on food types

• Darwin and Wallace presented their findings jointly

  • Natural selection – differential survival and reproduction of individuals due to differences in phenotype

  • Both formulated theory of natural selection, but Darwin expanded on common ancestry

Four Principles of Natural Selection

• Variation

  • There are differences between individuals of same species

• Overproduction

  • Species produce more offspring than the environment can support

• Competition

  • Limited resources means there’s competition for survival

• Selection

  • Traits that improve survival make it more likely for an individual to survive and reproduce (passing down that trait)

Caveats

• Natural selection is based on adaptation (traits that improve survival)

  • Keep in mind that there are evolutionary mechanisms other than natural selection

• Traits that are advantageous in one context may be disadvantageous in another context

• Adaptations don’t arise just because there is a “need”

• The longer it takes a species to reproduce, the longer it may take for evolutionary processes to have an effect on a population

• Natural selection does not lead to perfection of traits

  • Traits are more often “good enough” to get the job done; they may provide advantages in one context and disadvantages in another context

    • Ex: cheetahs have long and thin limb bones which allow them to run at faster speeds; however, their limbs are also prone to fracturing

• Individuals do not evolve or spawn adaptations in their lifetimes; Populations evolve

• Not every trait or characteristic is an adaptation

Adaptation

• Adaptation: inherited trait that improves survival and reproduction

  • The evolutionary term is different from everyday usage of the word

    • Scientific term does NOT refer to an individual adjusting to one’s environment

• Must be genetically inherited

  • Individuals cannot necessarily change their genes by changing their lifestyles

• Random mutation in DNA that does not affect survival?

  • Not an adaptation

• Byproduct of another characteristic?

  • Not an adaptation

    • Ex: Color of blood (byproduct of its chemistry – the color red is not an adaptation)

• Some traits may have been adaptations in the past but are no longer adaptations

• Some traits perform a function that does not improve survival (peacock tail feathers are more important for mating, for example)

• Many traits are neutral; few traits are adaptations

True or False?

1. Natural selection is not a random process.

   • T – NS is not random because environmental conditions lead to an increase in certain traits getting inherited.

2. Natural selection always removes harmful genes from the gene pool.

   • F – NS acts on traits that improve survival.  Furthermore, fitness doesn’t necessarily have anything to do with lifespan…reproduction plays a bigger role.  “Harmful” genes can continue to get passed down if they don’t affect reproduction…

3. Natural selection is the survival of the fittest.

   • F – NS involves survival AND reproduction.  Survival is only one part of it.  If you and others are being chased by zombies, you don’t have to be the fastest to survive…just faster than others.  NS doesn’t lead to perfection.  NS isn’t an “accomplishment.”  It doesn’t result in something “better.”

4. Organisms evolve in response to a change in an environment.

   • F – The issue with this statement is with the word “organisms” (implying individuals evolve) because evolution happens at the population-level.  It would be more accurate to say “populations evolve.”  

5. Applying antibiotics to a population of bacteria will cause a mutation for antibiotic resistance to arise.

   • F – Many bacterial species already have genetic resistance when born.  Mutations are random and are a separate force from natural selection.  Natural selection does not affect the rate of mutation.  It is more likely for natural selection to act on genetic variation that already exists in the population.

Photos:

• See Google slides below: