Natural selection and ecology flashcards

Natural selection is the process by which individuals with heritable traits better suited to their environment survive and reproduce more successfully, shifting allele frequencies in a population over time. Students must understand the four conditions required for natural selection: variation, heritability, differential survival and reproduction, and selection pressure. Ecology examines how organisms interact with each other and their abiotic environment, including concepts like population dynamics, carrying capacity, predator-prey relationships, and community structure. The connection between the two fields is critical: ecological pressures such as competition, predation, and resource availability act as agents of natural selection, driving evolutionary change. Students should also understand how fitness is measured, the types of natural selection (directional, stabilizing, disruptive), and how ecological relationships like coevolution and symbiosis reflect evolutionary history.

1. Card 1

   What are the four conditions required for natural selection to occur?

   Variation in traits, heritability of those traits, differential survival and reproduction, and a selection pressure acting on the population.

2. Card 2

   How is biological fitness defined in the context of natural selection?

   Fitness is the relative ability of an organism to survive and reproduce in its environment, passing its alleles to the next generation.

3. Card 3

   What is the difference between directional, stabilizing, and disruptive selection?

   Directional selection favors one extreme phenotype; stabilizing selection favors the intermediate; disruptive selection favors both extremes over the middle.

4. Card 4

   What is carrying capacity and how does it relate to population growth?

   Carrying capacity (K) is the maximum population size an environment can sustain. As a population approaches K, logistic growth slows due to limited resources.

5. Card 5

   What is the difference between r-selected and K-selected species?

   r-selected species reproduce rapidly with many offspring and little parental care; K-selected species produce fewer offspring with greater investment in each.

6. Card 6

   How do predator-prey relationships act as agents of natural selection?

   Predation creates selection pressure that favors prey traits aiding escape and predator traits aiding capture, driving coevolution between the two populations.

7. Card 7

   What is coevolution and give one ecological example?

   Coevolution is reciprocal evolutionary change between interacting species. Example: flowering plants and their pollinators evolving complementary structures together.

8. Card 8

   What distinguishes interspecific competition from intraspecific competition?

   Interspecific competition occurs between different species; intraspecific competition occurs within the same species and is often the stronger selective force.

9. Card 9

   What is a niche and how does competition shape it?

   A niche is the full range of conditions and resources a species uses. Character displacement can occur when competition causes species to evolve more distinct niches.

10. Card 10

    What is the difference between mutualism, commensalism, and parasitism?

    Mutualism benefits both species; commensalism benefits one with no effect on the other; parasitism benefits one organism while harming the host.

11. Card 11

    How does the concept of relative fitness connect allele frequency to natural selection?

    Alleles that increase relative fitness become more common over generations because carriers leave more offspring, shifting allele frequencies in the population.

12. Card 12

    Why does natural selection act on phenotype but evolution occurs at the level of genotype?

    Selection pressure acts on expressed phenotypes, but only heritable genetic changes in allele frequencies across generations constitute true evolutionary change.

• Students often say organisms 'choose' to adapt or that individuals evolve, when in reality natural selection acts on populations over generations, not on individual organisms during their lifetimes.
• A common error is confusing fitness with physical strength or size; biological fitness specifically means reproductive success and the ability to pass alleles to offspring, not general health or dominance.
• Students frequently assume that stabilizing selection leads to no evolutionary change, but it actively removes extreme phenotypes and maintains the current mean, which is itself a form of ongoing selection.

Planning your revision? Read how to revise AP Biology, or make cards from your own notes with the notes to flashcards tool.