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Biology LibreTexts

3: Evolution and Ecology

  • Page ID
    • 3.1: Origin of Biodiversity
    • 3.2: Mechanisms of Evolution
      Four factors that can change the allele frequencies of a population. Natural selection works by selecting for alleles that confer beneficial traits or behaviors, while selecting against those for deleterious qualities. Mutations introduce new alleles into a population. Genetic drift stems from the chance occurrence that some individuals have more offspring than others and results in changes in allele frequencies that are random in direction.
    • 3.3: Evidence of Evolution
      The evidence for evolution is found at all levels of organization in living things and in the extinct species we know about through fossils. Fossils provide evidence for the evolutionary change through now extinct forms that led to modern species. For example, there is a rich fossil record that shows the evolutionary transitions from horse ancestors to modern horses that document intermediate forms and a gradual adaptation t changing ecosystems.
    • 3.4: Speciation
      Speciation occurs along two main pathways: geographic separation (allopatric speciation) and through mechanisms that occur within a shared habitat (sympatric speciation). Both pathways force reproductive isolation between populations. Sympatric speciation can occur through errors in meiosis that form gametes with extra chromosomes, called polyploidy. Autopolyploidy occurs within a single species, whereas allopolyploidy occurs because of a mating between closely related species.
    • 3.5: Common Misconceptions about Evolution
      Although the theory of evolution initially generated some controversy, by 20 years after the publication of On the Origin of Species it was almost universally accepted by biologists, particularly younger biologists. Nevertheless, the theory of evolution is a difficult concept and misconceptions about how it works abound. In addition, there are those that reject it as an explanation for the diversity of life.
    • 3.7: Introduction to Ecology
    • 3.8: Organismal Ecology and Population Ecology
    • 3.9: 1.4 Linking Ecology and Evolution
      In 1973, evolutionary biologist Theodosius Dobzhansky wrote a now-famous essay titled Nothing in Biology Makes Sense Except in the Light of Evolution. In this essay, Dobzhansky argued that evolution is the underlying unifying theme for all of biological study and that understanding life on earth necessarily requires considering evolutionary processes and impacts. The title of this essay became a famous quote highlighting the foundational importance of evolution to all biological concepts and pro
    • 3.10: Community Ecology
      Populations typically do not live in isolation from other species. Populations that interact within a given habitat form a community. The number of species occupying the same habitat and their relative abundance is known as the diversity of the community. Areas with low species diversity, such as the glaciers of Antarctica, still contain a wide variety of living organisms, whereas the diversity of tropical rainforests is so great that it cannot be accurately assessed.
    • 3.11: Symbiosis
      There are many cases, however, where two species live in close association for long periods. Such associations are called symbiotic ("living together"). In symbiosis, at least one member of the pair benefits from the relationship. The other member may be injured (parasitism), relatively unaffected (commensalism) or may also benefit (mutualism).
    • 3.12: Organizing Life on Earth
    • 3.6: Micro and Macroevolution
      At its simplest, evolution is any change in heritable traits in a population of organisms across generations. These changes may be the result of natural selection, genetic drift, mutation, etc – processes that we will consider in depth later in the course. All populations experience evolutionary change, as influenced by their environment, their interactions with other organisms, and random chance. Like ecology, we can consider evolution at different scales.