How Biological Diversity Evolves

Biology and Society: Humanity’s Footprint

  • Humanity significantly impacts Earth's ecology and geology.

  • Ecology studies organism-environment relationships.

  • A biome is a major life zone defined by vegetation (terrestrial) or physical environment (aquatic).

  • Human impact includes species relocation, agriculture, manufactured materials, radioactivity, and climate change.

  • The Anthropocene is a proposed new epoch marked by high extinction rates and accelerated environmental change due to human activity.

What Is a Species?

  • Species: a group of populations with the potential to interbreed and produce fertile offspring.

  • Biological species concept limitations: asexual organisms and fossils.

  • Reproductive compatibility is key, not physical similarity.

Reproductive Barriers between Species

  • Reproductive barrier: prevents interbreeding between closely related species.

    • Prezygotic barriers: prevent mating or fertilization.

    • Postzygotic barriers: operate after interspecies mating and hybrid zygote formation.

Prezygotic Barriers Include:

  • Temporal Isolation

  • Habitat Isolation

  • Behavioral Isolation

  • Mechanical Isolation

  • Gametic Isolation

Postzygotic Barriers Include:

  • Reduced Hybrid Viability

  • Reduced Hybrid Fertility

  • Hybrid Breakdown

Evolution: Mechanisms of Speciation

  • Speciation occurs when a population is isolated from the parent species.

    • Allopatric speciation: geographic barrier isolates a population.

    • Sympatric speciation: new species arise within the same geographic area.

Allopatric Speciation

  • Involves geographic isolation leading to reproductive barriers.

Sympatric Speciation

  • Occurs within the same geographic area due to:

    • Polyploidy: extra chromosome set due to cell division errors (e.g., 2n2n to 4n4n).

    • Habitat complexity.

    • Sexual selection.

Polyploid Speciation

  • Can arise from a single parent species or hybridization of two species.

  • Many food plants are polyploids.

Island Showcases of Speciation

  • Islands like the Galápagos demonstrate speciation.

  • Isolation and diverse habitats promote species divergence.

  • Galápagos finches: 14 species with specialized beaks for different diets.

Observing Speciation in Progress

  • Speciation can be observed in populations diverging due to different food resources or breeding habitats.

Earth History and Macroevolution

  • Macroevolution: evolutionary change above the species level.

  • Includes mass extinctions and key adaptations.

  • Understanding macroevolution requires examining geologic time.

The Geologic Time Scale

  • Divides Earth's history into periods and epochs.

The Fossil Record

  • Uses radiometric dating to determine the age of rocks and fossils.

  • Plate tectonics theory: the Earth's crust is divided into plates that float on the mantle.

  • Continental drift: plate movements reshape the planet and alter environments.

Plate Tectonics and Biogeography

  • Continental drift impacts life's evolution.

  • Pangaea: supercontinent that formed about 250 million years ago.

  • Breakup of Pangaea caused geographic isolation and divergent evolution.

  • Biogeography studies the distribution of organisms.

Mass Extinctions and Explosive Diversifications of Life

  • Five mass extinctions in the last 540 million years, each eliminating at least 50% of species.

    • Permian extinction: 96% of marine species died.

    • Cretaceous extinction: eliminated dinosaurs (except birds).

  • Extinctions create new environmental opportunities for survivors.

Diversification of Mammals

  • Mammals diversified after the dinosaur extinction.

Mechanisms of Macroevolution: Large Effects from Small Genetic Changes

  • Evo-devo studies how genetic changes cause structural differences among species.

  • Changes in the rate, timing, and spatial pattern of development can lead to evolutionary transformations.

The Evolution of Biological Novelty: Adaptation of Old Structures for New Functions

  • Complex structures evolve in small steps.

  • Exaptations: structures that evolve in one context but are co-opted for another function.

  • Examples: feathers initially for insulation, later for flight.

From Simple to Complex Structures in Gradual Stages

  • Complex structures evolve from simpler versions with the same basic function.

  • Complex eyes evolved through incremental modifications.

Classifying the Diversity of Life: Classification and Phylogeny

  • Taxonomy: naming and classifying species.

  • Systematics: includes taxonomy and evolutionary relationships.

  • Phylogenetic trees: depict evolutionary history and hierarchical classification.

Identifying Homologous Characters

  • Homologous structures: similar due to common ancestry (divergent evolution).

  • Convergent evolution: analogous structures with similar functions but different origins.

  • Comparing embryonic development and DNA sequences reveals homology.

Inferring Phylogeny from Homologous Characters

  • Cladistics: groups organisms by common ancestry.

  • Clade: ancestral species and all its descendants.

  • Ingroup vs. Outgroup: comparing the group being studied to a related group that diverged earlier.

How Cladistics Is Shaking Phylogenetic Trees

  • Cladistics clarifies evolutionary relationships.

Classification: A Work in Progress

  • Classification systems have evolved from two kingdoms to five kingdoms to three domains.

  • Three-domain system: Bacteria, Archaea, and Eukarya.

Evolution Connection: Evolution in the Anthropocene

  • The Anthropocene offers opportunities to study evolutionary adaptation in human-impacted environments.

  • Examples: resistance to pollutants, adaptation to urban surfaces, and altered vocalizations to overcome noise pollution.