Evolution and Ecology: Study Guide for General Biology

Evolutionary Biology

Introduction to Evolution

Evolution is the process by which populations of organisms change over generations through variations in heritable traits. This section covers foundational concepts, mechanisms, and evidence supporting evolutionary theory.

• Darwin and Natural Selection: Charles Darwin proposed natural selection as the primary mechanism of evolution, where individuals with advantageous traits are more likely to survive and reproduce.

• Evidence for Evolution: Includes fossil records, comparative anatomy, embryology, molecular biology, and biogeography.

• Taxonomy and Classification: The science of naming and classifying organisms based on shared characteristics.

• Phylogenetic Trees: Diagrams that depict evolutionary relationships among species.

Key Terms:

• Homology: Similarity due to shared ancestry (e.g., vertebrate forelimbs).

• Analogy: Similarity due to convergent evolution, not common ancestry (e.g., wings of birds and insects).

• Convergent Evolution: Independent evolution of similar features in different lineages.

Mechanisms of Evolution

Evolutionary change is driven by several mechanisms that alter allele frequencies in populations over time.

• Genetic Variation: The raw material for evolution, arising from mutations, gene shuffling during meiosis, and other processes.

• Natural Selection: Differential survival and reproduction of individuals due to differences in phenotype.

• Genetic Drift: Random changes in allele frequencies, especially significant in small populations.

• Gene Flow: Movement of alleles between populations through migration.

• Mutation: The ultimate source of genetic variation.

Hardy-Weinberg Principle: Describes a non-evolving population where allele and genotype frequencies remain constant from generation to generation unless acted upon by evolutionary forces.

• Equation:

$p^2 + 2pq + q^2 = 1$

Where p and q are the frequencies of two alleles in a population.

• Applications: Used to estimate carrier frequencies of genetic diseases and to test if a population is evolving.

Speciation and the Origin of Species

Speciation is the process by which one species splits into two or more distinct species. It is central to understanding biodiversity.

• Biological Species Concept: Defines species as groups of interbreeding natural populations that are reproductively isolated from other such groups.

• Prezygotic Barriers: Prevent mating or fertilization between species (e.g., habitat, temporal, behavioral isolation).

• Postzygotic Barriers: Prevent hybrid offspring from developing into viable, fertile adults (e.g., reduced hybrid viability, reduced hybrid fertility).

• Allopatric Speciation: Occurs when populations are geographically separated.

• Sympatric Speciation: Occurs without geographic separation, often through polyploidy or behavioral changes.

Hybrid Zones: Regions where members of different species meet and mate, producing hybrids. Outcomes include reinforcement, fusion, or stability of hybrid zones.

Ecology

Introduction to Ecology

Ecology is the study of interactions between organisms and their environment, encompassing various levels of biological organization.

• Levels of Ecology:

  • Organismal

  • Population

  • Community

  • Ecosystem

  • Landscape

  • Global

• Biotic Factors: Living components of the environment (e.g., plants, animals, microbes).

• Abiotic Factors: Non-living components (e.g., temperature, water, sunlight, soil).

Biomes and Global Patterns

Biomes are major ecological communities defined by their climate, flora, and fauna. Global patterns of temperature, precipitation, and sunlight shape the distribution of biomes.

• Terrestrial Biomes: Include tropical forest, desert, savanna, temperate grassland, temperate broadleaf forest, northern coniferous forest, tundra.

• Aquatic Biomes: Characterized by physical environment (e.g., lakes, rivers, wetlands, estuaries, intertidal zones, oceanic pelagic zone, coral reefs, marine benthic zone).

Population Ecology

Population ecology examines factors that affect population size and composition over time.

• Population Dynamics: Study of how and why populations change in size and structure.

• Demography: Statistical study of populations, including birth rates, death rates, and age structure.

• Population Growth Models:

$\text{Exponential growth:} \ \frac{dN}{dt} = rN$

$\text{Logistic growth:} \ \frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right)$

• Carrying Capacity (K): Maximum population size that an environment can sustain.

• Life History Strategies: r-selection (high growth rate, low survival) vs. K-selection (low growth rate, high survival).

Community Ecology

Community ecology studies interactions between species living in the same area.

• Types of Interactions: Competition, predation, herbivory, symbiosis (mutualism, commensalism, parasitism).

• Resource Partitioning: Differentiation of niches that enables similar species to coexist.

• Ecological Niches: The role and position a species has in its environment.

Ecosystem Ecology

Ecosystem ecology focuses on energy flow and chemical cycling among the various biotic and abiotic components.

• Energy Flow: Describes the movement of energy through trophic levels (primary producers, consumers, decomposers).

• Biogeochemical Cycles: Pathways by which elements like carbon, nitrogen, and phosphorus circulate through ecosystems.

Global Change

Human activities are causing significant changes to Earth's ecosystems, including climate change, habitat destruction, and pollution.

• Threats: Habitat loss, invasive species, overharvesting, pollution, climate change.

• Biological Magnification: Increase in concentration of toxins as they move up the food chain.

• Ozone Depletion: Loss of ozone layer due to chemicals like CFCs.

• Carbon Dioxide Emissions: Contribute to global warming and climate change.

Summary Table: Mechanisms of Evolution

Mechanism	Description	Effect on Genetic Variation
Natural Selection	Favors advantageous traits, increases fitness	Can increase or decrease variation
Genetic Drift	Random changes in allele frequencies	Reduces variation, especially in small populations
Gene Flow	Movement of alleles between populations	Increases variation within populations, reduces differences between populations
Mutation	Random changes in DNA sequence	Introduces new variation

Example: The evolution of antibiotic resistance in bacteria is a real-world example of natural selection, where genetic variation and selection pressure from antibiotics lead to the proliferation of resistant strains.

Additional info: This guide expands on the provided outline with definitions, examples, and equations to ensure a comprehensive review for exam preparation.