Study Guide: Evolution and Ecology – General Biology Final Exam Review

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.

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 sources.

• 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; changes in DNA sequence.

Hardy-Weinberg Principle

The Hardy-Weinberg Principle provides a mathematical model to study genetic variation in populations under ideal conditions (no evolution).

• Equation:

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

$p + q = 1$

• p: Frequency of the dominant allele

• q: Frequency of the recessive allele

• p2: Frequency of homozygous dominant genotype

• 2pq: Frequency of heterozygous genotype

• q2: Frequency of homozygous recessive genotype

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, mechanical, gametic isolation).

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

• Allopatric Speciation: Occurs when populations are geographically separated.

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

Adaptive Evolution

Adaptive evolution results from the combined effects of genetic variation, gene flow, genetic drift, and natural selection, leading to changes in populations that enhance survival and reproduction.

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

• Harmful Alleles: Can become fixed in small populations due to genetic drift.

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, wind, rocks, soil).

Biomes

Biomes are major ecological communities defined by their climate, vegetation, and organisms.

• Terrestrial Biomes: Characterized by climate and dominant plant forms.

  • Tropical Forest

  • Desert

  • Savanna

  • Chaparral

  • Temperate Grassland

  • Temperate Broadleaf Forest

  • Northern Coniferous Forest

  • Tundra

• Aquatic Biomes: Characterized by physical environment.

  • Lakes (littoral, limnetic, benthic, pelagic zones)

  • Wetlands and Rivers

  • Estuaries

  • Intertidal Zones

  • Oceanic Pelagic Zone

  • Coral Reefs

  • Marine Benthic Zone

Population Ecology

Population ecology examines the 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:

  • Exponential Growth: $\frac{dN}{dt} = rN$

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

  • K: Carrying capacity (maximum population size the environment can sustain)

• Life History Strategies: Patterns of reproduction and survival (r-selected vs. K-selected species).

• Population Regulation: Density-dependent and density-independent factors.

Community Ecology

Community ecology studies the interactions between species within a community and how these interactions shape community structure and dynamics.

• Species Interactions:

  • Competition

  • Predation

  • Herbivory

  • Symbiosis (mutualism, commensalism, parasitism)

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

• Character Displacement: Tendency for characteristics to be more divergent in sympatric populations.

• Trophic Structure: Feeding relationships among organisms (food chains and food webs).

• Keystone Species: Species that have a disproportionately large effect on community structure.

Ecosystem Ecology

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

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

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

• Productivity: Rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances.

Global Change

Human activities are causing significant changes to Earth's ecosystems, affecting biodiversity and ecosystem services.

• Threats: Habitat destruction, pollution, overexploitation, invasive species, and climate change.

• Toxin Accumulation and Biological Magnification: Increase in concentration of toxins as they move up trophic levels.

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

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

Key Tables

Hardy-Weinberg Equilibrium Table

Genotype	Frequency
Homozygous Dominant (AA)	$p^2$
Heterozygous (Aa)	$2pq$
Homozygous Recessive (aa)	$q^2$

Population Growth Models

Model	Equation	Description
Exponential Growth	$\frac{dN}{dt} = rN$	Population grows without limits
Logistic Growth	$\frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right)$	Population growth slows as it approaches carrying capacity

Additional info: This study guide covers material relevant to chapters on evolution, population genetics, speciation, ecology, and global change, as outlined in standard General Biology textbooks.