Evolution, Speciation, and Ecology: General Biology Study Guide

Evolution: Introduction and Mechanisms

Major Contributors to Evolutionary Theory

Evolutionary biology explores the changes in genetic makeup of populations over time, driven by mechanisms such as natural selection, genetic drift, and gene flow. Foundational scientists include Charles Darwin, Jean-Baptiste Lamarck, Thomas Malthus, and Alfred Russel Wallace.

• Charles Darwin: Developed the theory of natural selection, emphasizing variation and differential reproductive success.

• Jean-Baptiste Lamarck: Proposed inheritance of acquired characteristics (now largely discredited).

• Thomas Malthus: Influenced Darwin with ideas about population growth and resource limitation.

• Alfred Russel Wallace: Independently conceived the theory of evolution by natural selection.

Key Terms in Evolution

• Adaptation: A trait that increases an organism's fitness in its environment.

• Homology: Similarity due to shared ancestry.

• Analogous Structures: Similar features due to convergent evolution, not common ancestry.

• Vestigial Organs: Structures with no current function, inherited from ancestors.

Darwin's Theory of Natural Selection

• Variation exists among individuals in a population.

• Some variations are heritable.

• More offspring are produced than the environment can support.

• Individuals with advantageous traits are more likely to survive and reproduce (differential reproductive success).

Evidence for Evolution

• Direct Observation: Examples include antibiotic resistance in bacteria.

• Homology: Anatomical, molecular, and developmental similarities among species.

• Fossil Record: Shows changes in species over time.

• Biogeography: Geographic distribution of species supports evolutionary relationships.

Mechanisms of Evolution

Genetic Variation and Population Genetics

Evolution is defined as a change in the genetic makeup of a population over time. Population genetics studies allele and genotype frequencies within populations.

• Allele Frequency: The proportion of a specific allele among all alleles in a population.

• Gene Pool: All alleles present in a population.

Hardy-Weinberg Principle

The Hardy-Weinberg equilibrium describes a non-evolving population. It provides a mathematical model for allele and genotype frequencies.

• Equation:

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

• p: Frequency of dominant allele

• q: Frequency of recessive allele

• p^2: Frequency of homozygous dominant genotype

• 2pq: Frequency of heterozygous genotype

• q^2: Frequency of homozygous recessive genotype

Factors That Disrupt Hardy-Weinberg Equilibrium

• Genetic drift

• Gene flow

• Mutation

• Non-random mating

• Natural selection

Mechanisms of Microevolution

• Genetic Drift: Random changes in allele frequencies, especially in small populations (e.g., bottleneck and founder effects).

• Gene Flow: Movement of alleles between populations.

• Mutation: Source of new genetic variation.

• Natural Selection: Differential reproductive success based on heritable traits.

Speciation

Definition and Types

Speciation is the process by which new species arise from existing ones. It can occur via different mechanisms:

• Allopatric Speciation: Populations are geographically separated.

• Sympatric Speciation: Populations diverge without geographic separation (e.g., polyploidy in plants).

Species Concepts

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

• Morphological Species Concept: Species are defined by physical characteristics.

• Ecological Species Concept: Species are defined by their ecological niche.

• Phylogenetic Species Concept: Species are the smallest group sharing a common ancestor.

Reproductive Isolating Mechanisms

• Prezygotic Barriers: Prevent mating or fertilization (habitat, temporal, behavioral, mechanical, gametic isolation).

• Postzygotic Barriers: Prevent hybrid offspring from developing into fertile adults (hybrid inviability, hybrid sterility, hybrid breakdown).

Ecology: Introduction and Levels of Organization

Levels of Ecological Organization

• Organism: Individual living entity.

• Population: Group of individuals of the same species in an area.

• Community: All populations of different species in an area.

• Ecosystem: Community plus abiotic environment.

• Landscape: Multiple ecosystems in a geographic area.

Abiotic and Biotic Factors

• Abiotic: Non-living factors (temperature, water, sunlight, wind, soil, climate).

• Biotic: Living factors (other organisms).

Biomes

Biomes are major ecological communities defined by climate and dominant vegetation.

Terrestrial Biomes	Aquatic Biomes
Tropical Forest	Wetlands
Desert	Lakes and Rivers
Temperate Grassland	Estuaries
Temperate Broadleaf Forest	Intertidal Zone
Coniferous Forest	Oceanic Pelagic Zone
Tundra	Coral Reefs

Population Ecology

Population Dynamics and Growth Models

• Population Density: Number of individuals per unit area.

• Dispersion: Pattern of spacing among individuals (clumped, uniform, random).

• Demography: Study of birth, death, and migration rates.

Population Growth Equations

• Exponential Growth: Population grows at a constant rate under ideal conditions.

$\frac{dN}{dt} = rN$

• Logistic Growth: Population growth slows as it approaches carrying capacity (K).

$\frac{dN}{dt} = rN \left( \frac{K-N}{K} \right)$

Life History Strategies

• r-selected species: High reproductive rate, short lifespan, many offspring.

• K-selected species: Low reproductive rate, long lifespan, few offspring, stable populations.

Community Ecology

Community Interactions

• Competition: (-/-) Both species are harmed by shared resource use.

• Predation: (+/-) One species benefits, the other is harmed.

• Herbivory: (+/-) Animal eats plant.

• Parasitism: (+/-) Parasite benefits, host is harmed.

• Mutualism: (+/+) Both species benefit.

• Commensalism: (+/0) One species benefits, the other is unaffected.

Defensive Adaptations

• Mechanical and chemical defenses in plants.

• Animal defenses: camouflage, mimicry, warning coloration.

Trophic Structure and Food Webs

• Food Chain: Sequence of energy transfer from producers to consumers.

• Food Web: Interconnected food chains in an ecosystem.

• Trophic Levels: Producers, primary consumers, secondary consumers, tertiary consumers.

Ecosystem Ecology

Energy Flow and Nutrient Cycles

• Energy Flow: Energy moves through trophic levels, with only about 10% transferred to the next level.

• Biogeochemical Cycles: Movement of elements through living and nonliving components.

Cycle	Main Features
Hydrologic (Water)	Evaporation, precipitation, runoff
Carbon	Photosynthesis, respiration, fossil fuels
Nitrogen	Nitrogen fixation, nitrification, denitrification
Phosphorus	Weathering of rocks, uptake by organisms

Human Impacts and Global Change

• Biological Magnification: Toxins become more concentrated in higher trophic levels.

• Depletion of Ozone: Caused by CFCs, increases UV radiation.

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

Additional info: These notes cover topics from chapters 22-56 in a typical General Biology curriculum, including evolution, speciation, population and community ecology, ecosystem processes, and global change. Equations and tables have been expanded for clarity and completeness.