Evolution, Speciation, and Ecology: Study Guide Notes

Evolutionary Biology and Ecology

Key Concepts in Evolution

This section covers foundational terms and processes in evolutionary biology, including mechanisms of evolution, species concepts, and the history of life on Earth.

• Homology and Homologous Structures: Homology refers to similarities between organisms due to shared ancestry. Homologous structures are anatomical features in different species that originated from a common ancestor, even if they serve different functions (e.g., the forelimbs of humans, whales, and bats).

• Evolutionary Trees: Also known as phylogenetic trees, these diagrams depict evolutionary relationships among species, showing patterns of descent from common ancestors.

• Mutation: A change in the DNA sequence. Mutations are the ultimate source of all new alleles and genetic variation in populations.

• Microevolution: Small-scale evolutionary changes within populations, typically involving changes in allele frequencies over generations.

• Natural Selection: The process by which individuals with advantageous traits survive and reproduce more successfully, increasing the frequency of those traits in the population. Fitness refers to an organism's ability to survive and reproduce in its environment.

• Artificial Selection: The intentional breeding of organisms by humans for desired traits (e.g., dog breeds, crop varieties).

• Sexual Selection: A form of natural selection where certain traits increase an individual's chances of mating (e.g., peacock feathers).

• Antibiotic Resistance: The evolution of bacteria that survive exposure to antibiotics, often due to mutations and selection pressure.

Speciation and Species Concepts

Speciation is the process by which new species arise. Several concepts are used to define what constitutes a species.

• Gene Pool: The total collection of genes and alleles in a population.

• Speciation: The formation of new species, often through reproductive isolation mechanisms.

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

• Ecological Species Concept: Defines species based on their ecological niche, focusing on unique adaptations to particular roles in a biological community.

• Phylogenetic Species Concept: Defines species as the smallest group of individuals sharing a common ancestor, forming one branch on the tree of life.

• Morphological Species Concept: Defines species based on observable physical traits and structural features.

Reproductive Isolation Mechanisms

• Prezygotic Barriers: Prevent mating or fertilization between species. Types include:

  • Temporal Isolation: Species breed at different times.

  • Habitat Isolation: Species live in different environments.

  • Behavioral Isolation: Differences in mating behaviors prevent interbreeding.

  • Mechanical Isolation: Physical differences prevent successful mating.

  • Gametic Isolation: Gametes (egg and sperm) are incompatible.

• Postzygotic Barriers: Occur after fertilization, reducing hybrid viability or fertility.

  • Reduced Hybrid Viability: Hybrids fail to develop or reach maturity.

  • Reduced Hybrid Fertility: Hybrids are sterile (e.g., mule).

Major Events in the History of Life

The history of life on Earth is divided into eons and eras, each marked by significant evolutionary events.

• Archaean Eon: Origin of life, first prokaryotes.

• Proterozoic Eon: First eukaryotes, multicellular life.

• Paleozoic Era: Appearance of plants, fungi, arthropods, and reptiles on land.

• Mesozoic Era: Age of reptiles (dinosaurs), first mammals and flowering plants.

• Cenozoic Era: Age of mammals, diversification of flowering plants.

• Order of Appearance in Geologic Record:

  1. Plants and fungi

  2. Arthropods

  3. Reptiles

  4. Flowering plants

Taxonomy and Classification

Taxonomy is the science of naming and classifying organisms. The binomial classification system assigns each species a two-part Latin name (genus and species).

• Taxonomic Categories (from most specific to most general):

Level	Example
Species	Homo sapiens
Genus	Homo
Family	Hominidae
Order	Primates
Class	Mammalia
Phylum	Chordata
Kingdom	Animalia
Domain	Eukarya

Ecology and Ecosystems

Levels of Ecological Organization

• Habitat: The specific environment where an organism lives.

• Population: A group of individuals of the same species living in a particular area.

• Community: All the populations of different species living and interacting in an area.

• Ecosystem: The community plus the nonliving (abiotic) environment.

Species Diversity

• Species Diversity: The variety of species in a community.

• Species Richness: The number of different species present.

• Species Composition: The identity of the species present in a community.

Biomes

Biomes are large ecological areas with distinct climate, flora, and fauna. Key characteristics differentiate biomes such as tundra, desert, rainforest, grassland, and taiga.

• Permafrost: Permanently frozen ground found in tundra biomes.

• Detritivores and Decomposers: Organisms that feed on dead organic matter, recycling nutrients in ecosystems (e.g., earthworms, fungi, bacteria).

Interspecific Interactions

• Competition: When two or more species compete for the same limited resource.

• Mutualism: Both species benefit from the interaction (e.g., bees and flowers).

• Predation: One organism (predator) kills and eats another (prey).

• Parasitism: One organism (parasite) benefits at the expense of another (host).

• Niche: The role and position a species has in its environment, including all its interactions with biotic and abiotic factors.

• Predator Avoidance Mechanisms: Adaptations such as camouflage, mimicry, and defensive behaviors that reduce predation risk.

Trophic Structure and Food Webs

• Trophic Structure: The feeding relationships among organisms in a community.

• Food Chain: A linear sequence of organisms through which nutrients and energy pass.

• Food Web: A complex network of interconnected food chains in an ecosystem.

• Producers: Autotrophs (e.g., plants) that produce energy-rich compounds from sunlight.

• Consumers: Organisms that obtain energy by eating other organisms.

  • Primary Consumers: Herbivores that eat producers.

  • Secondary Consumers: Carnivores that eat herbivores.

  • Tertiary Consumers: Carnivores that eat other carnivores.

  • Quaternary Consumers: Top predators at the highest trophic level.

Ecological Succession

• Ecological Succession: The process of change in the species structure of an ecological community over time.

• Primary Succession: Occurs in lifeless areas where soil has not yet formed (e.g., after a volcanic eruption).

• Secondary Succession: Occurs in areas where a disturbance has destroyed a community but left the soil intact (e.g., after a fire).

• Invasive Species: Non-native species that spread rapidly and disrupt local ecosystems.

Summary Table: Forms of Reproductive Isolation

Type	Definition	Example
Temporal Isolation	Species breed at different times	One species breeds in spring, another in fall
Habitat Isolation	Species live in different habitats	One species in water, another on land
Behavioral Isolation	Different courtship behaviors	Unique mating dances or calls
Mechanical Isolation	Physical differences prevent mating	Incompatible reproductive organs
Gametic Isolation	Gametes cannot fuse	Sperm cannot fertilize egg
Reduced Hybrid Viability	Hybrids fail to develop or survive	Hybrid embryos die early
Reduced Hybrid Fertility	Hybrids are sterile	Mule (horse-donkey hybrid)

Additional info:

• Understanding biomes involves recognizing climate, dominant vegetation, and adaptations of organisms.

• Major events in Earth's history are often dated using the fossil record and radiometric dating techniques.

• Species concepts are used in different contexts; for example, the biological species concept is most useful for sexually reproducing organisms.