General Biology Study Guide: Evolutionary History, Population Ecology, and Community Ecology

Chapter 15 – Tracing Evolutionary History

Taxonomy, Phylogeny, and Systematics

Understanding evolutionary history involves organizing and classifying organisms based on their relationships and characteristics.

• Taxonomy: The science of naming, describing, and classifying organisms into groups such as species, genus, family, etc.

• Systematics: The broader field that includes taxonomy and also studies evolutionary relationships among organisms.

• Phylogeny: The evolutionary history and relationships among species or groups of species.

Classification and Phylogenetic Trees

• Binomial Nomenclature: The two-part scientific naming system for organisms (e.g., Homo sapiens).

• Hierarchical Classification: Organisms are grouped into increasingly broad categories: species, genus, family, order, class, phylum, kingdom, domain.

• Phylogenetic Trees: Diagrams that represent evolutionary relationships. Each branch point represents a common ancestor.

• Cladistics: A method of systematics that groups organisms by common ancestry, using shared derived characteristics (synapomorphies).

• Homology vs. Analogy: Homologous structures are inherited from a common ancestor; analogous structures arise from convergent evolution.

Constructing Phylogenetic Trees

• Use morphological, molecular, and genetic data to hypothesize evolutionary relationships.

• Apply the principle of parsimony: the simplest explanation (fewest evolutionary changes) is preferred.

• Outgroups are used to help root the tree and infer ancestral traits.

Example: A phylogenetic tree showing the evolutionary relationships among mammals, birds, and reptiles based on shared characteristics.

Chapter 36 – Population Ecology

Population Definition and Dispersion

Population ecology studies the factors that affect population size and composition.

• Population: A group of individuals of the same species living in the same area at the same time.

• Dispersion Patterns: The way individuals are spaced within their area. Types include clumped, uniform, and random dispersion.

Population Growth Models

• Exponential Growth: Population increases under ideal conditions, represented by the equation: $\frac{dN}{dt} = rN$ where $N$ is population size, $r$ is the intrinsic rate of increase, and $t$ is time.

• Logistic Growth: Population growth slows as it approaches carrying capacity ($K$): $\frac{dN}{dt} = rN\left(1 - \frac{N}{K}\right)$

• Carrying Capacity ($K$): The maximum population size that an environment can sustain.

Population Regulation and Life History

• Density-dependent factors: Factors whose effects increase as population density increases (e.g., competition, predation, disease).

• Density-independent factors: Factors that affect populations regardless of density (e.g., weather, natural disasters).

• Life History Strategies: r-selected species (high reproductive rate, low survival) vs. K-selected species (low reproductive rate, high survival).

• Boom-and-bust cycles: Populations that undergo regular fluctuations in size due to resource availability or predation.

Example: The population cycles of snowshoe hares and lynx in boreal forests.

Chapter 37 – Community Ecology

Biological Communities and Interactions

A biological community consists of all the populations of different species that interact in a given area.

• Species Interactions: Competition, mutualism, predation, herbivory, parasitism, and pathogen effects.

• Examples: Bees pollinating flowers (mutualism), wolves preying on deer (predation), mistletoe on trees (parasitism).

Community Dynamics and Adaptations

• Community dynamics can drive the evolution of adaptations, such as camouflage or warning coloration.

• Species diversity is influenced by the number of species (richness) and their relative abundance (evenness).

Trophic Structure and Energy Flow

• Food Chains and Food Webs: Food chains show linear energy flow; food webs show complex feeding relationships.

• Trophic Levels: Producers (autotrophs), primary consumers (herbivores), secondary and tertiary consumers (carnivores), decomposers.

• Energy Transfer: Only about 10% of energy is transferred from one trophic level to the next; the rest is lost as heat.

• Biomass Pyramid: Shows the amount of living organic matter at each trophic level.

Trophic Level	Example Organism	Energy Available (%)
Producers	Grass	100
Primary Consumers	Grasshopper	10
Secondary Consumers	Frog	1
Tertiary Consumers	Snake	0.1

Primary Productivity

• Primary Productivity: The rate at which producers convert solar energy into chemical energy (biomass).

• Primary productivity limits the amount of energy available to higher trophic levels.

Example: Tropical rainforests have high primary productivity, supporting diverse and complex communities.