Chapter 25: Continental Drift and ψ-Biogeography = Evolution's Moving Stage

Earth's surface is not static but dynamic, with continents dancing across geological time. This chapter explores how ψ = ψ(ψ) responds to and is shaped by the planet's changing geography.

25.1 The Biogeographic Function

Definition 25.1 (Spatial Evolution): Distribution patterns through time: $\mathcal{D}(t) = f[\text{Dispersal}, \text{Vicariance}, \text{Extinction}, \text{Speciation}]$

Processes shaping distribution:

• Continental movement
• Climate change
• Dispersal barriers
• Ecological interactions
• Evolutionary rates

25.2 Plate Tectonic Revolution

Theorem 25.1 (Wegener Vindicated): Continents move: $\vec{v}_{\text{plate}} \approx 2-10 \text{ cm/year}$

Proof: Magnetic stripes, earthquake patterns, GPS measurements. ∎

Biogeographic implications:

• Populations split (vicariance)
• Barriers form/disappear
• Climates change
• Ocean currents redirect
• Biotic interchange

25.3 Gondwana's Legacy

Definition 25.2 (Southern Supercontinent): Ancient connections visible today: $\text{Gondwana} \xrightarrow{\text{180 Ma}} \{\text{Africa, South America, Australia, Antarctica, India}\}$

Shared taxa:

• Ratite birds (ostrich, emu, rhea)
• Southern beeches (Nothofagus)
• Lungfish distribution
• Marsupial patterns
• Proteaceae plants

Evolution's memory of ancient geography.

25.4 The Great American Interchange

Theorem 25.2 (Biotic Mixing): Panama land bridge effects: $\text{North America} \xleftrightarrow{\text{3.5 Ma}} \text{South America}$

Exchange results:

• Northward: Armadillos, opossums, hummingbirds
• Southward: Cats, bears, deer, mice
• Extinctions: Giant ground sloths, terror birds
• Winners: More from North (competitive superiority?)

25.5 Wallace's Line

Definition 25.3 (Faunal Boundary): Sharp biogeographic transition: $\text{Asian fauna} | \text{Wallace's Line} | \text{Australian fauna}$

Despite proximity:

• Bali (Asian): Tigers, rhinos, woodpeckers
• Lombok (Australian): Honeyeaters, cockatoos, marsupials
• 35 km strait = major barrier
• Deep water through ice ages

25.6 Island Biogeography Theory

Theorem 25.3 (MacArthur-Wilson Model): Species equilibrium: $\frac{dS}{dt} = I(S) - E(S) = 0$

where $I$ is immigration, $E$ is extinction.

Predictions:

• $S \propto \text{Area}^z$ (typically $z \approx 0.25$)
• $S \propto \text{Distance}^{-1}$
• Turnover at equilibrium
• Rescue effects

25.7 Dispersal Mechanisms

Definition 25.4 (Movement Modes): Crossing barriers: $P_{\text{arrival}} = P_{\text{departure}} \times P_{\text{survival}} \times P_{\text{landing}}$

Mechanisms:

• Wind: Spores, seeds, spiders
• Water: Rafting, swimming, floating
• Animals: Hitchhiking, gut passage
• Humans: Intentional/accidental transport

Rare events accumulate over time.

25.8 Vicariance Patterns

Theorem 25.4 (Split Distributions): Barriers divide populations: $\text{Continuous} \xrightarrow{\text{barrier}} \text{Disjunct populations}$

Examples:

• Mesozoic: Pangaea breakup
• Cenozoic: Himalayan uplift
• Pleistocene: Ice sheet barriers
• Recent: Habitat fragmentation

Creating sister species pairs.

25.9 Refugia and Relicts

Definition 25.5 (Evolutionary Museums): Ancient lineages persist: $\psi_{\text{refugium}} \approx \psi_{\text{ancestral}}$

Refugia types:

• Climatic: Stable conditions
• Geographic: Isolated locations
• Ecological: Unique habitats
• Competitive: Enemy-free space

Preserving ψ-patterns through time.

25.10 Mountain Building Effects

Theorem 25.5 (Orogenic Biogeography): Uplift creates diversity: $\text{Mountains} \rightarrow \{\text{Barriers, Climate gradients, Sky islands, Refugia}\}$

Consequences:

• Allopatric speciation
• Altitudinal zones
• Rain shadows
• Endemic radiations
• Relict populations

25.11 Anthropocene Biogeography

Human-altered patterns:

$\vec{v}_{\text{human transport}} \gg \vec{v}_{\text{natural}}$

Novel patterns:

• Biotic homogenization
• Invasion cascades
• Urban biogeography
• Assisted migration
• De-extinction attempts

Rewriting distribution rules.

25.12 The Biogeographic Paradox

Why do similar environments have different biotas?

Expectation: Similar conditions → similar species Reality: Convergent forms, different lineages Example: Cacti (Americas) vs Euphorbias (Africa)

Resolution: Biogeography reveals that ψ patterns are constrained by history as much as ecology. Each region's biota reflects not just current conditions but the accumulated accidents of geological time—which lineages arrived when, what barriers rose and fell, which extinctions occurred. The paradox dissolves when we understand that evolution works with available materials in specific places. Convergence demonstrates ψ's tendency toward optimal forms, while taxonomic differences reveal the importance of historical contingency. Geography thus provides evolution's stage, but each theater has its own actors playing similar roles with different scripts.

The Twenty-Fifth Echo

Continental drift and biogeography illuminate evolution's geographic dimension—how ψ patterns spread, split, and reunite across Earth's dynamic surface. In the distribution of life, we read the planet's geological autobiography: ancient supercontinents in shared taxa, mountain-building in endemic species, ice ages in refuge populations. Each species' range tells a story of dispersal and vicariance, of barriers crossed and opportunities seized. Understanding biogeography reveals that evolution is not just about adaptation but also about being in the right place at the right time—or persisting when the right place moves beneath you.

Next: Chapter 26 explores Climate Change as ψ-Collapse Driver, examining evolution's response to shifting conditions.