Lecture 9 - Macroevolution Biogeography

Biogeography definition

The study of how species and lineages are distributed across geographic space and how these patterns arise through evolutionary processes.

Historical biogeography

Examines how past geological events such as continental drift, mountain formation, and climate shifts shaped species distributions.

Ecological biogeography

Focuses on how current ecological factors like climate, habitat, and competition determine species ranges.

Vicariance

The splitting of a population by a geographic barrier (e.g., mountains, oceans), leading to divergence and speciation.

Dispersal

Movement of organisms across barriers into new regions, creating new populations that may diverge over time.

Continental drift

Movement of tectonic plates that separated ancient supercontinents (e.g., Pangaea, Gondwana), shaping global biodiversity patterns.

Gondwanan distribution

Lineages found across southern continents (e.g., Australia, Africa, South America) due to shared ancestry before continental breakup.

Laurasian distribution

Lineages distributed across northern continents due to shared evolutionary history on Laurasia.

Endemism

Species restricted to a specific geographic region; often results from long isolation or unique ecological conditions.

Island biogeography

Study of species richness and colonisation on islands; influenced by island size, distance from mainland, and dispersal ability.

Island rule

Small animals tend to become larger and large animals tend to become smaller on islands due to ecological release or resource limitation.

Adaptive radiation on islands

Islands promote rapid diversification due to ecological opportunity and reduced competition (e.g., Darwin’s finches).

Wallace’s Line

A deep ocean trench separating Asian and Australasian fauna, marking a major biogeographic boundary.

Wallace’s contributions

Identified biogeographic regions and independently conceived natural selection alongside Darwin.

Biogeographic realms

Large regions with distinct evolutionary histories (e.g., Nearctic, Palearctic, Afrotropical, Neotropical, Australasian).

Dispersal ability

Strongly influences species distributions; poor dispersers show strong geographic structuring, while good dispersers show wide ranges.

Range expansion

Occurs when species move into new areas due to climate change, human activity, or ecological opportunity.

Range contraction

Occurs when species lose habitat or climate suitability, often increasing extinction risk.

Phylogeography

Combines phylogenetics and biogeography to study how historical processes shaped genetic lineages across space.

Refugia

Areas where species survived past climate extremes (e.g., ice ages), later recolonising surrounding regions.

Postglacial recolonisation

Movement of species back into previously glaciated areas, leaving genetic signatures of expansion.

Dispersal vs vicariance debate

Determining whether species distributions arose from movement (dispersal) or geological separation (vicariance).

Key biogeographic processes

Include colonisation, extinction, vicariance, dispersal, and ecological filtering.

Ecological filtering

Only species with suitable traits can survive in a given environment, shaping community composition.

Niche conservatism

Tendency of species to retain ancestral ecological traits, limiting their ability to colonise new environments.

Human‑driven biogeography

Humans alter species distributions through introductions, extinctions, habitat change, and climate warming.

Invasive species biogeography

Introduced species can rapidly expand ranges, disrupt native communities, and alter evolutionary trajectories.

Macroecological patterns

Large‑scale patterns such as latitudinal diversity gradients, where species richness increases toward the equator.

Latitudinal diversity gradient

One of the strongest biogeographic patterns: tropical regions contain far more species than temperate or polar regions.