AP Syllabus focus:
‘Geological and meteorological events change habitats and ecosystem distributions, as shown by biogeographical studies.’
Geological and meteorological events can rapidly or gradually reshape Earth’s surface and climate. These abiotic changes alter where organisms can live, shifting species ranges, reorganising communities, and creating biogeographical patterns observed across regions and through time.
Geological events and habitat change
Geological processes often act over long timescales, but can also be sudden and severe.
Tectonics, mountain building, and land bridges
Plate movements alter continental positions, elevation, and connectivity between landmasses.
Convergent plate motion (subduction) deforms crust and drives volcanism, producing mountain belts and major changes in elevation. These tectonic landforms alter temperature and precipitation patterns and can act as dispersal barriers, reorganizing habitats and species ranges. Source
Mountain uplift changes temperature and precipitation with altitude, creating new climate zones and barriers to dispersal.
Land bridges and later separation (via rifting or sea-level change) can connect or isolate populations, affecting where species occur.
Earthquakes can trigger landslides and coastal uplift/subsidence, abruptly changing shoreline habitats.
Volcanism and new substrate
Volcanic activity can destroy habitats locally yet create new land and soils.
Lava flows and ashfall remove existing vegetation and alter water chemistry, reducing survival for many organisms.
New rock surfaces initially limit life to hardy colonisers; over time, weathering and organic matter accumulation increase habitat complexity, allowing more species to establish.
Glaciation and sea-level change
Ice advance/retreat and associated sea-level shifts reorganise ecosystems on continental scales.
A time-series shoreline map illustrating sea-level rise since the last glaciation, with past coastlines labeled by age (e.g., 18 ka) and relative sea level. Changes in sea level can inundate coastal habitats or expose continental shelves, reshaping available habitat and altering connectivity among populations. Source
Glaciers remove soil and biota, forcing range contractions into refuges.
Post-glacial retreat opens new habitat and migration corridors; many species track suitable temperature zones.
Sea-level rise can inundate coastal habitats, while sea-level fall can expose continental shelves, expanding or connecting terrestrial habitats.
Meteorological events and habitat change
Meteorological forces can restructure ecosystems on short timescales by changing moisture, temperature, and disturbance regimes.
Storms, floods, and coastal impacts
Hurricanes/cyclones cause windthrow, defoliation, and saltwater intrusion; these can reduce forest canopy cover and shift light availability and microclimates.
Flooding redistributes sediments and nutrients, scours riverbanks, and can convert terrestrial areas into wetlands (or vice versa as channels move).
Drought, heat, and fire weather
Drought reduces freshwater availability and primary productivity, increasing mortality and lowering reproductive success for drought-sensitive species.
Heat waves can exceed thermal tolerance limits, shifting distributions toward cooler microhabitats or higher latitudes/altitudes.
Hot, dry, windy conditions promote wildfire, which can rapidly convert habitat structure and favor fire-adapted species while excluding others.
Climate oscillations and shifting suitability
Large-scale climate patterns (e.g., El Niño/La Niña) alter regional rainfall and ocean temperatures.
A global sea-surface temperature anomaly map showing where ocean waters are warmer-than-average (reds) or cooler-than-average (blues). Such anomaly patterns underpin ENSO-related shifts in upwelling intensity and marine productivity, which can cascade through food webs and drive redistribution of marine species. Source
Changes in upwelling and sea-surface temperature can shift marine food availability, moving the distributions of fish, seabirds, and marine mammals.
On land, altered rainfall patterns can change plant community composition, which cascades to herbivores and predators through habitat and food changes.
Biogeographical studies: linking events to ecosystem distributions
Biogeography: the study of the distribution of organisms across space and time and the processes that shape those distributions.
Biogeographical evidence connects Earth-history events to present-day patterns.
Range shifts: species track suitable climate envelopes after glaciation, warming, or drying, producing poleward/upslope movement patterns.
Vicariance: geological splitting of habitats (uplift, rifting, sea-level rise) isolates populations, increasing divergence and producing regionally distinct species assemblages.
Dispersal and colonisation: storms can transport propagules (seeds, insects) to islands or new patches, changing local community composition.
Habitat fragmentation from landslides, shoreline changes, or floodplain rearrangement reduces connectivity, altering gene flow and local persistence.
Disturbance mosaics: repeated storms, fires, or floods create patchy habitats at different recovery stages, supporting different species across the landscape.
FAQ
They combine timing and pathways.
Geological dating (e.g., island age, uplift timing) compared with divergence-time estimates from genetic data.
Whether plausible routes existed (land bridges, stepping-stone islands) during the relevant period.
Mountains change conditions over short distances.
Temperature drops with altitude, and precipitation patterns shift (rain shadows). Steep gradients create distinct climate zones and limit dispersal across ridgelines.
Storms can act as dispersal vectors.
Rafting vegetation, windborne seeds, and transported insects can found new populations. Repeated colonisation can reshape island communities even when land area is unchanged.
Coasts are spatially constrained.
Small vertical sea-level shifts can move shorelines far horizontally, relocating beaches, salt marshes, mangroves, and estuaries, and fragmenting or connecting coastal habitats.
They preserve past community signals.
Pollen and charcoal layers indicate vegetation and fire history.
Microfossils and isotopes reflect temperature and moisture. These records can be matched to known climatic cycles to infer historical range shifts.
Practice Questions
Explain how glaciation can change the distribution of a terrestrial species. (2 marks)
Glaciation reduces suitable habitat/forces range contraction into refugia (1).
Post-glacial retreat allows recolonisation/range expansion, often poleward or upslope (1).
Describe how a major volcanic eruption could alter habitats and lead to different ecosystem distributions, and explain how biogeographical studies could support these changes. (5 marks)
Eruption removes existing vegetation/organisms via lava/ash, causing local extinction or displacement (1).
Creates new substrate with initially low soil nutrients, favouring pioneer species and changing community composition (1).
Habitat structure/microclimate changes (e.g., canopy loss, altered water chemistry) shift which species can persist (1).
Over time, colonisation and succession increase habitat complexity, producing a different distribution of species than pre-eruption (1).
Biogeographical support: mapping before/after distributions or comparing affected vs unaffected regions to link the event to range shifts/colonisation patterns (1).
