IB Biology Topic D4.3.6: Poleward and Upslope Range Shifts of Temperate Species Notes

Range shifts: species track their climate as the planet warms

1. As the planet warms, species shift their ranges to stay within their preferred temperature and climate envelope.
2. This usually means moving poleward toward higher latitudes or upslope toward cooler, higher elevations.

Species move because their old habitat drifts outside their tolerance

1. Temperature tolerance: many species tolerate only a narrow temperature range, so rising heat makes their current habitat unsuitable.
2. Habitat availability: cooler areas at higher latitudes or elevations provide refuge as conditions change.
3. Resource dependency: warming shifts food availability, breeding sites, and other resources that species must follow.

New Guinea's montane birds are climbing upslope as the lowlands warm

1. Tropical montane birds in New Guinea are shifting their ranges upslope as temperatures rise on the mountainsides.
2. By moving to cooler, higher elevations, each species stays within the temperature band it can tolerate.
3. High-elevation species are squeezed toward the mountaintops, where shrinking habitat drives competition and raises extinction risk.

North American trees are shifting their optimal zones northward

1. In North America, warming has pushed the ranges of some temperate tree species northward while their southern edges contract.
2. Species such as red maple (Acer rubrum) and American beech (Fagus grandifolia), which span much of eastern North America into southern Canada, are seeing their optimal zones move northward as the climate warms.
3. As tree ranges shift, forest composition changes, altering the balance for animals that depend on those trees for food and shelter.
4. Warmer, drier conditions at the southern edge can threaten the trees in areas they once occupied.

Range shifts ripple out into ecosystems, biodiversity, and people

1. Ecosystem disruption: arriving species can outcompete residents for resources and reshape food webs.
   1. New competitors entering an area can crowd out native species.
   2. Shifting distributions break existing predator-prey links.
2. Biodiversity loss: species with nowhere left to move, such as those at mountaintops, face a high risk of extinction.
3. Human impacts: changing tree distributions affect forestry, agriculture, and ecosystem services like carbon storage.

Range shifts happen in the ocean too: walleye pollock, a temperate fish, have shifted northward in the Bering Sea as the water warms.