IB ESS SL 3.3.7 Rewilding Questions

Figure 7(a): Fact file on North American beavers
• One family per square km of river. Family groups have two adults and up to three young (kits) born each year between April and June.
• Mortality rates are high due to severe weather, lack of suitable habitats and predation.
• Population estimated at 250 million before fur trade hunting; about 9 million today.
• Feed on tree bark.
• Build lodges from wood and mud for eating, sleeping and raising young; remain in lodges during winter; protect their lodge from other beavers.
• Beavers are being reintroduced in Europe to help restore wetlands.

Figure 9(a): Dossier sobre la función de los castores en el ecosistema (role of beavers in the ecosystem)
• Beavers build dams from sticks, creating ponds and slowing river flow.
• Ponds are less suitable for river fish such as brook trout, but provide new habitats for aquatic plants, dragonfly larvae, bullfrogs and other fish.
• Flooding can kill riverside trees when roots are submerged, creating more bird nesting sites.
• Marshy areas may form at pond edges. Grasses and sedges colonize nutrient-rich pond silt to form beaver meadow.
• Beaver meadows have more light, higher soil moisture, more nitrogen and different vegetation from adjacent river-edge forest.
• Dams may collapse after heavy rain or spring thaw, or if the beaver maintaining the dam is taken by a predator.