Biodiversity

Activities to try

1. 1

   Perturb a food web: remove a species and follow the ripple

   Why it works: Some species are keystones: their impact on the whole system is disproportionate to their size or numbers, because of the strong role they play (for example, controlling a plant-eater that would otherwise overgraze). Removing one keystone ripples through multiple levels of the food web and can even reshape physical features like rivers. Recovery after restoring a keystone can be incomplete or slow \u2014 ecosystems do not always bounce back easily from a keystone loss.

   1. Start from a connected food web (e.g. Yellowstone: wolves, elk, willow/aspen, beavers, songbirds, riverbanks) with a visible population indicator for each species.
   2. Predict in writing what will happen to elk, to willow and aspen, and to beavers/birds if the wolves are removed \u2014 before changing anything.
   3. Remove the wolves and observe the chain: the elk that wolves had kept in check increase, willows get grazed to almost nothing, beavers and songbirds that depended on the willows decline, and riverbanks become less stable as bank vegetation is lost.
   4. Restore the wolves and watch the system partially knit back together \u2014 fewer/warier elk, willows regrow, beavers return, banks steady \u2014 noting that recovery can be partial and slow, and some changes may not fully reverse.
   5. Repeat removing a minor, weakly connected species and compare how small the ripple is.
2. 2

   Predict-then-check: the Yellowstone wolves

   Why it works: Effects of losing or restoring a keystone species ripple through many levels, surprising a naive 'one-step' prediction. Interdependence means a single change can reshape an ecosystem.

   1. Read/hear the case: wolves were removed from Yellowstone for decades, then reintroduced.
   2. Before any reveal, predict with reasons what happened to the elk, to the willow and aspen, and to the rivers.
   3. Compare predictions with what scientists have reported: elk heavily browsed willow and aspen while wolves were gone; after wolves returned (alongside other changes such as elk hunting, more bears and cougars, and drought), willow and aspen recovered in some places, beaver colonies increased (helped by beavers released near the park), and some stream banks may be steadier \u2014 though recovery is patchy and scientists still debate how much was caused by wolves.
   4. Discuss why a one-step prediction like 'more elk' misses the far-reaching effects.
3. 3

   Biodiversity vs. abundance, and why variety means resilience

   Why it works: Biodiversity is the variety of different species, not the number of individuals. Greater variety is associated with greater stability and resilience and underpins services people rely on.

   1. Compare two ponds/fields: one with a million individuals of a single species, one with many different species. Decide which has higher biodiversity and justify it.
   2. Compare a species-rich food web with a species-poor one. In each, remove one link and describe what happens.
   3. Explain why the rich web often copes better with a loss (other species can fill similar roles \u2014 'backups'), while the sparse web is more likely to collapse \u2014 though even a rich web can change greatly if the lost species is a keystone with no backup.
   4. Name at least two ecosystem services that biodiversity supports (e.g. pollination, clean water, food).