The Biodiversity Crisis

Activities to try

1. 1

   Measure the crisis: species-area and population viability models

   Why it works: The crisis is defined by a measurable RATE far above background and by models with real uncertainty, not by rhetoric; species loss does not track habitat loss linearly, and a population above zero can still face a high projected risk of extinction.

   1. Work with a species-area relationship: change the amount of habitat lost and read off the projected species loss, noting whether halving habitat halves species (it does not — the relationship is non-linear, so halving habitat loses well under half of species).
   2. Work with a population viability model: set a population's size and variability over a chosen time span and observe how the extinction-probability curve rises as the population falls, with the minimum viable population threshold marked.
   3. Identify a case where a population still has survivors above zero yet has a high projected risk of sliding toward extinction, and name why (for example extinction debt, or small-population effects such as inbreeding, loss of genetic diversity and chance events that raise extinction risk when numbers fall below the minimum viable population).
   4. State in writing, for each model, what its inputs and outputs are and one assumption or source of uncertainty in the estimate.
2. 2

   Rate versus number: evaluating the 'extinction is natural' argument

   Why it works: Extinction is a normal background process; the crisis is the accelerated RATE (~100–1000× background) driven by human activity — reasoning from rate relative to background, not from the mere occurrence of extinction, is the key move.

   1. Read the claim 'Today's extinctions are just natural — there's no real crisis' and respond in writing using the idea of a background rate.
   2. Explain the difference between the NUMBER of extinctions and the RATE of extinction, and state which one signals a crisis.
   3. Plot the present-day extinction rate relative to the background rate and the 'big five' past mass-extinction episodes on a log-scale comparison, noting that today's elevated rate is discussed as a possible sixth mass extinction rather than a confirmed one, and name the human drivers (habitat loss, climate change, invasive species).
   4. Name at least one method scientists use to estimate the rate against background (e.g. species-area relationship, IUCN Red List categories).
3. 3

   Weighing a rewilding case: evidenced versus inferred

   Why it works: Rewilding outcomes are complex, multi-causal and contested; reintroduction can trigger far-reaching trophic cascades, but each causal link must be weighed against the evidence and possible confounds rather than accepted as a single-cause story.

   1. Follow the Yellowstone wolf reintroduction as a cause-effect chain: wolves → changes in herbivore behaviour/numbers → vegetation recovery → effects on riverbanks and courses.
   2. For each link in the chain, label whether it is directly measured/evidenced or inferred, and identify at least one confound (e.g. was a river change purely wolf-driven, or also affected by climate, drought, beaver populations or other factors?).
   3. Compare with a second case (Iberian lynx recovery) and state what the data do and do not show.
   4. Write a one-paragraph evidence-weighted judgement: how strong is the claim that reintroduction caused each outcome?