Data from: Extinction of rare fish predicts an abrupt loss of ecological function in the future of Amazonian streams

1. Species are going extinct a thousand times times faster than expected
due to human impacts. When the extinction of species culminates in functional loss,
ecosystem functioning is altered. Functional extinction risk depends on
taxonomic and functional rarity, with the non-redundant traits found in rare
species being the most vulnerable.

2. To investigate the relationship between taxonomic rarity and functional
extinction, we ran extinction simulations driven by taxonomic rarity. Firstly,
we sampled the fish fauna of 40 pristine Amazonian streams and compiled functional
traits related to the body size, defence, diet, stratification and activity of species.
Then, we removed species, beginning with the rarest and ending with the
commonest (and vice-versa) and compared the observed patterns with random
extinction at local and regional scales.

3. Following the removal of rare species, the functional rarity and body
size of the community both decreased, and functional extinctions occurred after
less than 10% of extinction at both spatial scales. Otherwise, the removal of
common species resulted in an increase in functional rarity at the local scale,
although widespread species ensured the persistence of a set of unique functional
traits at a regional scale. Additionally, more than 60% of the common species had
to go extinct before any functional extinction occurred at either scale.

4. If the ongoing mass extinction targets rare species, Amazonian stream
ecosystems will be impacted by the loss of fish species associated with
vulnerable functions.

5. We propose an extinction risk assessment based on the ecosystem, and
recommend that future studies apply our approach to other taxa and ecosystems, to
better understand the effects of human impacts on ecosystem functioning.