The term that best describes a large-scale dying out of a large percentage of all living organisms within an area over a short term is: Question 20 options: species at-risk modelling mass extinction biodiversity crisis

Sure, let's break down the options to find the term that best describes a large-scale dying out of a large percentage of all living organisms within an area over a short term:

1. Species at-risk: This term refers to species that are in danger of becoming extinct in the near future. It does not describe a large-scale dying out of many species at once.

2. Modelling: This term refers to the use of mathematical or computational simulations to predict or analyze complex systems. It is not related to the dying out of organisms.

3. Mass extinction: This term refers to an event in which a large percentage of all living organisms die out over a relatively short period of time. This fits the description given in the question.

4. Biodiversity crisis: This term refers to a significant and rapid decline in biodiversity, which can include the extinction of species, but it is broader and not necessarily limited to a short-term event.

Given these definitions, the term that best describes a large-scale dying out of a large percentage of all living organisms within an area over a short term is:

Mass extinction

So, the correct answer is:

mass extinction