A species is considered vulnerable when it has fewer than how many mature individuals?

A species is classified as vulnerable when its population consists of fewer than 10,000 mature individuals. This criterion, established by the International Union for Conservation of Nature (IUCN), is part of a broader assessment system aimed at determining the conservation status of species.

The thresholds set by IUCN provide a way to prioritize conservation actions based on the number of individuals within a species. When a species falls below 10,000 mature individuals, it indicates a significant risk of extinction, often due to factors such as habitat loss, overexploitation, or environmental changes. Recognizing this vulnerable status prompts conservation efforts aimed at increasing population numbers and mitigating threats to ensure the species' survival.

Understanding these classifications is crucial for effective ecology, conservation, and management strategies. The other options represent higher population thresholds that would not categorize a species as vulnerable, thus underscoring the importance of the specific figure of 10,000 in conservation discussions.