Mass extinctions represent significant and rapid declines in Earth's biodiversity, with five major events identified in the geological record, including the well-known extinction that eliminated the dinosaurs, attributed to a massive asteroid impact. This asteroid, estimated to be the size of Manhattan, dramatically altered life on Earth. Currently, we are experiencing a sixth mass extinction, referred to as the Holocene extinction, primarily driven by human activities.

Evidence of this ongoing extinction can be observed in the decline of large mammal populations following human arrival in various regions. For instance, while Africa has seen a relatively stable number of large mammals, areas like Australia, North America, and Madagascar have experienced significant population drops. This trend is theorized to stem from early human hunter-gatherer practices, where large mammals were hunted to near extinction for sustenance, leading to a shift towards agrarian societies once these resources were depleted.

Extinction can lead to an extinction vortex, a phenomenon where small population sizes create a downward spiral, making survival increasingly difficult. Small populations are particularly susceptible to inbreeding and genetic drift, which can exacerbate their decline. The concept of minimum viable population refers to the smallest population size that can sustain itself without facing extinction risks. Populations above this threshold are generally more stable and resilient.

Another important metric is the effective population size, which indicates the number of individuals in a population that contribute to the next generation's gene pool. This measure is crucial for assessing the genetic health and long-term viability of a population.

Additionally, the species-area relationship illustrates that larger habitats tend to support a greater number of species. This relationship is often represented by a species-area curve, which shows that as the area available to species increases, so does the diversity of species present. Understanding these dynamics is essential for conservation efforts aimed at mitigating biodiversity loss and preventing further extinctions.