Conservation Biology: Extinction & Biodiversity

Vocabulary flashcards covering extinction terminology, IUCN Red List criteria and quantitative thresholds, modern extinction rates, defaunation dimensions, and drivers of biodiversity loss.

Globally Extinct

A conservation status indicating that no living individual of a species exists anywhere in the world.

Extinct in the Wild (EW)

A status designating that a species survives solely in captivity, cultivation, or human-controlled settings such as zoos, botanical gardens, and aquaria.

Extirpated

Local extinction; a condition in which a species no longer exists in a specific geographic area where it once occurred, though it continues to survive elsewhere.

Functionally Extinct

A condition in which a species' abundance is reduced so drastically that it no longer fulfills its functional ecological role or exerts a significant impact on its biological community.

IUCN Red List

A global conservation assessment framework initiated in 1964 that classifies species across standardized risk categories (EX, EW, CR, EN, VU, NT, LC, DD, NE) based on expert evaluations and quantitative data.

IUCN Criterion A

An IUCN assessment metric based on population size reduction over $10$ years or $3$ generations, setting thresholds for reversible, understood, and ceased threats ($A1$: $CR > 90\%$, $EN > 70\%$, $VU > 50\%$) versus irreversible, ongoing, or unknown threats ($A2\text{--}4$: $CR > 80\%$, $EN > 50\%$, $VU > 30\%$).

Extent of Occurrence (EOO)

The spatial area encompassed within the shortest continuous imaginary boundary that includes all known sites of a taxon (IUCN Criterion B1 thresholds: $CR < 100\,\text{km}^2$, $EN < 5{,}000\,\text{km}^2$, $VU < 20{,}000\,\text{km}^2$).

Area of Occupancy (AOO)

The actual area occupied by a taxon within its extent of occurrence (IUCN Criterion B2 thresholds: $CR < 10\,\text{km}^2$, $EN < 500\,\text{km}^2$, $VU < 2{,}000\,\text{km}^2$).

IUCN Criterion C

A threat assessment metric based on small and continuously declining population numbers of mature individuals ($CR < 250$, $EN < 2{,}500$, $VU < 10{,}000$ mature individuals).

IUCN Criterion D

A metric assessing very small or restricted populations based solely on mature individual counts ($CR < 50$, $EN < 250$, $VU < 1{,}000$) or very restricted range/locations (Criterion D2: $< 20\,\text{km}^2$ or $\le 5$ locations).

IUCN Criterion E

A quantitative analysis framework (such as Population Viability Analysis) estimating the probability of extinction in the wild ($CR \ge 50\%$ in $10$ years or $3$ generations; $EN \ge 20\%$ in $20$ years or $5$ generations; $VU \ge 10\%$ in $100$ years).

Taxonomic Evaluation Bias

The discrepancy in IUCN assessment coverage across animal groups, where well-studied taxa like Birds ($100\%$), Amphibians ($90\%$), and Mammals ($89\%$) are extensively evaluated, while groups such as Insects ($1\%$) and Arachnids ($1\%$) remain largely unassessed.

Van Dyke's Salamander Survey

A Washington case study resurveying $38$ historic localities showing a $19\text{--}40\%$ ($\sim 30\%$) population loss linked to low surface cover within $5\,\text{m}$ of watercourses, qualifying the species for Endangered status under IUCN Criteria A and B despite an existing Least Concern designation.

Extinctions per Million Species-Years (E/MSY)

A standardized metric quantifying extinction rate defined by the equation $E/MSY = \frac{E}{S \times t} \times 10^6$, comparing the natural background rate of $0.1\text{--}2.0\,\text{E/MSY}$ to the modern vertebrate rate of $2.28\,\text{E/MSY}$.

Defaunation

The human-induced loss and decline of animal biodiversity, encompassing both the complete extinction of species and the systemic reduction in the abundance of individuals.

Population Decay

The chronic, progressive decline in both individual population size and geographic range area over time across a species' distribution.

Mass Mortality Events

Rapid, catastrophic die-off occurrences that eliminate more than $90\%$ of a local population within a very short timeframe.

Extinction Debt

The anticipated, delayed future extinction of species caused by past habitat destruction, environmental fragmentation, or habitat alteration.

Living Planet Index (LPI)

A population metric tracking $32{,}000$ populations across $5{,}230$ terrestrial, freshwater, and marine vertebrate species to quantify trends in global abundance relative to $1970$.

Allee Effects

Demographic mechanisms in small populations where low density leads to diminished individual fitness and population growth, driven by mate limitation, cooperative feeding loss, or compromised group defense.

Size-Differential Defaunation

A macroecological pattern where extinction and endangerment disproportionately impact larger-bodied species, evidenced by median body masses of Pleistocene extinct ($182\,\text{kg}$), Anthropocene extinct ($0.70\,\text{kg}$), Anthropocene threatened ($0.44\,\text{kg}$), and Anthropocene non-threatened ($0.06\,\text{kg}$) taxa.

Fishing Down the Food Web

The progressive depletion of large, high-trophic-level apex marine predators that forces fisheries to systematically target progressively smaller species at lower trophic levels.

Harvest-Induced Evolutionary Selection

Trait alteration resulting from selective harvesting of large individuals, exemplified by Atlantic cod shifting to mature approximately $1$ year earlier between the 1980s and 1990s.

IPAT Framework

An equation formalizing human environmental impact as the product of population, affluence, and technology: $\text{Impact } (I) = \text{Population } (P) \times \text{Affluence } (A) \times \text{Technology } (T)$.

Chytrid Pathogen

A fungal disease agent contributing to the amphibian crisis, threatening $53\%$ of critically endangered amphibians and directly driving $9$ of $11$ recent amphibian extinctions.

Ecosystem Collapse

The state of an ecosystem characterized by the virtual certainty that its key biotic or abiotic features will be globally lost and its native biota will no longer be sustained.