Quantifying the extinction vortex

Abstract

We developed a database of 10 wild vertebrate populations whose declines to extinction were monitored over at least 12 years. We quantitatively characterized the final declines of these well-monitored populations and tested key theoretical predictions about the process of extinction, obtaining two primary results. First, we found evidence of logarithmic scaling of time-to-extinction as a function of population size for each of the 10 populations. Second, two lines of evidence suggested that these extinction-bound populations collectively exhibited dynamics akin to those theoretically proposed to occur in extinction vortices. Specifically, retrospective analyses suggested that a population size of n individuals within a decade of extinction was somehow less valuable to persistence than the same population size was earlier. Likewise, both year-to-year rates of decline and year-to-year variability increased as the time-to-extinction decreased. Together, these results provide key empirical insights into extinction dynamics, an important topic that has received extensive theoretical attention.

Survival and divergence in a small group: The extraordinary genomic history of the endangered Apennine brown bear stragglers

“…This conservation paradigm, strictly related to the extinction vortex metaphor (5), is supported by empirical evidence (6)(7)(8), but it is challenged by studies showing that selection can be powerful also at small population sizes (9,10) and that survival and even demographic expansion can occur with almost no genomic variation (11). Interestingly, if extinction does not occur, drift in small isolated groups can produce, or contribute to, genetic and phenotypic divergence, possibly leading to speciation (12,13).…”

Does the terrestrial biosphere have planetary tipping points?

“…At low levels of aggregate habitat loss, when contiguous areas are reduced in area but retain connectivity, a biotic variable like abundance will typically decline proportionally with the amount of suitable habitat in a landscape. When habitats decline below a certain threshold, however, nonlinear changes emerge in response to shrinking patch size and increasing patch isolation, potentially enhanced by the Allee effect [41] and other synergies (see also [42,43]). Eventually, a tipping point is transgressed, after which patch sizes might become too small to sustain a local population, and isolation reduces dispersal ability between patches, reinforced by positive feedbacks and leading to metapopulation instability or collapse.…”

Time to competitive exclusion

“…A predictive theory of extinction is lacking, however (Belovsky et al 2002, Drake 2005, despite relatively accurate prediction of the time to decline to quasi-extinction (Brook et al 2000, Fagan andHolmes 2006). Answering these larger ecological questions will depend on improved understanding of the dynamics of particular populations, especially how population characteristics, interspecific interactions and environment influence extinction time.…”