The mechanism of background extinction

Abstract

Following publication of On the Origin of Species, biologists concentrated on and resolved the mechanisms of adaptation and speciation, but largely ignored extinction. Thus, extinction remained essentially a discipline of palaeontology. Adequate language is not available to describe extinction phenomena because they must be discussed in the passive voice, wherein populations simply ‘go extinct’ without reference to process, specifics, effects, or causality. Extinction is also described typically in terms of its dynamics (including rate or risk), and although correlative variables enhance our ability to predict extinction, they do not necessarily enable an understanding of process. Yet background extinction, like evolution, is a process requiring a functional explanation, without which it is impossible to formulate mechanisms. We define the mechanism of background extinction as a typically long‐term, multi‐generational loss of reproductive fitness. This simple concept has received little credence because of a perception that excess generation of progeny ensures population sustainability, and perhaps the misconception that the loss of reproductive fitness somehow constitutes selection against reproduction itself. During environmental shifts, reproductive fitness is compromised when biotic or abiotic extremes consistently exceed existing norms of reaction. Subsequent selection will now favour individual survival over reproductive fitness, initiating long‐term negative selection pressure and population decline. Background extinction consists typically of two intergrading phases: habitat attenuation and habitat dissolution. These processes generate the relict populations that characterize many species undergoing background extinction. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 255–268.

Population decline in Adenostoma sparsifolium (Rosaceae): an ecogenetic hypothesis for background extinction‡

“…Such species possess suites of reproductive and vegetative characteristics that are not adapted to the present climatic regimes (or other ecological factors) of the ecosystems in which they now occur. Such discordant traits are indicative of species in permanent decline and were probably adapted to survival and reproductive success in environments of the recent geological past (Ackerly, 2004; Wiens & Slaton, 2011).…”

“…Background extinctions must therefore account for the great majority of extinctions through biohistory and are considered by palaeontologists to have characteristics distinct from mass extinctions (Jablonski, 1986, 2005). Yet background extinction has received little empirical attention from the biological community (Raup, 1994; Wiens & Slaton, 2011).…”

“…We define the loss of reproductive fitness as the long‐term, continuous loss of reproductive potential ( r ) as a result of an adverse environmental shift. The selective agent is now the transformed environment in which almost no genotypes in the population are able to survive in sufficient numbers to offset adult mortality (Wiens & Slaton, 2011).…”

Can oncology recapitulate paleontology? Lessons from species extinctions

“…11 The vast majority (~95%) of these losses of species are due to background extinction, 12 where a normal or spontaneous process results in replacement of one species with another. 13 Although little is known about the processes and mechanisms of background extinction, it can be avoided by successful adaptation in the face of ecological changes, including environmental deterioration and harmful effects of other species (competitors or predators).…”

“…14 In multicellular organisms, background extinctions are thought to result from environmental challenges, or from long-term, multi-generational losses in reproductive fitness caused by genetic factors. 12 Background extinction can be driven by the failure of species to keep pace with a deteriorating environment, as can occur with a change in climate. 15 Also, a depressed rate of origination is as important as an increased extinction rate in reducing biodiversity.…”