Drastic population fluctuations explain the rapid extinction of the passenger pigeon

Abstract

To assess the role of human disturbances in species' extinction requires an understanding of the species population history before human impact. The passenger pigeon was once the most abundant bird in the world, with a population size estimated at 3-5 billion in the 1800s; its abrupt extinction in 1914 raises the question of how such an abundant bird could have been driven to extinction in mere decades. Although human exploitation is often blamed, the role of natural population dynamics in the passenger pigeon's extinction remains unexplored. Applying high-throughput sequencing technologies to obtain sequences from most of the genome, we calculated that the passenger pigeon's effective population size throughout the last million years was persistently about 1/10,000 of the 1800's estimated number of individuals, a ratio 1,000-times lower than typically found. This result suggests that the passenger pigeon was not always super abundant but experienced dramatic population fluctuations, resembling those of an "outbreak" species. Ecological niche models supported inference of drastic changes in the extent of its breeding range over the last glacial-interglacial cycle. An estimate of acorn-based carrying capacity during the past 21,000 y showed great year-to-year variations. Based on our results, we hypothesize that ecological conditions that dramatically reduced population size under natural conditions could have interacted with human exploitation in causing the passenger pigeon's rapid demise. Our study illustrates that even species as abundant as the passenger pigeon can be vulnerable to human threats if they are subject to dramatic population fluctuations, and provides a new perspective on the greatest human-caused extinction in recorded history

Past and potential future population dynamics of three grouse species using ecological and whole genome coalescent modeling

“…One such method is the Pairwise Sequentially Markovian Coalescent model (PSMC; Li & Durbin, 2011). It allows for the tracking of species’ effective population size ( N e ) from 10 thousand years ago (kya) through to Early Pleistocene/Late Pliocene (~3 million years ago [Mya]) from the genome of just one individual (Hung et al., 2014; Nadachowska‐Brzyska, Li, Smeds, Zhang, & Ellegren, 2015; Zhao et al., 2013). It therefore the ideal tool to study whether the changes in range size through time, as determined by SDM, reflect the changes in population size.…”

Lazarus ecology: Recovering the distribution and migratory patterns of the extinct Carolina parakeet

“…The potential for rediscovering our lost natural history has been on the minds of ecologists with the recent centennial anniversary of the death of the last captive passenger pigeon ( Ectopistes migratorius Linnaeus) in 1914, and the controversial “resighting” of the ivory‐billed woodpecker ( Campephilus principalis Linnaeus, Fitzpatrick et al., 2005 but see Sibley, Bevier, Patten, & Elphick, 2006). Indeed, much recent research has focused on these recently extinct, iconic North American birds (e.g., Gotelli, Chao, Colwell, Hwang, & Graves, 2012; Hung et al., 2014; Stanton, 2014), but this research largely focuses on attempts to determine exact extinction dates and immediate causes of extinction. By contrast, another iconic, extinct, North American bird, the Carolina parakeet ( Conuropsis carolinensis Linnaeus), has received relatively less attention, especially over the past 30 years.…”

Conserving migratory and nomadic species

“…Conversion of key refugia for the once abundant Rocky Mountain grasshopper (Melanoplus spretus) resulted in the extinction of a species that once existed in the USA in its trillions, and was thought to be an ineradicable pest (Lockwood & DeBrey 1990). Similarly, the passenger pigeon (Ectopistes migratorius) was once the most abundant bird in the world, with flocks of birds covering the sky for miles, yet recent research suggests that human exploitation coincided with natural population fluctuations to drive the species to extinction in just 50 years (Hung et al 2014). …”

“…The impact of fluctuations on population persistence is a function of the number of subpopulations and the synchronicity of fluctuation across those populations (Lawton et al 1994). Both theory and empirical evidence predict that extinction risk is higher in species with highly fluctuating populations (Pimm et al 1988;Hung et al 2014 . These species evolved in a landscape where environmental conditions are dynamic, and strategies such as opportunistic breeding and diet switching may facilitate the ability of arid-zone birds to recover from bottlenecks (Dean 2004).…”

“…Such questions will be difficult, if not impossible, to answer empirically, but simulation experiments may provide some insights (Keith et al 2008). Recent work on the demise of the passenger pigeon (Ectopistes migratorius; Hung et al 2014) highlights that even hugely abundant species can decline rapidly if fluctuating environmental conditions coincide with increased threats. The lack of ecological knowledge in most existing nomadic species limits our understanding of the thresholds beyond which nomads are unlikely to bounce back from range declines, and we lack understanding on the extent to which the ability to recover depends on the timing and frequency of fluctuations.…”