Catastrophic events and recovery from low densities in populations of otariids: implications for risk of extinction

Gerber, Leah R.; Hilborn, Ray

doi:10.1046/j.1365-2907.2001.00081.x

Cited by 95 publications

(94 citation statements)

References 55 publications

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“…Similar population recoveries following catastrophic events have been reported among otrariids (Gerber & Hilborn 2001). The recovery during the first years appeared to be slower than potentially allowed by the high survival rate of the individuals.…”

Section: Discussionsupporting

confidence: 78%

“…Small populations are at greater risk of extinction than large ones as a result of environmental variation or demographic stochasticity and processes, such as the Allee effect (Lande 1993, Mangel & Tier 1994, Courchamp et al 1999, Coulson et al 2001, Gerber & Hilborn 2001, Berec et al 2007, Good et al 2008, Melbourne & Hastings 2008. These general conclusions raise concerns for the conservation of small populations.…”

Section: Introductionmentioning

confidence: 99%

“…Similarly, small populations might recover from a catastrophic event and continue to grow faster than before the catastrophe (Martinez-Abrain et al 2012). The potential for fast growth after a catastrophic event, and the mechanisms that permit a population to increase in size towards carrying capacity, are poorly understood (Gerber & Hilborn 2001. Study of the resilience of small populations after a catastrophic event helps to identify the drivers and synergistic processes that explain and predict recoveries of populations of endangered species, and thus provides important information for the conservation of such populations.…”

Section: Introductionmentioning

confidence: 99%

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Population resilience of the Mediterranean monk seal Monachus monachus at Cabo Blanco peninsula

Martínez‐Jauregui¹,

Tavecchia²,

Cedenilla³

et al. 2012

Mar. Ecol. Prog. Ser.

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Environmental and demographic stochasticity alone can push small populations to extinction. However, some small populations can persist for a long time at a low density, maintaining potential for rapid growth. We investigated the demographic mechanisms underlying the response of the population of the Mediterranean monk seal Monachus monachus on the Cabo Blanco peninsula (Mauritania/Morocco). The population was dramatically reduced after a demographic crash in 1997, which was initially thought to have pushed the population toward extinction. Census data, individual-based data on presence−absence and breeding state data were obtained by direct observation, by photo-identification and through the analysis of video images at the only known breeding sites for the species. We found that the monk seal population at Cabo Blanco is recovering, with means of 31 (24.8, 36.8) sub-adults, 46 (42.3, 49.7) adult females and 39 (29.1, 48.4) adult males using the 2 breeding sites in 2007. The population structure is similar to proportions prior to the mass mortality event. Annual survival probabilities for sub-adults, adult females and adult males were 0.81 (0.676 to 0.904), 0.99 (0.926 to 0.998) and 0.87 (0.81 to 0.94), respectively. At present, juvenile survival is unknown, but the high survival of females and the high breeding potential are likely to be responsible for the population recovery.

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Section: Discussionsupporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Population resilience of the Mediterranean monk seal Monachus monachus at Cabo Blanco peninsula

Martínez‐Jauregui¹,

Tavecchia²,

Cedenilla³

et al. 2012

Mar. Ecol. Prog. Ser.

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“…only on-shelf foraging, will increase local intraspecifc competition and reduce the population's buffering against changes in the local environment, which may explain the slower recovery and smaller size of this population. Fluctuations in the recovery rate of other seal populations have been linked to environmental factors and in particular El Niño events (Gerber & Hilborn 2001). For example, Galapagos sea lions were severely affected by the 1982-83 El Niño event that caused increased mortality, local redistribution, and a slow recovery (Trill mich & Dellinger 1991).…”

Section: Discussionmentioning

confidence: 99%

Foraging behaviour in two Antarctic fur seal colonies with differing population recoveries

Staniland

Morton²,

Robinson³

et al. 2011

Mar. Ecol. Prog. Ser.

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We compared Antarctic fur seals Arctocephalus gazella breeding at 2 contrasting sites on South Georgia: one high density colony at Bird Island and one lower density colony at Cooper Bay. The population at Cooper Bay was considerably smaller than that at Bird Island despite ample suitable breeding area being available. At Cooper Bay, female seals were longer but weighed less than those breeding at Bird Island and, whilst both maintained the same rate of female pup growth, male pups grew faster at Cooper Bay. Although Bird Island seals dived deeper, they dived less often than Cooper Bay seals so that both populations spent comparable amounts of time in the bottom phase of dives actively foraging. Longer distance oceanic foraging trips that were observed at Bird Island were almost entirely absent from Cooper Bay. Both populations fed on Antarctic krill, but there was an absence of myctophid prey in the diet of seals at Cooper Bay. Evidence suggests that the favoured myctophid prey of fur seals at South Georgia, Protomyctophum choriodon, are absent from the colder waters around the south-east of the island. We propose that, if these energy-rich prey are unavailable in this region then seals at Cooper Bay may find it hard to offset the increased costs of foraging trips with longer duration and distance. This potentially reduced niche width means that the Cooper Bay population may be less buffered against environmental variability. Although food resources appeared to be sufficient during the period of our study, the south-eastern region of South Georgia has increased variability in food resources that, coupled with a smaller area in which to forage, might explain the reduced population size compared to the north-eastern end of the island.

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“…Previous comparative analyses fitting heavy-tailed distributions (distributions with higher probabilities of extreme events than the normal distribution) to time series have not accounted for an underlying population dynamics model (14-17). Alternatively, most examples of population dieoffs come from identifying sudden changes in abundance that exceed a chosen threshold of decline (9,(18)(19)(20). However, this approach does not distinguish events from expected dynamics.…”

mentioning

confidence: 99%

Black-swan events in animal populations

Anderson

Branch

Cooper

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

104

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Black swans are improbable events that nonetheless occur-often with profound consequences. Such events drive important transitions in social systems (e.g., banking collapses) and physical systems (e.g., earthquakes), and yet it remains unclear the extent to which ecological population numbers buffer or suffer from such extremes. Here, we estimate the prevalence and direction of black-swan events (heavy-tailed process noise) in 609 animal populations after accounting for population dynamics (productivity, density dependence, and typical stochasticity). We find strong evidence for black-swan events in ∼4% of populations. These events occur most frequently for birds (7%), mammals (5%), and insects (3%) and are not explained by any life-history covariates but tend to be driven by external perturbations such as climate, severe winters, predators, parasites, or the combined effect of multiple factors. Black-swan events manifest primarily as population die-offs and crashes (86%) rather than unexpected increases, and ignoring heavy-tailed process noise leads to an underestimate in the magnitude of population crashes. We suggest modelers consider heavy-tailed, downward-skewed probability distributions, such as the skewed Student t used here, when making forecasts of population abundance. Our results demonstrate the importance of both modeling heavy-tailed downward events in populations, and developing conservation strategies that are robust to ecological surprises.mass mortality | ecological surprises | population dynamics | die-offs | ecological risk M ajor surprises (black-swan events) happen more often than expected in financial, social, and natural systems (1-5). Massive unpredictable market swings are responsible for the majority of financial gains and losses (3), fatalities from the largest wars dwarf those from all others (6), and the frequency of the most damaging earthquakes has exceeded past expectations (5). In ecological systems, background rates of global extinction are punctuated by mass extinction (7), evolution is characterized by long periods of stasis interrupted by bursts of speciation (8), and billions of animals can die at once in mass mortality events (9).Indeed, such die-offs may be the most important element affecting population persistence (10) and their importance is likely to increase given projected increases in the frequency and magnitude of climate-related extremes (11). However, the overwhelming majority of population model-fitting and risk-forecasting assumes that deviations from model predictions can be represented by a normal distribution [on a log scale (e.g., refs. 12 and 13)]. If black swans occur, however, a normal distribution would underestimate the probability of extreme events occurring (3).Whereas there are many reports of black-swan events, only a flexible comparative approach consistently applied to a large number of time series can yield insights into the frequency, strength, and correlates of such events. We are unaware of such a comparative analysis. Previous comparative an...

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Catastrophic events and recovery from low densities in populations of otariids: implications for risk of extinction

Cited by 95 publications

References 55 publications

Population resilience of the Mediterranean monk seal Monachus monachus at Cabo Blanco peninsula

Population resilience of the Mediterranean monk seal Monachus monachus at Cabo Blanco peninsula

Foraging behaviour in two Antarctic fur seal colonies with differing population recoveries

Black-swan events in animal populations

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