Conservation biology of marine fishes: perceptions and caveats regarding assignment of extinction risk

2001 ◽  
Vol 58 (1) ◽  
pp. 108-121 ◽  
Author(s):  
Jeffrey A Hutchings
Keyword(s):  
Population Size ◽  
Extinction Risk ◽  
Population Decline ◽  
Empirical Support ◽  
Marine Fishes ◽  
Marine Biodiversity ◽  
Population Declines ◽  
High Fecundity ◽  
Reproductive Rates ◽  
Biological Extinction

Quantitative criteria used to assign species to categories of extinction risk may seriously overestimate these risks for marine fishes. Contemporary perception is that marine fishes may be less vulnerable to extinction than other taxa, because of great natural variability in abundance, high fecundity, rapid population growth, and an intrinsically high capability of recovering from low population size. Contrary to perception, however, there appears to be generally little theoretical or empirical support for the hypotheses that marine fish are more likely to experience large reductions in population size, to produce unusually high levels of recruitment, to have higher reproductive rates, or to recover more rapidly from prolonged population declines than nonmarine fishes. Although existing population-decline criteria may not accurately reflect probabilities of biological extinction, they do appear to reflect the converse-population recovery. Insufficient support for contemporary perceptions of their susceptibility to extinction, coupled with caveats associated with the assignment of extinction risk, suggest that significant increases in the population-decline thresholds used to assign marine fishes to at-risk categories would be inconsistent with a precautionary approach to fisheries management and the conservation of marine biodiversity.

scholarly journals Predicting how populations decline to extinction

2011 ◽  
Vol 366 (1577) ◽  
pp. 2577-2586 ◽  
Author(s):  
Ben Collen ◽  
Louise McRae ◽  
Stefanie Deinet ◽  
Adriana De Palma ◽  
Tharsila Carranza ◽  
...  
Keyword(s):  
At Risk ◽  
Extinction Risk ◽  
Mammalian Species ◽  
Local Population ◽  
Population Decline ◽  
Scale Up ◽  
Population Level ◽  
Biological Traits ◽  
Population Declines ◽  
Trend Data

Global species extinction typically represents the endpoint in a long sequence of population declines and local extinctions. In comparative studies of extinction risk of contemporary mammalian species, there appear to be some universal traits that may predispose taxa to an elevated risk of extinction. In local population-level studies, there are limited insights into the process of population decline and extinction. Moreover, there is still little appreciation of how local processes scale up to global patterns. Advancing the understanding of factors which predispose populations to rapid declines will benefit proactive conservation and may allow us to target at-risk populations as well as at-risk species. Here, we take mammalian population trend data from the largest repository of population abundance trends, and combine it with the PanTHERIA database on mammal traits to answer the question: what factors can be used to predict decline in mammalian abundance? We find in general that environmental variables are better determinants of cross-species population-level decline than intrinsic biological traits. For effective conservation, we must not only describe which species are at risk and why, but also prescribe ways to counteract this.

scholarly journals Coalescent models at small effective population sizes and population declines are positively misleading

2019 ◽  
Author(s):  
M. Elise Lauterbur
Keyword(s):  
Genetic Diversity ◽  
Sample Size ◽  
Population Size ◽  
Effective Population Size ◽  
Genetic Relationships ◽  
Population Decline ◽  
Population Declines ◽  
Effective Population ◽  
Analytical Approximations ◽  
Population Sizes

AbstractPopulation genetics employs two major models for conceptualizing genetic relationships among individuals – outcome-driven (coalescent) and process-driven (forward). These models are complementary, but the basic Kingman coalescent and its extensions make fundamental assumptions to allow analytical approximations: a constant effective population size much larger than the sample size. These make the probability of multiple coalescent events per generation negligible. Although these assumptions are often violated in species of conservation concern, conservation genetics often uses coalescent models of effective population sizes and trajectories in endangered species. Despite this, the effect of very small effective population sizes, and their interaction with bottlenecks and sample sizes, on such analyses of genetic diversity remains unexplored. Here, I use simulations to analyze the influence of small effective population size, population decline, and their relationship with sample size, on coalescent-based estimates of genetic diversity. Compared to forward process-based estimates, coalescent models significantly overestimate genetic diversity in oversampled populations with very small effective sizes. When sampled soon after a decline, coalescent models overestimate genetic diversity in small populations regardless of sample size. Such overestimates artificially inflate estimates of both bottleneck and population split times. For conservation applications with small effective population sizes, forward simulations that do not make population size assumptions are computationally tractable and should be considered instead of coalescent-based models. These findings underscore the importance of the theoretical basis of analytical techniques as applied to conservation questions.

scholarly journals Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus)

2017 ◽  
Author(s):  
Susan J Crockford
Keyword(s):  
Sea Ice ◽  
Population Size ◽  
Habitat Loss ◽  
Polar Bear ◽  
Population Decline ◽  
Ursus Maritimus ◽  
The Arctic ◽  
Polar Bears ◽  
Population Declines ◽  
Sea Ice Decline

The polar bear (Ursus maritimus) was the first species to be classified as threatened with extinction based on predictions of future conditions rather than current status. These predictions were made using expert-opinion forecasts of population declines linked to modeled habitat loss – first by the International Union for the Conservation of Nature (IUCN)’s Red List in 2006, and then by the United States Fish and Wildlife Service (USFWS) in 2008 under the Endangered Species Act (ESA), based on data collected to 2005 and 2006, respectively. Both assessments predicted significant population declines of polar bears would result by mid-century as a consequence of summer sea ice extent rapidly reaching 3-5 mkm2 on a regular basis: the IUCN predicted a >30% decline in total population, while the USFWS predicted the global population would decline by 67% (including total extirpation of ten subpopulations within two vulnerable ecoregions). Biologists involved in these conservation assessments had to make several critical assumptions about how polar bears might be affected by future habitat loss, since sea ice conditions predicted to occur by 2050 had not occurred prior to 2006. However, summer sea ice declines have been much faster than expected: low ice levels not expected until mid-century (about 3-5 mkm2) have occurred regularly since 2007. Realization of predicted sea ice levels allows the ‘rapid sea ice decline = population decline’ assumption for polar bears to be treated as a testable hypothesis. Data collected between 2007 and 2015 reveal that polar bear numbers have not declined as predicted and no subpopulation has been extirpated. Several subpopulations expected to be at high risk of decline remained stable and five showed increases in population size. Another at-risk subpopulation was not counted but showed marked improvement in reproductive parameters and body condition with less summer ice. As a consequence, the hypothesis that repeated summer sea ice levels of below 5 mkm2 will cause significant population declines in polar bears is rejected, a result that indicates the ESA and IUCN judgments to list polar bears as threatened based on future risks of habitat loss were scientifically unfounded and that similar predictions for Arctic seals and walrus may be likewise flawed. The lack of a demonstrable ‘rapid sea ice decline = population decline’ relationship for polar bears also potentially invalidates updated survival model outputs that predict catastrophic population declines should the Arctic become ice-free in summer.

scholarly journals Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus)

2017 ◽  
Author(s):  
Susan J Crockford
Keyword(s):  
Sea Ice ◽  
Population Size ◽  
Habitat Loss ◽  
Polar Bear ◽  
Population Decline ◽  
Ursus Maritimus ◽  
The Arctic ◽  
Polar Bears ◽  
Population Declines ◽  
Sea Ice Decline

The polar bear (Ursus maritimus) was the first species to be classified as threatened with extinction based on predictions of future conditions rather than current status. These predictions were made using expert-opinion forecasts of population declines linked to modeled habitat loss – first by the International Union for the Conservation of Nature (IUCN)’s Red List in 2006, and then by the United States Fish and Wildlife Service (USFWS) in 2008 under the Endangered Species Act (ESA), based on data collected to 2005 and 2006, respectively. Both assessments predicted significant population declines of polar bears would result by mid-century as a consequence of summer sea ice extent rapidly reaching 3-5 mkm2 on a regular basis: the IUCN predicted a >30% decline in total population, while the USFWS predicted the global population would decline by 67% (including total extirpation of ten subpopulations within two vulnerable ecoregions). Biologists involved in these conservation assessments had to make several critical assumptions about how polar bears might be affected by future habitat loss, since sea ice conditions predicted to occur by 2050 had not occurred prior to 2006. However, summer sea ice declines have been much faster than expected: low ice levels not expected until mid-century (about 3-5 mkm2) have occurred regularly since 2007. Realization of predicted sea ice levels allows the ‘rapid sea ice decline = population decline’ assumption for polar bears to be treated as a testable hypothesis. Data collected between 2007 and 2015 reveal that polar bear numbers have not declined as predicted and no subpopulation has been extirpated. Several subpopulations expected to be at high risk of decline remained stable and five showed increases in population size. Another at-risk subpopulation was not counted but showed marked improvement in reproductive parameters and body condition with less summer ice. As a consequence, the hypothesis that repeated summer sea ice levels of below 5 mkm2 will cause significant population declines in polar bears is rejected, a result that indicates the ESA and IUCN judgments to list polar bears as threatened based on future risks of habitat loss were scientifically unfounded and that similar predictions for Arctic seals and walrus may be likewise flawed. The lack of a demonstrable ‘rapid sea ice decline = population decline’ relationship for polar bears also potentially invalidates updated survival model outputs that predict catastrophic population declines should the Arctic become ice-free in summer.

scholarly journals Inferring the Demographic History of Japanese Eel (Anguilla japonica) from Genomic Data: Insights for Conservation and Fisheries Management

2021 ◽  
Author(s):  
Leanne Faulks ◽  
Prashant Kaushik ◽  
Shoji Taniguchi ◽  
Masashi Sekino ◽  
Reiichiro Nakamichi ◽  
...  
Keyword(s):  
Population Size ◽  
Environmental Conditions ◽  
Wildlife Conservation ◽  
Demographic History ◽  
Population Decline ◽  
Anguilla Japonica ◽  
Japanese Eel ◽  
Population Declines ◽  
Effective Population ◽  
History Of

Assessing the status or population size of species is a key task for wildlife conservation and the sustainable management of harvested species. In particular, assessing historical changes in population size provides an evolutionary perspective on current population dynamics and can help distinguish between anthropogenic and natural causes for population decline. Japanese eel (Anguilla japonica) is an endangered yet commercially important catadromous fish species. Here we assess the demographic history of Japanese eel using the pairwise and multiple sequentially Markovian coalescent methods. The analyses indicate a reduction in effective population size (Ne) from 38 000 to 10 000 individuals between 4 and 1 Ma, followed by an increase to 80 000 individuals, between 1 Ma and 22-30 kya. Approximately 22-30 kya there is evidence for a reduction in Ne to approximately 60 000 individuals. These events are likely due to changes in environmental conditions, such as sea level and oceanic currents, especially around the last glacial maximum (19-33 kya). The results of this study suggest that Japanese eel has experienced at least two population bottlenecks, interspersed by a period of population growth. This pattern of demographic history may make Japanese eel sensitive to current and future population declines. Conservation management of Japanese eel should focus on practical ways to prevent further population decline and the loss of genetic diversity that is essential for the species to adapt to changing environmental conditions such as climate change.

scholarly journals Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus)

2017 ◽  
Author(s):  
Susan J Crockford
Keyword(s):  
Sea Ice ◽  
Population Size ◽  
Habitat Loss ◽  
Polar Bear ◽  
Population Decline ◽  
Ursus Maritimus ◽  
The Arctic ◽  
Polar Bears ◽  
Population Declines ◽  
Sea Ice Decline

The polar bear (Ursus maritimus) was the first species to be classified as threatened with extinction based on predictions of future conditions rather than current status. These predictions were made using expert-opinion forecasts of population declines linked to modeled habitat loss – first by the International Union for the Conservation of Nature (IUCN)’s Red List in 2006, and then by the United States Fish and Wildlife Service (USFWS) in 2008 under the Endangered Species Act (ESA), based on data collected to 2005 and 2006, respectively. Both assessments predicted significant population declines of polar bears would result by mid-century as a consequence of summer sea ice extent rapidly reaching 3-5 mkm2 on a regular basis: the IUCN predicted a >30% decline in total population, while the USFWS predicted the global population would decline by 67% (including total extirpation of ten subpopulations within two vulnerable ecoregions). Biologists involved in these conservation assessments had to make several critical assumptions about how polar bears might be affected by future habitat loss, since sea ice conditions predicted to occur by 2050 had not occurred prior to 2006. However, summer sea ice declines have been much faster than expected: low ice levels not expected until mid-century (about 3-5 mkm2) have occurred regularly since 2007. Realization of predicted sea ice levels allows the ‘rapid sea ice decline = population decline’ assumption for polar bears to be treated as a testable hypothesis. Data collected between 2007 and 2015 reveal that polar bear numbers have not declined as predicted and no subpopulation has been extirpated. Several subpopulations expected to be at high risk of decline remained stable and five showed increases in population size. Another at-risk subpopulation was not counted but showed marked improvement in reproductive parameters and body condition with less summer ice. As a consequence, the hypothesis that repeated summer sea ice levels of below 5 mkm2 will cause significant population declines in polar bears is rejected, a result that indicates the ESA and IUCN judgments to list polar bears as threatened based on future risks of habitat loss were scientifically unfounded and that similar predictions for Arctic seals and walrus may be likewise flawed. The lack of a demonstrable ‘rapid sea ice decline = population decline’ relationship for polar bears also potentially invalidates updated survival model outputs that predict catastrophic population declines should the Arctic become ice-free in summer.

scholarly journals Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus)

2017 ◽  
Author(s):  
Susan J Crockford
Keyword(s):  
Sea Ice ◽  
Population Size ◽  
Habitat Loss ◽  
Polar Bear ◽  
Population Decline ◽  
Ursus Maritimus ◽  
The Arctic ◽  
Polar Bears ◽  
Population Declines ◽  
Sea Ice Decline

The polar bear (Ursus maritimus) was the first species to be classified as threatened with extinction based on predictions of future conditions rather than current status. These predictions were made using expert-opinion forecasts of population declines linked to modeled habitat loss – first by the International Union for the Conservation of Nature (IUCN)’s Red List in 2006, and then by the United States Fish and Wildlife Service (USFWS) in 2008 under the Endangered Species Act (ESA), based on data collected to 2005 and 2006, respectively. Both assessments predicted significant population declines of polar bears would result by mid-century as a consequence of summer sea ice extent reaching 3-5 mkm2 on a regular basis: the IUCN predicted a >30% decline in total population, while the USFWS predicted the global population would decline by 67% (including total extirpation of ten subpopulations within two vulnerable ecoregions). Biologists involved in these conservation assessments had to make several critical assumptions about how polar bears might be affected by future habitat loss, since sea ice conditions predicted to occur by 2050 had not occurred prior to 2006. However, summer sea ice declines have been much faster than expected: low ice levels not expected until mid-century (about 3-5 mkm2) have occurred regularly since 2007. Realization of predicted sea ice levels allows the ‘sea ice decline = population decline’ assumption for polar bears to be treated as a testable hypothesis. Data collected between 2007 and 2015 reveal that polar bear numbers have not declined as predicted and no subpopulation has been extirpated. Several subpopulations expected to be at high risk of decline have remained stable and at least one showed a marked increase in population size over the entire period. Another at-risk subpopulation was not counted but showed marked improvement in reproductive parameters and body condition with less summer ice. As a consequence, the hypothesis that repeated summer sea ice levels of below 5 mkm2 will cause significant population declines in polar bears is rejected. This result indicates that the ESA and IUCN judgments to list polar bears as threatened based on future risks of habitat loss were hasty generalizations that were scientifically unfounded, which suggests that similar predictions for Arctic seals and walrus may be likewise flawed, while the lack of a demonstrable ‘sea ice decline = population decline’ relationship for polar bears invalidates updated survival model outputs that predict catastrophic population declines should the Arctic become ice-free in summer.

Underwater but not out of sight: genetic monitoring of effective population size in the endangered North Sea houting (Coregonus oxyrhynchus)

2006 ◽  
Vol 63 (4) ◽  
pp. 780-787 ◽  
Author(s):  
Michael M Hansen ◽  
Einar E Nielsen ◽  
Karen-Lise D Mensberg
Keyword(s):  
Population Size ◽  
Effective Population Size ◽  
North Sea ◽  
Population Decline ◽  
Genetic Monitoring ◽  
Population Declines ◽  
Effective Population ◽  
The North ◽  
The North Sea ◽  
Temporal Method

We analysed 12 microsatellite DNA loci in temporal samples (1980, 1994, and 2002) from the only remaining indigenous population of the North Sea houting (Coregonus oxyrhynchus) in the Vidaa River, Denmark. Using a novel temporal method, we estimated effective population size (Ne) to be 577.4 (90% highest posterior density limits 297.2–3719.8). The same method was used to estimate Ne at the beginning and end of the sampled time interval, and the results were indicative of a relatively stable population. In contrast, tests for recent bottlenecks suggested population declines in the 1980 and 1994 samples, possibly reflecting declines prior to 1980 in the total North Sea houting population. To evaluate the usefulness of the two methods for routine genetic monitoring, we simulated population declines corresponding to reproduction by only 20 or 50 parents in 2002. For both simulated samples, the temporal method provided evidence for a population decline, whereas the test for bottlenecks did not suggest population decline. We conclude that the North Sea houting in the Vidaa River is not immediately threatened by inbreeding or loss of evolutionary potential, and the applied temporal method appears very useful for genetic monitoring of effective population size in endangered, isolated fish populations.

scholarly journals Cost-efficient factors in local public spending: Detecting relationships between local environments, population size and urban area category

2021 ◽  
pp. 239980832110038
Author(s):  
Hiroki Baba ◽  
Yasushi Asami
Keyword(s):  
Population Size ◽  
Urban Area ◽  
Urban Areas ◽  
Local Governments ◽  
Statistical Significance ◽  
Population Decline ◽  
Public Spending ◽  
Local Environment ◽  
Environment Factors ◽  
Major Factors

This study examines regional differences in local environment factors to better understand the sustainability of local governments indexed by per capita public spending. Under the condition of heterogeneous population size, we examine how factor characteristics differ depending on the spatial context represented by the urban area category. By employing a Cobb–Douglas cost function with congestion effects on public service provision, the estimated factors enable us to articulate major factors and differences in cost-efficiency between urban area categories. We found that statistical significance and even the signatures of local environment factors differ depending on the urban employment area category. Regarding factors such as the ratios of employees in secondary and tertiary industries, these did not tend to be statistically significant in small-sized urban areas, while small-sized cities in large-sized urban areas were likely to gain confidence intervals. Moreover, we did not observe any statistical significance for the ratio of elderly people due to the balance of spending between national and local governments. These findings could contribute to sustainable management of cities in the advent of population decline.

scholarly journals Large numbers of vertebrates began rapid population decline in the late 19th century

2016 ◽  
Vol 113 (49) ◽  
pp. 14079-14084 ◽  
Author(s):  
Haipeng Li ◽  
Jinggong Xiang-Yu ◽  
Guangyi Dai ◽  
Zhili Gu ◽  
Chen Ming ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Population Size ◽  
Threatened Species ◽  
Driving Forces ◽  
Population Decline ◽  
Cumulative Effect ◽  
Extinction Time ◽  
Time Period ◽  
Large Numbers ◽  
The Difference

Accelerated losses of biodiversity are a hallmark of the current era. Large declines of population size have been widely observed and currently 22,176 species are threatened by extinction. The time at which a threatened species began rapid population decline (RPD) and the rate of RPD provide important clues about the driving forces of population decline and anticipated extinction time. However, these parameters remain unknown for the vast majority of threatened species. Here we analyzed the genetic diversity data of nuclear and mitochondrial loci of 2,764 vertebrate species and found that the mean genetic diversity is lower in threatened species than in related nonthreatened species. Our coalescence-based modeling suggests that in many threatened species the RPD began ∼123 y ago (a 95% confidence interval of 20–260 y). This estimated date coincides with widespread industrialization and a profound change in global living ecosystems over the past two centuries. On average the population size declined by ∼25% every 10 y in a threatened species, and the population size was reduced to ∼5% of its ancestral size. Moreover, the ancestral size of threatened species was, on average, ∼22% smaller than that of nonthreatened species. Because the time period of RPD is short, the cumulative effect of RPD on genetic diversity is still not strong, so that the smaller ancestral size of threatened species may be the major cause of their reduced genetic diversity; RPD explains 24.1–37.5% of the difference in genetic diversity between threatened and nonthreatened species.

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