Rewriting the history of an extinction—was a population of Steller's sea cows (Hydrodamalis gigas) at St Lawrence Island also driven to extinction?

The Kommandorskiye Islands population of Steller''s sea cow (Hydrodamalis gigas) was extirpated ca 1768 CE. Until now, Steller''s sea cow was thought to be restricted in historic times to Bering and Copper Islands, Russia, with other records in the last millennium from the western Aleutian Islands. However, Steller''s sea cow bone has been obtained by the authors from St Lawrence Island, Alaska, which is significantly further north. Bone identity was verified using analysis of mitochondrial DNA. The nitrogen-15 (δ¹⁵N)/carbon-13 (δ¹³C) values for bone samples from St Lawrence Island were significantly (p ≤ 0.05) different from Bering Island samples, indicating a second population. Bone samples were dated to between 1030 and 1150 BP (approx. 800–920 CE). The samples date from close to the beginning of the mediaeval warm period, which could indicate that the population at St Lawrence Island was driven to extinction by climate change. A warming of the climate in the area may have changed the availability of kelp; alternatively or in addition, the animals may have been driven to extinction by the expansion of the Inuit from the Bering Strait region, possibly due to opening waterways, maybe following bowhead whales (Balaena mysticetus), or searching for iron and copper. This study provides evidence for a previously unknown population of sea cows in the North Pacific within the past 1000 years and a second Steller''s sea cow extirpation event in recent history.     

中国水獭保护现状及珠江口水獭种群重建探讨

顶级捕食者在生态系统中发挥着重要作用，受到研究者们的广泛关注。水獭作为很多淡水生态系统的顶级捕食者，在我国却长期处于被忽视的状态。我国分布有3种水獭--欧亚水獭、亚洲小爪水獭和江獭，曾经遍布我国中东部和东北地区，包括珠江口地区。但在20世纪，3种水獭均经历了大规模的种群下降，甚至区域性灭绝。在全球13种水獭中，已有3种（海獭、北美水獭和欧亚水獭）通过种群复壮和重引入实现了种群重建，这为其它水獭物种的种群重建提供了重要参考和建议。同国内其它地区类似，珠江口地区的水獭种群在20世纪后期大量减少，目前只在少数几个地点还有确切的欧亚水獭分布记录，亚洲小爪水獭和江獭已无近期记录。在珠江口重建水獭种群具有重要的生态意义和社会价值。本文对重建珠江口水獭种群的相关问题进行了分析。     

Climate‐driven ecological stability as a globally shared cause of Late Quaternary megafaunal extinctions: the Plaids and Stripes Hypothesis

Controversy persists about why so many large‐bodied mammal species went extinct around the end of the last ice age. Resolving this is important for understanding extinction processes in general, for assessing the ecological roles of humans, and for conserving remaining megafaunal species, many of which are endangered today. Here we explore an integrative hypothesis that asserts that an underlying cause of Late Quaternary megafaunal extinctions was a fundamental shift in the spatio‐temporal fabric of ecosystems worldwide. This shift was triggered by the loss of the millennial‐scale climate fluctuations that were characteristic of the ice age but ceased approximately 11700 years ago on most continents. Under ice‐age conditions, which prevailed for much of the preceding 2.6 Ma, these radical and rapid climate changes prevented many ecosystems from fully equilibrating with their contemporary climates. Instead of today's ‘striped’ world in which species' ranges have equilibrated with gradients of temperature, moisture, and seasonality, the ice‐age world was a disequilibrial ‘plaid’ in which species' ranges shifted rapidly and repeatedly over time and space, rarely catching up with contemporary climate. In the transient ecosystems that resulted, certain physiological, anatomical, and ecological attributes shared by megafaunal species pre‐adapted them for success. These traits included greater metabolic and locomotory efficiency, increased resistance to starvation, longer life spans, greater sensory ranges, and the ability to be nomadic or migratory. When the plaid world of the ice age ended, many of the advantages of being large were either lost or became disadvantages. For instance in a striped world, the low population densities and slow reproductive rates associated with large body size reduced the resiliency of megafaunal species to population bottlenecks. As the ice age ended, the downsides of being large in striped environments lowered the extinction thresholds of megafauna worldwide, which then increased the vulnerability of individual species to a variety of proximate threats they had previously tolerated, such as human predation, competition with other species, and habitat loss. For many megafaunal species, the plaid‐to‐stripes transition may have been near the base of a hierarchy of extinction causes whose relative importances varied geographically, temporally, and taxonomically.     

Applied zooarchaeology and Oregon Coast sea otters (Enhydra lutris)

The sea otter (Enhydra lutris) was nearly driven to extinction on the Pacific Coast in the 19th century due to intensive commercial hunting and the maritime fur trade. Despite successful reintroduction efforts elsewhere in North America, the Oregon sea otter population remains locally extirpated and listed as endangered. Prior study addressed precontact sea otter teeth from Oregon and found they were not significantly different in absolute size from modern California sea otter (Enhydra lutris nereis) teeth, and smaller than modern Alaska sea otter (Enhydra lutris lutris) teeth. These geographic groupings were later confirmed by an ancient DNA study. The conclusion that distinct geographic populations exist based on tooth size was founded on small samples. Larger samples of teeth, as well as new data on humeri and femora, indicate dimensions vary significantly along a latitudinal cline from California to Alaska. Morphometric analyses of ancient animal remains can be used to examine spatial relationships of phenotypic features and inform conservation biology decisions.     

Influence of occupation history and habitat on Washington sea otter diet

Habitat characteristics are primary determinants of nearshore marine communities. However, biological drivers like predation can also be important for community composition. Sea otters (Enhydra lutris ssp.) are a salient example of a keystone species exerting top‐down control on ecosystem community structure. The translocation and subsequent population growth and range expansion of the northern sea otter (Enhydra lutris kenyoni) in Washington State over the last five decades has created a spatio‐temporal gradient in sea otter occupation time and density, and acts as a natural experiment to quantify how sea otter population status and habitat type influence sea otter diet. We collected focal observations of sea otters foraging at sites across the gradient in varying habitat types between 2010 and 2017. We quantified sea otter diet composition and diversity, and long‐term rates of energy gain across the gradient. We found that sea otter diet diversity was positively correlated with cumulative sea otter density, while rate of energy gain was negatively correlated with cumulative density. Additionally, we found that habitat type explained 1.77 times more variance in sea otter diet composition than sea otter cumulative density. Long‐term diet studies can provide a broader picture of sea otter population status in Washington State.     

DETECTION OF SEA OTTERS IN BOAT-BASED SURVEYS OF PRINCE WILLIAM SOUND, ALASKA

Boat-based surveys have been commonly used to monitor sea otter populations, but there has been little quantitative work to evaluate detection biases that may affect these surveys. We used ground-based observers to investigate sea otter detection probabilities in a boat-based survey of Prince William Sound, Alaska. We estimated that 30% of the otters present on surveyed transects were not detected by boat crews. Approximately half (53%) of the undetected otters were missed because the otters left the transects, apparently in response to the approaching boat. Unbiased estimates of detection probabilities will be required for obtaining unbiased population estimates from boat-based surveys of sea otters. Therefore, boat-based surveys should include methods to estimate sea otter detection probabilities under the conditions specific to each survey. Unbiased estimation of detection probabilities with ground-based observers requires either that the ground crews detect all of the otters in observed subunits, or that there are no errors in determining which crews saw each detected otter. Ground-based observer methods may be appropriate in areas where nearly all of the sea otter habitat is potentially visible from ground-based vantage points.     

Climate,not Aboriginal landscape burning,controlled the historical demography and distribution of fire-sensitive conifer populations across Australia

Climate and fire are the key environmental factors that shape the distribution and demography of plant populations in Australia. Because of limited palaeoecological records in this arid continent, however, it is unclear as to which factor impacted vegetation more strongly, and what were the roles of fire regime changes owing to human activity and megafaunal extinction (since ca 50 kya). To address these questions, we analysed historical genetic, demographic and distributional changes in a widespread conifer species complex that paradoxically grows in fire-prone regions, yet is very sensitive to fire. Genetic demographic analysis showed that the arid populations experienced strong bottlenecks, consistent with range contractions during the Last Glacial Maximum (ca 20 kya) predicted by species distribution models. In southern temperate regions, the population sizes were estimated to have been mostly stable, followed by some expansion coinciding with climate amelioration at the end of the last glacial period. By contrast, in the flammable tropical savannahs, where fire risk is the highest, demographic analysis failed to detect significant population bottlenecks. Collectively, these results suggest that the impact of climate change overwhelmed any modifications to fire regimes by Aboriginal landscape burning and megafaunal extinction, a finding that probably also applies to other fire-prone vegetation across Australia.     

Genotype-specific IL8RA gene expression in bovine neutrophils in response to Escherichia coli lipopolysaccharide challenge

Associations between the AC150887.4:c.-1768T>A SNP (rs41255711), which is located in the 5' upstream region of the IL8RA gene (also known as CXCR1), and the estimated breeding values for somatic cell score in the first (P = 0.019) and second (P = 0.035) lactations were previously reported in a population of Canadian Holstein bulls. In the present study, we evaluated the impact of this SNP on the expression of IL8RA by qRT-PCR. Neutrophils were isolated from whole blood samples from a group of cows with genotypes c.-1768AA (n = 4), c.-1768AT (n = 5) and c.-1768TT (n = 5) after the cows had been challenged in vitro with lipopolysaccharide (LPS). This study demonstrated that LPS-induced expression of IL8RA in cows with the c.-1768AA genotype was significantly greater when compared with the c.-1768AT and c.-1768TT genotypes (P < 0.05) before as well as after in vitro LPS challenge.     

Reconstructing past ecological networks: the reconfiguration of seed-dispersal interactions after megafaunal extinction

The late Quaternary megafaunal extinction impacted ecological communities worldwide, and affected key ecological processes such as seed dispersal. The traits of several species of large-seeded plants are thought to have evolved in response to interactions with extinct megafauna, but how these extinctions affected the organization of interactions in seed-dispersal systems is poorly understood. Here, we combined ecological and paleontological data and network analyses to investigate how the structure of a species-rich seed-dispersal network could have changed from the Pleistocene to the present and examine the possible consequences of such changes. Our results indicate that the seed-dispersal network was organized into modules across the different time periods but has been reconfigured in different ways over time. The episode of megafaunal extinction and the arrival of humans changed how seed dispersers were distributed among network modules. However, the recent introduction of livestock into the seed-dispersal system partially restored the original network organization by strengthening the modular configuration. Moreover, after megafaunal extinctions, introduced species and some smaller native mammals became key components for the structure of the seed-dispersal network. We hypothesize that such changes in network structure affected both animal and plant assemblages, potentially contributing to the shaping of modern ecological communities. The ongoing extinction of key large vertebrates will lead to a variety of context-dependent rearranged ecological networks, most certainly affecting ecological and evolutionary processes.     

Human‐mediated extirpation of the unique Chatham Islands sea lion and implications for the conservation management of remaining New Zealand sea lion populations

While terrestrial megafaunal extinctions have been well characterized worldwide, our understanding of declines in marine megafauna remains limited. Here, we use ancient DNA analyses of prehistoric (<1450–1650 AD) sea lion specimens from New Zealand's isolated Chatham Islands to assess the demographic impacts of human settlement. These data suggest there was a large population of sea lions, unique to the Chatham Islands, at the time of Polynesian settlement. This distinct mitochondrial lineage became rapidly extinct within 200 years due to overhunting, paralleling the extirpation of a similarly large endemic mainland population. Whole mitogenomic analyses confirm substantial intraspecific diversity among prehistoric lineages. Demographic models suggest that even low harvest rates would likely have driven rapid extinction of these lineages. This study indicates that surviving Phocarctos populations are remnants of a once diverse and widespread sea lion assemblage, highlighting dramatic human impacts on endemic marine biodiversity. Our findings also suggest that Phocarctos bycatch in commercial fisheries may contribute to the ongoing population decline.     

Foraging strategies and prey switching in the California sea otter

Summary Southern sea otters (Enhydra lutris nereis), in recovering from near extinction, are gradually extending their range to include areas from which they have been absent for more than one hundred years. This study took advantage of the otters' relatively sudden arrival in the area near Santa Cruz, California, to monitor their prey selection in the first two years of residence there. Foraging observations revealed that sea urchins (Strongly-locentrotus franciscanus) were heavily preyed upon initially, but virtually disappeared from the diet after one year of sea otter residence. The disappearance of sea urchins was accompanied by an increased use of kelp crabs (Pugettia producta) and the appearance of clams (Gari californica) in the otters' diet. Abalones (Haliotis rufescens) and cancer crabs (Cancer spp.) remained fairly stable as dietary items throughout the two year period. An electivity index was used to quantify sea otter preferences, which corresponded closely with a ranking scheme based on energy intake/unit foraging time calculated for each major prey species. As predicted by optimal foraging theory, sea otters prefer food species of high rank and replace depleted dietary items with those of next highest rank. The process of dietary switching was analyzed with respect to foraging success rates, and it appears that poor success rates, associated with predation on an increasingly rarer prey species (sea urchins), drive sea otters to hunt for different prey. Both patch selection and search image formation appear to function in this process. The potential effects on community structure and stability of predators exhibiting a preference for the most profitable prey are discussed.     

KILLER WHALES AND MARINE MAMMAL TRENDS IN THE NORTH PACIFIC—A RE-EXAMINATION OF EVIDENCE FOR SEQUENTIAL MEGAFAUNA COLLAPSE AND THE PREY-SWITCHING HYPOTHESIS

Springer et al . (2003) contend that sequential declines occurred in North Pacific populations of harbor and fur seals, Steller sea lions, and sea otters. They hypothesize that these were due to increased predation by killer whales, when industrial whaling's removal of large whales as a supposed primary food source precipitated a prey switch. Using a regional approach, we reexamined whale catch data, killer whale predation observations, and the current biomass and trends of potential prey, and found little support for the prey-switching hypothesis. Large whale biomass in the Bering Sea did not decline as much as suggested by Springer et al ., and much of the reduction occurred 50–100 yr ago, well before the declines of pinnipeds and sea otters began; thus, the need to switch prey starting in the 1970s is doubtful. With the sole exception that the sea otter decline followed the decline of pinnipeds, the reported declines were not in fact sequential. Given this, it is unlikely that a sequential megafaunal collapse from whales to sea otters occurred. The spatial and temporal patterns of pinniped and sea otter population trends are more complex than Springer et al . suggest, and are often inconsistent with their hypothesis. Populations remained stable or increased in many areas, despite extensive historical whaling and high killer whale abundance. Furthermore, observed killer whale predation has largely involved pinnipeds and small cetaceans; there is little evidence that large whales were ever a major prey item in high latitudes. Small cetaceans (ignored by Springer et al .) were likely abundant throughout the period. Overall, we suggest that the Springer et al . hypothesis represents a misleading and simplistic view of events and trophic relationships within this complex marine ecosystem.     

Human influence on distribution and extinctions of the late Pleistocene Eurasian megafauna

Late Pleistocene extinctions are of interest to paleontological and anthropological research. In North America and Australia, human occupation occurred during a short period of time and overexploitation may have led to the extinction of mammalian megafauna. In northern Eurasia megafaunal extinctions are believed to have occurred over a relatively longer period of time, perhaps as a result of changing environmental conditions, but the picture is much less clear. To consider megafaunal extinction in Eurasia, we compare differences in the geographical distribution and commonness of extinct and extant species between paleontological and archaeological localities from the late middle Pleistocene to Holocene. Purely paleontological localities, as well as most extinct species, were distributed north of archaeological sites and of the extant species, suggesting that apart from possible differences in adaptations between humans and other species, humans could also have a detrimental effect on large mammal distribution. However, evidence for human overexploitation applies only to the extinct steppe bison Bison priscus. Other human-preferred species survive into the Holocene, including Rangifer tarandus, Equus ferus, Capreolus capreolus, Cervus elaphus, Equus hemionus, Saiga tatarica, and Sus scrofa. Mammuthus primigenius and Megaloceros giganteus were rare in archaeological sites. Carnivores appear little influenced by human presence, although they become rarer in Holocene archaeological sites. Overall, the data are consistent with the conclusion that humans acted as efficient hunters selecting for the most abundant species. Our study supports the idea that the late Pleistocene extinctions were environmentally driven by climatic changes that triggered habitat fragmentation, species range reduction, and population decrease, after which human interference either by direct hunting or via indirect activities probably became critical.     

Gene sequences for cytochromes p450 1A1 and 1A2: the need for biomarker development in sea otters (Enhydra lutris)

There has been recent public concern regarding the impacts of environmental pollution on populations of otters. Population level impacts have been seen with otter (Lutra lutra) populations in Europe due to polychlorinated biphenyls, and with some segments of the Prince William Sound, AK, sea otter (Enhydra lutris) population following the Exxon Valdez oil spill. Despite public interest in these animals and their ecological significance, there are few tools that allow for the study of otter's response to contaminant exposure. Cytochrome p450 1A (CYP1A) performs the first step in metabolizing many xenobiotics, including many polychlorinated biphenyls and polycyclic aromatic hydrocarbons. CYP1A induction is a frequently used biomarker of exposure to these compounds. Despite the potential importance of this gene in ecological risk assessment, the complete coding sequence has not been published for any otter species. This study's objective was to isolate the gene for CYP1A1 and CYP1A2 in sea otters using a series of PCR-based approaches. The coding sequences from CYP1A1 and CYP1A2 from sea otters were identified and published in GenBank. Both CYP1A sequences are homologous to those obtained from marine mammals and other carnivores. These sequences will be useful as tools for researchers assessing contaminant exposure in mustelid populations.     

Genetic diversity and population parameters of sea otters, Enhydra lutris, before fur trade extirpation from 1741-1911

All existing sea otter, Enhydra lutris, populations have suffered at least one historic population bottleneck stemming from the fur trade extirpations of the eighteenth and nineteenth centuries. We examined genetic variation, gene flow, and population structure at five microsatellite loci in samples from five pre-fur trade populations throughout the sea otter's historical range: California, Oregon, Washington, Alaska, and Russia. We then compared those values to genetic diversity and population structure found within five modern sea otter populations throughout their current range: California, Prince William Sound, Amchitka Island, Southeast Alaska and Washington. We found twice the genetic diversity in the pre-fur trade populations when compared to modern sea otters, a level of diversity that was similar to levels that are found in other mammal populations that have not experienced population bottlenecks. Even with the significant loss in genetic diversity modern sea otters have retained historical structure. There was greater gene flow before extirpation than that found among modern sea otter populations but the difference was not statistically significant. The most dramatic effect of pre fur trade population extirpation was the loss of genetic diversity. For long term conservation of these populations increasing gene flow and the maintenance of remnant genetic diversity should be encouraged.     

Prey selection in coastal Eurasian otters Lutra Iutra

Prey preferences and dietary differences between sex and age categories of Eurasian otters were studied in coastal Norwegian habitats Relative to their trapping frequency potential prey species with hard, spiny exoskeletons (crabs and sea urchins) or otherwise tough, spiny integuments (Labridae) were much less frequently found in spraints than fish species with soft integuments Spines did not protect fish with otherwise soft integuments from otter predation The number of non-fish taxa per otter stomach did not vary significantly between otter age categories despite presumed differences in hunting abilities (small cubs large cubs and subadults, adults) Relative frequency of occurrence of crabs and sea urchins was < 5% in the stomachs in each of these otter categories Anadromous, katadromous and freshwater fish species were infrequently eaten The coastal otter population during the study period probably had access to an adequate, and preferred, supply of marine fish prey
At the otter population level no prey size selection was conclusively demonstrated within the range of fish sizes sampled However, fish sizes eaten differed significantly between otter sex and age categories The fish sizes per stomach were on average larger in males than in females, regardless of age Adult males tended to eat the largest fishes Among the self provisioning age categories (subadult and adult otters) fish lengths differed significantly between otter males and females, but not between the otter age categories, and did not covary significantly with otter body length Fish eaten by females with old placental scars (potential mothers of fisheating cubs) were significantly smaller than those eaten by small cubs, provisioned by their mothers     

Ancient DNA reveals genotypic relationships among Oregon populations of the sea otter (<Emphasis Type="Italic">Enhydra lutris</Emphasis>)

The sea otter has experienced a dramatic population decline caused by intense human harvesting, followed by a century of recovery including relocation efforts to reestablish the species across its former range in the eastern Pacific. Although the otter was historically present along the coast in Oregon, there are currently no populations in this region and reintroduction efforts have failed. We examined the mtDNA genotypes of 16 pre-harvest otter samples from two Oregon locations in an attempt to determine the best genotypic match with extant populations. Our amplifications of a 222 base-pair portion of the control region from otters ranging in age from approximately 175–2000 years revealed four genotypes. The genotypic composition of pre-harvest otter populations appears to match best with those of contemporary populations from California and not from Alaska, where reintroduction stocks are typically derived.     

Clinical pathology and assessment of pathogen exposure in southern and Alaskan sea otters

The southern sea otter (Enhydra lutris nereis) population in California (USA) and the Alaskan sea otter (E. lutris kenyoni) population in the Aleutian Islands (USA) chain have recently declined. In order to evaluate disease as a contributing factor to the declines, health assessments of these two sea otter populations were conducted by evaluating hematologic and/or serum biochemical values and exposure to six marine and terrestrial pathogens using blood collected during ongoing studies from 1995 through 2000. Samples from 72 free-ranging Alaskan, 78 free-ranging southern, and (for pathogen exposure only) 41 debilitated southern sea otters in rehabilitation facilities were evaluated and compared to investigate regional differences. Serum chemistry and hematology values did not indicate a specific disease process as a cause for the declines. Statistically significant differences were found between free-ranging adult southern and Alaskan population mean serum levels of creatinine kinase, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, calcium, cholesterol, creatinine, glucose, phosphorous, total bilirubin, blood urea nitrogen, and sodium. These were likely due to varying parasite loads, contaminant exposures, and physiologic or nutrition statuses. No free-ranging sea otters had signs of disease at capture, and prevalences of exposure to calicivirus, Brucella spp., and Leptospira spp. were low. The high prevalence (35%) of antibodies to Toxoplasma gondii in free-ranging southern sea otters, lack of antibodies to this parasite in Alaskan sea otters, and the pathogen's propensity to cause mortality in southern sea otters suggests that this parasite may be important to sea otter population dynamics in California but not in Alaska. The evidence for exposure to pathogens of public health importance (e.g., Leptospira spp., T. gondii) in the southern sea otter population, and the na?veté of both populations to other pathogens (e.g., morbillivirus and Coccidiodes immitis) may have important implications for their management and recovery.     

SEA OTTER DIETS IN A DECLINING POPULATION IN ALASKA

Diet of sea otters ( Enhydra lutris ) using a haulout site on the north side of the Alaska Peninsula was determined from 50 scats. Dominant prey species were mussels ( Mytilus edulis ), followed by three species of clams ( Siliqua spp., Spisula polynyma , and Tellina lutea ), sand dollars ( Echinarachnius parma ), and helmet crabs ( Telmessus cheiragonus ). Our results support preliminary findings by Cim-berg et al. (1984) that this sea otter population preys heavily on mussels and that the presence of low caloric value sand dollars in their diet is significant. Coupled with population estimates, our results also provide evidence that this population of sea otters may be declining due, in part, to overdepletion of food resources.     

Inter-decadal patterns of population and dietary change in sea otters at Amchitka Island, Alaska

After having been hunted to near-extinction in the Pacific maritime fur trade, the sea otter population at Amchitka Island, Alaska increased from very low numbers in the early 1900s to near equilibrium density by the 1940s. The population persisted at or near equilibrium through the 1980s, but declined sharply in the 1990s in apparent response to increased killer whale predation. Sea otter diet and foraging behavior were studied at Amchitka from August 1992 to March 1994 and the data compared with similar information obtained during several earlier periods. In contrast with dietary patterns in the 1960s and 1970s, when the sea otter population was at or near equilibrium density and kelp-forest fishes were the dietary mainstay, these fishes were rarely eaten in the 1990s. Benthic invertebrates, particularly sea urchins, dominated the otter’s diet from early summer to mid-winter, then decreased in importance during late winter and spring when numerous Pacific smooth lumpsuckers (a large and easily captured oceanic fish) were eaten. The occurrence of spawning lumpsuckers in coastal waters apparently is episodic on a scale of years to decades. The otters’ recent dietary shift away from kelp-forest fishes is probably a response to the increased availability of lumpsuckers and sea urchins (both high-preference prey). Additionally, increased urchin densities have reduced kelp beds, thus further reducing the availability of kelp-forest fishes. Our findings suggest that dietary patterns reflect changes in population status and show how an ecosystem normally under top-down control and limited by coastal zone processes can be significantly perturbed by exogenous events. Received: 23 March 1999 / Accepted: 19 January 2000