The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform
Joann E Mellish - One of the best experts on this subject based on the ideXlab platform.
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predation on an upper trophic marine predator the steller sea lion evaluating high juvenile mortality in a density dependent conceptual framework
PLOS ONE, 2012Co-Authors: Markus Horning, Joann E MellishAbstract:The endangered western stock of the Steller sea lion (Eumetopias jubatus) – the largest of the Eared Seals – has declined by 80% from population levels encountered four decades ago. Current overall trends from the Gulf of Alaska to the Aleutian Islands appear neutral with strong regional heterogeneities. A published inferential model has been used to hypothesize a continuous decline in natality and depressed juvenile survival during the height of the decline in the mid-late 1980's, followed by the recent recovery of juvenile survival to pre-decline rates. However, these hypotheses have not been tested by direct means, and causes underlying past and present population trajectories remain unresolved and controversial. We determined post-weaning juvenile survival and causes of mortality using data received post-mortem via satellite from telemetry transmitters implanted into 36 juvenile Steller sea lions from 2005 through 2011. Data show high post-weaning mortality by predation in the eastern Gulf of Alaska region. To evaluate the impact of such high levels of predation, we developed a conceptual framework to integrate density dependent with density independent effects on vital rates and population trajectories. Our data and model do not support the hypothesized recent recovery of juvenile survival rates and reduced natality. Instead, our data demonstrate continued low juvenile survival in the Prince William Sound and Kenai Fjords region of the Gulf of Alaska. Our results on contemporary predation rates combined with the density dependent conceptual framework suggest predation on juvenile sea lions as the largest impediment to recovery of the species in the eastern Gulf of Alaska region. The framework also highlights the necessity for demographic models based on age-structured census data to incorporate the differential impact of predation on multiple vital rates.
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Predation on an upper trophic marine predator, the Steller sea lion: Evaluating high juvenile mortality in a density dependent conceptual framework
2012Co-Authors: Markus Horning, Joann E MellishAbstract:The endangered western stock of the Steller sea lion (Eumetopias jubatus) – the largest of the Eared Seals – has declined by 80 % from population levels encountered four decades ago. Current overall trends from the Gulf of Alaska to the Aleutian Islands appear neutral with strong regional heterogeneities. A published inferential model has been used to hypothesize a continuous decline in natality and depressed juvenile survival during the height of the decline in the mid-late 1980’s, followed by the recent recovery of juvenile survival to pre-decline rates. However, these hypotheses have not been tested by direct means, and causes underlying past and present population trajectories remain unresolved and controversial. We determined post-weaning juvenile survival and causes of mortality using data received post-mortem via satellite from telemetry transmitters implanted into 36 juvenile Steller sea lions from 2005 through 2011. Data show high post-weaning mortality by predation in the eastern Gulf of Alaska region. To evaluate the impact of such high levels of predation, we developed a conceptual framework to integrate density dependent with density independent effects on vital rates and population trajectories. Our data and model do not support the hypothesized recent recovery of juvenile survival rates and reduced natality. Instead, our data demonstrate continued low juvenile survival in the Prince William Sound and Kenai Fjords region of the Gulf of Alaska. Our results on contemporary predation rates combined with the density dependent conceptual framework suggest predation on juvenile sea lions as the largest impediment to recovery of the species in th
B. Louise Chilvers - One of the best experts on this subject based on the ideXlab platform.
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Eared Seals: Otariidae
Encyclopedia of Marine Mammals, 2018Co-Authors: B. Louise ChilversAbstract:Summary Eared Seals, or the Otariidae, belong to one of three pinniped groupings (the other two being the phocids (true Seals) and the odobenids (walrus). They comprise 16 extant species within seven genera and are commonly known either as sea lions (6 species) or fur Seals (10 species). Otariids have semiaquatic lifestyles, feeding and migrating in the sea, but breeding and resting on land. They reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans, but are absent from the North Atlantic. Four of the six sea lion species are listed as threatened by IUCN, while only 2 of the 10 fur seal species are at risk. All otariids species have experienced extreme overharvesting that in some cases lead to their near extinction. However, today the biggest human threat for many of the Eared Seals is interactions with fisheries resulting in entanglement and drowning.
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Unique and isolated: population structure has implications for management of the endangered New Zealand sea lion
Conservation Genetics, 2017Co-Authors: Catherine J. Collins, B. Louise Chilvers, Amy Osborne, Matt Taylor, Bruce C. RobertsonAbstract:Female otariids (Eared Seals) frequently display strong levels of philopatry, a behaviour that has the potential to influence population structure, particularly at the mitochondrial level. Conversely, male otariids often move between breeding colonies, likely facilitating nuclear gene flow between colonies. Such gender-specific movements have the potential to influence species population structure. Here we investigate the genetic population structure of the endangered New Zealand (NZ) sea lion, using nuclear (microsatellite) and mitochondrial molecular markers, with the intention to better inform conservation through identification of management units for the species. The strong levels of female philopatry in this species have potential to lead to population structure at the mitochondrial loci. In contrast, weak or no population structure is expected across nuclear loci. NZ sea lions were sampled from the main breeding areas across the species’ current distribution (three Auckland Islands sites, two Campbell Island sites, one Stewart Island site and one Otago Peninsula site). Individuals were screened for microsatellite ( n = 271; 16 loci) and mitochondrial ( n = 56; 1027 bp D-loop and 1189 bp cytb ). Despite a small ( c . 9880 individuals) population size, moderate levels of microsatellite variation are observed in the NZ sea lions, in contrast to low levels of mitochondrial genetic variation. Results from mitochondrial DNA analyses revealed no population structure, suggesting that the strong level of female philopatry in NZ sea lions alone is not sufficient to maintain genetic population structure. Due to the frequent male movements between breeding colonies, no population structure was detected across the nuclear loci either. The absence of genetic structure suggests that, from a genetic perspective, NZ sea lions can be considered to be a single population. Despite this, the differing impacts of threats (e.g. fisheries by-catch) to each individual breeding colony must also be taken into consideration when defining management units for this endangered species.
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Diverse foraging strategies in lactating New Zealand sea lions
Marine Ecology Progress Series, 2009Co-Authors: B. Louise Chilvers, I. S. WilkinsonAbstract:Diving and foraging behaviours of marine predators are thought to be coupled with species demographics, with benthic foraging species found to have small population sizes and low growth rates. This was thought to be the case for New Zealand (NZ) sea lions Phocarctos hookeri, previously identified as solely benthic foragers with a small declining population. Female NZ sea lions dive deeper and for longer than any other otariids (Eared Seals). They exceed their calculated aerobic dive limits (cADL) during 68% of all dives, indicating that they are operating near their max- imum physiological capacity. Recently, however, individual NZ sea lions have been found to have 2 distinct dive profile types or foraging patterns: a benthic diving profile and a deeper, more varied meso-pelagic diving profile. The ecological significance and implications of individual foraging specialisation in otariids have had limited attention in the past. Here, we compared the foraging behaviour of female NZ sea lions that use these 2 distinct dive profiles and discuss how the 2 forag- ing patterns may indicate differing prey choice, as well as their possible implications for individual reproductive ability and interactions with fisheries and, therefore, species demographics. Our ulti- mate goal is to understand the causes of this individual foraging specialisation and to incorporate such variation when determining management options for this threatened, declining species.
Steven L. Lima - One of the best experts on this subject based on the ideXlab platform.
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Unilateral Eye Closure and Interhemispheric EEG Asymmetry during Sleep in the Pigeon (Columba livia)
Brain behavior and evolution, 2001Co-Authors: Niels Christian Rattenborg, Charles J. Amlaner, Steven L. LimaAbstract:Aquatic mammals (i.e., Cetaceans, Eared Seals and manatees) and birds show interhemispheric asymmetries (IA) in slow-wave sleep-related electroencephalographic (EEG) activity, suggesting that the dept
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Behavioral, neurophysiological and evolutionary perspectives on unihemispheric sleep
Neuroscience and biobehavioral reviews, 2000Co-Authors: Niels Christian Rattenborg, Charles J. Amlaner, Steven L. LimaAbstract:Several animals mitigate the fundamental conflict between sleep and wakefulness by engaging in unihemispheric sleep, a unique state during which one cerebral hemisphere sleeps while the other remains awake. Among mammals, unihemispheric sleep is restricted to aquatic species (Cetaceans, Eared Seals and manatees). In contrast to mammals, unihemispheric sleep is widespread in birds, and may even occur in reptiles. Unihemispheric sleep allows surfacing to breathe in aquatic mammals and predator detection in birds. Despite the apparent utility in being able to sleep unihemispherically, very few mammals sleep in this manner. This is particularly interesting since the reptilian ancestors to mammals may have slept unihemispherically. The relative absence of unihemispheric sleep in mammals suggests that a trade off exists between unihemispheric sleep and other adaptive brain functions occurring during sleep or wakefulness. Presumably, the benefits of sleeping unihemispherically only outweigh the costs under extreme circumstances such as sleeping at sea. Ultimately, a greater understanding of the reasons for little unihemispheric sleep in mammals promises to provide insight into the functions of sleep, in general.
Valentina Franco-trecu - One of the best experts on this subject based on the ideXlab platform.
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Phylogenomic Discordance in the Eared Seals is best explained by Incomplete Lineage Sorting following Explosive Radiation in the Southern Hemisphere.
Systematic biology, 2020Co-Authors: Fernando Lopes, Larissa Rosa De Oliveira, Amanda Kessler, Yago Beux, Enrique A. Crespo, Susana Cárdenas-alayza, Patricia Majluf, Maritza Sepúlveda, Robert L. Brownell, Valentina Franco-trecuAbstract:The phylogeny and systematics of fur Seals and sea lions (Otariidae) have long been studied with diverse data types, including an increasing amount of molecular data. However, only a few phylogenetic relationships have reached acceptance because of strong gene-tree species tree discordance. Divergence times estimates in the group also vary largely between studies. These uncertainties impeded the understanding of the biogeographical history of the group, such as when and how trans-equatorial dispersal and subsequent speciation events occurred. Here we used high-coverage genome-wide sequencing for 14 of the 15 species of Otariidae to elucidate the phylogeny of the family and its bearing on the taxonomy and biogeographical history. Despite extreme topological discordance among gene trees, we found a fully supported species tree that agrees with the few well-accepted relationships and establishes monophyly of the genus Arctocephalus. Our data support a relatively recent trans-hemispheric dispersal at the base of a southern clade, which rapidly diversified into six major lineages between 3 to 2.5 Ma. Otaria diverged first, followed by Phocarctos and then four major lineages within Arctocephalus. However, we found Zalophus to be non-monophyletic, with California (Z. californianus) and Steller sea lions (Eumetopias jubatus) grouping closer than the Galapagos sea lion (Z. wollebaeki) with evidence for introgression between the two genera. Overall, the high degree of genealogical discordance was best explained by incomplete lineage sorting resulting from quasi-simultaneous speciation within the southern clade with introgresssion playing a subordinate role in explaining the incongruence among and within prior phylogenetic studies of the family.
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Gene-tree Species-tree Discordance in the Eared Seals is best explained by Incomplete Lineage Sorting following Explosive Radiation in the Southern Hemisphere
2020Co-Authors: Fernando Lopes, Larissa Rosa De Oliveira, Amanda Kessler, Enrique A. Crespo, Susana Cárdenas-alayza, Patricia Majluf, Maritza Sepúlveda, Robert L. Brownell, Valentina Franco-trecu, Diego Páez-rosasAbstract:The phylogeny and systematics of fur Seals and sea lions (Otariidae) have long been studied with diverse data types, including an increasing amount of molecular data. However, only a few phylogenetic relationships have reached acceptance pointing at strong gene-tree species tree discordance. Divergence times in the group also vary largely between studies. These uncertainties impeded the understanding of the biogeographical history of the group, such as when and how trans-equatorial dispersal and subsequent speciation events occurred. Here we used high-coverage whole genome-wide sequencing for 14 of the 15 species of Otariidae to elucidate the phylogeny of the family and its bearing on the taxonomy and biogeographical history. Despite extreme topological discordance among gene trees, we found a fully supported species tree that agrees with the few well-accepted relationships and establishes monophyly of the genus Arctocephalus. Our data support a relatively recent trans-hemispheric dispersal at the base of a southern clade, which rapidly diversified into six major lineages between 3 to 2.5 Mya. Otaria diverged first, followed by Phocarctos and then four major lineages within Arctocephalus. However, we found Zalophus to be non-monophyletic, with California (Z. californianus) and Steller sea lions (Eumetopias jubatus) grouping closer than the Galapagos sea lion (Z. wollebaeki) with evidence for introgression between the two genera. Overall, the high degree of genealogical discordance was best explained by incomplete lineage sorting resulting from quasi-simultaneous speciation within the southern clade with introgresssion playing a subordinate role in explaining the incongruence among and within prior phylogenetic studies of the family.
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Isotopic niche partitioning between two apex predators over time.
The Journal of animal ecology, 2017Co-Authors: Massimiliano Drago, Enrique A. Crespo, Valentina Franco-trecu, Luis Cardona, Damián G. Vales, Florencia Borella, Lisette Zenteno, Enrique M. Gonzáles, Pablo InchaustiAbstract:Stable isotope analyses have become an important tool in reconstructing diets, analysing resource use patterns, elucidating trophic relations among predators and understanding the structure of food webs. Here, we use stable carbon and nitrogen isotope ratios in bone collagen to reconstruct and compare the isotopic niches of adult South American fur Seals (Arctocephalus australis; n = 86) and sea lions (Otaria flavescens; n = 49) - two otariid species with marked morphological differences - in the Rio de la Plata estuary (Argentina - Uruguay) and the adjacent Atlantic Ocean during the second half of the 20th century and the beginning of the 21st century. Samples from the middle Holocene (n = 7 fur Seals and n = 5 sea lions) are also included in order to provide a reference point for characterizing resource partitioning before major anthropogenic modifications of the environment. We found that the South American fur Seals and South American sea lions had distinct isotopic niches during the middle Holocene. Isotopic niche segregation was similar at the beginning of the second half of the 20th century, but has diminished over time. The progressive convergence of the isotopic niches of these two otariids during the second half of the 20th century and the beginning of the 21st century is most likely due to the increased reliance of South American fur Seals on demersal prey. This recent dietary change in South American fur Seals can be explained by at least two non-mutually exclusive mechanisms: (i) the decrease in the abundance of sympatric South American sea lions as a consequence of small colony size and high pup mortality resulting from commercial sealing; and (ii) the decrease in the average size of demersal fishes due to intense fishing of the larger class sizes, which may have increased their accessibility to those Eared Seals with a smaller mouth gape, that is, South American fur Seals of both sexes and female South American sea lions.
Oliver Krüger - One of the best experts on this subject based on the ideXlab platform.
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Evolution of age at primiparity in pinnipeds in the absence of the quality-quantity trade-off in reproduction.
Ecology and evolution, 2019Co-Authors: Stephanie Kalberer, Fritz Trillmich, Eugene J. Derango, Oliver KrügerAbstract:Age at primiparity (AP) is a key life history trait which is crucial to the evolution of life history strategies. This trait is particularly interesting in pinnipeds (walrus, Eared Seals, and true Seals), which are monotocous animals. Thus, the commonly observed trade-off between offspring quality and quantity does not apply to this taxon. Therefore, comparative studies on the evolution of AP might shed light on other important evolutionary correlates when litter size is fixed. Using phylogenetic generalized least squares analyses, we found a strong negative and robust correlation between relative birth mass (mean pup birth mass as a proportion of mean adult female mass) and AP. Rather than trading-off an early start of reproduction with light relative offspring mass, this result suggests that pinnipeds exhibit either faster (i.e., higher relative offspring mass leading to shorter lactation length, and thus shorter interbirth interval) or slower life histories and that an early AP and a heavy relative offspring mass co-evolved into a comparatively fast life history strategy. On the other hand, AP was positively related to lactation length: A later start of reproduction was associated with a longer lactation length. Consequently, variation in AP in pinnipeds seems to be affected by an interplay between costs and benefits of early reproduction mediated by relative investment into the single offspring via relative birth mass and lactation length.
