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  1. Article ; Online: Robustly estimating the demographic contribution of immigration: Simulation, sensitivity analysis and seals.

    Christian, Murray / Oosthuizen, W Chris / Bester, Marthán N / de Bruyn, P J Nico

    The Journal of animal ecology

    2024  

    Abstract: Identifying important demographic drivers of population dynamics is fundamental for understanding life-history evolution and implementing effective conservation measures. Integrated population models (IPMs) coupled with transient life table response ... ...

    Abstract Identifying important demographic drivers of population dynamics is fundamental for understanding life-history evolution and implementing effective conservation measures. Integrated population models (IPMs) coupled with transient life table response experiments (tLTREs) allow ecologists to quantify the contributions of demographic parameters to observed population change. While IPMs can estimate parameters that are not estimable using any data source alone, for example, immigration, the estimated contribution of such parameters to population change is prone to bias. Currently, it is unclear when robust conclusions can be drawn from them. We sought to understand the drivers of a rebounding southern elephant seal population on Marion Island using the IPM-tLTRE framework, applied to count and mark-recapture data on 9500 female seals over nearly 40 years. Given the uncertainty around IPM-tLTRE estimates of immigration, we also aimed to investigate the utility of simulation and sensitivity analyses as general tools for evaluating the robustness of conclusions obtained in this framework. Using a Bayesian IPM and tLTRE analysis, we quantified the contributions of survival, immigration and population structure to population growth. We assessed the sensitivity of our estimates to choice of multivariate priors on immigration and other vital rates. To do so we make a novel application of Gaussian process priors, in comparison with commonly used shrinkage priors. Using simulation, we assessed our model's ability to estimate the demographic contribution of immigration under different levels of temporal variance in immigration. The tLTRE analysis suggested that adult survival and immigration were the most important drivers of recent population growth. While the contribution of immigration was sensitive to prior choices, the estimate was consistently large. Furthermore, our simulation study validated the importance of immigration by showing that our estimate of its demographic contribution is unlikely to result as a biased overestimate. Our results highlight the connectivity between distant populations of southern elephant seals, illustrating that female dispersal can be important in regulating the abundance of local populations even when natal site fidelity is high. More generally, we demonstrate how robust ecological conclusions may be obtained about immigration from the IPM-tLTRE framework, by combining sensitivity analysis and simulation.
    Language English
    Publishing date 2024-01-31
    Publishing country England
    Document type Journal Article
    ZDB-ID 3024-7
    ISSN 1365-2656 ; 0021-8790
    ISSN (online) 1365-2656
    ISSN 0021-8790
    DOI 10.1111/1365-2656.14053
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  2. Article ; Online: Canine morphometrics as a tool for distinguishing species, sex, and age class in Southern Ocean fur seals.

    Pretorius, Liezl E / Bester, Marthán N / Connan, Maëlle / Hofmeyr, G J Greg

    Journal of morphology

    2022  Volume 283, Issue 12, Page(s) 1546–1560

    Abstract: Carcasses resulting from natural mortalities are invaluable for use in scientific studies, provided species, sex, and age class are known. When such data are unavailable, identifying skeletal remains is necessary if one is to use the information ... ...

    Abstract Carcasses resulting from natural mortalities are invaluable for use in scientific studies, provided species, sex, and age class are known. When such data are unavailable, identifying skeletal remains is necessary if one is to use the information contained within samples. Teeth are amongst the best preserved skeletal remains owing to the durability of enamel and dentine. Here, we tested whether external measurements of canines could be used to distinguish two partially sympatric species of Southern Ocean fur seals, the Antarctic Arctocephalus gazella and Sub-Antarctic A. tropicalis fur seals. We also investigated whether the external measurements of canines could be used to determine the age, sex, as well as island of origin of the animals. Eight morphological variables (crown length, root length, crown width, root width, crown thickness, root thickness, total canine length, and count of external surface annular ridges) were recorded from canines of 340 individuals of known species, sex, and island of origin. The count of external annular ridges provided a good estimate of age, which was confirmed by counting the growth layer groups of sectioned teeth, especially for older animals (> 9 years old). External canine measurements proved useful in distinguishing species, as well as sex within and between species, particularly in adult animals. Species were more difficult to distinguish in females than in males. The islands of origin could only be inferred in male Antarctic fur seals. This study indicates that fur seal teeth of unknown provenance, found either in breeding colonies or as vagrants, provide evidence on species, sex, and age of the animal, which increases the value of associated samples. It further highlights the importance of external measurements of skeletal remains such as canine teeth in separating closely related species.
    MeSH term(s) Female ; Male ; Animals ; Fur Seals ; Body Remains ; Oceans and Seas ; Antarctic Regions
    Language English
    Publishing date 2022-11-15
    Publishing country United States
    Document type Journal Article
    ZDB-ID 3084-3
    ISSN 1097-4687 ; 0022-2887 ; 0362-2525
    ISSN (online) 1097-4687
    ISSN 0022-2887 ; 0362-2525
    DOI 10.1002/jmor.21521
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  3. Article ; Online: Density-related reproductive costs and natal conditions predict male life history in a highly polygynous mammal

    Lloyd, Kyle J. / Oosthuizen, W. Chris / Rotella, Jay J. / Bester, Marthán N. / de Bruyn, P.J.Nico

    Animal Behaviour. 2023 Apr. 18,

    2023  

    Abstract: Polygynous males allocate substantial resources to sexual traits and behaviours to improve their chances of winning competitions for mates often at the cost of body maintenance. However, the degree to which males experience these trade-offs can be ... ...

    Abstract Polygynous males allocate substantial resources to sexual traits and behaviours to improve their chances of winning competitions for mates often at the cost of body maintenance. However, the degree to which males experience these trade-offs can be influenced by external conditions. Studies are needed that assess whether polygynous male resource allocation decisions about life history traits are density dependent. We tested for an influence of density on age-specific life history traits in male southern elephant seals, Mirounga leonina, using a 34-year data set collected at Marion Island. Specifically, we determine whether life history varied with density-related factors for survival, improved breeding success (measured as social status) and recruitment age. This was done by selecting linear models that tested biological hypotheses about density-dependent covariates related to competition intensity during breeding and natal conditions, while accounting for known intrinsic effects such as age and social status. Baseline mortalities were higher for males that had accumulated above average reproductive costs for their age than males with below average costs. This reproductive cost was determined by the number of females per harem relative to the population average. Thus, males likely allocated more resources to reproduction and less to body maintenance at all ages when defending and servicing relatively large harems, and this cost was compounding for males that dominated large harems at a young age. Males born in years with few pups were more likely to be dominant breeders and recruit at an earlier age than males born in years with many pups. Thus, breeding success and recruitment age likely depended on the population density experienced during early life, suggesting lasting effects of natal conditions in a long-lived animal. We show how density-dependent factors interact with intrinsic determinants of resource allocation to determine variation in polygynous male life history with long-term consequences.
    Keywords Mirounga leonina ; animal behavior ; data collection ; life history ; males ; mammals ; polygyny ; population density ; resource allocation ; socioeconomic status ; breeding improvement ; cohort size ; competition intensity ; cumulative reproductive cost ; Marion Island ; recruitment age ; senescence ; southern elephant seal ; trade-off hypothesis
    Language English
    Dates of publication 2023-0418
    Publishing place Elsevier Ltd
    Document type Article ; Online
    Note Pre-press version ; Use and reproduction
    ZDB-ID 281-1
    ISSN 0003-3472
    ISSN 0003-3472
    DOI 10.1016/j.anbehav.2023.03.006
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  4. Article ; Online: Seal bites at sub-Antarctic Marion Island: Incidence, outcomes and treatment recommendations.

    Reisinger, Ryan R / Penfold, Miles / Bester, Marthán N / Steenkamp, Gerhard

    Journal of the South African Veterinary Association

    2020  Volume 91, Page(s) e1–e6

    Abstract: Seal biologists at Marion Island (Southern Ocean) are in frequent contact with seals. During research activities, biologists may be bitten by seals, yet no standardised protocol for treating such bites is in place. Information on 22 seal bite cases at ... ...

    Abstract Seal biologists at Marion Island (Southern Ocean) are in frequent contact with seals. During research activities, biologists may be bitten by seals, yet no standardised protocol for treating such bites is in place. Information on 22 seal bite cases at Marion Island was collected. Treatment of these bites varied, reflecting a need for standardised protocols for the treatment of bites. Recommendations for the in-field treatment of bites are presented. Five of the 22 cases had some symptoms which resembled 'seal finger' - a zoonotic infection, usually of the hands, that is contracted after a person comes into contact with tissues of seals or is bitten by one. However, in four of these cases, symptoms subsided within 4 days without antibiotic treatment; in the fifth case antibiotics were administered and symptoms subsided in 4 days. There is little evidence of the occurrence of seal finger at Marion Island, but this deserves further investigation.
    MeSH term(s) Adult ; Animals ; Antarctic Regions/epidemiology ; Anti-Bacterial Agents/therapeutic use ; Bites and Stings/epidemiology ; Bites and Stings/etiology ; Bites and Stings/therapy ; Female ; Fur Seals ; Humans ; Incidence ; Indian Ocean Islands/epidemiology ; Male ; Seals, Earless ; South Africa/epidemiology ; Young Adult ; Zoonoses/epidemiology ; Zoonoses/etiology ; Zoonoses/therapy
    Chemical Substances Anti-Bacterial Agents
    Language English
    Publishing date 2020-03-24
    Publishing country South Africa
    Document type Journal Article
    ZDB-ID 188571-6
    ISSN 2224-9435 ; 1019-9128 ; 0301-0732 ; 0038-2809
    ISSN (online) 2224-9435
    ISSN 1019-9128 ; 0301-0732 ; 0038-2809
    DOI 10.4102/jsava.v91i0.1720
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  5. Article ; Online: Positive early-late life-history trait correlations in elephant seals.

    Oosthuizen, W Chris / Péron, Guillaume / Pradel, Roger / Bester, Marthán N / de Bruyn, P J Nico

    Ecology

    2021  Volume 102, Issue 4, Page(s) e03288

    Abstract: Correlations between early- and late-life performance are a major prediction of life-history theory. Negative early-late correlations can emerge because biological processes are optimized for early but not late life (e.g., rapid development may ... ...

    Abstract Correlations between early- and late-life performance are a major prediction of life-history theory. Negative early-late correlations can emerge because biological processes are optimized for early but not late life (e.g., rapid development may accelerate the onset of senescence; "developmental theory of aging") or because allocation to early-life performance comes at a cost in terms of late-life performance (as in the disposable soma theory). But variation in genetic and environmental challenges that each individual has to cope with during early life may also lead to positive early-late life-history trait correlations (the "fixed heterogeneity" or "individual quality" hypothesis). We analyzed individual life-history trajectories of 7,420 known-age female southern elephant seals (Mirounga leonina) monitored over 36 yr to determine how actuarial senescence (a proxy for late-life performance) correlate with age at first reproduction (a proxy for early-life performance). As some breeding events may not be detected in this field study, we used a custom "multievent" hierarchical model to estimate the age at first reproduction and correlate it to other life-history traits. The probability of first reproduction was 0.34 at age 3, with most females breeding for the first time at age 4, and comparatively few at older ages. Females with an early age of first reproduction outperformed delayed breeders in all aspects we considered (survival, rate of senescence, net reproductive output) but one: early breeders appeared to have an onset of actuarial senescence 1 yr earlier compared to late breeders. Genetics and environmental conditions during early life likely explain the positive correlation between early- and late-life performance. Our results provide the first evidence of actuarial senescence in female southern elephant seals.
    MeSH term(s) Aging ; Animals ; Female ; Reproduction ; Seals, Earless
    Language English
    Publishing date 2021-03-11
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 2010140-5
    ISSN 1939-9170 ; 0012-9658
    ISSN (online) 1939-9170
    ISSN 0012-9658
    DOI 10.1002/ecy.3288
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  6. Article: Focal Palatitis (Previously Focal Palatine Erosions) in Captive Cheetahs (

    Steenkamp, Gerhard / Boy, Sonja C / van Staden, Paul J / Bester, Marthán N

    Frontiers in veterinary science

    2021  Volume 8, Page(s) 682150

    Abstract: Focal palatine erosion (FPE) is a misleading term that is used in the literature to describe inflammatory lesions associated with depressions of the palatal mucosa in cheetah. Cheetahs have large cheek teeth and these depressions are formed to ... ...

    Abstract Focal palatine erosion (FPE) is a misleading term that is used in the literature to describe inflammatory lesions associated with depressions of the palatal mucosa in cheetah. Cheetahs have large cheek teeth and these depressions are formed to accommodate them. Previously FPE was only described as a mandibular molar tooth malocclusion on the hard palate due to suspected rotation and super eruption of the mandibular molar teeth of cheetahs aged 18 months and older. Two hundred and fifty six cheetahs (135 male, 121 female), originating from two independent facilities, had their oral cavities evaluated as part of an annual health visit over a decade. Ninety-nine cheetahs were seen once, 59 cheetahs were seen twice, 33 were seen three times, 43 on four occasions, 16 on five occasions, 5 on six occasions, and 1 cheetah was seen seven times. Apart from these clinical cases a prospective study on 5 cheetah cubs (3 male and 2 female) was conducted to document their skull development and mandibular molar tooth eruption over a period of 25 months. Of the 261 cheetahs observed none developed rotation or super eruption of their mandibular molar teeth. The term FPE is a misnomer as these inflammatory lesions were found in palatal depressions opposing any of the cusps of all of the cheetah mandibular cheek teeth. It consisted mainly of deep ulcerations, inflammation and oedema and also micro abscess formation. In severe cases oro-nasal fistulas were present. Of all the depressions present on the cheetah's palate, the large one palatal to the 4th maxillary premolar tooth was most commonly affected. In the five cubs evaluated prospectively, focal palatitis was evident from the 7 month evaluation, before all the permanent teeth erupted. Conservative treatment of the inflamed depressions by removing the foreign material through curettage and copious flushing reduced the grade of the inflammation when observed on follow-up. Focal palatine erosion is an incorrect term used to describe focal palatitis that occurs randomly in cheetahs. This focal palatitis is often associated with foreign material trapped in the palatal depressions. Conservative management is sufficient to treat these animals without odontoplasties.
    Language English
    Publishing date 2021-07-12
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2834243-4
    ISSN 2297-1769
    ISSN 2297-1769
    DOI 10.3389/fvets.2021.682150
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  7. Article: Trade‐offs between age‐related breeding improvement and survival senescence in highly polygynous elephant seals: Dominant males always do better

    Lloyd, Kyle J / Oosthuizen, W. Chris / Bester, Marthán N / de Bruyn, P. J. Nico

    journal of animal ecology. 2020 Mar., v. 89, no. 3

    2020  

    Abstract: Life‐history trade‐off theory predicts that current reproduction can negatively affect survival and future reproduction. Few studies have assessed breeding costs for males of polygynous species compared to females, despite substantial variation in ... ...

    Abstract Life‐history trade‐off theory predicts that current reproduction can negatively affect survival and future reproduction. Few studies have assessed breeding costs for males of polygynous species compared to females, despite substantial variation in breeding success among individual males (e.g. subordinate cf. dominant breeders). Specifically, differentiating between the cost of attending breeding events, and the additional cost of successfully securing and mating females is lacking. We investigated whether trade‐offs are present in the highly polygynous male southern elephant seal Mirounga leonina using 34 years of individual‐level data. We compare age‐specific survival, recruitment and future breeding success probabilities of pre‐breeders (males yet to recruit) and breeders (subordinate and dominant social ranks) using multievent models. Pre‐breeders and breeders of overlapping ages had similar survival probabilities, suggesting that there was no attendance cost for early recruits. In addition, the probability of recruiting as a dominant breeder never exceeded recruitment probability as a subordinate breeder of the same age. Therefore, older pre‐breeders that delayed attendance costs generally did not improve their breeding success (probability of being dominant) at recruitment more than younger recruits. Rather, recruitment age may be a function of individual quality, with lower quality individuals requiring more time to socially mature. When comparing subordinate and dominant breeders, we found clear evidence for survival senescence, with subordinate breeders having a higher baseline mortality. In contrast, age‐specific future breeding success (probability of being dominant at t + 1) increased with age, with dominant breeders maintaining higher subsequent breeding success than subordinate breeders. The opposite trends in survival and future breeding success for both subordinate and dominant breeders may indicate a lifetime, population‐level trade‐off. However, we found no evidence to suggest that being a dominant breeder consecutively (and having a higher accumulated breeding cost) accelerated the rate of senescence when compared to individuals that were previously subordinate. Thus, males experienced actuarial senescence regardless of social rank, with dominant (and possibly high quality) breeders showing a reduced trade‐off between survival and future breeding success. We make several novel contributions to understanding polygynous male life histories and southern elephant seal demography.
    Keywords Mirounga leonina ; animal ecology ; demography ; life history ; males ; mortality ; polygyny ; probability ; social structure
    Language English
    Dates of publication 2020-03
    Size p. 897-909.
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note NAL-AP-2-clean ; JOURNAL ARTICLE
    ZDB-ID 3024-7
    ISSN 1365-2656 ; 0021-8790
    ISSN (online) 1365-2656
    ISSN 0021-8790
    DOI 10.1111/1365-2656.13145
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  8. Article ; Online: Determinants of moult haulout phenology and duration in southern elephant seals.

    de Kock, Leandri / Oosthuizen, W Chris / Beltran, Roxanne S / Bester, Marthán N / de Bruyn, P J Nico

    Scientific reports

    2021  Volume 11, Issue 1, Page(s) 13331

    Abstract: Phenological shifts are among the most obvious biological responses to environmental change, yet documented responses for Southern Ocean marine mammals are extremely rare. Marine mammals can respond to environmental changes through phenological ... ...

    Abstract Phenological shifts are among the most obvious biological responses to environmental change, yet documented responses for Southern Ocean marine mammals are extremely rare. Marine mammals can respond to environmental changes through phenological flexibility of their life-history events such as breeding and moulting. Southern elephant seals (Mirounga leonina) undergo an obligatory annual moult which involves the rapid shedding of epidermal skin and hair while seals fast ashore. We quantified the timing (phenology) and duration (the time from arrival ashore to departure) of the moult haulout of 4612 female elephant seals at Marion Island over 32 years. Using linear mixed-effects models, we investigated age, breeding state and environmental drivers of moult timing and haulout duration. We found no clear evidence for a temporal shift in moult phenology or its duration. Annual variation in moult arrival date and haulout duration was small relative to age and breeding effects, which explained more than 90% of the variance in moult arrival date and 25% in moult haulout duration. All environmental covariates we tested explained minimal variation in the data. Female elephant seals moulted progressively later as juveniles, but adults age 4 and older had similar moult start dates that depended on the breeding state of the female. In contrast, moult haulout duration was not constant with age among adults, but instead became shorter with increasing age. Moulting is energetically expensive and differences in the moult haulout duration are possibly due to individual variation in body mass and associated metabolizable energy reserves, although other drivers (e.g. hormones) may also be present. Individual-based data on moult arrival dates and haulout duration can be used as auxiliary data in demographic modelling and may be useful proxies of other important biological parameters such as body condition and breeding history.
    MeSH term(s) Animals ; Breeding/methods ; Female ; Molting/physiology ; Seals, Earless/physiology
    Language English
    Publishing date 2021-06-25
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 2615211-3
    ISSN 2045-2322 ; 2045-2322
    ISSN (online) 2045-2322
    ISSN 2045-2322
    DOI 10.1038/s41598-021-92635-9
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  9. Article ; Online: Publisher Correction: Determinants of moult haulout phenology and duration in southern elephant seals.

    de Kock, Leandri / Oosthuizen, W Chris / Beltran, Roxanne S / Bester, Marthán N / de Bruyn, P J Nico

    Scientific reports

    2021  Volume 11, Issue 1, Page(s) 14051

    Language English
    Publishing date 2021-07-01
    Publishing country England
    Document type Published Erratum
    ZDB-ID 2615211-3
    ISSN 2045-2322 ; 2045-2322
    ISSN (online) 2045-2322
    ISSN 2045-2322
    DOI 10.1038/s41598-021-93678-8
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  10. Article: Selective disappearance of frail juveniles: consequences for understanding social dominance in adult male elephant seals

    Lloyd, Kyle J / Oosthuizen, W. Chris / Fay, Rémi / Bester, Marthán N / Nico de Bruyn, P. J

    Oikos. 2020 Oct., v. 129, no. 10

    2020  

    Abstract: Individual heterogeneity is variation in trait expression observed among individuals of a population. Individual heterogeneity in the pre‐breeder stage of development is of importance given its eventual contribution to the breeding population's overall ... ...

    Abstract Individual heterogeneity is variation in trait expression observed among individuals of a population. Individual heterogeneity in the pre‐breeder stage of development is of importance given its eventual contribution to the breeding population's overall reproductive performance. Yet most studies do not consider the role of individual heterogeneity in pre‐breeders when investigating population processes. We investigated individual heterogeneity in the survival and recruitment probabilities of pre‐breeding male southern elephant seals Mirounga leonina using 34 years of data collected at Marion Island. Elephant seals are highly polygynous capital breeders, with few male offspring surviving to compete in breeding events and even fewer breeding successfully. Specifically, we fitted finite‐mixture models with two hidden groups that represented ‘robust’ and ‘frail’ individuals and compared the demographic rates of these groups to that of the population. Survival and recruitment as first‐time subordinate breeders could be distinguished between groups. Survival of both robust and frail pre‐breeders decreased from age 2, whilst differences between groups were maintained (ontogeny processes). Frail pre‐breeders had a much lower survival than the population average, suggesting that frail individuals were preferentially removed from the population (selective disappearance). Differences in recruitment probabilities were apparent from age 5 (earliest recorded age) and increased until age 7, with most recruits comprising robust pre‐breeders. Male pre‐breeders were more likely to be robust at age 2 when born in years with few conspecifics, suggesting that individual heterogeneity was determined, in part, by density‐dependent effects. A population projection model revealed that male breeders of every age class never consisted of more than 5% of frail recruits. Rather, the breeding population increasingly consisted of robust recruits that obtained social dominance with age. We demonstrated that individual heterogeneity in male pre‐breeder demographic rates was present and persistent throughout much of development and determined the proportion of adult males that obtained social dominance.
    Keywords Mirounga leonina ; adults ; age ; capital breeding ; data collection ; juveniles ; males ; models ; ontogeny ; polygyny ; population ; progeny ; reproductive performance ; social dominance
    Language English
    Dates of publication 2020-10
    Size p. 1566-1578.
    Publishing place Blackwell Publishing Ltd
    Document type Article
    Note NAL-light ; JOURNAL ARTICLE
    ZDB-ID 207359-6
    ISSN 0030-1299
    ISSN 0030-1299
    DOI 10.1111/oik.07434
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