Prolonged life after reproduction is difficult to explain evolutionarily unless it arises as a physiological side effect of increased longevity or it benefits related individuals (i.e., increases ...inclusive fitness). There is little evidence that postreproductive life spans are adaptive in nonhuman animals. By using multigenerational records for two killer whale (Orcinus orca) populations in which females can live for decades after their final parturition, we show that postreproductive mothers increase the survival of offspring, particularly their older male offspring. This finding may explain why female killer whales have evolved the longest postreproductive life span of all nonhuman animals.
1. Management decisions for threatened and endangered species require risks to be identified and prioritized, based on the degree to which they influence population dynamics. The potential for ...recovery of small populations at risk may be determined by multiple factors, including intrinsic population characteristics (inbreeding, sex ratios) and extrinsic variables (prey availability, disease, human disturbance). Using Bayesian statistical methods, the impact of each of these risk factors on demographic rates can be quantified and assigned probabilities to express uncertainty. 2. We assessed the impact of a wide range of factors on the fecundity of two threatened populations of killer whales Orcinus orca, specifically whether killer whale production is limited by availability of Chinook salmon Oncorhynchus tshawytscha. Additional variables included anthropogenic factors, climate variables, temporal effects, and population variables (population size, number of males, female age). 3. Our results indicate that killer whale fecundity is highly correlated with the abundance of Chinook salmon. For example, the probability of a female calving differed by 50% between years of low salmon abundance and high salmon abundance. Weak evidence exists for linking fecundity to other variables, such as sea surface temperature. 4. There was strong data support for reproductive senescence in female killer whales. This pattern of rapid maturity and gradual decline of fecundity with age commonly seen in terrestrial mammals has been documented in few marine mammal species. Maximum production for this species occurs between ages 20-22, and reproductive performance declines gradually to menopause over a period of 25 years. 5. Synthesis and applications. Our results provide strong evidence for reproductive senescence in killer whales, and more importantly, that killer whale fecundity is strongly tied to the abundance of Chinook salmon, a species that is susceptible to environmental variation and has high commercial value to fisheries. This strong predator-prey relationship highlights the importance of understanding which salmon populations overlap with killer whales seasonally and spatially, so that those salmon populations important as prey for killer whales can be identified and targeted for conservation efforts.
For the majority of social species, group composition is dynamic, and individuals are interconnected in a heterogeneous social network. Social network structure has far-reaching implications for the ...ecology of individuals and populations. However, we have little understanding of how ecological variables shape this structure. We used a long-term data set (1984–2007) to examine the relationship between food availability and social network structure in the endangered southern resident killer whales. During the summer months individuals in this population feed primarily on chinook salmon, Oncorhynchus tshawytscha, which show annual variation in abundance. We tested the hypothesis that temporal variation in chinook salmon will correlate with variation in social network structure. Using a null model that controlled for population demography, group size and sampling effort, we found a significant relationship between the connectivity of the social network and salmon abundance, with a more interconnected social network in years of high salmon abundance. Our results demonstrate that resource availability may be an important determinant of social network structure. Given the central importance of the social network for population processes such as the maintenance of cooperation and the transmission of information and disease, a change in social network structure caused by a change in food availability may have significant ecological and evolutionary consequences.
► Significant correlation between salmon abundance and social structure in resident killer whales. ► In years of high chinook salmon abundance the social structure is more interconnected. ► This may have implications for information or disease transfer, gene flow and mating dynamics. ► These effects occur independent of group size.
Menopause is a seemingly maladaptive life-history trait that is found in many long-lived mammals. There are two competing evolutionary hypotheses for this phenomenon; in the adaptive view of ...menopause, the cessation of reproduction may increase the fitness of older females; in the non-adaptive view, menopause may be explained by physiological deterioration with age. The decline and eventual cessation of reproduction has been documented in a number of mammalian species, however the evolutionary cause of this trait is unknown.
We examined a unique 30-year time series of killer whales, tracking the reproductive performance of individuals through time. Killer whales are extremely long-lived, and may have the longest documented post-reproductive lifespan of any mammal, including humans. We found no strong support for either of the adaptive hypotheses of menopause; there was little support for the presence of post-reproductive females benefitting their daughter's reproductive performance (interbirth interval and reproductive lifespan of daughters), or the number of mature recruits to the population. Oldest mothers (> 35) did appear to have a small positive impact on calf survival, suggesting that females may gain experience with age. There was mixed support for the grandmother hypothesis - grandoffspring survival probabilities were not influenced by living grandmothers, but grandmothers may positively influence survival of juveniles at a critical life stage.
Although existing data do not allow us to examine evolutionary tradeoffs between survival and reproduction for this species, we were able to examine the effect of maternal age on offspring survival. Our results are consistent with similar studies of other mammals - oldest mothers appear to be better mothers, producing calves with higher survival rates. Studies of juvenile survival in humans have reported positive benefits of grandmothers on newly weaned infants; our results indicate that 3-year old killer whales may experience a positive benefit from helpful grandmothers. While our research provides little support for menopause evolving to provide fitness benefits to mothers or grandmothers, our work supports previous research showing that menopause and long post-reproductive lifespans are not a human phenomenon.
Photographic identification catalogs of individual killer whales (Orcinus orca) over time provide a tool for remote health assessment. We retrospectively examined digital photographs of Southern ...Resident killer whales in the Salish Sea to characterize skin changes and to determine if they could be an indicator of individual, pod, or population health. Using photographs collected from 2004 through 2016 from 18,697 individual whale sightings, we identified six lesions (cephalopod, erosions, gray patches, gray targets, orange on gray, and pinpoint black discoloration). Of 141 whales that were alive at some point during the study, 99% had photographic evidence of skin lesions. Using a multivariate model including age, sex, pod, and matriline across time, the point prevalence of the two most prevalent lesions, gray patches and gray targets, varied between pods and between years and showed small differences between stage classes. Despite minor differences, we document a strong increase in point prevalence of both lesion types in all three pods from 2004 through 2016. The health significance of this is not clear, but the possible relationship between these lesions and decreasing body condition and immunocompetence in an endangered, non-recovering population is a concern. Understanding the etiology and pathogenesis of these lesions is important to better understand the health significance of these skin changes that are increasing in prevalence.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Identifying how social organization shapes individual behavior, survival, and fecundity of animals that live in groups can inform conservation efforts and improve forecasts of population abundance, ...even when the mechanism responsible for group-level differences is unknown. We constructed a hierarchical Bayesian model to quantify the relative variability in survival rates among different levels of social organization (matrilines and pods) of an endangered population of killer whales (Orcinus orca). Individual killer whales often participate in group activities such as prey sharing and cooperative hunting. The estimated age-specific survival probabilities and survivorship curves differed considerably among pods and to a lesser extent among matrilines (within pods). Across all pods, males had lower life expectancy than females. Differences in survival between pods may be caused by a combination of factors that vary across the population's range, including reduced prey availability, contaminants in prey, and human activity. Our modeling approach could be applied to demographic rates for other species and for parameters other than survival, including reproduction, prey selection, movement, and detection probabilities. La identificación de la forma en que la organización social moldea el comportamiento, la supervivencia y fecundidad individual de animales que viven en grupos puede informar a los esfuerzos de conservación y mejorar los pronósticos de abundancia poblacional, aun cuando no se conozca el mecanismo responsable de las diferencias a nivel de grupo. Construimos un modelo Bayesiano jerárquico para cuantificar la variabilidad relativa en las tasas de supervivencia entre diferentes niveles de organización social (matrilíneas y agrupaciones) de una población en peligro de ballenas asesinas (Orcinus orca). Las ballenas individuales a menudo participan en actividades grupales como compartición de presas y cacería cooperativa. Las probabilidades estimadas de supervivencia por edades específicas y las curvas de supervivencia difirieron considerablemente entre grupos y en menor medida entre matrilíneas (dentro de los grupos). En todos los grupos, los machos tuvieron menor esperanza de vida que las hembras. Las diferencias en supervivencia entre grupos pudo deberse a una reducción en la disponibilidad de presas, contaminantes en las presas y actividad humana. Nuestro método de modelado podría ser aplicado a las tasas demográficas de otras especies y para parámetros distintos a la supervivencia, incluyendo reproducción, selección de presas, desplazamiento y probabilidades de detección.
Alliances between reproductive males have been described in both cetacean and terrestrial mammal societies, and kin selection theory has often been invoked to explain these stable male coalitions. ...However, recent studies of bottlenose dolphins, Tursiops aduncus, in Australia suggest that mechanisms other than kinship are fundamental in the formation of male alliances. We supplemented skin biopsy sampling with the collection of faecal samples from individually recognized wild bottlenose dolphins, T.truncatus, to assess the role of kin selection in alliance membership in the northeast Bahamas. Stable alliances between pairs of males were identified based on association analyses of individual photoidentification data collected over 4 years. Molecular genetic analyses of tissue samples revealed highly significant correlations between patterns of association and both mitochondrial DNA haplotype identity and microsatellite relatedness, indicating that males within long-term alliances are more closely related than expected by chance. These data reinforce the high degree of plasticity previously reported within the genus Tursiops, and suggest that social and ecological differences between populations can markedly affect the role of kin selection in determining social alliances between male bottlenose dolphins.Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.
The Endangered southern resident population of killer whales Orcinus orca has been shown to be food-limited, and the availability of their primary prey, Chinook salmon Oncorhynchus tshawytscha, has ...been identified as a key covariate for the whales' individual survival and reproduction. We collected aerial photogrammetry data on individual whale size, which will help to better inform energetic calculations of food requirements, and we compared size-at-age data to make inferences about long-term growth trends. A helicopter was used to conduct 10 flights in September 2008, resulting in 2803 images from which useable measurements were possible for 66 individually identifiable whales, representing more than three-quarters of the population. Estimated whale lengths ranged from 2.7 m for a neonate whale in its first year of life, to a maximum of 7.2 m for a 31 yr old adult male. Adult males reached an average (asymptotic) size estimate ( plus or minus SE) of 6.9 plus or minus 0.2 m, with growth slowing notably after the age of 18 yr; this was significantly larger than the asymptotic size of 6.0 plus or minus 0.1 m for females, which was reached after the earlier age of 15 yr. Notably, there was no overlap between the ranges of estimated sizes of adult males (6.5 to 7.2 m) and females (5.5 to 6.4 m). On average, older adults (>30 yr) were 0.3 m (n = 14, p = 0.03) and 0.3 m (n = 5, p = 0.23) longer than the younger whales of adult age, for females and males, respectively; we hypothesize that a long-term reduction in food availability may have reduced early growth rates and subsequent adult size in recent decades.
Identifying how social organization shapes individual behavior, survival, and fecundity of animals that live in groups can inform conservation efforts and improve forecasts of population abundance, ...even when the mechanism responsible for group-level differences is unknown. We constructed a hierarchical Bayesian model to quantify the relative variability in survival rates among different levels of social organization (matrilines and pods) of an endangered population of killer whales (Orcinus orca). Individual killer whales often participate in group activities such as prey sharing and cooperative hunting. The estimated age-specific survival probabilities and survivorship curves differed considerably among pods and to a lesser extent among matrilines (within pods). Across all pods, males had lower life expectancy than females. Differences in survival between pods may be caused by a combination of factors that vary across the population's range, including reduced prey availability, contaminants in prey, and human activity. Our modeling approach could be applied to demographic rates for other species and for parameters other than survival, including reproduction, prey selection, movement, and detection probabilities.Original Abstract: Resumen:La identificacion de la forma en que la organizacion social moldea el comportamiento, la supervivencia y fecundidad individual de animales que viven en grupos puede informar a los esfuerzos de conservacion y mejorar los pronosticos de abundancia poblacional, aun cuando no se conozca el mecanismo responsable de las diferencias a nivel de grupo. Construimos un modelo Bayesiano jerarquico para cuantificar la variabilidad relativa en las tasas de supervivencia entre diferentes niveles de organizacion social (matrilineas y agrupaciones) de una poblacion en peligro de ballenas asesinas (Orcinus orca). Las ballenas individuales a menudo participan en actividades grupales como comparticion de presas y caceria cooperativa. Las probabilidades estimadas de supervivencia por edades especificas y las curvas de supervivencia difirieron considerablemente entre grupos y en menor medida entre matrilineas (dentro de los grupos). En todos los grupos, los machos tuvieron menor esperanza de vida que las hembras. Las diferencias en supervivencia entre grupos pudo deberse a una reduccion en la disponibilidad de presas, contaminantes en las presas y actividad humana. Nuestro metodo de modelado podria ser aplicado a las tasas demograficas de otras especies y para parametros distintos a la supervivencia, incluyendo reproduccion, seleccion de presas, desplazamiento y probabilidades de deteccion.
Identifying how social organization shapes individual behavior, survival, and fecundity of animals that live in groups can inform conservation efforts and improve forecasts of population abundance, ...even when the mechanism responsible for group-level differences is unknown. We constructed a hierarchical Bayesian model to quantify the relative variability in survival rates among different levels of social organization (matrilines and pods) of an endangered population of killer whales (Orcinus orca). Individual killer whales often participate in group activities such as prey sharing and cooperative hunting. The estimated age-specific survival probabilities and survivorship curves differed considerably among pods and to a lesser extent among matrilines (within pods). Across all pods, males had lower life expectancy than females. Differences in survival between pods may be caused by a combination of factors that vary across the population's range, including reduced prey availability, contaminants in prey, and human activity. Our modeling approach could be applied to demographic rates for other species and for parameters other than survival, including reproduction, prey selection, movement, and detection probabilities. Resumen: La identificación de la forma en que la organización social moldea el comportamiento, la supervivencia y fecundidad individual de animales que viven en grupos puede informar a los esfuerzos de conservación y mejorar los pronósticos de abundancia poblacional, aun cuando no se conozca el mecanismo responsable de las diferencias a nivel de grupo. Construimos un modelo Bayesiano jerárquico para cuantificar la variabilidad relativa en las tasas de supervivencia entre diferentes niveles de organización social (matrilíneas y agrupaciones) de una población en peligro de ballenas asesinas (Orcinus orca). Las ballenas individuales a menudo participan en actividades grupales como compartición de presas y cacería cooperativa. Las probabilidades estimadas de supervivencia por edades específicas y las curvas de supervivencia difirieron considerablemente entre grupos y en menor medida entre matrilíneas (dentro de los grupos). En todos los grupos, los machos tuvieron menor esperanza de vida que las hembras. Las diferencias en supervivencia entre grupos pudo deberse a una reducción en la disponibilidad de presas, contaminantes en las presas y actividad humana. Nuestro método de modelado podría ser aplicado a las tasas demográficas de otras especies y para parámetros distintos a la supervivencia, incluyendo reproducción, selección de presas, desplazamiento y probabilidades de detección. PUBLICATION ABSTRACT
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