Wolf in Sheep’s Clothing: Model Misspecification Undermines Tests of the Neutral Theory for Life Histories

Understanding the processes behind change in reproductive state along life-history trajectories is a salient research program in evolutionary ecology. Two processes, state dependence and heterogeneity, can drive the dynamics of change among states. Both processes can operate simultaneously, begging the difficult question of how to tease them apart in practice. The Neutral Theory for Life Histories (NTLH) holds that the bulk of variations in life-history trajectories is due to state dependence and is hence neutral: Once previous (breeding) state is taken into account, variations are mostly random. Lifetime reproductive success (LRS), the number of descendants produced over an individual\u27s reproductive life span, has been used to infer support for NTLH in natura. Support stemmed from accurate prediction of the population-level distribution of LRS with parameters estimated from a state dependence model. We show with Monte Carlo simulations that the current reliance of NTLH on LRS prediction in a null hypothesis framework easily leads to selecting a misspecified model, biased estimates and flawed inferences. Support for the NTLH can be spurious because of a systematic positive bias in estimated state dependence when heterogeneity is present in the data but ignored in the analysis. This bias can lead to spurious positive covariance between fitness components when there is in fact an underlying trade-off. Furthermore, neutrality implied by NTLH needs a clarification because of a probable disjunction between its common understanding by evolutionary ecologists and its translation into statistical models of life-history trajectories. Irrespective of what neutrality entails, testing hypotheses about the dynamics of change among states in life histories requires a multimodel framework because state dependence and heterogeneity can easily be mistaken for each other

Evaluating strategies for managing anthropogenic mortality on marine mammals : an R implementation with the package RLA

Funding: ADERA provided support for salaries (MA).Bycatch, the undesirable and non-intentional catch of non-target species in marine fisheries, is one of the main causes of mortality of marine mammals worldwide. When quantitative conservation objectives and management goals are clearly defined, computer-based procedures can be used to explore likely population dynamics under different management scenarios and estimate the levels of anthropogenic removals, including bycatch, that marine mammal populations may withstand. Two control rules for setting removal limits are the Potential Biological Removal (PBR) established under the US Marine Mammal Protection Act and the Removals Limit Algorithm (RLA) inspired from the Catch Limit Algorithm (CLA) developed under the Revised Management Procedure of the International Whaling Commission. The PBR and RLA control rules were tested in a Management Strategy Evaluation (MSE) framework. A key feature of PBR and RLA is to ensure conservation objectives are met in the face of the multiple uncertainties or biases that plague real-world data on marine mammals. We built a package named RLA in the R software to carry out MSE of control rules to set removal limits in marine mammal conservation. The package functionalities are illustrated by two case studies carried out under the auspices of the Oslo and Paris convention (OSPAR) (the Convention for the Protection of the Marine Environment of the North-East Atlantic) Marine Mammal Expert Group (OMMEG) in the context of the EU Marine Strategy Framework Directive. The first case study sought to tune the PBR control rule to the conservation objective of restoring, with a probability of 0.8, a cetacean population to 80% of carrying capacity after 100 years. The second case study sought to further develop a RLA to set removals limit on harbor porpoises in the North Sea with the same conservation objective as in the first case study. Estimation of the removals limit under the RLA control rule was carried out within the Bayesian paradigm. Outputs from the functions implemented in the package RLA allows the assessment of user-defined performance metrics, such as time to reach a given fraction of carrying capacity under a given level of removals compared to the time needed given no removals.Publisher PDFPeer reviewe

A Comprehensive Survey of Pelagic Megafauna: Their Distribution, Densities, and Taxonomic Richness in the Tropical Southwest Indian Ocean

The distribution and density of pelagic megafauna (marine mammals, seabirds, elasmobranches, and sea turtles) are important indicators of marine biodiversity, reflecting the condition of the underlying ecosystems. A dedicated aerial survey was conducted in the tropical Southwest Indian Ocean to map their distribution, the taxonomic diversity, and to estimate their densities to serve as a baseline for the area. This large survey across three ecological sub-regions revealed contrasting spatial distributions: maps of taxonomic richness of marine mammals and seabirds revealed different “hotspots” in the area. Densities were estimated for eight cetacean taxa with small and large Delphininae, or small Globicephalinae dominating, and for seven seabird taxa, with terns and noddies dominating. At the community level, the Southwest Indian Ocean megafauna was structured by the marine environment with strong differences between the Mozambique Channel and the Mascarene Islands, or between shelf and slope/oceanic habitats. Our results illustrate how multi-taxa aerial surveys are relevant and cost-effective monitoring tools for marine megafauna, allowing a community-wide approach

Looking for a needle in a haystack: inference about individual fitness components in a heterogeneous population

Studies of wild vertebrates have provided evidence of substantial differences in lifetime reproduction among individuals and the sequences of life history ‘states’ during life (breeding, nonbreeding, etc.). Such differences may reflect ‘fixed’ differences in fitness components among individuals determined before, or at the onset of reproductive life. Many retrospective life history studies have translated this idea by assuming a ‘latent’ unobserved heterogeneity resulting in a fixed hierarchy among individuals in fitness components. Alternatively, fixed differences among individuals are not necessarily needed to account for observed levels of individual heterogeneity in life histories. Individuals with identical fitness traits may stochastically experience different outcomes for breeding and survival through life that lead to a diversity of ‘state’ sequences with some individuals living longer and being more productive than others, by chance alone. The question is whether individuals differ in their underlying fitness components in ways that cannot be explained by observable ‘states’ such as age, previous breeding success, etc. Here, we compare statistical models that represent these opposing hypotheses, and mixtures of them, using data from kittiwakes. We constructed models that accounted for observed covariates, individual random effects (unobserved heterogeneity), first-order Markovian transitions between observed states, or combinations of these features. We show that individual sequences of states are better accounted for by models incorporating unobserved heterogeneity than by models including first-order Markov processes alone, or a combination of both. If we had not considered individual heterogeneity, models including Markovian transitions would have been the best performing ones. We also show that inference about age-related changes in fitness components is sensitive to incorporation of underlying individual heterogeneity in models. Our approach provides insight into the sources of individual heterogeneity in life histories, and can be applied to other data sets to examine the ubiquity of our results across the tree of life

Workshop on mitigation measures to reduce bycatch of short-beaked common dolphins in the Bay of Biscay (WKEMBYC2)

Following the special request from the DG MARE, the Workshop on mitigation measures to minimize bycatch of short-beaked common dolphins in the Bay of Biscay (WKEMBYC2) was established by ICES. WKEMBYC2 was tasked with updating and revaluating the scenarios previously proposed in the ICES special request advice in 2020. The group was asked to consider recent data on bycatch of common dolphins in commercial fisheries and total fishing effort in the Bay of Biscay and Iberian Coast ecosystem, as well as taking into account results from any mitigation trials carried out since the meeting in 2020. In section 2 of this report the efficacy of the scenarios provided during WKEMBYC in 2020 were reassessed using updated bycatch estimates calculated from at-sea monitoring and stranding data collected between 2019 and 2021. Scenarios and methods remained unchanged, to ensure comparability between both evaluations. Similarly, PBR values considered in the 2020 scenarios were again considered here, with the addition of the mPBR which was developed by OSPAR since the last workshop. The annual mortality due to bycatch inferred from French strandings in the Bay of Biscay and along the Western Channel was estimated at about 9,040 (95%CI [6,640 - 13,300]) common dolphins between 2019 and 2021. In the Bay of Biscay and Iberian Coast (areas 8 and 9), the mean annual bycatch estimated from at-sea observations between 2019-2021 across all métiers was 5938 (95% CI 3081-9700) common dolphins. The abundance estimate and PBR values used in this report were the same as those used in 2020; with common dolphin abundance estimated to be 634 286 (CV=0.307) for the European Atlantic Assessment Unit, and PBR for the species calcu-lated as 4926 individuals per year. The management objective of PBR is to ensure that “a population will remain at, or recover to, its maximum net productivity level (typically 50% of the populations carrying capacity), with 95% probability, within a 100-year period”. A modified PBR (mPBR) value of 985 was also used, with the management objective of ensuring “a population should be able to recover to or be maintained at 80% of carrying capacity, with probability 0.8, within a 100-year period”. Considering bycatch estimates calculated from at-sea monitoring, scenarios with a combination of pingers on OTM/PTB and at least 4-week closure in winter can reach the management objective of bycatch remaining below the PBR. The removal bycatch over a three-month period between the January and March winter period, and an addi-tional month closure in July/August potentially reduces bycatch below the mPBR level for at-sea monitoring bycatch estimates alone. Considering estimates inferred from strandings, a mini-mum of 6-week closure combined with pingers can achieve the objective of reducing bycatch below PBR. None of the scenarios can reduce bycatch below mPBR for either monitoring and stranding bycatch estimates. The narrower the fishery closure, the higher the risk of not achieving the management objective, as the peak of mortality can be missed. In section 3 of the report the workshop participants chose to further explore the scenarios with bycatch rates and estimate bycatch at a finer spatial and temporal scale and to consider additional mitigation measures based on results of newly conducted preliminary trials. This exploratory analysis allowed particular areas, métiers or periods with evidence of elevated bycatch rates to be identified at higher resolution, however, this approach requires significant at-sea monitoring in all strata. If such data were available, this method could be used to highlight specific areas, métiers and periods where particular effort in vessel observation should be deployed or mitigation measures implemented. WKEMBYC2 also recommended a series of monitoring actions to improve bycatch estimates, monitoring to data analysis, mitigation and the assessment of the northeast Atlantic common dolphin

Temporal correlations among demographic parameters are ubiquitous but highly variable across species

Temporal correlations among demographic parameters can strongly influence population dynamics. Our empirical knowledge, however, is very limited regarding the direction and the magnitude of these correlations and how they vary among demographic parameters and species’ life histories. Here, we use long-term demographic data from 15 bird and mammal species with contrasting pace of life to quantify correlation patterns among five key demographic parameters: juvenile and adult survival, reproductive probability, reproductive success and productivity. Correlations among demographic parameters were ubiquitous, more frequently positive than negative, but strongly differed across species. Correlations did not markedly change along the slow-fast continuum of life histories, suggesting that they were more strongly driven by ecological than evolutionary factors. As positive temporal demographic correlations decrease the mean of the long-run population growth rate, the common practice of ignoring temporal correlations in population models could lead to the underestimation of extinction risks in most species

Workshop on Mitigation Measures to Reduce Bycatch of Short-Beaked Common Dolphins in the Bay of Biscay (WKEMBYC2)

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Large‐scale modelling of deep‐diving cetacean habitats

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Capturado y registrado: potencial de las redes de varamientos para el estudio de las capturas accidentales de cetáceos

XII Congreso de la Sociedad Española de Cetáceos, 4 al 7 de octubre de 2021, onlineN

Foraging Fidelity as a Recipe for a Long Life: Foraging Strategy and Longevity in Male Southern Elephant Seals

Identifying individual factors affecting life-span has long been of interest for biologists and demographers: how do some individuals manage to dodge the forces of mortality when the vast majority does not? Answering this question is not straightforward, partly because of the arduous task of accurately estimating longevity in wild animals, and of the statistical difficulties in correlating time-varying ecological covariables with a single number (time-to-event). Here we investigated the relationship between foraging strategy and life-span in an elusive and large marine predator: the Southern Elephant Seal (Mirounga leonina). Using teeth recovered from dead males on îles Kerguelen, Southern Ocean, we first aged specimens. Then we used stable isotopic measurements of carbon () in dentin to study the effect of foraging location on individual life-span. Using a joint change-point/survival modelling approach which enabled us to describe the ontogenetic trajectory of foraging, we unveiled how a stable foraging strategy developed early in life positively covaried with longevity in male Southern Elephant Seals. Coupled with an appropriate statistical analysis, stable isotopes have the potential to tackle ecological questions of long standing interest but whose answer has been hampered by logistic constraints