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Compensation and additivity of anthropogenic mortality: Life-history effects and review of methods

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Compensation and additivity of anthropogenic mortality: Life-history effects and review of methods

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Abstract

Demographic compensation, the increase in average individual performance following a perturbation that reduces population size, and, its opposite, demographic overadditivity (or superadditivity) are central processes in both population ecology and wildlife management. A continuum of population responses to changes in cause-specific mortality exists, of which additivity and complete compensation constitute particular points. The position of a population on that continuum influences its ability to sustain exploitation and predation. Here I describe a method for quantifying where a population is on the continuum. Based on variance-covariance formulae, I describe a simple metric for the rate of compensation-additivity. I synthesize the results from 10 wildlife capture-recapture monitoring programmes from the literature and online databases, reviewing current statistical methods and the treatment of common sources of bias. These results are used to test hypotheses regarding the effects of life-history strategy, population density, average cause-specific mortality and age class on the rate of compensation-additivity. This comparative analysis highlights that long-lived species compensate less than short-lived species and that populations below their carrying capacity compensate less than those above.

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... The relationship between anthropogenic harvest and population growth rates of wild organisms is of major interest to population managers and resource consumers (Nichols et al., 1995;Péron, 2013;Sedinger & Herzog, 2012;Servanty et al., 2011) and has received considerable attention and debate (Anderson & Burnham, 1976;Burnham et al., 1984;Lebreton, 2005;Nichols et al., 1995;Péron, 2013;. Overexploitation can catastrophically impact wildlife populations (e.g. ...
... The relationship between anthropogenic harvest and population growth rates of wild organisms is of major interest to population managers and resource consumers (Nichols et al., 1995;Péron, 2013;Sedinger & Herzog, 2012;Servanty et al., 2011) and has received considerable attention and debate (Anderson & Burnham, 1976;Burnham et al., 1984;Lebreton, 2005;Nichols et al., 1995;Péron, 2013;. Overexploitation can catastrophically impact wildlife populations (e.g. ...
... For example, adult female North American hunting mortality probability was < 0.06 from 1974-2015, and hunting mortality probability was < 0.03 in 32 of 42 years (this paper, Devink et al., 2013). Increases in hunting mortality of 0.01 to 0.02 should not have large (>0.1) effects on survival, even if the effects of hunting were additive or depensatory, which would be rare in species such as teal that have rapid life histories (Koons et al., 2014;Péron, 2013). Anas platyrhynchos (Sparrowe & Patterson, 1987). ...
Article
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Harvest of wild organisms is an important component of human culture, economy, and recreation, but can also put species at risk of extinction. Decisions that guide successful management actions therefore rely on the ability of researchers to link changes in demographic processes to the anthropogenic actions or environmental changes that underlie variation in demographic parameters. Ecologists often use population models or maximum sustained yield curves to estimate the impacts of harvest on wildlife and fish populations. Applications of these models usually focus exclusively on the impact of harvest and often fail to consider adequately other potential, often collinear, mechanistic drivers of the observed relationships between harvest and demographic rates. In this study, we used an integrated population model and long‐term data (1973‐2016) to examine the relationships among hunting and natural mortality, the number of hunters, habitat conditions, and population size of blue‐winged teal (Spatula discors), an abundant North American dabbling duck with a relatively fast‐paced life history strategy. Over the last two and a half decades of the study, teal abundance tripled, hunting mortality probability increased slightly (<), and natural mortality probability increased substantially (>) at greater population densities. We demonstrate strong density‐dependent effects on natural mortality and fecundity as population density increased, indicative of compensatory harvest mortality and compensatory natality. Critically, an analysis that only assessed the relationship between survival and hunting mortality would spuriously indicate depensatory mortality due to multicollinearity between abundance, natural mortality, and hunting mortality. Our findings demonstrate that models that only consider the direct effect of hunting on survival or natural mortality can fail to accurately assess the mechanistic impact of hunting on population dynamics due to multicollinearity among demographic drivers. This multicollinearity limits inference and may have strong impacts on applied management actions globally.
... Capture-mark-recapture-resight and capture-mark-recovery data can be used to estimate demographic parameters such as true and apparent survival, site fidelity, movement and harvest rates, breeding propensity, demographic heterogeneity, and relationships among these parameters and environmental covariates (Brownie & Pollock, 1985;Cam, Link, Cooch, Monnat, & Danchin, 2002;Gimenez, Cam, & Gaillard, 2018;Kendall et al., 2013;Kendall, Nichols, & Hines, 1997). Estimating relationships between demographic parameters can lead to more effective conservation actions (Arnold, Afton, Anteau, Koons, & Nicolai, 2016;Servanty et al., 2010Servanty et al., , 2011, where biologists might direct conservation actions toward demographic components which are intrinsically linked, such as pre-and postfledging survival (Nicolai & Sedinger, 2012) or adjust anthropogenic harvest rates to affect population growth rates of wild organisms (Nichols, Runge, Johnson, & Williams, 2007;Péron, 2013;Runge et al., 2002;Williams & Johnson, 1995). Estimating relationships among demographic rates can also advance our understanding of individual heterogeneity, life-history trade-offs, and the evolution of life histories (Cam, Aubry, & Authier, 2016;Cam et al., 2002;Gimenez et al., 2018;Stearns, 1992). ...
... Previous methods have employed approaches to achieve independent samples by comparing estimates of survival from the marked sample with estimates of harvest of the total population (Anderson & Burnham, 1976) or by partitioning the capture-mark-recovery data (Nichols & Hines, 1983). Recently, work on the effects of harvest on survival has focused on understanding process correlations (ρ) between survival and harvest rates (Arnold et al., 2016;Bartzen & Dufour, 2017;Sedinger, White, Espinosa, Partee, & Braun, 2010), where a strong negative correlation suggests additive relationships between survival and harvest, and minimal or no correlation may be indicative of compensation or partial compensation, although these relationships are complex (Arnold et al., 2016;Péron, 2013). Others have focused on the correlation between natural mortality and harvest mortality (Péron, 2013;Servanty et al., 2010), where no correlation may be indicative of additive harvest, and a negative correlation may be indicative of compensatory harvest. ...
... Recently, work on the effects of harvest on survival has focused on understanding process correlations (ρ) between survival and harvest rates (Arnold et al., 2016;Bartzen & Dufour, 2017;Sedinger, White, Espinosa, Partee, & Braun, 2010), where a strong negative correlation suggests additive relationships between survival and harvest, and minimal or no correlation may be indicative of compensation or partial compensation, although these relationships are complex (Arnold et al., 2016;Péron, 2013). Others have focused on the correlation between natural mortality and harvest mortality (Péron, 2013;Servanty et al., 2010), where no correlation may be indicative of additive harvest, and a negative correlation may be indicative of compensatory harvest. Ecologists have both highlighted (Arnold et al., 2016;Péron, 2013;Servanty et al., 2010) and debated (Arnold, Afton, Anteau, Koons, & Nicolai, 2017;Lindberg, Boomer, Schmutz, & Walker, 2017) the utility of these approaches. ...
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Abstract Estimating correlations among demographic parameters is critical to understanding population dynamics and life‐history evolution, where correlations among parameters can inform our understanding of life‐history trade‐offs, result in effective applied conservation actions, and shed light on evolutionary ecology. The most common approaches rely on the multivariate normal distribution, and its conjugate inverse Wishart prior distribution. However, the inverse Wishart prior for the covariance matrix of multivariate normal distributions has a strong influence on posterior distributions. As an alternative to the inverse Wishart distribution, we individually parameterize the covariance matrix of a multivariate normal distribution to accurately estimate variances (σ2) of, and process correlations (ρ) between, demographic parameters. We evaluate this approach using simulated capture–mark–recapture data. We then use this method to examine process correlations between adult and juvenile survival of black brent geese marked on the Yukon–Kuskokwim River Delta, Alaska (1988–2014). Our parameterization consistently outperformed the conjugate inverse Wishart prior for simulated data, where the means of posterior distributions estimated using an inverse Wishart prior were substantially different from the values used to simulate the data. Brent adult and juvenile annual apparent survival rates were strongly positively correlated (ρ = 0.563, 95% CRI 0.181–0.823), suggesting that habitat conditions have significant effects on both adult and juvenile survival. We provide robust simulation tools, and our methods can readily be expanded for use in other capture–recapture or capture‐recovery frameworks. Further, our work reveals limits on the utility of these approaches when study duration or sample sizes are small.
... Rate of intraspecific killing among wolves is lower in exploited wolf populations, potentially suggesting compensatory mechanisms (Cubaynes et al. 2014). Contrarily, wolves are fairly long-lived and recovering over much of their range, making them poor candidates for compensation which is more prominent in short-lived species and populations at carrying capacity (Mech and Boitani 2003;Péron 2013). Development of statistical methods for understanding the spectrum of compensation to additivity while accounting for biases makes assessment of compensation of mortality sources in Wisconsin's wolf population very timely (Péron 2013;Schaub and Lebreton 2004;Servanty et al. 2010). ...
... Contrarily, wolves are fairly long-lived and recovering over much of their range, making them poor candidates for compensation which is more prominent in short-lived species and populations at carrying capacity (Mech and Boitani 2003;Péron 2013). Development of statistical methods for understanding the spectrum of compensation to additivity while accounting for biases makes assessment of compensation of mortality sources in Wisconsin's wolf population very timely (Péron 2013;Schaub and Lebreton 2004;Servanty et al. 2010). ...
... Our study area was north and central Wisconsin, USA (1979-2013. Wolves primarily occupied the northern (wolf harvest zones [WHZs] 1, 2, 3, and 4; Fig. 1) and central forest regions (WHZ 5) of Wisconsin (Mladenoff et al. 2009). ...
Article
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Populations of large terrestrial carnivores are in various stages of recovery worldwide and the question of whether there is compensation in mortality sources is relevant to conservation. Here, we show variation in Wisconsin wolf survival from 1979 to 2013 by jointly estimating the hazard of wolves’ radio-telemetry ending (endpoint) and endpoint cause. In previous analyses, wolves lost to radio-telemetry follow-up (collar loss) were censored from analysis, thereby assuming collar loss was unconfounded with mortality. Our approach allowed us to explicitly estimate hazard due to collar loss and did not require censoring these records from analysis. We found mean annual survival was 76% and mean annual causes of mortality were illegal killing (9.4%), natural and unknown causes (9.5%), and other human-caused mortality such as hunting, vehicle collisions and lethal control (5.1%). Illegal killing and natural mortality were highest during winter, causing wolf survival to decrease relative to summer. Mortality was highest during early recovery and lowest during a period of sustained population growth. Wolves again experienced higher risk of human-caused mortality relative to natural mortality as wolves expanded into areas with more human activity. We detected partial compensation in human- and natural-caused mortality since 2004 as the population saturated more available habitat. Prior to 2004, we detected additivity in mortality sources. Assessments of wolf survival and cause of mortality rates and the finding of partial compensation in mortality sources will inform wolf conservation and management efforts by identifying sources and sinks, finding areas of conservation need, and assessing management zone delineation.
... Discerning between different sources of mortality is a key challenge in ecology, evolutionary biology, and population management (Péron, 2013;Schaub & Lebreton, 2004;Wolfe et al., 2015). (Caswell, 2007a;Charlesworth, 1994;Koons et al., 2014). ...
... Many studies have estimated relationships between probabilities of dying from different causes across years or space in order to assess whether mortality from these causes are additive (not associated), compensatory (negatively associated) or depensatory (positively associated) (Bischof, Swenson, Yoccoz, Mysterud, & Gimenez, 2009;Péron, 2013;Servanty et al., 2010;Wolfe et al., 2015). One problem of using mortality probabilities in such studies is that they are, as explained above, intrinsically related; ...
... As shown in Figure 3, this intrinsic negative association may dominate empirical correlations between cause-specific mortality probabilities across years (or groups of individuals) even when correlations between the cause-specific mortality hazard rates across years (or groups) are strongly positive. Realizing this problem, researchers have come up with solutions to reduce "bias" 1 in correlations between causespecific mortality probabilities (Schaub & Lebreton, 2004;Servanty et al., 2010) or to interpret these correlations with respect to hypotheses for compensatory versus additive mortality patterns (Péron, 2013). However, when modelling mortality hazard rates, correlations can be interpreted directly; when partitioning mortality into one specific cause (e.g., "harvesting/ predation") and all other causes, a negative correlation between the mortality hazard rates among years indicates compensation, a positive correlation indicates depensation, and a correlation close to zero may indicate additivity. ...
Article
1Mortality is a key process in ecology and evolution, and much effort is spent on development and application of statistical and theoretical models involving mortality. Mortality takes place in continuous time, and a fundamental representation of mortality risks is the mortality hazard rate, which is the intensity of deadly events that an individual is exposed to at any point in time. In discrete‐time population models, however, the mortality process is represented by survival or mortality probabilities, which are aggregate functions of the mortality hazard rates within given intervals. In this commentary, we argue that focussing on mortality hazard rates, also when using discrete‐time models, aids the construction of biologically reasonable models and improves ecological inference. 2.We discuss three topics in population ecology where hazard rates can be particularly useful for biological inference, but are nevertheless often not used: (i) modelling of covariate effects, (ii) modelling of multiple sources of mortality and competing risks, and (iii) elasticity analyses of population growth rate with respect to demographic parameters. To facilitate estimation of cause‐specific mortality hazard rates, we provide extensions to the R package ‘marked’. 3.Using mortality hazard rates sometimes makes it easier to formulate biologically reasonable models with more directly interpretable parameterizations and more explicit assumptions. In particular, interpretations about relative differences between mortality hazard rates, or effects of relative changes in mortality hazard rates on population growth (elasticities), are often more meaningful than interpretations involving relative differences in survival (or mortality) probabilities or odds. 4.The concept of hazard rates is essential for understanding ecological and evolutionary processes and we give an intuitive explanation for this, using several examples. We provide some practical guidelines and suggestions for further methods developments. This article is protected by copyright. All rights reserved.
... Determining the conditions under which the hydra effect occurs in nature is of practical importance both for conserving populations harvested by humans (Anderson & Burnham, 1976;Pedersen et al., 2004;Péron, 2013) and for control of invasive species (e.g. garlic mustard; Pardini et al., 2009) and vectors of disease (Juliano, 2007). ...
... garlic mustard; Pardini et al., 2009) and vectors of disease (Juliano, 2007). If wildlife managers set inflated harvest quotas based on the assumption that hunting mortality is compensatory when it is actually additive, it could lead to over-exploitation, collapse and even extinction of the harvested species (Sale & Tolimieri, 2000;Pedersen et al., 2004;Pöysä, 2004;Péron, 2013). Conversely, when the management goal is controlling an invasive species or disease vector that is under density-dependent regulation, the hydra effect could cause the undesirable outcome of the target species increasing, rather than decreasing, in population size (Zipkin et al., 2009). ...
... Any mosquito control method that results in a low density of larvae prior to density-dependent regulation could potentially result in compensation or over-compensation. The relatively short generation times and high fecundity of mosquitoes increase their potential to rebound quickly from extrinsic perturbation, increasing the likelihood that compensation or over-compensation will occur (Péron, 2013). ...
Article
1. This study investigated the effects of strong density dependence on larval growth, development, and survival of the mosquito Culex restuans (Theobald). It also tested the hypothesis that density reduction early in larval development could result in as many or more individuals surviving to adulthood (compensation or over‐compensation, respectively), or increased reproductive performance via rapid development and greater adult size. 2. In a field study of a natural population of C. restuans, the effects of a 75% lower density on percentage survivorship to adulthood, number of adults, development time, adult size, adult longevity, and size dependent fecundity were tested. 3. No evidence was found of compensation or over‐compensation in adult production, or of effects of lower density on percentage survivorship. Low density yielded significant increases in adult size, adult longevity, and size‐dependent fecundity, and a decrease in development time. 4. Estimated per‐capita population growth rate was significantly greater in the low‐density treatment than in the high‐density treatment. It is inferred that this difference was due to greater per‐capita resources, which increased female size and fecundity, and reduced development time. Greater per‐capita population growth could therefore result from early mortality of larvae, meaning that the hydra effect, which predicts greater equilibrium population with, as opposed to without, extrinsic mortality, may be possible for these mosquitoes.
... Cette exploitation non-durable est particulièrement grave pour la mégafaune, c'est-à-dire des carnivores dont la masse est > 15 kg et pour des herbivores dont la masse est > 100 kg (Braje and Erlandson 2013, Lindsey et al. 2017, Ripple et al. 2017. Ces espèces sont souvent caractérisées par une survie des adultes relativement élevée et une fécondité relativement faible, ce qui les rend particulièrement vulnérables à une exploitation intensive (Gaillard et al. 2000, Lebreton 2005, Peron 2013). Un niveau d'exploitation excessif par l'homme est, en effet, l'hypothèse privilégiée pour expliquer l'extinction de la mégafaune de l'Australie et de l'Amérique du ...
... Compensatory mortality accounts for the possibility that some individuals harvested would have died anyway from nonhunting causes. For species with relatively low productivity and long generation time such as bison (Meagher 1986), compensation by natural mortality in a scenario of exploitation is expected to be low (Lebreton 2005, Peron 2013). We The proportion of individuals killed by anthrax (a in Fig. 2.1) was drawn randomly from between 2 and 10%, according to the range observed in WBNP (Salb et al. 2014) and PANP (Shury et al. 2009). ...
... Other sources of mortality, including wolf predation, would have to compensate for at least 55% of current harvest mortality to prevent population growth in the absence of harvest. For a species leaning more towards the K end of r-K selection spectrum such as bison (Meagher 1986, Eberhardt 2002, such a high level of compensation by natural mortality is unlikely (Lebreton 2005, Peron 2013). ...
Thesis
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Determining the factors that shape patterns of animal distribution and abundance is a major topic in contemporary ecological research. The overarching objective of my thesis was to better understand how one such factor, predation – in its broader meaning to include harvesting by humans – influences the links between space use and population dynamics. My work explores the links between predation risk, movement and habitat selection, mortality rates and the viability of a threatened population of large herbivore. The study system was the plains bison (Bison bison bison) population of Prince Albert National Park, Saskatchewan, subject most notably to predation by grey wolves (Canis lupus) and harvest by humans. In chapter 1, I use movement and habitat selection analyses to reveal the strategies of space use deployed by bison in response to wolves and vice-versa. From mid-summer to the onset of winter, bison reduced the time spent in patches rich in food as the long-term risk of encountering wolves there increased. Bison also left these patches more quickly when wolves were relatively close by. In winter, however, bison were observed to only react by moving away from nearby wolves. The absence of a bison response to the long-term risk of encountering wolves in winter could be explained by energetic constraints, as food is less digestible and movement more costly due to snow cover during this season. Although I reveal that perceived predation risk influences bison use of space, I show in chapter 2 that neither wolf predation nor disease (in the form of anthrax outbreaks) represent a threat to the viability of the population. Rather, the main reason behind a probability of population extinction of 66% over the next 50 years under current conditions is the legal, yet unregulated, harvest by native hunters. Bison are vulnerable to harvest when they leave the park to forage on rich food available in agricultural fields. My analyses refine our understanding of this pattern by showing that every additional 1% of time spent in fields with hunting permission from 2011 to 2016 increased the risk of harvest mortality by 9%. I also reveal that the time bison spend in such fields must drop by 70% for population abundance to remain stable at its current level in a scenario of continued wolf predation and anthrax outbreaks. More than 70% of bison use of fields with hunting permission were limited to just five fields. Management interventions targeting these riskier fields would be an effective short-term strategy to halt the population’s decline. Even though such an approach might lead bison to increase their use of other fields, the demographic impact of harvesting should consequently diminish, at least over the short term, given that harvesting is not permitted in most other fields used by bison. Finally, in chapter 3, I use an individual-based model to compare the relative effectiveness of different management interventions manipulating food profitability (i.e. the ratio between digestible energy and handling time) and distribution to reduce the time bison spend outside the park raiding crops and, thereby, the number of individuals harvested. My simulations suggest that draining meadows inside the park to increase the availability of natural forage there would not be very effective. However, my simulations also suggest that cultivating crops outside the park of lower profitability relative to natural forage inside the park would be a better intervention. My thesis reveals the dynamic and complex nature of the anti-predator movement and habitat selection strategies deployed by a large herbivore in a multi-prey system. My work also highlights the practical interest of linking spatial distribution to population viability to lead to more effective management interventions. The overall result is a thorough case study aimed at improving our ability, over the short term, to conserve populations vulnerable to threats which are distributed heterogeneously in space.
... In some other long-lived species of predators for which anthropogenic mortality matches or exceeds natural mortality, take appears to be compensated for -to some degree -by decreases in density-dependent feedback that lead to increases in other vital rates (Leberton 2005, Creel et al. 2010, Gantchoff et al. 2020. Péron (2013) evaluated the capacity for demographic compensation according to life history attributes across a range of taxa and found that such capacity is inversely related to generation time. Our estimate of generation time for golden eagles in the coterminous western U.S.A. is close to the maximum considered in Péron's (2013) analysis. ...
... Péron (2013) evaluated the capacity for demographic compensation according to life history attributes across a range of taxa and found that such capacity is inversely related to generation time. Our estimate of generation time for golden eagles in the coterminous western U.S.A. is close to the maximum considered in Péron's (2013) analysis. Thus, we would expect that the capacity to absorb added mortality, particularly take of adults, would be limited. ...
Article
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In the United States of America (U.S.A.), the Bald and Golden Eagle Protection Act prohibits take of golden eagles (Aquila chrysaetos) unless authorized by permit, and stipulates that all permitted take must be sustainable. Golden eagles are unintentionally killed in conjunction with many lawful activities (e.g., electrocution on power poles, collision with wind turbines). Managers who issue permits for incidental take of golden eagles must determine allowable take levels and manage permitted take accordingly. To aid managers in making these decisions in the western U.S.A., we used an integrated population model to obtain estimates of golden eagle vital rates and population size, and then used those estimates in a prescribed take level (PTL) model to estimate the allowable take level. Estimated mean annual survival rates for golden eagles ranged from 0.70 (95% credible interval = 0.66-0.74) for first-year birds to 0.90 (0.88-0.91) for adults. Models suggested a high proportion of adult female golden eagles attempted to breed and breeding pairs fledged a mean of 0.53 (0.39-0.72) young annually. Population size in the coterminous western U.S. has averaged ~31,800 individuals for several decades, with λ = 1.0 (0.96-1.05). The PTL model estimated a median allowable take limit of ~2242 (709-4248) individuals annually given a management objective of maintaining a stable population. We estimate that take averaged 2572 out of 4353 (59%) deaths annually, based on a representative sample of transmitter-tagged golden eagles. For the subset of golden eagles that were recovered and a cause of death determined, anthropogenic mortality accounted for an average of 74% of deaths after their first year; leading forms of take over all age classes were shooting (~670 per year), collisions (~611), electrocutions (~506), and poisoning (~427). Although observed take overlapped the credible interval of our allowable take estimate and the population overall has been stable, our findings indicate that additional take, unless mitigated for, may not be sustainable. Our analysis demonstrates the utility of the joint application of integrated population and prescribed take level models to management of incidental take of a protected species. This article is protected by copyright. All rights reserved.
... predation, starving) and that the loss does not exceed the demographic ability of a population to compensate for the losses. If mortality is compensated by an increase in survival of the remaining individuals, mortality from hunting and from other factors are negatively correlated (Williams 1997, Péron 2013. For grouse there is hardly any evidence for a compensation of mortality via increase in reproductive output (Ellison 1991). ...
... For grouse there is hardly any evidence for a compensation of mortality via increase in reproductive output (Ellison 1991). Reviews of studies on a large variety of species indicate that pure compensation hardly exists and mortality caused by exploitation is almost always both compensatory and additive (Sutherland 2001, Péron 2013). 2. Increasing populations can be exploited sustainably if harvest rate is not higher than the long-term growth rate (Wade 1998). ...
Article
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In the Canton of Ticino in southern Switzerland data from the monitoring programme for black grouse from 1981 to 2016 (population density, lek size, sex ratio in chicks and adults) were analysed together with information on bag statistics and hunting regulations to evaluate if mortality from hunting had an additive effect. In the study population the proportion of cocks at the beginning of the study period was only 23%. As hunting regulations for black grouse were tightened in the late 1970s the observed proportion of males showed an increase in particular during the first years but remained much lower than what would be expected from the sex ratio among chicks assuming equal survival between the sexes. The observed low proportion of adult males indicates a lower survival rate and as a consequence a smaller than natural lek size. High reproductive success two years before had a positive effect on lek size. The correlation coefficient between hunting bag and population size index increased with increasing hunting pressure and showed a decline over the years. Bag size in the period with a high hunting pressure (1981-1999, many hunting days) was driven by population density whereas in the second period (2000-2016, few hunting days) it was driven by hunting regulations. Our analysis showed that hunting affects population structure and presents indirect evidence that mortality due to hunting is additive. The study also shows that hunting management has to be continuously adapted to changes in the size and structure of the population as well as changes in habitat conditions. It is therefore essential to continue long-term monitoring of population size and of demographic parameters.
... Fluctuations in the size of recruitment-driven populations are more strongly influenced by environmental stochasticity than survival-restricted populations (Saether et al., 2004). Consequently, mortality for K-selection species will more likely be additive while rselection species may compensate for collision mortality with a reduction in mortality from other causes or increased reproduction (Peron, 2013). Assessing additive effects may therefore prove to be more problematic in r-selection species. ...
... Assessing additive effects may therefore prove to be more problematic in r-selection species. The extent of additive versus compensatory density-dependent responses to collision mortality is however not yet well understood, and difficult to study (Diffendorfer et al., 2015;Horswill et al., 2017;Peron, 2013). ...
Article
The expansion of wind energy poses challenges to policy-and decision-makers to address conflicts with wildlife. Conflicts are associated with impacts of existing and planned projects on wildlife, and associated difficulties of prediction where impacts are subject to considerable uncertainty. Many post-construction studies have demonstrated adverse effects on individuals of various bird and bat species. These effects may come in the form of collision-induced mortality or behavioral or physiological changes reducing the fitness of individuals exposed to wind energy facilities. Upscaling these individual effects to population impacts provides information on the true value of interest from a conservation point of view. This paper identifies methodological issues associated when moving from individual effects to population impacts in the context of wind energy. Distinct methodological approaches to predict population impacts are described using published case studies. The various choices of study design and metrics available to detect significant changes at the population level are further assessed based on these. Ways to derive impact thresholds relevant for decision-making are discussed in detail. Robust monitoring schemes and sophisticated modelling techniques may inevitably be unable to describe the whole complexity of wind and wildlife interactions and the natural variability of animal populations. Still, they will provide an improved understanding of the response of wildlife to wind energy and better-informed policies to support risk-based decision-making. Policies that support the use of adaptive management will promote assessments at the population level. Providing information to adequately balance the development of wind energy with the persistence of wildlife populations.
... Overlooking this potential increase in survival and fecundity in response to hunting losses may overestimate the impact of hunting. However, long-lived species such as flying-foxes are expected to show little compensation for hunting mortality (Péron 2013). Moreover, this potential bias is compensated for, although to an unknown extent, by ''crippling losses'', i.e. animals wounded but not recovered by hunters and therefore not recorded in bags. ...
... Vertebrate species with slow life history strategies, such as flying-foxes, are particularly vulnerable to additional anthropogenic mortality sources (Niel and Lebreton 2005;Péron 2013). Recent studies highlight the unsustainability of hunting concerning P. rufus and Eidolon dupreanum in Madagascar (Brook et al. 2019), P. vampyrus in Peninsular Malaysia (Epstein et al. 2009), P. tonganus in Niue island, South Pacific (Brooke and Tschapka 2002) and P. poliocephalus in Australia (McIlwee and Martin 2002). ...
Article
Hunting is a major threat to many species of wildlife. However, managing hunting systems to ensure their sustainability requires a thorough demographic knowledge about the impact of hunting. Here we develop a framework integrating ecological, modelling and sociological data to achieve a sustainability assessment of flying-fox hunting in New Caledonia and assess the relative merits of alternative management policies. Using age-specific stochastic population models, we found that the current annual hunting rate [5.5−8.5%] is likely to lead to a severe decline (− 79%) of Pteropus populations over the next 30 years. However, a majority of hunters surveyed (60%) were willing to soften their practices, offering an opportunity for adaptive management. Recurrent temporary hunting ban (at least 1 year out of 2) in combination with protected areas (≥ 25%) appears as the most effective and most accepted management option. Our integrative approach appears to be a promising method for ensuring that traditional hunting systems can remain sustainable in a rapidly changing world.
... Population growth rate in long-lived bird species is often sensitive to changes in adult survival (Bentzen and Powell, 2012;Servanty et al., 2014;Valle et al., 2018;Wheeler et al., 2019), and population responses to harvest in longer-lived bird species are generally more additive than compensatory (Gauthier et al., 2001;Schaub and Lebreton, 2004;Péron, 2013). Recent estimates of impacts from hunting for other long-lived species have either found no evidence for compensatory responses (Cooley et al., 2009;Creel and Rotella, 2010;Robinson et al., 2014), or weak evidence of it (Pederson et al., 2003;Sandercock et al., 2011). ...
... Only a few studies have addressed sandhill crane population responses to hunting pressure (Péron, 2013;Krapu et al., 2019;Pearse et al., 2020). The purpose of this study was to estimate how implementation of a fall sandhill crane hunt in Wisconsin, a core breeding area (Lacy et al., 2015), might impact local crane subpopulations. ...
Article
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Recent examinations of hunting’s impact on populations of long-lived species illustrate the rarity of strong compensatory responses. The extent to which sandhill crane populations exhibit compensatory, partially compensatory, or additive responses to harvest mortality is poorly known. To examine how sandhill crane harvests might impact resident, breeding crane populations, we simulated harvests of a well-studied population of individually marked birds at varying harvest intensities and degrees of selectivity within the social structure of territorial and non-territorial cranes. Simulations occurred in a demographically-explicit stochastic population model developed from a previous long-term (2000-2014) study of a sandhill crane population at carrying capacity in southcentral Wisconsin, USA. Non-selective harvest models that did not account for reproductive lags after territorial birds replaced lost mates produced additive responses and resulted in declining populations when ≥ 7% of the population was harvested annually. When models of non-selective harvest incorporated reproductive lags, this threshold was reduced to ≥ 5%. Harvesting at or above 5% harvest intensities continuously decreased population size over a 100-year period. In all models of selective harvests, when only non-territorial birds were harvested, all populations returned to equilibrium. Population responses to harvest are sensitive to the number of territorial birds harvested, and this sensitivity increases when accounting for lags in reproduction stemming from mortality-induced mate replacement. If possible, limiting harvest of territorial birds from any one specific population would help maintain stability of populations when implementing a hunt. This study provides evidence for harvest impacts at a localized scale, and it represents an important first step toward better understanding the potential impacts of hunting on population responses at a regional scale, especially where resident, territorial birds might be harvested.
... Compensatory mortality accounts for the possibility that some individuals harvested would have died anyway from non-hunting causes. For species with relatively low productivity and long generation time such as bison (Meagher, 1986), compensation by natural mortality in a scenario of exploitation is expected to be low (Lebreton, 2005;Peron, 2013). We defined a binary variable h to indicate the presence (=1) or absence (=0) of harvest mortality in each scenario (Fig. 1) and ran 1000 simulations comprising 50 years of simulation for any given set of parameters. ...
... Other sources of mortality, including wolf predation, would have to compensate for at least 55% of current harvest mortality to prevent population growth in the absence of harvest. For a species leaning more towards the K end of r-K selection spectrum such as bison (Meagher, 1986;Eberhardt, 2002), such a high level of compensation by natural mortality is unlikely (Lebreton, 2005;Peron, 2013). ...
Article
Animal excursions out of protected areas are a source of human-wildlife conflict and can lead animals into ecological traps. These arise when animals prefer areas of their habitat conferring lower fitness than other available areas. Ecological traps should become increasingly common as humans continue to alter habitats, yet their impact on population viability has rarely been documented and there is limited knowledge on how to disarm them. Moreover, although spatial factors such as the proportion of trap habitat in the landscape are crucial in determining the probability of extinction, few studies have attempted to link animal use of space to demography to obtain insights into how to release trapped populations. Here we tackle these gaps using a stochastic, spatially explicit matrix model parametrized with empirical data. We show that a free-ranging population of plains bison (Bison bison bison) caught in an ecological trap caused by legal but unregulated hunting has a 66% probability of extinction over the next 50 years under current conditions. By linking the time bison spent in fields with hunting permission to survival and population persistence, we show that bison use of such fields must decrease by 70% to ensure population viability. Our approach narrowed down the ecological trap to < 1% of the population's range during the hunting period. Targeting this limited portion of the landscape would hence be a cost-effective strategy to disarm the trap. We show that a spatially explicit approach to demography can refine conservation strategies to avoid potentially onerous and ineffective interventions.
... Mortality associated with WVCs is likely additive to the population, especially if the species has a protracted juvenile stage, small clutch or litter sizes, or few nonhuman sources of adult mortality (Livaitis and Tash 2008). This means that any individual that dies from the 'additive' cause would have survived if this cause was removed (Péron 2013). Long-lived species have naturally low population growth rates and have evolved strategies aimed at minimizing adult natural mortality. ...
... Long-lived species have naturally low population growth rates and have evolved strategies aimed at minimizing adult natural mortality. They are thus less able to sustain exploitation and are also less able to compensate for increases in anthropogenic mortality, such as WVCs, by decreases in natural mortality or increased productivity (Péron 2013). ...
... For hunting, we used empirical data (see above) to estimate the proportion of first-winter birds among all birds shot, and allocated the Sr Sex ratio 0.5 -Assumed The impact of hunting and oiling on Brünnich's guillemots M. Frederiksen et al. remaining mortality to older age classes proportional to their relative abundance (see also . We assumed that anthropogenic mortality was completely additive to natural mortality, which is typically the case for long-lived animals such as guillemots (Péron 2013), and consistent with a precautionary approach to harvest management (Government of Canada 2017). Stochastic values of demographic parameters were generated by drawing random values from beta distributions with means and SDs from the literature (Table 1). ...
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Brünnich's guillemot (Uria lomvia), or thick-billed murre, is an abundant pan-Arctic seabird, but several Atlantic breeding populations are declining. The species is subject to traditional harvest in the important wintering areas off west Greenland and Newfoundland, and has been subject to chronic oil pollution on the east coast of Canada. Until recently, knowledge of winter distribution has been insufficient to assess the impact of these mortality sources on specific breeding populations. We collate existing information on mortality from bag statistics in Greenland and Canada and studies of oiling off Newfoundland, as well as new data on age distribution in the harvest. Based on the results of recent tracking studies, we construct a spatially explicit population model that allocates hunting and oiling mortality to breeding populations and estimates the relative impact on their growth rate. Results indicate that annual population growth rate is depressed by 0.011-0.041 (approximately 1%-4%) by anthropogenic mortality sources. In addition to affecting local breeders, hunting in Greenland mainly affects declining breeding populations in Svalbard and Iceland, while hunting and oiling in Newfoundland mainly affect guillemots breeding in Arctic Canada and northwest Greenland, where most populations are relatively stable. The strongest relative impact is predicted on the small breeding population in Atlantic Canada, which winters mainly on the Newfoundland Shelf and therefore is exposed to both hunting and oiling. Our results clarify the relationships between hunting in Greenland and Canada and growth of specific breeding populations, and thus have major implications for harvest management of guillemots.
... Differences in body condition between decoy-harvested and jump-shot individuals are likely a reflection of population heterogeneity resulting from individual variation in decisions or abilities to allocate time, energy, and nutrients to enhance their fitness (Stearns 1992, Vedder andBouwhuis 2018). Consequently, heterogenous body condition has been linked to partially explain differential fitness rates, such that poorer quality individuals have increased probabilities of mortality (Conroy et al. 1989, Sedinger and Herzog 2012, Péron 2013 or reduced breeding propensity (Béchet et al. 2004, Souchay et al. 2014. Therefore, in our study, observed differences in body condition within and between harvest types suggest nonhomogenous survival rates among adult lesser snow and Ross's geese. ...
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Evidence that decoy harvest techniques primarily remove individuals of poorer body condition is well established in short‐lived duck species; however, there is limited support for condition bias in longer‐lived waterfowl species, such as geese, where decoy harvest is considered primarily additive because of their high natural survival rates. We evaluated support for the harvest condition bias hypothesis of 2 long‐lived waterfowl species, the lesser snow goose (Anser caerulescens caerulescens) and Ross’s goose (Anser rossii). We used proximate analysis to quantify lipid and protein content of lesser snow and Ross’s geese collected during the Light Goose Conservation Order (LGCO) in 2015 and 2016 during spring migration in Arkansas, Missouri, Nebraska, and South Dakota, USA. In each state, LGCO participants collected birds using traditional decoy techniques and we collected birds from the general population using jumpshooting tactics. Total body lipid content in both lesser snow and Ross’s geese varied with age, region of harvest, and harvest type (decoy or jump‐shooting). On average, adult lesser snow and Ross’s geese harvested over decoys had 60 g and 41 g, respectively, fewer lipids than conspecifics collected using jumpshooting. We observed lower lipid reserves in decoy‐shot geese in all 4 states sampled despite general gains in lipid reserves as migration chronology progressed. Our data support that the harvest condition bias extends to longer‐lived waterfowl species and during a life‐history event (spring migration) in which harvest is not normally observed. In the case of overabundant light geese, the disproportionate harvest of poorerconditioned lesser snow and Ross’s geese may serve as an additional challenge against any realized effects of harvest to reduce the population, in addition to extremely low harvest rates.
... In theory, there is a potential confounding effect of "extrinsic" causes of mortality on the estimation of actuarial senescence because variation in extrinsic mortality can influence the number of individuals that live to experience senescence and because mortality from different causes may exhibit different age-specific patterns [26]. However, in most cases, including the present study, the different factors of mortality operate in a compensatory way, meaning that supressing one factor of mortality-for example, predation-may not eventually improve the life expectancy [27], in part because exposure to extrinsic factors of mortality over evolutionary times has shaped the intrinsic deterioration in performance with age [11] and in part because extrinsic causes of mortality are rarely fully additive. For example, predators often select the weaker individuals with intrinsically lower chances of survival. ...
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The concept of actuarial senescence (defined here as the increase in mortality hazard with age) is often confounded with life span duration, which obscures the relative role of age-dependent and age-independent processes in shaping the variation in life span. We use the opportunity afforded by the Species360 database, a collection of individual life span records in captivity, to analyze age-specific mortality patterns in relation to variation in life span. We report evidence of actuarial senescence across 96 mammal species. We identify the life stage (juvenile, prime-age, or senescent) that contributes the most to the observed variation in life span across species. Actuarial senescence only accounted for 35%-50% of the variance in life span across species, depending on the body mass category. We computed the sensitivity and elasticity of life span to five parameters that represent the three stages of the age-specific mortality curve-namely, the duration of the juvenile stage, the mean juvenile mortality, the prime-age (i.e., minimum) adult mortality, the age at the onset of actuarial senescence, and the rate of actuarial senescence. Next, we computed the between-species variance in these five parameters. Combining the two steps, we computed the relative contribution of each of the five parameters to the variance in life span across species. Variation in life span was increasingly driven by the intensity of actuarial senescence and decreasingly driven by prime-age adult mortality from small to large species because of changes in the elasticity of life span to these parameters, even if all the adult survival parameters consistently exhibited a canalization pattern of weaker variability among long-lived species than among short-lived ones. Our work unambiguously demonstrates that life span cannot be used to measure the strength of actuarial senescence, because a substantial and variable proportion of life span variation across mammals is not related to actuarial senescence metrics.
... This change of habitat also increases the risk of predation (Brøseth and Pedersen, 2010). As a consequence, understanding how hunting interacts with other causes of mortality has become a central goal in animal ecology (Péron, 2013, see e.g. Sandercock et al., 2011 for a case study on willow ptarmigan). ...
... Accurate estimation of the level of compensation, and of the demographic rate by which this compensation takes place, is key to determining sustainable harvest rates (Weinbaum et al., 2013). In addition to compensatory responses involving reproduction and survival (Péron, 2013), immigration can compensate for hunting-related losses in harvested populations. Radio-tracking of the willow ptarmigan (Lagopus lagopus) in Scandinavia revealed non-compensatory mortality whereas annual counts suggest almost complete compensation (Hörnell-Willebrand, Willebrand & Smith, 2014). ...
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The demography of a population is often reduced to the apparent (or local) survival of individuals and their realised fecundity within a study area defined according to logistical constraints rather than landscape features. Such demographics are then used to infer whether a local population contributes positively to population dynamics across a wider landscape context. Such a simplistic approach ignores a fundamental process underpinning population dynamics: dispersal. Indeed, it has long been accepted that immigration contributed by dispersers that emigrated from neighbouring populations may strongly influence the net growth of a local population. To date however, we lack a clear picture of how widely immigration rate varies both among and within populations, in relation to extrinsic and intrinsic ecological conditions, even for the best‐studied avian and mammalian populations. This empirical knowledge gap precludes the emergence of a sound conceptual framework that ought to inform conservation and population ecology. This review, conducted on both birds and mammals, has thus three complementary objectives. First, we describe and evaluate the relative merits of methods used to quantify immigration and how they relate to widely applicable metrics. We identify two simple and unifying metrics to measure immigration: the immigration rate it defined as the ratio of the number of immigrants present in the population at time t + 1 and the total breeding population in year t, and πt, the proportion of immigrants among new recruits (i.e. new breeders). Two recently developed methods are likely to provide the most valuable data on immigration in the near future: individual parentage (rather than population) assignments based on genetic sampling, and spatially explicit integrated population models combining multiple sources of demographic data (survival, fecundity and population counts). Second, we report on a systematic literature review of studies providing a quantitative measure of immigration. Although the diversity of methods employed precludes detailed analyses, it appears that the number of immigrants exceeds locally born individuals in recruitment for most avian populations (median πt = 0.57, N = 45 estimates from 37 studies), a figure twofold higher than estimated for mammalian populations (median πt = 0.26, N = 33 estimates from 11 studies). Third, recent quantitative studies reveal that immigration can be the main driver of temporal variation in population growth rates, across a wide array of demographic and spatial contexts. To what extent immigration acts as a regulatory process has however been considered only rarely to date and deserves more attention. Overall, it is likely that most populations benefit from immigrants without necessarily being sink populations. Furthermore, we suggest that quantitative estimates of immigration should be core to future demographic studies and plead for more empirical evidence about the ways in which immigration interacts with local demographic processes to shape population dynamics. Finally, we discuss how to tackle spatial population dynamics by exploring, beyond the classical source–sink framework, the extent to which populations exchange individuals according to spatial scale and type of population distribution throughout the landscape.
... For example, effects of climate on demographic rates and population size can be stronger at high density than at low density because when climate conditions are bad, food resources are more limiting if the population is at or above carrying capacity (see Gamelon et al. 2017 (Bonenfant et al. 2009), being for instance more likely to colonize habitats of better quality instead of occupying less optimal places (MacCall 1990;Marshall & Frank 1995). In contrast, reduced population sizes can be associated with lower demographic performance for the remaining individuals via Allee effects such as higher risk of starvation due to stress (reviewed by Courchamp, Berec & Gascoigne 2008;Péron 2013). The interplay between climate and density dependence (Gamelon et al. 2017;Hansen et al. 2019), and between harvest and density dependence (Boyce, Sinclair & White 1999;Sandercock et al. 2011) have been well studied, but an integrative approach to the combined effects of harvesting and climate on density-regulated populations remains lacking. ...
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1.In marine and terrestrial ecosystems, organisms are affected by environmental variations that cause fluctuations in population size. The harvest‐interaction hypothesis predicts that environmentally‐induced fluctuations in population size are magnified by harvesting. Empirical evidence is urgently needed in the context of global change because greater fluctuations will increase extinction risk. 2.Here, we review theoretical and empirical work that has addressed the harvest‐interaction hypothesis in fish, birds and mammals. We identify the mechanisms by which harvesting might make population size more variable over time and thereby increase the risk of extinction. 3.Theoretical models show that harvest can modify population structure in time and space, and that changes in the amplitude and synchrony of population dynamics both increase extinction risk. Empirical evidence indicates that fishing amplifies the effects of environmental changes on the population variability, but no empirical study of terrestrial species has tested for amplified environmentally‐induced fluctuations due to hunting. 4.Synthesis and applications. In terrestrial species, theoretical studies have evaluated how environmentally‐induced fluctuations in population size are magnified by different harvest strategies, but there is now an urgent need for an empirical evaluation of this hypothesis. Future research is needed to explore how hunting and climate interact and to test whether hunting enhances environmentally induced fluctuations in population numbers of terrestrial species. This article is protected by copyright. All rights reserved.
... Full compensation of fishing mortality by other sources of mortality has not been observed in natural systems (Froese et al., 2016). It has been argued that the degree of fisheries compensation is expected to be on a continuum between compensatory and additive (Myers & Quinn, 2002;Péron, 2013). Further investigations are required to better assess the degree of fisheries compensation in the Barents Sea and to verify that the current conclusions are robust in the case of mortalities being partially additive and partially compensatory. ...
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Temporal variability in abundance and composition of species in marine ecosystems results from a combination of internal processes, external drivers, and stochasticity. One way to explore the temporal variability in an ecosystem is through temporal stability, measured using the inverse of the coefficient of variation for biomass of single species. The effect of temperature and fisheries on the variability of the Barents Sea food web is still poorly understood. To address this question, we simulate the possible dynamics of Barents Sea food web under different temperature and fishery scenarios using a simple food‐web model (Non‐Deterministic Network Dynamic [NDND]). The NDND model, which is based on chance and necessity (CaN), defines the state space of the ecosystem using its structural constraints (necessity) and explores it stochastically (chance). The effects of temperature and fisheries on stability are explored both separately and combined. The simulation results suggest that increasing temperature has a negative effect on species biomass and increasing fisheries triggers compensatory dynamics of fish species. There is a major intra‐scenario variability in temporal stability, while individual scenarios of temperature and fisheries display a weak negative impact and no effect on stability, respectively. However, combined scenarios indicate that fisheries amplify the effects of temperature on stability, while increasing temperature leads to a shift from synergistic to antagonistic effects between these two drivers.
... In contrast, the additivity hypothesis predicts that individuals that die from the additive cause would have survived if this cause were removed. Péron (2013) showed that in reality, these two hypotheses are extreme points on a gradient of possible population responses to changes in mortality patterns and that long-lived species and populations under the carrying capacity tend to "compensate" less than short-lived species and populations above carrying capacity. There is also evidence that partial compensation can occur up to some harvest level, after which the additional harvest becomes additive (Skalski, Ryding, & Millspaugh, 2005). ...
Article
Worldwide, many shark populations are classified as data poor, making it difficult to assess their status. However, for many sharks, their longevity, late maturation and low production of pups make them highly vulnerable to exploitation and highlight the need to assess their status. We compared reference points and stock status estimated from full stock assessments for 33 shark populations with those derived analytically, empirically or through simulation. There was excellent agreement between overfished status estimated from an assessment and determined from analytical methods using life history and an index of abundance; in 70% of cases, the analytical estimate of status was robust to assumptions of initial index depletion. We reviewed the ratio between fishing mortality at MSY (FMSY) and natural mortality (M) for chondrichthyans, from published studies and shark stock assessments. We then compared conclusions on overfishing status from the stock assessments to those derived with FMSY proxies and found very good agreement. Finally, we conducted a simulation study across representative life‐history parameters and different fishery selectivity patterns to explore the resulting range of FMSY to M ratios. As a rule of thumb, FMSY should not exceed 0.20M for low productivity stocks, 0.50M for stocks of intermediate productivity and 0.80M for the most productive shark stocks when immature individuals are harvested, which is the norm in the vast majority of cases examined. A triage method is proposed that provides a roadmap for using these data‐limited methods as an initial step towards assessment of stock status and sustainability of chondrichtyans.
... Gray wolf abundance and range expanded in Idaho, USA, from the initial translocation in 1995 to at least 856 wolves, filling most of the available habitat by 2009 (Idaho Department of Fish and Game [IDFG] and Nez Perce Tribe [NPT] 2015). During this recovery period, the state of Idaho gained partial management authority with federal oversight in 2006 (Norton and Kempthorne 2006) and then near complete management authority in May 2011 (U.S. Fish and Wildlife Service [USFWS] 2011) when wolves were delisted. With federal support, initial monitoring of the recovering wolf population by IDFG and NPT was intensive with the goal of radio-collaring !1 wolf in each pack statewide, documenting reproduction at pup-rearing sites, and recording pack counts via fixed-wing aerial flights (Mitchell et al. 2008). ...
... A scarcity of smooth materials also decreased cannibalism frequency because of a lower efficiency of case enlargement. As a result, the higher mortality arising from roughened case materials was compensated for by the decrease in the frequency of cannibalism ("compensated mortality" [50]). Cannibals rapidly enlarged their cases after consuming conspecifics. ...
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Resource availability often determines the intensity of cannibalism, which has a considerable effect on population size distribution and individual life history. Larvae of the caddisfly Psilotreta kisoensis build portable cases from sedimentary sands and often display cannibalism. For this species, the availability of preferable case material is a critical factor that affects larval fitness, and material is locally variable depending on the underlying geology. In this study, we investigated how sand quality as a case material determines cannibalism frequency among larvae and, in turn, how the differential cannibalism frequency affects the body-size distribution and voltinism. Rearing experiments within a cohort revealed that a bimodal size distribution developed regardless of material quality. However, as the preferable material became abundant, the proportion of larger to smaller individuals increased. Consecutive experiments suggested that smaller larvae were more frequently cannibalized by larger ones and excluded from the population when preferable smooth material was abundant. This frequent cannibalism resulted in a bimodal size distribution with a significantly higher proportion of larger compared to smaller individuals. The size-dependent cannibalism was significantly suppressed when the larvae were raised in an environment with a scarcity of the preferable case material. This is probably because larvae cannot enjoy the benefit of rapid growth by cannibalism due to the difficulties in enlarging their case. At low cannibalism the growth of smaller individuals was stunted, and this was probably due to risk of cannibalism by larger individuals. This growth reduction in small individuals led to a bimodal size-distribution but with a lower proportion of larger to smaller individuals compared to at high cannibalism. A field study in two streams showed a similar size distribution of larvae as was found in the rearing experiment. The bimodal ratio has consequences for life history, since a size-bimodal population causes a cohort splitting: only larvae that were fully grown at 1 year had a univoltine life cycle, whereas larvae with a stunted growth continued their larval life for another year (semivoltine). This study suggests that availability of preferable case building material is an important factor that affects cannibalism, which in turn affects larval population size structure and cohort splitting.
... The slow demography of our study populations make them less able to tolerate disproportional mortality to adults (i.e. excessive predation or harvesting rates) compared to populations from core areas (Lebreton 2005, Péron 2013, Okamoto 2018). ...
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Investigating how and why the life history and demographic traits of a species vary across its range is fundamental to understand its evolution and population ecology and then develop sustainable management recommendations. At the margins of a species' distribution range, populations are expected to exhibit a slower pace of life than in core areas, making them less able to withstand pressures that impact survival. To explore these questions, we estimated age and sex-dependent seasonal survival probabilities using 305 radio-tagged birds monitored over a 18-year period in two alpine rock ptarmigan populations at the southern limit of their distribution, one in the Alps and one in the Pyrenees. We also estimated fecundity of both populations and then conducted sensitivity analysis as well as population viability analyses using deterministic and stochastic population models. Annual survival probability was high in both populations (0.65 for adults and 0.60 for juveniles), but reproductive success was much lower in the Alps (0.55 chicks per hen in the Alps vs 1.19 in the Pyrenees). The results showed that adult survival was the most sensitive demographic parameter. While population in the Pyrenees was stable (=1.01; 0.871.16), the other in the Alps appeared to be strongly declining (=0.81; 0.720.91) and this difference was clearly driven by differences of fecundity. While our findings confirm that our peripheral populations are associated with a slower pace of life, they present the particularity to be situated both at the edge and at high altitude. A more systematic study of peripheral population at higher latitude or on island may provide new insight on inter-pop variations of pace of life that would be useful for manager of these cold-adapted species. Key-words: Life history traits, demography, matrix model, telemetry, population viability analysis, age-class survival, fecundity.
... Severe weather conditions in winter have in fact been found to influence woodcock survival rate (Hoodless and Coulson 1994, Tavecchia et al. 2002, Péron et al. 2011a, which decreases when earthworms become inaccessible, as happens with cold spells in winter (Péron et al. 2011a). On the other hand, survival rate in game species may be strongly influenced by hunting pressure itself, if mortality associated with hunting is additive instead of compensatory (Péron 2013). Indeed, a study in France has described spatial differences in annual survival of woodcock in relation to hunting pressure (Péron et al. 2011b(Péron et al. , 2012, with woodcock annual survival being lower in those areas with higher hunting pressure. ...
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Survival and mobility have important implications for population management for game species. These parameters are influenced by both intrinsic and extrinsic factors. We describe movements (commuting flights between diurnal refuges and nocturnal feeding places; and escape flights during cold spells) and winter survival rate of Eurasian Woodcock (Scolopax rusticola) wintering in Spain. We also evaluate factors influencing these variables, using 51 radio-tracked birds over three winters (2008/2009, 2009/2010, and 2010/2011). Commuting flight distances were estimated at 961.5 ± 1041.9 m, and variations were mainly explained by age and temperature (they decreased with lower temperatures and were lower for first-winter birds). Three cold spells occurred in 2009/2010; 80% of woodcocks monitored that winter showed escape flights, moving > 20 km, and went back to their previous wintering place when the effects of cold spells finished (about 8 days later). Of monitored woodcocks, 54.9% survived the winter. The most frequent cause of death was hunting, affecting mainly first-winter birds. Woodcock survival was lower in areas with more hunting days per week, and in Mediterranean than in Atlantic climate regions. Our results highlight the importance of monitoring survival and factors affecting it. Also, these results underline the importance of developing future studies to understand the importance of Mediterranean regions, the use of refuge places during cold spells, and hunting pressure there.
... This can happen, for example, when recruitment of new individuals overcompensates for adult mortality via a response to lowered adult population densities in either fecundity or juvenile survival. The assumption that such overcompensation occurs is a major element in regulating harvests via hunting and fishing (14)(15)(16). Empirical evidence for its occurrence in nature outside of anthropogenic influences is scant. There is evidence for it in some laboratory populations (17)(18)(19), but experiments with natural predators have produced equivocal evidence (20,21). ...
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Significance Does increased mortality from novel predators or parasites always lead to decreased prey or host population sizes? Theory says no, but we have too few examples of such compensatory effects to answer this question conclusively. We address this gap using long-term data from populations recently invaded by a nematode parasite. We combine analyses of the subsequent changes in population dynamics with comparable data from an uninfected population and laboratory assays of the effect of the parasite on fitness components. Our results show that the negative effect of the novel parasite was short-lived. The host population quickly recovered, even while experiencing high levels of parasite prevalence (72%). Host recovery was a consequence of increased survival and a density-dependent increase in recruitment.
... Poaching of older males occurred throughout the study. The lower and more variable survival of males likely resulting from the additive nature of illegal harvest (Péron 2013) during their prime reproductive years is of conservation concern. ...
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Abstract Diagnosing age‐specific influences on demographic trends and their drivers in at‐risk wildlife species can support the development of targeted conservation interventions. Such information also underpins understanding of life history. Here, we assess age‐specific demography in wild African elephants, a species whose life history is marked by long life and extreme parental investment. During the 20‐yr study, survival and its variation were similar between adults and juveniles in contrast to relationships found among many large‐bodied mammals. Prospective analysis on age‐specific Leslie matrices for females demonstrated survival is more influential than fecundity on λ, with sensitivity of both decreasing with age. Results aggregated by stage classes indicate young adults (9–18 yr) demonstrated the highest elasticity, followed by preparous juveniles (3–8 yr). Mature adults (36+ yr) had the lowest aggregate elasticity value. Retrospective analysis parameterized by data from the early and latter periods of the study, characterized by low then high human impact (faster and slower growth, respectively), demonstrated fecundity (particularly for adults; 19–35 yr) explained the greatest variation in λ observed during the period of low human impact, while survival (particularly juvenile and adult) was more influential during the high human impact period. The oldest females (mature adult stage) weakly influenced population growth despite demonstrating the highest fecundity and their behavioral importance in elephant society. Multiple regression models on survival showed the negative effects of human impacts and population size were the strongest correlates across sexes and ages. Annual rainfall, our metric for environmental conditions, was weakly informative. The presence of dependent young was positively correlated with survival for breeding females, suggesting condition‐based mortality filtering during pregnancy. Notwithstanding the stabilizing effect of high juvenile survival on elephant population growth, demographic processes in elephants were similar to those shaping life history in other large herbivores. Implications of the study results with respect to the conservation of elephants and analysis of demographic impact of poaching are discussed, along with the study's relevance to theories regarding the evolution of life history and parental care.
... Further, we assumed all anthropogenic-related fatalities are additive (i.e. not compensated for at the population level by density-dependent or other processes) [63], that fatalities are constant through time and across avian age classes, and that all simulated fatalities were adults (electronic supplementary material, table S3). Future research could evaluate these processes, as well as alternative assumptions, to improve understanding of renewable effects on bird populations. ...
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Renewable energy production can kill individual birds, but little is known about how it affects avian populations. We assessed the vulnerability of populations for 23 priority bird species killed at wind and solar facilities in California, USA. Bayesian hierarchical models suggested that 48% of these species were vulnerable to population-level effects from added fatalities caused by renewables and other sources. Effects of renewables extended far beyond the location of energy production to impact bird populations in distant regions across continental migration networks. Populations of species associated with grasslands where turbines were located were most vulnerable to wind. Populations of nocturnal migrant species were most vulnerable to solar, despite not typically being associated with deserts where the solar facilities we evaluated were located. Our findings indicate that addressing declines of North American bird populations requires consideration of the effects of renewables and other anthropogenic threats on both nearby and distant populations of vulnerable species.
... Uno de los grandes debates que ha existido durante tiempo es el grado en el que la caza afecta a las poblaciones. La mortalidad por caza puede ser aditiva o compensatoria con respecto a otras causas de mortalidad [390,391] . En el primer caso, toda muerte provocada por la caza es una muerte adicional a la que hubiera ocurrido sin que la caza existiera. ...
... For instance, several important aspects and limitations are not further discussed, including the importance of having reliable and frequent estimates for both population sizes and harvest levels, the need for a relevant delineation of management units (especially for migrants), or the importance of taking into account all additional mortality sources in calculations. In the PTL approach, the continuum of possible population responses to harvest levels (compensatory-additivity/depensatory, Péron, 2013) is also overlooked, as well as some components of the underlying population dynamics (e.g., demographic stochasticity). Most often, these aspects are either imprecise or unknown in a context of limited demographic data. ...
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Bird harvest for recreational purposes or as a source for food is an important activity worldwide. Assessing or mitigating the impact of these additional sources of mortality on bird populations is therefore crucial issue. The sustainability of harvest levels is however rarely documented, because knowledge of their population dynamics remains rudimentary for many bird species. Some helpful approaches using limited demographic data can be used to provide initial assessment of the sustainable use of harvested bird populations, and help adjusting harvest levels accordingly. The Demographic Invariant Method (DIM) is used to detect overharvesting. In complement, the Potential Take Level (PTL) approach may allow setting a level of take with regard to management objectives and/or to assess whether current harvest levels meet these objectives. Here, we present the R package popharvest that implements these two approaches in a simple and straightforward way. The package provides users with a set of flexible functions whose arguments can be adapted to existing knowledge about population dynamics. Also, popharvest enables users to test scenarios or propagate uncertainty in demographic parameters to the assessment of sustainability through easily programming Monte Carlo simulations. The simplicity of the package makes it a useful toolbox for wildlife managers or policymakers. This paper provides them with backgrounds about the DIM and PTL approaches and illustrates the use of popharvest's functionalities in this context. The paper introduces a didactic overview of two approaches that can be used to assess the sustainability of harvest regimes of birds when demographic knowledge is limited. These approaches are implemented in a new R package providing wildlife managers with a useful toolbox for prioritizing research works or management actions.
... A key point is whether anthropogenic mortality is entirely compensatory or has an additive component. If the latter, then the high anthropogenic mortality could be contributing to global declines as fewer birds recruit, diminishing the numerical response (Sinclair and Pech 1996;Péron 2013). Tawny owls show a similar numerical response during the breeding season, albeit a resident owl with short natal dispersal, with high fecundity during vole peaks driven by new recruits breeding in those years, yet that fecundity has relatively little importance for overall tawny owl population dynamics compared with adult survival (Karell et al. 2009). ...
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Highly mobile predators can show strong numerical responses to pulsed resources, sometimes resulting in irruptions where large numbers of young invade landscapes at a continental scale. High production of young in irruption years may have a strong influence on the population dynamics unless immature survival is reduced compared to non-irruption years. This could occur if subordinate individuals (mainly immatures) are forced into suboptimal habitats due to density-dependent effects in irruption years. To test whether irruptive individuals had lower survival than non-irruptive ones, we combined necropsy results (N = 365) with telemetry (N = 185) from more than 20 years to record timing and causes of mortality in snowy owls (Bubo scandiacus), which irrupt into eastern North America during winter following high breeding output caused by lemming peaks in the Arctic. Mortality was more than four times higher in irruption years than non-irruption years, but only for immatures, and occurred disproportionately in early winter for immatures, but not adults. Mortality was also higher in eastern North America, where owl abundance fluctuates considerably between years, compared to core winter regions of the Arctic and Prairies where populations are more stable. Most mortality was not due to starvation, but rather associated with human activity, especially vehicle collisions. We conclude that immature snowy owls that irrupt into eastern North America are limited by density-dependent factors, such as increased competition forcing individuals to occupy risky human-altered habitats. For highly mobile, irruptive animals, resource pulses may have a limited impact on population dynamics due to low subsequent survival of breeding output during the nonbreeding season.
... The particularity of the Saracco et al. study is that they accommodated transience at the bird ringing locations, that is, an excess of individuals captured only once(Pradel et al. 1997)-an important nuisance parameter to accommodate when individuals are not site-faithful.Péron et al. (2011) used the spline method to delineate population sinks as areas where the predicted overwinter survival probability of Eurasian woodcocks (Scolopax rusticola) fell below the population renewal rate, itself a function of spatially invariant fecundity and summer survival rates. Their results confirm the additive nature of hunting mortality(Péron 2013) and ...
... Population modelling could be further used on existing data sets, such as from nationwide citizen science projects, to accurately estimate yearly road mortality or, for populations with both road mortality and density estimates, an estimate of local demographic compensation. Another informed approach could incorporate population density, the sex and age of casualties and other sources of mortality into the framework of compensation-additive mortality [131]. This explores whether road mortality is compensatory and removes the already "doomed surplus" in a population or is additive by increasing total mortality [55]. ...
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Transport infrastructure is a pervasive element in modern landscapes and continues to expand to meet the demands of a growing human population and its associated resource consumption. Road-induced mortality is often thought to be a major contributor to the marked declines of European hedgehog populations. This review synthesizes available evidence on the population-level impacts of road mortality and the threat to population viability for the five hedgehog species in Europe. Local and national studies suggest that road mortality can cause significant depletions in population sizes, predominantly removing adult males. Traffic collisions are a probable cause of fragmentation effects, subsequently undermining ecological processes such as dispersal, as well as the genetic variance and fitness of isolated populations. Further studies are necessary to improve population estimates and explicitly examine the consequences of sex- and age-specific mortality rates. Hedgehogs have been reported to use crossing structures, such as road tunnels, yet evaluations of mitigation measures for population survival probability are largely absent. This highlights the need for robust studies that consider population dynamics and genetics in response to mitigation. In light of ongoing declines of hedgehog populations, it is paramount that applied research is prioritised and integrated into a holistic spatial planning process.
... Overlooking this potential increase in survival and fecundity in response to hunting losses may overestimate the impact of hunting. However, long-lived species such as flying-foxes are expected to show little compensation for hunting mortality (Péron, 2013). Moreover, this potential bias is compensated for, although to an unknown extent, by crippling losses, i.e. animals wounded but not recovered by hunters and therefore not recorded in bags. ...
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Habitat degradation, invasive species and overexploitation are currently the three main threats to biodiversity. Here we present a study on the population status of two sympatric flying fox species, Pteropus ornatus (endemic) and P. tonganus (native), and the impact of hunting and predation by the feral cat Felis catus in New Caledonia. The study of flying fox roost occupancy in the North Province shows a 33% disapearance in 40 years. The flying fox population on Grande Terre is estimated at about 735,000 individuals (of both species) and the annual hunting rate at 7%. Integrated stochastic modelling of this population suggests that current harvesting levels could lead to a decline of up to 80% in the next 30 years. Temporary hunting ban and/or protected areas appear, in addition to being combinable, to be the most acceptable and effective management options for hunters. An analysis of the data available worldwide shows that all forms of cats prey on bats in all habitats and that this threat is probably largely underestimated. Finally, initial results suggest that flying fox predation by feral cats in New Caledonia is of the same order of magnitude as hunting. This study proposes a framework for assessing the sustainability of hunting game species in an integrated adaptive management approach, taking into account other threat factors such as invasive species.
... It is therefore vital to understand the ecological factors that influence mortality in Iberian hare populations, given the taxonomic importance of this endemic species and the significant role it plays in the ecology and rural economy of the region. Demographic compensation is a frequent response in short-lived species 33 such as the Iberian hare. Therefore, road collisions, as a type of additive mortality, must be considered in management or hunting plans for this species. ...
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The Iberian hare (Lepus granatensis) is an important small game species endemic to the Iberian Peninsula for which the incidence of roadkill is unknown. We surveyed Iberian hare–vehicle accidents on road networks in southern Spain, focusing on roads that mainly run through favorable habitats for this species: Mediterranean landscapes with plots of arable crops, olive groves, and vineyards. We recorded roadkills over a five-month period, estimated hare accident densities on roads, and compared these numbers to hare hunting yields in adjoining hunting estates. We also analyzed the spatial patterns of and potential factors influencing hare roadkills. We detected the existence of black spots for hare roadkills in areas with high landscape heterogeneity that also included embankments and nearby crossroads and had high traffic intensity. Hare roadkill levels ranged from 5% to 25% of the annual harvest of hares killed on neighboring hunting estates. We suggest that road collisions should be considered in Iberian hare conservation in addition to hunting, since they may represent an additive source of mortality. Game managers should address the issue of hare roadkill in harvest planning to compensate for hare accidents, adjusting hunting quotas to account for this unnatural source of mortality. Our results suggest future directions for applied research in road ecology, including further work on demographic compensation and roadkill mitigation.
... Another potential weakness in demographic models may be the assumption of anthropogenic mortality as additive to natural mortality (Péron, 2013). Clearly separating natural from anthropogenic mortality is itself dubious and some authors assume general rates for both types (Aanes et al., 2007). ...
... L'estimation du niveau de compensation et du taux démographique impliqué dans cette compensation est alors essentielle pour déterminer le taux de prélève-ment maximal durable (Weinbaum et al., 2013). Outre les réponses compensatoires impliquant la reproduction et la survie (Péron, 2013), l'immigration peut elle-aussi compenser l'impact de la chasse. Le suivi radio-télémétrique du Lagopède des saules Lagopus lagopus en Scandinavie a révélé une mortalité liée à la chasse faiblement compensatoire, alors que les comptages annuels, sur lesquels sont basés les quotas de prélèvements, suggèrent une compensation presque complète (Hörnell-Willebrand, Willebrand & Smith, 2014). ...
... Harvest has typically been considered compensatory to natural mortality (Errington 1945, Allen 1947, Lack 1954, Bartmann et al. 1992, Caudill et al. 2017), but there are examples of harvest being partially additive (Williams et al. 2004, Sandercock et al. 2011). There is a knowledge gap about interactions between vital rates and harvest pressure under varying degrees of compensation (Roseberry 1979, Sandercock et al. 2011, Péron 2013. Closing that knowledge gap could lead to harvest strategies that meet stakeholder objectives more effectively (e.g., Koons et al. 2014). ...
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Density dependence, immigration, and emigration can considerably influence wildlife population demographics. Population models used to evaluate common actions like predator management and harvest in the absence of these processes may lead to poor management decisions. We built a novel population simulation model for the northern bobwhite (Colinus virginianus; bobwhite) that included implicit spatial structure (ingress and egress of individuals), density dependence, and harvest. We used 42 years of data (1970-2012) from a relatively stable population to create and validate the simulation model. We then used this simulation model to predict the effect of meso-mammal trap and removal, a management action that increases bobwhite fecundity, on population abundance, cumulative harvest through 50 years, and extirpation risk. We conducted a population sensitivity analysis to understand the implications of meso-mammal trap and removal to populations with varying vital rates. Incorporating ingress and egress of individuals and density dependence improved the understanding of bobwhite population dynamics and reduced the uncertainty about the efficacy of predator management across a range of environmental conditions. Increased number of immigration sources decreased extirpation risk and increased bobwhite abundance. A key outcome of our modeling process was that density-dependent processes did not fully compensate for harvest. Cumulative harvest through 50 years increased with increasing harvest rate but started to decline when harvest rate was >0.35 for populations with meso-mammal removal and 0.25-0.30 for populations without meso-mammal removal. Meso-mammal removal increased the harvest capacity of populations and produced greater harvest opportunity over time. Meso-mammal removal also buffered populations from extirpation risk resulting from too few immigration sources. Practitioners often ignore the contribution of immigration and emigration to local demographics or assume density-independent vital rates; however, recent literature reviews and our study indicate that these processes are important to the understanding of animal ecology and management. In the interest of the conservation of species that are hunted and at risk of extirpation in some geographies, predator management may increase hunter success and be a tool to reduce extirpation risk, although the degree of effectiveness likely varies geographically. This manuscript could serve as a framework for predicting the effects of management on bobwhite at the population level.
... For example, it has been demonstrated several times that the ratio of blue duikers to larger species of duiker increases along gradients of hunting pressure [15,63], probably under the combined influence of hunter selectivity and of the faster pace of life of the blue duiker relative to larger species. The change over time in the ratio of large to small species [8] or the ratio of long-lived to short-lived species [64] could therefore constitute an efficient indicator of the defaunation process. ...
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Bushmeat is a major source of protein and income in tropical regions but is often over-harvested. A better monitoring of bushmeat stocks could help achieve sustainability. We used a combination of simulations and transect survey data collected from blue duikers (Philantomba monticola) in the Lomako wildlife reserve, Democratic Republic of the Congo, to investigate the use of transect-based distance sampling to monitor bushmeat stocks. The comparison of dung piles and direct observations of duikers evidenced that animals avoided both the transects in the absence of observers, and the observers themselves. This type of behavioural response appeared common in a literature survey. It causes a negative bias in the estimates of population densities from the standard distance sampling methodology. This negative bias would lead to over-pessimistic predictions of population viability, especially if the behavioural response is more intense in the locations where the animals are hunted. In turn, this would lead to excessively conservative management recommendations. To correct for the effect of the behavioural response of the animals to either the transects or the observers, we recommend recording both the forward and perpendicular distances to the observers (2D distance sampling), not just the perpendicular distance. We also recommend multiple-observer protocols. As a cautionary note, we also demonstrate a scenario where the intensity of the behavioural response is too high to reliably estimate the abundance of the population. As a perspective, we outline the general principles of a local stakeholder-based program combining distance sampling with less intensive types of ecological indicators to monitor wildlife populations.
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A central challenge in applied ecology is understanding the effect of anthropogenic fatalities on wildlife populations and predicting which populations may be particularly vulnerable and in greatest need of management attention. We used three approaches to investigate the potential effects of fatalities from collisions with wind turbines on 14 raptor species for both current (106 GW) and anticipated future (241 GW) levels of installed wind energy capacity in the United States. Our goals were to identify species at relatively high vs low risk of experiencing population declines from turbine collisions and to also compare results generated from these approaches. Two of the approaches used a calculated turbine‐caused mortality rate to decrement population growth, where population trends were derived either from the North American Breeding Bird Survey or from a matrix model parameterized from literature‐derived demographic values. The third approach was potential biological removal, which estimates the number of fatalities that allow a population to reach and maintain its optimal sustainable population set by management objectives. Different results among the methods reveal substantial gaps in knowledge and uncertainty in both demographic parameters and species‐specific estimates of fatalities from wind turbines. Our results suggest that, of the 14 species studied, those with relatively higher potential of population‐level impacts from wind turbine collisions included barn owl, ferruginous hawk, golden eagle, American kestrel, and red‐tailed hawk. Burrowing owl, Cooper’s hawk, great horned owl, northern harrier, turkey vulture, and osprey had a relatively lower potential for population impacts, and results were not easily interpretable for merlin, prairie falcon, and Swainson’s hawk. Projections of current levels of fatalities to future wind energy scenarios at 241 GW of installed capacity suggest some species could experience population declines because of turbine collisions. Populations of those species may benefit from research to identify tools to prevent or reduce raptor collisions with wind turbines.
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The Common Pochard (Aythya ferina) is a regular diving duck species in the western Palearctic. However, a worrisome decline of its wintering population led to an up-listed IUCN status from “Least Concern” to “Vulnerable”. This species is still hunted in Europe despite this decline. Hence, one may wonder about the sustainability of its harvest. The aim of this work was to understand the population dynamics of this species, and the drivers of these mechanisms. For this purpose, we assessed the declining trend in northwestern Europe using the mid-january censuses. Then, we studied the migratory connectivity with the two others flyways, in order to better understand the origin of the decline. Finally, we assessed two main demographic parameters (survival rate and nesting success) and combined these into a matrix population model. This model allowed us to assess an asymptotic growth rate and to determine the key demographic parameters on which management actions should focus. The main results of this thesis indicate that the decrease in productivity in Europe and in Russia could have been the main reason of the decline. However, given the limited human action to improve Pochard productivity, only breeding habitat improvement could be considered. Such improvements could be easily considered in Europe, but not in Siberia, the main breeding region characterized by a large area and a strong geographic isolation. Survival rates were lower in France than in neighbouring countries, possibly owing to a greater hunting pressure. A more moderate hunting pressure could lead to higher survival rates, and a balanced growth rate. Setting up an adaptative harvest management scheme could help reaching defined management goals, by annually adapting hunting quotas to current knowledge and assessment of Pochard population size.
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Mountains are reservoirs of biodiversity whose strong altitudinal gradients over short distances are associated with strong spatial heterogeneity of local environmental conditions. While biodiversity has so far been rather well preserved in mountains due to poor accessibility, predictions of ongoing climate change suggest even more rapid and marked effects in mountains than in plains. My main objective is to understand how global change are impacting the population dynamics of mountain galliformes. My work has shown (1) a strong heterogeneity of demographic strategies between populations of rock ptarmigan (Lagopus muta) (2) that black grouse populations (Tetrao tetrix) show spatially very heterogeneous trends, influenced by local conditions (3) that for such species that are difficult to count and show strong spatial and interannual variability it is necessary to rely on long-term monitoring to reach a satifactory statistical power to detect a decline.
Chapter
A large and growing variety of anthropogenic (i.e., human-related) activities threaten birds from the most common to the most critically endangered. Unlike natural threats, such as depredation by native predators and death from storms, the vast majority of anthropogenic mortality factors for birds are recent, emerging since the nineteenth century or more recently. Many bird species are affected by several anthropogenic threats. For example, many Neotropical migrant songbirds face habitat loss on both breeding and wintering grounds, as well as along migratory pathways (i.e., stopover habitat), and they can also die by colliding with many types of man-made structures. In this chapter, we refer to mortality as the general phenomenon or overall amount of bird death from one or more causes, mortality rate as the number of deaths in an area or time period, and fatality as individual occurrences of bird death. In this chapter, we focus on purposeful and incidental direct mortality sources. Major indirect threats are covered elsewhere, including climate change (chapter 24) and habitat loss (chapter 25). Space constraints prevent us from exhaustively covering every direct mortality source. We therefore focus on sources that have received substantial research or are increasingly relevant because of substantial public or conservation attention. The relatively nascent state of the field means that most information about anthropogenic mortality is descriptive, and there is tremendous opportunity for future research to test mortality mechanisms and effects using a hypothetico-deductive approach. Finally, interpreting the overall magnitude of impact for each mortality source and comparing different mortality sources would ideally include consideration of the total number of birds. Yet there are no such scientifically derived estimates for North America, and devising such an estimate is beyond the scope of this chapter. Nonetheless, to provide rough context for the severity of the mortality sources we describe, it is worth considering an often-cited (albeit speculative) estimate of 10–20 billion total birds in North America (USFWS 2002).
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The worldwide decline of seabird populations due to the combined effects of global and regional changes is creating immense challenges for managers and conser-vationists. Predicting population responses to proposed management strategies could provide the most effective tools to prevent, halt and reverse ongoing declines. System dynamic modelling frameworks are considered particularly relevant to interrelate biological, ecological and environmental characteristics and to predict population trends. A system dynamics model was designed, compiling diverse information concerning a relict population of the European Shag located in western Iberia, to outline the most effective management options for its conservation. The simulations demonstrate that mortality caused by invasive animals and bycatch mortality were the main reasons for the current population decline. Without management interventions, a decrease of 8% was projected for the next decade, which could be mitigated by specific conservation actions. The results show the usefulness of dynamic modelling frameworks to understand local cause-effect relationships and species responses to ecosystem management under changing environmental conditions. We highlight that the framework proposed, after specific parameterization, could be easily adaptable to other species within similar socio-ecological systems.
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Im deutschen Recht hat sich der Maßstab der signifikanten Erhöhung des Tötungsrisikos im Vergleich zum allgemeinen Lebensrisiko als Kriterium für die Unzulässigkeit von Vorhaben etabliert, es fehlt aber an Richtlinien für die Beurteilung des Signifikanzkriteriums aus § 44 Abs. 5 BNatSchG. Hier wird eine Möglichkeit zur objektiven Beurteilung anhand bewährter wissenschaftlicher Methoden vorgeschlagen, die grundsätzlich auf alle Wirbeltiere anwendbar ist. Eine objektive Bestimmung des allgemeinen Lebensrisikos ist möglich durch umfangreiche Erkenntnisse zu Überlebenswahrscheinlichkeiten besonders bei Vögeln und Fledermäusen. Die Prognose vorhabenbedingter Tötungsrisiken beruht derzeit vor allem auf Untersuchungen an verwirklichten Vorhaben, die durch Monitoringauflagen bei Genehmigungen ergänzt werden können. Zusätzlich zum individuenbezogenen Risiko muss unter Umständen auch die additive Wirkung von Mortalität auf Populationsebene mit dem „ORNIS-Kriterium“ beurteilt werden, um eine Verschlechterung des Erhaltungszustandes auszuschließen. Bei Überschreitung der Referenzwerte bzw. Signifikanzschwellen kann eine Ausnahmeprüfung nach § 45 Abs. 7 BNatSchG folgen. Fallbeispiele zeigen, wie eine objektive Beurteilung des Tötungsrisikos für bekannte Risiken durch Windenergieanlagen bereits möglich ist.
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Migratory species form an important component of biodiversity; they link ecosystems across the globe, but are increasingly threatened by global environmental change. Understanding and mitigating threats requires knowledge of how demographic processes operate throughout the annual cycle, but this can be difficult to achieve when breeding and non‐breeding grounds are widely separated. Our goal is to quantify the importance of variability in survival during the breeding and non‐breeding seasons in determining variation in annual survival using a single population and, more broadly, the extent to which annual survival across species reflects variation in probability of surviving the migratory period. We use a 25 year dataset in which individuals of a long‐distance migratory bird, the alpine swift Tachymarptis melba, were captured towards the beginning and end of each breeding season to estimate age‐ and season‐specific survival probabilities and incorporate explicit estimation of the correlations in survival between age‐classes and seasons. Monthly survival was higher during the breeding period than during the rest of the year and strongly affected by conditions in the breeding season; effects that remained apparent in the following non‐breeding season, but not subsequently. Recruitment of juveniles was dependent on the timing of breeding, being higher if egg‐laying commenced before the median date, and substantially lower if not. Across migratory bird species, variation in annual survival largely reflects variation in the probability of surviving the migratory period. Using a double‐capture approach, even within a single season, provides valuable insights into the demography of migratory species, which will help understand the extent and impacts of the threats they face in a changing world.
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1. The management of sustainable harvest of animal populations is of great ecological and conservation importance. Development of formal quantitative tools to estimate and mitigate the impacts of harvest on animal populations has positively impacted conservation efforts. 2. The vast majority of existing harvest models, however, do not simultaneously estimate ecological and harvest impacts on demographic parameters and population trends. Given that the impacts of ecological drivers are often equal to or greater than the effects of harvest, and can covary with harvest, this disconnect has the potential to lead to flawed inference. 3. In this study, we used Bayesian hierarchical models and a 43‐year capture‐mark‐recovery dataset from 404,241 female mallards (Anas platyrhynchos) released in the North American midcontinent to estimate mallard demographic parameters. Further, we model the dynamics of waterfowl hunters and habitat, and the direct and indirect effects of anthropogenic and ecological processes on mallard demographic parameters. 4. We demonstrate that density‐dependence, habitat conditions, and harvest can simultaneously impact demographic parameters of female mallards, and discuss implications for existing and future harvest management models. 5. Our results demonstrate the importance of controlling for multicollinearity among demographic drivers in harvest management models, and provide evidence for multiple mechanisms that lead to partial compensation of mallard harvest. We provide a novel model structure to assess these relationships that may allow for improved inference and prediction in future iterations of harvest management models across taxa.
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For migratory birds, sustainable harvest management based on quantitative modelling needs cross-border hunting bag statistics. At the European scale, proper modelling requires both reliable and mutually compatible hunting bag data between regions and countries. Owing to the absence of harmonisation among the different hunting bag collecting schemes in Europe and the lack of methodological metadata, adaptive management at the flyway scale is currently extremely challenging for a number of species. For improving the current state of affairs, we expose statistical concepts, terminology and issues inherent to hunting bag data collection schemes; identify the multiplicity of error sources for being able to judge the quality of hunting bag statistics; call for a harmonisation process; discuss the origin of the hurdles in the production of standardised hunting bag statistics at the European scale; and suggest some potential avenues for future actions for overcoming them.
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Canalization is an abstract term that describes unknown developmental mechanisms that reduce phenotypic variation. A trait can be canalized against environmental perturbations (e.g., changes in temperature or nutrient quality), or genetic perturbations (e.g., mutations or recombination); this paper is about genetic canalization. Stabilizing selection should improve the canalization of traits, and the degree of canalization should be positively correlated with the traits' impact on fitness. Experiments testing this idea should measure the canalization of a series of traits whose impact on fitness is known or can be inferred, exclude differences among traits in the number of loci and alleles segregating as an explanation for the pattern of variability found, and distinguish between canalization against genetic and environmental variation. These conditions were met by three experiments within which the variation of fitness components among Drosophila melanogaster lines was measured and among which the genetic contribution to the variation among lines was clearly different. The canalization of the traits increased with their impact on fitness and did not depend on the degree of genetic differences among lines. That the flies used had been transformed by a P-element insert suggests that canalization was also effective against novel genetic variation. The results reported here cannot be explained by the classical hypothesis of reduction in the number of loci segregating for traits with greater impact on fitness and confirm that traits with greater impact on fitness are more strongly canalized. This pattern of canalization reveals an underappreciated role for development in microevolution. There is differential genetic canalization of fitness components in D. melanogaster.
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We estimated survival rates of greater sage-grouse (Centrocercus urophasianus) in North Park, Colorado, USA, from band-recovery data of 6,021 birds banded during spring, 1973-1990, with recoveries through 1993. Average annual adult female survival (S̄ = 0.59, SE = 0.011) was greater than average adult male survival (S̄ = 0.37, SE = 0.007), and average subadult (<1 yr old at time of banding) female survival (S̄ = 0.77, SE = 0.030) was greater than average subadult male survival (S̄ = 0.63, SE = 0.034). Four weather covariates (spring and winter precipitation and temperature) did not contribute to predicting annual survival.
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Using field data on fecundity, age at first reproduction and adult life expectancy, we reconsider the so-called r-K gradient by analyzing relationships between these three demographic parameters in 80 mammal species and 114 bird species. After the allometric effect of adult body weight is removed, the three variables remain correlated. The existence of demographic tactics which are independent of adult body weight is demonstrated by multivariate analyses of these variables. These analyses confirm the importance of ecological and phylogenetic constraints. The main structure is a time-scale gradient ranking species according to turn-over, both in birds and mammals. A second gradient ranking species according to iteroparity level appears significantly both in birds and mammals. In mammals, this pattern is related to patterns of parental investment.
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This article considers the statistical issues relevant to the comparative method in evolutionary biology. A generalized Linear model (GLM) is presented for the analysis of comparative data, which can be used to address questions regarding the relationship between traits or between traits and environments, the rate of phenotypic evolution, the degree of phylogenetic effect, and the ancestral state of a character. Our approach thus emphasizes the similarity among evolutionary questions asked in comparative studies. We then discuss ways of specifying the sources of error involved in a comparative study (e.g., measurement error, error due to evolution along a phylogeny, error due to misspecification of a phylogeny) and show how the impact of these sources of error can be taken into account in a comparative analysis. In contrast to most existing phylogenetic comparative methods, our procedure offers substantial flexibility in the choice of microevolutionary assumptions underlying the statistical analysis, allowing researchers to choose assumptions that are most appropriate for their particular set of data and evolutionary question. In developing the approach, we also propose novel ways of incorporating within-species variation and/or measurement error into phylogenetic analyses, of estimating ancestral states, and of considering both continuous (quantitative) and categorical (qualitative or ''state'') characters in the same analysis.
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1. Populations experiencing localized mortality can recover in the short term by net movement of individuals from adjacent areas, a process called compensatory immigration or spillover. Little is known about the factors influencing the magnitude of compensatory immigration or its impact on source populations. Such information is important for understanding metapopulation dynamics, the use of protected areas for conservation, management of exploited populations and pest control. 2. Using two small, territorial damselfish species (Stegastes diencaeus and S. adustus) in their naturally fragmented habitat, we quantified compensatory immigration in response to localized mortality, assessed its impact on adjacent source populations and examined the importance of potential immigrants, habitat quality and landscape connectivity as limiting factors. On seven experimental sites, we repeatedly removed 15% of the initial population size until none remained and immigration ceased. 3. Immigrants replaced 16–72% of original residents in S. diencaeus and 0–69% in S. adustus. The proportion of the source population that immigrated into depleted areas varied from 9% to 61% in S. diencaeus and from 3% to 21% in S. adustus. In S. diencaeus, compensatory immigration was strongly affected by habitat quality, to a lesser extent by the abundance of potential immigrants and not by landscape connectivity. In S. adustus, immigration was strongly affected by the density of potential migrants and not by habitat quality and landscape connectivity. On two control sites, immigration in the absence of creation of vacancies was extremely rare. 4. Immigration occurred in response to localized mortality and was therefore compensatory. It was highly variable, sometimes producing substantial impacts on both depleted and source populations. The magnitude of compensatory immigration was influenced primarily by the availability of immigrants and by the potential improvement in territory quality that they could achieve by immigrating and not by their ability to reach the depleted area.
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Density‐dependence is a key concept in population dynamics. Here, we review how body mass and demographic parameters vary with population density in large herbivores. The demographic parameters we consider are age‐ and sex‐specific reproduction, survival and dispersal. As population density increases, the body mass of large herbivores typically declines, affecting individual performance traits such as age of first reproduction and juvenile survival. We documented density‐dependent variations in reproductive rates for many species from the Arctic to subtropical zones, both with and without predation. At high density, a trade‐off between growth and reproduction delays the age of primiparity and often increases the costs of reproduction, decreasing both survival and future reproductive success of adult females. Density‐dependent preweaning juvenile survival occurs more often in polytocous than monotocous species, while the effects of density on post‐weaning juvenile survival are independent of litter size. Responses of adult survival to density are much less marked than for juvenile survival, and may be exaggerated by density‐dependent changes in age structure. The role of density‐dependent dispersal in population dynamics remains uncertain, because very few studies have examined it. For sexually dimorphic species, we found little support for higher sensitivity to increasing density in the life history traits of males compared to females, except for young age classes. It remains unclear whether males of dimorphic species are sensitive to male density, female density or a combination of both. Eberhardt's model predicting a sequential effect of density on demographic parameters (from juvenile survival to adult survival) was supported by 9 of 10 case studies. In addition, population density at birth can also lead to cohort effects, including a direct effect on juvenile survival and long‐term effects on average cohort performance as adults. Density effects typically interact with weather, increasing in strength in years of harsh weather. For some species, the synchronization between plant phenology and reproductive cycle is a key process in population dynamics. The timing of late gestation as a function of plant phenology determines whether density‐dependence influences juvenile survival or adult female reproduction. The detection of density‐dependence can be made difficult by nonlinear relationships with density, high sampling variability, lagged responses to density changes, changes in population age structure, and temporal variation in the main factors limiting population growth. The negative feedbacks of population size on individual performance, and hence on life history traits, are thus only expected in particular ecological contexts and are most often restricted to certain age‐specific demographic traits.
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Context. Despite their economic importance and intensive management, many game bird species, including the northern bobwhite Colinus virginianus, are in decline. Declines may be explained, at least in part, by low survival due perhaps to poor habitat quality, high predation or excessive hunting pressure. Aims. This study sought to estimate and model annual/seasonal survival probabilities, to evaluate factors influencing them and to determine the cause-specific mortality rates for northern bobwhites subject to varying levels of harvest on the Babcock–Webb Wildlife Management Area (BW area), south Florida, USA. Methods. We applied Cox’s proportional hazard models to data collected from 2066 radio-tagged bobwhites during 2002–2008 to test for intrinsic and extrinsic factors affecting survival and the non-parametric cumulative incidence function estimator to estimate cause-specific mortality rates. Key results. Mean annual survival (0.091 +- 0.006) in the BW area was lower than most estimates reported for other bobwhite populations. Annual survival differed between adults (0.111 +- 0.008) and juveniles (0.052 +- 0.008), and varied among years. Survival in winter (October–March; 0.295 +- 0.014) was similar to that in summer (April–September; 0.307 +- 0.013). Density of food strips (i.e. long and narrow food plots) did not influence survival, but hunting effort (number of hunters per day per km2) had a substantial negative impact on survival. In the lightly hunted field trial zone, winter (October–March) survival was significantly higher (0.414 +- 0.035) than in the other more heavily hunted management zones (0.319 +- 0.016). Cause-specific mortality analyses revealed that bobwhite mortality during summer (April–September) was mainly due to raptor (39.7%) and mammalian predation (35.6%), whereas hunting was the primary cause of mortality during winter (47.1%). Conclusions. Our results highlight the potential role of harvest as an important cause of the northern bobwhite population declines in south Florida. High mortality during winter may reduce recruitment of juveniles to the reproductive segment of the population, and ultimately the population growth. Implications. Our results suggest that reduction in hunting pressure may be necessary to reverse the declining population trends in heavily hunted game species in public lands, such as the northern bobwhites in the BW area.
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Compensatory mortality or natality can operate as a consequence of seasonally driven mechanisms of density dependence. Our objective is to clarify the relationship between compensation and density dependence in population models for vertebrates when seasonality is present. Field studies of a variety of species have demonstrated that due to compensation, predation or human harvest may not influence spring-breeding or pre-harvest-season densities. Compensation seems to contradict most harvesting and predation models because these models predict that harvests or predation will always reduce equilibrium population size. In these population models sustainable harvests are attainable because of density dependence. The apparent discrepancy is attributable to the failure of most population models to incorporate the details of environmental seasonality. We review seasonally explicit models of population dynamics to illustrate how density dependence is the mechanism behind compensatory mortality and natality. Even though spring-breeding or pre-season densities can remain unaffected or even increased by harvesting, harvesting or predation generally reduces the integral of population size. Compensatory mortality and natality are often cited as the basis for sustainable harvests of wildlife populations.