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Abstract

1.Selective hunting can affect demographic characteristics and phenotypic traits of the targeted species. Hunting systems often involve harvesting quotas based on sex, age and/or size categories to avoid selective pressure. However, it is difficult to assess if such regulations deter hunters from targeting larger ‘trophy’ animals with longer horns that may have evolutionary consequences. 2.Here, we compile 44′088 annually resolved and absolutely dated measurements of Alpine ibex (Capra ibex) horn growth increments from 8′355 males, harvested between 1978 and 2013, in the eastern Swiss Canton of Grisons. We aim to determine if male ibex with longer horns were preferentially targeted, causing animals with early rapid horn growth to have shorter lives, and whether such hunting selection translated into long‐term trends in horn size over the past four decades. 3.Results show that medium‐ to longer‐horned adult males had a higher probability of being harvested than shorter‐horned individuals of the same age, and that regulations do affect the hunters’ behaviour. Nevertheless, phenotypic traits like horn length, as well as body size and weight, remained stable over the study period. 4.Though selective trophy hunting still occurs, it did not cause a measurable evolutionary response in Grisons’ Alpine ibex populations; managed and surveyed since 1978. Nevertheless, further research is needed to understand if phenotypic trait development is co‐influenced by other, potentially compensatory factors that may possibly mask the effects of selective, long‐term hunting pressure. This article is protected by copyright. All rights reserved.

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... Declining morphological trait sizes have also been associated with selective hunting pressure [25-28]; the directed removal of animals with specific traits. Yet again, the lack of sufficiently long and wellreplicated datasets complicates any systematic assessment of species' evolutionary responses to intensive trophy harvesting [29,30]. Hence, it remains debatable whether a properly managed hunting system can be used as a conservation tool for maintaining sustainability [31,32]. ...
... No trends are found in the weight, size and age of the harvested animals within and between the species-specific autumnal hunting seasons. Moreover, trophy selection and supplementary feeding of GR's wild ungulate populations is prohibited [29]. ...
... Unlike previous work [3][4][5][6][7][8][9][10][11][12][13][14][16][17][18][19][20], this study finds body mass and size of wild ungulates was stable during the past decades, when temperatures increased [45]. During the same period of time, GR's persistent management of natural resources resulted in approximately constant population sizes of each species studied [29,40]. ...
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In many species, decreasing body size has been associated with increasing temperatures. Although climate-induced phenotypic shifts, and evolutionary impacts, can affect the structure and functioning of marine and terrestrial ecosystems through biological and metabolic rules, evidence for shrinking body size is often challenged by (i) relatively short intervals of observation, (ii) a limited number of individuals, and (iii) confinement to small and isolated populations. To overcome these issues and provide important multi-species, long-term information for conservation managers and scientists, we compiled and analysed 222 961 measurements of eviscerated body weight, 170 729 measurements of hind foot length and 145 980 measurements of lower jaw length, in the four most abundant Alpine ungulate species: ibex (Capra ibex), chamois (Rupicapra rupicapra), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Regardless of age, sex and phylogeny, the body mass and size of these sympatric animals, from the eastern Swiss Alps, remained stable between 1991 and 2013. Neither global warming nor local hunting influenced the fitness of the wild ungulates studied at a detectable level. However, we cannot rule out possible counteracting effects of enhanced nutritional resources associated with longer and warmer growing seasons, as well as the animals' ability to migrate along extensive elevational gradients in the highly diversified alpine landscape of this study.
... Declining morphological trait sizes have also been associated with selective hunting pressure [25][26][27][28]; the directed removal of animals with specific traits. Yet again, the lack of sufficiently long and wellreplicated datasets complicates any systematic assessment of species' evolutionary responses to intensive trophy harvesting [29,30]. Hence, it remains debatable whether a properly managed hunting system can be used as a conservation tool for maintaining sustainability [31,32]. ...
... No trends are found in the weight, size and age of the harvested animals within and between the species-specific autumnal hunting seasons. Moreover, trophy selection and supplementary feeding of GR's wild ungulate populations is prohibited [29]. ...
... Unlike previous work [3][4][5][6][7][8][9][10][11][12][13][14][16][17][18][19][20], this study finds body mass and size of wild ungulates was stable during the past decades, when temperatures increased [45]. During the same period of time, GR's persistent management of natural resources resulted in approximately constant population sizes of each species studied [29,40]. ...
Article
In many species, decreasing body size has been associated with increasing temperatures. Although climate-induced phenotypic shifts, and evolutionary impacts, can affect the structure and functioning of marine and terrestrial ecosystems through biological and metabolic rules, evidence for shrinking body size is often challenged by (i) relatively short intervals of observation, (ii) a limited number of individuals, and (iii) confinement to small and isolated populations. To overcome these issues and provide important multi-species, long-term information for conservation managers and scientists, we compiled and analysed 222 961 measurements of eviscerated body weight, 170 729 measurements of hind foot length and 145 980 measurements of lower jaw length, in the four most abundant Alpine ungulate species: ibex (Capra ibex), chamois (Rupicapra rupicapra), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Regardless of age, sex and phylogeny, the body mass and size of these sympatric animals, from the eastern Swiss Alps, remained stable between 1991 and 2013. Neither global warming nor local hunting influenced the fitness of the wild ungulates studied at a detectable level. However, we cannot rule out possible counteracting effects of enhanced nutritional resources associated with longer and warmer growing seasons, as well as the animals' ability to migrate along extensive elevational gradients in the highly diversified alpine landscape of this study.
... For example, in many jurisdictions in North America, harvest of male deer whose antlers have fewer than a specified number of tines is illegal. When hunting is for meat or recreation, however, it is less selective (Mysterud 2011) and regulations sometimes include quotas for specific sex-age classes (Büntgen et al. 2018). The main characteristics of large mammals that affect vulnerability to hunting are behavior (Leclerc et al. 2017) and morphology (Festa-Bianchet 2017). ...
... A recent study of ibex in Switzerland found that although hunters preferred to take males with long horns, selection was very weak and did not result in a temporal change in horn size (Büntgen et al. 2018). Ibex in Switzerland are hunted with age-specific quotas, and hunters are penalized if they harvest a male outside the assigned narrow age class. ...
... Those regulations substantially limit the potential for selective hunting, with the exception of males in the oldest age class (11 years and older), which have likely had a chance to reproduce. Male ibex shot at 5-7 years of age, for example, had horns that were only 5-17 mm (1-3%) longer than those grown by the same age by males harvested at an older age (Büntgen et al. 2018). That compares with a 70% difference in early horn growth according to age at harvest for Stone's sheep rams in Canada (Douhard et al. 2016b). ...
Article
Intense selective harvest of large mammals who carry the largest weapons may lead to an evolutionary shrinkage of those weapons. Currently, evidence suggesting evolutionary effects of harvest is limited to a few species of Bovidae and only 1 study has obtained data indicating a genetic effect. To have an evolutionary impact, harvest must be intense, persistent over time, similar over a large area without an effective source of unselected immigrants, and remove large individuals before they have a chance to breed. Many current harvest schemes do not fulfill all of these requirements, and they are unlikely to cause evolution. Before changes in weapon size over time are attributed to evolution, potential environmental sources of change, mainly density and climate, must be considered. We suggest that the role of weapon size in determining reproductive success, especially in interaction with male age, will determine whether or not intensive selective harvests may have evolutionary consequences. Age at harvest is a very important variable to consider. Changes in age structure over time may reveal underlying changes in harvest pressure or selectivity. A lack of data hampers our ability to assess the potential evolutionary effects of selective hunting. We provide a list of research hypotheses required to advance our ability to assess the evolutionary sustainability of current management practices.
... Among ungulates selectively harvested based on the size or shape of their weapons, results from long-term studies of three species of wild sheep are consistent with hunting-induced evolution of smaller horn size (bighorn sheep, Ovis canadensis Shaw, 1804 (Pigeon et al. 2016); Stone sheep, Ovis dalli Nelson, 1884 (Douhard et al. 2016); and European mouflon, Ovis gmelini Blyth, 1841 (Garel et al. 2007)). Some studies of hunted ungulates, however, do not suggest an evolutionary change and point instead to possible effects of climate change on horn growth (Rughetti and Festa-Bianchet 2010;Büntgen et al. 2018). So far, there is no clear evidence of hunter-induced decline in antler size, and evolutionary change in weaponry is expected under a restrictive set of conditions (Festa-Bianchet and Mysterud 2018). ...
Article
Trophy hunting can affect weapon size of wild animals through both demographic and evolutionary changes. In bighorn sheep (Ovis canadensis Shaw, 1804), intense harvest of young males with fast-growing horns may have partly driven long-term decreases in horn size. These selective effects could be dampened if migrants from protected areas, not subject to artificial selection, survived and reproduced within hunted populations. Bighorn rams undertake long-distance breeding migrations in the weeks preceding the late-November rut. We analysed records of >7 800 trophy bighorn rams shot from 1974 to 2019 in Alberta, Canada, to test the hypothesis that high harvest pressure during breeding migrations was correlated with a greater decrease in horn size. We compared areas with and without a pronounced harvest peak in late October, when male breeding migrations begin. Areas without a pronounced harvest peak in late October, that likely experienced a lower harvest rate, showed a similar temporal decline in horn size, but no increase in age at harvest suggesting a possibly weaker decline in horn growth. Our study suggests that unselected immigrants from protected areas could partly buffer the effects of intense trophy hunting only if harvest pressure was reduced when breeding migrations commence.
... Because this species is the primary prey for the endangered snow leopard in some regions (e.g., the Khunjerab National Park, Pakistan), trophy hunting in these areas would further reduce the food availability for snow leopard, which goes against the ultimate objective of endangered species conservation. Considering that the trophy hunting policy is a way of artificial selection, large-horned males are becoming targets and hunted (Bergeron et al., 2008;Buntgen et al., 2018;Von Hardenberg et al., 2007). Ultimately, it is assumed that such a policy will jeopardize the survival of healthy genes and lower the group's evolutionary potential (Sarrazin and Barbault, 1996). ...
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The Asiatic ibex (Capra sibirica), the largest member of the genus Capra, is widely distributed in Central and South Asia. It is a primitive ibex species of the family Bovidae that is distinct from other ibex species. The Asiatic ibex is distributed in highland landscapes characterized by challenging terrains that have resulted in incomplete knowledge of this species. To understand the research advances in this species, this review summarizes the taxonomic position, global distribution, population size, foraging ecology, sexual segregation, health threat by diseases, and potential threats and conservation biology. Besides, this species is facing increasing impacts of anthropogenic activities and habitat loss induced by global climate change. It also proposes new research perspectives and priorities to understand the advanced ecology of the Asiatic ibex. We also highlight a suite of research gaps that require multidisciplinary approaches. These will increase understanding of the evolution, biology, ecology, and epidemiology of this species.
... Horn growth in Nubian ibex males appears to start plateauing at ca. age 7-8, which was generally younger than seen in other ibex species, e.g., ≥11 to ≥13 in Alpine ibex depending upon the population (Bergeron et al. 2010;Büntgen et al. 2018;Toïgo et al. 1999; this can be as low as 7-8 year for populations likely experiencing significant resource stress; Bergeron et al. 2008) and >10 in Spanish ibex (Capra pyrenaica; Granados et al. 2001). Like other ibex, all measures of male horn length were strongly related to age of males, e.g., age accounted for ≥85% of the variation in OHL and IHL; similarly, age was found to be the strongest predictor of horn length in other species of ibex (Fandos 1995). ...
Article
Documenting patterns of horn growth and horn-age relationships of Nubian ibex ( Capra nubiana ) can contribute to a more comprehensive understanding of their natural history, horn development in ibex in general, and future conservation of the species. Our specific objectives included (1) documenting age-horn growth patterns; (2) contrasting horn growth patterns of Nubian ibex with other ibex species; and (3) determining whether horn development accurately reflects age of Nubian ibex in Sinai, Egypt. As expected, all male and female horn measurements had significant relationships with age. Horn growth in males started plateauing at ca. age 7–8, whereas female horn growth started plateauing at ca. age 4–6. The extremely arid environment of Nubian ibex in the Sinai may account for the slowing of horn growth at a younger age than seen in populations of some other ibex species. We found a significant relationship between the number of horn ridges and age, indicating that counting horn ridges provides a viable method of aging males to within ±1 y. Thus counting horn ridges may be a useful and non-invasive method to determine age or age class, which can further our understanding of age structure, the natural history, and management of Nubian ibex populations.
... Measurement uncertainty between different individual observers was negligible because we followed a strict standardized protocol. We excluded the outermost annual growth segment from our analyses because of abrasion (Álvarez 1990;Büntgen et al. 2014Büntgen et al. , 2018 and maternal effects (Giacometti et al. 2002). The range of ages (1-17 yrs, ̅ x = 11.4 yrs) of ibex resulted in 10-15 growth segments per horn (Fig. 2B). ...
Article
Size‐selective harvesting of wild ungulates can trigger a range of ecological and evolutionary consequences. It remains unclear how environmental conditions, including changes in habitat, climate, and local weather conditions, dilute or strengthen the effects of trophy hunting. We analyzed horn length measurements of 2,815 male ibex (Capra pyrenaica) that were harvested from 1995 to 2017 in Els Ports de Tortosa i Beseit National Hunting Reserve in northeastern Spain. We used linear mixed models to determine the magnitude of inter‐individual horn growth variability and partial least square path models to evaluate long‐term effects of environmental change, population size, and hunting strategy on horn growth. Age‐specific horn length significantly decreased over the study period, and nearly a quarter (23%) of its annual variation was attributed to individual heterogeneity among males. The encroachment of pine (Pinus spp.) forests had a negative effect on annual horn growth, possibly through nutritional impoverishment. The harvesting of trophy and selective individuals (e.g., small‐horned males) from the entire population increased horn growth, probably because it reduced the competition for resources and prevented breeding of these smaller males. Local weather conditions and population size did not influence horn growth. Our study demonstrates how habitat changes are altering the horn growth of male ibex. We suggest that habitat interventions, such the thinning of pine forests, can contribute to securing the sustainability of trophy hunting. Even in situations where size‐selective harvesting is not causing a detectable phenotypic response, management actions leading to the expansion of preferred land cover types, such as grass‐rich open areas, can have a positive effect on ungulate fitness. Forest encroachment on open meadows and heterogeneous grasslands is pervasive throughout Mediterranean ecosystems. Therefore, our management recommendations can be extended to the landscape level, which will have the potential to mitigate the side effects of habitat deterioration on the phenotypic traits of wild ibex. © 2020 The Wildlife Society. The encroachment of coniferous forests and the consequent loss of natural pastures had a negative effect on the annual horn growth of male ibex inhabiting a Mediterranean ecosystem. The selective harvesting of small‐horned males had a positive effect on annual horn growth. The expansion of grass‐rich open areas should be prioritized to reduce the negative effects of habitat deterioration on the phenotypic traits of male ibex.
... On the other, there are no demonstrations of genetically based changes in fishery stocks (Heino et al. 2015), although harvesting has been shown to decrease levels of neutral genetic variation (Allendorf et al. 2008). With respect to trophy hunting, not all exploited populations display significant phenotype changes (Buntgen et al. 2018) and the single compelling quantitative genetic study in the literature shows a lower rate of genetic change than phenotypic change (Pigeon et al. 2016). A recent theoretical study ) suggested that observed rates of phenotypic change in male ornaments are 1-2 orders of magnitude higher than would be possible with realistic quantitative genetic parameters. ...
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Experimental studies of evolution performed in nature and the associated demonstration of rapid evolution, observable on a time scale of months to years, were an acclaimed novelty in the 1980–1990s. Contemporary evolution is now considered ordinary and is an integrated feature of many areas of research. This shift from extraordinary to ordinary reflects a change in the perception of evolution. It was formerly thought of as a historical process, perceived through the footprints left in the fossil record or living organisms. It is now seen as a contemporary process that acts in real time. Here we review how this shift occurred and its consequences for fields as diverse as wildlife management, conservation biology, and ecosystems ecology. Incorporating contemporary evolution in these fields has caused old questions to be recast, changed the answers, caused new and previously inconceivable questions to be addressed, and inspired the development of new subdisciplines. We argue further that the potential of contemporary evolution has yet to be fulfilled. Incorporating evolutionary dynamics in any research program can provide a better assessment of how and why organisms and communities came to be as they are than is attainable without an explicit treatment of these dynamics.
Article
Variation in age of primiparity is important for population dynamics and wildlife management because it can affect population growth. Using a novel technique based on the trade-off between annual horn growth and reproduction, we estimated the age of primiparity for 2274 female mountain goats (Oreamnos americanus, de Blainville 1816) harvested across British Columbia, Canada, from 1976 to 2019. We then investigated spatio-temporal variation in the probability that harvested females were primiparous when aged three, four or five years and older using Bayesian ordinal regressions. We found that the probability of primiparity at three years decreased over time in nearly all mountain ranges. In the Coastal Mountain range, however, the probability of primiparity at age three significantly increased. These results suggest that the large coastal populations of mountain goats could be more resilient to harvest than other populations in British Columbia, which may be experiencing environmental effects promoting later primiparity. Models predicting age of primiparity from annual growth measures are a valuable tool for wildlife management and could help conservation of many species. _____________________________________________________________________________________ L’âge à la primiparité est une composante importante de la dynamique des populations et de la gestion de la faune, car elle peut influencer la croissance des populations. Utilisant une technique novatrice reposant sur les compromis entre la croissance annuelle des cornes et la reproduction, nous avons estimé l’âge à la primiparité de 2274 chèvres de montagne (Oreamnos americanus (Blainville, 1816)) femelles récoltées en Colombie-Britannique (Canada) de 1976 à 2019. Ensuite, en utilisant des régressions ordinales bayésiennes, nous avons examiné les tendances spatiotemporelles de la probabilité que les femelles soient primipares à 3, 4 ou 5 ans et plus. Nous avons constaté un déclin temporel de la probabilité de récolter une femelle primipare à 3 ans dans presque toutes les chaînes de montagnes de la province. Cependant, dans la chaîne de montagne côtière, cette probabilité augmente significativement au fil du temps. Ces résultats semblent indiquer que les grandes populations côtières de chèvres de montagne seraient plus résilientes aux récoltes annuelles que d’autres populations en Colombie-Britannique, chez lesquelles la primiparité pourrait être retardée par des effets environnementaux. Les modèles qui prédisent l’âge à la primiparité à partir de mesures de la croissance annuelle constituent un outil à fort potentiel pour la gestion de la faune et pourraient s’avérer utiles pour la conservation de plusieurs espèces.
Article
Intra- and intersexual selection drives the evolution of secondary sexual traits, leading to increased body size, trait size and generally increased reproductive success in bearers with the largest, most attractive traits. Evolutionary change through natural selection is often thought of primarily in terms of genetic changes through mutations and adaptive selection. However, this view ignores the role of the plasticity in phenotypes and behaviour and its impact on accelerating or decelerating the expression of sexually selected traits. Here, we argue that sudden changes in selection pressures (e.g. predation pressure) may cause a cascade of behavioural responses, leading to a rapid change in the size of such traits. We propose that selective removal of individuals with the most prominent traits (such as large antlers or horns in male ungulates) induces behavioural changes in the surviving males, leading to a reduction in the growth of these traits (phenotypic expression). To test this idea, we used an individual-based simulation, parametrized with empirical data of male bighorn sheep, Ovis candensis. Our model shows that the expression (phenotype, not genotype) of the trait under selection (here horn size) can be negatively impacted, if the biggest, most dominant males in the population are removed. While the selective removal of prime males opens breeding opportunities for younger, smaller males, we predicted that it would come at the expense of growth and maintenance. As predicted, we observed a rapid decline in average male horn length in our model. We argue that this decline happens because smaller males, instead of allocating energy into growth, divert this energy towards participation in mating activities that are typically exclusively available to prime males. While our model deals with ecological life-history trade-offs, it cannot predict evolutionary outcomes. However, this nongenetic mechanism is important for the understanding of evolutionary processes because it describes how heritable traits can rapidly change because of behavioural plasticity, long before any genetic changes might be detectable.
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Horns, antlers, and other horn-like structures are products of sexual selection, confer reproductive advantages, and are heritable and honest indicators of individual quality. In addition to serving key biological functions, horns and antlers garner societal interest that, when combined with the powerful motivation to acquire trophy animals, likely has spawned a growing hornographic culture fixated on males with exceptional horn-like structures. The concern that harvest of large, fast-growing males may cause evolutionary change to the very trait being sought has been the source of controversy in the popular and scientific literature over the past 2 decades. Mountain sheep (i.e., bighorn and thinhorn; Ovis spp.), possibly the only large ungulates in North America managed almost exclusively as trophy species throughout their ranges, embody this controversy, which has led to polarizing views among scientists and stakeholders as to how mountain sheep should be managed. Our goal in this commentary was to discuss the relative contributions of the key ecological and intrinsic factors that influence horn growth, how those factors might interact with harvest strategies, and identify what determinants of horn size are most amenable to management and most effective in achieving desired outcomes. Despite repeated results demonstrating that age or nutrition frequently override genetic contributions to size of horns, attention has been given to the role of genetics and its relationship to harvest of mountain sheep. Given the hyperbole surrounding trophy management and big horns, we suggest the importance of females in the management of mountain sheep has been largely forgotten. Maternal condition can instigate life-long effects on size and growth of males (via maternal effects), and abundance of females, in turn, affects nutritional limitation within populations through density-dependent feedbacks. If production of males with large horns is an objective, we contend that management programs should, integrate monitoring of nutritional status of populations, and where evidence indicates nutritional limitation through density dependence, seek to regulate abundance and per capita nutrition via harvest of females. We propose that extrinsic regulation (i.e., removal by harvest or translocation) is the most effective way to manage per capita availability of forage resources and, thus, nutritional limitation on growth of males. Not only can female harvest improve growth in body size and horns of males through enhanced nutrition of growing males and their mothers, such management also 1) may yield a nutritional buffer against environmental stochasticity and erratic population fluctuations, 2) be employed in areas where other management alternatives such as habitat manipulation may not be feasible, 3) may reduce frequency or magnitude of epizootic die-offs, and 4) will increase hunter opportunity and involvement in management. Ultimately, we call for greater recognition of the pervasive role of the ewe, and other female ungulates, in the production of trophy males, and that accordingly, females be better integrated into harvest and management programs. © 2017 The Wildlife Society.
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Trophy hunting, the selective removal of animals for human recreation, can contribute to conservation when appropriately managed. Yet, little is known about how harvest rates or different definitions of trophy affect age structure and trophy size in harvested animals and in survivors because no controlled studies exist. To investigate the impacts of different management regimes, we developed an individual-based model for bighorn sheep (Ovis canadensis), based on empirical data on survival from a protected population and data on horn growth from 2 populations that differed in their growth rates. One population showed slow horn growth and the other population fast horn growth. We subjected these model populations to varying harvest rates and 2 different hunting regulations: 4/5 curl and full-curl definitions of a trophy male. We found that the effect of hunting regulations depends on horn growth rate. In populations with fast horn growth, the effects of trophy hunting on male age structure and horn size were greater and the effect of a change in the definition of legal male smaller than in populations with slow growth rates. High harvest rates led to a younger age structure and smaller horn size. Both effects were weakened by a more restrictive definition of trophy male. As harvest rates increased past 40% of legal males, the number of males harvested increased only marginally because an increasing proportion of the harvested males included those that had just become legal. Although our simulation focused on bighorn sheep, the link between horn growth rate and harvest effects may be applicable for any size-selective harvest regime.
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Warming-induced range shifts along elevational and latitudinal gradients have been observed in several species from various taxa. The mobility and behavioral plasticity of large endothermic mammals, however, complicate the detection of climatic effects on their spatial distributions. Here, we analyzed 230,565 hunting locations of the four most abundant ungulate species in the European Alps: ibex, chamois, red deer, and roe deer. Year-to-year and inter-decadal range shifts toward higher elevations in Switzerland coincided with warmer, snow-free, and thus more favorable autumn conditions in the same area. The average harvest elevation of ibex, chamois, and red deer significantly increased between 1991 and 2013. Although this trend is anticipated to continue, behavioral plasticity may allow the Alpine ibex and other mountain ungulates to buffer some of the associated consequences of climate change. Our results demonstrate the utility of well-replicated hunting archives to supplement shorter but more precise monitoring data. This study also provides independent evidence of animal range shifts in response to environmental change at interannual and multi-decadal time-scales.
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The development of male secondary sexual characters such as antlers or horns has substantial biological and socio-economic importance because in many species these traits affect male fitness positively through sexual selection and negatively through trophy hunting. Both environmental conditions and selective hunting can affect horn growth but their relative importance remains unexplored. We first examined how a large-scale climate index, the Pacific Decadal Oscillation (PDO), local weather and population density influenced both absolute and relative annual horn growth from birth to three years of male bighorn sheep Ovis canadensis over 42 years. We then examined the relative influence of environmental conditions and evolution mainly driven by trophy hunting on male horn length at three years of age. Horn growth was positively influenced by low population density and warm spring temperature, suggesting that ongoing climate change should lead to larger horns. Seasonal values of PDO were highly correlated. Horn growth increased with PDO in spring or summer at low density, but was weak at high density regardless of PDO. The interaction between population density and PDO in spring or summer accounted for a similar proportion of the observed annual variation in horn growth (32% or 37%) as did the additive effects of spring temperature and density (34%). When environmental conditions deteriorated, males allocated relatively more resources to summer mass gain than to horn growth, suggesting a conservative strategy favoring maintenance of condition over allocation to secondary sexual characters. Population density explained 27% of the variation in horn length, while evolutionary effects explained 9% of the variance. Thus, our study underlines the importance of both evolution and phenotypic plasticity on the development of a secondary sexual trait. This article is protected by copyright. All rights reserved.
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Hunting is the predominant way of controlling many wildlife populations devoid of large carnivores. It subjects animals to mortality rates that far exceed natural rates and that differ markedly in which age, sex, or size classes are removed relative to those of natural predators. To explain the emerging selection pattern we develop behavioral microfoundations for a hunting model, emphasizing in particular the constraints given by the formal and informal norms, rules, and regulations that govern the hunter's choice. We show how a shorter remaining season, competition among hunters, lower sighting probabilities, and higher costs all lead to lower reservation values, i.e., an increased likelihood of shooting a particular animal. Using a unique dataset on seen and shot deer from Norway, we test and confirm the theoretical predictions in a recreational and meat-motivated hunting system. To achieve sustainability, future wildlife management should account for this predictable selection pressure.
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Potential evolutionary consequences of selective hunting of mammals are controversial because of limited evidence and important socio-economic impacts. Several ecological and management variables facilitate evolutionary responses to selection for horn, tusk or antler size, including strong selective hunting pressure; harvest of males with large horns, tusks or antlers before they can breed; unavailable or ineffective sources of unselected immigrants; and age-dependent relationships between horn, tusk or antler size and male mating success. Plastic responses of male horns, tusks and antlers to environment are probably more common than evolutionary changes. Evidence for evolutionary effects of selective hunting is strong for large mammals where biological characteristics and hunting regulations combine to favour them.
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Selective harvest may lead to rapid evolutionary change. For large herbivores, trophy hunting removes males with large horns. That artificial selection, operating in opposition to sexual selection, can lead to undesirable consequences for management and conservation. There have been no comparisons of long-term changes in trophy size under contrasting harvest pressures. We analyzed horn measurements of Stone's rams (Ovis dalli stonei) harvested over 37 years in two large regions of British Columbia, Canada, with marked differences in hunting pressure to identify when selective hunting may cause a long-term decrease in horn growth. Under strong selective harvest, horn growth early in life and the number of males harvested declined by 12% and 45%, respectively, over the study period. Horn shape also changed over time: horn length became shorter for a given base circumference, likely because horn base is not a direct target of hunter selection. In contrast, under relatively lower hunting pressure, there were no detectable temporal trends in early horn growth, number of males harvested, or horn length relative to base circumference. Trophy hunting is an important recreational activity and can generate substantial revenues for conservation. By providing a reproductive advantage to males with smaller horns and reducing the availability of desirable trophies, however, excessive harvest may have the undesirable long-term consequences of reducing both the harvest and the horn size of rams. These consequences can be avoided by limiting offtake.
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The potential for selective harvests to induce rapid evolutionary change is an important question for conservation and evolutionary biology, with numerous biological, social and economic implications. We analyze 39 years of phenotypic data on horn size in bighorn sheep (Ovis canadensis) subject to intense trophy hunting for 23 years, after which harvests nearly ceased. Our analyses revealed a significant decline in genetic value for horn length of rams, consistent with an evolutionary response to artificial selection on this trait. The probability that the observed change in male horn length was due solely to drift is 9.9%. Female horn length and male horn base, traits genetically correlated to the trait under selection, showed weak declining trends. There was no temporal trend in genetic value for female horn base circumference, a trait not directly targeted by selective hunting and not genetically correlated with male horn length. The decline in genetic value for male horn length stopped, but was not reversed, when hunting pressure was drastically reduced. Our analysis provides support for the contention that selective hunting led to a reduction in horn length through evolutionary change. It also confirms that after artificial selection stops, recovery through natural selection is slow. This article is protected by copyright. All rights reserved.
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International pressure to ban trophy hunting is increasing. However, we argue that trophy hunting can be an important conservation tool, provided it can be done in controlled manner to benefit biodiversity conservation and local people. Where political, and governance structures are adequate, trophy hunting can help address the ongoing loss of species.
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Many agencies and researchers use data from harvested animals to study temporal trends in phenotype. For large mammals, complete harvest records are typically only available for the past few decades, but records of the largest trophies have been collected for over a century. To examine whether record books and data from male bighorn sheep (Ovis canadensis) harvested under a minimum-curl regulation could detect temporal trends in horn length, we simulated populations of trophy-harvested male bighorn sheep where horn length was modeled to increase, remain stable, and decrease over time. All populations experienced a simulated harvest based on a minimum horn length, but only horns in the longest 5% of the initial distribution were entered in a fictional record book. We then assessed whether monitoring of harvested and “record” males detected temporal trends. Data from selective harvest underestimated declines and initially underestimated increases, but qualitatively detected both trends. Record-book entries, however, severely underestimated increases and did not detect declines, suggesting that they should not be used to monitor population trends. When these biases are taken into account, complete trophy harvest records can provide useful biological information.
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Selective harvest may lead to rapid evolutionary change. For large herbivores, trophy hunting removes males with large horns. That artificial selection, operating in opposition to sexual selection, can lead to undesirable consequences for management and conservation. There have been no comparisons of long-term changes in trophy size under contrasting harvest pressures. We analyzed horn measurements of Stone's rams (Ovis dalli stonei) harvested over 37 years in two large regions of British Columbia, Canada, with marked differences in hunting pressure to identify when selective hunting may cause a long-term decrease in horn growth. Under strong selective harvest, horn growth early in life and the number of males harvested declined by 12% and 45%, respectively, over the study period. Horn shape also changed over time: horn length became shorter for a given base circumference, likely because horn base is not a direct target of hunter selection. In contrast, under relatively lower hunting pressure, there were no detectable temporal trends in early horn growth, number of males harvested, or horn length relative to base circumference. Trophy hunting is an important recreational activity and can generate substantial revenues for conservation. By providing a reproductive advantage to males with smaller horns and reducing the availability of desirable trophies, however, excessive harvest may have the undesirable long-term consequences of reducing both the harvest and the horn size of rams. These consequences can be avoided by limiting offtake.
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For species living in seasonal environments the understanding of demographic processes requires identifying the environmental factors during spring and summer that shape phenotypic variation. We assessed the effects of plant phenology and population abundance during spring—summer on variation in autumn body mass among cohorts (1995—2006) of juvenile alpine chamois (Rupicapra rupicapra). We computed several metrics based on the normalized difference vegetation index (NDVI) to assess interannual variation in plant phenology and productivity. Body mass of both sexes decreased similarly during years with late springs (-20%) and with increasing population abundance (-15%), with no interactive effect. Our results also suggested that forage quality more than forage quantity influenced body mass of juveniles. Variation in body mass of juveniles thus can be used as an indicator of the relationship between chamois populations and their environment. This study also demonstrates the utility of satellite-based data in increasing our understanding of the consequences of spring—summer conditions on life-history traits.
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Many studies have recorded phenotypic changes in natural populations and attributed them to climate change. However, controversy and uncertainty has arisen around three levels of inference in such studies. First, it has proven difficult to conclusively distinguish whether phenotypic changes are genetically based or the result of phenotypic plasticity. Second, whether or not the change is adaptive is usually assumed rather than tested. Third, inferences that climate change is the specific causal agent have rarely involved the testing - and exclusion - of other potential drivers. We here review the various ways in which the above inferences have been attempted, and evaluate the strength of support that each approach can provide. This methodological assessment sets the stage for 11 accompanying review articles that attempt comprehensive syntheses of what is currently known - and not known - about responses to climate change in a variety of taxa and in theory. Summarizing and relying on the results of these reviews, we arrive at the conclusion that evidence for genetic adaptation to climate change has been found in some systems, but is still relatively scarce. Most importantly, it is clear that more studies are needed - and these must employ better inferential methods - before general conclusions can be drawn. Overall, we hope that the present paper and special issue provide inspiration for future research and guidelines on best practices for its execution.
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Direct effects of climate change on animal physiology, and indirect impacts from disruption of seasonal synchrony and breakdown of trophic interactions are particularly severe in Arctic and Alpine ecosystems. Unravelling biotic from abiotic drivers, however, remains challenging because high-resolution animal population data are often limited in space and time. Here, we show that variation in annual horn growth (an indirect proxy for individual performance) of 8043 male Alpine ibex (Capra ibex) over the past four decades is well synchronised among eight disjunct colonies in the eastern Swiss Alps. Elevated March to May temperatures, causing premature melting of Alpine snowcover, earlier plant phenology and subsequent improvement of ibex food resources, fuelled annual horn growth. These results reveal dependency of local trophic interactions on large-scale climate dynamics, and provide evidence that declining herbivore performance is not a universal response to global warming even for high-altitude populations that are also harvested.
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Hunting remains the cornerstone of the North American model of wildlife conservation and management. Nevertheless, research has indicated the potential for hunting to adversely influence size of horn-like structures of some ungulates. In polygynous ungulates, mating success of males is strongly correlated with body size and size of horn-like structures; consequently, sexual selection has favored the development of large horns and antlers. Horn-like structures are biologically important and are of great cultural interest, both of which highlight the need to identify long-term trends in size of those structures, and understand the underlying mechanisms responsible for such trends. We evaluated trends in horn and antler size of trophy males (individuals exhibiting exceptionally large horns or antlers) recorded from 1900 to 2008 in Records of North American Big Game, which comprised >22,000 records among 25 trophy categories encompassing the geographic extent of species occupying North America. The long-term and broad-scale nature of those data neutralized localized effects of climate and population dynamics, making it possible to detect meaningful changes in size of horn-like structures among trophy males over the past century; however, ages of individual specimens were not available, which prevented us from evaluating age-class specific changes in size. Therefore, we used a weight-of-evidence approach based on differences among trophy categories in life-history characteristics, geographic distribution, morphological attributes, and harvest regimes to discriminate among competing hypotheses for explaining long-term trends in horn and antler size of trophy ungulates, and provide directions for future research. These hypotheses were young male age structure caused by intensive harvest of males (H1), genetic change as a result of selective male harvest (H2), a sociological effect (H3), effects of climate (H4), and habitat alteration (H5). Although the number of entries per decade has increased for most trophy categories, trends in size of horn-like structures were negative and significant for 11 of 17 antlered categories and 3 of 8 horned categories. Mean predicted declines during 1950–2008 were 1.87% and 0.68% for categories of trophy antlers and horns, respectively. Our results were not consistent with a sociological effect (H3), nutritional limitation imposed by climate (H4), or habitat alteration (H5) as potential explanations for long-term trends in size of trophies. In contrast, our results were consistent with a harvest-based explanation. Two of the 3 species that experienced the most conservative harvest regimes in North America (i.e., bighorn sheep [Ovis canadensis] and bison [Bison bison]) did not exhibit a significant, long-term trend in horn size. In addition, horn size of pronghorn (Antilocapra americana), which are capable of attaining peak horn size by 2–3 years of age, increased significantly over the past century. Both of those results provide support for the intensive-harvest hypothesis, which predicts that harvest of males has gradually shifted age structure towards younger, and thus smaller, males. The absence of a significant trend for mountain goats (Oreamnos americanus), which are difficult to accurately judge size of horns in the field, provided some support for the selective-harvest hypothesis. One other prediction that followed from the selective-harvest hypothesis was not supported; horned game were not more susceptible to reductions in size. A harvest-induced reduction in age structure can increase the number of males that are harvested prior to attaining peak horn or antler size, whereas genetic change imposed by selective harvest may be less likely to occur in free-ranging populations when other factors, such as age and nutrition, can override genetic potential for size. Long-term trends in the size of trophy horn-like structures provide the incentive to evaluate the appropriateness of the current harvest paradigm, wherein harvest is focused largely on males; although the lack of information on age of specimens prevented us from rigorously differentiating among causal mechanisms. Disentangling potential mechanisms underpinning long-term trends in horn and antler size is a daunting task, but one that is worthy of additional research focused on elucidating the relative influence of nutrition and effects (both demographic and genetic) of harvest.
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Determining how climate change will affect global ecology and ecosystem services is one of the next important frontiers in environmental science. Many species already exhibit smaller sizes as a result of climate change and many others are likely to shrink in response to continued climate change, following fundamental ecological and metabolic rules. This could negatively impact both crop plants and protein sources such as fish that are important for human nutrition. Furthermore, heterogeneity in response is likely to upset ecosystem balances. We discuss future research directions to better understand the trend and help ameliorate the trophic cascades and loss of biodiversity that will probably result from continued decreases in organism size.
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Global warming is expected to cause earlier springs and increased primary productivity in the Arctic. These changes may improve food availability for Arctic herbivores, but may also have negative effects by generating a mismatch between the surge of high quality food in the spring and the timing of reproduction. We analyzed a 10 year dataset of satellite derived measures of vegetation green-up, population densities, calf body masses and female reproductive success in 19 reindeer () populations in Northern Norway. An early onset of spring and high peak plant productivity had positive effects on calf autumn body masses and female reproductive success. In addition, body masses and reproductive success were both negatively related to population density. The quantity of food available, as determined by the onset of vegetation green-up and plant productivity over the summer were the main drivers of body mass growth and reproductive success. We found no evidence for an effect of the speed of spring green-up. Nor did we detect a negative mismatch between early springs and subsequent recruitment. Effects of global warming on plant productivity and onset of spring is likely to positively affect sub-Arctic reindeer.
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Time series analysis plays an important role in the detection of mechanisms that drive population fluctuations. However, long time series are rare, with ungulate data sets usually not exceeding 50 years. In this article, we describe a long-term data set of population density indices of five ungulate species obtained from the analysis of bag records collected in the Castelporziano Preserve, Rome, Italy. Hunting statistics are often used as proxies for population density; however, in the case of long time series for large mammals, there are no comparative studies to assess the validity of such data. We evaluated the ungulate time series, using two different approaches: we 1) compared hunting statistics with independent animal counts, and 2) assessed whether or not habitat composition of the drive areas was representative of habitat availability in the whole estate. Regressions between bag data and animal counts gave significant results only for three species, whereas bag data corrected for hunted area were significantly correlated to animal counts for all five species. The results suggest that use of bag records not corrected for hunting effort and without any previous validation could lead to misleading estimates of abundance indices. Finally, our analysis showed that density indices of the five species were not significantly affected by the selection of habitats where hunting drives were organised. Our data set may contribute to the understanding of ungulate ecology in the Mediterranean environment.
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Factors affecting horn size in wild Caprinae are of biological and socio-economic interest because several species are selectively harvested on the basis of this heritable character. We analysed temporal trends in horn size in two mountain ungulates from south-eastern Spain, the Iberian wild goat Capra pyrenaica and the aoudad Ammotragus lervia. Trophy harvest is the main way in which these two species are exploited, although ‘poor-quality’ aoudads are also selectively removed. In recent years, both populations have suffered drastic decreases in number due to outbreaks of sarcoptic mange that led to the suspension of hunting for several years. Horn length in harvested male wild goats and aoudads declined during our study period. Over an 18-year period, the mean age of male goats shot as trophies rose by four years, while the age of trophy-harvested aoudads decreased by around six months over a 9-year period. Age and environmental conditions during the first few years of life explained 20% of variance in horn size in Iberian wild goat and 53% in aoudad. Population density early in life explained much of the reduction in goat horn size over time. Nevertheless, the major fall in population densities after the sarcoptic mange outbreaks did not lead to a recovery in horn size in either species. We suggest that the selective removal of large-horned animals may contribute to a decline in horn size. Other factors that may also explain the observed pattern include changes in interspecific competition, long-lasting maternal effects and reduced carrying capacity due to overgrazing during high density periods. Unfortunately, our data sets did not allow us to account for the possible effects of these factors.
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ABSTRACT  In ungulates, big males with large weapons typically outcompete other males over access to estrous females. In many species, rapid early growth leads to large adult mass and weapon size. We compared males in one hunted and one protected population of Alpine chamois (Rupicapra rupicapra) to examine the relationship between horn length and body mass. We assessed whether early development and hunter selectivity affected age-specific patterns of body and horn size and whether sport hunting could be an artificial selection pressure favoring smaller horns. Adult horn length was mostly independent of body mass. For adult males, the coefficient of variation of horn length (0.06) was <50% of that for body mass (0.16), suggesting that horn length presents a lower potential for selection and may be less important for male mating success than is body mass. Surprisingly, early development did not affect adult mass because of apparent compensatory growth. We found few differences in body and horn size between hunted and protected populations, suggesting the absence of strong effects of hunting on male phenotype. If horn length has a limited role in male reproductive success, hunter selectivity for males with longer horns is unlikely to lead to an artificial selective pressure on horn size. These results imply that the potential evolutionary effects of selective hunting depend on how the characteristics selected by hunters affect individual reproductive success.
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We studied long-term cohort effects on chest girth and horn length in a recently established population of alpine ibex (Capra ibex ibex). Environmental conditions of the year of birth affected chest girth and first-annual increment of horns of males but did not affect chest girth and horns of females. Females compensated for a slow horn growth during their Ist year of life, whereas males did not. Level of polygyny of the species and environmental conditions experienced by the population could account for the occurrence of long-term cohort effects in male growth and its absence in female growth. Abundance of food resources throughout the study period allowed females to show compensatory growth. However, evolutionary constraints on growth that may exist in males of polygynous species may have prevented males from showing compensatory growth.
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In the South Luangwa National Park and the adjacent Lupande Game Management Area, located in Zambia's Eastern Province, the fraction of adult tuskless female elephants increased from 10·5% in 1969 to 38·2% in 1989, apparently as a direct result of selective illegal ivory hunting. From 1989 to 1993, the fraction of adult tuskless females declined from 38·2% to 28·70%, as a result of immigration of a relatively larger fraction of tusked females from adjacent Game Management Areas. Tusklessness appears to run in families and is sex-linked. Dans le Parc National de la Luangwa Sud et dans l'Aire de Gestion de la Faune de Lupande voisine, dans la province Orientale de Zambie, la proportion de femelles éléphants sans défenses est passée de 10,5% en 1969 à 38,2%, en 1989, suite directe semble-t-il de la chasse sélective pour l'ivoire. De 1989 à 1993, la proportion de femelles adultes sans défenses a baissé de 38,2%à 28,7%, en raison notamment de l'arrivée d'un assez grand nombre de femelles avec défenses en provenance des zones de gestion de la faune adjacentes, mais aussi à cause d'un changement de sex-ratio en faveur des mâles. L'absence de défences semble être un caractère familial et lié au sexe de l'animal.
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Using a long-term data set on the fluctuations of a reintroduced Swiss pop- ulation of ibex we estimated the parameters in a stochastic population model with theta- logistic density regulation, and how the environmental stochasticity was related to different climate variables. Our aim was to examine quantitatively the relative effects of variation in parameters describing the expected dynamics and the environmental stochasticity as well as the uncertainties in them for the development of reliable population projections. The specific growth rater1 was 0.14. Density regulation mainly happened close to the carrying capacity K, indicating that the commonly used assumption in population ecology of loglinear density regulation is not always valid. Annual variation in the point estimates of the en- vironmental stochasticity was correlated with winter climate. Uncertainties in parameter estimates were high, especially in the estimates of density regulation and r1. In order to examine the dynamical consequences of the estimates as well as the uncertainties in them, we constructed Population Prediction Intervals (PPI). A PPI is the stochastic interval that includes the unknown population size with probability (1 2a ). Analyses of factors affecting the width of the PPI showed that the form of the density regulation as well as uncertainties in model parameters should be estimated when making projections of future fluctuations of introduced populations.
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We wanted to test whether ewe hunting would cause a decline in population size or in trophy ram production, and whether a reduction in ewe density would increase the size of ram horns. Thus, we examined the consequences of a bighorn sheep (Ovis canadensis) ewe hunting season through an experimental manipulation of an isolated population in Alberta, 1972-91. The number of ewes remained stable during 9 years despite yearly removals of 12-24% of the total ewe population. The removals did not affect (P > 0.5) ewe mortality due to other causes, lamb production by adult ewes, or lamb survival. The prevalence of lactation among 2-year-old ewes was higher (P < 0.001) during the removal than afterwards. The survival of orphan and non-orphan lambs was similar (P > 0.1). The number of trophy rams in the population and the number shot by hunters were independent (P > 0.5) of ewe numbers A threefold increase in ewe numbers over the 10-year post-removal period did not affect the number of trophy rams (P > 0.5), but rams born during the removal years had larger horns at 4 and 5 years of age than rams born in the post-removal years (P < 0.05). Our study illustrates that ewe hunting seasons have the potential to limit population increase and can increase trophy ram size. In the absence of significant predation, about 12% of the ewes could be harvested annually, based upon conservative estimates of herd size in summer. We caution against ewe removals in populations with a history of pneumonia, because in these herds, population growth following die-offs appears slow and density-independent, and hunting mortality would likely be additive.
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Despite considerable empirical and theoretical work on the individual and population consequences of early development, little is known about the correlations between early mass and adult size or lifetime reproductive success of free-ranging mammals. Using a 26-year study of bighorn sheep (Ovis canadensis), we examined how mass as a lamb and mass gain as a yearling affected adult mass for both sexes, horn length of males and lifetime reproductive success of females at different population densities. Mass as a 3-week-old lamb was either weakly or not correlated with adult mass, horn length of adult males, or the number of lambs weaned over a ewe's lifetime. Weaning mass was correlated with most of these variables when the number of ewes in the population was taken into account. When weaning mass was controlled through partial correlation, mass as a yearling was correlated with adult mass of ewes but not with ewe reproductive success or with adult mass or horn length of rams. Lamb mass and number of ewes
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P. 2008: Can ground counts reliably monitor ibex Capra ibex populations? -Wildl. Biol. 14: 489-499. Although ground counts are often used to monitor ungulate popu-lations, several studies show that counts of ungulates have low precision and often underestimate population size. We assessed the reliability of ibex Capra ibex counts as performed in French national parks, by analysing up to 23 years of annual censuses of six ibex populations for which a subset of animals were individually marked. We compared the population growth rate obtained from census data (estimated by use of four different methods) with the growth rate calculated from a de-mographic model including parameters estimated from capture-mark-recapture methods. The correlations between count-based estimates and growth rate obtained from demographic models were adequate to suggest that ground counts can monitor trends in population size of ibex, provided that the occasional undercounts are identified. Sub-stantial undercounts in some years led to biologically impossible values of yearly population growth (l>1.35) and, in the longest time series available, to marked autocorrelations in counts. Managers should rep-licate counts within the same year to check for underestimated counts. To reduce errors, population biologists analysing time series of ungu-late counts should check the plausibility of annual growth rates esti-mated from two consecutive counts.
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We used extensive data from a long-term study of great tits (Parus major) in the United Kingdom and Netherlands to better understand how genetic signatures of selection translate into variation in fitness and phenotypes. We found that genomic regions under differential selection contained candidate genes for bill morphology and used genetic architecture analyses to confirm that these genes, especially the collagen gene COL4A5, explained variation in bill length. COL4A5 variation was associated with reproductive success, which, combined with spatiotemporal patterns of bill length, suggested ongoing selection for longer bills in the United Kingdom. Last, bill length and COL4A5 variation were associated with usage of feeders, suggesting that longer bills may have evolved in the United Kingdom as a response to supplementary feeding.
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The description of horn growth patterns is of utmost importance for the sustainable management of wild ungulate populations subjected to intense trophy hunting. This is a topic of renewed interest because horn growth patterns seem to be contingent on region and population. We sampled 2145 male Iberian ibexes (Capra pyrenaica) evenly distributed across the Els Ports de Tortosa i Beseit National Game Reserve, NE Spain. A total of 24,615 annual horn growth segments were measured and used to describe horn growth patterns of male ibexes and to test whether compensatory horn growth occurs in an heterogeneous area. We found that individual heterogeneity explained more than a quarter (27.75%) of the variability in annual segment length and that habitat characteristics foster significant phenotypic differences among male ibexes. Our results corroborate previous studies by demonstrating that compensatory horn growth in male ibexes, as in other members of the tribe Caprini, is inexistent. Our study goes one step further and suggests that compensatory horn growth in male ibexes is neither promoted by cohort effects nor by habitat differences. The absence of compensatory horn growth has important management implications, namely: (i) male ibexes are not able to recover from a bad start, and (ii) the species is prone to evolutionary effects from trophy hunting. We emphasize that the study of just one proxy of horn growth may hamper the current knowledge about compensatory mechanisms in wild ungulates and imperil the development of effective management measures.
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1. Sport hunting of wildlife can play a role in conservation but can also drive population declines if not managed sustainably. Previous simulation modelling found that large felid species could theoretically be hunted sustainably by restricting harvests to older individuals that have likely reproduced. Several African countries currently use age-based hunting for lions although the outcomes have yet to be evaluated in a wild population. 2. Here we provide the first empirical evidence that a system of incentives sufficiently encouraged age-based hunting and reduced offtake of a wild felid, thereby reducing the potential risk of unsustainable hunting on a threatened species. We examined long-term hunting data and the lion population trend in Niassa National Reserve, Mozambique. 3. To incentivise hunter compliance, a 'points' system was developed which rewards operators that harvest lions older than the 6-year minimum trophy age recommended for sustainable hunting and penalises operators that hunt 'underage' lions (<4 years). A key component of this system is the ecological application of key physical traits that predictably change with age in order to estimate (by hunters) and validate (by authorities) trophy individuals' ages pre-and post-mortem, respectively. Analysis of 138 lion hunts and 87 lion trophies from 2003-2015 Accepted Article This article is protected by copyright. All rights reserved. revealed that after enforcement of age restrictions in 2006, hunters shifted harvests to suitably aged lions (>6 years), from 25% of offtakes in 2004 to 100% by 2014. 4. Simultaneously, the number of lions and percentage of quota harvested decreased, resulting in lower lion offtakes. Following an initial decrease after enforcement of the aging system, the percentage of hunts harvesting lions stabilised, demonstrating that hunters successfully located and aged older lions. 5. Synthesis and applications. Evidence suggests that age restrictions combined with an incentive-based points system regulated sport hunting and reduced pressure on the lion population. We attribute the successful implementation of this management system to: 1) committed, consistent enforcement by management authorities, 2) genuine involvement of all stakeholders from the start, 3) annual auditing by an independent third party, 4) the reliable, transparent, straightforward aging process, and 5) the simple, pragmatic points system for incentivising hunter compliance. Our study demonstrates that the use of age restrictions can increase the selectivity of sport hunting and lower trophy offtakes to reduce the possibility of unsustainable sport hunting negatively impacting species populations in the absence of reliable estimates of population size. It must be noted, however, that there was no measurable change in the lion numbers over the past decade that could be attributed to the implementation of this policy alone.
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Summary. Recent work by Reiss and Ogden provides a theoretical basis for sometimes preferring restricted maximum likelihood (REML) to generalized cross-validation (GCV) for smoothing parameter selection in semiparametric regression. However, existing REML or marginal likelihood (ML) based methods for semiparametric generalized linear models (GLMs) use iterative REML or ML estimation of the smoothing parameters of working linear approximations to the GLM. Such indirect schemes need not converge and fail to do so in a non-negligible proportion of practical analyses. By contrast, very reliable prediction error criteria smoothing parameter selection methods are available, based on direct optimization of GCV, or related criteria, for the GLM itself. Since such methods directly optimize properly defined functions of the smoothing parameters, they have much more reliable convergence properties. The paper develops the first such method for REML or ML estimation of smoothing parameters. A Laplace approximation is used to obtain an approximate REML or ML for any GLM, which is suitable for efficient direct optimization. This REML or ML criterion requires that Newton–Raphson iteration, rather than Fisher scoring, be used for GLM fitting, and a computationally stable approach to this is proposed. The REML or ML criterion itself is optimized by a Newton method, with the derivatives required obtained by a mixture of implicit differentiation and direct methods. The method will cope with numerical rank deficiency in the fitted model and in fact provides a slight improvement in numerical robustness on the earlier method of Wood for prediction error criteria based smoothness selection. Simulation results suggest that the new REML and ML methods offer some improvement in mean-square error performance relative to GCV or Akaike's information criterion in most cases, without the small number of severe undersmoothing failures to which Akaike's information criterion and GCV are prone. This is achieved at the same computational cost as GCV or Akaike's information criterion. The new approach also eliminates the convergence failures of previous REML- or ML-based approaches for penalized GLMs and usually has lower computational cost than these alternatives. Example applications are presented in adaptive smoothing, scalar on function regression and generalized additive model selection.
Book
The first edition of this book has established itself as one of the leading references on generalized additive models (GAMs), and the only book on the topic to be introductory in nature with a wealth of practical examples and software implementation. It is self-contained, providing the necessary background in linear models, linear mixed models, and generalized linear models (GLMs), before presenting a balanced treatment of the theory and applications of GAMs and related models. The author bases his approach on a framework of penalized regression splines, and while firmly focused on the practical aspects of GAMs, discussions include fairly full explanations of the theory underlying the methods. Use of R software helps explain the theory and illustrates the practical application of the methodology. Each chapter contains an extensive set of exercises, with solutions in an appendix or in the book’s R data package gamair, to enable use as a course text or for self-study.
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Secondary sexual traits in males of polygynous species are important determinants of reproductive success. It is, however, unknown if and how the development of continuously growing traits at different life-stages is related to reproduction in long-lived male mammals. In this study, we evaluated the relationship of early and late horn growth on social status and reproduction in long-lived male Alpine ibex (Capra ibex). For this, we analysed individual horn growth and assessed its effect on dominance and reproduction. No evidence was detected for compensatory horn growth, as late-life horn growth positively depended on early-life horn growth in males. Still, individuals with longer horn segments grown during early adulthood experienced a stronger age-dependent length decline in annual horn growth during the late development. Accordingly, a divergence between individual growth potential and realized horn growth late in life has to be assumed. Residual age-specific horn length and length of early grown horn segments both positively affected dominance and reproductive success, whereas, contrary to our expectation, no significant effect of the length of horn segments grown during the late development was detected. Suspected higher somatic costs incurred by high-quality males during their late development might at least partly be responsible for this finding. Overall, our study suggests that the total length of horns and their early development in long-lived male Alpine ibex is a reliable indicator of reproductive success and that individuals may be unable to compensate for poor early-life growth performance at a later point in life.
Article
Clarifying the emergent fitness associated with sexually selected traits under the current, increasingly anthropogenic selection regimes is important to understand ongoing evolutionary changes in nature and inform the conservation management of endangered species. Several reasons exist why sexual selection may affect extinction risk. Increased risk may result either from inherent trade‐offs between sexually selected traits and viability traits or from selective hunting of sexually selected species. Reduced risk is also possible, for instance if the preference for high‐performing mates characteristic of sexually selected species has beneficial genetic consequences for the population. Here, I show that the threat level of bovid species increases with large male horn size. This is the first time, to my knowledge, that sexually selected weaponry has been shown to increase extinction risk at the interspecific level. However, threat level was unrelated to another trait under sexual selection, sexual body size dimorphism, indicating that the effect of sexual selection on extinction risk depends on trait‐specific interactions with extrinsic factors. The results suggest that the higher threat level of long‐horned species is not primarily due to current trophy hunting practices and rather point to environmentally induced viability costs as a possible main driver. Still, the fact that long‐horned species are known to be preferred by trophy hunters highlights the importance of continuously monitoring trophy hunting practices to assure their long‐term sustainability.
Article
In red deer, yearling antler length is a largely nutrition-mediated phenotypic character, and is therefore sometimes used as an indirect estimate of range quality and population condition. However, the parameters affecting yearling antler length have been little studied. We analyse the contributions of density, weather and maternal effects on yearling antler length of 581 individual stags born 1970-1996 on the Isle of Rum (Scotland). We show that antler length is a good measure of yearling condition: the probability of overwinter survival in yearlings that developed antlers was 3 times higher than for yearlings that did not develop antlers, and yearling antler length was correlated with the number of antler points the following year. Between years, variation in yearling antler length was best explained by variation in red deer density and June temperature at 12 months of age. Both of these variables were negatively correlated with antler length, and most likely this effect is due to changes in nutrient availability. Population density affects biomass availability for the individual, while low temperatures in early summer prolong the availability of high forage quality. At the individual level, antler length increased with birth weight and decreased with birth date, reflecting the persistent and pervasive influence of conditions in early life.
Article
Reintroductions and other conservation translocations have become increasingly important conservation tools, albeit with variable success. Genetic variation is one factor, which may influence reintroduction success. Genetic variation in reintroduced populations can be augmented by increasing the number of founders or by admixing animals from different source populations. At present there is no clear understanding of the relative importance of the two. Here we address this question by combining detailed demographic information about the reintroduction history of 40 Alpine ibex populations with genetic data from neutral markers, including coalescent-based estimates of the number of genetic founders. Number of genetic founders was a better predictor of present-day genetic variation than number of released founders, indicating that differential survival of founders can substantially affect the genetic variation of reintroduced populations. The degree of admixture in the founder group had about twice as much impact on genetic variation than the number of founders. Thus, to maintain genetic variation in reintroduced populations, releasing animals from different sources might be more important than releasing many animals from a single source. This even applies to cases such as the Alpine ibex where all individuals descended from a single ancestral population, and where the admixture was only between sub-populations created by the reintroduction program and thus between populations with relatively little genetic differentiation.
Article
In West and Central Africa large carnivores have become increasingly rare as a consequence of rapid habitat destruction and lack of resources for protected area management. The Bénoué Complex (23,394km2) in northern Cameroon is a regionally critical area for large mammal conservation. In the complex lions (Panthera leo), leopards (Panthera pardus) and spotted hyenas (Crocuta crocuta) are formally protected in three national parks and 28 hunting zones. Over-hunting may be having a strong additive effect precipitating declines in large carnivore numbers across the complex. We used a coarse level track index method to estimate the relative abundance of these three species both in hunting zones and national parks. The results were interpreted with respect to ungulate abundance, and hunting impact. There was no significant difference between the densities of medium to larger species of ungulates in the hunting zones and the national parks, and no difference in leopard and spotted hyena densities in the respective areas. However, lions occurred at significantly lower densities in the hunting zones, and even in the national parks occurred at significantly lower densities than prey biomass would predict.
Article
The comparison of two treatments generally falls into one of the following two categories: (a) we may have a number of replications for each of the two treatments, which are unpaired, or (b) we may have a number of paired comparisons leading to a series of differences, some of which may be positive and some negative. The appropriate methods for testing the significance of the differences of the means in these two cases are described in most of the textbooks on statistical methods.
Article
Large horns or antlers require a high energy allocation to produce and carry both physiological and social reproductive costs. Following the principle of energy allocation that implies trade-offs among fitness components, growing large weapons early in life should thus reduce future growth and survival. Evidence for such costs is ambiguous, however, partly because individual heterogeneity can counterbalance trade-offs. Individuals with larger horns or antlers may be of better quality and thus have a greater capacity to survive. We investigated trade-offs between male early horn growth and future horn growth, baseline mortality, onset of actuarial senescence, and rate of ageing in an Alpine ibex (Capra ibex ibex) population. Horn growth of males in early life was positively correlated to their horn length throughout their entire life. Cohort variation and individual heterogeneity both accounted for among-individual variation in horn length, suggesting both long-lasting effects of early life conditions and individual-specific horn growth trajectories. Early horn growth did not influence annual survival until 12 years of age, indicating that males do not invest in horn growth at survival costs over most of their lifetime. However, males with fast-growing horns early in life tended to have lower survival at very old ages. Individual heterogeneity, along with the particular life-history tactic of male ibex (weak participation to the rut until an old age after which they burn out in high mating investment), are likely to explain why the expected trade-off between horn growth and survival does not show up, at least until very old ages.
Article
Horn growth in the Caprinae is affected by several factors including age and nutrition, and analysis of annual horn increments can be used to interpret past events. We documented patterns of horn growth in male alpine ibexes (Capra ibex ibex) in the central European Alps and analyzed relationships between annual horn increments, weather, and plant phenology in 2 different climatic regions during 1981-1990. Age accounted for 50% of total variance in horn growth in male alpine ibexes 1-6 years of age. Horn growth differed among climatic regions and calendar years. In years with early onset of vegetation growth, horn growth was enhanced uniformly over all age classes in both climatic regions. Horn growth was a function of ambient temperature during March-May and of plant phenology in spring, implicating onset of growth of vegetation and availability of food resources. Duration of growth of vegetation was assumed to be directly related to date of vegetation onset, but further studies are necessary to test this hypothesis.
Article
Senescence can be defined as accelerating phenotypic deterioration with old age. For traits that grow throughout life, such as the horns of some ungulates, senescence may be expressed as a decrease in annual growth rates, or an increase in asymmetry, in the years preceding death. Age-specific yearly horn-growth segments of 378 male Alpine ibex Capra ibex L. that died from natural causes were analysed in the Gran Paradiso National Park (Italian Alps). Horn annuli displayed fluctuating asymmetry. The hypothesis that asymmetry and size of the annuli of the horns could predict annual survival probability was tested. It was found that between 5 and 11 years of age, male ibex that grew shorter annuli than the average for the population had a greater probability of mortality over the following years than those with greater rates of horn growth. Horn asymmetry and mortality rates were not significantly correlated. Annulus size, reflecting the onset of senescence, seemed to be a better indicator of individual q
Article
1. Harvesting of large mammals is usually not random, and directional selection has been identified as the main cause of rapid evolution. However, selective harvesting in meat and recreational hunting cultures does not automatically imply directional selection for trait size. 2. Harvesting selectivity is more than a matter of hunter preference. Selection is influenced by management regulations, hunting methods, animal trait variance, behaviour and abundance. Most studies of hunter selection only report age- or sex-specific selection, or differences in trait size selection among hunting methods or groups of hunters, rather than trait size relative to the age-specific means required for directional selection. 3. Synthesis and applications. Managers aiming to avoid rapid evolution should not only consider directional selection and trophy hunting but also mitigate other important evolutionary forces such as harvesting intensity per se, and sexual selection processes that are affected by skewed sex ratios and age structures.
Article
Recent work by Reiss and Ogden provides a theoretical basis for sometimes preferring restricted maximum likelihood (REML) to generalized cross-validation (GCV) for smoothing parameter selection in semiparametric regression. However, existing REML or marginal likelihood (ML) based methods for semiparametric generalized linear models (GLMs) use iterative REML or ML estimation of the smoothing parameters of working linear approximations to the GLM. Such indirect schemes need not converge and fail to do so in a non-negligible proportion of practical analyses. By contrast, very reliable prediction error criteria smoothing parameter selection methods are available, based on direct optimization of GCV, or related criteria, for the GLM itself. Since such methods directly optimize properly defined functions of the smoothing parameters, they have much more reliable convergence properties. The paper develops the first such method for REML or ML estimation of smoothing parameters. A Laplace approximation is used to obtain an approximate REML or ML for any GLM, which is suitable for efficient direct optimization. This REML or ML criterion requires that Newton-Raphson iteration, rather than Fisher scoring, be used for GLM fitting, and a computationally stable approach to this is proposed. The REML or ML criterion itself is optimized by a Newton method, with the derivatives required obtained by a mixture of implicit differentiation and direct methods. The method will cope with numerical rank deficiency in the fitted model and in fact provides a slight improvement in numerical robustness on the earlier method of Wood for prediction error criteria based smoothness selection. Simulation results suggest that the new REML and ML methods offer some improvement in mean-square error performance relative to GCV or Akaike's information criterion in most cases, without the small number of severe undersmoothing failures to which Akaike's information criterion and GCV are prone. This is achieved at the same computational cost as GCV or Akaike's information criterion. The new approach also eliminates the convergence failures of previous REML-or ML-based approaches for penalized GLMs and usually has lower computational cost than these alternatives. Example applications are presented in adaptive smoothing, scalar on function regression and generalized additive model selection.
Article
In the following report the settlement dynamics of alpine ibex since the time of its near extinction during the 19th century are outlined and the actual distribution of this species freely living in the Alps is presented on a map. The last ibex surviving into the 20th century were confined to the Graj Alps. In 1906 pure fawns could be obtained from poachers from the region of Gran-Paradiso. In 1911 the first ibex raised in captivity (St. Gallen) could be released into the wild. This species has also been bred since 1915 in the nature park Harder near Interlaken. Three of the 12 free living colonies founded by 1938 showed an unexpectedly rapid development, while others remained comparatively small, and some even vanished completely. The paramount importance of environment for the successful settlement of this species was recognized. The catching of free living ibex permitted the rapid establishment of new colonies. These colonies were established also with the aim of limiting the damage inflicted upon forests and croplands. Until the mid 1970s no hunting was deemed necessary to control the populations. Today the alpine ibex is distributed throughout the entire Alps; from the Sea Alps in the West to the Styrian Limestone Alps and Karawank Alps in the East and can be found in all alpine countries. The total population amounts to 24,000–28,000 animals. The species can be considered safe from extinction under present circumstances, although the significance of the low genetic variability of some populations has not been fully evaluated. Measures for the proper management of this species have become more important since the carrying capacity has been reached for those areas deemed suitable habitats, and since some countries report overpopulated colonies.