Article

Evolutionary responses to harvesting in ungulates

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Abstract

1. We investigate the evolutionary responses to harvesting in ungulates using a state-dependent, stochastic, density-dependent individual-based model of red deer Cervus elaphus (L.) females subject to different harvesting regimes. 2. The population's mean weight at first reproduction shifts towards light weights as harvesting increases, and its distribution changes from a single peak distribution under very low or high harvest rates, to a bimodal distribution under intermediate harvest rates. 3. These results suggest that, consistent with previous studies on aquatic species, harvesting-induced mortality may drive adaptive responses in ungulates by reducing the fitness benefits from adult survival and growth in favour of early and lightweight reproduction. 4. Selective harvesting for heavy animals has no additional effect on the evolutionarily stable strategy, suggesting that harvest rate is more important than the degree of selectivity in driving adaptive responses. However, selective harvesting of light females is positively associated with maturation weights even higher than those of a nonharvested population, probably due to the reduction in the fitness value of the offspring. 5. The average number of weight at maturation strategies in the population declines but the total number of strategies across all simulations increases with harvest rate, suggesting that harvesting-induced selection on weight at maturity overcomes the increase in strategy diversity expected from density-dependent release. 6. Yield initially increases with harvesting due to enhanced productivity of light females experiencing density-dependent release. However, it crashes under intense harvesting resulting in a population skewed to light, young and, therefore, less reproductive animals.

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... In several ungulate populations in Europe and North America, sport hunting is the main cause of adult mortality (Langvatn & Loison 1999;McCorquodale 1999;Ballard et al. 2000;Festa-Bianchet 2003;Mysterud, Solberg & Yoccoz 2005;Milner et al. 2006). Harvest may have strong effects on population dynamics (Milner, Nilsen & Andreassen 2007;Femberg & Roy 2008), and potential evolutionary effects on phenotype and life-history traits [ (Proaktor, Coulson & Milner-Gulland 2007;Pigeon et al. 2016), but see (Mysterud 2011;Rivrud et al. 2013)]. In ungulates, survival of adult females has higher elasticity for population growth compared to reproductive parameters or to survival of other age-sex classes (Gaillard, Festa-Bianchet & Yoccoz 1998;Gaillard et al. 2000). ...
... Intense harvest of pre-reproductive females and selective harvest of non-lactating adult females may also have long-term evolutionary consequences on reproductive strategies (Proaktor, Coulson & Milner-Gulland 2007). Lifetime reproductive success should have low heritability because genes that increase fitness should be rapidly fixed (Fisher 1958;Mousseau & Roff 1987). ...
... The harvest-induced decrease in life expectancy should select for high reproductive investment in early life. Although simulations support this hypothesis (Proaktor, Coulson & Milner-Gulland 2007), there is no empirical evidence for it (Mysterud, Yoccoz & Langvatn 2009). Early primiparity may reduce future reproduction and possibly survival ). ...
Article
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Female ungulates are often selectively harvested according to their reproductive status. Because ungulate population growth depends heavily on adult female survival, it is crucial to understand the effects of this selective harvest. Recent studies revealed persistent individual differences in female reproductive potential, with a positive correlation of reproductive success over consecutive years. If current reproduction is correlated with lifetime reproductive success, then selective harvest of non-lactating females should remove individuals of low reproductive potential, with lower impact on population growth than random harvest. If lifetime reproductive success has a genetic basis, selective harvest may also increase the proportion of successful females. We used an individual-based model to understand the short-term effects of harvest intensity and hunter selectivity on population dynamics, accounting for both heterogeneity in reproductive potential and orphan survival. We also explored the long-term effect of harvest as a selective pressure on female heterogeneity. Selective harvest of non-lactating females reduced survival to primiparity compared to random harvest, because of high harvest rates of pre-reproductive females. After primiparity, however, females of higher reproductive potential had higher survival under selective than random harvest. Therefore, the overall effect on population dynamics depends on a trade-off between a high harvest of pre-reproductive females and a reduced harvest of reproductive females with high reproductive potential. Female heterogeneity and the length of the pre-reproductive period affected this trade-off. Over the short term, high heterogeneity in reproductive potential of pre-reproductive females made selective harvest the most effective strategy to maintain a high population growth rate. With low heterogeneity and little effects of orphaning on juvenile mortality, however, random harvest had a lower impact on population growth than selective harvest. Over the long term, selective female harvest may increase the proportion of successful reproducers in the population. Synthesis and applications. Selective harvests of non-lactating females appear justified only if female heterogeneity in reproductive potential and/or orphan mortality are very high. Because pre-reproductive females will be subject to intense harvest, selective harvest may reduce population growth rate compared to random harvest in species with late primiparity, especially if most pre-reproductive female normally survive to primiparity. When heterogeneity in reproductive potential and orphan mortality are low, random female harvest appears preferable to selective harvest. Female ungulates are often selectively harvested according to their reproductive status. Because ungulate population growth depends heavily on adult female survival, it is crucial to understand the effects of this selective harvest. Recent studies revealed persistent individual differences in female reproductive potential, with a positive correlation of reproductive success over consecutive years. If current reproduction is correlated with lifetime reproductive success, then selective harvest of non-lactating females should remove individuals of low reproductive potential, with lower impact on population growth than random harvest. If lifetime reproductive success has a genetic basis, selective harvest may also increase the proportion of successful females. We used an individual-based model to understand the short-term effects of harvest intensity and hunter selectivity on population dynamics, accounting for both heterogeneity in reproductive potential and orphan survival. We also explored the long-term effect of harvest as a selective pressure on female heterogeneity. Selective harvest of non-lactating females reduced survival to primiparity compared to random harvest, because of high harvest rates of pre-reproductive females. After primiparity, however, females of higher reproductive potential had higher survival under selective than random harvest. Therefore, the overall effect on population dynamics depends on a trade-off between a high harvest of pre-reproductive females and a reduced harvest of reproductive females with high reproductive potential. Female heterogeneity and the length of the pre-reproductive period affected this trade-off. Over the short term, high heterogeneity in reproductive potential of pre-reproductive females made selective harvest the most effective strategy to maintain a high population growth rate. With low heterogeneity and little effects of orphaning on juvenile mortality, however, random harvest had a lower impact on population growth than selective harvest. Over the long term, selective female harvest may increase the proportion of successful reproducers in the population. Synthesis and applications. Selective harvests of non-lactating females appear justified only if female heterogeneity in reproductive potential and/or orphan mortality are very high. Because pre-reproductive females will be subject to intense harvest, selective harvest may reduce population growth rate compared to random harvest in species with late primiparity, especially if most pre-reproductive female normally survive to primiparity. When heterogeneity in reproductive potential and orphan mortality are low, random female harvest appears preferable to selective harvest.
... Nowadays, human harvest is the most important mortality factor for wild ungulates in Europe Since selective hunting could differ considerably from natural mortality, among which predation is usually the most important cause , there is a growing concern about possible negative side-effects of human harvest (Ginsberg and Milner-Gulland 1994;Proaktor et al. 2007;Apollonio et al. 2010). However, there have been few attempts to compare ungulate mortality patterns between human harvest and natural predation within the same ecosystem (but see for example ). ...
... However, such diversity may not be something unwanted. Since researchers are becoming increasingly concerned about negative evolutionary and genetic side-effects of selection in human harvest (Harris et al. 2002;Festa-Bianchet 2003;Proaktor et al. 2007), diversity in hunting systems may mitigate some of these negative effects on a larger scale and especially in transboundary populations that are under the influence of different management regimes. Such an example was already observed in a transboundary brown bear population, where different hunting restrictions in the two neighbouring countries seem to buffer strong demographic effects of selective hunting in one of the countries (Krofel et al. 2012a). ...
... Apollonio et al. 2010). Hunting can strongly affect demographic parameters(Langvatn and Loison 1999; Ginsberg and Milner-Gulland 1994), genetic(Harris et al. 2002) and morphological characteristics(Coltman et al. 2003), reproduction, social structure, behavior and evolution of ungulates in the harvested populations(Festa-Bianchet 2003;Milner et al. 2007;Apollonio et al. 2010;Mysterud 2010;Proaktor et al. 2007;Ciuti et al. 2012). ...
Thesis
Full-text available
Interspecific interactions are often the key factor affecting structure of animal communities. In this study we obtained first precise data on several predation aspects of Eurasian lynx (Lynx lynx) in the Dinaric Mountains, tested applicability of new methods for monitoring interspecific interactions in lynx and explored interactions between lynx and scavengers, especially effects of kleptoparasitism by brown bears (Ursus arctos). Dinaric lynx mainly hunted European roe deer (Capreolus capreolus) and, in contrast to other regions in Europe, also frequently fed on the edible dormice (Glis glis). We successfully applied analysis of GPS location clusters method to study ecology of the Eurasian and demonstrated the possibility for remote estimation of kill rates using this approach. Compared to the human harvest, lynx more often killed roe deer in poor nutritional condition, adult animals and adult females. We observed stronger demographic selection in predation on red deer (Cervus elaphus). Average lynx kill rate was estimated to 48 roe deer/year and was lower than the current human harvest. We estimated that lynx could on average kill up to 14% of local roe deer density. While human harvest increased with higher roe deer density, lynx predation was similar across the gradient of roe deer densities. Predators may have an important role in buffering unwanted side-effects of harvest of wild ungulates. Among scavengers, it seems that the brown bear has the strongest influence on the Eurasian lynx. Effects of the bear kleptoparasitism depend on the proportion of lynx kills found by bears and the time when bears find prey remains. In the Dinaric Mountains, brown bears found 32% of lynx prey remains and 15% of all biomass of large prey killed by lynx was lost to bears. In response, lynx increased their kill rate by 23% but were able to compensate for only 59% of the losses. The frequency of bear scavenging was strongly dependent on bear activity patterns. We suggest that ursid scavenging, by promoting the hunting of smaller prey, may have played an important role in the evolution of the Lynx genus as well as other predators in the Holarctic. Data available so far indicate relatively low level of competition between gray wolves and Eurasian lynx.
... Nowadays, human harvest is the most important mortality factor for the wild ungulates in Europe (Festa-Bianchet 2003;Apollonio et al. 2010). Hunting can strongly affect demographic parameters (Langvatn and Loison 1999;Ginsberg and Milner-Gulland 1994), genetic (Harris et al. 2002) and morphological characteristics (Coltman et al. 2003), reproduction, social structure, behavior, and evolution of ungulates in the harvested populations (Festa-Bianchet 2003;Milner et al. 2007;Proaktor et al. 2007;Apollonio et al. 2010;Mysterud 2010;Ciuti et al. 2012). Since selective hunting could differ considerably from natural mortality, among which predation is usually the most important cause (Jedrzejewski et al. 2011), there is a growing concern about possible negative side effects of human harvest (Ginsberg and Milner-Gulland 1994;Proaktor et al. 2007;Apollonio et al. 2010). ...
... Hunting can strongly affect demographic parameters (Langvatn and Loison 1999;Ginsberg and Milner-Gulland 1994), genetic (Harris et al. 2002) and morphological characteristics (Coltman et al. 2003), reproduction, social structure, behavior, and evolution of ungulates in the harvested populations (Festa-Bianchet 2003;Milner et al. 2007;Proaktor et al. 2007;Apollonio et al. 2010;Mysterud 2010;Ciuti et al. 2012). Since selective hunting could differ considerably from natural mortality, among which predation is usually the most important cause (Jedrzejewski et al. 2011), there is a growing concern about possible negative side effects of human harvest (Ginsberg and Milner-Gulland 1994;Proaktor et al. 2007;Apollonio et al. 2010). However, there have been surprisingly few studies comparing ungulate mortality patterns between human harvest and natural predation within the same ecosystem (but see for example Wright et al. 2006 and Andersen et al. 2007). ...
... However, such diversity may not be something unwanted. Since researchers are becoming increasingly concerned about negative evolutionary and genetic side effects of selection in human harvest (Harris et al. 2002;Festa-Bianchet 2003;Proaktor et al. 2007), diversity in hunting systems may mitigate some of these negative effects on a larger scale and especially in transboundary populations that are under the influence of different management regimes. Such an example was already observed in a transboundary brown bear population, where different hunting restrictions in the two neighbouring countries seem to buffer strong demographic effects of selective hunting in one of the countries . ...
Conference Paper
Predation has an important role in many community interactions. It may affect the population structure and also the evolution of the prey species, especially if hunting is selective towards particular individuals. Roe deer (Capreolus capreolus) represents the main prey species of Eurasian lynx (Lynx lynx) throughout most parts of Europe, therefore predation by lynx may have important impact on roe deer populations. We will present results of a study on lynx predation in Northern Dinaric Mountains. Through inspection of prey remains we determined the importance of roe deer as a prey species for lynx in this area and tested the hypothesis that lynx selectively kills particular individuals within individual prey species. According to the results lynx positively selected roe deer, which was also the most important prey species for lynx in Northern Dinaric Mountains. Analysis of fat content in a bone marrow of roe deer showed that lynx preferentially killed animals in poor condition. Besides, the average marrow fat content was lower in roe deer killed by prey lynx compared to those that died in traffic accidents. Using values from the analysis of marrow fat content we also estimated the proportion of compensatory mortality among the mortality sustained by lynx predation. We determined sex and age structure of killed animals, which differed among different prey species. In larger species a selection towards females and younger animals was observed, which is consistent with the predictions of the theory of selective predation. In roe deer no obvious selection towards particular age or sex class was observed. Thus the lynx predation upon roe deer appears to affect more the size of deer population and to a lesser extent its demographic structure. Through selective killing of substandard individuals lynx predation may also have important role in the natural selection of roe deer.
... Many studies investigating trade-offs between offspring mass and number consider the average effect of litter/clutch size [9][10][11][12][13] assuming that, in a given environment, parents should produce an optimal number of offspring [9] and allocate resources equally among them [3]. This assumption is challenged however by empirical observations showing large within litter/clutch variation in offspring mass [14]. ...
... Although it is easily conceivable that size-selective harvest regimes can alter patterns of natural selection and cause demographic changes in wildlife populations, such effects are usually less expected and thereby less studied in harvest regimes that are not size selective 9 . However, theoretical models show that size-independent harvest can also induce selective pressures on life history traits [10][11][12][13] , and recent empirical work has documented harvest selectivity for age, sex, and behavioral traits in the wild [14][15][16] . Despite its importance for management, we still know very little about the consequences of such selectivity on population processes. ...
... Beside the impact of natural predation, human hunting is the most important mortality factor ) influencing demographic parameters (Langvatn & Loison, 1999), genetic - ( Harris et al., 2002) and social structure, reproduction and behavior of wild ungulates in Europe Proaktor et al., 2007;Milner et al., 2007). Different hunting systems exist throughout Europe including different hunting intensity, restrictions and practices concerning hunting season and demographic structure of harvested animals (Putman, 2010). ...
... Nowadays, human hunting builds the most important mortality factor for wild ungulates in Europe and are therefore strongly affecting the biology of populations . Researchers are becoming increasingly concerned about negative evolutionary and genetic side effects caused by selection of hunters (Harris et al., 2002;Proaktor et al., 2007) which can be buffered by predators like the lynx. Lynx predation could e.g. ...
Thesis
In the field of wildlife biology, the understanding of large predator-ungulate relationships is crucial especially for the management of wildlife and forest. Only few studies analyzed predations pattern of the Eurasian lynx Lynx lynx on ungulates which build the main prey species for lynx in Europe. This study examined the predation pattern of reintroduced lynx on roe deer Capreolus capreolus and red deer Cervus elaphus within the years 2006 – 2016 in the Harz Mountains, Germany. Besides, a comparison was conducted between lynx-killed and hunted animals of both species to detect potential differences in hunting preferences. For the analysis, 224 lynx kills (177 roe deer, 47 red deer) and 174 hunted animals (61 roe deer, 113 red deer) were analyzed regarding the sex, age and relative condition. The study revealed that lynx prefer to hunt mostly adult roe deer (54 %) and among them more females (72 %) than males while no sign for a lynx preference for malnourished animals was found. Furthermore, male and female lynx did not differ in their preferences. Compared to hunted roe deer, differences were detected since more adult females were collected for lynx while yearlings of both sexes built the majority of hunting bags. Among red deer, lynx kills comprised mostly calves and females while indicating no poor physical condition. Red deer killed by male lynx comprised both sexes while kills of female lynx included only females. No adult male red deer were found. In contrast, hunted animals indicated no preference for any sex or age group while femur fat content was higher compared to lynx kills. Observed lynx preferences for roe deer and red deer may indicate a selective pattern of lynx in the Harz Mountains. However, no statements about the selectivity of lynx are currently possible due to missing information about the standing prey populations. Having that in mind, it can only be assumed that lynx have a strong effect on roe deer population due to the preference for adult females. In contrast, the preference for red deer calves would not have a significant impact regarding the population dynamics since reproducing females are not influenced. Next to the hunt, lynx preference for roe deer may be additive and should be therefore considered for the hunting schedules when selection will be evidenced. In conclusion, hunting preferences of both predators differ which indicate that hunting does not replace natural predation at all.
... Adaptive evolution on ecological time scales (microevolution) is strongly influenced by the standing level of additive genetic variance and selection expressed as the covariance of phenotype and fitness (Price, 1972;Lande, 1979). In exploited populations, the natural direction of evolutionary changes may be substantially affected by the phenotypic characteristics of harvested individuals and the increased mortality added by harvesting (Saether et al., 2001;Law, 2007;Proaktor et al., 2007;Allendorf and Hard, 2009;Darimont et al., 2009;Engen et al., 2014b). Sustainable harvest strategies should consequently include considerations of how harvest selection might interfere with natural selection and how this in turn will affect phenotypic evolution (Dunlop et al., 2009;Hutchings, 2009;Hendry et al., 2011;Kuparinen and Hutchings, 2012;Laugen et al., 2014). ...
... The strength and form of selection resulting from harvest-induced and natural causes of mortality and fecundity, and which age classes are more strongly affected, are important determinants for the outcome of selective harvest Edeline et al., 2007;Proaktor et al., 2007;Mysterud, 2011;Olsen and Moland, 2011;Engen et al., 2012Engen et al., , 2014b. In age-structured populations, the contribution of an individual to future generations (reproductive value) depends on age-specific transitions among different phenotypic categories affecting their fecundity and survival (Caughley, 1966;Caswell, 2001;Coulson et al., 2010;Saether et al., 2013). ...
Article
Empirical evidence strongly indicates that human exploitation has frequently led to rapid evolutionary changes in wild populations, yet the mechanisms involved are often poorly understood. Here we applied a recently developed demographic framework for analysing selection to data from a 20-year study of a wild population of moose, Alces alces. In this population, a genetic pedigree has been established all the way back to founders. We demonstrate harvest-induced directional selection for delayed birth dates in males and reduced body mass as calf in females. During the study period, birth date was delayed by 0.81 days per year for both sexes, while no significant changes occurred in calf body mass. Quantitative genetic analyses indicated that both traits harboured significant additive genetic variance. These results show that selective harvesting can induce strong selection which oppose natural selection. This may cause evolution of less favourable phenotypes that become maladaptive once harvesting ceases. This article is protected by copyright. All rights reserved.
... This is an important yet complicating finding with respect to the interpretation of how individual respond to climate. The fact that females allocated slightly more to reproduction (R), and consequently less to survival (S), when climatic conditions were harsh/detrimental was unexpected (e.g., Adams, 2005), but can be explained by how density dependence was implemented through the gain function (Bårdsen et al., 2011: S1;Proaktor, Coulson, & Milner-Gulland, 2007): density constrain the realized value a given allocation had on offspring (R) and female (S) autumn body mass. In sum, this means that density did not restrict allocation in the harsh/detrimental environments where density was low, as opposed to the high density found in the more beneficial/ benign environments. ...
... In northern Fennoscandia, for example, high reindeer abundance results in smaller animals that are more vulnerable to unfavorable conditions Tveraa et al., 2007) as they are most likely to die anyway (e.g., Tveraa et al., 2003). Predators typically target small, young, and weakened individuals while human slaughter strategies comes in many forms depending on the way animals are selected for harvest (e.g., Naess, Bårdsen, & Tveraa, 2012;Proaktor et al., 2007). The evolutionary impacts of predation and harvest might thus dramatically differ. ...
Article
Full-text available
If we want to understand how climate change affects long-lived organisms, we must know how individuals allocate resources between current reproduction and survival. This trade-off is affected by expected environmental conditions, but the extent to which density independent (DI) and density dependent (DD) processes interact in shaping individual life histories is less clear. Female reindeer (or caribou: Rangifer tarandus) are a monotocous large herbivore with a circumpolar distribution. Individuals that experience unpredictable and potentially harsh winters typically adopt risk averse strategies where they allocate more resources to building own body reserves during summer and less to reproduction. Such a strategy implies that the females do not reproduce or that they produce fewer or smaller offspring. A risk averse strategy thus results in females with large autumn body reserves, which is known to increase their survival probabilities if the coming winter is harsh. In contrast, females experiencing predictable winters may adopt a more risk prone strategy in which they allocate more resources to reproduction as they do not need as many resources to buffer potentially adverse winter conditions. This study uses a seasonal state-dependent model showing that DD and DI processes interact to affect the evolution of reproductive strategies and population dynamics for reindeer. The model was run across a wide range of different winter climatic scenarios: One set of simulations where the average and variability of the environment was manipulated and one set where the frequency of good and poor winters increased. Both reproductive allocation and population dynamics of reindeer were affected by a combination of DI and DD processes even though they were confounded (harsh climates resulted in lowered density). Individual strategies responded, in line with a risk sensitive reproductive allocation, to climatic conditions and in a similar fashion across the two climatic manipulations.
... Although it is easily conceivable that size-selective harvest regimes can alter patterns of natural selection and cause demographic changes in wildlife populations, such effects are usually less expected and thereby less studied in harvest regimes that are not size selective 9 . However, theoretical models show that size-independent harvest can also induce selective pressures on life history traits [10][11][12][13] , and recent empirical work has documented harvest selectivity for age, sex, and behavioral traits in the wild [14][15][16] . Despite its importance for management, we still know very little about the consequences of such selectivity on population processes. ...
... Prolonged maternal care provides a buffer against high hunting pressure, as it protects adult females, which are the most productive segment of the population 37 , as well as yearlings, which are the most vulnerable individuals 28 . This implies that the relative frequency of female reproductive tactics may alternate over time in the population depending on the level of human exploitation, as previously suggested by a mathematical modeling based on red deer (Cervus elaphus) life histories 11 . Over our 22-year study period and under intermediate values of hunting pressure, both tactics showed similar fitness, which suggests that the two phenotypes will likely be maintained in the population, as it is the case in many other brown bear populations 49,50 . ...
Article
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As an important extrinsic source of mortality, harvest should select for fast reproduction and accelerated life histories. However, if vulnerability to harvest depends upon female reproductive status, patterns of selectivity could diverge and favor alternative reproductive behaviors. Here, using more than 20 years of detailed data on survival and reproduction in a hunted large carnivore population, we show that protecting females with dependent young, a widespread hunting regulation, provides a survival benefit to females providing longer maternal care. This survival gain compensates for the females' reduced reproductive output, especially at high hunting pressure, where the fitness benefit of prolonged periods of maternal care outweighs that of shorter maternal care. Our study shows that hunting regulation can indirectly promote slower life histories by modulating the fitness benefit of maternal care tactics. We provide empirical evidence that harvest regulation can induce artificial selection on female life history traits and affect demographic processes.
... High-yield harvesting regimes have been shown to cause the rapid and often unwanted evolution of life history traits, including growth rates, biomass productivity and body size, in harvested populations (Hendry et al. 2011). These populations are usually sexually reproducing vertebrates (game animals, ungulates and fish; Conover and Munch 2002;Coltman et al. 2003;Garel et al. 2007;Proaktor et al. 2007;Enberg et al. 2009) or plants (Law and Salick 2005;Mooney and McGraw 2009) with relatively long generation times, for whom evolutionary change relies largely on standing genetic variation (Hendry et al. 2011). Yet for clonal organisms, generation times are often poorly defined and mutations, or other sources of novel variation arising in somatic growth, may contribute to evolutionary change when standing variation is low or depleted (Gill et al. 1995;Fagerström et al. 1998;Orive 2001). ...
... Despite significant potential for continual high-yield harvesting to exert selective pressures on life history traits (Law 2000;Reznick and Ghalambor 2005;Proaktor et al. 2007;Enberg et al. 2009;Hendry et al. 2011), its potential impacts beyond Week 12 ...
Article
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Plastic changes in the growth and productivity of algae in response to environment and stocking density are well established. In contrast, the capacity for such changes to persist once environmental differences cease, potentially signalling an evolutionary response, have rarely been tested for algae in intensive production systems. We tested whether continuous differences in harvesting regime (a high stocking density/low-yield regime versus low stocking density/high-yield regime) generated changes in biomass productivity and other growth metrics within several strains of the clonal macroalga Oedogonium (Chlorophyta, Oedogoniales) and whether such changes persisted once differential harvesting yields ceased. We found considerable plasticity in growth rate and biomass productivity over a 12-week period of active selection (i.e. repeated high-yield and low-yield harvesting of clonal lineages within strains) and that strains responded differently to this selection pressure over time. While small, but significant, differences in growth rates of clonal lineages exposed to high-yield vs low-yield harvesting regimes were maintained after prolonged culture under a common selection regime (i.e. medium-yield harvesting), differences in biomass productivity were not. There was no evidence for positive or negative effects of maintaining multiple strains in polyculture on growth and biomass productivity. Overall, we detected limited potential for evolutionary responses to harvesting regime in the main commercial trait of interest—biomass productivity. This outcome is important for commercial cultivation in intensive production systems, since it identifies a low risk that harvesting practices will impact negatively on biomass productivity in the longer term.
... Both the average age at maturity and average age at first reproduction tend to increase when competition for resources is high, for example, when a population approaches or exceeds carrying capacity (Boonstra, 1994). Conversely, these parameters typically decline in a population substantially depleted by predation or human hunting pressure (Proaktor et al., 2007;Sergeant, 2011). These life history traits can thus provide information about population status. ...
... The correspondence between the timing of the change point in Zn concentrations and documented lows and highs in walrus abundance is compelling and suggests that age cp might be a valuable tool for monitoring population status. Because the average age at sexual matu- rity is expected to change in response to the availability of resources, stress levels, etc. (Boonstra, 1994;Proaktor et al., 2007) and is not influenced only by the abundance of animals in a population, age cp could be particularly useful as a management tool for walruses as arctic and sub-arctic marine environments change. Average age cp increased substantially between the 2000-04 and 2005-09 time periods, jumping from the lowest value in the record to one of the two highest (Fig. 5). ...
Article
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Age at maturity is an important parameter in many demographic models and, for some species, can be difficult to obtain using traditional methods. Incremental growth structures act as biological archives, recording information throughout an organism's life and possibly allowing for the reconstruction of life history events. Concentrations of zinc (Zn) in animal tissues are known to be linked to life history, physiology and reproduction and may be retained in incremental growth structures. This study reconstructed lifetime Zn concentrations in teeth (n = 93) of female Pacific walruses (Odobenus rosmarus divergens) collected from 1932-2016. Zn displayed a characteristic pattern of accumulation, with a change point marking the beginning of a lifelong, linear increase in Zn concentrations. We hypothesized that this change point marks the onset of reproductive maturity. The age at which the change point occurred (age cp) was estimated by counting tooth cementum growth layers. These estimates closely matched literature values of timing of first ovulation in female walruses. Total number of ovulations (estimated from ovary corpora counts from paired tooth/ovary specimens) was closely related to reproductive lifespan (total lifespan-age cp ; R 2 = 0.70). Further, age cp tracked changes in Pacific walrus population size as a proportion of carrying capacity, decreasing when the population was depleted by commercial hunting and peaking when carrying capacity was exceeded. This novel approach will aid walrus management, and is likely applicable to other species, offering a potentially powerful tool for research, management and conservation of wildlife populations.
... Det har blitt økt fokus på konsekvensene av høsting på ville hjortedyrbestander, men foreslåtte mulige effekter har i liten grad vaert dokumentert , Proaktor et al. 2007, Bischof et al. 2008, Saether et al. 2009, Mysterud and Bischof 2010, Mysterud 2011, 2012. Det har for eksempel vaert foreslått at få og i hovedsak unge bukker/okser i bestanden etter jakt kan føre til redusert drektighet, forsinket kalving og økt variasjon i kalvetidspunkt. ...
... Med dagens forvaltningsregime for svalbardrein, der kalver, simler og bukker i stor grad høstes i henhold til deres respektive andeler i bestanden, er det derfor sannsynlig at den viktigste effekten av jakt vil vaere en redusert forventet levealder hos reinsdyrene. Det har vaert vist med modeller at kortere forventet levelalder kan føre til forandringer i hjorteviltbestander mot lavere alder og vekt ved første reproduksjon (Proaktor et al. 2007). ...
Technical Report
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Svalbardreinen er en unik underart av reinsdyr (Rangifer tarandus platyrhynchus) som bare finnes på Svalbard. Dette innebærer at forvaltningen av arten skal være i overensstemmelse med Svalbardlovens høye miljøkrav. Jakt på svalbardrein er forbeholdt lokalbefolkningen på Svalbard og er lokalisert til Nordenskiöld Land. Siden jakt ble tillatt i 1983 har jaktuttaket økt fra 117 dyr til det dobbelte. I ”Plan for forvaltning av svalbardrein” utarbeidet av Sysselmannen på Svalbard i 2009 ble det påpekt at det ikke har vært gjort noen vurdering av hvor stor effekt dagens forvaltningspraksis med hensyn på jakt, har på bestanden av svalbardrein. I denne rapporten benytter vi matematiske modeller for bestandsdynamikken til svalbardrein til å vurdere dette. De viktigste funnene Resultatene tyder på at jaktuttaket av svalbardrein under dagens forvaltningspraksis har små effekter på bestandene av svalbardrein. Den viktigste gruppen dyr i bestandsdynamikken til svalbardrein er de voksne simlene. Vi anslår at man kan ta ut opptil 13 % av bestanden av voksne simler årlig uten at bestanden vil bli betydelig redusert. For de siste 10 år beregner vi at uttaket av voksne simler ligget på 4-10 % av bestanden. Sannsynligvis kan man ta ut 400-450 dyr årlig på hele Nordenskiöld Land, noe som innebærer mulighet for fortsatt vekst i antall fellingsløyver. I tillegg til å ha lite effekt på bestandsstørrelsene har jakten slik den praktiseres og forvaltes også lite effekt på kjønnsfordelingen i bestanden. Dagens uttak av like mange bukker som simler synes å stabilisere kjønnsfordelingen nært den fordelingen man ville hatt uten jakt. Det er mulig å øke uttaket av bukker, men dette vil kunne føre til en betydelig skjevere kjønnsfordeling i bestandene. Miljøgevinst Arbeidet gir en avklaring på spørsmålet om hvor stor effekt rekreasjonsjakten på svalbardrein har på bestandene. Den gir støtte til dagens forvaltningspraksis og dermed faglig støtte til at dagens rekreasjonsjakt på svalbardrein kan fortsette. Forslag til tiltak Rapporten foreslår ingen umiddelbare tiltak, men rapporten gir innspill til de vurderinger som bør gjøres hvis det blir aktuelt å fortsette å øke jaktuttaket. Hva er viktig for miljøforvaltningen? Analysene tyder på at det totalt kan felles oppimot 450 rein på Nordenskiöld Land årlig. I dag gis det 300-350 fellingstillatelser årlig hvorav 60 % blir benyttet. Hvis andelen som benytter fellingstillatelsen øker betydelig vil dette innebære en betydelig vekst i antall dyr felt innenfor jaktområdene. Det er mulig at dette vil kunne gi lokal overbeskatning i enkelte jaktområder. Dette vil være avhengig av hvor isolerte bestandene i jaktområdene er fra bestandene i omliggende områder der det ikke jaktes. De varslede klimaforandringene i Arktis kan forandre levevilkårene til svalbardreinen dramatisk. Forvaltningen må derfor være forberedt på at jaktuttaket kan måtte justeres. Oppfølging Det anbefales at man undersøker i hvilken grad bestandene i de forskjellige jaktområdene er isolerte fra bestandene i omliggende områder. Særlig gjelder det jaktområdene ved Grønnfjorden og Sassendalen. For å utvikle bedre bestandsmodeller for svalbardrein trengs det en innsats for å bedre estimatene på kalvers overlevelse gjennom vinteren, og en bedre forståelse for hvordan klimatisk variasjon påvirker bestandene.
... Modified from Hertel et al. (2016), which we published as an open-access paper under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/). evolutionary effects of directed selection during heavy human harvesting (Coltman et al. 2003;Festa-Bianchet 2003;Proaktor et al. 2007;Allendorf & Hard 2009;Darimot et al. 2009;Mysterud 2011). Brown bears were persecuted systematically for many centuries in Europe, but for a relatively short time (< 150 years) by humans with modern weapons in North America and Asia (Zedrosser et al. 2011). ...
... This hypothesis is difficult to test scientifically, but there are indications of human-induced selection in brown bears. For example, Zedrosser et al. (2011) compared brown bear populations worldwide and found that a long persecution history was associated with greater mean litter size at the population level, which is consistent with evolutionary theory and modeling results (Proaktor et al. 2007). Human-induced selection can occur rapidly, as Van de Walle et al. (2018) documented that a hunting regulation that protected female brown bears with cubs indirectly promoted slower life histories by modulating the fitness benefit of maternal care tactics during a 20-year period of relatively high hunting harvest. ...
Chapter
Humans disturb bears in many ways, either directly when they encounter humans or indirectly by changing their behavior and way of life to avoid humans, human activity, and infrastructure. Here we summarize research on how brown bears normally react when encountering humans, what a human encounter may entail for a bear, and whether bears habituate or change their behavior toward humans with increased exposure. Based on this, we also discuss: (a) how our knowledge of brown bear behavior may help people to deal with their fear of bears, and not limit their use of outdoor areas with bears; (b) how human presence, activity, and infrastructure have an indirect effect on bears, that is, how bears change their movement pattern, use of terrain and vegetation, and daily activity pattern to avoid humans; (c) how human disturbance influence foraging and denning, which is crucial for brown bear growth and reproduction; and (d) apparent differences among continents in brown bear behavior toward humans and whether this may have an evolutionary cause.
... Harvest can increase the number of successful mating young males (Poteaux et al., 2009), thus disrupting social organizations (Lane et al., 2011;Lott, 1991). Although older and larger males have higher breeding success in polygynous species (Andersson, 1994), disruptions to male social structure do not require selective harvest (Bischof et al., 2008;Proaktor et al., 2007). ...
... Effects from harvest are most pronounced with repeated, intensive harvest and when selection occurs in both sexes (Festa-Bianchet & Mysterud, 2018). And, harvest intensity can outweigh selection as a driver of changes to genetic composition and/or induce adaptive responses in populations (Proaktor et al., 2007) and be detrimental to population genetics, and thus persistence, that is, decrease effective population size (Allendorf & Hard, 2009). Sudden environmental changes may threaten harvested populations and increase their extinction risk (Cameron et al., 2016). ...
Article
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Harvest can disrupt wildlife populations by removing adults with naturally high survival. This can reshape sociospatial structure, genetic composition, fitness, and potentially affect evolution. Genetic tools can detect changes in local, fine-scale genetic structure (FGS) and assess the interplay between harvest-caused social and FGS in populations. We used data on 1614 brown bears, Ursus arctos, genotyped with 16 microsatellites, to investigate whether harvest intensity (mean low: 0.13 from 1990 to 2005, mean high: 0.28 from 2006 to 2011) caused changes in FGS among matrilines (8 matrilines; 109 females ≥4 years of age), sex-specific survival and putative dispersal distances, female spatial genetic autocorrelation, matriline persistence, and male mating patterns. Increased harvest decreased FGS of matrilines. Female dispersal distances decreased, and male reproductive success was redistributed more evenly. Adult males had lower survival during high harvest, suggesting that higher male turnover caused this redistribution and helped explain decreased structure among matrilines, despite shorter female dispersal distances. Adult female survival and survival probability of both mother and daughter were lower during high harvest, indicating that matriline persistence was also lower. Our findings indicate a crucial role of regulated harvest in shaping populations, decreasing differences among “groups,” even for solitary-living species, and potentially altering the evolutionary trajectory of wild populations. © 2020 The Authors. Evolutionary Applications published by John Wiley & Sons Ltd
... Néanmoins, la chasse peut avoir des effets sur la structure d'âge, sur le rapport des sexes des adultes et, à la naissance, sur le développement phénotypique sur les composantes biodémographiques (voir boîte 2) et sur le comportement (figure 1, Festa-Bianchet 2003;Milner et al. 2007;Proaktor et al. 2007). ...
... Il y a de plus en plus d'évidences des conséquences de la chasse sur l'évolution des grands mammifères Milner et al. 2007;Proaktor et al. 2007). Selon Milner et al. (2007), les règlements de chasse en place pour les ongulés induisent souvent une chasse sélective qui a généralement pour effet de retirer artificiellement 24 une grande partie d'un groupe sexe-âge ou des individus selon leurs caractéristiques phénotypiques, ce qui a des conséquences sur l'évolution de ces espèces ). ...
Technical Report
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Alors que les populations de cerf de Virginie (Odocoileus virginianus) atteignent les niveaux les plus élevés répertoriés dans l’histoire de l’aménagement de la faune au Québec et ailleurs en Amérique du Nord, on dénote un intérêt croissant pour l’application de mesures visant à modifier la structure des populations et les caractéristiques des animaux prélevés par la chasse. La chasse sélective constitue l’un des outils de gestion disponibles pour atteindre ces objectifs. Nous nous sommes intéressés aux conséquences potentielles de l’application de mesures de Restriction sur la taille légale des bois (RTLB) des cerfs abattus à la chasse (autres que la présence de bois ≥ 7 cm) sur les composantes biodémographiques des populations de cerfs. Nous avons effectué une revue de la littérature scientifique se rapportant aux composantes biodémographiques des cerfs qui pourraient être influencées par l'application de RTLB (développement phénotypique, survie et succès reproducteur des différents segments de la population et structure démographique des populations). Nous présentons des statistiques sur la chasse, les caractéristiques phénotypiques des animaux, la structure de la population et le rapport des sexes dans certains États américains appliquant différentes mesures de RTLB. Enfin, nous avons intégré les connaissances biodémographiques des cerfs dans des modèles de dynamique des populations qui permettent d’évaluer différents scénarios de RTLB sur les cerfs du sud du Québec (zones de chasse 4, 5 et 6). Une première constatation ressort à la suite de nos travaux : le manque de connaissances quant à la structure d’âge et de sexe attendue dans une population pas ou peu exploitée, mais soumise à la prédation. Néanmoins, les modalités de chasse actuelles entraînent un déséquilibre du ratio des sexes en faveur des femelles et de la structure d’âge du segment mâle en faveur des jeunes mâles. Bien que ces conditions ne semblent pas compromettre la productivité des populations de cerfs au Québec comme ailleurs, une augmentation de l’âge moyen des mâles, par l’intermédiaire de mesures de RTLB jusqu’à l’âge auquel ils atteignent leur masse asymptotique (3 ou 4 ans), permettrait l’expression des caractères sexuels secondaires des cerfs mâles. Le choix du partenaire sexuel sur la base de ces caractères par les femelles pourrait exercer des effets positifs sur l’âge de la première reproduction, la survie des faons, la masse adulte et le rapport des sexes à la naissance. L’abondance de cerf, laquelle iv influence la disponibilité des ressources et la condition physique des individus, constitue un autre facteur influençant le phénotype. La mise en place de RTBL devrait donc se faire en combinaison avec des mesures de contrôle de l’abondance, notamment avec la récolte de femelles. Des mesures plus restrictives de RTLB ont pour effet de réduire la récolte de mâles de l’ordre de 30 % durant les deux premières années de leur application, le tout suivi d’un rétablissement du niveau de récolte. Toutes les mesures de RTLB examinées permettent d’augmenter l’âge moyen des animaux récoltés à court terme. Toutefois, certaines mesures de RTLB peuvent créer une sélection contre le phénotype sélectionné à plus long terme. En effet, les mesures les moins restrictives, plus particulièrement celles qui limitent la récolte aux animaux dont les bois ≥ 2 pointes sur un côté (ou 4 pointes au total), ont pour effet d’éliminer les jeunes animaux qui présentent le meilleur potentiel phénotypique. À long terme, ces mesures risquent de diminuer la masse et la taille des bois des cerfs matures, puisqu’elles peuvent courtcircuiter le processus de sélection sexuelle par les femelles. Plusieurs des entités administratives qui ont mis en place des mesures de RTLB au cours des dernières années, l’ont fait dans un contexte expérimental et sur une portion de leur territoire. Les résultats de ces expérimentations donneront bientôt un meilleur éclairage sur l’effet de ces mesures de chasse sélective.
... However, hunting-induced selection on these traits is likely to have limited consequences for population dynamics of such species due to the weak correlation between body mass (or correlated secondary sexual traits value), and reproductive performance in mammals (Kuparinen & Festa-Bianchet, 2017), compared with fishes. Hunting-induced selection acting directly on female reproductive traits has a much greater potential to affect population dynamics (Rughetti & Festa-Bianchet, 2014;Servanty et al., 2011), although it has rarely been investigated (but see Proaktor et al., 2007;Rughetti & Festa-Bianchet, 2014). Therefore, a step forward in our understanding of the large-scale impacts of harvest would be facilitated by an evaluation of the demographic effects of changes in female reproductive traits in general, but especially in long-lived species. ...
... This may explain why wild animal populations of the same species experiencing different levels of mortality often show contrasting life-history strategies (Servanty et al., 2011;Zedrosser et al., 2011). Modeling and empirical studies have revealed that an increase in extrinsic mortality can select for earlier age at maturation, higher probability to reproduce, and increased litter/clutch size (Olsen et al., 2004;Proaktor et al., 2007). On the other hand, the nonrandom and systematic removal of specific phenotypes from a population due to hunting can also generate selection toward "shielding" traits (i.e., traits that afford a certain level of protection to individuals). ...
Article
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Harvest, through its intensity and regulation, often results in selection on female reproductive traits. Changes in female traits can have demographic consequences, as they are fundamental in shaping population dynamics. It is thus imperative to understand and quantify the demographic consequences of changes in female reproductive traits to better understand and anticipate population trajectories under different harvest intensities and regulations. Here, using a dynamic, frequency‐dependent, population model of the intensively hunted brown bear (Ursus arctos) population in Sweden, we quantify and compare population responses to changes in four reproductive traits susceptible to harvest‐induced selection: litter size, weaning age, age at first reproduction, and annual probability to reproduce. We did so for different hunting quotas and under four possible hunting regulations: (i) no individuals are protected, (ii) mothers but not dependent offspring are protected, (iii) mothers and dependent offspring of the year (cubs) are protected, and (iv) entire family groups are protected (i.e., mothers and dependent offspring of any age). We found that population growth rate declines sharply with increasing hunting quotas. Increases in litter size and the probability to reproduce have the greatest potential to affect population growth rate. Population growth rate increases the most when mothers are protected. Adding protection on offspring (of any age), however, reduces the availability of bears for hunting, which feeds back to increase hunting pressure on the non‐protected categories of individuals, leading to reduced population growth. Finally, we found that changes in reproductive traits can dampen population declines at very high hunting quotas, but only when protecting mothers. Our results illustrate that changes in female reproductive traits may have context‐dependent consequences for demography. Thus, to predict population consequences of harvest‐induced selection in wild populations, it is critical to integrate both hunting intensity and regulation, especially if hunting selectivity targets female reproductive strategies.
... Most commonly it is driven by the desire to shoot males with large " trophies " (Geist 1986) and avoid shooting females with offspring to enhance population growth (Milner et al. 2011). This can considerably affect sex ratio, age structure, and effective size of the population and consequently influence survival, growth, and reproduction of red deer (Proaktor et al. 2007; Mysterud 2014). The effects of selective hunting pressure on the population are difficult to predict since the genetic variability of the population may be affected by changes in population size, migration, and mating selection pattern (Mysterud 2014). ...
Article
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Due to a restriction of the distributional range of European red deer (Cervus elaphus L.) during the Quaternary and subsequent recolonization of Europe from different refugia, a clear phylogeographical pattern in genetic structure has been revealed using mitochondrial DNA markers. In Central Europe, 2 distinct, eastern and western, lineages of European red deer are present; however, admixture between them has not yet been studied in detail. We used mitochondrial DNA (control region and cytochrome b gene) sequences and 22 microsatellite loci from 522 individuals to investigate the genetic diversity of red deer in what might be expected to be an intermediate zone. We discovered a high number of unique mtDNA haplotypes belonging to each lineage and high levels of genetic diversity (cyt b H = 0.867, D-loop H = 0.914). The same structuring of red deer populations was also revealed by microsatellite analysis, with results from both analyses thus suggesting a suture zone between the 2 lineages. Despite the fact that postglacial recolonization of Central Europe by red deer occurred more than 10000 years ago, the degree of admixture between the 2 lineages is relatively small, with only 10.8% admixed individuals detected. Direct translocations of animals by humans have slightly blurred the pattern in this region; however, this blurring was more apparent when using maternally inherited markers than nuclear markers. © The American Genetic Association 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
... Many harvesting models are purely demographic and ignore the evolutionary influence of harvesting (Hilborn and Walters 1992;Caswell 2001;Walters and Martell 2004). In contrast, empirical evidence accumulated over the past decades for a wide range of taxa has unequivocally shown that harvesting often generates evolutionary changes that typically reduce the phenotypic quality or economic value of harvested individuals (Law 2000;Kuparinen and Merilä 2007;Proaktor et al. 2007;Allendorf et al. 2008;Allendorf and Hard 2009;Eikeset et al. 2013). In general, the mag-nitude of phenotypic evolution caused by human exploitation is much larger than that induced by natural predators in nonexploited populations (Darimont et al. 2009). ...
Article
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Abstract There is now considerable empirical evidence that evolutionary changes in many phenotypic characters, such as body mass, age at maturation, and timing of breeding, often occur in populations subject to intense harvesting over longer periods. Here, we analyze the evolutionary component of the selection due to nonselective harvesting, which will operate even under selective harvesting and may generate a large evolutionary response. If phenotype affects susceptibility to density dependence-for example, through resource limitation-then nonselective harvesting can induce evolutionary change through its effect on population density. We provide a model for evolution of a quantitative character in such a fluctuating density-dependent population, using the diffusion approximation to describe jointly the temporal changes in mean phenotype and log population size. We show how nonselective harvesting in particular generates r-selection governed by genetic variation in the strength of density regulation and the magnitude of population fluctuations. We show that r-selection caused by nonselective harvesting is proportional to the mean fraction of the population harvested. We then compare the short-term as well as the long-term evolutionary impact of nonselective harvesting for different harvesting strategies by using the mean harvest fraction for different strategies. This comparison is performed for three different harvesting strategies: constant, proportional, and threshold harvesting. The more ecologically sustainable strategies also produce smaller evolutionary changes.
... Evolutionary and genetic consequences of hunting should also be considered, especially when the population is heavily exploited, as is the case with brown bears in Slovenia. Evolutionary changes caused by selective hunting have been documented in several harvested large mammal species (e.g., bighorn sheep [Ovis canadensis], Coltman et al. 2003; mouflon [Ovis gmelini musimon], Garel et al. 2007; red deer [Cervus elaphus], Proaktor et al. 2007). Consequently, some authors have proposed that managers should strive to mimic natural mortality patterns (Harris et al. 2002). ...
Conference Paper
Because of large home ranges, low population densities, and long dispersal distances, brown bear and other large carnivore populations often extend over several administrative borders, and are consequently subject to sometimes very different management regimes. Since many populations are transboundary in nature, it is vital that their conservation and management are done in a coordinated and cooperative manner between all administrative units sharing such population. This is also recommended by the Guidelines for population level management plans for large carnivores in Europe. However, very little is known about the effects of harvesting on demography of a population that has different management regimes and harvesting strategies employed in different parts of its range. Brown bears (Ursus arctos) in Slovenia are a perfect study case for this problem: 1.) Slovenia represents only a part of the larger brown bear population, 2.) structure and the number of bears removed from population in Slovenia differs considerably from the neighbouring countries, 3.) bears in Slovenia are intensely managed and human-caused mortality represents the majority of all recorded mortality, and 4.) good long-term monitoring data about the removed bears are available. Bears in Slovenia are the north-western part of the Dinaric-Pindos population. The landscape continues without any physical barriers towards south-east into neighbouring Croatia, and the bears readily cross the national border. We have observed significant changes in demographic structure at the periphery of the bear population in Slovenia, with a steep decline of both bear densities and proportion of females towards the population edge in the north. The behaviour and space use of bears at the periphery also differs considerably from those of the bears in the core area (e.g. males at the periphery have larger home range sizes and appear to perform directional movements during the mating season). We analyzed demographic structure of the recorded brown bears that were removed from population in Slovenia in the 1998-2008 period (n = 927). Most bears were removed through hunting (78 %) or in traffic accidents (18 %). Most of the bears removed from population in Slovenia are young (the average age of all removed bears is 2.3 years), which is in strong contrast with neighbouring Croatia, where mainly adult males with high trophy values are harvested. According to the data from a mark-recapture study using noninvasive genetics performed in 2007, approximately 25 % of the bears living in Slovenia were removed each year, which is much higher than in other brown bear populations. Using virtual population analysis and stochastic age- and sex- structured models we have shown that such high removal rates were only possible because of a steady influx of immigrating bears from neighbouring Croatia, where removal rates during the study period were much lower. Slovenia thus represents a sink for the Dinaric-Pindos brown bear population. However, even with the high removal rate, the bear numbers in Slovenia were generally increasing during the study period. This justified the high removal rates in order to reach stabilization of the population growth, which was set as the national bear management goal. In our case, the adaptive management based on monitoring of population trends through systematic observations at constant feeding places and previous harvesting quotas enabled the managers to achieve this goal, which could be missed if only absolute data on reproductive potential and survival rates were considered with no regard to the immigration from Croatia, which apparently influences the population dynamics in Slovenia. Whether neighbouring countries should strive to equalize the number and structure of the harvested animals is disputable. But as our study shows, it is crucial that situation in neighbouring countries that share the population is monitored, and that management is coordinated. For example, recent increase in bear hunting quotas in Croatia will probably decrease the immigration rate to Slovenia. This will have to be adequately taken into consideration when planning the future harvest in Slovenia.
... In addition, game managers should be concerned about inbreeding as it signals genetic change in a harvested population. Such changes generally make it more difficult to manage populations in a sustainable manner (Ratner and Lande 2001;Proaktor et al. 2007). ...
Article
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A heterozygosity–fitness correlations (HFCs) may reflect inbreeding depression, but the extent to which they do so is debated. HFCs are particularly likely to occur after demographic disturbances such as population bottleneck or admixture. We here study HFC in an introduced and isolated ungulate population of white-tailed deer Odocoileus virginianus in Finland founded in 1934 by four individuals. A total of 422 ≥ 1-year-old white-tailed deer were collected in the 2012 hunting season in southern Finland and genotyped for 14 microsatellite loci. We find significant identity disequilibrium as estimated by g2. Heterozygosity was positively associated with size- and age-corrected body mass, but not with jaw size or (in males) antler score. Because of the relatively high identity disequilibrium, heterozygosity of the marker panel explained 51% of variation in inbreeding. Inbreeding explained approximately 4% of the variation in body mass and is thus a minor, although significant source of variation in body mass in this population. The study of HFC is attractive for game- and conservation-oriented wildlife management because it presents an affordable and readily used approach for genetic monitoring that allowing identification of fitness costs associated with genetic substructuring in what may seem like a homogeneous population.
... Classic strategies, such as managing for maximum sustained yield (MSY), have traditionally focused on optimizing a single quantity of interest, such as the abundance of a species, a habitat type or a particular state of an ecosystem. Decades of failure in the management of harvestable species, including examples such as the collapse of the cod fishery and the California anchovy fishery (Hutchings 2000), the mismanagement of fire regimes in the USA (Huggard & Gomez 2001), changes in life history traits (Proaktor et al. 2007) such as trophy size in big horn sheep (Coltman et al. 2003) and predator control measures that have had unintended side effects (Beschta 2005, Lessard et al. 2005, Tverra et al. 2007, have convincingly demonstrated many of the weaknesses of MSY or 'optimal-state' approaches. Attempts to optimize economic returns, physical connectivity or other single-system properties are typically doomed to failure in the long-term because of related, critical variables that are negatively affected by such management (Holling & Meffe 1996). ...
Article
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Early efforts in wildlifemanagement focused on reducing population variability and maximizing yields of selected species. Later, Aldo Leopold proposed the concept of habitat management as superior to population management, and more recently, ecosystem management, whereby ecological processes are conserved or mimicked, has come into favour. Managing for resilience builds upon these roots, and focuses on maintaining key processes and relationships in socialecological systems so that they are robust to a great variety of external or internal perturbations at a range of ecological and social scales. Managing for resilience focuses on system-level characteristics and processes, and the endurance of system properties in the face of social or ecological surprise. Managing for resilience consists of actively maintaining a diversity of functions and homeostatic feedbacks, steering systems away from thresholds of potential concern, increasing the ability of the system to maintain structuring processes and feedbacks under a wide range of conditions, and increasing the capacity of a system to cope with change through learning and adaptation. The critical aspect of managing for resilience, and therefore ecosystem management, is undertaking adaptive management to reduce uncertainty and actively managing to avoid thresholds in situations where maintaining resilience is desired. Managing adaptively for resilience is the approach best suited for coping with external shocks and surprises given the non-linear complex dynamics arising from linked social-ecological systems.
... Environmental changes caused by human disturbances, such as sports activities (CREEL et al., 2002) and tourism (BARJA et al., 2007;VAN METER, et al., 2009), can also influence the wildlife. However, the actual effect of human disturbance on animal populations is poorly known (FRID;DILL, 2002;BÉCHET et al., 2004;PROAKTOR et al., 2007;BEKESSY et al., 2009). Ecotourism and recreational activities are growing worldwide, especially in protected areas (BALMFORD et al., 2009) and it can even contribute to the biodiversity conservation (ZAÚ, 2014). ...
... Auch, wenn es darum geht, gezielt alte und kranke Tiere zu erlegen, sind die Sinne der menschlichen Jäger überfordert. Zudem wurde bereits nachgewiesen, dass die Jagd auch die genetische Struktur über einen veränderten Genfluss, genetische Drift und die Selektion bestimmter Eigenschaften verändert (PROAKTOR et al., 2007;ALLEN-DORF et al., 2008). ...
Article
National parks, as a category for protected areas, are a relatively recent creation. With the exception of the Swiss National Park (1914), all other European national parks were established after 1970. According to proclaimed goals, natural processes in the national parks are to be allowed to develop free of human interference. The methods by which these aims are to be achieved in respect to the management of large wild animals are a subject of much controversy: hunting traditions and forestry practices play important roles and generally accepted management standards are nonexistent. In view of these facts, we undertook this project to develop a set of criteria that can be used to assess methods for the management of red reer in regard to their approximation of natural conditions and that are suited to evaluate the quality of protected areas. Near natural areas are defined as areas in which the animals are not fed, hunting is not allowed, and populations are regulated by natural processes. In order to assess the current situation in the central European national parks, questionnaires were sent to 20 national park administrations in countries that have red deer populations. A total of 16 national parks took part in the study (table 1). Questions focused on features of the protected area, the red deer population characteristics, types of management measures, and related general conditions. Red deer management practices (table 4) in the individual protected areas were then evaluated with the aid of criteria that had been developed for determining the degree to which they emulate natural conditions (table 2). As indicated by the results, red deer are managed to a great or very great degree in most of the protected areas (figure 2). This is not in accordance with the proclaimed goals of national parks. With the exception of the Swiss National Park, red deer Populations are strongly manipulated in all of the other protected areas that participated in this study, especially in regard to population development (regulatory culling, feeding), spatial-temporal behaviour (stress due to hunting and recreational activities), and genetics (selection as an effect of hunting). In contrast, mechanisms of natural regulation, such as those caused by the presence of large predators, have only been of subordinate significance.
... Att jakt kan påverka hjortdjurs beteende och val av habitat har påvisats i flertalet studier (Swenson, 1982;Reyna-Hurtado & Tanner, 2005;Benhaiem et al., 2008) men trots detta finns det relativt lite forskning om huruvida hjortdjur förändrar sitt rörelsemönster och användning av sitt normala hemområde i förhållande till pågående jakt. Det saknas även studier som undersöker vilka indirekta samt kort -och långsiktiga effekter detta kan ha på djurlivet (Milner-Gulland et al., 2004;Proaktor et al., 2007;Sunde et al., 2009). Jakt utförd av människan är den huvudsakliga dödsorsaken för hovdjur i största delen av Europa men även annan mänsklig störning kan påverka djurlivet negativt under andra aktiviteter. ...
... Aside from selective harvesting, there is also theoretical and empirical evidence showing that increased mortality due to severe nonselective harvesting can lead to reduction in body size for age as a result of selection for faster maturation schedules (Olsen et al. 2004(Olsen et al. , 2005Engen et al. 2014). Specifically, high mortality selects for early maturation at a small size because under a higher harvest pressure, individuals that begin reproduction at younger ages and at small body sizes have a greater chance of reproducing compared with individuals that become reproductively mature at older ages and large body sizes (Proaktor et al. 2007). Empirical support for this hypothesis comes mostly from fish (Law 2000(Law , 2001Olsen et al. 2005;Reznick and Ghalambor 2005;Carlson et al. 2007;Swain et al. 2007;Diaz Pauli and Heino 2014;Kendall et al. 2014), but few studies have tested this proposition in mammals (Mysterud et al. 2009;Prowse et al. 2015). ...
Article
Harvesting of wild populations can cause the evolution of morphological, behavioral, and life history traits that may compromise natural or sexual selection. Despite the vulnerability of large mammals to rapid population decline from harvesting, the evolutionary effects of harvesting on mega-fauna have received limited attention. In elephants, illegal ivory harvesting disproportionately affects older age classes and males because they carry large tusks, but its' effects on tusk size for age or tusk size for stature are less understood. We tested whether severe historical elephant harvests eliminated large tuskers among survivors and whether elephants born thereafter had smaller tusks. Adjusting for the influence of shoulder height – a metric strongly correlated with body size and age and often used as a proxy for age – we compared tusk size for elephants sampled in 1966–1968, prior to severe ivory harvesting in the late 1970s and early 1980s, with tusk size of survivors and elephants born during population recovery in the mid-1990s. In a regional population, tusk length declined by ˜21% in male and by ˜27% in female elephants born during population recovery, while tusk length declined by 22% in males and 37% in females among survivors. Tusk circumference at lip declined by 5% in males but not in females born during population recovery, whereas tusk circumference reduced by 8% in male and by 11% in female survivors. In a single subpopulation, mean tusk length at mean basal tusk circumference declined by 12.4% in males and 21% in females. Tusk size varied between elephant social groups. Tusk homogeneity within social groups and the often high genetic similarity within social groups suggest that tusk size may be heritable. Our findings support a hypothesis of selection of large tuskers by poachers as a driver of the decline in tusk size for age proxy and contemporary tusk evolution in African elephants.
... Often, the sex-age distribution of harvested animals is very different from that of animals that die of natural causes (Wright et al. 2006), possibly altering selective pressures for age-specific reproductive effort and the level of competition for mates among males. While there is substantial evidence that commercial fisheries have altered lifehistory tactics in exploited populations, often selecting for younger age and smaller size at maturity (Hutchings 2009), the limited evidence available for ungulates does not currently suggest that life-history effects are widespread (Proaktor et al. 2007, Mysterud et al. 2009). Both hunter preference and hunting regulations can have profound effects on the sex-age structure of the harvest. ...
... We found marginal evidence that density-dependence was more pronounced in populations with less hunting pressure. This is in line with a release from density-dependence due to harvest, which in turn increases the recruitment rate of the populations (Proaktor et al. 2007). Thus, while hunting intensity may affect the recruitment rate of populations, it generally does not affect the specific deterministic growth rate which we estimated with our models (Saether, pers.comm). ...
... Controversy aside, the 30-year elephant culling regime in Kruger provided a valuable case study. Much has been written on the topic of culling, also for species other than elephant (see Walker et al., 1987;Cumming et al., 1997;proaktor et al., 2007). In general, it seems that the reduction in density through culling inflates population growth rate, most likely by releasing vital rates (age at first calving and inter-calving interval) from limitations set by density dependence (for elephants see Whyte et al., 1998;Van aarde et al., 1999). ...
... Our results concur with this prediction, because we observed that adult beavers of larger families and/or with kits were more likely to avoid areas with a high risk of meeting humans (agricultural areas, and roads) than adults of smaller families or without kits. Predation, hunting, and exploitation can have long-lasting behavioral and evolutionary effects on wildlife populations (Creel et al. 2007;Proaktor et al. 2007;Zedrosser et al. 2011). Even if human hunting and natural predation are currently low in our study population, such lasting risk avoidance effects are not surprising. ...
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Habitat selection is a context-dependent mechanism, in which both the internal state as well as external factors affect the behavior and decisions of an individual. This is well known for polygamous mammals, which are typically sexually dimorphic, and often express great variability in behavior and habitat selection between individuals as well between the sexes. Among monogamous mammals, however, variability in habitat selection should be explained by group characteristics and the presence of offspring rather than by sex. We evaluated this hypothesis in a socially monogamous rodent, the Eurasian beaver (Castor fiber), in a saturated Norwegian population. For the first time in this species we applied GPS tracking devices (N = 22 adult beavers, in 15 territories, 2009–2013), and used resource selection functions (i) to document population-wide habitat selection and the importance of ‘territory’ therein, and (ii) to evaluate which socio-ecological factors explained potential individual differences in habitat selection. We found that variation in habitat selection was stronger between territories than between years or individuals nested by territory. We identified that family size and the presence of kits, but not sex, explained individual variation in habitat selection. Adults with kits and/or larger families tended to exhibit low risk-taking behavior (avoiding human-related variables such as roads, buildings, and agricultural land), and stayed close to their main lodge (parental care). Our results show that habitat selection is a context-dependent mechanism even in a species which expresses very little behavioral and morphological dimorphism. Electronic supplementary material The online version of this article (doi:10.1007/s00442-015-3388-1) contains supplementary material, which is available to authorized users.
... The extent of the trade is such that the collection of civet oil, from the anal glands, has impacted the conservation of at least three genera (Civettictis, Viverra, and Viverricula) [20]. Because hunting is known to reduce the size of a population and may affect the demography by altering age and sex structures and disrupt social systems [21][22][23][24][25][26]. Thus may have an impact on in situ conservation in general [21,22]. ...
Article
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Comparative genomics of 12S and 16S rRNAs, cytochrome b (Cyt b) and the control region (CR) of mtDNA genome are commonly used in phylogenetics and wildlife forensics. We document the genetic characteristics and sequence variations of 12S rRNA (384 bp) in Indian civets, viz., the common palm civet (Paradoxurus hermaphroditus) (n=9), small Indian civet (Viverricula indica) (n=7) and Himalayan palm civet (Paguma larvata) (n=5). The nucleotide compositions vary from 17.6% to 36.3%, and found one to two haplotypes in all three civet species. Observed sequence divergence was 0.001 to 0.002 and 0.057 to 0.110 within and between species respectively. The nucleotide diversity was 0.00102 to 0.00184. Tajima's D value was negative (-0.097256 to-1.36240) but statistically non-significant in all three species. Based on genetic characteristics, we discuss the use of observed forensically informative nucleotide sequencing (FINS) and topology in species identification for forensic purposes among these three civet species.
... these two pathways are difficult to disentangle [13][14][15]. For example, in ungulates, both high adult female mortality and greater resource abundance are expected to lead to earlier primiparity [16][17][18]. If hunting increases female mortality and lowers population density, its evolutionary and ecological effects will be confused [19]. ...
Article
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Commercial and recreational harvests create selection pressures for fitness-related phenotypic traits that are partly under genetic control. Consequently, harvesting can drive evolution in targeted traits. However, the quantification of harvest-induced evolutionary life history and phenotypic changes is challenging, because both density-dependent feedback and environmental changes may also affect these changes through phenotypic plasticity. Here, we synthesize current knowledge and uncertainties on six key points: (i) whether or not harvest-induced evolution is happening, (ii) whether or not it is beneficial, (iii) how it shapes biological systems, (iv) how it could be avoided, (v) its importance relative to other drivers of phenotypic changes, and (vi) whether or not it should be explicitly accounted for in management. We do this by reviewing findings from aquatic systems exposed to fishing and terrestrial systems targeted by hunting. Evidence from aquatic systems emphasizes evolutionary effects on age and size at maturity, while in terrestrial systems changes are seen in weapon size and date of parturition. We suggest that while harvest-induced evolution is likely to occur and negatively affect populations, the rate of evolutionary changes and their ecological implications can be managed efficiently by simply reducing harvest intensity. This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences'.
... Low survival changes the trade-off between reproduction and survival (Gamelon et al. 2011). In populations where hunting is intensive, females of iteroparous species (reproduction in several reproductive events) may not get more than one breeding occasion and should favor any strategy maximizing their reproductive output early in life (Proaktor et al. 2007). Multi-male mating can be favored in such context. ...
Thesis
The wild boar (Sus scrofa scrofa) is a peculiar species. It is an appreciated game species for hunters, a nightmare for farmers and a subject of debate for the society in general. The tenfold increase of the population over the last decades in France and all over Europe, despite increased hunting pressure, generated great human-wildlife conflict. The wild boar is responsible for great economic losses due to vehicle collision, diseases transmission and damaged crops and ecosystems. Improving management strategies becomes a prime interest to avoid such conflicts, or at least keep them under control. Obtaining information on the species is a first step toward good management strategies. The objective of my work is, in a first part, to characterize the mating system of the wild boar and to identify some parameters, especially hunting, influencing the reproductive processes. The second part focus on the investigation of the influence of the mating system on wild boar life history traits. My researches are based on the study of several populations contrasting in their hunting practices and on longitudinal data of a highly monitored population. The study is based on data collected on wild boars killed by hunting. Genotypes were obtained for pregnant females and their litter and paternity analyses were realized to measure the number of fathers in a litter and estimate multiple paternity rates (proportion of litter sired by more than one father). I was able to show that the mating system is mainly promiscuous (several males mate with several females) contrasting with the polygyny (a dominant male monopolizing a group of females) usually described in this species. Moreover, reproductive processes, estimated by the number of mates of a female and the multiple paternity rates, are influenced by hunting variations in a population. I also showed that number of fathers has positive effect on female fecundity. High rates of multiple paternity together with high genetic diversity were found in a heavily hunted population, suggesting multiple paternity may buffer yearly bottlenecks. However, the increase of number of fathers is not associated with increase of within-litter variation
... It is important to note that there are many non-climatic factors that can influence mass, fecundity, and/or survival in ungulates, some of which may interact with climatic factors (e.g., Herfindal et al. 2006a). These include population density (Forchhammer et al. 1998;Kjellander et al. 2006;Tveraa et al. 2013), maternal effects (age, previous reproduction, cohort effects) (Bårdsen and Tveraa 2012;Feder et al. 2008;Forchhammer et al. 2001), birth date (Feder et al. 2008), topography (Mysterud et al. 2001a;Mysterud et al. 2001b;Pettorelli et al. 2005a), latitude (Saether 1985Sand et al. 1995), and harvest rate (Proaktor et al. 2007;Sand 1996). While we do not have the detailed data to account for many of these, age structure of hunted females is similar both across our study regions and over time (Fredrik Widemo, unpublished data). ...
Article
As global temperatures continue to rise, increases in the frequency and intensity of climatic extremes will likely outpace average temperature increases, and may have outsized impacts on biological populations. Moose (Alces alces) are adapted to cold weather and populations are declining at the southern edge of the species’ range. Moose therefore make a suitable case study to examine the relationship between population performance and both climatic averages and the frequency of rare, intense climatic events. More than twenty years of slaughter weights and moose observations collected by hunting teams across all of Sweden show that early calf recruitment has declined throughout Sweden and calf mass has also declined, particularly in central and southern Sweden. Spring weather affected mean calf mass, which declined with higher average temperatures, more frequent very hot days (days in the 95th percentile for maximum temperature) and less precipitation during this season, though in the case of hot days only when high temperatures coincided with low rainfall. This supports previous observations of moose sensitivity to both direct heat stress and the negative impacts of hot, dry spring weather on forage quality. Recruitment was similarly impacted, and the interaction between the previous year’s temperature and precipitation supports a lagged effect of weather on recruitment, via female condition. Finally, cold winter temperatures and deeper snow were associated with reduced calf mass during the following autumn, while deeper snow was additionally linked to fewer calves per female. Our results suggest that similar patterns may exist for averages and the frequency of extreme values, but it is important to examine both in order to improve biological relevance. The significant and ongoing declines in calf mass in southern populations and calf recruitment throughout Sweden should serve as an early warning that Eurasian moose may suffer from climate change in similar ways to North American moose. We discuss conservation management strategies, both in terms of harvest as well as landscape management, that may help mitigate the observed patterns.
... Body condition may also be affected by predation. If snakes pursue more active avoidance behaviours or are hesitant to feed, they may decrease in body condition, as seen in snowshoe hares (Sheriff et al., 2011) or heavily harvested ungulates (Proaktor et al., 2007). We also observe the opposite in BTS: improved body condition correlated with increased management efforts and exposure to humans (i.e. ...
Article
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Invasive species can exert rapid depletion of resources after introduction and, in turn, affect their own population density. Additionally, management actions can have direct and indirect effects on demography. Physiological variables can predict demographic change but are often restricted to snapshots-in-time and delayed confirmation of changes in population density reduces their utility. To evaluate the relationships between physiology and demography, we assessed metrics of individual and demographic stress (baseline and 1-h corticosterone (CORT), body condition and bacterial killing ability) in the invasive snake Boiga irregularis on Guam collected in intervals of 10–15 years. We also assessed potential discrepancies between different methods of measuring hormones [radioimmunoassay (RIA) versus enzyme immunoassay (EIA)]. The magnitude of difference between RIA and EIA was negligible and did not change gross interpretation of our results. We found that body condition was higher in recent samples (2003 and 2018) versus older (1992–93) samples. We found corresponding differences in baseline CORT, with higher baseline CORT in older, poorer body condition samples. Hormonal response to acute stress was higher in 2018 relative to 2003. We also found a weak relationship between circulating CORT and bacterial killing ability among 2018 samples, but the biological significance of the relationship is not clear. In an effort to develop hypotheses for future investigation of the links between physiology and demography in this and other systems, we discuss how the changes in CORT and body condition may reflect changes in population dynamics, resource availability or management pressure. Ultimately, we advocate for the synchronization of physiology and management studies to advance the field of applied conservation physiology.
... Alternatively, reaction norms may allow individual males to modulate the phenotypic expression of a single genotype across a range of environments 3,4,19,50,51 . Continuous hunting exploitation has been reported to produce changes in sex-traits due to the harvesting of animals with the largest trophies 52-55 , sometimes with micro-evolutionary consequences 56,57 . The case presented here could be the first one to show that hunting exploitation leads to a reduction in sex-traits due not to the removal of large trophies themselves but to changes in the population conditions (i.e. ...
Article
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Theory predicts that the plastic expression of sex-traits should be modulated not only by their production costs but also by the benefits derived from the presence of rivals and mates, yet there is a paucity of evidence for an adaptive response of sex-trait expression to social environment. We studied antler size, a costly and plastic sex trait, and tooth wear, a trait related to food intake and longevity, in over 4,000 male Iberian red deer (Cervus elaphus hispanicus) from 56 wild populations characterized by two contrasting management practices that affect male age structure and adult sex-ratio. As a consequence, these populations exhibit high and low levels of male-male competition for mating opportunities. We hypothesized that males under conditions of low intra-sexual competition would develop smaller antlers, after controlling for body size and age, than males under conditions of high intra-sexual competition, thus reducing energy demands (i.e. reducing intake and food comminution), and as a consequence, leading to less tooth wear and a concomitant longer potential lifespan. Our results supported these predictions. To reject possible uncontrolled factors that may have occurred in the wild populations, we carried out an experimental design on red deer in captivity, placing males in separate plots with females or with rival males during the period of antler growth. Males living with rivals grew larger antlers than males living in a female environment, which corroborates the results found in the wild populations. As far as we know, these results show, for the first time, the modulation of a sexual trait and its costs on longevity conditional upon the level of intra-sexual competition.
... Harvesting acts as a strong selective pressure for early reproduction (Conover and Munch 2002;Festa-Bianchet 2003;Proaktor et al. 2007). High body growth rates allow individuals to reach the threshold size for reproduction early in life (Ricklefs 1969;Gadgil and Bossert 1970). ...
Article
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From current theories on life-history evolution, fast early-life growth to reach early reproduction in heavily hunted populations should be favored despite the possible occurrence of mortality costs later on. However, fast growth may also be associated with better individual quality and thereby lower mortality, obscuring a clear trade-off between early-life growth and survival. Moreover, fast early-life growth can be associated with sex-specific mortality costs related to resource acquisition and allocation throughout an individual’s lifetime. In this study, we explore how individual growth early in life affects age-specific mortality of both sexes in a heavily hunted population. Using longitudinal data from an intensively hunted population of wild boar (Sus scrofa), and capture–mark–recapture–recovery models, we first estimated age-specific overall mortality and expressed it as a function of early-life growth rate. Overall mortality models showed that faster-growing males experienced lower mortality at all ages. Female overall mortality was not strongly related to early-life growth rate. We then split overall mortality into its two components (i.e., non-hunting mortality vs. hunting mortality) to explore the relationship between growth early in life and mortality from each cause. Faster-growing males experienced lower non-hunting mortality as subadults and lower hunting mortality marginal on age. Females of all age classes did not display a strong association between their early-life growth rate and either mortality type. Our study does not provide evidence for a clear trade-off between early-life growth and mortality.
... Such a relationship, however, was absent in Na Guardia, where small females produced a similar number of eggs than large ones and the smallest reproducing female was 83% of the estimated asymptotic body size. An early start of the reproduction and the absence of a size-dependent fecundity suggested a similar strategy to that observed in mainland populations or in populations under predatory or hunting pressure (Castilla and Bauwens 2000;Perera and Pérez-Mellado 2002;Hutchings 2004;Proaktor et al. 2007). A selective force acting against larger sizes may have selected for early breeding individuals changing the strategy of the individuals and, consequently, their realized body size. ...
Article
Recently isolated populations offer a good biological model to infer the evolutionary forces responsible for the current divergences across populations. We coupled genetic, morphometric, ecological, and demographic analyses from three island populations of the endemic Balearic Wall Lizard, Podarcis lilfordi, (Balearic archipelago, Spain) to infer the mechanisms underlying the observed differences in body size. For each population, we described plant community structure, derived a biotic capacity index, and used individual-based data on 1369 lizards captured and released during 6 yr (2009–2015) to estimate population density and body growth patterns. We used genetic data collected on 80 individuals (∼27 for each population) to infer genetic divergences across islets and population history. Body size divergences cannot be explained by the ecological or population characteristics. Individual growth was slower in the smallest island, where lizards reached the largest average body size. In addition to having the highest density, results suggested that resource availability does not constrain asymptotic body size, but the speed at which individuals reach it does. The Approximate Bayesian Computation used to infer population history from genetic data supported the occurrence of two bottlenecks in the islet with the highest anthropogenic footprint. We emphasize the need to integrate ecological and genetic data and the importance of considering the effects of past human disturbance as an additional force in being able to model present island fauna.
... Some commercially exploited species, however, are difficult or impossible to survey in the wild, such that managers perforce must rely upon monitoring parameters from the harvest to assess sustainability (Fitzgerald et al. 1991;Fitzgerald 2012;Natusch et al. 2016bNatusch et al. , 2019b. If a harvest is so intense as to affect substantially the wild populations that support it, we expect to see changes through time in demographic attributes of the offtake (Proaktor et al. 2007, Sharpe and Hendry 2009, Fitzgerald 2012). For example, over-exploitation likely will result in decreasing rates of capture, decreased mean body sizes, and changes in parameters such as sex ratio, age structure, and reproductive output within the sample of harvested animals (Fitzgerald 2012, Natusch et al. 2019a. ...
Article
Wildlife populations exposed to intense harvesting often exhibit shifts in attributes of the commercial offtake (e.g., numbers, body sizes, body condition, sex ratios, size at maturation, reproductive frequency). To look for such changes, we examined >2,500 specimens of field‐collected blood pythons (Python brongersmai) brought to 2 processing facilities in North Sumatra over 2 survey periods (1996–1997 and 2014–2015). Over the 18 years between our surveys, approximately 900,000 blood pythons were taken from Indonesia for the commercial trade; North Sumatra accounted for about 35% of that trade volume. Between survey periods, numbers of snakes brought to 1 processing facility decreased and mean body size increased, whereas at the second facility numbers and sizes of snakes remained the same. Overall, the pythons collected in 2015–2016 were thinner‐bodied than in 1996–1997, with fewer immature animals and a reduced size at maturation and reproductive frequency among females. Clutch size relative to maternal size decreased also. These temporal shifts in python demographics likely reflect a response to harvesting, although ecosystem changes may have played a role. Compared to other squamate reptiles, blood pythons may be more vulnerable to over‐harvesting because most snakes are intensively collected from discrete habitat patches (oil palm plantations), and the species can be targeted by specific hunting methods. To ensure sustainability of the harvest, we recommend minimum and maximum size limits for skins used in the commercial trade, and more intensive monitoring at processing facilities. © 2019 The Wildlife Society. Wild harvesting of hundreds of thousands of blood pythons from North Sumatra, Indonesia, has resulted in demographic changes to populations that may be indicative of unsustainable levels of offtake. Our results underpin the need to ensure representative sampling of python processing facilities, appropriate management tools (e.g., size limits), and ongoing monitoring.
... Environmental changes caused by human disturbances, such as sports activities (CREEL et al., 2002) and tourism (BARJA et al., 2007;VAN METER, et al., 2009), can also influence the wildlife. However, the actual effect of human disturbance on animal populations is poorly known (FRID;DILL, 2002;BÉCHET et al., 2004;PROAKTOR et al., 2007;BEKESSY et al., 2009). Ecotourism and recreational activities are growing worldwide, especially in protected areas (BALMFORD et al., 2009) and it can even contribute to the biodiversity conservation (ZAÚ, 2014). ...
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Ecotourism is an important tool for biodiversity conservation in protected areas. However, high visitation rates and intensive public use can affect the wildlife. The present study aimed to evaluate vertebrate foraging in areas under different levels of human influence in the Tijuca National Park, a protected area within the metropolitan area of Rio de Janeiro, Brazil. We used baits to attract vertebrates in areas with and without visitor facilities, at distances of 5, 35, and 100 meters from the road. We have analyzed the removal of bait by vertebrates in such treatments and identify higher consumption associated to greater human presence. The presence of visitors and visitor facilities (e.g., parking lots, barbecue pits, picnic tables, and playgrounds) significantly increases bait consumption. Park managers should consider the negative impacts of tourism on wildlife searching for ways to minimize them. RESUMO O ecoturismo é uma importante ferramenta para a conservação da biodiversidade em áreas protegidas. No entanto, as altas taxas de visitação e uso público intensivo podem afetar a fauna em áreas protegidas. O objetivo deste estudo foi avaliar o forrageamento de vertebrados em áreas sob diferentes influências antrópicas no Parque Nacional da Tijuca: uma unidade de proteção integral dentro da metrópole do Rio de Janeiro, Brasil. Foram usadas iscas em áreas com e sem infraestrutura para visitantes, em distâncias de 5, 35 e 100 metros das margens da estrada, dentro de cada sítio de estudo. Análises apontaram que em áreas onde a presença humana é menos constante, o consumo de iscas de bananas foi menos intenso. A interferência causada por visitantes do parque sobre a intensidade do consumo de isca é significativa e influenciada por estruturas de visitação como estacionamento, churrasqueiras, mesas de piquenique e playground. Gestores de parques devem considerar tais impactos do turismo, visando minimizar influências negativas sobre a fauna. PALAVRAS-CHAVE: Gestão de Unidade de Conservação; Uso Público; Parque Nacional da Tijuca; Ecoturismo; Efeito de Borda.
... Studies led on harvested animal populations have provided valuable insight on the key role of age-specific mortality on life history evolution. For instance, there is growing evidence that high hunting mortality on the adult class can induce evolutionary changes such as earlier age at maturity and reduced body size (Proaktor et al., 2007). On the contrary, a removal of non-mature juvenile individuals may mimic natural mortality and predation pattern and thus limit undesirable evolutionary responses due to harvesting (Milner et al., 2011). ...
... Intense harvesting could have evolutionary effects on lifehistory strategies simply by lowering population density (Engen et al. 2014) or by changing age-specific mortality rates (Proaktor et al. 2007). While there is abundant evidence of harvest-induced life-history evolution in fishes (Kuparinen and Festa-Bianchet 2017), evidence in mammals is very limited (Gamelon et al. 2011;Zedrosser et al. 2011;Kvalnes et al. 2016). ...
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.
... Despite the ubiquity of harvesting ungulates for food and trophies (Proaktor, Coulson & Milner-Gulland, 2007;Ripple et al., 2015), an understanding of the population-wide effects of hunting on the behavior of survivors remains fragmentary. Events commonly associated with hunting such as firearm discharge, observing downed conspecifics, pursuit by motor vehicles, and/or the presence of humans in close proximity for extended periods of time may produce behavioral changes in survivors. ...
Article
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The impact of hunting (selective harvest, trophy hunting) on the demography of mammals is well documented. However, despite continual year-round hunting of bison in some populations, little is known about how the behavior of survivors may be altered. Therefore, in this initial study, we used focal-animal observations in adjacent populations of continually hunted and protected Plains bison ( Bison bison bison ) in western South Dakota, to examine the potential impact of hunting on bellowing rate—an important behavior that serves to intimidate rival bulls and potentially influences mate choice by females. In addition to hunting, we investigated how the number of attendant males, number of adult females, group size, and number of days from the start of rut influenced bellowing rate. Bulls bellowed an order of magnitude more often in the protected population than in the hunted populations, whereas bellowing rate was not significantly different in the hunted populations. Hunting was significantly and negatively associated with bellowing rate, while all other predictors were found to be positively associated with bellowing rate. Furthermore, the impact of hunting on bellowing rate became more pronounced (i.e., dampened bellowing rate more strongly) as the number of attendant males increased. Changes in bellowing behavior of bulls (and possibly mate choice by cows) can alter breeding opportunities. Therefore, our data suggest the need for studies with broader-scale geographical and temporal replication to determine the extent that continual year-round hunting has on bellowing rate of bison during the rut. If reduced bellowing is associated with human hunting on a larger scale, then wildlife managers may need to adjust hunting rate and duration, timing (season), and the time lag between hunting events in order to insure that bison are able to express their full repertoire of natural mating behaviors.
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Evolutionary responses to indirect selection pressures imposed by intensive harvesting are increasingly common. While artificial selection has shown that biochemical components can show rapid and dramatic evolution, it remains unclear as to whether intensive harvesting can inadvertently induce changes in the biochemistry of harvested populations. For applications such as algal culture, many of the desirable bioproducts could evolve in response to harvesting, reducing cost‐effectiveness, but experimental tests are lacking. We used an experimental evolution approach where we imposed heavy and light harvesting regimes on multiple lines of an alga of commercial interest for twelve cycles of harvesting and then placed all lines in a common garden regime for four cycles. We have previously shown that lines in a heavy harvesting regimes evolve a ‘live fast’ phenotype with higher growth rates relative to light harvesting regimes. Here, we show that algal biochemistry also shows evolutionary responses, though they were temporarily masked by differences in density under the different harvesting regimes. Heavy harvesting regimes, relative to light harvesting regimes, had reduced productivity of desirable bioproducts, particularly fatty acids. We suggest that commercial operators wishing to maximise productivity of desirable bioproducts should maintain mother cultures, kept at higher densities (which tend to select for desirable phenotypes), and periodically restart their intensively harvested cultures to minimise the negative consequences of biochemical evolution. Our study shows that the burgeoning algal culture industry should pay careful attention to the role of evolution in intensively harvested crops as these effects are nontrivial if subtle. This article is protected by copyright. All rights reserved.
Technical Report
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In Denmark, red deer (Cervus elaphus) are legal quarry (subject to no quotas) throughout the hunting season (1 September – 31 January) for anyone holding a valid license to hunt on their own land (more than 1 hectare) or on rented ground (larger than 5 hectares). As a consequence, in most parts of Denmark, multiple land owners and hunters on rented ground compete for the same individuals without any overall plan or coordination of the culling of local populations. The disadvantages of such a lack of management (for instance, the apparent deficit of mature stags because of high hunting pressure before reaching maturity) have been debated for decades. To contribute factual information to this debate, the demographic composition of two Danish red deer populations with contrasting land owner structure and hunting regimes were analysed and compared, from Djursland (hunting seasons 2008/9-2012/13) and Oksbøl red deer reserve (1985/86-2012/13). Djursland (1417 km2, the easternmost tip of Jutland) represents a ‘typical’ Danish landscape, comprising multiple owners of small or larger estates each of which run their own hunting practices. In this area, 1-year old males were protected in an effort to increase the proportion of mature stags in the population. During a five-year period, hunters on Djursland voluntarily delivered jaws from hunted red deer for age determination and morphometric information. The population on the Oksbøl red deer reserve (163 km2, south western Jutland) is managed by the Danish Nature Agency, with the aim of maintaining a stable red deer population with a high proportion of mature stags through a deliberate harvesting policy. On Oksbøl, the age of all harvested and deer found dead had been estimated on the basis of teeth wear (although the validity of this locally developed age estimation method had never been tested on independent data). The aims of this analysis were (i) to test and calibrate the wear-based age es-timation method used on Oksbøl against independent data, (ii) to describe the demographic composition of the two populations from age at death dis-tributions, and (iii) to establish population models from this information. Since data was also available on the number of points on antlers, weight, pregnancy and lactation rates, relationships between these variables and age, population density and date were also calculated. In summary, the results are as follows: 1. From a reference material of 37 individuals of known age (marked before 2 years old), true age correlated closely (R2 = 97%) and accurately (no bias) with age estimated from the number of incremental lines in teeth ce-mentum layers (‘method 1’), although with a precision of ±2 years for any given individual. Age estimation based on dentin layers can thus be con-sidered as a reliable method to estimate age of Danish red deer. 2. Age estimated from tooth wear in 15 red deer from Oksbøl correlated closely with age estimated from dental lines (R2 = 92 %). However, the age estimated from the number of dentin lines was on average 49.5 % higher (p< 0.0001) than that estimated from tooth wear, suggesting that the locally developed wear based age determination method systematically underestimated the age of dead red deer. A deer estimated to be 10 years old on the basis of the tooth wear method would, on average, be estimated to be 15 years old from counts of dentin lines. 3. The demographic composition of the Oksbøl population was constructed based on life tables established from 4278 aged females and 2896 males which died between 1990/91 and 2012/13. Females had an estimated annual mortality (based on adjusted age distribution from method 2 cal-culated at the start of the hunting season) of 33% as calves and 15-20% for all older age classes. This was equivalent to a spring population of females which consisted of 19% yearlings/calves from the preceding summer, 13% 2-year olds, 11% 3-year olds and 55% 4+ year olds. Males had an estimated annual mortality of 45% for calves, 35% for 1-3 year olds, and 20% for stags from 4 years of age, equivalent to an male age composition of 26% yearlings, 17% 2-years olds, 11% 3-years olds, 26% 4-7 year olds and 21% of 8 years of age or older. At the start of the rutting season, the population consisted of 2.6 hinds (i.e. females aged 1½ years old or older) for every stag aged 2½ years or more and 5.7 hinds for every stag aged 5½ year or more. 4. The demographic composition of the Djursland population was con-structed based on life tables established from 895 aged females and 622 males which died between 2008/09 and 2012/13. Seventy-four unsexed calves where assumed to represent an even sex distribution and were di-vided equally within the male and female life tables. Females had an es-timated annual mortality (calculated from the start of the hunting season) of 23% as calves and 20% as 1-7 year olds, and 34 of 8 years of age or older. This was equivalent to a spring female population of 22% yearlings/calves from the preceding summer, 18% 2-year olds, 15% 3-year olds and 45% 4+ year olds. Males had an estimated annual mortality of 24% for calves, 4% for yearlings, 26% for 2-year olds, and about 50% for 3-7 years of age. An apparent reduction in annual mortality after 8 years of age (24%) may be an artefact caused by a few old stags escaped from captivity. The estimated age distribution of males in spring thus consisted of 29% yearlings, 28% 2-year olds, 21% 3-year olds, 11% 4 year olds and 11% of 5 years of age or older. At the start of the rutting season, the population consisted of 1.8 hinds for every stag aged 2½ year or more, and 8.1 hinds for every stag aged 5½ year or more. 5. The population effect of protecting 1-year old males from hunting on Djursland could not be estimated rigorously because of the lack of refer-ence material (because protection was implemented throughout the sam-pling period) but could be cautiously estimated as a difference in mortality between yearlings and calves and 2-year old stags of about 20%. Ac-cordingly, without the protection of yearling males from hunting, the number of all older age groups of males would probably be 20% lower than observed. 6. Male body weight increased with age until the 5th year on Djursland and 10th year at Oksbøl. In both populations, female body weights increased with age until their 3rd year. Females from Djursland weighed on average 12% more than females from Oksbøl (methodological differences pre-cluded comparisons of stags between populations). In both populations, calf weights increased by 6-7 kg for both sexes during the first 2 months of the hunting season. During the same period the weight of adult stags decreased because of rutting activities. Calves from the Oksbøl population weighed 8-9% less in those years (mid 1990s) when population density peaked at almost twice the size as in the 1980s and after 2000. In 1- and 2-year old males, there was a 12% difference in body weight between cohorts born during the highest and lowest population densities. 7. The number of antler points increased until 8-15 years of age, reaching an average of 11 but with considerable (±3) individual variation. In both populations 2/3 of all males had at least 10 points at 5 years of age and 80-90% had at least 10 points at 8 years of age. The proportion of stags with 14 points or more peaked at c.25% during 12-15 years of age. 8. In both population more females than males were reported amongst the grown individuals (Djursland: 60% females, Oksbøl: 58% females) even though the sex ratio amongst calves was close to unity. In Oksbøl, the female: male ratio varied from 50:50 for individuals from cohorts born during lowest population densities to 65:35 for cohorts born during greatest densities. Since the sex-ratio of (dead) calves did not vary signifi-cantly as a function of population density, the female biases sex ratio of adults is likely to reflect increased emigration of stags under dense popu-lation conditions. On Djursland, the apparent female-biased sex ratio in the population may be the result of a campaign aimed at ceasing the growth of the population by targeting hinds and/or lower reporting fre-quencies for stags than for hinds. 9. Data on pregnancy and lactation rates were available from Djursland only. Here, 88% of all hinds on Djursland were pregnant, divided between 64% amongst 1-year old and 91% of older hinds. At the start of the hunting season 79% of all hinds were lactating (i.e. being with calf), based on 57% of the 2-old and 82% of older hinds. 10. On the basis of estimated age specific mortalities for each population and observed fecundity on Djursland (extrapolated to Oksbøl), population growth rates were estimated to be =1.02 at Oksbøl and 1.00 at Djursland. Since the population at Oksbøl remained about the same from the 1980ies to 2012/13, the predicted positive growth rate for the Oksbøl population might be the result of the substituted fecundity rates in the model (taken from the Djursland population) exceeding the true rates of the Oksbøl population. A population model incorporating a fecundity rate estimated from Djursland and no hunting mortality (99% annual survival until 8th years of age, 80% annual survival after that age), predicted an annual population growth rate of =1.21, which is equal to a doubling of the population size in four years. Estimates are given for population growth rates under different combinations of female age specific annual survival. 11. The estimated population patterns for the Oksbøl and Djursland popula-tions are discussed in relation to five dominant (but partly opposing) population objectives to: (i) maximise the number of harvested individuals relative to the population size (‘game ranch model’), (ii) maximise the number of harvested mature stags relative to the size of the population (‘trophy model’), (iii) maintain a ‘high’ proportion of mature stags in the living population, (iv) attain a ‘sustainable’ harvesting (several defini-tions), and (v) sustain an intended ‘natural’ demographic composition. 12. In terms of number of harvested individuals relative to the size of the winter population, the populations at Oksbøl and Djursland resulted in a yield of 37 and 32 harvested individuals/ 100 individuals in the winter population. This was 55-60% of the maximum possible number of har-vested individuals in a population managed for that purpose (game ranch model: 62/100), about the same number as harvested in a population managed to maintain an intended natural demographic composition (34/100) and half the number harvested in a population managed to maximize the number of harvested stags of at least 8 years of age. 13. On Djursland, 0.4 mature stags (defined as at least 8 years of age) were harvested per 100 individuals in the spring population. This constitutes 4% of the harvest from a population managed to maximize the harvest of mature stags (trophy model: 8.7/100), 15% of the harvest from a popula-tion with an intended natural demographic composition (2.6/100) and one third the number of mature stags harvested at Oksbøl (1.2/100) or in a population managed in order to optimize meat harvest (game ranch model). Without protection of 1-year old males, the yield of mature stags would probably have been 20% lower than observed. In addition to providing hunters with a very low yield of mature stags, in an evolution-ary perspective, the low average longevity of stags on Djursland creates a real risk of selecting for earlier maturity and smaller body size. 14. Even though the harvest policy on Oksbøl resulted in a three times higher harvest of mature stags relative to the population size than on Djursland and a less biased ratio between the numbers of hinds and mature stags, a change in age-specific culling towards a higher harvest of calves and individuals older than 8 years compared to present would double the harvest of mature stags as well as their proportion of the live population. This would also be in line with the general mortality pattern observed in naturally regulated ungulate populations elsewhere. 15. If managers aim to increase the number of mature stags in the population as well as in the overall hunting yield, the most efficient tool would be to protect all immature stags from hunting until they have reached the re-quired size for harvest and mating.
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Mathematical models are used to explore the evolutionary and demographic consequences of size-selective harvesting and natural selection in populations with discrete, nonoverlapping generations. We specify the harvesting intensity and size selectivity in terms of both the phenotypic criterion for harvesting and the demographic goal of harvesting. The phenotypic criterion is defined by a threshold that specifies the minimum size of individuals harvested, while the demographic goal defines the desired catch or escapement from the harvest. Models use either a constant phenotypic threshold, or a variable phenotypic threshold that moves each year to remain a fixed distance from the mean size prior to harvest. Demographic goals are defined as a desired yield or escapement, measured in abundance or biomass. We find that all combinations of phenotypic criteria and demographic goals can produce evolutionary changes in equilibrium mean size and abundance when harvesting is size selective. Reductions in mean size are more severe under harvesting scenarios for which it is not possible to fully satisfy the demographic goals of harvesting at equilibrium. Models with a variable phenotypic threshold always produce a characteristic equilibrium for mean size and abundance for a given set of harvesting and natural selection parameters, regardless of the initial population characteristics. For some combinations of parameters, constant-threshold models produce alternative equilibria for the mean size and abundance. Our results suggest that the evolutionary effects of selective harvesting warrant consideration in long-term conservation and management planning.
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Population substructure and the effects of scale have recently received much theoretical attention, but few studies have examined these factors in free-living populations of vertebrates. We used > 200000 sightings of recognized females recorded over a continuous 20-yr period to explore population substructure and spatial heterogeneity in red deer on the Isle of Rum, Scotland. We used hierarchical cluster analysis to group individuals together by their proximities in space, and we explored the influence of scale, considering scales ranging between the whole population and groups of one or two individuals. Intermediate scales were isolated as being the best at describing calf winter survival, the key factor in determining future population density. The most statistically explanatory scale isolated a population substructure related to vegetation, with higher local densities occurring around herb-rich Festuca-Agrostis grassland. Calves at high local density were most likely to die. Patterns of local population density varied between seasons in relation to food availability. High-resolution scales were the best descriptors of calf winter survival in summer; coarser scales were better in winter. In both summer and winter, local population density was more important than total population density in influencing calf winter survival. The effects on calf survival of local population density during the summer interacted significantly with calf sex and the mother's reproductive status. In this study, the technique of grouping animals by their proximity in space was more realistic and informative than discrete spatial divisions of the study area.
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As part of a study of performance in Red deer (Cervus elaphus L.) at high population density on Scottish hill-land, the annual cycles of body weight and condition in selected classes of deer were investigated. The research was done on Rhum, a 10,600 ha island off the west coast of Scotland with an isolated population of about 1500 Red deer. Samples of deer were shot at different times of year, and various physical characteristics of the animals were assessed. The four classes of deer chosen for study comprised: stags, hinds supporting calves (“milk” hinds), and hinds without calves (“yeld” hinds), all aged 5–10 years, and calves. These represented the three main kinds of mature full-grown deer, and immature deer at the stage of maximum growth potential. Seven sampling periods of two weeks each in July, September, October, November, February, March and April-May covered the main features of the annual life cycle. Achieving biologically meaningful results depended very much on animal selection, and on the consistency and intensity of sampling. Therefore the background and results of the shooting plan are discussed in some detail before considering the biological findings of the study. All four classes of Red deer showed well defined trends in body weight and condition over the year, and it was clear that body weight and condition were strongly correlated within each class; the maxima and minima in body weight and condition coincided exactly. Similarities amongst the four classes were undoubtedly related to the underlying seasonal trends in environmental factors such as food and climate; deer mostly showed gains in weight and condition from spring to autumn and losses during winter. Differences amongst the three classes of adult deer were mainly attributable to aspects of reproduction, but there were two-way relationships between these and the annual cycles of body weight and condition. Maximum body weight and condition in stags coincided with the start of the rutting season (late September to late November), but stags lost about 14–17% carcase weight and most discernible fatty tissue during the rut. Milk hinds showed lower body weights and fat reserves than yeld hinds over most of the year reflecting the effects of pregnancy and lactation. Moreover, hinds in good condition achieved a higher pregnancy rate than those in poor condition. Thus many hinds must breed successfully one year but fail the following year on account of poor condition resulting from the effects of pregnancy and lactation in a nutritionally poor environment. Calves grew actively from the calving period in late May and June until late October, but there was a severe growth check from late November until late March with most body constituents either declining or remaining constant. However, skeletal growth apparently continued slowly over the winter period. As might be expected, the best hinds had the best calves. In adult deer the weights of livers and kidneys showed distinct annual cycles, but these were out of phase with the cycles in body weight and condition. Possible reasons are discussed briefly. In addition, the trends in kidney weights are discussed in relation to the kidney-fat-index as a measure of condition. There were distinct annual cycles also in the amounts of ingested food material in adults of both sexes. Hinds showed smaller amounts, suggesting a lower food intake, in winter than summer. The amounts in stags were very much lower during the rutting season, and much higher immediately afterwards, than at any other time of year; it is well known that stags almost cease feeding whilst rutting.
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A small-variance approximation technique for examining the evolution of reproductive effort is developed, using a decomposition of fitness into arithmetic mean and variance components. Trait values often translate nonlinearly into fitness components such as offspring number or growth rate. A nonlinear relationship between phenotypic traits and fitness implies that the expected value of the fitness component will be a function of the arithmetic mean and variance in the traits influencing a given fitness component. The maximum expression of traits is often, however, a function of reproductive effort. Reproductive effort then influences the mean and variance in traits that affect fitness. Consequently, we can use these techniques to determine the optimal allocation of resources to current reproduction via their effects on the distribution of trait values. The optimal pattern of allocation is influenced by the quality and variability of the habitat and by the curvature of the trait-fitness relationship. The full range of adaptive responses, from semelparity to different degrees of iteroparity, can be predicted from the model. The model is extended to cases where reproductive effort can be partitioned into different offspring types, as offspring produced through chasmogamous and cleistogamous flowers. When more than one type of offspring is produced, then reproductive risks can be spread across offspring types and the conditions favoring semelparity are less restrictive. Semelparity is especially favored if the offspring types exhibit negative covariance in their contributions to growth rate. -from Authors
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Bighorn sheep (Ovis canadensis) are restricted in distribution and numbers relative to presettlement conditions. Some populations have alledgedly suffered losses of fitness resulting from small, insular populations and a breeding system that reduces effective population size. Large horns in rams, which confer breeding superiority, are absent from some populations, and this absence may result in part from loss of genetic variability. We investigated the relationship among allozyme variability, population history, and horn growth in bighorn sheep from the Rocky Mountains. Heterozygosity was higher for bighorn sheep than has been reported for Dall sheep (O. dalli). Heterozygosity and allelic variability were marginally related to effective population size for the proceeding 15 years. Horn growth was significantly higher in more heterozygous than in less heterozygous rams for years 6, 7, and 8 of life. By the end of year 8, more heterozygous rams had 13% higher horn volumes than less heterozygous rams. Mos
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Though it has been widely predicted that in animals in which reproductive value declines with age, reproductive effort should increase toward the end of the lifespan, analysis of changes in reproductive effort are impeded by fundamental difficulties in measuring the costs of reproduction. Energetic measures may not reflect the effects of breeding on subsequent survival and breeding success, especially in organisms in which body size increases with age, while attempts to estimate reproductive costs directly are complicated by positive correlations between breeding success and parental survival. Though the long-lived birds and mammals are among the most promising organisms on which to test the theory that reproductive effort increases with age, measures of fecundity commonly decline with increasing maternal age. Some recent evidence suggests, however, that offspring survival may improve toward the end of the lifespan