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Illegal tusk harvest and the decline of tusk size in the African elephant
Abstract and Figures
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.
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... Both modern poaching and historical trophy hunting are selective in the individuals killed. Given the high price of rhino horn, and increased social status for hunters that kill rhinos with the largest horns, we expect that individual rhinos with the longest horns might be targeted, consistent with similar selective hunting that has been reported in other taxa (Chiyo et al., 2015;Coltman et al., 2003;Festa-Bianchet et al., 2014). In other megaherbivores, selective harvesting of this kind has led to directional selection, whereby a strong selective hunting pressure has resulted in a reduction in the frequency of the desired trait (Coltman et al., 2003). ...
... In other megaherbivores, selective harvesting of this kind has led to directional selection, whereby a strong selective hunting pressure has resulted in a reduction in the frequency of the desired trait (Coltman et al., 2003). For example, directional selection due to trophy hunting has driven declines in tusk size in elephants and horn length in wild sheep (Chiyo et al., 2015;Coltman et al., 2003;Festa-Bianchet et al., 2014;Garel et al., 2007). These trends have been demonstrated using both in situ measurements of individuals and studies of museum collections. ...
... We also found a small but significant decline in relative horn length over time across all species. These results could be indicative of directional selection in response to hunting pressures, as has been noted in obvious features such as horns and tusks in other taxa (Chiyo et al., 2015;Coltman et al., 2003;Festa-Bianchet et al., 2014). In these cases, preferential hunting selection for individuals with larger horns or tusks resulted in individuals with smaller features surviving and reproducing more, passing on these traits to future generations, and resulting in an evolutionary change. ...
Online image repositories can offer a freely accessible, information‐rich and cost‐effective alternative to museum collections for studying long‐term changes in human interactions with nature and ecological and evolutionary change. The Rhino Resource Center (RRC) is one example, curated by experts and holding a collection of >4000 rhino images, including both artistic portrayals (1481–2021) and photographs (taken between 1862–2021), and representing a potentially valuable case study to investigate the utility of online image repositories for research into large vertebrates and, potentially, other well‐recorded smaller taxa. The five extant species of rhino are all threatened by habitat loss and human hunting and therefore are an important focus for conservation research.
We used the RRC for two separate research approaches: (i) assessing the changing representations and human interactions with rhinos using 3158 images (1531 pieces of artwork and 1627 photographs); and (ii) determining to what extent morphological data can be extracted from photographs to assess changes in horn length over time, using a sample size of 80 photographs of rhinos taken in profile view.
We found that African rhino species have become more commonly depicted in images, compared to Asian rhino species over time. During the age of European imperialism (between the 16th and 20th centuries), rhinos were commonly portrayed as hunting trophies, but since the mid‐20th century, they have been increasingly portrayed in a conservation context, reflecting a change in emphasis from a more to less consumptive relationship between humans and rhinos. Finally, we found evidence for declining horn length over time across species, perhaps related to selective pressure of hunting, and indicating a utility for image‐based approaches in understanding societal perceptions of large vertebrates and trait evolution.
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... If one sex is targeted, hunting can lead to skewed sex ratios (Marealle et al., 2010;Christensen & Fox, 2014;Festa-Bianchet & Mysterud, 2018). Males are often targeted for their ornaments, such as horns and tusks (Holmern et al., 2006;Chiyo, Obanda, & Korir, 2015). Skewed sex ratios can lead to demographic shifts including changes in effective population sizes, leading to loss of genetic diversity and an increase in inbreeding as well as conflict over mates (Harris, Wall, & Allendorf, 2002;Charlesworth, 2009;Wedekind, 2012;Rosche et al., 2018). ...
... Hunted sex ratio analyses can highlight subsequent changes to population dynamics and breeding behaviour due to sex-skewed hunting (Downing, 1981;Ginsberg & Milner-Gulland, 1994;Mondol, Mailand, & Wasser, 2014;Hagen, Sedinger, & Braun, 2018). One sex may therefore be more vulnerable to hunting than the other due to the presence of desired morphological features or as a consequence of behaviour (Giroux & B edard, 1986;Coltman et al., 2003;Mondol et al., 2014;Chiyo et al., 2015;Loveridge et al., 2016). Analysing sex ratios of hunted individuals can therefore inform conservation management and aid future population studies. ...
Hunted wildlife can often be used to answer questions about wild individuals. Sex ratios of hunted individuals can be important for understanding changes in population demographics and viability. Here we determined the sex ratio of the illegally hunted helmeted hornbill Rhinoplax vigil , a critically endangered species from Southeast Asia, to examine their vulnerability to hunters. Using casques seized in Hong Kong SAR between 2012 and 2016, we identified the sex of seized individuals using morphological and molecular methods as well as discriminant analysis. As R. vigil females can spend up to 6 months of the year sealed into tree cavity nests, they are reliant on males for food. The unique breeding ecology of this elusive species means that males are more likely to be observed than females throughout the year. These behavioural differences mean that there are several potential outcomes which may be observed in the sex ratio of the seized casques, depending on hunting strategies. Our results suggest that sex identification is possible via visual inspection of the gular skin colour and beak‐tip markings, but when these are not available, genetic methods or morphological measurements can be used. Our findings also indicated a primarily male‐biased sex ratio across the seizures; however, females, as well as juveniles, were also present in seizures. Although removing one sex from the wild can cause shifts in demographic dynamics over time, illegal and unsustainable hunting of any measure of a critically endangered species will ultimately heighten its risk of extinction. These methods and results are useful to conservationists and researchers interested in further study of hornbill populations and their viability and are ultimately important for the conservation and management of this critically endangered species.
... These could be important factors to include in models of poaching, since poacher decision-making is likely affected by elephant locations within a protected area (Beale et al., 2018;Maingi et al., 2012), and elephant locations and behaviours may differ according to individual-level differences. For example, female and male elephants may differ in their movements (Moss and Poole, 1983), social associations (Moss and Poole, 1983), behaviours (Chiyo and Cochrane, 2005), and susceptibility to poaching (Chiyo et al., 2015), all of which could affect their whereabouts at any given time and thus poacher decision-making. Elephants may also exhibit temporally-based differences in behaviour, for example herds seasonally aggregating (Moss and Poole, 1983), which could affect poacher decision-making over time, and thus the effectiveness of law enforcement strategies. ...
... In the scenario where poachers are adaptive and law enforcement adaptively follow matriarchal herds, significantly more poachers are caught and significantly fewer elephants are killed. This strategy of following matriarchal herds could leave adult male elephants vulnerable to poaching, since they are already disproportionately targeted by poachers due to their larger tusk size (Chiyo et al., 2015), but results show that this strategy protects both male and female elephants more than the strategy of patrolling in a set distribution. Game theoretical models have focussed mainly on planning effective patrol routes as the main poaching mitigation strategy (e.g. ...
African elephants (Loxodonta africana) have undergone serious declines in the past century due to poaching for their ivory. Wildlife managers face significant challenges when planning poaching mitigation strategies, bounded by financial and logistical constraints. Quantitative models can provide practical insights for management, and many ‘equation-based’ and game theoretical models have been applied to poaching mitigation to-date. ‘Equation-based’ models are advantageous in many respects, and widely used, but face difficulties when working with complex and dynamic systems like poaching, and often require significant simplifications to be made to the model specification. Game theoretical models can incorporate adaptive responses of poachers and rangers to dynamic systems but abstract the behavioural and ecological information on elephants. Managers and policymakers would benefit from a supplementary modelling technique. Agent-based models (ABMs) can supplement and expand upon the existing work done in this field. These represent the behaviours and objectives of individuals, providing analyses of how bottom-up interactions affect a system on the macro level. ABMs present the opportunity to model the complex interdependencies between law enforcement strategies, adaptive poacher decision-making, and the ecology and behaviour of elephants. To illustrate the utility of ABMs for poaching mitigation, an exploratory ABM was developed that predicts how interactions between elephants, poachers, and law enforcement affect poaching levels within a virtual protected area. Two poacher decision-making strategies are simulated: one in which poachers move randomly throughout the landscape, and one in which poachers adaptively decide where to hunt based on their memories of elephant and ranger whereabouts. Additionally, two law enforcement strategies are tested: one in which rangers patrol according to a prescribed distribution and another in which rangers adaptively follow matriarchal herds. Overall, adaptive poachers and adaptive law enforcement performed significantly better at their relevant goals than randomly moving poachers and the law enforcement strategy in which rangers have a prescribed distribution of effort. This demonstrates how ABMs can allow for more complex formulations and inform new poaching mitigation strategies. The aim is for this model to be developed into a useful management support tool and applied to real-world scenarios to inform decision-making, and several possible refinements and avenues for future research and development are suggested.
... Such high mortality levels can induce strong selection pressure to alter behaviour [12], selecting against migratory behaviour [13] and for manoeuvrability [14]. (b) Selection to avoid hunting or harvesting: humans target individuals with preferred traits, selecting against traits such as long ivory tusks [15]. (c) Selection in novel communities: both abiotic and biotic selection pressures are reshaped when humans bring together species in new assemblages, as found in cardinals nesting in introduced honeysuckles [16]. ...
... Hunting pressures have long been studied for the selective pressures induced, including an early analysis by Haldane [31] documenting the decline in foxes of the silver coat variant, which was highly prized by trappers. From reductions in tusk size among elephants [15] to horn size among bighorn sheep [32], hunting selects for those traits that keep animals out of the cross-hairs [30]. ...
Humans have dramatically altered the planet over the course of a century, from the acidity of our oceans to the fragmentation of our landscapes and the temperature of our climate. Species find themselves in novel environments, within communities assembled from never before encountered mixtures of invasives and natives. The speed with which the biotic and abiotic environment of species has changed has already altered the evolutionary trajectory of species, a trend that promises to escalate. In this article, I reflect upon this altered course of evolution. Human activities have reshaped selection pressures, favouring individuals that better survive in our built landscapes, that avoid our hunting and fishing, and that best tolerate the species that we have introduced. Human-altered selection pressures have also modified how organisms live and move through the landscape, and even the nature of reproduction and genome structure. Humans are also shaping selection pressures at the species level, and I discuss how species traits are affecting both extinction and speciation rates in the Anthropocene.
... On the contrary, the trophy sizes for Cape buffalo and greater kudu have not changed for the period 2004-2015 in Matetsi Safari Area as reported in some countries, e.g., Tanzania [44] and South Africa [56,57]. Most of the documented studies done on African elephant relates to illegal hunting effects on the tusk size instead of trophy hunting related issues and as such there were no comparative studies [81]. However, we note that most illegal hunting of elephants target the large tuskers and as such could have the same effect of trophy hunting. ...
... Variations in trophy size and age at harvest could be as a result of several factors including (1) use of the fixed quota system that reduces the density or availability of old trophy individuals with the requisite trophy sizes, (2) lack of consistent age based trophy harvesting policy that penalises the harvesting of young individuals [46,62,64], (3) habitat quality heterogeneity that affect horn development and growth of trophy species [82,83], and (4) possible effects of illegal harvesting that may vary with area and degree of protection [81]. However, there is uncertainty on the contribution of illegal harvesting activities on the trophy size of these herbivores as in some instances some poachers tend to select horn size for their kills in the same manner as regulated trophy hunting [24]. ...
The selective nature of trophy hunting may cause changes in desirable phenotypic traits in harvested species. A decline in trophy size of preferred species may reduce hunting destination competitiveness thus compromising the sustainability of trophy hunting as a conservation tool. We explored the trophy quality and trends in harvesting patterns (i.e., 2004–2015) of Cape buffalo (Syncerus caffer), African elephant (Loxodonta africana), greater kudu (Tragelaphus strepsiceros) and sable (Hippotragus niger) in Matetsi Safari Area, northwest Zimbabwe. We used long-term data on horn and tusk size, age, quota size allocation and offtake levels of selected species. To analyse the effect of year, area and age on the trophy size, quota size and offtake levels, we used linear mixed models. One sample t-test was used to compare observed trophy size with Safari Club International (SCI) minimum score. Trophy sizes for Cape buffalo and African elephant were below the SCI minimum score. Greater kudu trophy sizes were within the minimum score threshold whereas sable trophy sizes were above the SCI minimum score between 2004 and 2015. Age at harvest for Cape buffalo, kudu and sable increased whilst that of elephant remained constant between 2004 and 2015. Quota size allocated for buffalo and the corresponding offtake levels declined over time. Offtake levels of African elephant and Greater kudu declined whilst the quota size did not change between 2004 and 2015. The quota size for sable increased whilst the offtake levels fluctuated without changing for the period 2004–2015. The trophy size and harvesting patterns in these species pose a conservation and management dilemma on the sustainability of trophy hunting in this area. We recommend: (1) temporal and spatial rotational resting of hunting areas to create refuge to improve trophy quality and maintenance of genetic diversity, and (2) introduction of variable trophy fee pricing system based on trophy size.
... Evidence of harvest-induced changes in life-history traits of terrestrial species is limited (Gamelon et al., 2011;Kvalnes et al., 2016;Van de Walle et al., 2021;Zedrosser et al., 2011). Some ungulates selectively harvested based on the size or shape of their weapons (horns, antlers, or tusks) showed phenotypic changes consistent with hunting-induced evolution (aoudad, Ammotragus lervia and Iberian ibex, Capra pyrenaica, Pérez et al., 2011; sable antelope, Hippotragus niger, Crosmary et al., 2013;African elephant, Loxodonta africana, Campbell-Staton et al., 2021;Chiyo et al., 2015;bighorn sheep, Ovis canadensis, Pigeon et al., 2016; stone sheep, Ovis dalli stonei, Douhard et al., 2017; and European mouflon, Ovis gmelini, Garel et al., 2007). Other studies of hunted ungulates, however, documented no clear evidence of harvest-induced evolutionary changes in weaponry, suggesting that an evolutionary response to selective hunting is only expected under very restrictive conditions (Büntgen et al., 2018;Festa-Bianchet & Mysterud, 2018;Rughetti & Festa-Bianchet, 2010). ...
In terrestrial and marine ecosystems, migrants from protected areas may buffer the risk of harvest‐induced evolutionary changes in exploited populations that face strong selective harvest pressures. Understanding the mechanisms favoring genetic rescue through migration could help ensure evolutionarily sustainable harvest outside protected areas and conserve genetic diversity inside those areas. We developed a stochastic individual‐based metapopulation model to evaluate the potential for migration from protected areas to mitigate the evolutionary consequences of selective harvest. We parameterized the model with detailed data from individual monitoring of two populations of bighorn sheep subjected to trophy hunting. We tracked horn length through time in a large protected and a trophy‐hunted populations connected through male breeding migrations. We quantified and compared declines in horn length and rescue potential under various combinations of migration rate, hunting rate in hunted areas and temporal overlap in timing of harvest and migrations, which affects the migrants' survival and chances to breed within exploited areas. Our simulations suggest that the effects of size‐selective harvest on male horn length in hunted populations can be dampened or avoided if harvest pressure is low, migration rate is substantial, and migrants leaving protected areas have a low risk of being shot. Intense size‐selective harvest impacts the phenotypic and genetic diversity in horn length, and population structure through changes in proportions of large‐horned males, sex ratio and age structure. When hunting pressure is high and overlaps with male migrations, effects of selective removal also emerge in the protected population, so that instead of a genetic rescue of hunted populations, our model predicts undesirable effects inside protected areas. Our results stress the importance of a landscape approach to management, to promote genetic rescue from protected areas and limit ecological and evolutionary impacts of harvest on both harvested and protected populations.
... For instance, the reduction in the frequency of the silver morph in red fox (Vulpes vulpes) in Canada resulted from selective harvesting for the fur trade (Haldane, 1942). Elephants have long been exploited for ivory (Wittemyer et al., 2014) and as poachers usually target large-tusked individuals, average tusk sizes have declined by roughly 24% since the 1970s in certain heavily exploited populations, owing to artificial selection (Chiyo, Obanda & Korir, 2015). The evolutionary consequences of exploitation has also been shown in ungulate horn sizes (Pigeon et al., 2016), although this remains a topic of debate (Coulson et al., 2018). ...
Wildlife trade is a key driver of extinction risk, affecting at least 24% of terrestrial vertebrates. The persistent removal of species can have profound impacts on species extinction risk and selection within populations. We draw together the first review of characteristics known to drive species use – identifying species with larger body sizes, greater abundance, increased rarity or certain morphological traits valued by consumers as being particularly prevalent in trade. We then review the ecological implications of this trade‐driven selection, revealing direct effects of trade on natural selection and populations for traded species, which includes selection against desirable traits. Additionally, there exists a positive feedback loop between rarity and trade and depleted populations tend to have easy human access points, which can result in species being harvested to extinction and has the potential to alter source–sink dynamics. Wider cascading ecosystem repercussions from trade‐induced declines include altered seed dispersal networks, trophic cascades, long‐term compositional changes in plant communities, altered forest carbon stocks, and the introduction of harmful invasive species. Because it occurs across multiple scales with diverse drivers, wildlife trade requires multi‐faceted conservation actions to maintain biodiversity and ecological function, including regulatory and enforcement approaches, bottom‐up and community‐based interventions, captive breeding or wildlife farming, and conservation translocations and trophic rewilding. We highlight three emergent research themes at the intersection of trade and community ecology: (1) functional impacts of trade; (2) altered provisioning of ecosystem services; and (3) prevalence of trade‐dispersed diseases. Outside of the primary objective that exploitation is sustainable for traded species, we must urgently incorporate consideration of the broader consequences for other species and ecosystem processes when quantifying sustainability.
... The selective removal of 'desirable' morphological traits from individual populations through these processes is well-documented (Darimont et al., 2009). For example, hunting has led to a documented reduction in the tusk size of African elephants Loxodonta africana (Chiyo et al., 2015), horn size in sable antelope Hippotragus niger (Crosmary et al., 2013), and antler size in moose Alces alces (Schmidt et al., 2007) and deer (Allendorf & Hard, 2009). ...
The artificial selection of traits in wildlife populations through hunting and fishing has been well documented. However, despite their rising popularity, the role that artificial selection may play in non‐extractive wildlife activities, for example, recreational feeding activities, remains unknown.
If only a subset of a population takes advantage of human‐wildlife feeding interactions, and if this results in different fitness advantages for these individuals, then artificial selection may be at work. We have tested this hypothesis using a wild fallow deer population living at the edge of a capital city as our model population.
In contrast to previous assumptions on the randomness of human‐wildlife feeding interactions, we found that a limited non‐random portion of an entire population is continuously engaging with people. We found that the willingness to beg for food from humans exists on a continuum of inter‐individual repeatable behaviour; which ranges from risk‐taking individuals repeatedly seeking and obtaining food, to shyer individuals avoiding human contact and not receiving food at all, despite all individuals having received equal exposure to human presence from birth and coexisting in the same herds together. Bolder individuals obtain significantly more food directly from humans, resulting in early interception of food offerings and preventing other individuals from obtaining supplemental feeding.
Those females that beg consistently also produce significantly heavier fawns (300–500 g heavier), which may provide their offspring with a survival advantage. This indicates that these interactions result in disparity in diet and nutrition across the population, impacting associated physiology and reproduction, and may result in artificial selection of the begging behavioural trait.
This is the first time that this consistent variation in behaviour and its potential link to artificial selection has been identified in a wildlife population and reveals new potential effects of human‐wildlife feeding interactions in other species across both terrestrial and aquatic habitats.
... For instance, poachers profiting from pet trade prefer to capture immature individuals as the most economically desirable commodity [30], eliminating gregarious 'brokers' who engage in frequent or diverse social interactions [31,32]. As another example, trophy hunters target individuals with prominent features, such as elephants with big tusks [33,34], killing the oldest and socioecologically experienced conspecifics [35][36][37][38][39]. ...
Selective harvest, such as poaching, impacts group-living animals directly through mortality of individuals with desirable traits, and indirectly by altering the structure of their social networks. Understanding the relationship between disturbance-induced, structural network changes and group performance in wild animals remains an outstanding problem. To address this problem, we evaluated the immediate effect of disturbance on group sociality in African savanna elephants-an example, group-living species threatened by poaching. Drawing on static association data from ten free-ranging groups, we constructed one empirically based, population-wide network and 100 virtual networks; performed a series of experiments 'poaching' the oldest, socially central or random individuals; and quantified the immediate change in the theoretical indices of network connectivity and efficiency of social diffusion. Although the social networks never broke down, targeted elimination of the socially central conspecifics, regardless of age, decreased network connectivity and efficiency. These findings hint at the need to further study resilience by modeling network reorganization and interaction-mediated socioecological learning, empirical data permitting. The main contribution of our work is in quantifying connectivity together with global efficiency in multiple social networks that feature the sociodemographic diversity likely found in wild elephant populations. The basic design of our simulation makes it adaptable for hypothesis testing about the consequences of anthropogenic disturbance or lethal management on social interactions in a variety of group-living species with limited, real-world data.
... For example, it has revealed an artificial bias in sex ratio in natural populations from different areas of the world, due to the selective poaching towards large tusk-bearing (i.e. male) elephants (Vidya et al., 2003;Chiyo et al., 2015). In areas where human-elephant conflicts occur, knowing the sex of the raiding individuals might help mitigating tensions, by integrating the known differences in the crop feeding behavior between males and females (Sukumar & Gadgil, 1988;Hoare, 1999;Smith & Kasiki, 2000). ...
Le conflit humains-faune sauvage est très fréquent en Afrique, et est amené à s’intensifier du fait de l’expansion de l’agriculture, et de la réduction et la fragmentation de l’habitat. Les pertes liées à la consommation ou dégradation des cultures créent de l’insécurité alimentaire, ce qui accroit la pauvreté et entrave le soutien local aux efforts de conservation. Les éléphants sont souvent considérés comme les animaux responsables de la majorité des conflits. S’appuyant sur une approche pluridisciplinaire associant génétique, morphologie, sciences sociales, et eco-éthologie, notre étude vise (1) à mieux caractériser les acteurs et les interactions dans une zone située à la lisière d’une aire protégée, où vivent les deux espèces d’éléphants, et où le conflit est exacerbé par la proximité des cultures humaines et de l’habitat des éléphants ; et (2) à proposer des mesures efficaces et non violentes adaptées au contexte local. Les perspectives sont de soumettre des recommandations pour la gestion du conflit humain-faune sauvage, afin de contribuer à une meilleure protection des champs et par conséquent à l’amélioration des conditions de vie des communautés locales, ainsi qu’à la réduction des pressions de braconnage sur la faune sauvage du parc. Nous avons tout d’abord montré que les deux espèces d’éléphants d’Afrique ainsi que des individus hybrides sont présents dans la zone de Sebitoli, au nord du parc national de Kibale en Ouganda. L’étude de leur comportement en forêt et lors des incursions dans les champs montre qu’ils vivent en groupes mixtes ne permettant pas de caractériser des incursions typiques d’éléphants de forêt et d’autres typiques des éléphants de savane. Plutôt que d’adapter les recommandations de mesures de protection des cultures contre les incursions selon les espèces d’éléphants, il apparait indispensable que les mesures soient adaptées au contexte géographique, foncier, économique et social de chaque village, en tenant compte du comportement nocturne des éléphants mais aussi des autres espèces participant au conflit entre humains et faune sauvage, notamment des espèces menacées et protégées comme les chimpanzés. La diminution des interactions négatives entre humains et faune sauvage est indispensable à une cohabitation pacifique. Cela nécessite de comprendre les besoins de chaque parti et repose sur un équilibre entre développement humain et conservation de la biodiversité.
... The elimination of such 'keystone informants' and the resulting disruption of information transfer pathways is likely to have a largely detrimental effect on the surviving members of the group. Yet, hunters and ivory poachers preferentially target older individuals, as these have more prominent tusks (Chiyo et al. 2015, Wasser et al. 2015. ...
Information use constitutes the key aspect of phenotype–environment interactions for any organism living in a heterogeneous environment, as information increases the chances of making the decisions that match the current perceived state of the world. Information use is ubiquitous in a variety of contexts and organisms throughout their lifetime are inter-woven into complex information webs, in which information is constantly produced, gained, and transmitted among conspecifics and heterospecifics. Due to increasingly disruptive anthropogenic changes to the Earth’s support system, this information dimension of individuals’ lives is now being increasingly deteriorated by human-induced rapid environmental changes. Here, we argue that one of the more pressing challenges for the field of the Ecology of Information – the study of how organisms acquire and use information and the ecological significance of informed decision-making – is to expand the current framework and strengthen its bridge to conservation biology. Building on recent theoretical and empirical advances in the field of Ecology of Information, we first emphasize the far-reaching ecological ramifications of information use and provide an overview of how individuals’ informed decision-making scales up to affect population and community dynamics. Next, we highlight how recent human-induced rapid environmental changes deteriorate information acquisition, use and transmission in natural systems, thereby disrupting nature’s information webs. The omission of information from conservation actions can have largely detrimental effects. Thus, there is an urgent need for ecologists and conservation biologists to explicitly trace and quantify the flows of information in ecological systems, and the diversity of information sources used by living organisms for decision-making and to establish collective efforts to preserve nature’s information webs.
... Commercial fishing in general has contributed to decreased age and size at sexual maturity across taxa (Sharpe and Hendry 2009). Similarly, pressure imposed by trophy hunting has been shown to elicit the evolution of less 'showy' phenotypes as well as smaller adult body sizes across a variety of taxa (e.g., Fenberg and Roy 2008;Chiyo et al. 2015;Pigeon et al. 2016), emphasizing the magnitude of evolutionary change over ecologicallyrelevant time scales that can emerge when strong directional selection is imposed on traits with underlying additive genetic variation. ...
Control methods that target specific traits of an invasive species can produce results contrary to the aims of management. If targeted phenotypes exhibit heritability, then it follows that the invasive species could evolve greater resistance to the applied control measures over time. Additional complications emerge if those traits targeted by control are also inversely related to reproductive success. Given this, prudent considerations for invasive species management are to quantify the heritability of traits selected through control measures and gauge their relationship with reproductive success. Herein we provide a case study utilizing long-term field data and a multi-generational pedigree of an experimentally-closed population of brown treesnakes (N = 426; Boiga irregularis) on Guam. We employed an “animal model” to estimate the narrow-sense heritability (h2) for annual body condition, a trait related to both susceptibility to a primary tool used for brown treesnake control (i.e., live-lure traps) and annual reproductive success. Annual body condition displayed significant heritability [h2 = 0.149 (95% highest posterior density interval: 0.059–0.220)]. Considering a negative effect of body condition on susceptibility to trap capture but positive effect on reproductive success, significant heritability of body condition suggests the potential for live-lure traps to lose efficacy over time while also eliciting an undesirable effect on brown treesnake fecundity. Our results highlight the potential for negative repercussions that can stem from management actions, while also serving to underscore the evolutionary implications that are often overlooked but subsumed within invasive species control.
... Our results contribute to the growing body of evidence suggesting that older male elephants are of particular importance to elephant conservation efforts (Chiyo et al. 2011;Archie and Chiyo 2012). Older males are at greater risk from poaching or hunting (Chiyo et al. 2015) as they are typically larger, with bigger tusks, and maybe more likely to be alone (Poole 1994). Previous studies have shown that the loss of older males increases reproductive skew (Ishengoma et al. 2008), decreasing genetic diversity in wild populations (Archie and Chiyo 2012). ...
Social animals live in complex and variable socio-ecological environments where individuals adapt their behavior to local conditions. Recently, there have been calls for studies of animal social networks to take account of temporal dynamics in social relationships as these have implications for the spread of information and disease, group cohesion, and the drivers of sociality, and there is evidence that maintaining stable social relationships has fitness benefits. It has recently been recognized that male elephants form strong social bonds with other males. The nature of these relationships, and thus network structure, may vary over time in response to varying environmental conditions and as individuals age. Using social network analysis, we examine the stability of relationships and network centrality in a population of male African elephants. Our results suggest that males may maintain stable social relationships with others over time. Older males show greater stability in network centrality than younger males, suggesting younger males face uncertainty in transitioning to adult society. For elephants, where older individuals function as social repositories of knowledge, maintaining a social network underpinned by older males could be of particular importance.
... La pression exercée par la récolte peut induire des changements évolutifs dans les populations animales sauvages (Harris et al., 2002;Chiyo et al., 2015;. ...
... Human degradation of traditional wilderness areas makes once inaccessible elephant habitats susceptible to poaching (Graham et al., 2009) . Ivory poachers target the individuals with the most prominent tusks (Wasser et al., 2015) , resulting in the elimination of the largest and oldest group members (Chiyo et al., 2015) . Most studies exploring the effects of poaching have focused on demographic changes in vulnerable populations (Bradshaw and Schore, 2007;Gobush et al., 2008) and movement behavior near poaching hotspot proxies (Goldenberg et al., 2018;Ihwagi et al., 2015) . ...
Selective harvest, such as poaching, impacts group-living animals directly through mortality of individuals with desirable traits, and indirectly by altering the structure of their social networks. Understanding the relationship between the structural network changes and group performance in wild animals remains an outstanding problem. To address this knowledge gap, we evaluate the immediate effect of disturbance on group sociality in African savanna elephants — an example, group-living species threatened by poaching. Drawing on static association data from one free ranging population, we constructed 100 virtual networks; performed a series of experiments ‘poaching’ the oldest, socially central or random individuals; and quantified the immediate change in the theoretical indices of network connectivity and efficiency of social diffusion. Although the virtual networks never broke down, targeted elimination of the socially central conspecifics, regardless of age, decreased network connectivity and efficiency. These findings hint at the need to further study resilience by modeling network reorganization and interaction-mediated socioecological learning, empirical data permitting. Our work is unique in quantifying connectivity together with global efficiency in multiple virtual networks that represent the sociodemographic diversity of elephant populations likely found in the wild. The basic design of our simulation platform makes it adaptable for hypothesis testing about the consequences of anthropogenic disturbance or lethal management on social interactions in a variety of group-living species with limited, real-world data.
Author Summary
We consider the immediate response of animal groups to human disturbance by using the African savanna elephant as an example of a group-living species threatened by poaching. Previous research in one elephant population showed that poaching-induced mortality reduced social interaction among distantly related elephants, but not among close kin. Whether this type of resilience indicates that affected populations function similarity before and after poaching is an open problem. Understanding it is important because poaching often targets the largest and most socially and ecologically experienced group members. Drawing on empirical association data, we simulated poaching in 100 virtual elephant populations and eliminated the most senior or sociable members. Targeted poaching of sociable conspecifics was more impactful. Although it did not lead to population breakdown, it hampered theoretical features of interspecific associations that in other systems have been associated with group cohesion and the efficiency of transferring social information. Our findings suggest that further inquiry into the relationship between resilience to poaching and group performance is warranted. In addition, our simulation platform offers a generalizable basis for hypothesis testing in other social species, wild or captive, subject to exploitation by humans.
... Older elephants have larger tusk sizes, which makes them holders of a bigger and more appealing trophy. The selection of these specimens will have consequences for the future generations, as has been proved in an investigation of elephants in southern Kenya [48]: both surviving individuals and those who born after the ivory harvest showed a decrease in tusk circumference at lip and tusk length, especially females, which can be justified by the greater tendency to seek large tusks in groups of elephants (usually related to females). This phenotypic change is based on genetic changes and the possibility of the disappearance of the ivory bearing gene can cause difficulties for the defence and feeding, but it can also represent hope for the future of the species [49]. ...
... . In large terrestrial animals subjected to trophy hunting or ivory trade, selective harvest of primarily superior and sexually dominant males has been shown to induce artificial selection and hence evolution towards smaller horn size, reduction in male body size or, in the case of elephants, loss of tusks (Chiyo et al., 2015;Coltman et al., 2003;Martin, Festa-Bianchet, Coltman, & Pelletier, 2016;Pigeon, Festa-Bianchet, Coltman, & Pelletier, 2016). Such conspicuous traits are fundamental to the outcome of competitive interactions and are the results of strong sexual selection (Swain, Sinclair, & Mark Hanson, 2007;Wilber, 1989;Woolmer, Woo, & Bayes, 2013). ...
Marine protected areas (MPAs) are increasingly implemented worldwide to maintain and restore depleted populations. However, despite our knowledge on the myriad of positive responses to protection, there are few empirical studies on the ability to conserve species’ mating patterns and secondary sexual traits. In male European lobsters (Homarus gammarus), the size of claws relative to body size correlates positively with male mating success and is presumably under sexual selection. At the same time, an intensive trap fishery exerts selection against large claws in males. MPAs could therefore be expected to resolve these conflicting selective pressures and preserve males with large claws. We explored this hypothesis by contrasting claw size of males and females in three pairs of MPAs and nearby fished areas in Southern Norway. By finding that male lobsters have up to 8 % larger claws inside MPAs compared to similarly sized males in fished areas, our study provides evidence that MPAs rescue a secondary sexual trait. Recovery from harvest selection acting on claws is the most likely explanation, however, the higher abundance of lobster inside MPAs does not rule out a plastic response on claw size due to increased competition. Regardless of the underlying cause, our study demonstrates (1) the value of protected areas as a management tool for mitigating fishery‐induced evolution, and (2) that MPAs help maintaining the scope for sexual selection in populations with vulnerable life‐histories and complex mating system.
... It is also worth noting that genetic and phenotypic evolution can occur very rapidly, in some cases within 10 generations. 166,167 This suggests that rapid changes can occur within one animal colony based on both genetics and environment, resulting in adaptations to a particular genetic manipulation that are almost impossible to predict and must be regularly and fully characterized in order for the resulting data to be interpreted. ...
Neurological disease is killing us. While there have long been attempts to develop therapies for both acute and chronic neurological diseases, no current treatments are curative. Additionally, therapeutic development for neurological disease takes 15 years and often costs several billion dollars. More than 96% of these therapies will fail in late stage clinical trials. Engineering novel treatment interventions for neurological disease can improve outcomes and quality of life for millions; however, therapeutics should be designed with the underlying physiology and pathology in mind. In this perspective, we aim to unpack the importance of, and need to understand, the physiology of neurological disease. We first dive into the normal physiological considerations that should guide experimental design, and then assess the pathophysiological factors of acute and chronic neurological disease that should direct treatment design. We provide an analysis of a nanobased therapeutic intervention that proved successful in translation due to incorporation of physiology at all stages of the research process. We also provide an opinion on the importance of keeping a high-level view to designing and administering treatment interventions. Finally, we close with an implementation strategy for applying a disease-directed engineering approach. Our assessment encourages embracing the complexity of neurological disease, as well as increasing efforts to provide system-level thinking in our development of therapeutics for neurological disease.
... For example, the economic impact of evolution toward smaller body size in harvested fish species has been argued to be of minor economic impact compared with the decline in population size induced by harvesting (Heino et al. 2015). Similarly, harvest-induced evolution in wild species has rarely been documented to have a negative impact on species that we want to protect but may instead actually improve their chances of survival-as in cases of smaller antler size or loss of tusks, which reduce desirability for trophy hunters (Chiyo et al. 2015). However, larger scale consequences of harvest-induced trait changes cannot be ruled out and may alter trophic cascades, nutrient cycling, and ecosystem stability, especially when harvesting targets ecosystem engineers or keystone species (Palkovacs et al. 2018). ...
The Anthropocene biosphere constitutes an unprecedented phase in the evolution of life on Earth with one species, humans, exerting extensive control. The increasing intensity of anthropogenic forces in the twenty-first century has widespread implications for attempts to govern both human-dominated ecosystems and the last remaining wild ecosystems. Here, we review how evolutionary biology can inform governance and policies in the Anthropocene, focusing on five governance challenges that span biodiversity, environmental management, food and other biomass production, and human health. The five challenges are: ( a) evolutionary feedbacks, ( b) maintaining resilience, ( c) alleviating constraints, ( d) coevolutionary disruption, and ( e) biotechnology. Strategies for governing these dynamics will themselves have to be coevolutionary, as eco-evolutionary and social dynamics change in response to each other.
Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 50 is November 4, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... For example, reduced tusk size in some heavily-hunted elephants in Africa (e.g. Chiyo et al., 2015) is a selective pressure in response to hunting that favour large tusks-this is distinct from Addo's female elephants that have lost their tusks even in the absence of selective hunting pressure. ...
... For example, reduced tusk size in some heavily-hunted elephants in Africa (e.g. Chiyo et al., 2015) is a selective pressure in response to hunting that favour large tusks-this is distinct from Addo's female elephants that have lost their tusks even in the absence of selective hunting pressure. ...
... Indeed, selective harvesting can directionally change sexually selected traits (e.g. Chiyo, Obanda, & Korir, 2015, Pigeon, Festa-Bianchet, Coltman, & Pelletier, 2016, Sordalen et al., 2018, but the role of sexual selection in FIE remains largely unexplored (but see Sordalen et al., 2018). ...
The role of sexual selection in the context of harvest‐induced evolution is poorly understood. However, elevated and trait‐selective harvesting of wild populations may change sexually selected traits, which in turn can affect mate choice and reproduction.
We experimentally evaluated the potential for fisheries‐induced evolution of mating behaviour and reproductive allocation in fish.
We used an experimental system of zebrafish ( Danio rerio ) lines exposed to large, small or random (i.e. control) size‐selective mortality. The large‐harvested line represented a treatment simulating the typical case in fisheries where the largest individuals are preferentially harvested. We used a full factorial design of spawning trials with size‐matched individuals to control for the systematic impact of body size during reproduction, thereby singling out possible changes in mating behaviour and reproductive allocation.
Both small size‐selective mortality and large size‐selective mortality left a legacy on male mating behaviour by elevating intersexual aggression. However, there was no evidence for line‐assortative reproductive allocation. Females of all lines preferentially allocated eggs to the generally less aggressive males of the random‐harvested control line. Females of the large‐harvested line showed enhanced reproductive performance, and males of the large‐harvested line had the highest egg fertilization rate among all males. These findings can be explained as an evolutionary adaptation by which individuals of the large‐harvested line display an enhanced reproductive performance early in life to offset the increased probability of adult mortality due to harvest.
Our results suggest that the large‐harvested line evolved behaviourally mediated reproductive adaptations that could increase the rate of recovery when populations adapted to high fishing pressure come into secondary contact with other populations.
... For instance, the collapse of the Atlantic cod fishery in the late 20 th century is attributed to heavy fishing pressure that, in addition to reducing population size, also drove the evolution of earlier sexual maturity and lower reproductive rates (Olsen et al., 2004). Similarly, pressure imposed by trophy hunting also elicits the evolution of less 'showy' phenotypes as well as smaller adult body sizes (e.g., Fenberg & Roy, 2008;Chiyo, Obanda, & Korir, 2015;Pigeon, Festa-Bianchet, Coltman, & Pelletier, 2016). Both examples emphasize the magnitude of evolutionary change that can result over ecologically-relevant time scales when strong directional selection is imposed on traits that maintain additive genetic variation. ...
... An analysis of 3 species of African antelope within the same hunting area provided inconsistent results, with horn size increasing over time in one species and decreasing in another (Crosmary et al. 2013). Intense poaching pressure may have selected for smaller tusks in African elephants (Loxodonta africana- Chiyo et al. 2015), but age was not directly included in the analysis and the case for evolutionary change is weakened by the lack of clear evidence that poachers spare elephants with smaller tusks. Lockwood et al. (2007) reported that very intense artificial selection favoring males with large antlers had strong effects on antler phenotype of captive white-tailed deer over about 4 generations. ...
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.
... African elephant, Loxodonta africana, populations have experienced increased ivory poaching over recent years, which typically targets older animals for their larger tusks (Chiyo, Obanda, & Korir, 2015;Wittemyer, Daballen, & Douglas-Hamilton, 2013;Wittemyer et al., 2014). Older females act as repositories of information (McComb, Moss, Durant, Baker, & Sayialel, 2001), affect the calving success of family members (Lee, Fishlock, Webber, & Moss, 2016), and provide access to preferred resources through their dominance status and ecological knowledge (Foley, Pettorelli, & Foley, 2008;Wittemyer, Getz, Vollrath, & Douglas-Hamilton, 2007). ...
Social environments are fundamental to fitness in many species. In disrupted societies, the loss of important partners may alter social environments for surviving individuals. African elephants, Loxodonta africana, have experienced age-selective mortality linked to the ivory trade, and the resulting social costs for surviving young elephants are unknown. In this study, we followed orphaned female elephants and nonorphaned counterparts in Kenya's Samburu and Buffalo Springs National Reserves to elucidate whether orphaning and related dispersal behaviour incur social costs. There were clear social differences between orphans and nonorphans, most notably in that orphans tended to receive more aggression than nonorphans. Dispersal from natal groups was a behaviour found exclusively among orphans. Differences in social environments of orphans that remained in their natal groups and those that dispersed were also found in the form of dispersed orphans receiving more aggression while feeding than those that remained in their natal group. Our results suggest that orphaning in elephants is associated with social costs, and that these costs are amplified for orphans that disperse from their natal groups. Future research should identify the relationship between the social costs of being an orphan and fitness, which may be important to the recovery of populations affected by the ivory trade and other forms of disruption.
... Strong selection from human harvesting capable of causing evolution has now been reported as occurring in a variety of taxa, including marine and freshwater fish and wildlife populations (Allendorf and Hard, 2009;Chiyo et al., 2015;Douhard et al., 2017;Heino et al., 2015;Kvalnes et al., 2016). Here, we provide an assessment of whether FIE is expected to occur within the Laurentian Great Lakes (herein referred to as Great Lakes) and whether it should be of concern from a management perspective. ...
Fisheries are selective, capturing fish based on their body size, behaviour, life stage, or location. Over time, if harvest pressure is strong enough and variation in traits heritable, evolution can occur that affects key aspects of the ecology of fish stocks. Most compelling examples of rapid evolution in response to harvest have come from marine systems. Here, we review the state of knowledge on fisheries-induced evolution (FIE) in the Laurentian Great Lakes where subsistence, commercial, and recreational fisheries have operated for centuries. We conclude that stocks experienced harvest rates high enough and for long enough to undergo evolution. While historical fisheries exploited more juveniles, some contemporary Great Lakes fisheries target primarily adult size-classes thus reducing current selection for earlier maturation; however, other traits and behaviours could evolve (e.g., growth, timing of spawning, boldness). While commercial harvest previously dominated, recreational fishing is now expected to be a strong contributor to harvest selection in the Great Lakes. Environmental variation, density-dependence, invasive species, and the genetic legacy of population bottlenecks and stocking interact with, and make it more challenging to detect, FIE in the Great Lakes than in marine systems. Case studies are presented for Great Lakes stocks of yellow perch Perca flavescens and lake whitefish Coregonus clupeaformis for which FIE has been investigated. The evidence for FIE in the Great Lakes is currently sparse, potentially because of the low research focus on this topic or because of the interacting influence of environmental variation and anthropogenic stressors.
... First, they do not have the same dimensions. The tusks of today's African elephants vary between 50cm and over 2 meters, but hunt and poaching have caused a progressive diminution of those maximal dimensions, as individuals with longer tusks were the more sought after (Chiyo, Obanda, and Korir 2015). The cementum layer (the exterior of the tooth, that must be removed to access the ivory proper) is relatively thin, and primary dentine (i.e. ...
... Female elephants exhibit matriarchal social structure [23,24], and older adults are linked to resource access [27], ecological and social knowledge [25,51] and calf survival [26,52,53]. Ivory poaching tends to target older animals for their larger tusks, reducing population age structure [54,55]. Since matriarchs are targeted, this causes orphaning and alters family unit structure. ...
Repeated use of the same areas may benefit animals as they exploit familiar sites, leading to consistent home ranges over time that can span generations. Changing risk landscapes may reduce benefits associated with home range fidelity, however, and philopatric animals may alter movement in response to new pressures. Despite the importance of range changes to ecological and evolutionary processes, little tracking data have been collected over the long-term nor has range change been recorded in response to human pressures across generations. Here, we investigate the relationships between ecological, demographic and human variables and elephant ranging behaviour across generations using 16 years of tracking data from nine distinct female social groups in a population of elephants in northern Kenya that was heavily affected by ivory poaching during the latter half of the study. Nearly all groups—including those that did not experience loss of mature adults— exhibited a shift north over time, apparently in response to increased poaching in the southern extent of the study area. However, loss of mature adults appeared to be the primary indicator of range shifts and expansions, as generational turnover was a significant predictor of range size increases and range centroid shifts. Range expansions and northward shifts were associated with higher primary productivity and lower poached carcass densities, while westward shifts exhibited a trend to areas with higher values of primary productivity and higher poached carcass densities relative to former ranges. Together these results suggest a trade-off between resource access, mobility and safety. We discuss the relevance of these results to elephant conservation efforts and directions meriting further exploration in this disrupted society of a keystone species. © 2018 The Author(s) Published by the Royal Society. All rights reserved.
... The higher proportion of tuskless individuals was another consistent feature of poached populations sampled in 2009. This finding is in agreement with previous studies that have highlighted increased tusklessness in local elephant populations subject to heavy illegal harvesting (Poole, 1989;Jachmann et al., 1995;Whitehouse, 2002), and also concurs with a recent study showing a decline in tusk size in recovering populations (Chiyo et al., 2015). In comparison to the relatively undisturbed elephant population of Amboseli NP, which shows a proportion of tuskless adults of less than 1% (Poole, 1989;Moss et al., 2011), a proportion of 6-8%, as found in populations experiencing medium to high poaching in 2009 and in the Ruaha population in 2015, is unusually high (Poole and Thomsen, 1989). ...
The management of conflicts between wildlife conservation and agricultural practices often involves the implementation of strategies aimed at reducing the cost of wildlife impacts on crops. Vital to the success of these strategies is the perception that changes in management efforts are synchronised relative to changes in impact levels, yet this expectation is never evaluated. We assess the level of synchrony between time series of population counts and management effort in the context of conflicts between agriculture and five populations of large grazing birds in northern Europe. We reveal inconsistent patterns of synchrony and asynchrony between changes in population counts and impact management effort relating to population harvesting, monetary payments or scaring practices. This variation is likely due to differing management aims, the existence of lags between management decisions and population monitoring, and the inconsistent use of predictive models across case studies. Overall, our findings highlight the need for more adaptive and timely responses of management to changes in target species numbers so as not to unexpectedly increase social conflicts and jeopardise the status of wildlife populations.
... The higher proportion of tuskless individuals was another consistent feature of poached populations sampled in 2009. This finding is in agreement with previous studies that have highlighted increased tusklessness in local elephant populations subject to heavy illegal harvesting (Poole, 1989;Jachmann et al., 1995;Whitehouse, 2002), and also concurs with a recent study showing a decline in tusk size in recovering populations (Chiyo et al., 2015). In comparison to the relatively undisturbed elephant population of Amboseli NP, which shows a proportion of tuskless adults of less than 1% (Poole, 1989;Moss et al., 2011), a proportion of 6-8%, as found in populations experiencing medium to high poaching in 2009 and in the Ruaha population in 2015, is unusually high (Poole and Thomsen, 1989). ...
Detecting and monitoring illegal harvesting pressure on wild populations is challenging due to the cryptic nature of poaching activities. Although change in population age structure has been suggested as an indicator of harvesting pressure, few studies have tested its validity when based on short-term field surveys. Using data from rapid demographic assessment surveys carried out in 2009 at six sites in Tanzania, we examined whether African elephant populations experiencing contrasting levels of poaching pressure showed significant differences in their age structure, operational sex ratio (i.e. adult males to adult females), dependent individual to adult female ratio at the group level, and proportion of tuskless individuals. We also compared similar metrics between the population sampled in Ruaha National Park in 2009 and again in 2015 following a suspected increase in poaching. Elephant populations experiencing medium and high levels of poaching in 2009 were characterised by fewer calves and old individuals, a reduced number of adult males relative to adult females, and a lower ratio of calves to adult females within groups. We also found a higher proportion of tuskless individuals in poached populations (> 6%). Changes in age structure in the Ruaha population between 2009 and 15 were similar to those observed across sites in 2009. Our findings are consistent with previous work documenting how the loss of older individuals targeted for their larger tusks-decreases recruitment and survival of elephant calves. Illegal killing for ivory is a huge threat to the survival of African elephants. In this context, the present study contributes towards validating the use of age structure as an indicator of poaching pressure in elephant populations, but also in other wildlife populations where illegal offtake is targeted at specific age classes.
... First, there is limited direct evidence from terrestrial ecosystems linking trait changes to ecological outcomes. In addition to behavioral changes, harvest in terrestrial species often affects sexually selected traits such as horns, antlers, and tusks (Chiyo et al. 2015;Pigeon et al. 2016). Such traits can serve as defensive weapons against predators, and their reduction or loss may have implications for predator-prey interactions, which deserve further study. ...
Harvest of wild animals and plants is pervasive, exerts ecological and evolutionary pressure on populations, and is known to drive rapid changes in organismal traits. Although the factors that lead to rapid trait changes have received increased attention, the ecological consequences of harvest-driven trait changes are less appreciated. We review recent evidence that harvest-driven trait changes can affect community and ecosystem processes. Growing experimental evidence, modeling studies, and field observations have revealed that common responses to harvest include changes in life-history and behavioral traits, which have the potential to reshape the ecology of harvested systems. On the basis of existing evidence, we propose a set of general mechanisms that link harvest-driven trait changes to ecological processes, including trophic cascades, nutrient dynamics, keystone interactions, ecosystem stability, and habitat use. Managing harvested ecosystems sustainably may require strategies that account for harvest-driven trait changes. We recommend that trait changes be monitored closely as part of ecosystem-based management plans, especially in cases where targeted traits are known to affect important aspects of ecosystem function.
... As an example, the Huli "Wigmen" of Papua New Guinea use the plumes, and sometimes entire specimens, of male birds of paradise in the construction of their elaborate headwear [1]. Finally, illegal poaching of animals such as elephants for the ivory trade also targets animals with the greatest expression of secondary sexual traits [2]. ...
Humans commonly harvest animals based on their expression of secondary sexual traits such as horns or antlers. This selective harvest is thought to have little effect on harvested populations because offtake rates are low and usually only the males are targeted. These arguments do not, however, take the relationship between secondary sexual trait expression and animal condition into account: there is increasing evidence that in many cases the degree of expression of such traits is correlated with an animal’s overall well-being, which is partly determined by their genetic match to the environment. Using an individual-based model,we find that when there is directional environmental change, selective harvest of males with the largest secondary sexual traits can lead to extinction in otherwise resilient populations. When harvest is not selective, the males best suited to a new environment gain the majority of matings and beneficial alleles spread rapidly. When these bestadapted males are removed, however, their beneficial alleles are lost, leading to extinction. Given the current changes happening globally, these results suggest that trophy hunting and other cases of selective harvest (such as certain types of insect collection) should be managed with extreme care whenever populations are faced with changing conditions. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
... Female African savannah elephants (Loxodonta africana) form matriarchal societies in which daughters remain with their mothers and other female relatives in multi-generational groups for life 20,21 . The disproportionate poaching of older elephants for their larger ivory 22,23 removes critical social partners that offer ecological knowledge and resource access 19,24,25 . Aberrant behavior has been recorded in male elephant orphans that experienced impoverished social environments 10 . ...
Compensatory social behavior in nonhuman animals following maternal loss has been documented, but understanding of how orphans allocate bonding to reconstruct their social networks is limited. Successful social integration may be critical to survival and reproduction for highly social species and, therefore, may be tied to population persistence. We examined the social partners involved in affiliative interactions of female orphans and non-orphans in an elephant population in Samburu, northern Kenya that experienced heightened adult mortality driven by drought and intense ivory poaching. We contrasted partners across different competitive contexts to gain insight to the influence of resource availability on social interactions. Though the number of partners did not differ between orphans and non-orphans, their types of social partners did. Orphans interacted with sisters and matriarchs less while feeding than did non-orphans, but otherwise their affiliates were similar. While resting under spatially concentrated shade, orphans had markedly less access to mature adults but affiliated instead with sisters, bulls, and age mates. Orphan propensity to strengthen bonds with non-dominant animals appears to offer routes to social integration following maternal loss, but lack of interaction with adult females suggests orphans may experience decreased resource access and associated fitness costs in this matriarchal society.
... However, failure to address social issues, such as inequitable distribution of hunting revenues and the involvement of communities, can undermine the success of hunting operations . Illegal harvesting of species reduces the number of animals available for trophy hunting (Balme et al. 2009, Chiyo et al. 2015 and impacts not only the survival of species but also impacts on the revenue awarded to communities who bear important costs from conservation (Hutton and Leader-Williams 2003, Jorge et al. 2013, Challander and MacMillan 2014. The monitoring of cross-border populations is, however, compounded by the legal landscape in which the species occur (Selier et al. in review), and is reliant on effective cooperation between range states and buy in from politicians within these countries (Di Minin and Toivonen 2015, Selier et al. in review). ...
Transfrontier conservation areas potentially play a key role in conserving biodiversity and promoting socioeconomic development. However, socio-political factors often affect their effectiveness in achieving biodiversity conservation and sustainable development objectives. Following a transdisciplinary approach, I assessed the challenges and opportunities in conserving and managing the African elephant (Loxodonta africana) population within the Greater Mapungubwe Transfrontier Conservation Area (GMTFCA) in Botswana, South Africa and Zimbabwe, southern Africa.
The results showed that the current rate of offtake of bull elephant in the GMTFCA is unsustainable. At current rates of hunting, in fact, trophy bulls were predicted to disappear from the population in less than 10 years. Elephant densities were higher in South Africa and Botswana where the gross domestic product is higher. In addition, elephant densities were higher at sites where the proportion of agricultural land around them was the lowest and where vegetation productivity was the highest. Trophy hunting, as well as other localised human activities, also affected the distribution of elephant within sites, forcing them to trade-off between disturbance avoidance and the availability of food and water. While at the international level, a significant body of law and policy relevant to elephant conservation exists, I found that there was little cooperation among Botswana, South Africa and Zimbabwe, and a lack of implementation of these provisions on a national and trilateral level.
Overall, this study confirmed that poverty was an important factor affecting elephant abundance at the country level, but highlighted that, at the site level, anthropogenic disturbance played a crucial role. A revision of the current hunting quotas within each country and the establishment of a single multi-jurisdictional (cross-border) management authority regulating the hunting of elephant is needed. Further, to reduce the impact of increasing human populations and agricultural expansion, the development of coordinated legislation and policies to improve land use planning, and the development of conservation corridors to link current protected areas, is needed.
The issues regarding the management of this elephant population illustrate the significant challenges involved in achieving a comprehensive, consistent and effective implementation of a transboundary population approach. Southern African countries make an important contribution to elephant conservation and could soon become the last stronghold of elephant conservation in sub-Saharan Africa. Therefore, immediate actions are needed to reduce pressures from human activities in order to enhance the long-term persistence of the species.
... Finally, species in which both sexes grow horns, tusks or antlers that are the target of selective hunting may show faster evolutionary change than species where females are not selectively hunted. That may be the case, for example, for African elephants Loxodonta africana (Chiyo et al. 2015). ...
Potential evolutionary consequences of selective hunting of mammals are controversial because of limited evidence and important socio-economic impacts. Several ecological and management variables facilitate evolutionary responses to selection for horn, tusk or antler size, including strong selective hunting pressure; harvest of males with large horns, tusks or antlers before they can breed; unavailable or ineffective sources of unselected immigrants; and age-dependent relationships between horn, tusk or antler size and male mating success. Plastic responses of male horns, tusks and antlers to environment are probably more common than evolutionary changes. Evidence for evolutionary effects of selective hunting is strong for large mammals where biological characteristics and hunting regulations combine to favour them.
... In TME, the elephant population experienced pronounced poaching in 1970s and 1980s (Prins et al., 1994;Foley and Faust, 2010), with limited levels of poaching more recently (Kioko et al., 2013), compared to other parts of Tanzania (EIA, 2014). Poaching can cause significant increase in stress levels of elephants often resulting in long lasting effects (Foley et al., 2001), due to the loss of social benefits such as cooperative parenting, foraging and defense as the older more experienced individuals are likely to be targeted (Maisels et al., 2013;Chiyo et al., 2015). ...
The underlying causes of temporal gland secretion (TGS) in African elephants are not well understood. In order to better understand TGS predisposing factors, we assessed TGS in relation to a suite of intrinsic and environmental variables in free ranging elephants. TGS monitoring was done in fully protected areas of Lake Manyara National Park (LMNP) and Tarangire National Park (TNP) and Manyara Ranch (MR), a semi-protected multiple use area. Using a hierarchical modeling approach that accounted for the nested data structure, we found that TGS was mainly associated with elephant-specific variables. The likelihood of TGS increased with elephant age. Female elephants were more likely to show TGS than male elephants. In larger groups, females were less likely to have TGS, whereas the likelihood for TGS increased with group size in male elephants. This information enhances our understanding of TGS, and its importance as physiological marker.
After a long-standing debate, African elephants are now considered by the IUCN as two distinct species: savannah elephants (Loxodonta africana), listed as endangered on the IUCN Red List of Threatened Species, and forest elephants (Loxodonta cyclotis), critically endangered. Both are severely threatened by forest loss, fragmentation and degradation due to agriculture expansion, as well as by illegal ivory trade. Although the two species have different habitat preferences, their range overlaps in some ecotones; despite an ancient separation between these two species, hybrids have been reported in five locations. The main hybrid hotspot is located on the Democratic Republic of Congo-Uganda border and still remains understudied. Using 15 microsatellites, we investigated this hybridization zone by determining the species and hybrid status of 177 fecal samples collected in the area of Sebitoli, at the extreme North of Kibale National Park. Surprisingly for a forest area, no pure forest elephants were detected. Out of the 91 individuals sampled, a very large proportion (81.3%) were hybrid individuals mainly from a second generation or more. Only 18.7% of pure savannah elephants were detected, all originating from the DRC-Uganda border. Further analyses are necessary to assess the age of this hybridization zone. Our results emphasize that hybrids and savannah elephants can successfully range in forested area. They also show that forest elephants are rare even in their native habitat. In the current context of high threat faced by African elephant species, it is crucial to strengthen conservation efforts for these species before it is too late.
It is important to determine the sex of elephants from their samples—faeces from the field or seized ivory—for forensic reasons or to understand population demography and genetic structure. Molecular sexing methods developed in the last two decades have often shown limited efficiency, particularly in terms of sensitivity and specificity, due to the degradation of DNA in these samples. These limitations have also prevented their use with ancient DNA samples of elephants or mammoths. Here we propose a novel TaqMan-MGB qPCR assay to address these difficulties. We designed it specifically to allow the characterization of the genetic sex for highly degraded samples of all elephantine taxa (elephants and mammoths). In vitro experiments demonstrated a high level of sensitivity and low contamination risks. We applied this assay in two actual case studies where it consistently recovered the right genotype for specimens of known sex a priori. In the context of a modern conservation survey of African elephants, it allowed determining the sex for over 99% of fecal samples. In a paleogenetic analysis of woolly mammoths, it produced a robust hypothesis of the sex for over 65% of the specimens out of three PCR replicates. This simple, rapid, and cost-effective procedure makes it readily applicable to large sample sizes.
Intra- and intersexual selection drives the evolution of secondary sexual traits, leading to increased body size, trait size and generally increased reproductive success in bearers with the largest, most attractive traits. Evolutionary change through natural selection is often thought of primarily in terms of genetic changes through mutations and adaptive selection. However, this view ignores the role of the plasticity in phenotypes and behaviour and its impact on accelerating or decelerating the expression of sexually selected traits. Here, we argue that sudden changes in selection pressures (e.g. predation pressure) may cause a cascade of behavioural responses, leading to a rapid change in the size of such traits. We propose that selective removal of individuals with the most prominent traits (such as large antlers or horns in male ungulates) induces behavioural changes in the surviving males, leading to a reduction in the growth of these traits (phenotypic expression). To test this idea, we used an individual-based simulation, parametrized with empirical data of male bighorn sheep, Ovis candensis. Our model shows that the expression (phenotype, not genotype) of the trait under selection (here horn size) can be negatively impacted, if the biggest, most dominant males in the population are removed. While the selective removal of prime males opens breeding opportunities for younger, smaller males, we predicted that it would come at the expense of growth and maintenance. As predicted, we observed a rapid decline in average male horn length in our model. We argue that this decline happens because smaller males, instead of allocating energy into growth, divert this energy towards participation in mating activities that are typically exclusively available to prime males. While our model deals with ecological life-history trade-offs, it cannot predict evolutionary outcomes. However, this nongenetic mechanism is important for the understanding of evolutionary processes because it describes how heritable traits can rapidly change because of behavioural plasticity, long before any genetic changes might be detectable.
In long-lived social species, older individuals can provide fitness benefits to their groupmates through the imparting of ecological knowledge. Research in this area has largely focused on females in matrilineal societies where, for example, older female African savannah elephants (Loxodonta africana) are most effective at making decisions crucial to herd survival, and old post-reproductive female resident killer whales (Orcinus orca) lead collective movements in hunting grounds. In contrast, little is known about the role of older males as leaders in long-lived social species. By analysing leadership patterns of all-male African savannah elephant traveling groups along elephant pathways in Makgadikgadi Pans National Park, Botswana, we found that the oldest males were more likely to lead collective movements. Our results challenge the assumption that older male elephants are redundant in the population and raise concerns over the biased removal of old bulls that currently occurs in both legal trophy hunting and illegal poaching. Selective harvesting of older males could have detrimental effects on the wider elephant society through loss of leaders crucial to younger male navigation in unknown, risky environments.
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.
Tsavo Trust is an action‐orientated, field‐based, not‐for‐profit conservation organization headquartered in Tsavo, Kenya. In association with Kenya Wildlife Service and other partners, Tsavo Trust utilizes a unique strategy to work on direct wildlife‐conservation projects. Tsavo Trust also engages with specific local communities in the stewardship of conservancies, in order to encourage participation in conservation activities that benefit the marginalized people who live on the border of the formal Protected Area. Tsavo Trust recognizes the importance of a holistic approach to biodiversity conservation, using a combination of professional wildlife conservation activities, grass‐roots community engagement, valued partnerships and committed supporters to create a virtuous circle for the protection of Tsavo. The mission is to conserve the vast wilderness of the Tsavo Conservation Area, which encompasses Kenya's biggest Protected Area, and is home to Kenya's largest elephant population, including several iconic ‘Tuskers’, and numerous high‐value species. Tsavo Conservation Area is one of the few truly wild places with significant wildlife left in Africa. This national heritage is under threat and faces multiple challenges, including wildlife crime, climate change and habitat loss. At the time of writing, the Tsavo elephant population contains eight bull ‘Tuskers’ and five iconic cow ‘Tuskers’, as well as c . 26 younger bulls that may emerge as ‘Tuskers’ in the next 5 years. Tsavo Trust's work focuses on four core programmes: ‘Wildlife Conservation Program: Big Tusker Project’, ‘Community Conservancy Program’, ‘Animal Welfare Program’ and ‘Conservation Partnerships’. Through the Big Tusker Project, Tsavo Trust, in partnership with Kenya Wildlife Service, provides extra protection for the last ‘Super Tuskers’ of Tsavo using aerial surveillance and mobile ground‐based units.
Dental and skeletal development provide a measure of physiological age that can be used to predict the optimal timing for treatment in orthodontic, orthopaedic or paediatric clinical practice or to estimate chronological age of child skeletal remains in forensic or archaeological contexts. Because the environmental sensitivity of skeletal and dental development can affect the ability to predict treatment timing and accuracy of age estimations, it is important to understand how these two tissues respond differently to environmental insults, such disease or malnutrition. This paper reviews the literature that supports the general assertion that dental development is less affected by environmental quality than skeletal development. It is concluded that the environmental sensitivity of tooth formation (compared to tooth eruption) has been rarely assessed and that there is a paucity of studies that examine the development of both tissues against socioeconomic and nutritional status or non-genetic disease.
Although much biological research depends upon species diagnoses, taxonomic expertise is collapsing. We are convinced that the sole prospect for a sustainable identification capability lies in the construction of systems that employ DNA sequences as taxon 'barcodes'. We establish that the mitochondrial gene cytochrome c oxidase I (COI) can serve as the core of a global bioidentification system for animals. First, we demonstrate that COI profiles, derived from the low-density sampling of higher taxonomic categories, ordinarily assign newly analysed taxa to the appropriate phylum or order. Second, we demonstrate that species-level assignments can be obtained by creating comprehensive COI profiles. A model COI profile, based upon the analysis of a single individual from each of 200 closely allied species of lepidopterans, was 100% successful in correctly identifying subsequent specimens. When fully developed, a COI identification system will provide a reliable, cost-effective and accessible solution to the current problem of species identification. Its assembly will also generate important new insights into the diversification of life and the rules of molecular evolution.
Population genomics has the potential to improve studies of evolutionary genetics, molecular ecology and conservation biology, by facilitating the identification of adaptive molecular variation and by improving the estimation of important parameters such as population size, migration rates and phylogenetic relationships. There has been much excitement in the recent literature about the identification of adaptive molecular variation using the population-genomic approach. However, the most useful contribution of the genomics model to population genetics will be improving inferences about population demography and evolutionary history.
Although the incidence of abalone poaching is increasing in South Africa, several alleged poachers have been acquitted in cases where the state has been unable to prove that the confiscated meat is of the local abalone, Haliotis midae. This species is illegally exported to the Far East by poaching syndicates, a practice that is undermining the legitimate industry. To solve this, a polymerase chain reaction (PCR) technique that targets a portion of the lysin gene of several abalone species and unequivocally distinguishes between H. midae and H. spadicea (a sympatric congeneric) has been developed. The PCR primers specifically amplify approximately 1,300 bp of genomic DNA from dried, cooked, and fresh abalone tissue. A smaller fragment of 146 bp is used for canned abalone. Restriction fragment length polymorphism (RFLP) exploit interspecific polymorphisms that discriminate between these two species. The method can also be used to identify H. rubra and can easily be adapted to other abalone species under the same threat of overexploitation.
ABSTRACf Likelihood methods for the von Bertalanffy growth curve are examined under the assumption of independent, normallydistributederrors. The following are examined: determiningthe bestmethod of estimation, relationships between methods of estimation, failure of ll88U.IIlptions, constructing con fidence regions, and applying likelihood ratio teats. An example is presented illustrating many of the. methods discussed in theory. The paper may be viewed as an application of classic nonlinear least squares methods to the von Bertalanffy curve. Assuch, the concepts diBCUBBed are generallyapplicable and the papermay serve as an introduction to nonlinear least squares.
The ancestor of recent vertebrate teeth was a tooth-like structure on the outer body surface of jawless fishes. Over the course of 500,000,000 years of evolution, many of those structures migrated into the mouth cavity. In addition, the total number of teeth per dentition generally decreased and teeth morphological complexity increased. Teeth form mainly on the jaws within the mouth cavity through mutual, delicate interactions between dental epithelium and oral ectomesenchyme. These interactions involve spatially restricted expression of several, teeth-related genes and the secretion of various transcription and signaling factors. Congenital disturbances in tooth formation, acquired dental diseases and odontogenic tumors affect millions of people and rank human oral pathology as the second most frequent clinical problem. On the basis of substantial experimental evidence and advances in bioengineering, many scientists strongly believe that a deep knowledge of the evolutionary relationships and the cellular and molecular mechanisms regulating the morphogenesis of a given tooth in its natural position, in vivo, will be useful in the near future to prevent and treat teeth pathologies and malformations and for in vitro and in vivo teeth tissue regeneration.
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.
The great white shark, Carcharodon carcharias, is the most widely protected elasmobranch in the world, and is classified as Vulnerable by the IUCN and listed on Appendix III of CITES. Monitoring of trade in white shark products and enforcement of harvest and trade prohibitions is problematic, however, in large part due to difficulties in identifying marketed shark parts (e.g., dried fins, meat and processed carcasses) to species level. To address these conservation and management problems, we have developed a rapid, molecular diagnostic assay based on species-specific PCR primer design for accurate identification of white shark body parts, including dried fins. The assay is novel in several respects: It employs a multiplex PCR assay utilizing both nuclear (ribosomal internal transcribed spacer 2) and mitochondrial (cytochrome b) loci simultaneously to achieve a highly robust measure of diagnostic accuracy; it is very sensitive, detecting the presence of white shark DNA in a mixture of genomic DNAs from up to ten different commercially fished shark species pooled together in a single PCR tube; and it successfully identifies white shark DNA from globally distributed animals. In addition to its utility for white shark trade monitoring and conservation applications, this highly streamlined, bi-organelle, multiplex PCR assay may prove useful as a general model for the design of genetic assays aimed at detecting body parts from other protected and threatened species.
Spatial and temporal trends and variation in life-history traits, including age and length at maturation, can be influenced by environmental and anthropogenic processes, including size-selective exploitation. Spawning adults in many wild Alaskan sockeye salmon populations have become shorter at a given age over the past half-century, but their age composition has not changed. These fish have been exploited by a gillnet fishery since the late 1800s that has tended to remove the larger fish. Using a rare, long-term dataset, we estimated probabilistic maturation reaction norms (PMRNs) for males and females in nine populations in two basins and correlated these changes with fishery size selection and intensity to determine whether such selection contributed to microevolutionary changes in maturation length. PMRN midpoints decreased in six of nine populations for both sexes, consistent with the harvest. These results support the hypothesis that environmental changes in the ocean (likely from competition) combined with adaptive microevolution (decreased PMRNs) have produced the observed life-history patterns. PMRNs did not decrease in all populations, and we documented differences in magnitude and consistency of size selection and exploitation rates among populations. Incorporating evolutionary considerations and tracking further changes in life-history traits can support continued sustainable exploitation and productivity in these and other exploited natural resources.
Long-term data (1974–2011) from harvested bighorn rams (Ovis canadensis) in Alberta, Canada, suggested a reduction in horn size and in the proportion of trophy rams in the provincial population over time. Age at harvest increased over time, suggesting slower horn growth. Rams that experienced favorable environmental conditions early in life had rapid horn growth and were harvested at a younger age than rams with slower horn growth. Guided nonresident hunters did not harvest larger rams than residents, suggesting that few large rams were available. Resident hunter success declined in recent years. Despite an apparently stable population, successive cohorts produced a decreasing harvest of trophy rams. We suggest that unrestricted harvest based on a threshold horn size led to a decline in the availability of trophy rams. That decline is partly an inevitable consequence of selective hunting that removes larger rams. Although our analysis does not establish that evolution of smaller horns caused the observed decline in both horn size and harvest of trophy rams, we suggest that intensive trophy hunting may have artificially selected for a decrease in horn growth rate. © 2013 The Wildlife Society.
Very few studies have ever focused on the elephants that are wounded or killed as local communities attempt to scare these animals away from their settlements and farms, or on the cases in which local people take revenge after elephants have killed or injured humans. On the other hand, local communities live in close proximity to elephants and hence can play a positive role in elephant conservation by informing the authorities of the presence of injured elephants.
Between 2007 and 2011, 129 elephants were monitored in Masai Mara (Kenya), of which 54 had various types of active (intentionally caused) or passive (non-intentionally caused) injuries. Also studied were 75 random control samples of apparently unaffected animals. The observed active injuries were as expected biased by age, with adults suffering more harm; on the other hand, no such bias was observed in the case of passive injuries. Bias was also observed in elephant sex since more males than females were passively and actively injured. Cases of passive and active injuries in elephants were negatively related to the proximity to roads and farms; the distribution of injured elephants was not affected by the presence of either human settlements or water sources. Overall more elephants were actively injured during the dry season than the wet season as expected. Local communities play a positive role by informing KWS authorities of the presence of injured elephants and reported 43% of all cases of injured elephants.
Our results suggest that the negative effect of local communities on elephants could be predicted by elephant proximity to farms and roads. In addition, local communities may be able to play a more positive role in elephant conservation given that they are key informants in the early detection of injured elephants.
By estimating probabilistic reaction norms for age and size at maturation, we show that maturation schedules of Atlantic cod (Gadus morhua) off Labrador and Newfoundland shifted toward earlier ages and smaller sizes during the late 1980s and early 1990s, when these populations underwent a severe collapse in biomass and subsequently were closed for directed commercial fishing. We also demonstrate that this trend towards maturation at younger ages and smaller sizes is halted and even shows signs of reversal during the closure of the fisheries. In addition, our analysis reveals that males tend to mature earlier and at a smaller size than females and that maturation age and size decrease with increasing latitude. Importantly, the maturation reaction norms presented here are robust to variation in survival and growth (through phenotypic plasticity) and are thus strongly indicative of rapid evolutionary changes in cod matu- ration as well as of spatial and sex-specific genetic variation. We therefore suggest that maturation reaction norms can provide helpful reference points for managing harvested populations with evolving life histories.
Life history theory predicts that high adult mortality rates select for earlier maturity and increased reproduction. If such evolution occurs in response to the commercial exploitation of natural fish populations, then the correlated reduction in body size would reduce the yield of the fishery. Earlier maturity and reduced body size are seen in commercially exploited populations. Here, we compare the life histories of natural populations of guppies (Poecilia reticulata) from Trinidad that live in either high- or low-predation environments, which serve as surrogates for the presence or absence of commercial fishing. We can quantify mortality rate and life history variables, including age and size at maturity, in the laboratory and in nature. We have manipulated mortality rates in nature and measured the rate of evolution. High mortality selects for earlier maturity at a smaller size, as observed in commercial fisheries and as predicted by theory. Furthermore, the nature and magnitude of predator-induced mortality are comparable to those caused by commercial fishing. The rate of evolution in guppies predicts similar evolution in commercial fisheries on a time scale of decades. These attributes support arguments that humans, like predators, have acted as an agent of selection when exploiting populations of fish.
We describe the development of a genetic assay for the identification of the tropical hardwood ramin Gonystylus spp., a CITES-listed genus subject to illegal international trade. Sam- ples representing different ramin species, confamilial genera and morphologically similar taxa were obtained. DNA extraction from leaf material and wood products was achieved using com- mercially available kits. Five chloroplast genes were examined for Single Nucleotide Polymor- phism (SNP) loci capable of discriminating ramin. A locus within the matK gene was selected and a TaqMan® assay designed for sample genotyping. The assay was validated against different spe- cies to demonstrate its specificity and reproducibility. The final assay provides a robust, cost-effec- tive, transferable method for identifying processed ramin. The research represents a feasibility study, addressing each of the steps required to develop a genetic identification assay for enforce- ment use; however, it should be noted that further work is required to produce a fully validated forensic identification tool.
Post-natal growth in the African elephant (Loxodonta africana) was described using three alternative mathematical models, and two age estimation schedules. Von Bertalanffy, Gompertz and Logistic equations all provided adequate models of post-natal growth in a species for which age estimation methods are largely unsubstantiated. Gompertz and Logistic models overestimated pre-weaning growth and underestimated adult size. Self-accelerating growth is of short duration (one and three years in females and males, respectively), and we found no evidence of a secondary growth spurt in males. Males, nevertheless, continue to grow throughout their lifespan, while females reach asymptotic size at the age of 35–40 years. We found no evidence of differences in growth rate of males and females up to 10 years, and there does not seem to be differential investment in male and female offspring. Growth rates of captive elephants differ substantially from all wild populations studied and may not serve as adequate references for the revision of existing age estimation schedules.
The Atlantic herring Clupea harengus has played a pivotal role in the formulation of ideas relating to population structuring in marine fishes, yet considerable uncertainty remains as to the extent to which phenotypic and genetic differentiation coincide in such a highly mobile species. In this study, we examined genetic population structure across the major herring spawning aggregations in the North Sea and adjacent waters over 2 years, 2002 and 2003. We analysed 1660 spawning individuals across 9 microsatellite loci. Data were analysed using several approaches, taking into account the effect of location, year-class and sex, as well as pooling all individuals together, making no assumption as to the number of populations present in the data set. The results suggest the presence of a genetically homogeneous unit off Northern Scotland, and a temporally stable pattern of isolation by distance determined predominantly by the divergence of the English Channel samples and, in 2003, by the Norwegian spring spawners. Our data suggest that the current view of North Sea herring as a unit-stock might be adequate, but confirm the considerable degree of demographic independence of the herring populations in the English Channel. Despite major recent population collapses, genetic data indicated no evidence of bottlenecks affecting the genetic diversity of extant North Sea herring populations. Finally, despite evidence of weak population structuring, we discuss the risks of underestimating population differentiation in marine fish of large population sizes, and with reference to herring population history and dynamics, we attempt to reconcile the existing theories on herring population structure.
Growth from conception to reproductive onset in African elephants (Loxodonta africana) provides insights into phenotypic plasticity, individual adaptive plastic responses and facultative maternal investment. Using growth for 867 and life histories for 2652 elephants over 40 years, we demonstrate that maternal inexperience plus drought in early life result in reduced growth rates for sons and higher mortality for both sexes. Slow growth during early lactation was associated with smaller adult size, later age at first reproduction, reduced lifetime survival and consequently limited reproductive output. These enduring effects of trading slow early growth against immediate survival were apparent over the very long term; delayed downstream consequences were unexpected for a species with a maximum longevity of 70+ years and unpredictable environmental experiences.
An international multi-laboratory project was conducted to develop a standardized DNA database for Chinook salmon (Oncorhynchus tshawytscha). This project was in response to the needs of the Chinook Technical Committee of the Pacific Salmon Commission to identify stock composition of Chinook salmon caught in fisheries during their oceanic migrations. Nine genetics laboratories identified 13 microsatellite loci that could be reproducibty assayed in each of the laboratories. To test that the loci were reproducible among laboratories, blind tests were conducted to verify scoring consistency for the nearly 500 total alleles. Once standardized, a dataset of over 16,000 Chinook salmon representing 110 putative populations was constructed ranging throughout the area of interest of the Pacific Salmon Commission from Southeast Alaska to the Sacramento River in California. The dataset differentiates the major known genetic lineages of Chinook salmon and provides a tool for genetic stock identification of samples collected from mixed fisheries. A diverse group of scientists representing the disciplines of fishery management, genetics, fishery administration, population dynamics, and sampling theory are now developing recommendations for the integration of these genetic data into ocean salmon management.
In 1985 many African elephant populations, which had been monitored for a decade or more, were either in rapid decline or down to a fraction of their former size. The author examines regional trends and information on key populations with reference to the critical factors affecting the survival of the African elephant, most significantly poaching and the illegal trade in ivory
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@article{ORX:4958396,author = {Douglas-Hamilton,I.},title = {African elephants: population trends and their causes},journal = {Oryx},volume = {21},issue = {01},month = {1},year = {1987},issn = {1365-3008},pages = {11--24},numpages = {14},doi = {10.1017/S0030605300020433},URL = {http://journals.cambridge.org/article_S0030605300020433},}
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African elephants: population trends and their causes
I. Douglas-Hamilton (1987).
Oryx , Volume 21 , Issue01 , January 1987, pp 11-24
http://journals.cambridge.org/action/displayAbstract?aid=4958396
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African elephants: population trends and their causes
I. Douglas-Hamilton January 1987
Oryx,
,Volume21,
Issue01,
January 1987,
pp 11-24
http://journals.cambridge.org/abstract_S0030605300020433
I. Douglas-Hamilton
(1987).
African elephants: population trends and their causes.
Oryx,
21,
pp 11-24.
doi:10.1017/S0030605300020433.
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Operators of hunting safaries in Botswana have long noted that tusks of trophy animals shot by their clients usually exceed expectations based on estimates made from observations of the live elephant. Their previous experience in East Africa makes them underestimate the weight of ivory carried by the Botswana animals. This suggested that significant morphological differences might be present in various elephant populations which might prove to be genetic markers by which the distribution and movements of herds to and from a large geographic area might be detected. Such markers would permit estimation of the degree of interchange between contiguous populations as in Rhodesia and Botswana or between a game reserve and adjacent hunting areas.
Abstract Huge breeding aggregations of red-sided garter snakes (Thamnophis sirtalis parietalis) at overwintering dens in Manitoba provide a unique opportunity to identify sources of mortality and to clarify factors that influence a snake's vulnerability to these factors. Comparisons of sexes, body sizes, and body condition of more than 1000 dead snakes versus live animals sampled at the same time reveal significant biases. Three primary sources of mortality were identified. Predation by crows, Corvus brachyrhynchos (590 snakes killed), was focussed mostly on small snakes of both sexes. Crows generally removed the snake's liver and left the carcass, but very small snakes were sometimes brought back to the nest. Suffocation beneath massive piles of other snakes within the den (301 dead animals) involved mostly small males and (to a lesser extent) large females; snakes in poor body condition were particularly vulnerable. Many emaciated snakes (in= 142, mostly females) also died without overt injuries, probably due to depleted energy reserves. These biases in vulnerability are readily interpretable from information on behavioral ecology of the snakes. For example, sex biases in mortality reflect differences in postemergence behavior and locomotor capacity, the greater attractiveness of larger females to males, and the high energy costs of reproduction for females.
Assignment methods, which use genetic information to ascertain population membership of individuals or groups of individuals, have been used in recent years to study a wide range of evolutionary and ecological processes. In applied studies, the first step of articulating the biological question(s) to be addressed should be followed by selection of the method(s) best suited for the analysis. However, this first step often receives less attention than it should, and the recent proliferation of assignment methods has made the selection step challenging. Here, we review assignment methods and discuss how to match the appropriate methods with the underlying biological questions for several common problems in ecology and conservation (assessing population structure ; measuring dispersal and hybridization; and foren-sics and mixture analysis). We also identify several topics for future research that should ensure that this field remains dynamic and productive.
We determined the gender of deer samples using polymerase chain reaction primers to the sry gene located on the Y chromosome of mammalian males. Primers to the ZFX/ZFY genes were added to the same amplification reaction as a control against amplification failure. The sry fragment amplified from deer DNA was partially sequenced. Sequence alignment with published bp sequences from other mammals and get migration indicate the fragment is 174 bp long. In a blind test, tissue samples from 100 individual deer and elk of known sex were correctly gender-typed. DNA from deer bloodstains and hair samples was successfully amplified and typed. Under known limiting DNA conditions, the duplex reaction results were reliable and no false positive females were observed. DNA detection on gels stained with SYBR green was more sensitive than with ethidium bromide. DNA from wildlife forensic samples confiscated between 1990 and 1997 was extracted with Chelex 100 and tested. Twenty-four out of 31 different evidence items tested were successfully gender-typed: 15 out of 21 bloodstains, 5 out of 6 hairs, and 4 out of 4 tissue samples.
In Asian elephant Elephas maximus Linnaeus, 1758 tuskless bulls or maknas are generally rare. Only in Sri Lanka 93% of subadult and adult bulls have been reported to be maknas. Using historical records and computer simulations we demonstrate that simulation in man-made. The following mechanisms were identified to be associated with a loss of tuskers: (1) When using elephants, man has always preffered tuskers. (2) Selective hunting and capturing frequently led to a decrease of tuskers in wild-living populations. (3) The impact of selective unting and capturing was highest in isolated populations, such as Sri Lanka. (4) Selective removal of tuskers for protecting a maximum wild-living male population resulted in an increase of maknas.
We assess tooth-based age criteria for African elephants developed by Laws in relation to known-aged individuals in the Amboseli elephant population. Laws’s technique remains a robust and useful mechanism for age determination, although we suggest revisions to the oldest age categories. Blind age assignment to jaws of unknown sex using the Laws criteria resulted in misclassification of M4 and M5; measures overlapped too much to differentiate these teeth by sex. Sexes could be reliably distinguished after age 30 or XIX in tooth category by two measures: mandible thickness and width of the ascending ramus, but individuals of the same known age differed in tooth wear and progression rates. Such variation needs to be incorporated in the error assigned to tooth age categories. Ages at death of found jaws (n = 266) were similar to results of survival analysis from all demographic data (n = 2455), excluding calves whose jaws decompose because of weathering and scavengers. Jaw-based models of age at death need correction for the inability to detect this early mortality, which artificially extends mean longevity by up to 6 years.
1.Life-history theory predicts the progressive dwarfing of animal populations that are subjected to chronic mortality stress but the evolutionary impact of harvesting terrestrial herbivores has seldom been tested. In Australia, marsupials of the genus Macropus (kangaroos and wallabies) are subjected to size-selective commercial harvesting. Mathematical modelling suggests that harvest quotas (ca. 10–20% of population estimates annually) could be driving body-size evolution in these species.2.We tested this hypothesis for three harvested macropod species with continental-scale distributions. To do so, we measured more than 2 000 macropod skulls sourced from wildlife collections spanning the last 130 years. We analysed these data using spatial Bayesian models that controlled for the age and sex of specimens as well as environmental drivers and island effects.3.We found no evidence for the hypothesized decline in body size for any species; rather, models that fit trend terms supported minor body size increases over time. This apparently counterintuitive result is consistent with reduced mortality due to a depauperate predator guild and increased primary productivity of grassland vegetation following European settlement in Australia.4.Spatial patterns in macropod body size supported the heat dissipation limit and productivity hypotheses proposed to explain geographic body-size variation (i.e., skull size increased with decreasing summer maximum temperature and increasing rainfall, respectively).5.There is no empirical evidence that size-selective harvesting has driven the evolution of smaller body size in Australian macropods. Bayesian models are appropriate for investigating the long-term impact of human harvesting because they can impute missing data, fit non-linear growth models and account for non-random spatial sampling inherent in wildlife collections.This article is protected by copyright. All rights reserved.
There is evidence that fisheries are altering the phenotypic composition of fish populations, often in ways that may reduce the value of fish stocks for the exploiters. Despite the increasing number of theoretical and field studies, there is still debate as to whether these changes are genetic, can be reversed, and are occurring rapidly enough to be considered in fisheries management. We review the contribution that selection experiments have already provided with respect to the study of the evolutionary effect of fisheries, identify issues that still require more study, and outline future directions for doing so. Selection experiments have already been crucial in showing that harvesting can lead to phenotypic and genetic evolution over relatively short time frames. Furthermore, the experiments have shown the changes involve many other traits than those under direct selection, and that these changes tend to have population‐level consequences, including a decreasing fisheries yield. However, experiments focused on fisheries‐induced evolution that fulfil all our requirements are still lacking. Future studies should have more controlled and realistic set‐ups and assess genetic changes in maturation and growth (i.e. traits most often reported to change) to be more relevant to exploited populations in the wild. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 485–503.