Introduction
Large carnivores are declining, mostly as a result of habitat loss and conflict with people (Ripple et al., Reference Ripple, Estes, Beschta, Wilmers, Ritchie and Hebblewhite2014). This conflict is often characterized by predation of livestock and in some cases by predation on people, and human encroachment on predator habitat. The identification of appropriate and acceptable conflict reduction measures is important for conserving large carnivores and addressing human societal goals. Including the perspectives and expectations of multiple stakeholders, especially grassroots stakeholders, is critical for developing acceptable measures (Redpath et al., Reference Redpath, Linnell, Festa-Bianchet, Boitani, Bunnefeld and Dickman2017).
Unresolved conflict between people and tigers Panthera tigris in Asia is one of the most critical threats to conservation of this species. Tigers attack and threaten both people and livestock (Goodrich et al., Reference Goodrich, Seryodkin, Miquelle and Bereznuk2011). This leads to socio-economic and psychological distress amongst affected local communities (Barua et al., Reference Barua, Bhagwat and Jadhav2013), retaliatory killings of tigers and reduced support for their conservation (Lamichhane et al., Reference Lamichhane, Persoon, Leirs, Musters, Subedi and Gairhe2017; Dhungana et al., Reference Dhungana, Maraseni, Silwal, Aryal and Karki2022). Although such conflicts are reported from all areas where tigers and people co-occur, their extent and nature vary widely (Goodrich, Reference Goodrich2010).
Historical efforts were focused on lethal control of tigers, but with the precipitous decline of tiger populations in the 20th century the use of non-lethal measures has gained momentum (Treves & Karanth, Reference Treves and Karanth2003). Conflict reduction measures are of three types: (1) preventative measures to avoid conflict before it occurs, (2) reactive measures to end or alleviate an existing conflict, and (3) mitigation measures to reduce the impacts of ongoing conflict (Goodrich, Reference Goodrich2010). Commonly adopted conflict reduction measures include tiger translocations, predation early-warning systems, use of deterrents, insurance and compensation payments, habitat management and conservation education about tigers (Goodrich, Reference Goodrich2010; Lamichhane et al., Reference Lamichhane, Persoon, Leirs, Musters, Subedi and Gairhe2017; Karanth et al., Reference Karanth, Gupta and Vanamamalai2018). Decision-makers are often responsible for mitigating conflict despite the differences of opinion amongst stakeholders, lack of resources and uncertainty of success (Barlow et al., Reference Barlow, Greenwood, Ahmad and Smith2010). Although selection of appropriate measures to reduce conflict depends on multiple socio-economic, ecological and technological factors, a multi-stakeholder approach to developing human–carnivore conflict reduction strategies is most likely to succeed because such an approach considers concerns and priorities from a range of people whose roles are critical for achieving conservation goals (Treves et al., Reference Treves, Wallace and White2009; Barlow et al., Reference Barlow, Greenwood, Ahmad and Smith2010). Identifying mutually acceptable conflict reduction measures can help reconcile differences amongst stakeholders and develop the joint ownership and social acceptability (Treves et al., Reference Treves, Wallace and White2009) of measures that could meet most stakeholder expectations.
The tiger is a flagship species in Nepal. As a result of successful conservation, in 2022 Nepal became one of the first countries to nearly triple its tiger population compared to 2009 estimates. Tigers in Nepal occur mainly in three isolated subpopulations in and around five national parks (DNPWC & DFSC, 2022). The increase of the tiger population began in the late 1990s, associated with the better management of national parks, designation of managed buffer zones around national parks and the implementation of community forestry programmes (CNP, 2018). This followed the introduction of a landscape approach through the Terai Arc Landscape Strategy and Action Plan (2005–2015) and associated enhancement of transboundary cooperation between India and Nepal for conservation. The landscape approach involves the conservation of ecosystems of the Terai and Churia hills to ensure ecological, economic and socio-cultural integrity across multiple land uses (MoFSC, 2015; Acharya et al., Reference Acharya, Maraseni and Cockfield2019). These initiatives resulted in the growth of tiger populations in Nepal from 121 individuals in 2009 (Karki et al., Reference Karki, Jnawali, Shrestha, Pandey, Gurung and Thapa2009) to 198 in 2013 (Dhakal et al., Reference Dhakal, Karki, Jnawali, Subedi, Pradhan and Malla2014) and 355 in 2022 (DNPWC & DFSC, 2022). However, this conservation success has come at a cost. In Nepal, human casualties attributed to tigers have quadrupled from nine people/year during 2010–2014 (Acharya et al., Reference Acharya, Paudel, Neupane and Köhl2016) to 36 people in the fiscal year 2021/2022 (DNPWC, 2022). In Bardia National Park in particular, the tiger population increased from 18 in 2009 (Karki et al., Reference Karki, Jnawali, Shrestha, Pandey, Gurung and Thapa2009) to 125 in 2022 (DNPWC & DFSC, 2022), and human casualties attributed to tigers increased from one person/year during 1994–2007 (Bhattarai & Fischer, Reference Bhattarai and Fischer2014) to 18 people in the fiscal year 2020/2021 (BNP, 2021). Various conflict reduction measures such as removal of tigers, compensation payments and livestock husbandry improvements have been implemented (Silwal et al., Reference Silwal, Kolejka, Bhatta, Rayamajhi, Sharma and Poudel2017; BNP, 2021; DNPWC, 2022), although these require regular review and improvement to reduce conflict further.
Chitwan National Park has the largest population of tigers in Nepal, with an increase from 91 in 2009 (Karki et al., Reference Karki, Jnawali, Shrestha, Pandey, Gurung and Thapa2009) to 128 in 2022 (DNPWC & DFSC, 2022). Incidents of human–tiger conflict are frequent in this Park (Silwal et al., Reference Silwal, Kolejka, Bhatta, Rayamajhi, Sharma and Poudel2017), with an increase in annual human casualties attributed to tigers from two to 10 during 2007–2014 (Dhungana et al., Reference Dhungana, Tommaso, Karki, Dhakal, Lamichhane and Bumrungsri2018) and the removal of 17 tigers involved in conflict during 2007–2016 (Lamichhane et al., Reference Lamichhane, Persoon, Leirs, Musters, Subedi and Gairhe2017). Previous studies of human–tiger conflict in Chitwan National Park have mainly investigated conflict patterns (Silwal et al., Reference Silwal, Kolejka, Bhatta, Rayamajhi, Sharma and Poudel2017; Dhungana et al., Reference Dhungana, Tommaso, Karki, Dhakal, Lamichhane and Bumrungsri2018; Lamichhane et al., Reference Lamichhane, Persoon, Leirs, Poudel, Subedi and Pokheral2018), local attitudes towards tigers (Carter et al., Reference Carter, Riley, Shortridge, Shrestha and Liu2014; Dhungana et al., Reference Dhungana, Maraseni, Silwal, Aryal and Karki2022) and management approaches such as removal, compensation payments and electric fencing (Sapkota et al., Reference Sapkota, Aryal, Baral, Hayward and Raubenheimer2014, Dhungana et al., Reference Dhungana, Savini, Karki and Bumrungsri2016; Lamichhane et al., Reference Lamichhane, Persoon, Leirs, Musters, Subedi and Gairhe2017). Given that conflict patterns tend to change over time and the success of conflict-mitigation measures depends largely on the support of key conservation stakeholders, understanding the perspectives of different stakeholders regarding conflict reduction measures is vital for successful management interventions (Treves et al., Reference Treves, Wallace and White2009). Information on the views of the various stakeholders regarding conflict reduction measures is lacking for Chitwan National Park (Silwal et al., Reference Silwal, Kolejka, Bhatta, Rayamajhi, Sharma and Poudel2017; Lamichhane et al., Reference Lamichhane, Persoon, Leirs, Poudel, Subedi and Pokheral2018).
We aimed to identify a set of potential measures to mitigate human–tiger conflict in and around Chitwan National Park and to assess the prioritization of potential conflict reduction measures amongst the various stakeholders (victims, tiger conservation beneficiaries and National Park managers). Our overall objective was to enhance the ability of managers to mitigate human–tiger conflict and conserve tigers. The identification of the priorities of stakeholders regarding adoption of conflict reduction measures has implications for human–tiger conflict mitigation in Chitwan National Park and in other areas with similar socio-ecological settings.
Study area
Chitwan National Park (Fig. 1), a UNESCO World Heritage Site, is the oldest protected area in Nepal and is home to globally threatened species including the tiger, Asian elephant Elephas maximus, gaur or Indian bison Bos gaurus, greater one-horned rhinoceros Rhinoceros unicornis, gharial Gavialis gangeticus and leopard Panthera pardus. The interior area of the National Park (952 km2) encompasses wooded sal Shorea robusta-dominated forest and riparian habitats supporting a mosaic of grasslands, wetlands and rivers. The 729 km2 National Park buffer zone includes human settlements (nearly 70,000 households in 2011; CBS, 2012). The majority of inhabitants engage in farming and livestock husbandry. The buffer zone is one of the historical settlement areas of marginalized ethnic groups (e.g. Bote, Majhi, Kumal and Tharu), who are provided with regulated permission for fishing and other customary activities to preserve their Indigenous heritage and support their daily livelihoods (CNP, 2018). A total of 22 buffer zone user committees have been formed to provide regulated access to the resources available in the National Park and its buffer zone for the local communities, and to engage them in conservation activities. The tiger in Chitwan National Park is regarded as the source population for the surrounding areas in Nepal and areas bordering India (Silwal et al., Reference Silwal, Kolejka, Bhatta, Rayamajhi, Sharma and Poudel2017).
Fig. 1 Location of Chitwan National Park, Nepal, and its surrounding buffer zone, depicting land cover, the four management sectors (units) and 22 buffer zone user committees. (Readers of the printed journal are referred to the online article for a colour version of this figure.)
Methods
Identification of potential conflict reduction measures
We identified potential human–tiger conflict reduction measures through a review of the relevant literature (Barlow et al., Reference Barlow, Greenwood, Ahmad and Smith2010; Goodrich, Reference Goodrich2010; Goodrich et al., Reference Goodrich, Seryodkin, Miquelle and Bereznuk2011; Silwal et al., Reference Silwal, Kolejka, Bhatta, Rayamajhi, Sharma and Poudel2017), including journal articles, published and unpublished official documents and/or reports, and relevant web pages. We then refined the list of measures through 14 key informant interviews with officials of Chitwan National Park (5), the Department of National Parks and Wildlife Conservation (5) and representatives of buffer zone user committees (4) using a checklist and open-ended questions, in January 2022. Finally, we determined revised potential conflict reduction measures and then a subset identified as the most useful, through a workshop organized in Sauraha, near Chitwan National Park, in February 2022. The subset was then prioritized using a questionnaire survey after the workshop with a wider group of participants, in February 2022. We conducted all surveys and workshops in Nepali and obtained the prior informed consent of all respondents.
The workshop involved 46 conservation stakeholders in nine categories (Table 1): farmers, forest users, Indigenous groups (fishers), tourist guides, safari operators, tour and hotel operators, business operators, local NGOs and National Park officials. We selected participants to ensure equitable representation from all four National Park management units, to avoid potential bias. One participant from each of the two NGOs was invited, and for the remaining eight categories we requested that the respective association/network/organization send an equal number of participants from each of the four management units. The respective association/network/organization independently selected the representatives. We screened the participant list for any bias and found that all management units were represented except for the tour and business operator categories, for which no representation from one management unit (Madi) could be provided (because the nominated representative was absent). Because of resource constraints, we did not include other potential stakeholders such as journalists, civil society representatives, conservation partners or the general public.
Table 1 Details of the various stakeholder groups who participated in the workshop for the identification of human–tiger Panthera tigris conflict reduction measures in Chitwan National Park, Nepal (Fig. 1).
Evaluation (prioritization) of conflict reduction measures
We initially identified 22 conflict reduction measures, which we categorized as preventative, mitigative or reactive (Goodrich, Reference Goodrich2010). Through discussion in the workshop and by unanimous consent of participants, we identified a subset of nine potential measures from the initial 22: (1) compensation payments, (2) capture and translocation of tigers involved in conflict, (3) monitoring and tracking of tigers, (4) deterring tigers from entering unsuitable habitats, (5) construction of tiger-proof fences around human settlements and farmlands, (6) habitat and tiger prey management, (7) improvement of livestock corrals, (8) avoidance of grazing in depredation hotspots, and (9) conservation education and awareness activities.
To investigate the priority of these nine measures amongst victims, beneficiaries and managers of tiger conservation, we categorized local stakeholders into four categories: (1) farmers and forest users, (2) fishers (local Indigenous groups), (3) tourism or conservation beneficiaries (including tourist guides, safari operators, tour and hotel operators and business operators), and (4) National Park managers (National Park and NGO officials). We regarded farmers, forest users and fishers as the primary victims of tiger conservation, tourism and business operators as the primary beneficiaries of tiger conservation, and the National Park officials as the tiger conservation managers.
We selected respondents for the questionnaire survey randomly from each of the four stakeholder categories, using a table of random numbers, and equally from amongst the four National Park management units. For farmers and forest users, we selected 45 households from each of the four management units using the household list available from the respective buffer zone user committee. If any selected household was not a farming household, we selected the next farmer household. Each respondent had to be older than 18 years and preferably the household head. For fishers, we selected 15 from each management unit using the fishers list available from the National Park office (the National Park maintains a register of people holding a fishing permit). For tourism beneficiaries, we surveyed two respondents from each association or network of six groups (tourist guide, elephant safari, Jeep safari, tour agency, hotel, shop) using the member lists of the respective association or network in the four management units. For National Park managers, the respondents comprised three National Park staff members from each management unit and one from an NGO. The questionnaires were completed in face-to-face interviews. In total, we surveyed 301 people (180 farmers, 60 fishers, 48 tourism beneficiaries and 13 National Park managers), from whom we received 281 completed questionnaires (93.4%; 197 men, 84 women) representing 168 farmers, 56 fishers, 44 tourism beneficiaries and 13 National Park managers.
In the questionnaire, respondents were required to rank each of the nine conflict-mitigating measures in order of priority on a scale of 1 (lowest priority) to 9 (highest priority) for use in reducing conflict incidents. For each stakeholder group we calculated the score of each measure as (modified from Maraseni, Reference Maraseni2008):
where Wi is the number of respondents selecting a particular measure W (i = 1–9) corresponding to a particular rank R (j = 1–9), Rj is the assigned rank (j = 1–9) of a particular measure and N is the total number of respondents in the respective stakeholder group. The higher the overall score of a particular measure in a stakeholder group, the higher the rank of the corresponding measure in that group.
Results
Of the 22 potential conflict reduction measures identified, 12 were preventative, five reactive and five mitigative (Table 2). Priority of the nine measures that were identified in the workshop varied substantially between potential tiger victims, tourism beneficiaries and National Park managers (Fig. 2). Both farmer and fisher groups assigned the highest priority to the construction of tiger-proof fences around settlements and farmlands (electric, barbed or mesh wire) and the second highest to compensation payments. Farmers gave third priority to the improvement of livestock corrals, whereas fishers chose the enhancement of conservation awareness amongst communities. Beneficiaries of tiger conservation through tourism assigned the highest priority to habitat and prey management and selected compensation payments and conservation awareness as their second and third priorities, respectively. National Park managers assigned the highest priority to compensation payments, followed by habitat and prey management and then conservation awareness (Fig. 2). On average, compensation payments received the highest priority score (6.60), followed by tiger-proof fencing (6.39) and habitat and prey management (6.07).
Table 2 The 22 potential human–tiger conflict reduction measures for Chitwan National Park, Nepal (Fig. 2). Asterisks (*) mark the nine measures identified by workshop participants as potentially being the most useful.
Fig. 2 Prioritization of the nine human–tiger conflict reduction measures (Table 2) by four groups of stakeholders (Table 1) in Chitwan National Park, Nepal, identified using questionnaire surveys. The score of each measure on a scale of 1–9 indicates its priority within the corresponding stakeholder category; the higher the score, the higher its priority (see text for details).
Discussion
Human–tiger conflict reduction measures primarily involve the implementation of certain interventions to manage tigers, people or livestock. However, the feasibility of any measure depends on the magnitude, nature and extent of its impact, the characteristics of the species involved, the socio-ecological context and the availability of the resources necessary for implementation. This study identified a wide range of measures, from direct management of tigers, habitat and prey to infrastructure development, the regulation of people entering the Park and management of domesticated animals.
Over 50% of the conflict reduction measures identified in this study were preventative, indicating that the conservation stakeholders prefer to solve problems before they arise. Such an approach is encouraged, to reduce conflict incidents (Goodrich, Reference Goodrich2010). The measures identified in our study also include both hard measures (e.g. lethal control of tigers and relocation of villages) and soft measures (e.g. habitat management and conservation awareness). Although the hard measures could have immediate effect, such measures should be employed only when absolutely necessary, considering their ethical, political, socio-economic and ecological ramifications. Soft measures may take more time to produce a favourable outcome but are perhaps best from the viewpoint of applicability and sustainability. We therefore recommend a combination of measures, to enhance their overall efficiency and effectiveness.
However, our study did not identify some previously reported measures, including the use of guard dogs (Khan, Reference Khan2009), wearing masks and fibreglass headgear, erecting electrified dummies, dredging water channels, digging freshwater ponds (Rishi, Reference Rishi1988; Barlow et al., Reference Barlow, Greenwood, Ahmad and Smith2010) and aversive geofencing technologies (Wall et al., Reference Wall, Wittemyer, Klinkenberg and Douglas-Hamilton2014). Such measures require further testing and evaluation before they can be considered feasible for use in Chitwan National Park.
Prioritization of potential conflict reduction measures is important because of the scarcity of resources and differences in preference amongst stakeholders. We found the various conservation stakeholders had differing priorities for conflict reduction measures (Fig. 2). The primary victims of tiger attacks preferred the construction of tiger-proof fences, whereas the beneficiary groups preferred habitat and prey management, and National Park managers preferred compensation payments. Compensation payments were the only measure in the top three priorities of all four stakeholder groups. The preference of potential victims for tiger-proof fencing over the other measures indicates the desire of this group to avoid tiger attacks rather than to receive compensation for attacks after they occur.
Unlike other preventative measures such as prey management, victims could have perceived tiger-proof fencing to provide immediate and effective protection against tigers. However, this measure was not amongst the top three priorities for the beneficiary groups and National Park managers, perhaps because these stakeholders are unsure of its effectiveness, perceive that it could disrupt tiger dispersal, or are familiar with the high costs of fence installation and ongoing maintenance (Sapkota et al., Reference Sapkota, Aryal, Baral, Hayward and Raubenheimer2014; Lamichhane et al., Reference Lamichhane, Persoon, Leirs, Musters, Subedi and Gairhe2017). A study on the efficacy of electric fencing from the eastern sector of Chitwan National Park, where the Asian elephant, greater one-horned rhinoceros, wild boar Sus scrofa and tiger were the main species involved in conflict incidents, reported a reduction in livestock losses of only 30–60% after implementing fencing (Sapkota et al., Reference Sapkota, Aryal, Baral, Hayward and Raubenheimer2014). As knowledge of the effectiveness of fences for mitigating conflict with tigers appears to be limited, we suggest undertaking pilot studies to evaluate the effectiveness of such structures before any widespread implementation.
An emerging alternative measure to conventional fencing is aversive geofencing technology. This involves capturing an animal, fitting it with an aversive geofencing device, releasing it, and creating virtual fence lines around areas such as farmlands. If the animal approaches the virtual fence, it is repelled by an automated audio warning or a mild electric shock. This technology has been used to limit conflicts with the African elephant Loxodonta africana in Kenya (Wall et al., Reference Wall, Wittemyer, Klinkenberg and Douglas-Hamilton2014) and Asian elephant in Sri Lanka (Cabral de Mel et al., Reference Cabral de Mel, Seneweera, de Mel, Dangolla, Weerakoon, Maraseni and Allen2022), has been trialled with success on lions Panthera leo in Botswana (Weise et al., Reference Weise, Hauptmeier, Stratford, Hayward, Aal and Heuer2019) and is being deployed on dingoes Canis familiaris in Australia (B. Allen, pers. comm, July 2022). Because of its lower cost compared to physical fencing structures (Wall et al., Reference Wall, Wittemyer, Klinkenberg and Douglas-Hamilton2014) and the proportion of problem animals being small (e.g. < 5% of tigers in Chitwan National Park; Lamichhane et al., Reference Lamichhane, Persoon, Leirs, Musters, Subedi and Gairhe2017), this approach could potentially revolutionize tiger conflict management in key situations. We recommend trialling this technology in Chitwan National Park on tigers involved in conflict and perhaps also on other species.
The habitat and prey management measure received the highest priority amongst tourism beneficiaries and also ranked second highest amongst National Park managers (Fig. 2). Globally, the management of grassland, forest and wetland habitats is a commonly recommended preventative measures to reduce incidents of human–carnivore conflict (Goodrich, Reference Goodrich2010). Such habitat management programmes aim to increase wild prey densities and the carrying capacity of protected areas for predators, thus reducing the likelihood of predators roaming beyond the protected area. As habitat management interventions in Chitwan National Park are mainly concentrated inside the Park, expansion of such activities to community forests and other forested areas outside the National Park has been encouraged (CNP, 2018). The prey density in Chitwan National Park and the surrounding areas is 100 animals/km2 (DNPWC & DFSC, 2022). Prey populations could be further augmented by reintroducing prey species such as the swamp deer Cervus duvaucelii, wild water buffalo Bubalus arnee and blackbuck Antilope cervicapra from other areas in Nepal, and by reducing poaching of prey and their killing by feral or stray domestic dogs. Such prey augmentation programmes should, however, also consider the potential for associated crop damage on local farms.
National Park managers gave the highest priority to compensation payments, which was also the second most preferred measure amongst farmers, fishers and tourism beneficiaries (Fig. 2). A preference for this measure could be attributed to the feasibility of implementation and because it directly supports the victim or their dependents. We recommend further studies to determine whether there are any additional reasons for the prioritization of this measure. Compensation payments aim to succeed by developing community tolerance towards wildlife, by alleviating impacts rather than by reducing conflict incidents (Goodrich, Reference Goodrich2010), so implementation of this measure alone should not be encouraged. A better approach may be to focus on preventative measures to avoid the occurrence of conflict incidents. Compensation payment measures have been adopted globally yet are controversial (Karanth et al., Reference Karanth, Gupta and Vanamamalai2018). Proponents argue that compensation enhances community tolerance and ownership and decreases retaliatory killings of wildlife (Agarwala et al., Reference Agarwala, Kumar, Treves and Naughton-Treves2010; Persson et al., Reference Persson, Rauset and Chapron2015), but opponents claim it is subject to fraud and is non-transparent, inadequate and bureaucratic, and time-consuming to implement (Ogra & Badola, Reference Ogra and Badola2008; Watve et al., Reference Watve, Patel, Bayani and Patil2016). Putting an economic value on human life is also ethically problematic (Shilongo et al., Reference Shilongo, Sam and Simuela2018). The creation of an insurance scheme is also an option because of the increasing financial liabilities and the priorities of Nepal for physical infrastructure and economic development rather than wildlife conservation (Aryal et al., Reference Aryal, Dhungana and Silwal2021). Despite these issues, considering the prioritization of this measure by several stakeholder groups and the absence of any indication of fraud or misappropriation of compensation payments in the study area (Dhungana et al., Reference Dhungana, Savini, Karki and Bumrungsri2016), we recommend that the current compensation payment scheme continues alongside the other prioritized preventative and reactive measures that we identified.
The differences in priorities that we documented between groups of stakeholders could have resulted from variation in the costs and benefits of different measures and in the roles and responsibilities amongst these stakeholders in tiger conservation and any previous experiences with tigers. Considering the discrepancies in priorities between stakeholder groups, we recommend that National Park managers take a leadership role in mediating the different priorities amongst stakeholders when selecting conflict reduction measures. Differences could be addressed through minimization of the costs of conflict on affected communities, sharing conservation benefits amongst affected communities, the optimal and equitable allocation of available resources, the involvement of the private sector in conflict reduction, and the strengthening of trust and cooperation amongst all stakeholders. Implementing the measures we identified in this research in and around Chitwan National Park could address human–tiger conflicts sustainably in ways that benefit both people and tigers.
Author contributions
Study conception and design: all authors; material preparation, fieldwork, analysis: RD, TM, GP, RR; writing: RD; revision: all authors.
Acknowledgements
We thank The Rufford Foundation (28875-B) for financial support and the Department of National Parks and Wildlife Conservation and Chitwan National Park staff, Prakash Upreti, field assistants and community members for their help in data collection and stakeholder consultations.
Conflicts of interest
None.
Ethical standards
This work abided by the Oryx guidelines on ethical standards and complied with the ethical code of conduct of the Department of National Parks and Wildlife Conservation (Ref. no. 076/77 Eco 60, 1767) and Chitwan National Park, which provided the permit for this research.
Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.
Open access
