Appraising carnivore ( Mammalia : Carnivora ) studies in Bangladesh from 1971 to 2019 bibliographic retrieves : trends , biases , and opportunities

In contrast to <7% natural forest covers and >1,000 people living km-2, Bangladesh, one of the smallest countries in Asia, shelters 28 carnivorous mammals. The species are of six families, nearly half of the entire carnivore diversity of the Indian Subcontinent. Carnivores of Bangladesh are little understood and they are disappearing fast despite receiving stern protection. Yet, there has been no assessment on the status of existing knowledge. A review was aimed to assess the existing knowledge and evaluate the research trends in country’s mammalian carnivores. Peer-reviewed works published from 1971 to 2019 were skimmed and categorized systematically according to five traits: publication type, research topic, time of publication, region, and species of study. In a total of 95 works examined, substantial numbers were on tiger (n=45) and the Sundarbans (n=47). In imbalance to action plans procured for tiger conservation, 14 carnivores have never been exclusively studied in Bangladesh. Of the research topics, preference was evident for wildlife management and conflict analyses as there were 31 scientific papers out of 63 in these categories. Inventory compilation for books (18 of 24) comprised the next preferred subject. The assessment could identify gaps in related knowledge in different regions of the country. Eastern region has experienced a meagre amount of work, although its mixed evergreen forests have larger combined area than the Sundarbans, and is known for its higher richness of diversity. Exclusive works outside legally defined protected areas were also low. We found no works in northwestern and southern Bangladesh. In the last two decades, the temporal trajectory of research effort has been more, and the topics have started to diversify. In order to improve conservation practices, we stress that gaps in knowledge pertaining to region or subject may be bridged with contemporary study techniques. This is crucial to highlight the status of carnivore species that are otherwise ‘elusive’, ‘apparently absent’, or ‘least-known’.


INTRODUCTION
Carnivora that constitute the fifth largest mammalian order faces taxon-wide existential crisis (Inskip & Zimmermann 2009; Ripple et al. 2014). According to IUCN (2019), 88 species are threatened with a trend of decreasing population. Conserving carnivores is now a major concern worldwide (Treves & Karanth 2003).
The concern is in recognition of the fact that for a stable and diverse community of wild animals, carnivorous mammals exert intangible influences. They can act as apex predators and their absence often Bangladesh is the world's 92 nd largest country covering an area of 147,610km 2 and the 8 th most populous with about 165.6 million people. Also, the country is rich in biodiversity and harbors 138 extant mammals; 28 of which are carnivores (IUCN Bangladesh 2015; .
Geographically, Bangladesh is traversed by the Tropic of Cancer, and there exists a transition zone between the Indo-Himalayan and the Indo-Chinese sub-regions of the Oriental realm, which are considered advantageous to form wildlife habitats (Corlett 2007;Feeroz 2013;. Historical anecdotes indicate about the rich presence of carnivores all over Bangladesh once. Many carnivore species have now become restricted to certain areas or are known only from sporadic encounters . The carnivores of Bangladesh are in six terrestrial families: Viverridae, Felidae, Herpestidae, Canidae, Ursidae, and Mustelidae. The Bengal Tiger Panthera tigris is the country's national animal. Three other large carnivores, the Indian Wolf Canis lupus, Striped Hyena Hyaena hyaena, and Sloth Bear Melursus ursinus are deemed to be extinct in Bangladesh . If compared to more diverse carnivore assemblages of neighboring India (57 species), Nepal (47), and Bhutan (39) and their respective habitat diversity, the inventory of Bangladesh is still considerable given its <7% natural forest cover and >1000 people living km -2 (Wangchuk 2004;NFA 2007;Menon 2014;Amin et al. 2018).
Carnivores are still present in all the three major forest types of Bangladesh (IUCN Bangladesh 2015) ( Fig. 1). The Sundarbans mangroves support the only stable Tiger population in the country. Wet deciduous forests which once swathed from central to north and northwest, is now extremely fragmented, but continue to be known for civets, mongooses, Felis and Prionailurus cats. Concentrations of mixed evergreen forests are in eastern regions typified by hills, streams, rugged terrain, and, in cases, tea-gardens on the periphery. Eastern forests are long credited for every native carnivore. Apart from the forests, homestead jungle and wetland vegetation support small mammals. Although protected under several formal definitions, here, threats to wildlife and wildlife habitats are surmounting because of encroachment, altercation, destruction, high-dependency on forest products, agro-industries, trafficking, persecution, and retaliatory killings, to name but a few .
We find no comprehensive assessment of the status of existing knowledge on mammalian predators of Bangladesh. But on global or regional scales, extensive reviews tend to highlight species in critical research needs, and steer conservation interventions to new perspectives as exemplified by Dalerum Dalerum et al. (2008) reviewed the status and decline of carnivore guilds in continental perspective. All these reviews were systemic in assessing literary works. These have stressed on knowledge gap and research bias only to envisage better and bolder scheming of conservation pursuits.
In order to make an appraisal of the works on mammalian carnivores of Bangladesh, here we have proceeded with three objectives: (1) to construct a systematic compilation of peer-reviewed researches, (2) to identify taxonomic and knowledge bias in these studies, and (3) to assess their geographic trend within the country and the temporal trajectories.

Consideration of literature
We restricted our search to the following types of publications: peer-reviewed scientific papers, peerreviewed book/book chapters, conservation action plans, and doctoral theses completed from 1971 to 2019. We observed project reports within this period but excluded them from analyses. We did not consider conference abstracts, MS theses and non-scholarly articles.
We have considered only mammalian carnivores reportedly living within the geopolitical boundary of Bangladesh. To enlist the extant carnivores for consideration, we consulted , and Ahmed et al. (2009). To obtain insight to assessment of threat at the regional and global levels, respectively, we used IUCN Bangladesh (2015) and IUCN (2019).

Sourcing literature
Works were collected using three primary research databases, i.e., Google Scholar, BioMedCentral, and Web of Science. To intensify in-depth search, we followed preset keywords in English. Our search protocol was based on Pullin & Stewart (2006), and we included 'species name' (scientific or common) and 'Bangladesh' in every attempt. In addition to the pair of obligatory words we used the following keywords in combination: 'attitude', 'behavior', 'camera-trap', 'coexistence', 'conflict', 'depredation', 'distribution', 'diversity', 'ecology', 'mortality', 'new record', 'prey', and 'zoonotic disease'. We followed the search pattern for every extant carnivore species of the country. We also looked for key wildlife biologists of Bangladesh during searches to obtain maximum results.
In addition to the three primary searches online, relevant books and journals were accessed from Professor Yousufzai Seminar Library repository of the Department of Zoology, University of Dhaka. This was carried out to acquire older works that could have missed digital indexing.

Categorization under pre-defined themes
We observed the respective aims and outcomes of the obtained works. Then, we categorized them under six pre-determined research themes. We construed the categorization after consulting verde Arregoitia (2016), Broto & Mortelliti (2018), and Inskip & Zimmermann (2009). The definition and scope for each category are given in Table 1.
Studies were examined to ascertain whether each of these dealt with a single species or multiple species or any particular group (taxa higher than genus). If multiple

Ecology
Ecological study, breeding behavior, feeding behavior, territorial behavior, activity pattern, home range, habitat preference.

Wildlife management and conflict analysis
Ethno-zoological aspects, human-carnivore interactions, threat analysis, environmental impact, climatic impact, wildlife poaching and trade, anthropogenic effects and perceptions, conservation genetics, research in recovery strategies, conservation action plan.

Population dynamics
Population status, population size, population density.

Zoonotic and anthroponotic disease
Case studies on these diseases.

Consideration of protected area (PA)
7.1. Inside PA Researches that considered any protected area declared under international or regional definition, i.e., national park, wildlife sanctuary, reserve forest, ecologically critical area, eco-park, RAMSAR site as study site.

Outside PA
Researches that did not consider any of the above as study site.

Both
Researches that encompassed study area covering both protected and non-protected habitats.

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species names were specified in a single work, we added the work to tally count of each pertinent species, however, if any study approached a group (for example, a taxonomic family), we kept it to the mentioned group. For example,  assessed bears of Bangladesh, we counted the work for the 'ursids' rather than each of the three bears of the country. We also considered the works that covered all wildlife or all mammals or all carnivores of Bangladesh and kept the count to 'wildlife', 'mammals', and 'carnivores', consecutively (Table 1; Appendices 1-2).

Spatial and temporal classification
We followed  where seven geographical regions have been defined to characterize wildlife distribution in Bangladesh and recreated the map for the review (Table 1). We put a particular work to a specific region, considering whether the respective work's study area fell within the geographic region. If multiple regions were specified in a single work, we added the work to tally count of each respective region, however, if any work considers the country, we accredited the count to 'Bangladesh'.
The works were also classified on their consideration of protected area (PA) and assorted into three groups: outside PA, inside PA or both (Table 1).
To assess the research trajectory in time, we considered two trends: year-wise pattern and a cumulative rate. We assigned a study to the year it was published. For tracking changes in publication types and research topics, works were classified into six time periods, each of a decade: 1971-1980, 1981-1990, 1991-2000, 2001-2010, 2011-2019. Time trajectory was initiated from 1971; this was when Bangladesh had gained independence.

Analyses
We summed the total number of works for each pertinent species, and, thus, identified the moststudied and the least-studied species. We summed the number of studies tallied for a research topic to check the bias among topics. In manner alike, to point out the geographic/temporal pattern, we considered the total number of works assigned to a region or a year.

A brief on the reviewed literature
We found 95 peer-reviewed works on carnivores of Bangladesh completed within the considered timeframe, i.e., 1971-2019. Of these, 63 (66.3%) were peerreviewed scientific papers, six (6.3%) doctoral theses, 24 (25.3%) books. There were two action plans (2.1%) on Tiger. In addition, we came across seven project reports (Appendix 1) that were excluded from our analysis. All these 102 works we extracted through literature search are provided in Appendix 2.
When we compared the research topics to publication types, Figure 1 also showed a preference for books in terms of inventory build-ups (n=18). Although a few books covered the topic of wildlife management and conflict analysis, we found no book on other topics. We came across only nine papers on discovery and distribution update whereas 14 papers were there on ecology.

Species-wise trend in studies
Of After segregating the number of publications which targeted at threatened carnivores on both national and global assessments, we found that 14 species were without any dedicated work at all. Table 2 shows the comparison and the species without any research. On the other hand, 66 studies were found exclusively dedicated to 14 carnivore species. The studies covered six felids, four mustelids, two herpestids and one for each of a canid and a viverrid species. There are 29 studies which considered higher or multiple taxa: two for the felids, two for the ursids, one for all carnivore mammals of Bangladesh, six for all mammals, and 18

The most-and the least-studied species
The highest number of publications (n=45) was on Tiger. It experienced all types of publications. Considering the topic, wildlife management and conflict analysis were the most common subjects for studies on Tiger (Fig. 2). In Bangladesh, Tiger is the only carnivore with a conservation action plan that has been formulated twice ( (Fig. 2).

Region-wise trend in studies
A total of 47 studies were found in southwestern region, followed by 12 studies in southeast, 10 from northeast, and seven from central region ( Table  3) Bangladesh is considered as the study site in 22 studies (Appendix 1). We projected the regions according to number of works and number of species exclusively targeted across regions (Fig. 3). Since 1971, there is no study from southern and northwestern regions (Fig. 3a). Figure 3b indicates the inadequacy in consideration of the number of species in different regions.
Of the 95 works considered for the analyses, 25 carried out the research in both protected and nonprotected areas, and 57 of these exclusively considered the protected areas. Only 13 works took non-protected areas as study sites (Appendix 1).

Year-wise trend in studies
Only after the year 2000, the number of scientific publications has started to show a noticeable increase (Fig. 4). The highest number of publications were in 2008, 2013, and 2018 (n=7 for each year) (Fig. 4a). We could not find any particular reason behind these spikes; 10 publications on Tiger were found from these three years (n=4 in 2008, 4 in 2013, 2 in 2018). No scientific paper, however, was found until 1974, perhaps because it took some time for the conditions to become conducive for field research after the independence. It was the two recent decades (2001-2010 and 2011-2019) when carnivore studies in Bangladesh gained momentum. These periods were also a leap for conservation science and inventory compilation ventures. Only the current     decade is the period in which we found all seven considered research topics (Fig. 4).

DISCUSSION
Severe discrepancies are evidently observed in research trends considering carnivore mammals of Bangladesh. Gaps and biases are present in every criterion that we considered. Species-wise preference, thematic trends, geographic distribution often leaned toward certain species or certain area, likely to have been influenced by conservation and management interests. Involvement in carnivore researches and interest in diverse species are on the rise. It is, however, worrisome that Bangladesh is at risk of losing more than half of its carnivore diversity, but, deployment of novel methodologies to study elusive and 'apparently absent' species is still very sketchy.

Highlighting the least-known and the least-understood species
Researches on Tiger, a flagship species of Bangladesh, make over half of all carnivore research counts. On the contrary, a single study was found on an occurrence record of leopard. The Indian Leopard Panthera pardus was thought to have been extirpated from Bangladesh. Among media reports, that may sometime form the beginning to a proper field research (Singh 2020), the term 'leopard' appears to be confused with that of Fishing Cat. In the last 12 years, based on verifiable media reports, however, there were instances of 16 Leopards appearing from northern and eastern corners of Bangladesh, each from different cases; six of which were killed as retaliatory responses (Akash et al. submitted). Bear is another charismatic carnivore yet got only one published scientific paper and one book chapter on status assessment IUCN Bangladesh 2015). Some species are recorded in recent times (Binturong Arctictis binturong,  . 3a) and the number of species (in Fig. 3b). Appendices 1 and 2 detail out the works and the classification scheme used in these projections.

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Crab-eating mongoose, Large-toothed Ferret Badger, Yellow-throated Marten, and Hog Badger Arctonyx collaris) or have only distant sightings (Small-toothed Palm Civet Arctogalidia trivirgata) but no further scientific investigations have been carried out. When the Tiger is the only carnivore to get its conservation action plan twice, 14 other extant carnivores of Bangladesh lack any sort of scientific documentation.

Approaching contemporary study techniques
Our review has highlighted the scattered and scarce data on 28 carnivores from 1971 to 2019 (Table 3, Fig. 4). It is also observed that IUCN Bangladesh (2015) assessed the country's carnivores mostly through sighting records or expert opinions. Of course, as implied in Singh (2020), all technical accounts may not follow from planned, long-term field research. Figures 3 and 4 clarify the clear lack in study effort. For example, although southeastern region is known for many carnivores, studies in this region have targeted only two species. Again, while there appears a preference for works like mitigation of conflicts and assessment of biodiversity, there is a certain deficit in species-or taxa-oriented ecological studies (Fig. 4). These can be attributed to challenges of encountering wild carnivores and the rugged terrain in certain areas. Non-invasive and novel technologies such as remote camera-trapping, radio-collaring, and systematic analytical approaches (species distribution modelling, density estimates) which can resolve these difficulties are limited to studies on the Tiger and, to a lesser extent, the jackal (Poche et al. 1987; Khan 2012; . It is true that, in many cases, the duration allowed and funds available determine the type of research work. Sometimes, these are opportunistic

Emphasizing the hypothetical 'empty forest'
We found that the majority of studies (n=47) carried out in the Sundarbans, exclusively focused on Tigerrelated management and conflict issues (Table 3, Fig. 3a). Southeastern Bangladesh, though ranked the second, lagged far behind relative to the number of publications (n= 12), and performed mostly on the diversity and richness of certain protected areas (Feeroz et   , , and CCA (2016) showed the presence of apex predators and umbrella species from these areas. On further interesting note, in the recent years, Rahman (2017) and Zakir (2019), two unpublished MS theses, targeted least-known carnivores of northeastern Bangladesh, carried out camera-trap surveys, and showed some remarkable findings including the Asian Golden Cat and the Asian Wild Dog Cuon alpinus. Therefore, it is necessary to plan for large-scale structured camera-trapping, that could reveal the status of the carnivore fauna and their ecological associates in these hypothetical 'empty forests'.

Addressing newer research scopes
For northwestern, central, northern, and southern regions, Figure 3b  The species are at risk, continuously persecuted across Bangladesh, at forest peripheries, fragmented patches and homestead jungles. Whereas Tiger in Bangladesh has been studied under broad spectra, their ecology, risk assessment, local perception and conflict management for these lesser species living outside protected areas have never been tried. Future research can put small carnivores as umbrella species for the fast disappearing village/peri-urban groves and wet deciduous forest.
Tiger is undoubtedly a flagship icon for Bangladesh, yet, the country harbors many other remarkable carnivores and unique habitats. Our knowledge on most of their ecology and management strategies are at a bare minimum. This paucity hinders adequate regional and global conservation attention and practices. Therefore, this assessment of the trend of research on mammalian carnivores highlights the gaps in research. Developing more comprehensive knowledge and researched data are expected to aid in future management across the regions where scientific investments have been traditionally low, the availability of data have been sparse and action for conservation is an exigency.