Research trends and knowledge gaps in the ecology of dung beetles (Coleoptera: Scarabaeidae) in savannas

Abstract

Savannas are recognized as one of the world’s most biodiverse ecosystems. However, these environments have the highest rates of habitat loss due to land use and climate-induced alterations in fire regimes. The combination of these threats, along with knowledge gaps in biodiversity, represents formidable challenges to conservation efforts in these regions. Dung beetles, vital for comprehending the impact of land use on savannas, have yet to undergo comprehensive study. To address this gap, we conducted a systematic review of the current state of knowledge regarding dung beetles distributed in savannas within Neotropical, Afrotropical, and Australasia zoogeographic regions. We describe the encompassing geographical distribution, research topics, studied habitats, and key metrics assessed in existing studies. Our results reveal a pronounced focus on Neotropical savannas highlighting a substantial deficit in dung beetle ecology knowledge within Afro-tropical and Australasian savannas. Most articles focused on savanna grasslands, woodlands, and human-introduced habitats such as pastures. The predominant articles focused on community patterns, habitat replacement, and degradation. Noteworthy metrics included abundance, richness, and species composition. Diversity indexes and functional diversity were also relatively well-explored metrics. However, across all zoogeographic regions, aspects of dung beetle behavior, reproductive biology, and physiology remain inadequately explored. In conclusion, urgent research efforts are imperative, emphasizing the need for comprehensive metrics, including biomass, morphometrics, and ecological functions of dung beetles, to advance our understanding of their significance and roles within savannas.

Introduction

Savannas are globally acknowledged as ecosystems of immense biodiversity and are distinguished by their unique endemic species (both animals and plants) (Ratter et al. 1997, Myers et al. 2000, Andresen 2005, Murphy et al. 2016). These ecosystems confer a multitude of indispensable services to humanity, including food production, water provision, and carbon sequestration and regulation (Greiner et al. 2009, Marchant 2010, Williams et al. 2022).

Despite their substantial ecological value, savannas are among the most threatened natural systems worldwide (Myers et al. 2000, Murphy et al. 2016), by the rapid land-use expansion and climate change, which induce alterations in fire regimes (Beerling and Osborne 2006, Hoffman and Vogel 2008, Andersen et al. 2012, Williams et al. 2022). For example, over the past 2 decades, Neotropical savannas (e.g., Cerrado), have witnessed a loss of approximately 50% of their original area to agricultural commodities like soybean, sugarcane, corn, and livestock pasture (Klink and Machado 2005, Gomes et al. 2019, Aragão et al. 2022, Tovar et al. 2023).

The transformation of pristine savanna landscapes into anthropogenic environments invariably results in detrimental impacts on biodiversity, ecosystem functionality, and consequently, human well-being (Fischer and Lindenmayer 2007, Watson et al. 2016, López-Bedoya et al. 2022a). Therefore, conservation initiatives in savannas are of paramount importance (Overbeck et al. 2022), particularly given the disproportionately low, percentage of savannas currently under protection (19.7%) (Watson et al. 2016, Williams et al. 2022, Lewis et al. 2023).

Different efforts have resulted in the creation of global databases for biodiversity, with an emphasis on vertebrate groups such as birds, mammals, and herpetofauna (Jenkins et al. 2013, López-Bedoya et al. 2022b, Tan et al. 2023). However, there are still significant gaps in our understanding of the global distribution of biodiversity, especially about the invertebrates and their conservation significance (Kier et al. 2005, Murphy et al. 2016). In addition, there is a conspicuous paucity of knowledge about the biodiversity in savannas (Parr et al. 2014, Murphy et al. 2016).

In the savannas, conservation efforts have often been less effective than in other biomes, primarily due to the scarcity of biological information or the fragmented of knowledge concerning biodiversity (Sankaran 2009, Hortal et al. 2015). Thus, it is imperative to assess the current state of biodiversity in savannas, focusing on taxonomic groups that exhibit high diversity and extreme vulnerability to habitat loss, and that also play pivotal ecological roles in these ecosystems.

Dung beetles (Coleoptera: Scarabaeinae) represent a widely distributed insect group with a significant presence in savannas (Hanski and Cambefort 1991). These organisms constitute the soil macrobiota of savannas, with the majority of adults primarily utilizing mammal dung as their food source and as a reproductive medium (Halffter and Matthews 1966, Halffter and Edmonds 1982). They play a fundamental role in the natural management of organic matter by significantly contributing to the removal, burial, and decomposition of substantial quantities of dung (Hanski and Cambefort 1991, Anduaga 2004, Nervo et al. 2014). Furthermore, through their dung resource management activities, dung beetles perform a range of essential functions and services crucial for the maintenance and functioning of the savannas. These services include nutrient cycling and soil aeration (Nichols et al. 2008, Doube 2018), parasite control (Ridsdill-Smith and Simmons 2009), secondary seed dispersal (Kunz and Krell 2011), and the mitigation of greenhouse gas emissions (specifically, methane and nitrous oxide) originating from dung (Slade et al. 2016).

Here, we have undertaken a systematic literature review to comprehensively assess trends and gaps in knowledge concerning dung beetles in savannas. Our objective was to achieve a more thorough understanding of the interaction between these organisms and the savannas, to offer insights for future investigations. Our findings suggest that research on dung beetles in savannas has evolved significantly over time, with a growing emphasis on understanding the ecological significance of these insects in savannas. Most studies have been concentrated in South American savannas, with a smaller number of studies conducted in Afrotropical and Australian savannas. Prevailing subjects of inquiry in studies on dung beetles in savannas include community patterns, and effects of habitat replacement, and degradation on dung beetles. Studies have focused on a variety of savannas, including savanna grasslands and woodlands, and other habitats such as pasturelands, agricultural lands, and urban areas. Commonly assessed metrics in the literature include species diversity, abundance, species composition as well as diversity indexes, and functional diversity metrics. Our review highlights the need for further research on the ecological roles of dung beetles in savannas, particularly in understudied regions such as Afrotropical and Australian savannas.

Materials and Methods

Selection of Savannas

We adopted the framework proposed by Olson et al. (2001) and Jung et al. (2020), who provided the information on the geographic extent of savannas worldwide. Lastly, we target only savannas within Neotropical, Afrotropical, and Australasia zoogeographic regions according to Olson et al. (2001), and Davis et al. (2002), because these regions present higher rates of natural ecosystems loss (Bawa et al. 2004, Barlow et al. 2018, Williams et al. 2022) coupled with the highest levels of dung beetle biodiversity (Davis et al. 2002).

Data Search

We conducted a bibliographic search in the Web of Science, Scopus, and Scielo databases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology (Moher et al. 2009) (see Supplementary Fig. S1). We focused on a date range between 1991 to March 2023. To avoid bias related to information duplication, we do not include information before 1991, because Hanski and Cambefort (1991) performed a review of savannas focusing on dung beetles. We searched for articles that included at least one of the keywords mentioned in the following equation in their titles, abstracts, and/or full texts: (“dung beetle*” OR scarabaei* OR scarab* OR “scarab beetle*” OR “coprophagous beetle*” OR “necrophagous beetle*”) AND (savanna* OR “tropical grassland” OR “native grassland*” OR grassland* OR “native pasture” OR “dry forest” OR “rupestrian field*” OR llano* OR chaparral OR Pantanal OR Miombo* OR Mopane*) in 3 languages: English, Portuguese, and Spanish. These terms were selected as they are the most commonly used in scientific articles to refer to the taxonomic group and biomes of our interest.

Literature Inclusion and Exclusion Criteria

We included in our database only articles that met the following criteria: (i) papers published in indexed journals. By selecting indexed articles, we improved the quality of the information in our review, because these articles have undergone rigorous peer review, ensuring clear and replicable method descriptions, along with accurate and reliable results. Following these criteria, we eliminated the gray literature such as thesis, monographs unpublished dissertations, as well as conference abstracts. Additionally, we also removed review articles and book chapters to avoid problems related to duplication of information; (ii) papers that address at least one native savanna area (i.e., woodlands or savannas grasslands) in their methodology, which may also include comparisons with other natural and/or anthropogenic systems (i.e., nonsavanna environments, pasturelands, etc.). This ensures a more comprehensive and contextualized analysis of the relationship between dung beetles and the savannas.

We initially identified a total of 1,056 articles in the accessed databases (Supplementary Fig. S1). Subsequently, we eliminated 467 duplicates, for example, documents that appeared more than once in different databases (Supplementary Fig. S1). We then evaluated the abstracts of 589 papers, of which 354 did not meet the proposed criteria and were consequently excluded. Finally, we thoroughly reviewed the full text of 235 papers, ultimately excluding 61 papers that do not align with the study’s objectives. After following this rigorous process, our final database consisted of 174 papers (see Supplementary Fig. S1 and Supplementary Table S1 for further details).

Data Extraction

For each paper, we extracted the following variables: (i) year of publication; (ii) geographical information, including country, zoogeographical region, and geographical coordinates from the study locality, provided in each article; (iii) study topic; (iv) type of sampled habitat, and (v) assessed metrics (i.e., richness, abundance, species composition, biomass, diversity index, functional diversity, morphometry, ecological functions, and descriptive observations). Study topics were categorized after analyzing the papers into 3 main categories: Ecosystem, Community, and Population. Within the Ecosystem category, we have: (i) “Habitat replacement” for papers that assess the effects generated by the disturbance of natural areas by human actions, where there are changes in land use and replacement of natural area by an anthropized environment; and (ii) “Habitat degradation” for papers that assess the effects generated by the disturbance of natural areas by human actions or natural events. Here, natural habitats are still maintained, with no change in land use, but with impacts leading to degradation (e.g., deforestation, exotic species, etc.). In the Community category, we have 3 subcategories: (i) “Community patterns” for papers that assess the effects of biotic and/or abiotic factors on different parameters of the dung beetle community; (ii) “Species distributions” for papers that address the geographic distribution of dung beetles; and (iii) “Inventories” for studies that aim to characterize the dung beetle fauna of a specific location. In the Population category, we have 4 subcategories: (i) “Behavior” for papers that assess patterns of behavior and activity of dung beetles; (ii) “Reproductive biology” for papers that describe aspects related to the reproductive biology of species; (iii) “Physiology” for papers that assess aspects related to the physiology of dung beetles; and (iv) “Bait attractivity” for papers that address the selection and consumption of food resources by dung beetles.

Sampled habitats were categorized as follows: savanna woodlands (closed canopy); and savanna grasslands (open canopy). Pasturelands encompassing secondary and permanent grasslands are sometimes subjected to treatments like fertilization or re-seeding (e.g., introduced pastures) (Jung et al. 2020). Agricultural areas encompassing large-scale cultivation of crops, including tree and shrub plantations (e.g., Eucalyptus), as well as the cultivation of crops such as coffee, soybeans, corn, and sugarcane. Urban areas were defined as metropolitan and commercial areas predominated by asphalt, concrete, and rooftops, including houses, buildings, and parks (Jung et al. 2020). Unidentified habitats cover areas that were either not identified by the authors or lacked clear information about the specific habitat characteristics.

It is important to note that each paper may address more than one topic at the same time, and these topics may be nested within one or more categories. For example, papers that address both “Community patterns” and “Habitat replacement” can be found in Jankielsohn et al. (2001) and Tovar et al. (2023) (Supplementary Table S1). Additionally, a single study may have been conducted in more than one different habitat (e.g., savanna grasslands and agricultural areas in Davis et al. 2005, Chaves et al. 2017, Gebert et al. 2019), or used different response metrics for dung beetles (e.g., richness, abundance, biomass in (Almeida and Louzada 2009, Barraza et al. 2010).

Results

General Trends

We found 174 papers on dung beetles in savannas published between 1991 and 2023 (Supplementary Table S1). We found a clear increase in the number of published articles over time (see Supplementary Fig. 1). It is possible to observe a lower publication frequency between 1991 and 2006 grouping 18% of the published articles. From 2007 to the present, the number of studies addressing dung beetles in savannas showed a marked increase with 82% of published articles (Fig. 1). The majority of studies were conducted in the Neotropical region (125 articles), followed by the Afrotropical region (49), and Australasia region (2 articles) (Fig. 2). The studies were distributed across 21 countries, with 12 countries in the African continent, 8 countries in the Neotropical region (corresponding to Central and South America), and 1 country in the Australasia region (Fig. 2). Brazil had the highest number of publications (81 articles), accounting for approximately 46% of the total recorded (see Supplementary Fig. S2). Following Brazil were Colombia and South Africa, both with 28 articles each, representing around 16% of the total (Supplementary Fig. S2). Among the less represented countries were Australia (about 1%), Ecuador, Nicaragua, and Uganda (each <1%) (Supplementary Fig. S2).

Study Topics, Habitat Types, and Evaluated Metrics

The majority of papers on dung beetles in savannas evaluated “Community patterns” (84%), followed by studies assessing the effects of “Habitat replacement” (33%), “Bait Attractivity” (23%), and “Habitat degradation” (17%) (Fig. 3). The topics “Species distributions” (11.5%), “Inventories” (8.6%), “Behavior” (8.6%), “Reproductive Biology” (2%), and “Physiology” (1.7%) were less common in the articles (Fig. 3).

When we reviewed the type of habitat, we found that many studies were conducted in savanna grasslands and savanna woodlands (both at 64%) (Fig. 4), followed by studies in Pasturelands (about 30%). Agricultural areas were represented in 23% of the studies (Fig. 4). Urban areas were studied in a smaller percentage of studies (about 1%), while approximately 2% of the studies either lacked sufficient data or the information about the study area was absent.

Abundance was the most evaluated metric in nearly all studies (about 98%), followed by Richness (90%), Species Composition (59%), Diversity Index (58.6%), and Functional Diversity (41%) (Fig. 5). The least evaluated metrics were Biomass and Morphometry, both represented in 19% of the studies, followed by Ecological Functions (11%). Studies assessing “Descriptive Observations” of species were less common (about 7%) (Fig. 5).

Discussion

We highlight notable trends and knowledge gaps about dung beetles in savannas, offer recommendations for future research, and discuss the implications of these findings for conserving these environments. The understanding of the ecology and diversity of dung beetles in savannas is still quite limited, especially in Afrotropical and Australasian regions. Most articles have focused on savanna grasslands and savanna woodlands, as well as pasturelands (e.g., introduced pastures), primarily assessing the effects of habitat substitution and degradation on community patterns. We noted a limited knowledge regarding issues related to behavior, reproductive biology, and physiology of dung beetles across all zoogeographic regions. Finally, we found that the main metrics used were abundance, richness, and species composition, and the complementary metrics such as biomass, morphometrics, and ecological functions were less used.

The number of publications on dung beetles in savannas has fluctuated over time, with a publication increase from 1991 to the present, particularly from 2007 to the present. This shift can be attributed to the release of the chapter “Dung beetles in tropical savannas” in the book “Ecology of Dung Beetles” by Hanski and Cambefort (1991). This fundamental chapter intricately delves into the interaction between dung beetles and savannas, serving as a crucial catalyst for stimulating research and inspiring other scientists to explore this field. Additionally, the major publication frequency from 2007 to the present could be related to the categorization of dung beetles as a good bioindicator group (Nichols et al. 2007). Consequently, the use of dung beetles as indicator taxa to study different ecological interactions and human impacts on savannas influenced the major frequency of publications.

Between 2014 and 2015 a discernible decline was observed in the number of publications. This dip coincides with the occurrence of the last El Niño event, suggesting a plausible correlation between these 2 factors. El Niño is recognized for inducing significant climatic variations across different regions globally, including periods of drought or intense rainfall (Timmermann et al. 2018). The extreme weather conditions associated with El Niño, such as prolonged droughts or heavy rains, can impede field research on dung beetles, leading to fewer opportunities for data collection and subsequently resulting in a reduction in the number of publications. Moreover, El Niño-induced climate changes may impact the availability of resources for dung beetles and influence the distribution of the populations of these beetles (França et al. 2020).

Neotropical, Afrotropical, and Australasian Savannas

The major proportion of articles were conducted in the Neotropical region (especially in Brazil). The disproportionated geographical distribution can be related to the academic infrastructure (i.e., Universities) (Mora-Aguilar et al. 2023), or financial support (López-Bedoya et al. 2024). Furthermore, in the Neotropical region, the major extension of savanna areas was found in Brazil (i.e., Cerrado, Pantanal). These savannas have a higher diversity of fauna and flora (Klink and Machado 2005, Junk et al. 2006, Mendonça et al. 2008), and represent an important economic issue due to the agrarian use (FAO 2023). In this sense, the agrarian expansion and natural ecosystem degradation derived from a major number of investigations focusing on the effects of anthropic practices on biodiversity.

Dung beetles exhibit remarkable diversity in these savanna habitats and play important roles in these ecosystems. The increase in research on dung beetles reflects the need to understand how these organisms interact with changes in habitats, influencing processes such as decomposition, nutrient cycling, and, consequently, the maintenance of biodiversity. We believe that this set of factors provides an environment for studies related to dung beetles in Brazil, allowing significant advances in understanding the ecology and biodiversity associated with these organisms.

However, there is a knowledge gap in the ecology and diversity of dung beetles in other regions of South America, indicated primarily by the low number of articles recorded in Colombia, Mexico, Argentina, and Bolivia. These information gaps have been similarly identified in other Neotropical countries with savanna (Noriega et al. 2015), as well as in other biomes with high biodiversity and vulnerability of natural ecosystems (López-Bedoya et al. 2024). We could not find any records of articles in the savannas of Venezuela. The Llanos, which are the second largest region dominated by savannas in South America, are located in Venezuela and Colombia (Medina and Silva 1990, Boval et al. 2017). Over the years, the Llanos have been affected by the expansion of agriculture and livestock farming with an estimated 15.5% of these ecosystems already replaced (Huertas 2014).

In the Afrotropical region, we have recorded a few studies, which were mainly concentrated in South Africa. Although the taxonomy of dung beetles is relatively well-known in African savannas, the number of ecological studies in these regions is still low (Hanski and Cambefort 1991, Giller and Doube 1994). Furthermore, we observed that little research has been conducted on the use of these organisms as indicators of habitat quality, especially in South African grasslands (McGeoch et al. 2002, Tocco et al. 2018). This pattern is intriguing, as there is a growing invasion of commercial agriculture and livestock farming in these regions, where a significant portion of savannas has already had their vegetation modified for crop cultivation and establishment of livestock (Davis et al. 2002, 2012, Lascaleia et al. 2018).

We also observed that the ecology of dung beetle communities, particularly in the grasslands of the Australian savanna, is still poorly understood (Doube and MacQueen 1991, Carvalho et al. 2020). This knowledge deficiency is noteworthy although Australian savannas just cover approximately 10% of the total land area, they are home to many native dung beetle species, with over 500 species already identified (Olson et al. 2001, Faleiro et al. 2008).

Dung Beetles’ Ecology Knowledge and Savanna Conservation

Dung beetles are commonly found in the neotropical region, where they exhibit high levels of diversity (Davis et al. 2002). As a result, the majority of ecological studies have been focused on this region (Doube and MacQueen 1991, Hanski and Cambefort 1991). It is essential to conduct more studies on dung beetles in savanna regions such as the Afrotropical and Australian, as well as in some under-sampled locations in South America. Such studies can help improve our understanding of species composition and conservation needs in these regions.

Moreover, it is crucial to have prior knowledge of how diversity is structured within the area of interest for any conservation strategy to be effective (McNaughton 1994, Sankaran 2009). Therefore, gaps in the knowledge of savanna dung beetle ecology and diversity can present an obstacle to the implementation of management and conservation plans, as well as hinder the identification of priority areas for savanna conservation.

Finally, the lack of information about dung beetles, particularly in Latin American countries such as Colombia, Venezuela, and Bolivia, can be attributed to various factors, including logistical constraints related to accessibility to study sites, as well as a lack of financial investment and adequate research infrastructure (Ciocca and Delgado 2017, Barlow et al. 2018, Carvalho et al. 2023).

Trends and Gaps in Study Topics

The most evaluated topics in the articles were community patterns, followed by studies testing the effects of habitat replacement and degradation on dung beetles. Neotropical regions face the highest rates of land use change and degradation (Barlow et al. 2018, López-Bedoya et al. 2021), with agriculture and livestock farming being the primary drivers of transformation in savannas (Overbeck et al. 2022, Tovar et al. 2023). Therefore, it is expected that researchers have directed their studies toward understanding the impacts of habitat conversion on dung beetle communities. Additionally, it is common for many researchers to use dung beetles for comparisons between native and anthropogenic environments, as these organisms have been considered excellent bioindicators, providing an efficient way to assess the impacts of land use changes on biodiversity and ecosystem integrity (McGeoch et al. 2002, Spector 2006, Gardner et al. 2008, Carvalho et al. 2020).

Our review identified a lack of knowledge regarding the behavior, reproductive biology, and physiology of dung beetle species in savannas. Pioneering works conducted by Halffter and Matthews (1966) and Halffter and Edmonds (1982) on the natural history and nesting behaviors of these species were instrumental in advancing our understanding of the underlying mechanisms of individual species’ responses to their environment. We emphasize the importance of conducting further studies in this regard, particularly because this foundational information, coupled with research examining the responses of dung beetle communities to changes in land use, can form an integrated system, enabling a deeper understanding of both the persistence and loss of biodiversity in for example, savannas modified by human activity.

Habitat Type

The majority of the research of the articles were conducted in savanna grasslands and woodlands, followed by anthropogenic environments such as introduced pastures, agricultural areas (e.g., Eucalyptus plantation, corn, coffee, soybean crops, among others), and lastly urban areas. These results are expected given that natural savanna grasslands and woodlands cover an extensive area across the Earth’s surface (Boval et al. 2017, Hutley and Setterfield 2019). Additionally, upon analyzing the articles, we observed that the majority of authors made comparisons of dung beetle diversity between native savanna areas (grasses and woodlands) and anthropogenic environments (introduced pastures and Eucalyptus plantations). This comparison is particularly relevant considering that livestock farming is the most widely distributed land use sector, and pastures cover about 30% of the planet’s surface (Bruinsma 2017).

In Brazil, for example, most studies focused on both native and exotic pastures in the Cerrado and Pantanal regions (Almeida et al. 2011, Correa et al. 2016, 2019, Macedo et al. 2020). Besides, the conversion of native pastures into exotic pastures for cattle breeding and feeding is predominant, especially in the Pantanal region, which currently supports the second-largest cattle herd in Brazil (5.8 million individuals). In addition to livestock farming, intensive agriculture has been growing in Brazil, and the Brazilian Cerrado has become an important source of crops like soybeans, corn, cotton, and sugarcane over the past 30–50 years (Klink et al. 2020), along with livestock and forest monoculture activities (Lahsen et al. 2016, Velazco et al. 2019). Therefore, understanding the impacts of substitution and degradation on dung beetle communities in these 2 important South American savannas is fundamental, as such research can provide a foundation for conservation and management policies to protect biodiversity in these environments.

We identified a lack of studies assessing the effect of urbanization on dung beetle communities. In this context, more efforts should be directed in this regard, as significant savanna-like the Cerrado, for example, have been facing high rates of urbanization (Duarte and Leite 2020). Additionally, the biome represents approximately 60% of Brazil’s agricultural production including soybeans, maize, cotton, and sugar cane. The important agricultural centers are located near the areas of Cerrado in Brazil, for example, the region known as Matopiba, which corresponds to the junction of covered municipalities that exclusively contain vegetative mosaics of the biome in the states of Maranhão, Tocantins, Piauí and Bahia (Reis et al. 2017, Pires 2020). It has been reported that the expansion of urban centers can have a strong influence on the structure of dung beetle communities, primarily leading to species loss (Korasaki et al. 2012, Frizzas et al. 2020). Therefore, dung beetles can serve as important key components for monitoring biodiversity response to urbanization, and consequently contribute to the success of conservation efforts.

Evaluated Metrics

The most commonly assessed metrics in dung beetles in the studies are abundance and species richness, followed by species composition, diversity index, and functional diversity. Taxonomic metrics such as abundance, richness, and species composition are traditionally used because they are relatively easy to understand and can be obtained through passive sampling without additional manipulations, measurements, or data acquisition (Saint-Germain et al. 2007, López-Bedoya et al. 2024). These metrics have been employed to assess the impacts of various anthropogenic disturbances on dung beetle communities. However, it is important to note that these metrics provide limited information and may not be good indicators of species’ importance in ecosystems because data can be influenced by generalist species with higher abundances (Hooper et al. 2005, Magurran 2016).

Complementary metrics related to functional attributes and species traits (e.g., biomass) can be more informative and allow for the investigation of, for example, the relationship and contribution of different dung beetle species to ecosystem functioning (Noriega et al. 2018, De Castro-Arrazola et al. 2022). Although there has been an increase in the use of biomass in dung beetle studies in recent decades (Gillett and Barr 2018, Correa et al. 2019, Nependa et al. 2021), this was one of the least assessed metrics in the studies, followed by morphometry. Cultid-Medina and Escobar (2016) suggest that biomass can provide additional information when the objective is to assess, for example, the impacts of land use on dung beetle community structure, as well as to describe the functional role of dung beetles in ecosystems. Additionally, biomass is considered a key variable for understanding energy flow, productivity, and food chain dynamics (Brown et al. 2004, Saint-Germain et al. 2007).

Although research evaluating dung beetles from a functional perspective is growing, functional diversity was assessed in just under half of the articles recorded in this review. Dung beetles have been considered a good functional model and exhibit high plasticity in response to environmental conditions and resource availability (Audino et al. 2014). Nonetheless, the study of dung beetles’ functional diversity still has limitations, primarily associated with the restricted assessment of functional traits, especially the traits related to the physiological information of species (Silva and Hernández 2015, Griffiths et al. 2016).

Few studies have assessed the ecological functions of dung beetles in their natural habitats which indicates that knowledge and use of this type of metric are still quite limited. Among the ecological functions commonly measured in the reviewed studies were, dung removal, seed dispersal, and soil bioturbation (movement and mixing of soil with particles) (Nichols et al. 2008, Braga et al. 2013, Arellano et al. 2023). Arellano et al. (2023) observed a similar pattern, recording only 18 articles that evaluated at least one function performed by beetles in pastures. These data are concerning, as quantifying and understanding the ecological functions performed by dung beetles form the basis for measuring ecosystem functioning and comprehending the impacts of land use changes on biodiversity (Nichols et al. 2008, Braga et al. 2013).

Directions for Future Research

Our review highlights the trends and gaps in dung beetle ecology in savannas. We emphasize the importance of prioritizing studies in less explored regions such as some countries in South America, as well as the Afrotropical and Australasian regions. The absence of information in these locations promotes different biodiversity knowledge shortfalls and ultimately impedes the generation and effective application of conservation strategies based on accurate data. In this context, we also recommend that more studies be conducted in critically threatened savannas, particularly concerning the assessment of dung beetle biodiversity in savannas affected by urban and agricultural expansion. Understanding the impacts of these activities on dung beetles may be essential in clarifying the response of dung beetles to degradation and providing insights into guiding conservation strategies in these areas.

We also suggest that researchers should expand their knowledge of the behavior, reproductive biology, and physiology of dung beetle species in savannas, as well as make use of complementary metrics such as biomass, ecological functions, and functional diversity. These aspects are crucial for understanding the individual responses of dung beetles to the environment, and their contribution to the functioning of savannas.

Supplementary Material

Supplementary material is available at Annals of the Entomological Society of America online.

Acknowledgments

We thank our colleague Wanda (PPGECO-UFLA) for their assistance with the elaborated map in the QGIS software. We also thank the Federal University of Lavras (UFLA) for logistical support. We thank CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for the financing of this work. And we thank the Minas Gerais State Agency for Research and Development (FAPEMIG).

Funding

This work was financed by CAPES (Coordination for the Improvement of Higher Education Personnel) and by FAPEMIG (research support foundation in the state of Minas Gerais).

Author Contributions

Nayara Reis (Conceptualization [Lead], Data curation [Lead], Formal analysis [Lead], Investigation [Lead], Methodology [Lead], Project administration [Lead], Validation [Lead], Visualization [Lead], Writing—original draft [Lead], Writing—review & editing [Lead]), Pablo Lopez (Conceptualization [Supporting], Data curation [Supporting], Investigation [Supporting], Methodology [Supporting], Project administration [Supporting], Validation [Supporting], Visualization [Supporting], Writing—original draft [Supporting], Writing—review & editing [Supporting]), and Julio Louzada (Conceptualization [Supporting], Funding acquisition [Lead], Investigation [Supporting], Methodology [Supporting], Project administration [Lead], Resources [Lead], Supervision [Lead], Validation [Lead], Writing—original draft [Supporting], Writing—review & editing [Supporting])

References