Dung Quality Implications for Fecundity and Ecosystem Services of Temperature Dung Beetles

Abstract

<p>Globally, dung beetles are recognised as important ecosystem engineers due to their ability to bury large amounts of animal dung. In Australia, the native dung beetle fauna do not have the capability to process introduced cattle dung consistently, resulting in a breeding medium for nuisance fly species and nematodes. This unprocessed livestock dung smothers the pasture, reducing the availability of viable pasture for rearing livestock. Communities of exotic dung beetles were successfully established in Australia between 1960-2020, with the primary aim to process large quantities of cattle dung. Since establishment, very limited work has investigated their current distribution across agricultural landscapes and, how they respond both spatially and temporally to different livestock management practices. </p> <p>The aim of this dissertation was to investigate how dung quality influences the community structure and population dynamics of northern NSW dung beetles. It primarily investigated the introduced dung beetle community in northern NSW, Australia, identify key abiotic factors for colonization and reproduction, and any reciprocal effects, and provide a targeted assessment of the response of introduced dung beetle species to cattle dung derived from different pasture types. The dissertation is structured around an introduction and literature review (Chapter 1), four data chapters and a synthesis chapter (Chapter 6). Also included are appendices that provide a publication and data collected during the thesis. The dissertation addressed four objectives which are the basis of the research chapters: Objective 1 (Chapter 2) to establish the main abiotic factors driving the introduced dung beetle community in northern NSW. Objective 2 (Chapter 3) to establish how pasture species, and combinations, influence dung quality and dung beetle reproduction and progeny traits. Objective 3 (Chapter 4) to determine how pasture species/combinations influence the field colonisation and burial of dung by the dung beetle community on the New England Tablelands. Objective 4 (Chapter 5) to establish how the dung beetle <i>Onthophagus binodis</i> interacts with dung pH and the reproductive consequences of this interaction.</p> <p>The dung beetle communities of northern NSW (Chapter 2) were sampled by a national citizen science project, and identified that the communities strongly varied spatially across locations, and that mean monthly minimum temperature positively influenced the abundance and species richness of dung beetles at all sites. Sixteen introduced and eight native dung beetle species were identified with <i>Labarrus lividus</i> (42%) being the most prevalent followed by <i>Euoniticellus intermedius</i> (16.2%). Paracoprids were the dominant functional guild across northern NSW. It is concerning that the dung beetle communities of northern NSW were dominated by a single or few species, by which to provide the majority of the ecosystem services in livestock dominated landscapes. </p> <p>The influence of pasture type (Chapter 3) on cattle dung quality was investigated across three dominant temperate dung beetle species <i>(Euoniticellus africanus</i>,<i> E. intermedius and</i> <i>Onthophagus binodis</i>) under controlled conditions to determine the impact on brood production and phenological changes in progeny. The dung of cattle grazed on three pasture types (improved native, forage oat & rye/clover pasture – dung type) were collected and quantified. Pasture type influenced the chemical parameters of dung quality, with nitrogen likely an important parameter for determining progeny size. Rye/clover derived dung had the highest nitrogen content and produced the largest (longer total length and wider pronotums) progeny of female <i>E. intermedius</i>, and both males and females of <i>O. binodis</i>. </p> <p>An Australian dung beetle community study (Chapter 4) in the field was conducted to determine the colonization (abundance and species richness) and subsequent burial of three different dung types. Three dung types were accessible to the temperate dung beetle community on the New England Tablelands for 24 hours every month for twelve months. Across the three pasture types, 13 species of dung beetle were trapped from 11,174 specimens, with <i>Onthophagus binodis</i> (49.7%), <i>Aphodius fimetarius</i> (24.4%) and <i>L. lividus</i> (17.1%) having the highest abundances. Abundance and species richness were influenced by month and local landscape, with weak evidence (p=0.1-0.05), that abundance was influenced by pasture types, whereas dung burial (organic matter) was strongly influenced (p = 0.0001) by month and pasture type. How a more diverse community responds to different dung conditions requires further investigation.</p> <p>Previous investigations determined that cattle dung pH was a likely contributing factor to dung beetle colonization and reproductive success. The influence of cattle dung pH on dung beetle reproduction was investigated using the dominant temperate dung beetle species <i>Onthophagus binodis</i> (Chapter 5). A single previous study (Dadour and Cook 1996 <i>Environmental Entomology</i> 25) hypothesised that <i>O. binodis</i> could not reproduce in cattle dung below 6.3, such as that produced by grain fed cattle dung. To test this, beetles were reared in dung with artificially manipulated pH (7.3, 7.0, 6.0 and 5.0), and their broods and progeny were assessed. The pH of cattle dung influenced development time, ellipsoid volume of brood balls, and offspring width and length. Notably, <i>O. binodis</i> offspring were larger from pH 6.0 dung compared to the other pH treatments. The results indicate that dung pH is a key driver of brood success refuting the earlier study.</p> <p>The research outlined in this dissertation provides a valuable understanding of the current distribution of introduced dung beetle species in northern NSW, and particularly the role of cattle diet in resultant dung quality, and subsequent dung beetle colonisation and reproductive success. Researchers, livestock producers, landcare groups and best practice management for dung beetle research will all benefit from the information presented within this dissertation. This dissertation expands the current knowledge of dietary impacts on dung beetles within Australia on three common pasture types. The thesis provides novel findings of the tolerance of <i>O. binodis</i> to cattle dung pH which highlights that past research has made assumptions without investigating further. Additionally, the ecology of dung beetles to different pasture types improves the understanding the fragility of the ecosystem services of the New England Tablelands while helping within applied management by encouraging higher nitrogen forages to improve dung beetle reproduction and colonisation.</p>