Aspects of temporal resource partitioning among dung beetles (Coleoptera: Scarabaeidae) of the Kizilirmak Delta on the Black Sea Coast of Turkey

Abstract

Local assemblages of dung beetles in natural and altered ecosystems worldwide contribute to a suite of ecological functions and ecosystem services, including bioturbation and pest and parasite suppression. There is generally a strong competitive hierarchy for the dung resource among the three main guilds or functional groups of dung beetle species, with ball rollers more competitive than tunnellers, and tunnellers more competitive than dung dwellers.How are inferior competitors able to co-occur or coexist with superior competitors? Temporal resource partitioning is one of the mechanisms that can facilitate co-occurrence and coexistence in local assemblages. The primary purpose of this study was to investigate if, and how, temporal resource partitioning manifests at the interspecific, intraguild and interguild levels in a warm, temperate climate assemblage of dung beetles (Coleoptera: Scarabaeidae; Aphodiinae, Scarabaeinae) in the Kizilirmak Delta on the central Black Sea coast of northern Turkey.Twenty three species of dung beetles in three guilds were recorded in a seasonal survey of natural dung pads in 2013. In the summer of 2014, the effects of dung pad size on ball production by the large dung ball roller, Scarabaeus sacer (L.) were investigated with standardised dung pads. Ball production by S. sacer was concentrated on a small number of pads of the three largest sizes. Ball size increased but the number of balls produced per 100 g of dung decreased with increasing pad size. Ball production and time of day were significantly related (P < 0.01).In the summers of 2014 and 2015, standardised dung pads were used in two field experiments at the same site that investigated the effects of dung pad deposition time and exposure period, and their interaction, on species richness, abundance and biomass. During the experiments, an additional four dung beetle species were collected, bringing the total number to 27 species that included one ball rolling, 17 dung dwelling and nine tunnelling species. The large ball roller, S. sacer L., and small and medium-sized tunnellers, dominated assemblages in the first 24 h but they were then superseded by dwellers. Succession was highly compressed, with maximum abundance at 12 h and maximum species richness at 24 h. Regression analysis demonstrated a significant relationship (P < 0.01) between species richness and the inverse of the Berger-Parker dominance index (d); i.e., as the number of species increased, the abundance of individual species became more even.In addition, ANOVA was used to model the temporal dung use patterns of the dwelling and tunnelling guilds and correlation analysis was used to determine the interspecific and interguild relationships that underpin those patterns. ANOVA revealed significant effects of dung deposition time, dung exposure period, and their interaction, on the mean abundance of guilds. The tunnelling species appear to have been aggregated firstly by relatively synchronous diel activity and then by habitat filtering along the gradient of decreasing moisture content. ‘Limiting similarity’, which postulates that competitive exclusion limits the coexistence of taxa that are too similar in their traits, appears to have then restricted the number of tunnelling species that could be both concurrent and abundant. Conversely, dung dwelling species dispersed relatively uniformly across the six dung deposition times which meant they were able to exploit ‘temporal refuges’, i.e., dung pads with lower densities of tunnelling species which are generally superior competitors. Furthermore, both these guilds were most active during periods that reduced the potential for competition with the dominant competitor S. sacer, which was most active in the late dusk and early night.Separately, the patterns of interspecific, intraguild and interguild association or aggregation were investigated with correlation analysis to better understand their potential role in temporal resource partitioning. The general pattern of correlations was consistent between 2014 and 2015, with strong, positive correlations between the tunnelling species, low correlations between tunnelling and dung dwelling species, and low correlations between the dung dwelling species. This pattern of correlations indicated that temporal separation, and by inference, temporal resource partitioning, was occurring between the dung dwelling and tunnelling guilds. The mostly strong associations between tunnelling species may have reflected higher levels of negative, intraspecific interactions than negative, interspecific interactions, and similar competitive abilities.The generally strong, congeneric aggregation of the tunnelling Onthophagus spp. and Euoniticellus spp. may lend support to contemporary coexistence theory’s contention that increasing phylogenetic proximity, or relatedness, does not necessarily lead to competitive exclusion. Overall, the results of this study suggest that its methodology, supplemented by additional temporal and spatial experiments, can provide even deeper insights into the mechanisms underpinning the co-occurrence and coexistence of dung beetles, other dung fauna, fauna in other ephemeral resource patches, and insect faunas in general.