Temporal niche partitioning of Swiss black scavenger flies in relation to season and substrate age (Diptera, Sepsidae)

Abstract

Understanding why and how multiple species manage to coexist represents a primary goal of ecological and evolutionary research. This is of particular relevance for communities that depend on resource rich ephemeral habitats that are prone to high intra- and interspecific competition. Black scavenger flies (Diptera: Sepsidae) are common and abundant acalyptrate flies associated with livestock dung decomposition in human-influenced agricultural grasslands worldwide. Several widespread sepsid species with apparently very similar ecological niches coexist in Europe, but despite their ecological role and their use in evolutionary ecological research, our understanding of their ecological niches and spatio-temporal distribution is still rudimentary. To gain a better understanding of their ecology, we here investigate niche partitioning at two temporal scales. First, we monitored the seasonal occurrence, often related to thermal preference, over multiple years and sites in Switzerland that differ in altitude. Secondly, we also investigate fine-scale temporal succession on dairy cow pastures. In accordance with their altitudinal and latitudinal distribution in Europe, some species were common over the entire season with a peak in summer, hence classified as warm-loving, whereas others were primarily present in spring or autumn. Phenological differences thus likely contribute to species coexistence throughout the season. However, the community also showed pronounced species turnover related to cow pat age. Some species colonize particularly fresh dung and are gradually replaced by others. Furthermore, the correlation between co-occurrence and phylogenetic distance of species revealed significant under-dispersion, indicating that more closely related species are frequently recovered at the same location. As a whole, our data suggests temporal niche differentiation of closely related species that likely facilitates the rather high species diversity on Swiss cattle pastures. The underlying mechanisms allowing close relatives to co-occur however require further scrutiny.

Sexual size dimorphism is associated with reproductive life history trait differentiation in coexisting sepsid flies

“…Although all species investigated here (except T. minor) commonly co-occur on livestock excrements (at least in Central Europe), the mechanisms that allow more than 10 closely related species of the genus Sepsis to co-exist in the same habitat remain contentious even after this study. Previous studies suggested little larval substrate specialization (Laux et al 2019) and only minor geographic, altitudinal or seasonal (including diurnal) variation in occurrence (Rohner et al 2014(Rohner et al , 2015(Rohner et al , 2019. Therefore these species have largely overlapping ecological niches.…”

“…Traits characterizing male and female mating behavior furthermore align well along the slow-fast reproductive continuum (Table 2). The most abundant and relatively large species S. cynipsea, S. punctum and S. thoracica (Rohner et al 2015(Rohner et al , 2019Busso and Blanckenhorn 2018a; Fig. 1) feature clutch sizes of around 45 -60 large eggs (ca.…”

“…With the exception of S. duplicata, the body size of the sepsid flies covered here does not vary tremendously. We know little about predation (or parasite) pressure on sepsids in the field (but see Busso and Blanckenhorn 2018c), but doubt that it differs strongly for the species treated here given they largely share the same (micro)habitat on pastures (Rohner et al 2015(Rohner et al , 2019. As we primarily studied species from north-central Switzerland, latitudinal variation was not an issue here.…”

“…Multiple widespread species with apparently very similar ecological niches coexist in Europe, and all 12 Sepsis species occurring in Switzerland may be found on the same pasture (Rohner et al 2014(Rohner et al , 2015(Rohner et al , 2019. Sepsids have received considerable attention in behavioral ecology and evolutionary research because of their diverse mating systems (Eberhard 2001a(Eberhard , 2003Kraushaar and Blanckenhorn 2002;Mühlhäuser and Blanckenhorn 2002;Martin and Hosken 2004;Tan et al 2011;Puniamoorthy 2014; and extraordinary secondary sexual morphology of forelegs and convergently evolved abdominal appendages ( Eberhard 2001b;Bowsher and Nijhout 2009;Bowsher et al 2013;Herath et al 2015;Baur et al 2019Baur et al , 2020.…”

The role of larval substrate specialization and female oviposition in mediating species diversity of closely-related sepsid flies (Diptera: Sepsidae)

“…In conclusion, we found little variation in the preferences for different types of dung and performance of 7 (9) closely related and common dung fl ies. Preferences for different types of dung thus cannot account for, or defi ne, the niche differentiation of these species that regularly co-exist in the same pastures or other sites in Switzerland and elsewhere (Rohner et al, 2014(Rohner et al, , 2015(Rohner et al, , 2019. We further found that oviposition preference of adults correlated with larval performance, indicating the oviposition behaviour of gravid fl y females is adaptive.…”