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.
Highlights
The mechanisms driving species diversity and its persistence are of paramount interest in ecological research
Saltella nigripes, most Themira spp., Sepsis nigripes, S. luteipes and S. biflexuosa are generally rare on Swiss dairy cow pastures
S. violacea and S. thoracica were absent to rare at high altitude sites >1000 m
Summary
The mechanisms driving species diversity and its persistence are of paramount interest in ecological research. In spite of longstanding and continuing scientific scrutiny, the phenomenal species diversity observed on earth, within ecological guilds, remains puzzling (Tilman 1982, Levine and HilleRisLambers 2009) This is in part due to the challenges in uncovering the mechanisms driving species co-occurrence, because environmental filtering and interspecific competition (among other processes) can act in all aspects of an organism’s life including what individuals eat, where and when they develop and reproduce, and what (abiotic) environmental conditions they prefer (Chesson 2000).
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