Abstract
Beetles are the most diverse animal clade on the planet, and understanding the mechanisms underlying their diversity patterns is critical to understanding animal biodiversity in general. Using carrion beetles (Silphidae; Coleoptera), I test the more-individuals hypothesis (MIH), consisting of positive climatic impacts on food resources leading to increased abundance and then diversity. I also test competing mechanistic hypotheses, including interacting effects of climate, local vegetation, habitat diversity, habitat heterogeneity, soil diversity, and elevational area. Carrion beetle species richness and abundances were estimated using 40 standardized pitfall traps set for 90 days at 30 survey sites on two elevational gradients in the Front Range and San Juan Mountains, Colorado, USA. Standardized measurements assessed 13 vegetative characteristics, food resources (mammal abundances), soil diversity, habitat diversity, elevational area, temperature, precipitation and net primary productivity at each site. Structural equation models were used to test competing diversity hypotheses and mechanisms. Species richness peaked at intermediate elevations on both gradients, whereas abundance was unimodal on one gradient and decreasing on the other. The MIH mechanism was rejected; all four potential SEM model constructions were unsupported and the majority of all SEM models did not support relationships between abundance and diversity or climate and food resources. The best SEM model included direct influences of temperature, vegetation biomass, and food resources but with separate effects on diversity and abundance. Carrion beetles were more diverse and abundant in sites with dense understory vegetation and warm temperatures, while higher abundances were also linked to more food resources. This climate-biotic relationship is likely due to a need for microclimates and microhabitats to mediate physiological tradeoffs of desiccation and thermoregulation with predation. This suggests a general hypothesis for beetle diversity and abundance, particularly on arid-based mountains globally.
Highlights
Improving our understanding of the patterns and drivers of diversity on the planet is necessary for knowledgeable conservation in times of anthropogenic destruction
Silphid elevational species richness peaked at mid-elevations on both mountains, lower in the foothills in the Front Range and closer to midmountain in the more arid San Juans (Fig. 3)
Temperature declined and precipitation increased with elevation on both mountains (Fig. 3a, d), while regional NPP was unimodal with maximum productivity at upper mid-elevations (Fig. 3b, e)
Summary
Improving our understanding of the patterns and drivers of diversity on the planet is necessary for knowledgeable conservation in times of anthropogenic destruction. Vertebrates are a very narrow slice of animal diversity, only 5%, whereas insects are 80% of described species (e.g., Erwin 1982, May 1988). Beetles (Coleoptera) are the most successful animal clade on the planet with more than 400,000 beetle species described so far (e.g., Stork et al 2015). Our global and regional understanding of beetle diversity patterns lags enormously behind vertebrates. Like most clades of insects, are most diverse in the tropics (Erwin 1982), but beyond that our knowledge of patterns and underlying mechanisms for beetle diversity are scant (e.g., Werenkraut and Ruggiero 2011, Beck et al 2012; Fattorini 2014, Gebert et al 2020). More mechanistic studies on beetles could lead to fresh perspectives and directions
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