Introduction

Materials and methods

Study Site

The 3,840 hectare MPG Ranch is a privately-owned conservation property in west-central Montana, in the Bitterroot River Valley and Sapphire Mountains of Missoula County (Fig. 1). Elevations range from 975m at the valley floor along the Bitterroot River, to 1860m on Mount Baldy, its highest point. The region has a mild, semi-arid climate with cool, moist winters and warm, dry summers. Mean precipitation ranges from 300mm at the valley floor to 350mm on mountain summits; most precipitation occurs in the winter as snow. Mean temperatures for the nearby town of Stevensville range from -3.6°C in December to 20.0°C in July.

Figure 1.  

Map of Montana and surrounding states with Missoula County boundary and property locations marked.

For over a century prior to 2009, this property had been managed for livestock and agricultural crop production. During that time, most of the lower elevation grasslands were replaced with irrigated crops or introduced forage grasses. These areas are now out of production and undergoing restoration treatments to return them to a more natural state. Livestock has also been removed from the property as part of the restoration effort, and native ungulates (elk, mule deer, and whitetail deer) currently comprise the majority of vertebrate grazers. Habitats on the property include riparian bottomlands, dry open forests, mid-elevation sagebrush steppe and grasslands, montane grasslands, and montane mixed-conifer forest.

The MPG North, an associated 81 hectare conservation property separated from MPG Ranch by over 100 kilometers, is located in the Swan River Valley, also in Missoula County (Fig. 1), at an elevation of 1200m. The climate in the Swan River Valley is cooler and wetter than the Bitterroot River Valley. At the nearby town of Seeley Lake, mean temperatures range from -6.1°C in December to 17.5°C in July, and mean annual preciptiation is 530mm. MPG North's habitat consists of mixed-conifer forest and clearings, and some small wetlands.

Analysis

Between 2013 and 2015 we collected a total of 64,747 bees representing 229 species and morphospecies across 38 genera in 5 bee families (Suppl. material 1). We had a total of 558 collection events (unique combinations of site and collection date). The number of species we collected is near the number of species we would expect to find in our study area based on species accumulation estimates, which predict the number of bee species in the area to be 255 (Fig. 2). Net collections yielded a total of 110 species, only three of which were species not also collected by pantraps. This number is lower than would be expected based on previous studies showing from 23% and 53% of the bee species collected by net to be unique when compared to pantraps (Grundel et al. 2011, Roulston et al. 2007, Wilson et al. 2008). This may be due to the reduced net collection time period (30 minutes instead of 60 minutes). In addition, many of the net collectors had no prior experience with insect collecting. Increased collection periods and improved collector training could raise the number of unique net collected species.

Figure 2.  

Species accumulation curve generated for bee species sampled in 558 collection events between 2013 and 2015. Species estimates were generated using EstimateS. The blue line represents the mean species accumulation, and the light blue shaded area represents the upper and lower bound of 95% confidence interval for species estimate.

Discussion

Acknowledgements

Author contributions

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Supplementary material