Contrasting effects of land cover on nesting habitat use and reproductive output for bumble bees

Abstract

O_LIUnderstanding habitat quality is central to understanding the distributions of species on the landscape, as well as to conserving and restoring at-risk species. Although it is well-known that many species require different resources throughout their life cycles, pollinator conservation efforts focus almost exclusively on forage resources. C_LIO_LIHere, we evaluate nesting habitat for bumble bees by locating nests directly on the landscape. We compared colony density and colony reproductive output for Bombus impatiens, the common eastern bumble bee, across three different land cover types (hay fields, meadows, and forests). We also recorded nest site characteristics, e.g., the position of each nest site, for all Bombus nests located during surveys to tease apart species-specific patterns of habitat use. C_LIO_LIWe found that B. impatiens nests exclusively underground in two natural land cover types, forests and meadows, but not in hay fields. B. impatiens nested at similar densities in both in meadows and forests, but colonies in forests had much higher reproductive output. C_LIO_LIIn contrast to B. impatiens, B. griseocollis frequently nested on the surface of the ground and was almost always found in meadows. B. bimaculatis nests were primarily below ground in meadows. B. perplexis nested below ground in all three habitat types, including hay fields. C_LIO_LIFor some bumble bee species in this system, e.g., B. griseocollis and B. bimaculatis, meadows, the habitat type with abundant forage resources, may be sufficient to maintain them throughout their life cycles. However, B. impatiens might benefit from heterogeneous landscapes with forests and meadows. Further research would be needed to evaluate whether hay fields are high-quality nesting sites for the one species that used them, B. perplexis. C_LIO_LISynthesis and applications. In the past, Bombus nesting studies have been perceived as prohibitively labor-intensive. This example shows that it is possible to directly measure nesting habitat use and quality for bumble bee species. Applying these methods to more areas, especially areas where at-risk Bombus spp. are abundant, is an important next step for identifying bumble bee habitat needs throughout their life cycles. C_LI