Do resources or natural enemies drive bee population dynamics in fragmented habitats?

Published source details Steffan-Dewenter I. & Schiele S. (2008) Do resources or natural enemies drive bee population dynamics in fragmented habitats?. Ecology, 89, 1375-1387.
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This study is summarised as evidence for the following.

	Action	Category
	Provide nest boxes for bees (solitary bees or bumblebees) Action Link

Provide nest boxes for bees (solitary bees or bumblebees)

A replicated study of 30 orchard meadows in Lower Saxony, Germany (Steffan-Dewenter & Schiele 2008) found that increasing nest site availability resulted in an increase of red mason bee Osmia rufa local population size from 80 to 2,740 brood cells/site from 1998 to 2002. Each trap nest contained an average of four red mason bee brood cells in common reed Phragmites australis stems. The mean proportion of suitable stems used by the red mason bee increased from 1% in 1998 to 26% in 2002 (highest 96%). The proportion of orchard meadows occupied by the red mason bee also increased, from 84% in 1998 to 100% in 2001 and 2002. Following removal of all brood cells in 2003, figures returned to those of 1998. Habitat connectivity did not affect the number of red mason bee brood cells/site. Population size and rates of parasitism (1992: 93%, 2002: 100% of populations) significantly affected population growth rates. The proportion of brood cells of other bee and wasp (Hymenoptera) species in traps decreased with increasing red mason bee occupancy. At each site, 12 trap nests (of 153 common reed segments) were installed each year. Nests were collected in September and then returned to the same posts in the spring (along with new traps).