Results
We collected 144 bees of 37 species in the understory, 170 bees of 31 species in the midstory, 198 bees of 36 species in the canopy, and 167 bees of 28 species in the aerosphere above the canopy, for a total of 679 bees of 75 species across strata (Table A2; full details in Data.xlsx of supporting information). Twelve specimens could not be identified to species due to body damage and were not included in species richness or composition analyses. After accounting for differences among individual trees, generalized linear mixed models found that there were significantly more bees and bee species in the understory than within, or above, the canopy (Fig. 2c & 2f). Interaction terms (abundance: 𝛸2(3 ) = 19.0, P < 0.0005; richness: 𝛸2(3 ) = 16.4, P < 0.001) demonstrated that bee abundance (𝛸2(7 ) = 24.1; P < 0.005) and species richness (𝛸2(7 ) = 30.8; P < 0.0001) changed among strata throughout the study period (Fig. 2b & 2e; Fig. A2). Specifically, bee abundance and species richness were highest within the understory during the spring months (April and May) and decreased as the season progressed, while more bees and more species were encountered in and above canopy layers during the summer months (Fig. 1, 2a & 2d). Species composition of the bee community above the canopy was significantly different from the understory, midstory, and canopy layers (Fig. 1) but there were no statistical differences among the lower strata (Table A3; Fig. A3). More generally, abundant species were collected across strata (Fig. A4), whereas 13 species occurred only above the canopy (Table 1).