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).