Biological parameters
We investigated the relationships between colony size and four
biological parameters of stingless bee colonies: (i) external activity
(in the field, before lab counts - non-invasive), (ii) egg-laying rate
(in the field, before lab counts - moderately invasive –hives were
opened to paint the brood cells), (iii) food stores (in the lab –
invasive –all pollen/nectar pots were weighed), (iv) brood cells
(immature bees; in lab - extremely invasive –all brood cells were
removed and counted) (Figure S2 and S3). These parameters were chosen
since they reflect the intensity of resource gathering by colonies and
their reproductive rates, factors likely linked to population size.
Moreover, they are easily measurable, allowing their replication in
other species.
Measurement of external activity and egg-laying rates were done in
situ , seven days before the counting of adult bees in the laboratory,
whereas measurement of brood cells and food stocks were obtained during
counts of adult bees (see previous section), to avoid excessive handling
of the colonies.
To estimate (i) external activity of colonies, we counted the number of
workers returning to the colony over 5 min per hour (Hilário et al.
2000). Data were collected during the peak activity period for all
species (0900 and 1100; two survey hours per day), for five consecutive
days, to obtain the average number of bees returning to the nest. On
rainy days, data were not collected. To evaluate (ii) the egg-laying
rate, the edge of the newest brood comb (in Melipona andS. aff. postica ) was marked with water-based acrylic
paints, and after 24 h the new cells were counted. For F.
longipes and P. minima , all constructed cells were painted and
after 24 h, all new cells were counted. This procedure was repeated for
all species during three consecutive days. From this data we calculated
the average number of new cells constructed over a three-day period.
For the evaluation of (iii) amount of food stocks, we weighed all the
food pots of the colonies (honey and pollen) using a precision balance
(Toledo™ Prix 3; minimal load: 5g) for all species, except P.
minima , for which we used a precision balance Master™; minimal load:
0.02g). To obtain the (iv) number of brood cells (i.e., immature bees)
in species that construct brood combs in horizontal layers
(Melipona spp. and S. aff, postica ), brood combs
were individually measured and photographed for counting of cells. InF. longipes and P. minima , in which brood cells are built
in loose bunches of cells (Roubik 2006), brood cells were marked with
water-based acrylic paints and manually counted (Figure S3).