Relationships between colony size and biological parameters
The number of brood cells was the biological parameter that best
explained colony size, followed by the external activity and egg-laying
rate (Table 2 and Figure 1). As brood counts involved highly invasive
sampling (complete removal of brood comb), which would likely lead to
eventual death of the colony, we also considered the second candidate
model as the most viable proxy for colony size.
The number of brood cells was the
biological parameter that best explained colony size, followed by the
external activity and egg-laying rate (Table 2 and Figure 1). The linear
regression of each biological parameter tested, and the number of adult
bees showed a strong relationship with the external activity for two of
the species evaluated (M. flavolineata : R2 =
0.193; M. fasciculata : R2 = 0.752; S.aff. postica : R2 = 0.313; F. longipes :
R2 = 0.221; P. minima : R2 =
0.559), while there was a strong relationship with the laying rate in
four species (M. flavolineata : R2 =
0.654; M. fasciculata : R2 = 0.879; S.aff. postica : R2 = 0.055; F. longipes :
R2 = 0.575; P. minima : R2 =
0.726). In only one species there was a strong relationship with the
food stocks (M. flavolineata : R2 = 0.0003;M. fasciculata : R2 = 0.872; S. aff.
postica : R2 = 0.014; F. longipes :
R2 = 0.109; P. minima : R2 =
0.104), and there was a strong relationship with the number of brood
cells in all species evaluated (M. flavolineata :
R2 = 0.596; M. fasciculata :
R2 = 0.908; S. aff. postica :
R2 = 0.562; F. longipes : R2 =
0.784; P. minima : R2 = 0.752) (Figure 2).
The formulae that provided an estimation of population size for all
species, by using a simple regression, are: (1) External activity:
Y=45.9*X + 448.9; p<0.001; R2=0.913; (2)
Brood cells: Y=0.905*X - 21.6; p<0.001,
R2=0.964; (3) Egg-laying rate: Y=25.9*X + 372.5;
p<0.001; R2=0.906. The number of food stocks
was not significant in the simple regression (p<0.108;
R2=0.052).