Skip to main content
. 2018 Nov 2;13(11):e0204460. doi: 10.1371/journal.pone.0204460

Table 1. Effect of ecosystem services providers (pollinators and biocontrol agents) and nitrogen application on productivity per flower (g) and overall land productivity (kg ha-1) of common bean (P. vulgaris) farms.

Response variable (Y) Explanatory terms Weight AICc ∆AICc
Productivity per flower DN DE N DN*N
Model1 - - X - 0.269 63.9 0.00
Model2 - X X - 0.134 65.3 1.39
Model3 X - - 0.113 65.7 1.74
Model4 X - X X 0.111 65.7 1.78
Average model: log(Y/(2-Y))=-1.32+(638.5-6.8*N)*DN+0.016*N-45.1*DE
Overall land productivity DN DE N DN*N
Model 1 - - - - 0.287 110.3 0.00
Model 2 X - - 0.135 111.8 1.51
Model 3 - X - - 0.124 112.0 1.68
Average model: log(Y/(5300-Y))= -014 + 54.25*DN –86.2*DE

Models were selected based on the Akaike information criterion corrected to small sample size (AICc), and all models with a variation of AICc (ΔAICc) lower than 2 units were considered in the average model, the contribution being proportional to the model weight. As productivity models typically follow a sigmoid relationship (i.e. have established maximum and minimum values) we applied a logit transformation, using the maximum value of productivity per flower rounded to units (2 g) and productivity per ha rounded to hundreds (5300 kg.ha-1) as the top asymptote.

DN = Density of native pollinators

DE = Density of exotic pollinators (A. mellifera)

N = Nitrogen input

X = terms that were included in the models (Gaussian distribution for productivity per flower, and log transformed for overall land productivity to normalize residuals)

* = two-way interaction between explanatory variables or multiplication in the equation