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