Ecological Archives A017-084-A1

Melina Campero, Stefanie Slos, Frans Ollevier, and Robby Stoks. 2007. Sublethal pesticide concentrations and predation jointly shape life history: behavioral and physiological mechanisms. Ecological Applications 17:2111–2122.

Appendix A. Direct, indirect, and total effects of pesticide stress, predation risk, and their interaction on response variables.

Path coefficients were standardized, i.e., scaled to make their standard derivations equal to unity. The direct effects accounts for the effects of the stressors on response variables without the involvement of a third variable (paths 1–15 Fig. 1; also shown in Fig. 4). The indirect effects are the effects of the stressors on response variables channeled through food ingestion and food assimilation. Indirect effects are quantified as the sum of the products of path coefficients of the chains linking a stressor with a response variable (see worked out example below). Finally, the total effects are the sum of the direct and indirect effects of each stressor on the response variables.

Example to calculate the strength and sign of an indirect effect.

The indirect effect of predation stress on growth rate in the atrazine treatment is calculated as the sum of the products of the path coefficient of two chains. The first chain links predation risk to growth rate through the direct effect of predation on ingested food (-0.82), the direct effect of ingested food on assimilated food (0.90) and the direct effect of assimilated food on growth rate (0.63). The total contribution of this chain to the indirect effect is -0.82 × 0.90 × 0.63 = -0.465. The second chain links predation risk to growth rate through the direct effect of predation on assimilated food (-0.09) and the direct effect of assimilated food on growth rate (0.63). The contribution of the second chain is -0.09 × 0.63 = -0.057. The indirect effect is the sum of the contribution of both chains, being
(-0.465) + (-0.057) = -0.52.

TABLE A1. Direct, indirect, and total effects of pesticide stress and predation stress on response variables. Where Pest × Pred = Pesticide stress × predation risk.


 

Direct

 

Indirect

 

Total

 
 
 
 

Pesticide

Predation risk

Pest × Pred

 

Pesticide

Predation risk

Pest × Pred

 

Pesticide

Predation risk

Pest × Pred


Atrazine

                     

Ingested food

-0.15

-0.82

0.05

 

--

--

--

 

-0.15

-0.82

0.05

Assimilated food

0.37

-0.09

0.15

 

0.01

-0.73

0.01

 

0.11

-0.82

0.16

Growth rate

-0.13

-0.28

-0.12

 

0.15

-0.52

0.05

 

0.02

-0.80

-0.07

Development time

0.11

0.25

-0.18

 

0.06

0.47

-0.01

 

0.17

0.72

-0.19

Head width

0.10

0.20

-0.51

 

-0.03

-0.25

0.01

 

0.29

-0.05

-0.50

                     

Carbaryl

                   

Ingested food

-0.01

-0.73

-0.04

 

--

--

--

 

-0.01

-0.73

-0.04

Assimilated food

-0.09

-0.31

0.04

 

-0.01

-0.51

-0.03

 

-0.10

-0.82

0.01

Growth rate

0.12

-0.25

-0.11

 

-0.07

-0.55

0.01

 

0.05

-0.80

-0.10

Development time

0.01

0.22

-0.05

 

0.05

0.47

-0.01

 

0.06

0.69

-0.06

Head width

0.23

0.08

-0.33

 

-0.02

-0.16

0.00

 

0.21

-0.08

-0.33

                     

Endosulfan

                   

Ingested food

0.14

-0.77

-0.22

 

--

--

--

 

0.14

-0.77

-0.22

Assimilated food

0.00

-0.11

-0.09

 

0.13

-0.69

-0.09

 

0.13

-0.80

-0.18

Growth rate

0.15

-0.21

-0.27

 

0.08

-0.51

-0.11

 

0.23

-0.72

-0.38

Development time

0.08

0.38

0.02

 

-0.21

0.33

0.07

 

-0.13

0.71

0.09

Head width

0.56

-0.08

-0.62

 

0.02

-0.10

-0.02

 

0.58

-0.18

-0.64



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