I am trying to understand the effect that distance has on Hg levels in birds of 4 different species. I am most interested in the main effect of distance but I am including species as an interaction term bc hg levels do vary by species. However, I am not sure that I am interpreting the R output correctly.
This is the model that I am using:
lm(formula = blood_hg - 1 ~ GIS_distance * species - 1, data = Adult_Bird)
I included the "-1" so that R does not automatically use one of the species as the reference. Also, writing the model this way, I am hoping that the results will show the effect of species on bodd_hg rather the interaction with distance.
Here is the R output:
Residuals: Min 1Q Median 3Q Max -3.4342 -0.4637 -0.1594 0.3469 3.2214 Coefficients: Estimate Std. Error t value Pr(>|t|) GIS_distance -0.0046170 0.0016497 -2.799 0.005493 ** speciesCACH 0.6061536 0.1764384 3.435 0.000682 *** speciesCARW 3.9002870 0.2088432 18.676 < 2e-16 *** speciesEABL 0.0848200 0.0989441 0.857 0.392047 speciesHOWR 0.5478451 0.1413647 3.875 0.000133 *** GIS_distance:speciesCARW -0.0133468 0.0026402 -5.055 7.83e-07 *** GIS_distance:speciesEABL 0.0030014 0.0017731 1.693 0.091638 . GIS_distance:speciesHOWR 0.0005963 0.0020599 0.289 0.772442 --- Residual standard error: 0.8194 on 277 degrees of freedom (19 observations deleted due to missingness) Multiple R-squared: 0.6023, Adjusted R-squared: 0.5908 F-statistic: 52.44 on 8 and 277 DF, p-value: < 2.2e-16
My main question is how to interpret the interaction of GIS_distace and Species? And if what I am concerned with is the interaction of blood_hg and species, how do I manipulate the model to show me that?
I am learning so any advice is helpful! Thank you!!