Hi,

 

I am trying to compare the slopes and y-intercepts of the power curves
between two plant species to see if they follow similar trends
(photosynthesis y-axis, stomatal conductance x-axis). I can fit linear
regression lines to the data and run the stats using an ANCOVA, but the
specific parameters require I fit a 2 Parameter Power Curve to the data.
Is running an ANCOVA with the abline function the best bet here, or does
R have a specific function to fit and compare power curves?

 

Here is my code thus far, and I was able to compare the linear
regressions lines with this code, but the data requires a power curve
fit. Any thoughts? Any help is much appreciated, Steve

 

###compares slope

mod1<-aov(photosynthesis~conductance*species,data=data)

summary(mod1)

 

###compares y-intercept

mod2<-aov(photosynthesis ~ conductance +species,data=data)

summary(mod2)

 

anova(mod1,mod2)

 

BA<-subset(data,species=="B.attenuata")

BM<-subset(data,species=="B.menziesii")

 

reg1<-lm(photosynthesis ~ conductance,data=BA)

summary(reg1)

 

reg2<-lm(photosynthesis ~ conductance,data=BM)

summary(reg2)

 

plot(photosynthesis ~ conductance, data=data, type='n')

points(BA$conductance,BA$photosynthesis, pch=20)

points(BM$conductance,BM$photosynthesis, pch=10)

abline(reg1, lty=1)

abline(reg2, lty=2)

 

reg.todo<-lm(photosynthesis~species/conductance-1, data=data)

summary(reg.todo)

 

 

 


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