[R-sig-eco] sunflower pollination analysis

[Mariano Devoto]

Hi. I am trying to model the visits of pollinators to sunflower heads in a
field experiment. My response variable is the number of insect visits in
15' periods looking at a variable number of flower heads at a time. The
experiment includes three sunflower hybrids. Samples were taken at three
distances from the field margin (2, 20 and 100m). There are two complete
blocks in the experiment. I added the number of flower heads as an offset
variable as they varied among samples.

Here is a workable code:

require(RCurl) #need this to download data from Google Drive
my.file <- getURL("
https://docs.google.com/spreadsheets/d/e/2PACX-1vQq-Clbksm1S3Qq2_V9FBuEfUVno11Dytk0v9eJ2j7e7FpXHYqigaqJlcTyt5u2ipfVUjrKbAFL294e/pub?output=csv
")
sunflower_data <- read.csv(textConnection(my.file), head=T)
str(sunflower_data)
model1 <- glm(visits ~ offset(cap) + block + hybrid + distance,
family=poisson, data=sunflower_data)
summary(model1)
plot(model1)
#First diagnostic plot suggests residuals have a trend
#Other diagnostic plots suggest observation #35 is too influential, so...

model2 <- glm(visits ~ offset(cap) + block + hybrid + distance,
family=poisson, data=sunflower_data[-35,])
summary(model2)
plot(model2)
#things look a bit better, but residuals in diagnostic plot #1 still show a
trend. What should I try next?

Any advice is much appreciated.

Mariano

*Dr. Mariano Devoto*

Profesor Adjunto - Cátedra de Botánica General, Facultad de Agronomía de la
UBA
Investigador Adjunto del CONICET

Av. San Martín 4453 - C1417DSE - C. A. de Buenos Aires - Argentina
+5411 4524-8069
*https://www.researchgate.net/profile/Mariano_Devoto
<https://www.researchgate.net/profile/Mariano_Devoto>*

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