Tengo la siguiente parcela

require(ggplot2)

dtf <- structure(list(Variance = c(5.213, 1.377, 0.858, 0.613, 0.412, 0.229, 0.139, 0.094, 0.064), Component = structure(1:9, .Label = c("PC1", "PC2", "PC3", "PC4", "PC5", "PC6", "PC7", "PC8", "PC9"), class = "factor")), .Names = c("Variance", "Component"), row.names = c(NA, -9L), class = "data.frame")

ggplot(dtf, aes(x = Component, y = Variance)) +
geom_point()

Simplemente me gustaría conectar los puntos con líneas rectas. Lo intenté+geom_line() pero eso generó un error