R 使用scale_x_continuous复制ggplot 2中的离散x轴

我需要在ggplot上方和下方显示x轴的标签，并与相应的数据点对齐.我已经用必要的数据和美学创建了一个ggplot，但我很难复制x轴，因为它是一个分类变量.

由于scale_x_discrete不可能复制轴，因此我try 使用scale_x_continuous()，用断点拆分类别变量，并将字符载体定义为标签. "plot"是我的数据和美学ggplot. 变量"birds$species_list"是一个包含鸟类物种名称的因子，按百分比值增加排序.

library(ggplot2)
library(data.table)

birds <- data.frame(species_name= c("eagle", "eagle", "robin", "vulture", "bee-eater"),
                 overall.percentage = c(12, 33, 19, 20, 15))

# reorder the species according to their lowest percentage value
x <- setDT(birds)[,.(.(sort(overall.percentage))), species_name]
birds[
  setorder(setDT(transpose(x[[2]]))[,species_name := x[[1]]])[,order := .I],
  on = "species_name", order := order]

plot<-
    ggplot(birds, aes(x=reorder(species_name, order), overall.percentage)) +
    geom_point(position = position_jitter(w = 0.25, h = 0))
    
plot + scale_x_continuous(breaks = 1:length(unique(birds$species_name)),
                     labels = as.character(unique(birds$species_name)),
                     sec.axis = dup_axis())

正如之前网上问题所建议的那样，我也try 了这个代码.

plot + scale_x_continuous(breaks = 1:length(unique(birds$species_name)),
                          labels = as.character(unique(birds$species_name)),
                          sec_axis(~.,
                                   breaks = 1:length(unique(birds$species_name)),
                                   labels = as.character(unique(birds$species_name))))

我原本希望代码能够成功复制我的图中的x轴，但总是向我返回错误"将离散值提供给连续比例". 这可能是与订购操作相关的问题吗？

任何建议都将不胜感激，提前感谢！