重新排列ggplot中的标签y轴

我试图从ggplot中以字母顺序显示类别（Y中的物种）和连续变量（X中）之间的ggplot标记y轴。但是，我在Y轴的顶部得到了按字母顺序排列的最后一个种类，而在底部又显示了按字母顺序排列的第一个种类。

由于我是新手，所以我无法显示图像，但是它看起来像是y轴上的物种列表，并且对于每个物种，均表示一个点，其标准误差条对应于相应的x值（平均值）。并在该物种的顶部呈现“林鸭”，在底部呈现“阿尔卑斯雨燕”​​（中间按字母顺序排列）。

我想提出相反的建议（在顶部和底部都是“木鸭”物种Alpine Swift）。

我用来绘制图形的命令如下：

# getting data for the error bars
limits<-aes(xmax=mydata$Xvalues+mydata$Xvalues_SD,
        xmin=(mydata$Xvalues-mydata$Xvalues_SD))

# plot graph
graph<-ggplot(data=mydata,aes(x = Xvalues, y = species))
       +scale_y_discrete("Species")
       +scale_x_continuous(" ")+geom_point()+theme_bw()+geom_errorbarh(limits)

我尝试先订购数据集，然后再上传数据并运行图形。我还尝试使用以下命令对物种因子进行重新排序：

mydata$species <- ordered(mydata$species, levels=c("Alpine Swift","Azure-winged Magpie","Barn Swallow","Black-browed Albatross","Blue Tit1","Blue Tit2","Blue-footed Booby","Collared Flycatcher","Common Barn Owl","Common Buzzard","Eurasian Sparrowhawk","European Oystercatcher","Florida Scrub-Jay","Goshawk","Great Tit","Green Woodhoopoe","Grey-headed Albatross","House Sparrow","Indigo Bunting","Lesser Snow Goose","Long-tailed Tit","Meadow Pipit","Merlin","Mute Swan","Osprey","Pied Flycatcher","Pinyon Jay","Sheychelles Warbler","Short-tailed Shearwater","Siberian Jay","Tawny Owl","Ural Owl","Wandering Albatross","Western Gull1","Western Gull2","Wood Duck"))

但我得到相同的图。

如何更改Y轴的顺序？