Spatial variation in herbivory, climate and isolation predict plant height and fruit phenotype in Plectritis congesta island populations

Climate and herbivory can each drive natural selection on plant traits, but may interact to give rise to different patterns in trait distributions when surveyed across island populations. These different patterns may arise because the occurrence of ungulate herbivores often varies across archipelagos, potentially leading to strong and abrupt spatial heterogeneity in the direction or intensity of natural selection. In contrast, climate tends to vary gradually and thus is more likely to lead to gradual clines in trait values. Population isolation may also affect trait values, given that random genetic drift may fix alleles or traits in the absence of gene flow, or because gene flow between populations with similar or opposing selection pressures may augment or swamp the effects of selection. Here, we estimate the independent and interactive effects of deer, climate and isolation on fruit phenotype and plant height in 285 Plectritis congesta populations at 77 island and 44 mainland sites i...