The trait and host plant ecology of aphids and their distribution and abundance in the United Kingdom

Aim  We characterized the annual populations of 170 aphid species by their log abundance, site occupancy and site continuity (i.e. the persistence of species in time) and used this information to make predictions about groups of species that displayed characteristic patterns. By doing so, we aimed to identify commonalities in functional traits (host-alternation; mode of reproduction; life-cycle plasticity; median body size) and host plant geographic range sizes that may indicate why some species are common and others not. Location  The population dynamics of winged aphids at 27 locations in the United Kingdom were studied. Methods  The annual numbers of aphids were studied using a dataset comprising over 11 million individuals across 509 site-years. Traits and host plants were analysed using linear mixed effects models and nonlinear regression models. Results  Linear mixed effects models showed that the fixed effects of host alternation and winter host plant area of occupancy were important in predicting log abundance, site occupancy and site continuity. Life-cycle plasticity was also a significant effect, although not for log abundance. Relationships between site continuity, site occupancy and log abundance were strongly nonlinear. Site continuity always lagged site occupancy, indicating that species were less likely to retain previously occupied sites when abundances were low. Main conclusions  Aphid traits are a better paradigm than taxonomic relatedness in explaining macroecological patterns. Host alternation induces an annual flux of migrants that engenders higher annual log abundances, consistent with the theory that species with high local densities tend to confer a much wider distribution than those with low densities. The abundance of aphids is monotonically related to the geographic range size of their winter host, suggestive of a strong bottom-up effect (i.e. resource controlled). The areas of occupancy (AOO) of winter host plants constrain aphids to low abundances because a greater proportion of hosts are trees and shrubs which tend to have smaller AOO than herbs and grasses, the common summer host types.