The invertebrate communities associated with a Chrysanthemum coronarium-invaded coastal sage scrub area in Southern California

The escape of ornamental plants is a main pathway of invasion into many ecosystems. Non-native plants can alter basal resources and abiotic factors leading to effects that ripple throughout an ecosystem. Invertebrates mediate these effects—responding quickly to abiotic and primary producer changes and, in turn, influencing other species. Invasions are of particular concern in the coastal sage scrub ecosystems of Southern California, where habitat loss and urban encroachment increase invasive species propagule sources and decrease native community resistance. The introduced annual Chrysanthemum coronarium (crown daisy) is a common invader with largely undocumented community-level effects. Our study tested the relationships between the invasive Chrysanthemum and a coastal scrub invertebrate community using a field study at the Tijuana River Estuary. We found similar or lower abundances and diversity of canopy fauna in the presence of Chrysanthemum. Community composition dramatically differed, however, in the presence Chrysanthemum, which was associated with higher abundances of dipterans, wasps and flower beetles, and lower abundances of hemipterans and thysanopterans than native shrubs. Differences in communities were consistent at the species- and order-levels, and were associated with the generally greater plant biomass and shadier conditions afforded by the natives. This study reveals that even a proportionally small amount of Chrysanthemum may shift the invertebrate community through alterations of abiotic properties and plant biomass. We recommend that Chrysanthemum be removed at the first sign of invasion or that spread is prevented since effects on the invertebrate community are dramatic and occur quickly.