DOI: 10.5061/dryad.05qfttf4p
title: Data from: Darwin’s naturalization conundrum reconciled by changes of species interactions

description: Although phylogenetic distance between native and exotic species has a
 close link with their interactions, it is still unclear how environmental
 stresses and species interactions influence the relationship between
 phylogenetic distance and biological invasions. Here we assessed the
 effect of invader-native phylogenetic distance on the growth of the
 invader (Symphyotrichum subulatum) under three levels of drought (no,
 moderate or intensive drought). Under no drought, interspecific
 competition between close relatives was the
 dominant process, and native communities more closely related to the
 invader showed higher resistance to invasion, supporting Darwin’s
 naturalization hypothesis. In contrast, under intensive drought,
 facilitation between close relatives by
 mutualism with arbuscular mycorrhizal fungi (AMF) became more
 important, and the invader became more successful in
 their more closely related native communities, supporting the
 pre-adaptation hypothesis. The colonization rate of AMF
 of the invader was higher in more closely related native
 communities regardless
 of the drought treatment, but
 it was only positively related to invader biomass under intensive drought. Therefore, the shift of species interactions from competition to facilitation may be ascribed to the promotion of AMF to invasion occurring under intensive drought, which leads to the effect of closely related natives on the invader shifting from negative to positive. Our results provide a new angle to resolve Darwin’s naturalization conundrum from the change of species interactions along a stress gradient, and provide important clues for invasion management when species interactions change in response to global climatic change.
description: Experimental plant communities with five levels of species
 richness (1, 2, 4, 8 and 16 species) were constructed at Taizhou
 University (28°39′N, 121°23′E) in Taizhou, Zhejiang Province, China. The
 species pool consisted of 16 native herbaceous
 species (<em>Antenoron filiforme, Achyranthes aspera, Solanum
 nigrum, Penthorum chinense, Sesbania cannabina, Patrinia scabiosaefolia,
 Eclipta prostrata, Polygonum chinense, Bidens pilosa, Perilla frutescens,
 Artemisia migoana, Justicia procumbens, Persicaria lapathifolia, Lolium
 perenne, Cichorium intybus, </em>and <em>Medicago
 sativa</em>) were selected to stimulate natural
 communities. <em>Patrinia scabiosaefolia</em> (Valerianaceae),
 <em>Achyranthes aspera</em> (Amaranthaceae), <em>Solanum
 nigrum </em>(Solanaceae) and <em>Artemisia</em>
 <em>migoana </em>(Asteraceae) are usually dominant species. We
 constructed a total of 46 communities with different species compositions:
 one monoculture for each of the 16 species, 10 two-species mixtures, 10
 four-species mixtures, 9 eight-species mixtures and one 16-species
 mixture. Each of the two-, four- or eight-species mixtures had a different
 species composition, and the species were randomly chosen from the species
 pool. All the 45 communities of the one-, two-, four- and eight-species
 mixture were replicated six times, and the community of the 16-species
 mixture was replicated 30 times, resulting in a total of 300 communities.
 The six replicates of the 45 communities were randomly assigned to the six
 combinations of three drought intensity treatments (no, moderate and
 intensive drought) and two invasion treatments (with or without an exotic
 plant invasion; as described in the next two sections); the 30 replicates
 of the 16-species mixture were also randomly assigned to the six treatment
 combinations of drought and invasion, with five replicates
 each.  We harvested the communities in all containers
 in October 2016. The biomass of most species almost reached to the
 highest value in October. In each container, aboveground living plants
 were sorted to species, dried to constant mass at 80°C and weighed. As
 some pathogens seemed to specifically infect <em>Medicago
 sativa</em>, no plants of this species survived at the end of the
 experiment. As the monocultures of
 <em>M</em>. <em>sativa </em>had no living plants,
 these containers (one in each of the six treatment combinations of drought
 and invasion) were not included in data analysis. Consequently, there
 was a final sample of 49 plots in each of six treatments.