Fig 3. One of the pairs of pollen transfer networks from invaded (top) and non-invaded habitats (bottom).

Plant stigma species are shown at the bottom of each network, whilst pollen types are at the top. Plant stigma species and pollen types are represented by rectangles, the size of which reflects their abundance; triangles connect the two if the pollen type is found on the stigma species, and the width of the triangle is related to the frequency of the interaction. Red interactions are those with balsam pollen, i.e. balsam pollen grains were found on the stigmas of the species with which it is linked. Codes for species are: 1- Arctium minus; 2 –Buddleja davidii; 3- Calystegia sepium; 4- Circaea lutetiana; 5 –Cirsium arvense; 6 –Clematis vitalba; 7 –Dipsacus pilosus; 8 –Epilobium hirsutum; 9 –Filipendula ulmaria; 10 –Heracleum sphondylium; 11 –Rosa pimpinellifolia; 12 –Rubus fruticosus; 13 –Vicia sepium; 14 –Silene dioica; 15 –Asteraceae 1; 16 –Dipsacus sp.; 17 –Epilobium sp.; 18 –Impatiens glandulifera; 19 –Morphotype (hereafter, M) 1; 20 –M10; 21 –M16; 22 –M4; 23 –M5; 24 –M6; 25 –M9; 26 –Sonchus asper; 27 Taraxacum sp.; 28 –Asteraceae 4; 29 –Centaurea nigra; 30 –Cirsium sp.; 31 –Epilobium parviflorum; 32 –Geranium robertianum; 33 –Hypericum tetrapterum; 34 –M11; 35 –M12; 36 –M13; 37 –M14; 38 –non identified; 39 –Silene dioica; 40 –Sonchus sp.; 41 –Stachys sylvatica; 42 –Taraxacum officinale; 43 –Trifolium sp.; 44 –Trifolium dubium; 45 –Trifolium pratense; 46 –Trifolium repens.