Appendix S1 A detailed description of the ecological and life history correlates examined
and additional references cited.
Supplementary methods
SPECIES FILTERING
There were 28 species comprised of more than one subspecies (75 subspecies in total) with
differing ecological responses (‘invasive’, ‘threatened’ or neither). For 17 species where one
or more of the subspecies were listed as ‘invasive’ or ‘threatened’, the ‘invasive’ or
‘threatened’ subspecies were retained, while subspecies which were neither ‘invasive’ nor
‘threatened’ were removed (Group A in Table S1). One species had five subspecies listed,
none of which were considered ‘invasive’ or ‘threatened’; for this we only included the best
described (i.e., with the most trait data available) subspecies. In eight species where all
subspecies were coded as ‘threatened’, only the best described subspecies per species was
obtained (Group B in Table S1). Finally, two species were comprised of one ‘threatened’ and
one ‘invasive’ subspecies each – both species were omitted from the dataset (i.e., all four
subspecies) (Group C in Table S1). This left a total of 8906 species in the final database (see
Appendix S3 for full species list).
ECOLOGICAL AND LIFE HISTORY ATTRIBUTES
For each of the species we compiled attributes hypothesised to relate to a species’ propensity
to become threatened/extinct (Thompson 1994; Turner et al. 1994; McIntyre, Lavorel &
Tremont 1995; Duncan & Young 2000; Walker & Preston 2006; Sodhi et al. 2008), invasive
(Pyšek, Prach & Smilauer 1995; Lake & Leishman 2004; Hamilton et al. 2005; Cadotte,
Murray & Lovett-Doust 2006), as well as traits linked to general plant survival strategies
(Westoby 1998). These included:
1
Native geographical range [RG]: The extent of a species’ native range dictates a large
component of its propensity to become invasive or threatened (Heger & Trepl 2003; Croci, Le
Quilliec & Clergeau 2007). This is based on the notion that widespread species tend to have a
higher capacity to tolerate new environments given that they have already encountered a
variety of climatic and habitat conditions in their evolutionary history and acquired a
relatively higher phenotypic or genotypic plasticity (Sax & Brown 2000; Croci et al. 2007).
We therefore hypothesised that the range of invasive species would be larger than noninvasive species. Using the geographic-specific data collected, species were classified into
one of three ordinal categories of native geographic range — [1] species distributed over one
floristic (geographic) kingdom, [2] species spanning two kingdoms, or [3] species spanning
three floristic kingdoms.
Altitudinal distribution [ALT]: To inspect ‘range’ occupancy in a vertical plane (as opposed
to the horizontal plane described by geographical range), we considered altitudinal range as a
potential correlate of threat and invasiveness. Indeed, higher-altitude species tend to be
represented by fewer invasive species (Pauchard & Alaback 2004; Becker et al. 2005), and
higher-elevation specialists may be more susceptible to changing climates and land-use than
lower-elevation generalists (e.g., Pounds & Crump 1994; Paul et al. 2005; Pounds et al.
2006). Further, Hegde and Ellstrand (1999) found that rare plant species had lower maximum
elevations than common species. We hypothesised that altitudinally restricted species would
be more susceptible to threat than lowland or mixed altitudinal-range species. Minimum and
maximum altitudes for each species were collated from multiple sources. Species were
classified as lowland [1], upland (montane) [2], or mixed [3]. Lowland species were defined
by an altitudinal range of 0 to 1500 m; montane species had an altitudinal range > 1500 m.
Exact descriptors of altitudinal range were used instead of raw altitudinal data whenever
available. Descriptors indicating an upland/montane habitat included ‘alpine belt’, ‘subalpine
2
belt’, ‘montane’ and ‘uplands’. Descriptors of lowland habitat included ‘lowlands’, ‘plains’
and ‘foothills’.
Habitat [HBT]: The type of habitat occupied by a species may influence its distribution given
the variation in abiotic factors (e.g., geology, rainfall, land-use, etc.) that dictate habitat
distributions (Pocock et al. 2006). Previous work has found a strong effect of habitat type on
plant species rarity (Peat & Fitter 1994; Quinn et al. 1994; Pocock et al. 2006) and extinction
risk (Sodhi et al. 2008). Species were categorised into one of three habitat classes based on
canopy cover: closed forest [1], open habitats [2], or mixed [3]. Closed forest was defined as
forests with > 30 % canopy cover (i.e., evergreen rainforest, tropical moist forest, semideciduous forest, deciduous forest, tropical/sub-tropical dry forest and mixed forest) (United
Nations Environmental Programme-World Conservation Monitoring Centre 2002). Habitats
with less canopy cover, such as woodlands, savannas, forest edges, grasslands and ruderal
places, were coded as ‘open habitat’. We hypothesise that open- and mixed-habitat species are
more likely to be invasive, and less likely to be threatened.
Plant height [HT]: Extinction risk in some plant groups has been linked to organism size
(Thompson 1994; Walker & Preston 2006), although not in others (e.g., Sodhi et al. 2008).
Height is also used to predict the incidence of alienism (Pyšek & Richardson 2007). We
categorised average plant height as an ordered factor ≤ 1.0 m [1], > 1.0 to 10.0 m [2], or >
10.0 m [3]. We also considered this variable as a continuous covariate on the log10 scale
assuming median values in each category (i.e., log10[0.5], log10[5] and log10[15]). To ensure
consistency in the interpretation of taxonomic descriptions in the Floras, all the heights
recorded in different Floras were noted for each plant, and the largest value was used for
classification.
Life cycle [LC]: It has been reported that weedy species tend more often to be annuals
(Sutherland 2004), even though in some cases naturalised legumes may tend to be perennial
3
(Wu, Chaw & Rejmánek ). Species were classified as monocarpic annual/biennial [1], or
polycarpic perennial [2].
Habit [HAB]: A plant’s life form can be an important determinant of a species’ proneness to
invasion (Sutherland 2004; Pyšek & Richardson 2007), extinction (Sodhi et al. 2008),
longevity (and hence, persistence probability in larger and scattered habitats – Clapham, Tutin
& Warburg 1952; Kelly 1996; Kelly & Woodward 1996). Species were placed into one of
four ordered growth habit (life form) categories ranging from smallest/lowest to
largest/tallest: non-climbing herb [1], climber/vine/liana [2], non-climbing shrub [3], or.
tree/treelet [4].
Floral display [FD]: Larger floral displays in some alien plant species have been linked to
their relatively higher pollination rates when compared to sympatric native species (Brown,
Mitchell & Graham 2002; Ghazoul 2002). We therefore hypothesised that invasive legumes
might, on average, have larger floral displays than non-invasive species. Two categories of
floral display were identified: solitary flowers [1] or inflorescence [2]. Species with solitary
flowers or a lax inflorescence, with the lower limit of one flower, were classified as solitary
flowers. Species with two- to many-flowered inflorescence were inflorescent species.
Hooks on fruit [HK]: Invasiveness has been linked to the capacity of plants to disperse
propagules (Grotkopp, Rejmánek & Rost 2002; Sutherland 2004), such that invasive species
may be more likely to possess morphological attributes such as hooks to increase fruit
dispersal capacity. Each species was classified as having [1] or not having [0] hooks on its
fruit surface. Hooks were broadly interpreted as projections that can serve to attach fruit to
animal bodies for dispersal. Species with fruit surfaces described as uncinate, hooked, spiny,
or having stiff/sharp hairs (Harris & Harris 1994) were considered ‘hooked’. Species without
descriptors that suggest a positive fruit attachment potential (e.g., glabrous, glaucous, viscid,
4
ciliate, sericeous, pubescent, lanate, woolly, tomentose, velutinous, villous, hispidulose) were
considered ‘not hooked’.
Fruit dehiscence [DEH]: The timing and ease with which fruits dehisce may facilitate the
access to and dispersal of seeds from certain categories of plants (e.g., Wender, Polisetty &
Donohue 2005; Jongejans et al. 2007). Indeed, comparisons between rare and common plant
species in Britain and California suggest that rare species tend to have more dehiscent fruits
than common ones (Hegde & Ellstrand 1999). We hypothesised that species with more
dehiscent fruits may have a higher proneness to becoming invasive given the predicted easier
access to of seeds to propagule dispersers. Species were categorised as having dehiscent or
tardily dehiscent fruits [1] or as with indehiscent fruits [0].
Seed size [SS]: Another attribute commonly associated with invasiveness and plant rarity is
small seed size (Rejmánek & Richardson 1996; Pocock et al. 2006). Species with small seeds
may be expected to have better propagule dispersal capacity and so may be better invaders
(Rejmánek & Richardson 1996; Pocock et al. 2006); whereas larger seeds may require animal
dispersal (Pocock et al. 2006) such that habitat loss may confer an additional disadvantage to
species relying on dispersers that are themselves threatened with extinction (Brook, Sodhi &
Bradshaw 2008). Upper limits of seed length were recorded for each species from all
available descriptions. Using the maximum upper limit of seed length, each species was
categorised into one of three ordered classes of seed length: ≤ 1.0 cm [1], > 1.0 to 2.0 cm [2],
or > 2.0 cm [3].
Armament [ARM]: Spines and prickles can deter small and large mammal herbivory
(Cooper & Owen-Smith 1986; Belovsky et al. 1991; Cooper & Ginnett 1998) and increase the
likelihood of invasiveness (Sutherland 2004). Legume species can be armed [1] or not [0] by
recurved prickles (e.g., Acacia subg. Aculeiferum, various Erythrina spp., various Caesalpinia
5
spp.), sharp stipular spines (e.g., Acacia subg. Acacia) and modified thorny rachi (e.g.,
various Astragalus spp.).
Indumentum (hairs) [HR]: The presence of indumentum or hairs has been shown to protect
leaves of Verbascum thapsus (Woodman & Fernandes 1991) and Miconia albicans (Paleari &
Santos 1998) against herbivory. Woodman & Fernandes (1991) also found that leaf hairs
represent an evapotranspirative barrier against water loss. Thus, we hypothesised that the
presence of hairs would reduce the likelihood of becoming threatened and increase the
proneness to invasiveness. Species with hairs on at least one of the four vegetative parts
recorded (i.e., stem/branchlets; petiole/rachis; leaf surface; leaf margin) were considered hairy
[1]. The alternate category [0] included hairless, glabrous or only slightly hairy species.
Leaf length [LL]: Leaf length was used as an index of leaf mass, which is correlated with leaf
life span, photosynthetic rate, nutrient concentration, and palatability to herbivores (Royer et
al. 2007). We hypothesised that shorter-leaf species would be more susceptible to threat than
longer-leaf species, although larger leaf area may confer invasiveness advantages (Hamilton
et al. 2005; Pyšek & Richardson 2007). Upper limits of leaf lamina length for the most basic
unit of the leaf (leaf lamina for simple leaves; leaflet lamina for compound leaves) were
recorded for each species from all available descriptions. Using the maximum upper limit of
lamina length, each species was classified into one of six ordered categories: ≤ 4.0 cm [1], >
4.0 to 8.0 cm [2], > 8.0 to 12.0 cm [3], > 12.0 to 16.0 cm [4], > 16.0 to 20.0 cm [5], or > 20.0
cm [6]. We also considered in a second analysis a continuous covariate of leaf length on the
log10 scale assuming the median point of each category (i.e., log10[2], log10[6], log10[10],
log10[14], log10[18], log10[22]). See Methods in main text for details.
Pollination syndrome has also been shown to affect plant extinction risk (Sodhi et al. 2008).
However, most legumes are thought to be pollinated by insects (entomophily) (Leppik 1966)
6
as opposed to birds, bats and wind (Arroyo 1981; Janzen 1989). Coupled with a lack of
specific data, we believed pollination was tightly correlated with phylogeny and so we did not
include this variable. Clonality has been hypothesised to relate to extinction and invasion risk
in plants (Alpert, Bone & Holzapfel 2000; Rejmánek 2000; Burns 2006; Pocock et al. 2006;
Pyšek & Richardson 2007; Sodhi et al. 2008). However, there are few ecological data
available for clonality for most legumes. We were therefore unsuccessful in finding familywide data on clonality. Owing also to the many types of clonal architecture in both
herbaceous and woody plants (Klimeš et al. 1997; Peterson & Jones 1997), it would be
perilous to infer limited types of vegetative reproduction. We therefore omitted this variable
from the list of correlates considered.
Note that all data are available from the authors upon request.
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