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Table 2. Mean minimum residence time (MRT) for species with different invasion status in regional
floras. Means bearing the same letter within a region are not significantly different at
p
= 0.05 in
ANOVA or LSD test. Invasion status follows the definition in Richardson et al. [42] and Pyˇek et al.
[35].
Minimum residence time
Region
Invasion status
Mean
S.D.
n
Source
Azores
casual
57.5 a
65.1
210
[28]
Azores
naturalized
102.8 b
69.8
700
[28]
Czech Republic
casual
76.3 b
51.4
523
[29]
Czech Republic
invasive
140.0 a
41.5
54
[29]
Czech Republic
naturalized (excl. invasive)
126.3 a
47.8
114
[29]
Czech Republic
naturalized
130.7 a
46.2
168
[29]
New Zealand
invasive
106.1 a
31.3
11
[32]
New Zealand
naturalized
63.0 b
37.3
22
[32]
Importance of the residence time relative to other factors
The probability of invasion success increases with residence time [24] but in
particular floras, a long minimum residence time does not always correlate
with more localities. For example, among Fabaceae in Taiwan several genera
have more than one naturalized species with similar MRTs and these species
differ in invasion success; some occupy many habitats whereas others have
never spread out. Four of the six naturalized species of the genus
Crotalaria
have similar MRTs but the numbers of recorded localities range from four to
70. Wu et al. [26] suggested two explanations: i) the species with more local-
ities might have been spread more efficiently by human activities or, ii) they
differ in their invasiveness. As pointed out above, the higher the variation in
invasiveness of individual species and the more important the effect of local
conditions and recipient vegetation, the less important residence time will be
for determining the result of invasion.
To obtain an insight into the role residence time plays relative to other fac-
tors, current frequency of alien species in the Czech Republic was related to
several life history characteristics that were used as explanatory variables and
so was MRT of each species in the data set. The minimal adequate model
explained 52% of variance in the frequency of alien species (F = 7.40; df = 28,
197; P < 0.001). Grime's life strategy, area of origin and dispersal mode had a
direct effect on the number of localities, while life history and height signifi-
cantly contributed to the explained variation in interactions with other vari-
ables (Tab. 3). MRT did not exhibit a direct effect on the number of localities
but significantly interacted with both life strategy and life history. Compared
to other factors, the effect of MRT was very strong. Its interaction with
Grime's life strategy and species' life history explained 35.9% of variance
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