Residence time determines the distribution of alien plants - Invasive Plants: Ecological and Agricultural Aspects - page 64

documented for Taiwan. In this country, there was a clear acceleration of
records of alien species about ten years after political events in 1940s to
1960s, which were associated with massive immigration of Chinese from the
mainland [27].
Of the three regions shown in Figure 1, the increase in records of alien spe-
cies is most regular for the Czech Republic. A previous paper [6] showed that
the record of cumulative species numbers over time in this country was not
significantly affected by research intensity which has been quite high since
the beginning of the 19th century and fairly steady over the last 50 years or
so [29, 46]. In any case, Figure 1 documents that alien species differ in their
residence time and that the three data sets provide a reasonable basis for eval-
uating the effects of residence time on the current distribution of alien species
in these regions.
Range and frequency
For all data sets, a significant relationship between the range/frequency of
aliens and their MRT was found, and most models are highly significant. The
percentage of variation in the data explained by MRT varies between 4.1 and
39.6, with higher values reached where complete data sets including both
groups of aliens, i.e., naturalized and casual, were considered (Tab. 1). This
can be regarded as strong evidence that residence time is an important factor
affecting the range and frequency of alien species in various regions, includ-
ing examples of continental (Czech Republic) and island floras (Azores, New
Zealand, Hawaii) from Old (Azores, Czech Republic) and New World
(Hawaii, New Zealand). The same relationships are indicated for complete
alien floras and their subsets (Tab. 1). Additional evidence for a close rela-
tionship between the number of reported localities of alien species and MRT
comes from literature data on naturalized grasses in Venezuela (R 2 = 63%,
n = 111, P < 0.001; [23]) and naturalized taxa of Fabaceae in Taiwan
(R 2 = 23%, n = 48, P < 0.01; [26]). The latter result can be compared with
those obtained for alien representatives of the same family in the Czech
Republic, where the number of current localities is also significantly related to
MRT (R 2 = 50%, n = 56, P < 0.0001; data from Pyˇek et al. [29]). Rejmánek
et al. [23]), using the data on alien plant species recorded in five north-west-
ern states of the USA, also found a significant dependence of the number of
occupied counties on the minimum residence time (R 2 = 18%, n = 132,
P < 0.001). Finally, even for as few as seven invading plants in Kenya [47], the
number of herbarium specimens highly significantly depended on the species'
residence time (R 2 = 82%, n = 7, P < 0.01).
Available data are too scarce to allow a rigorous statistical analysis of
detailed patterns, but some conclusions can be drawn from comparing the sta-
tistical parameters of regressions summarized in Table 1. Before this can be
done, some theoretical considerations need to be outlined, that is what can be