Biology Reference
In-Depth Information
Fig. 2.29
Relative pathway importance for each recipient region. Biocontrol = dark blue, cargo = red,
food = yellow, “intentional” = green, nursery trade = blue, and pet trade = brown
Other regions have a less-skewed distribution of pathways, but most are still domi-
nated by two (Fig. 2.29). Some introduction pathways were not represented in parti-
cular regions. For example, biocontrol introductions are lacking for Africa, Asia,
and the Mediterranean Islands; introductions for food are unreported for Africa and
Australia; and the nursery pathway is unrepresented among introductions to the
Mediterranean Islands (Fig. 2.29).
One may also contrast success rate and pathway importance not by geographical
region but by type of landform, in particular contrasting patterns between islands
and continents. If one contrasts rate of successful establishment onto islands vs.
continents, one finds the rate considerably higher in the former than the latter (35%
vs. 12%), a difference that is statistically significant (G = 279.468, DF = 1, p =
4.90e
−63
). This difference is mostly due to higher establishment success rate on
small islands. If one contrasts small islands (<6,000 km
2
), large islands (>8,000 km
2
),
and continents with each other, one finds the rate of successful establishment on
small islands to be more than twice that on large islands and approximately four
times that on continents (Fig. 2.30), a difference that is again statistically significant
(G = 388.377, DF = 2, p = 4.62e
−85
). Conversely, if one contrasts large islands with
continents (Fig. 2.30), a difference remains between the two but is of much less
magnitude (G = 14.37, DF = 1, p = 0.00015). Islands thus appear more susceptible
to successful establishment of alien populations than do continental areas, and
islands smaller than the size of Puerto Rico are especially so.
