Biology Reference
In-Depth Information
duced arthropod herbivores. They found that alien herbivorous arthro-
pods tended to be generalists.These arthropods also showed no change in
range of crop plants they used through time.Thus, the primary evolution-
ary process at the community level in Japan was the gradual adaptation of
native herbivores to use introduced plants of families to which they were
already specialized.
Accumulation of Herbivorous Arthropods
by Noncrop Plants
Both woody and herbaceous plants introduced to new continental areas
accumulate herbivorous insects rapidly. Several studies have examined the
frequency of insects and other organisms associated with tree species in
the British Isles. Southwood (1961) examined the numbers of herbivo-
rous insects on British trees in relation to their postglacial appearance and
abundance and compared numbers of insects on trees in Britain with
those in other areas. He found a strong positive relationship between
numbers of insects and the frequency of Quaternary fossil remains of the
species, a measure that he considered to combine postglacial length of
presence and general abundance of the various native species. He also
noted that most species introduced since Roman times supported fewer
herbivorous insect species. The maple,
Acer pseudoplatanus
, introduced
about 1250
A
.
D
., supported only 15 insect species, whereas the native
maple,
A. campestre
, supported 26 species. The insect fauna of the intro-
duced oak,
Quercus ilex
, introduced about 1580
A
.
D
., consisted of only 2
species, whereas native oaks,
Q. robur
and
Q. petraea
, supported 284 species.
Southwood (1961) also called attention to the fact that species of
spruce (
Picea abies
), larch (
Larix decidua
), and fir (
Abies
spp.), all introduced
to the British Isles within the last 500 yr, supported many fewer herbiv-
orous insects in Britain than in Russia. He suggested that this difference
was largely related to the much more extensive distribution of these
species on the continent, as well as on their longer postglacial presence.
Strong (1974b, 1974c) reexamined Southwood's (1961) data, pointing
out that the relationship of number of insect species with the Quaternary
age-abundance estimates implied that the number of species associated
with each tree would continue to increase indefinitely. Strong used esti-
mates of the present areal range of the various tree species in Britain and
found that a very strong relationship existed between number of insect
species and the range of the tree species in square kilometers. Based on
