The ecology of biological invasions: past, present and future - Invasive Plants: Ecological and Agricultural Aspects - page 14

that lives among D. polymorpha shells, and in 1990 by two fish species
( Neogobius melanostomus and Proterorhinus marmoratus ) that feed exten-
sively on E. ischnus as juveniles and D . polymorpha as adults [89]. In addition
to individual accounts of facilitative interactions like these, accelerating inva-
sion rates have been noted in some of the world's best-studied ecosystems [89,
91]. However, it is erroneous to infer invasional meltdown based on invasion
rate alone, since a time lag in the discovery of invaders can create the appear-
ance of an increasing invasion rate [92]. Nevertheless, facilitative interactions
are increasingly recognized among biological invaders, both with and without
a co-evolutionary history, suggesting that the IFH may be more widespread
than is currently appreciated.
Evolution of increased competitive ability (EICA) hypothesis
First proposed by Blossey and Nötzold [93], the EICA hypothesis may be
thought of as both a variant of the ERH, and a subset of the SIA hypothesis
(see below) but one that acts over evolutionary, rather than ecological
timescales. The EICA hypothesis predicts that an invader, long released from
enemies in its native range, could reallocate resources formerly used for
defense to growth, reproduction and other attributes generally increasing com-
petitive abilities [94, 95]. Thus, while the ERH predicts a 'regulatory' release
from enemies, the EICA predicts a 'compensatory' release. In support of
EICA, Blossey and Nötzold [93] found that introduced individuals of Lythrum
salicaria had higher biomass than their native genotypes. Siemann and Roger
[96] investigated the preference of the grasshopper Melanoplus angustipennis
for Chinese tallow tree ( Sapium sebiferum ) from native (China) and introduced
(Texas) populations. When given the choice between Sapium seedlings from
China and Texas, M. angustipennis preferred Texas Sapium foliage compared
to foliage from China. Invasive genotypes of Sapium exhibited lower resist-
ance to herbivory by Melanopline grasshoppers, suggesting that the success of
Sapium as an invader in North America could be due to reallocation of
resources from defense to growth [97]. EICA is not universally supported. Vilà
et al. [94] tested the EICA hypothesis using Hypericum perforatum. The com-
petitive ability of native H. perforatum from Europe was compared with that
of introduced H. perforatum from N. America where plants were grown in
absence of specialist herbivores. Native species were also compared with H.
perforatum from western North America where plants are subjected to biolog-
ical control for more than five decades. Introduced and native H. perforatum
plants showed no differences, counter to the predictions of the EICA hypoth-
esis. Bossdorf et al. [98] compared native and introduced Alliaria petiolata
with respect to their palatability and tolerance to simulated herbivory. Higher
feeding rates of a specialist weevil ( Centorhynchus scrobicollis ) were
observed on introduced A. petiolata plants . A generalist caterpillar
( Spodoptera littoralis ) showed no preference, revealing that introduced A.