Agriculture Reference
In-Depth Information
cies are often selected for research studies because they are highly invasive and
problematic in their area [25]. This is not surprising, but it makes it difficult to
decide which native species should be chosen for comparison. Should the exot-
ic be compared to an equally aggressive native species, or to a nonaggressive
native? These choices have the potential to greatly impact the conclusions that
are reached [25]. By focusing on the overall effects (i.e., mean of several spe-
cies responses) of exotic species, the biases from individual (“outlier”) species
are likely to be lessened. Thus, by replicating species, we may be able to
increase the predictive power of invasive species ecology.
Finally, in addition to finding mean growth rate was higher in exotics than
in natives in monocultures at our study site, we also found that exotic species
can have especially large effects on productivity in mixture [40]. The higher
growth rate of exotics in mixture [40] is potentially very important because it
1) may partially explain why exotic species are commonly associated with
lower species diversity (i.e., exotics are causing diversity loss), and 2) could
lead to altered ecosystem process rates. These issues deserve further study.
Acknowledgements
I thank Dan Haug for help with finding and organizing literature sources and Wayne Polley and two
anonymous reviewers for helpful comments on an earlier version of this manuscript.
References
1 D'Antonio CM, Vitousek PM (1992) Biological invasions by exotic grasses, the grass-fire cycle,
and global change.
Ann Rev Ecol Syst
23: 63-87
2 Vitousek P (1994) Beyond global warming: ecology and global change.
Ecology
75: 1861-1877
3 Christian JM, Wilson SD (1999) Long-term ecosystem impacts of an introduced grass in the
northern great plains.
Ecology
80: 2397-2407
4 Cully AC, Cully Jr, JF, Hiebert RD (2002) Invasion of exotic plant species in tallgrass prairie frag-
ments.
Conser Biol
17: 990-998
5 Callaway RM, Aschehoug ET (2000) Invasive plants
versus
their new and old neighbors: a mech-
anism for exotic invasion.
Science
290: 521-523
6 Callaway RM, Thelon GC, Rodriguez A, Holben WE (2004) Soil biota and exotic plant invasion.
Nature
427: 731-733
7 Seabloom EW, Borer ET, Boucher VL, Burton RS, Cottingham KL, Goldwasser L, Gram WK,
Kendall BE, Micheli F (2003) Competition, seed limitation, disturbance, and reestablishment of
California native annual forbs.
Ecol Appl
13: 575-592
8 Caldwell MM, Richards JH, Johnson DA, Nowak RS, Dzurec RS (1981) Coping with herbivory:
photosynthetic capacity and resource allocation in two semiarid
Agropyron
bunchgrasses.
Oecologia
50: 14-24
9 Richards J (1984) Root growth response to defoliation in two
Agropyron
bunchgrasses: field
observations with an improved periscope.
Oecologia
64: 21-25
10 Pyke D (1990) Comparative demography of co-occurring introduced and native tussock grasses:
persistence and potential expansion.
Oecologia
82: 537-543
11 Wilsey BJ, Polley HW (2003) Effects of seed additions and grazing history on diversity and
aboveground productivity of sub-humid grasslands.
Ecology
84: 920-932
12 Wilcove DS, Rothstein D, Dubow J, Phillips A, Losos E (1998) Quantifying threats to imperilled
species in the United States.
Bioscience
48: 607-615
13 Levine JM, D'Antonio CM (1999) Elton revisited: a review of evidence linking diversity and inva-
sibility.
Oikos
87: 15-26
14 Olden JD, Poff NL (2003) Toward a mechanistic understanding and prediction of biotic homoge-
Search WWH ::
Custom Search