Defining a regional approach for invasive plant research and management - Invasive Plants: Ecological and Agricultural Aspects - page 134

tion in the gut [69]. Invasive plant seeds, including those of E. esula, Crupina
vulgaris , C. biebersteinii , and Lonicera maackii have been recovered from
feces and found viable in numerous studies [70-73]. Observations at our study
sites suggest that ungulates may be the primary dispersers, as they browse P.
recta seed heads in the fall [74]. To verify these observations, studies are
underway to determine whether herbivores (cattle, elk, deer, quail, wild
turkey) consume and transport viable P. recta seeds.
Beyond abilities to disperse seeds, ungulates have profound impact on the
structure and composition of plant communities [75, 76]. However, the role of
ungulates as contributors to the establishment and spread of non-native inva-
sive plants is not well known. Little information is available on use of P. recta
by ungulates, although it is reportedly avoided by most grazing animals [50].
Despite reports suggesting that P. recta is minimally grazed, substantial ungu-
late herbivory of the species in infested areas of northeastern Oregon have
been observed. A study is in progress to determine whether grazing by cattle
or native ungulates directly or indirectly affects the density and demography
of P. recta . This study employs three grazing treatments - extant grazing (cat-
tle, elk, and deer herbivory), deer and elk herbivory only, and total exclusion.
Pollination
The spread of an invasive plant species, especially those that reproduce only
by seed, may depend on how successful plants are at competing for the serv-
ice of resident pollinators. Basic information on the pollination biology and
ecology of most invasive plant species is lacking. This information is neces-
sary especially for those species that require out-crossing to produce viable
seed. The sparse literature available on pollination biology of P. recta indicates
that P. recta can set seeds without pollinators and that fewer but larger seeds
are produced on pollinator-excluded plants [54]. McIver et al. [77] are defin-
ing the insect pollinator community for P. recta . This research evaluates the
dependency of P. recta on insect pollinators for seed production compared to
co-occurring native Potentilla species. Pollinator-excluded plants are evaluat-
ed for seed set, seed size, and germination rate. Flower quality comparisons
rate the ability of P. recta and native Potentilla species to attract pollinators via
pollen and nectar production. The degree of fidelity of pollen transfer within
and among Potentilla species is being determined. Results thus far have found
that P. recta produces flowers with nectar richer in sugar and seed heads twice
the mass as compared to native Potentilla species. Final results from this study
will help clarify P. recta reproductive ecology and the ecological relationship
of P. recta with other species within the community it invades.
Interference/competition
Plant mortality, growth, and fecundity, are key biological mechanisms that can
provide insight into the way invasive species affect the habitats into which they
are introduced [78-80]. This is especially true if the mechanisms are density
dependent [81]. If density dependence is a factor in the overall ecological suc-