- Library Home /
- Search Collections /
- Open Collections /
- Browse Collections /
- UBC Theses and Dissertations /
- Exotic herbivores facilitate the exotic grasses they...
Open Collections
UBC Theses and Dissertations
UBC Theses and Dissertations
Exotic herbivores facilitate the exotic grasses they graze : mechanisms for an unexpected "invasional meltdown" Best, Rebecca Jane
Abstract
Native communities increasingly host exotic species at multiple trophic levels, but most current hypotheses about community invasibility consider only a single invader. In addition to the simultaneous effects of native herbivores and native plant competitors on community invasibility, we must also consider the possibility of positive or negative feedback cycles between exotic species at multiple trophic levels. Though examples of mutually-beneficial interactions between exotic species have been described, and the possibility of subsequent "invasional meltdown" scenarios raised, few studies have been quantitative or mechanistic. I studied the co-invasion of an endangered island ecosystem by exotic Canada geese (Branta canadensis) and eight exotic annual grasses to estimate the synergistic effects of novel inter- and intra-trophic interactions on the invasion success of the grasses. Geese fed selectively on the exotic grasses, causing them to produce a higher number of short stems. This appeared to be an efficient reproductive and competitive strategy, allowing the grasses to form dense lawns with reduced occurrence of native forbs not adapted to compete under grazing or with grass. The demographic success of the exotic grasses was thus a product of both novel inter-trophic interactions with geese and novel intratrophic interactions with the native plant community. In combination, these interactions produced an unexpected outcome. Current theory suggests the grasses should be limited by a selective enemy, but my work shows that co-evolved grazer and grass strategies benefited exotic species at both trophic levels. Selective herbivory by geese also facilitated their dispersal of exotic grass seed between heavily invaded feeding areas and small islands used for nesting. In sum, selective herbivory by geese resulted in the spread and proliferation of their preferred food source. This unexpected case of positive feedback between invaders suggests two avenues for strengthening current theoretical frameworks. Robust hypotheses for predicting invasion success must account for multiple novel interactions, and for the degree of shared evolutionary context between multiple invaders.
Item Metadata
Title |
Exotic herbivores facilitate the exotic grasses they graze : mechanisms for an unexpected "invasional meltdown"
|
Creator | |
Publisher |
University of British Columbia
|
Date Issued |
2007
|
Description |
Native communities increasingly host exotic species at multiple trophic levels, but
most current hypotheses about community invasibility consider only a single invader. In
addition to the simultaneous effects of native herbivores and native plant competitors on
community invasibility, we must also consider the possibility of positive or negative
feedback cycles between exotic species at multiple trophic levels. Though examples of
mutually-beneficial interactions between exotic species have been described, and the
possibility of subsequent "invasional meltdown" scenarios raised, few studies have been
quantitative or mechanistic. I studied the co-invasion of an endangered island ecosystem by
exotic Canada geese (Branta canadensis) and eight exotic annual grasses to estimate the
synergistic effects of novel inter- and intra-trophic interactions on the invasion success of the
grasses. Geese fed selectively on the exotic grasses, causing them to produce a higher
number of short stems. This appeared to be an efficient reproductive and competitive
strategy, allowing the grasses to form dense lawns with reduced occurrence of native forbs
not adapted to compete under grazing or with grass. The demographic success of the exotic
grasses was thus a product of both novel inter-trophic interactions with geese and novel intratrophic
interactions with the native plant community. In combination, these interactions
produced an unexpected outcome. Current theory suggests the grasses should be limited by a
selective enemy, but my work shows that co-evolved grazer and grass strategies benefited
exotic species at both trophic levels. Selective herbivory by geese also facilitated their
dispersal of exotic grass seed between heavily invaded feeding areas and small islands used
for nesting. In sum, selective herbivory by geese resulted in the spread and proliferation of
their preferred food source. This unexpected case of positive feedback between invaders suggests two avenues for strengthening current theoretical frameworks. Robust hypotheses
for predicting invasion success must account for multiple novel interactions, and for the
degree of shared evolutionary context between multiple invaders.
|
Genre | |
Type | |
Language |
eng
|
Date Available |
2011-02-28
|
Provider |
Vancouver : University of British Columbia Library
|
Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
|
DOI |
10.14288/1.0074931
|
URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
|
Campus | |
Scholarly Level |
Graduate
|
Aggregated Source Repository |
DSpace
|
Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.