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UBC Theses and Dissertations
Net interactions in an annual plant community in the Negev Desert, Israel Lortie, Christopher James
Abstract
In most plant communities, neighbours are likely to interact in at least two ways - negatively through competition and positively by facilitation. However, typically only the end product of these interactions is measured thereby detecting only the outcome, not the interactions themselves. This thesis focuses on understanding net interactions within an annual plant community in the Negev Desert, Israel by measuring the effects of spatial pattern, seed density, plant density, and specific species effects at different life-stages (by successive measurements) and levels of abiotic stress. I first tested the assumption that seeds in seed banks are generally clumped. Using geostatistics, a consistent clump size of 85cm² was detected across time, stress level, and seed size. There was however variation in the amount of seed present on the dune over time. Subsequently, I experimentally manipulated both the fine scale spatial pattern of patches of seed and the local density of seeds in small patches. Increasing local seed density generally had negative effects on measures of plant growth, whereas patches of seed with adjacent planted patches had increased performance. These results suggest that there is interference between seeds and plants within patches but positive interactions between the patches. The more general effects of density dependence were also tested at the seed and emergent plant levels. Emergence of seedlings was negatively affected by increases in seed density which also supports the interpretation that seed-seed interference may be occurring in this plant community. Mean plant size was negatively affected by increases in plant density, but survival was unaffected. Finally, I tested the prediction that a larger annual, Erodium laciniatum, acts as a benefactor species to nearby smaller annuals. Erodium was either added to or removed from patches of seed or vegetation. In both experiments, Erodium acted as a benefactor by increasing performance of neighbours (i.e., aboveground biomass or survival). Hence, competition and facilitation both play important roles in this plant community and their relative importance is influenced by life stage but not by level of abiotic stress. These studies are the first to demonstrate facilitation similar to shrub-understorey systems but at a much finer spatial scale.
Item Metadata
Title |
Net interactions in an annual plant community in the Negev Desert, Israel
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2002
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Description |
In most plant communities, neighbours are likely to interact in at least two ways - negatively
through competition and positively by facilitation. However, typically only the end product of
these interactions is measured thereby detecting only the outcome, not the interactions
themselves. This thesis focuses on understanding net interactions within an annual plant
community in the Negev Desert, Israel by measuring the effects of spatial pattern, seed density,
plant density, and specific species effects at different life-stages (by successive measurements)
and levels of abiotic stress. I first tested the assumption that seeds in seed banks are generally
clumped. Using geostatistics, a consistent clump size of 85cm² was detected across time,
stress level, and seed size. There was however variation in the amount of seed present on the
dune over time. Subsequently, I experimentally manipulated both the fine scale spatial pattern
of patches of seed and the local density of seeds in small patches. Increasing local seed
density generally had negative effects on measures of plant growth, whereas patches of seed
with adjacent planted patches had increased performance. These results suggest that there is
interference between seeds and plants within patches but positive interactions between the
patches. The more general effects of density dependence were also tested at the seed and
emergent plant levels. Emergence of seedlings was negatively affected by increases in seed
density which also supports the interpretation that seed-seed interference may be occurring in
this plant community. Mean plant size was negatively affected by increases in plant density, but
survival was unaffected. Finally, I tested the prediction that a larger annual, Erodium laciniatum,
acts as a benefactor species to nearby smaller annuals. Erodium was either added to or
removed from patches of seed or vegetation. In both experiments, Erodium acted as a
benefactor by increasing performance of neighbours (i.e., aboveground biomass or survival).
Hence, competition and facilitation both play important roles in this plant community and their
relative importance is influenced by life stage but not by level of abiotic stress. These studies
are the first to demonstrate facilitation similar to shrub-understorey systems but at a much finer
spatial scale.
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Extent |
10872934 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-09-23
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Provider |
Vancouver : University of British Columbia Library
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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.
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DOI |
10.14288/1.0090524
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2002-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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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.