1
Background Methods Results Discussion Leaf herbivory is best predicted by plant chemistry Specific Leaf Area (cm^2/g) Leaf Herbivory (%) The interaction between herbivores and plants is influential in structuring and regulating global ecosystems. Theoretical data predicts, however, that primary and secondary producers will not react in the same way to increasing temperature (1). Models which provide an understanding of the herbivore-plant relationship will therefore be essential in dealing with the impacts of global climate change. A prominent hypothesis in plant ecology posits that key plant traits can be used to model herbivory (2). There are debates, however, over whether traits can substitute species identification without masking important information from models. Our study was designed to contribute to the body of literature assessing trait-based models of invertebrate leaf herbivory. This study tested whether plant height, trichome density, chemical composition, leaf area, specific leaf area, and leaf matter dry content, traits that appears to structure plant-environment relationships within regions and across bioregions, are able to predict the impact of herbivores on plant performance. In this study, we asked: 1) Are plant height, trichome density, chemical composition, leaf area, specific leaf area and leaf matter dry content useful predictors of invertebrate leaf herbivory? 2) Does invertebrate leaf herbivory predict the overall impact of herbivores on plant biomass? 1.A 1.B 2.A 2.B Figure 1: a) Mean percent leaf herbivory is shown for all species. Species abbreviations are the first letters of the genus and species 1.b) Categories of trichome density follow the procedure described in (3). S referrers to species with secondary defense compounds. 2.a) Correlation between species mean specific leaf area and mean percent herbivory in the pilot study done on 8 species using the same methodology in 2013 (r= -0.85, p=0.008). Each point is a species. 2.b) Mean specific leaf area, calculated across treatments. We tested these questions on 8 species found in tall grass prairie or old fields in a pilot study in May-Sept. 2013 and expanded the study to 23 species in May-Sept. 2014. Plants were grown in field plots protected from aerial invertebrate herbivores or exposed to invertebrate herbivores, using mosquito nets that were intact (Fig. 1A) or mosquito nets with holes cut into them. Plants were grown for 12 weeks at the Koffler Scientific Reserve (10 replicates with all species included in each replicate). In the second month of growth, plants were surveyed weekly for height, number of leaves and leaf herbivory. 2 leaves per plant were sampled on the 7 th week of experiment to obtain measurements for leaf traits. We then used multiple regression models to determine the relationship between leaf herbivory and the measured traits. Pilot study (Box 2) Specific leaf area is negatively correlated with percent leaf herbivory (r=-0.85, p=.008, Fig. 2 A). Specific leaf area was not related to the overall effect of herbivore exclusion on biomass D. canadense was the only species to exhibit a plastic response of SLA to herbivory; SLA was higher in the herbivory treatment (p=0.048). Current study (Box 1) Multiple regression analysis determined that the best herbivory model would contain only data relating to chemical composition of leaves (p=.004). -Project supervisor Dr. Benjamin Gilbert. -Funding provided by NSERC USRA, CGCS Internship -Koffler Scientific Reserve and U of T Earth Science Greenhouse Staff Acknowledgments Although specific leaf area and invertebrate leaf herbivory were correlated in the pilot study, preliminary data suggests that the correlation was found to be non-significant upon analysis with a sample of 23 species. Similarly, the correlation between leaf herbivory and plant height, leaf dry matter content, and leaf area is also non-significant. The model with the strongest predictive power considered only the presence of secondary defense compounds . This is an expected result that implies the experimental community is behaving as expected. We note that our study was done on young plants, and that ontological shifts in leaf traits and plant-herbivore interactions may be common (4). Future work will consider ontological changes, leaf carbon and nitrogen concentration, as well as herbivores that feed on non-leaf tissues. A B C Image 1: A) Experimental enclosure (herbivores excluded). B) Ants on Asclepias tuberosa. C) Broad-nose weevil on Desmodium canadense. Species list Current study: Amorpha canescens Andropogon gerardii Aster laevis Aster oolentangiensis Asclepias syriaca Asclepias speciosa Ceanothus americanus Cirsium discolor Desmodium canadense Desmodium illinoense Eupatorium altissimum Euphorbia corollata Lupinus perennis Monarda punctata Nicotiana rustica Parthenium integrifolium Psoralea onobrychis Psoralea tenuiflora Pycnanthemum pilosum Silphium terebinthinaceum Satureja vulgaris Veronica catenata Pilot study: Desmodium illononse, Desmodium canadense, Monarda fistulosa, Monarda puncata, Asclepias tuberosa, Asclepias syriaca, Liatris aspera, Coreopsis lanceolata, Literature Cited: 1. O’Conner, M., Gilber, B., Brown, J. B. 2011. The American Naturalist 178: 627-37. 2. McGill, B., Enquist, B., Weiher, E & Westob, M. 2006. Trends in ecology & evolution 21: 178-85. 3. Carmon, D., Lajeunesse, M.J. & Johnson, M.T. 2011. Functional Ecology 25: 358-367. 4. Boege, K. & Marquis R. J. 2005. Trends in ecology & evolution 20(8): 441-448

Alexandra Mushka

Embed Size (px)

Citation preview

Page 1: Alexandra Mushka

Background

Methods

Results

Discussion

Leaf herbivory is best predicted by plant chemistry

Specific Leaf Area (cm^2/g)

Leaf

Her

bivo

ry (%

)

The interaction between herbivores and plants is influential in structuring and regulating global ecosystems. Theoretical data predicts, however, that primary and secondary producers will not react in the same way to increasing temperature (1). Models which provide an understanding of the herbivore-plant relationship will therefore be essential in dealing with the impacts of global climate change. A prominent hypothesis in plant ecology posits that key plant traits can be used to model herbivory (2). There are debates, however, over whether traits can substitute species identification without masking important information from models. Our study was designed to contribute to the body of literature assessing trait-based models of invertebrate leaf herbivory. This study tested whether plant height, trichome density, chemical composition, leaf area, specific leaf area, and leaf matter dry content, traits that appears to structure plant-environment relationships within regions and across bioregions, are able to predict the impact of herbivores on plant performance. In this study, we asked: 1)  Are plant height, trichome density, chemical composition, leaf

area, specific leaf area and leaf matter dry content useful predictors of invertebrate leaf herbivory?

2)  Does invertebrate leaf herbivory predict the overall impact of herbivores on plant biomass?

1.A  

1.B  

2.A   2.B  

Figure 1: a) Mean percent leaf herbivory is shown for all species. Species abbreviations are the first letters of the genus and species 1.b) Categories of trichome density follow the procedure described in (3). S referrers to species with secondary defense compounds. 2.a) Correlation between species mean specific leaf area and mean percent herbivory in the pilot study done on 8 species using the same methodology in 2013 (r= -0.85, p=0.008). Each point is a species. 2.b) Mean specific leaf area, calculated across treatments.

We tested these questions on 8 species found in tall grass prairie or old fields in a pilot study in May-Sept. 2013 and expanded the study to 23 species in May-Sept. 2014. Plants were grown in field plots protected from aerial invertebrate herbivores or exposed to invertebrate herbivores, using mosquito nets that were intact (Fig. 1A) or mosquito nets with holes cut into them. Plants were grown for 12 weeks at the Koffler Scientific Reserve (10 replicates with all species included in each replicate). In the second month of growth, plants were surveyed weekly for height, number of leaves and leaf herbivory. 2 leaves per plant were sampled on the 7th week of experiment to obtain measurements for leaf traits. We then used multiple regression models to determine the relationship between leaf herbivory and the measured traits.

Pilot study (Box 2) Specific leaf area is negatively correlated with percent leaf herbivory (r=-0.85, p=.008, Fig. 2 A). Specific leaf area was not related to the overall effect of herbivore exclusion on biomass D. canadense was the only species to exhibit a plastic response of SLA to herbivory; SLA was higher in the herbivory treatment (p=0.048). Current study (Box 1) Multiple regression analysis determined that the best herbivory model would contain only data relating to chemical composition of leaves (p=.004).

-Project supervisor Dr. Benjamin Gilbert. -Funding provided by NSERC USRA, CGCS Internship -Koffler Scientific Reserve and U of T Earth Science Greenhouse Staff

Acknowledgments

Although specific leaf area and invertebrate leaf herbivory were correlated in the pilot study, preliminary data suggests that the correlation was found to be non-significant upon analysis with a sample of 23 species. Similarly, the correlation between leaf herbivory and plant height, leaf dry matter content, and leaf area is also non-significant. The model with the strongest predictive power considered only the presence of secondary defense compounds. This is an expected result that implies the experimental community is behaving as expected. We note that our study was done on young plants, and that ontological shifts in leaf traits and plant-herbivore interactions may be common (4). Future work will consider ontological changes, leaf carbon and nitrogen concentration, as well as herbivores that feed on non-leaf tissues.

A   B   C  

Image 1: A) Experimental enclosure (herbivores excluded). B) Ants on Asclepias tuberosa. C) Broad-nose weevil on Desmodium canadense.

Species list Current study: Amorpha canescens Andropogon gerardii Aster laevis Aster oolentangiensis Asclepias syriaca Asclepias speciosa Ceanothus americanus Cirsium discolor Desmodium canadense Desmodium illinoense Eupatorium altissimum Euphorbia corollata Lupinus perennis Monarda punctata Nicotiana rustica Parthenium integrifolium Psoralea onobrychis Psoralea tenuiflora Pycnanthemum pilosum Silphium terebinthinaceum Satureja vulgaris Veronica catenata Pilot study: Desmodium illononse, Desmodium canadense, Monarda fistulosa, Monarda puncata, Asclepias tuberosa, Asclepias syriaca, Liatris aspera, Coreopsis lanceolata, Literature Cited: 1.  O’Conner, M., Gilber, B., Brown, J. B. 2011. The American Naturalist 178: 627-37. 2.  McGill, B., Enquist, B., Weiher, E & Westob, M. 2006. Trends in ecology & evolution 21: 178-85. 3.  Carmon, D., Lajeunesse, M.J. & Johnson, M.T. 2011. Functional Ecology 25: 358-367. 4.  Boege, K. & Marquis R. J. 2005. Trends in ecology & evolution 20(8): 441-448