Publications
Arbuscular mycorrhizal fungi enhance the growth of the exotic species Ambrosia artemisiifolia.
This article describes how the Arbuscular Mycorrhizal Fungi (AMF) that symbiotically associate with the roots of plants can augment the growth of an exotic species and reduce the growth of a co-occurring native species. This suggests a possible mechanism for the advantage that invasive plants have in replacing native plants in an ecosystem.
When the plants were growing together and separately, our experiments measured the AMF colonization rate of roots, AMF diversity in roots, dry weight of plants, carbon content, nitrogen concentration, phosphorus concentration, and potassium concentration of plants.
There were two sets of experiments, field and greenhouse.
The field experiments were set up and maintained for 8 years. Then the roots were examined for AMF colonization, and the exotic had more hyphae, arbuscles, and spores than the native. The AMF species diversity differed, with the native having less when grown together with the exotic. The AMF species Funneliformis mosseae was abundant in the exotic roots but not in the native, so that species was used in the greenhouse experiments.
The greenhouse experiments used sterile soil, inoculated with Funneliformis mosseae or not, and growing in pots with both species together or separately. Plant success was measured in several ways, all showing that the exotic had an advantage over the native when growing together:
The AMF colonization rate was greater for the exotic.
The dry biomass was greater for the exotic.
The total carbon was greater for the exotic.
The nitrogen and phosphorous concentrations were greater at all concentrations for the exotic.
The potassium concentration was greater at 3 of the 4 concentrations studied for the exotic.
These experiments were done in China at the Langfang Experimental Station near Beijing, with Ambrosia artemisiifolia (ragweed, a herbaceous Asteraceae) as the exotic, and Setaria viridis (green foxtail, a grass Poaceae) as the native. In China ragweed is very invasive and its allergenic pollen is an important public health concern. In natural areas the invasive ragweed is replacing the native green foxtail. We have an opposite situation in the U.S. where ragweed is native, and green foxtail is introduced but not invasive.
When the plants were growing together and separately, our experiments measured the AMF colonization rate of roots, AMF diversity in roots, dry weight of plants, carbon content, nitrogen concentration, phosphorus concentration, and potassium concentration of plants.
There were two sets of experiments, field and greenhouse.
The field experiments were set up and maintained for 8 years. Then the roots were examined for AMF colonization, and the exotic had more hyphae, arbuscles, and spores than the native. The AMF species diversity differed, with the native having less when grown together with the exotic. The AMF species Funneliformis mosseae was abundant in the exotic roots but not in the native, so that species was used in the greenhouse experiments.
The greenhouse experiments used sterile soil, inoculated with Funneliformis mosseae or not, and growing in pots with both species together or separately. Plant success was measured in several ways, all showing that the exotic had an advantage over the native when growing together:
The AMF colonization rate was greater for the exotic.
The dry biomass was greater for the exotic.
The total carbon was greater for the exotic.
The nitrogen and phosphorous concentrations were greater at all concentrations for the exotic.
The potassium concentration was greater at 3 of the 4 concentrations studied for the exotic.
These experiments were done in China at the Langfang Experimental Station near Beijing, with Ambrosia artemisiifolia (ragweed, a herbaceous Asteraceae) as the exotic, and Setaria viridis (green foxtail, a grass Poaceae) as the native. In China ragweed is very invasive and its allergenic pollen is an important public health concern. In natural areas the invasive ragweed is replacing the native green foxtail. We have an opposite situation in the U.S. where ragweed is native, and green foxtail is introduced but not invasive.
Kong, L., X. Chen, E.H. Yerger, Q. Li, F. Chen, H. Xu, F. Zhang. 2021. Arbuscular mycorrhizal fungi enhance the growth of the exotic species Ambrosia artemisiifolia. Journal of Plant Ecology. rtab087, https://doi.org/10.1093/jpe/rtab087
| kong_2021_amf_enhance_the_growth_of_the_exotic_ambrosia.pdf |
AM fungi facilitate the competitive growth of two invasive species, Ambrosia artemisiifolia and Bidens pilosa.
Arbuscular Mycorrhizal Fungi (AMF) are symbiotic with roots of most plants. They assist the plant with acquisition of nutrients and receive sugars in return. Our experiments show that AMF are involved in the interaction between native and invasive plants when growing close together, as in a natural area that is being overtaken by non-native plants.
Our data show a small but consistent advantage to the invasive plant over the native plant when growing together and AMF are present. The invasive plant has more colonization by AMF on the roots, more biomass gain, and more nitrogen and phosphorous accumulation during photosynthesis than the native plant. Also the AMF spores isolated from the rhizosphere soil of the exotic under field conditions increase the competitive ability of the exotic species under greenhouse conditions. Our results show that the AMF interactions play an important role in the invasiveness of the exotic. This may be a possible mechanism for the growth advantage of invasive plants.
These experiments were done in China, near Bejing, with 2 plant species invasive there: Ambrosia artemisiifolia (ragweed) and Bidens pilosa (hairy beggar ticks). The native species they are replacing in natural areas is Setaria viridis (green foxtail). Oppositely in the U.S., ragweed is native through the eastern U.S., hairy beggar ticks is native in the southeastern U.S., and green foxtail is introduced by not invasive throughout the U.S.
Our data show a small but consistent advantage to the invasive plant over the native plant when growing together and AMF are present. The invasive plant has more colonization by AMF on the roots, more biomass gain, and more nitrogen and phosphorous accumulation during photosynthesis than the native plant. Also the AMF spores isolated from the rhizosphere soil of the exotic under field conditions increase the competitive ability of the exotic species under greenhouse conditions. Our results show that the AMF interactions play an important role in the invasiveness of the exotic. This may be a possible mechanism for the growth advantage of invasive plants.
These experiments were done in China, near Bejing, with 2 plant species invasive there: Ambrosia artemisiifolia (ragweed) and Bidens pilosa (hairy beggar ticks). The native species they are replacing in natural areas is Setaria viridis (green foxtail). Oppositely in the U.S., ragweed is native through the eastern U.S., hairy beggar ticks is native in the southeastern U.S., and green foxtail is introduced by not invasive throughout the U.S.
Zhang, F., Q. Li, E.H. Yerger, X. Chen, Q. Shi, F. Wan. 2018. AM fungi facilitate the competitive growth of two invasive species, Ambrosia artemisiifolia and Bidens pilosa. Mycorrhiza 28: 703-715. https://doi.org/10.1007/s00572-018-0866-4
| zhang_2018_amf_facilitate_the_competitive_growth_of_2_invasive_species.pdf |
Opposing deer and caterpillar foraging preferences may prevent reductions in songbird prey biomass in historically overbrowsed forests.
Our data show that forest song birds feed preferentially on caterpillars found on pin cherry (Prunus pensylvanica) and black cherry (Prunus serotina) in forests of Pennsylvania. Deer also prefer to feed on pin cherry, and their overbrowsing decimates populations of these trees, thus reducing available caterpillar prey for songbirds. However, deer avoid browsing on black cherry, leaving foliage and caterpillars that songbirds will also feed on. As the largest forest herbivore, deer feeding causes forest abundance of pin cherry trees to decline, and abundance of black cherry trees to increase. This shift in tree species availability in the forest seems to balance for the birds because similar species of palatable moth caterpillars are found on both trees.
Godfrey, Rebekah K., Ellen H. Yerger, Tim J. Nuttle. 2018. Opposing deer and caterpillar foraging preferences may prevent reductions in songbird prey biomass in historically overbrowsed forests. Ecology and Evolution 8: 560-571. https://doi.org/10.1002/ece3.3497
| godfrey_2017_opposing_deer_and_caterpillar_foraging_preferences_may_prevent_reductions_in_songbird_prey.pdf |
The indirect impact of long-term overbrowsing on insects in the Allegheny National Forest region of Pennsylvania.
Deer continuously excluded for 60 years outside a fenced exclosure dramatically exhibited the depauperate plant community caused by over-browsing in a Pennsylvania forest. We found that aboveground insect abundance, species richness, and species diversity were up to 50% higher inside the fenced exclosure versus outside. Conversely, litter insect abundance and species diversity were consistently higher outside the exclosure. Even when the plant communities are in close proximity, the insect communities change composition.
Chips, Michael J., Ellen H. Yerger, Arpad Hervanek, Tim Nuttle, Alejandro A. Royo, Jonathan N. Pruitt, Terrence P. McGlynn, Cynthia L. Riggall, and Walter P. Carson. 2015. The Indirect Impact of Long-Term Overbrowsing on Insects in the Allegheny National Forest Region of Pennsylvania. Northeastern Naturalist 22(4): 782-797.
| chips_2015_indirect_impact_of_long_term_overbrowsing_on_insects_in_forests_of_pa.pdf |
Impacts of Climate Change on Commonly Encountered Forest Lepidoptera of Pennsylvania.
This is a report on Lepidoptera phenology currently, and predicted impacts of climate change, for the PA Department of Conservation and Natural Resources, Wild Resource Conservation Program. Caterpillars are important prey resources for breeding songbirds since they are the principle means by which the photosynthetic energy of forest ecosystems are passed to the next trophic level.
Keating, R., E. Yerger, T. Nuttle. 2013. Impacts of Climate Change on Commonly Encountered Forest Lepidoptera of Pennsylvania. Report prepared for the Pennsylvania Department of Conservation and Natural Resources,
Wild Resource Conservation Program (WRCP-010383).
Keating, R., E. Yerger, T. Nuttle. 2013. Impacts of Climate Change on Commonly Encountered Forest Lepidoptera of Pennsylvania. Report prepared for the Pennsylvania Department of Conservation and Natural Resources,
Wild Resource Conservation Program (WRCP-010383).
| keating_et_al_2013_lepidoptera_climate_change_phenology.pdf |
Climate Change Impacts on Pennsylvania Forest Songbirds against the Backdrop of Gas Development and Historical Deer Browsing.
The PA Department of Conservation and Natural Resources, Wild Resource Conservation Program, funded our study on Climate Change Vulnerability Impacts on Forest Songbirds. This is the report.
Cullen,E., E. Yerger, S. Stoleson, T. Nuttle. 2013. Climate Change Impacts on Pennsylvania Forest Songbirds against the Backdrop of Gas Development and Historical Deer Browsing. Report prepared for the Pennsylvania Department of
Conservation and Natural Resources, Wild Resource Conservation Program (WRCP-010376).
Cullen,E., E. Yerger, S. Stoleson, T. Nuttle. 2013. Climate Change Impacts on Pennsylvania Forest Songbirds against the Backdrop of Gas Development and Historical Deer Browsing. Report prepared for the Pennsylvania Department of
Conservation and Natural Resources, Wild Resource Conservation Program (WRCP-010376).
| cullen_et_al_2013_forest_songbirds_report_wrcp.pdf |
Indirect effects of pandemic deer overabundance inferred from caterpillar-host relations.
Larval lepidoptera are important canopy herbivores and prey resources. Their distribution and abundance on tree species in the Allegheny National Forest is compared to trees overgrazed by deer.
Wheatall, L., T. Nuttle, and E.H. Yerger. 2013. Indirect effects of pandemic deer overabundance inferred from caterpillar-host relations. Conservation Biology 27(5): 1107-1116.
Wheatall, L., T. Nuttle, and E.H. Yerger. 2013. Indirect effects of pandemic deer overabundance inferred from caterpillar-host relations. Conservation Biology 27(5): 1107-1116.
| wheatall_et_al_2013_conservation_biology_27_1107.pdf |
Legacy of top-down herbivore pressure ricochets back up multiple trophic levels in forest canopies over 30 years.
This paper describes how 10 years of deer overgrazing in the Allegheny National Forest of Pennsylvania from 1979 to 1990 still influences the forest tree community today. High deer density 30 years ago is correlated with significant reductions in current tree species diversity, canopy foliage density, canopy insect density, and bird density.
Nuttle,T., E. H. Yerger, S. H. Stoleson, and T. E. Ristau. 2011. Legacy of top-down herbivore pressure ricochets back up multiple trophic levels in forest canopies over 30 years. Ecosphere 2: 1-11.
https://doi.org/10.1890/ES10-00108.1
Nuttle,T., E. H. Yerger, S. H. Stoleson, and T. E. Ristau. 2011. Legacy of top-down herbivore pressure ricochets back up multiple trophic levels in forest canopies over 30 years. Ecosphere 2: 1-11.
https://doi.org/10.1890/ES10-00108.1
| nuttle_et_al_2011_ecosphere.pdf |
Student perspectives on introductory biology labs designed to develop relevant skills and core competencies.
Students have a unique perspective on introductory biology labs designed to develop relevant skills and core competencies. Overall students prefer the high technology labs over the basic skill labs.
Yerger, E. H. 2012. Student perspectives on introductory biology labs designed to develop
relevant skills and core competencies. In Robert E. Yager, ed., Exemplary College Science Teaching. National Science Teachers Association Press. Chapter 6.
Yerger, E. H. 2012. Student perspectives on introductory biology labs designed to develop
relevant skills and core competencies. In Robert E. Yager, ed., Exemplary College Science Teaching. National Science Teachers Association Press. Chapter 6.
| yerger_2013_labs_designed.pdf |
Assessments that Assist in Motivating Students.
Assessments can do more than generate a grade for a course. They can motivate students to learn if thoughtfully designed.
Yerger, E.H. 2008. Assessments that Assist in Motivating Students. In Linda W. Crow, Donald French, and Tom Lord, eds., College Science Teacher’s Guide to Assessment. National Science Teachers Association Press. ISBN-13: 978-1-93353-111-3.
Yerger, E.H. 2008. Assessments that Assist in Motivating Students. In Linda W. Crow, Donald French, and Tom Lord, eds., College Science Teacher’s Guide to Assessment. National Science Teachers Association Press. ISBN-13: 978-1-93353-111-3.
| yerger_2008_assessments.pdf |
Natural causes and rates of early larval mortality in gypsy moths (Lepidoptera: Lymantriidae) sampled from field populations in different density states.
Populations of gypsy moths across the Northeastern US vary in quality. Populations in the outbreak stage showed higher mortality and lower hatch success of young larvae. Populations at the leading edge of infestations had better early larval survival. These results are also discussed in relation to mortality caused by the nucleopolyhedrosis virus.
Yerger, E.H., and M.C. Rossiter. 1996. Natural causes and rates of early larval mortality in gypsy moths (Lepidoptera:
Lymantriidae) sampled from field populations in different density states. Environmental Entomology 25: 1002-1011.
Yerger, E.H., and M.C. Rossiter. 1996. Natural causes and rates of early larval mortality in gypsy moths (Lepidoptera:
Lymantriidae) sampled from field populations in different density states. Environmental Entomology 25: 1002-1011.
| yerger_1996_gypsy_moth_mortality.pdf |
Species distribution of biochemical and morphological characters associated with small pest resistance in Pelargonium xhortorum.
Grazzini, R., D. Hesk, E. Yerger, D. Cox-Foster, J. Medford, R. Craig, R.O. Mumma. 1995. Species distribution of biochemical and morphological characters associated with small pest resistance in Pelargonium
xhortorum. J. Amer. Soc. Hort. Sci. 120(2): 336-342.
xhortorum. J. Amer. Soc. Hort. Sci. 120(2): 336-342.
| grazzini_1995_species.pdf |
Distribution of anacardic acids associated with small pest resistance among cultivars of Pelargonium xhortorum.
Grazzini, R., D. Hesk, E. Yerger, D. Cox-Foster, J. Medford, R. Craig, R.O. Mumma. 1995. Distribution of anacardic acids associated with small pest resistance among cultivars of Pelargonium xhortorum. J. Amer. Soc. Hort. Sci. 120(2):
343-346.
343-346.
| grazzini_1995_distribution.pdf |
A Rapid Method for Isolating Glandular Trichomes.
I developed this method to isolate the trichomes (sticky hairs) of geranium plants by freezing the tissue in liquid nitrogen and then vortexing it with chunks of dry ice. The trichomes are so brittle they knock off. If you immediately pour all this through a piece of window screen, the trichomes fall through, are relatively pure, and are in fairly large quantities. This procedure also works to isolate tomato trichomes.
Yerger, E.H., R.A. Grazzini, D. Hesk, D.L. Cox-Foster, R. Craig and R.O. Mumma. 1992. A Rapid Method for Isolating
Glandular Trichomes. Plant Physiol. 99: 1-7.
Yerger, E.H., R.A. Grazzini, D. Hesk, D.L. Cox-Foster, R. Craig and R.O. Mumma. 1992. A Rapid Method for Isolating
Glandular Trichomes. Plant Physiol. 99: 1-7.
| yerger_1992_trichome_method.pdf |
Inactivation and mutagenesis by phototoxins using Escherichia coli strains differing in sensitivity to near- and far- ultraviolet light.
Tuveson, R.W., M.R. Berenbaum, and E.E. Heininger. 1986. Inactivation and mutagenesis by phototoxins using Escherichia coli strains differing in sensitivity to near- and far- ultraviolet light. J. Chem. Ecol. 12: 933-948.
| tuveson_1986.pdf |
