Progress 09/01/06 to 08/31/11
Outputs
OUTPUTS: In addition to disseminating the research to the academic community through peer-reviewed publications, our findings were communicated through a number of presentations nationally and internationally: (1) Liebhold, A.M. "Spatial Dynamics of Forest Insects" Eco-lunch Seminar presented at National Center for Ecology and Analysis, Sept. 2, 2010; (2) Liebhold, A.M. "Spatial Dynamics of Forest Insect Outbreaks". Special invited seminar, Yokohama National University, Yokohama, Japan September 21, 2010; (3) Liebhold, A.M. "Population Ecology of the Gypsy Moth Invasion of North America". Feb. 14, 2011. Forestry and Forest Products Laboratory, Tsukuba, Japan; (4) de-Camino-Beck, T., O. N. Bjornstad, A. M. Liebhold, and P. C. Tobin. 2010. Estimating invasion speed through Wombling of waiting times. USDA Interagency Research Forum on Invasive Species, Annapolis, MD; (5) Tobin, P. C. 2011. Allee dynamics: exploiting an Achilles' heel in the management of non-native species. Department of Entomology, Ohio State University, Columbus/Wooster, OH. The project furthermore supports the development and maintenance of the NCF package for R -- A package for analyzing spatial (cross-)covariance and synchrony disseminated through the R project (www.r-project.org). While the site does not keep download statistics, the package is acknowledged in at least 37 peer-reviewed publications according to the Web of Science. Other notable outputs from previous reporting periods are two keynote addresses: (1) at the 23rd Symposium of the Society of Population Ecology, Sapporo, Japan in 2007 and (2) at the 18th Tree Protection Cooperative Programme / Center of Excellence in Tree Health Biotechnology in Pretoria, South Africa in 2008. The PIs have given around 40 presentations nationally and internationally during the project period. Three graduate students and one post-doctoral fellow were trained with partial support from the grant. PARTICIPANTS: Ottar N. Bjornstad (PI) led the Penn State University-based portion of the project and supervised theoretical model development and statistical analyses. Andrew M. Liebhold (co-PI) and Patrick C. Tobin (co-PI) jointly led the USDA Forest Service portion of the project including curating the historical data and analyzing invasion speeds. Dr. Tomas de-Camino-Beck was a postdoctoral fellow jointly supervised by ONB and AML. The field work was carried out in part by AML with help from staff at the Forest Service Northern Research Station, and in part ONB with help from graduate students Angela Luis, Lindsay Beck-Johnson and Lawrence Chien. TARGET AUDIENCES: The target audience is in part the academic community involved in the study of invasions and outbreaks of forest insect pests, and in part advisory to the 'Slow-the-Spread' program, a cooperative effort between the USDA Forest Service and 10 participating U.S. States, which aims to minimize the rate of gypsy moth invasion into new areas and the consequent damage it causes. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This project had three goals: (1) Characterize post-invasion synchronization among gypsy moth populations, (2) Investigate the role of trophic interactions in synchronization , and (3) Examine how habitat heterogeneity leads to differences in gypsy moth dynamics and synchronization. The AFRI grant allowed us to take a three-pronged mathematical, statistical and empirical approach to address the goals. With respect to goal one, we used a combination of models and analysis of historical data to show that dynamics are asynchronous along the invasion front because of Allee effects (Johnson et al 2006 Nature) and that the strength of the Allee effect determines invasion speed (Tobin et al 2007 Ecology Letters). We then developed new statistical methods to measure the speed of post-invasion synchronization and showed that synchronization was surprisingly rapid (Bjornstad et al 2008 Population Ecology). With respect to goal two, we developed theoretical models to understand why xeric forest types have significantly more frequent outbreaks, and showed that it is the consequence of differences in the strengths of trophic interactions (Bjornstad et al. 2010 Ecology). We also developed new models for how climate influence frequency of masting events (a key driver of synchrony) (Satake and Bjornstad 2008 Population Ecology). With respect to goal three, Bjornstad et al. (2010 Ecology) detailed how heterogeneities affects dynamics. There were also a number of emergent outcomes including: The development of a new statistical method for estimating local spread rates from historical quarantine data (de-Camino-Beck, in revision); New ways of modeling temperature dependent insect dynamics under climate change (Yamanaka et al, in press, American Naturalist); And a new combined mathematical and empirical study on how entomophaga affects the Gypsy moth - virus interaction is on its way. The project has so far resulted in 14 publications in international peer reviewed journals with strong indicators that the research is having a significant impact on the field; The papers have already been cited 130 times. Moreover the statistical package developed and maintained is frequently used by the academic community (see 'Outputs').
Publications
- Tobin, P. C., L. Berec, and A. M. Liebhold. 2011. Exploiting Alle effects for managing biological invasions. Ecology Letters 14:615-624.
- Vercken, E., A. M. Kramer, P. C Tobin, and J. M. Drake. 2011. Critical patch size generated by Allee effect in gypsy moth, Lymantria dispar (L.). Ecology Letters 14:179-186.
- Yamanaka, T., W. A. Nelson, K. Uchimura, and O. N. Bjornstad. 2011. Generation separation in simple structured life-cycles: models and 48 years of field data on a tea tortrix moth. American Naturalist (In Press).
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Progress 09/01/09 to 08/31/10
Outputs
OUTPUTS: In addition to disseminating the research to the academic community through peer-reviewed publications, our findings were communicated through a number of presentations at the Ecological Society of America meeting in Pittsburg in August 2010 (1) Kramer, A.M., Vercken, E., Tobin, P. and Drake, J.M. 'Allee effects induce critical area for establishment in the Gypsy moth', (2) Haynes, K.J., Liebhold, A.M. and Johnson, D.M. 'Evidence of shifts in the periodicity of gypsymoth populations during the 20th century, (3) Bjornstad, O.N., Liebhold, A.M. and Robinet, C. Geographic variation in North American Gypsy moth, Subharmonics, generalist predatiors and spatial coupling. PARTICIPANTS: Ottar N. Bjornstad (PI) led the Penn State University-based portion of the project and supervised theoretical model development and statistical analyses. Andrew M. Liebhold (co-PI) and Patrick C. Tobin (co-PI) jointly led the USDA Forest Service portion of the project including curating the historical data and analyzing invasion speeds. Dr. Tomas de-Camino-Beck was a postdoctoral fellow jointly supervised by ONB and AML. The field work was carried out in part by AML with help from staff at the Northeastern Branch of the Forest service, and in part ONB with help from graduate students Angela Luis, Lindsay Beck-Johnson and Lawrence Chien. TARGET AUDIENCES: The target audience is in part the academic community involved in the study of invasions and outbreaks of forest insect pests, and in part advisory to the 'Slow-the-Spread' campaign of USDA forest service to help mitigate the damage caused by the ongoing gypsy moth invasion. PROJECT MODIFICATIONS: The project period was extended through a 1-year no-cost extension.
Impacts
This project has three goals: (1) Characterize post-invasion synchronization among gypsy moth populations, (2) Investigate the role of trophic interactions in synchronization (3) Examine how habitat heterogeneity leads to differences in gypsy moth dynamics and synchronization. Our theoretical work on how certain xeric forest types have significantly more frequent outbreaks others was published in Ecology. The postdoctoral fellow on the project, Dr Tomas de-Camino-Beck, lead the development of a new statistical method for estimating spread rates from historical quarantine data. This work has been submitted for publication in Ecology. Follow-up applications looking at determinants of local invasion rates are in progress. We continued the field studies of fixed-quadrat sites across the invasion front, from Pennsylvania through West-Virginia and Virginia. These field measurements represented year four of the planned four years of study. We are about to start analyzing the data (during the 1-year non-cost extension of the grant). A new combined mathematical and empirical study on how entomophaga affects the Gypsy moth - virus interaction is ongoing.
Publications
- Gilbert, M. and A. Liebhold. 2010. Comparing methods for measuring the rate of spread of invading populations. Ecography 33:809-817. http://dx.doi.org/10.1111/j.1600-0587.2009.06018.x.
- Holmes, T. P., A. M. Liebhold, K. F. Kovacs, and B. Von Holle. 2010. A spatial-dynamic value transfer model of economic losses from a biological invasion. Ecological Economics 70:86-95.
- Brockerhoff, E. G., A. M. Liebhold, B. Richardson and D. M. Suckling. 2010. Eradication of invasive forest insects: concepts, methods, costs and benefits. New Zealand Journal of Forestry Science 40 suppl. 2010) pp. S117-S135.
- Bjornstad, O. N., C. Robinet, and A. M. Liebhold. 2010. Geographic variation in the North-American gypsy moth cycles: sub-harmonics, generalist predators and spatial coupling. Ecology 91(1):106-118.
- Liebhold, A. M. and P. C. Tobin. 2010. Exploiting the Achilles Heels of Pest Invasions: Allee Effects, Stratified Dispersal and Management of Forest Insect Establishment and Spread. New Zealand Journal of Forestry Science 40 suppl. (2010) pp. S25-S33.
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Progress 09/01/08 to 08/31/09
Outputs
OUTPUTS: In addition to disseminating the research to the academic community through peer-reviewed publications, our findings were communicated through a number of seminars and presentations at various universities, and national and international meetings: Tobin, P. C. 2009. Allee effects and mating success in gypsy moth population dynamics. Department of Entomology, University of Wisconsin, Madison, WI. Tobin, P. C. 2009. Allee effects and biological invasions: exploiting an Achilles' Heel in management strategies. Department of Entomology, Purdue University, LaFayette, IN. Tobin, P. C. 2009. The ecology, geopolitics, and economics of area-wide management of invading gypsy moth populations. Keynote Presentation, Annual Meeting of NCERA-148, Migration and Dispersal of Agriculturally-Important Biota, Blacksburg, VA. Tobin, P. C. 2009. The role of Allee effects in biological invasions. Presented in the symposium, "Invasive Species Research," North Central Branch of the Entomological Society of America, St. Louis, MO. PARTICIPANTS: Ottar N. Bjornstad (PI) led the Penn State University-based portion of the project and supervised theoretical model development and statistical analyses. Andrew M. Liebhold (co-PI) and Patrick C. Tobin (co-PI) jointly led the USDA Forest Service portion of the project including curating the historical data and analyzing invasion speeds. Dr. Tomas de-Camino-Beck was a postdoctoral fellow jointly supervised by ONB and AML. The field work was carried out in part by AML with help from staff at the Northeastern Branch of the Forest service, and in part ONB with help from graduate students Angela Luis and Lindsay Beck-Johnson. TARGET AUDIENCES: The target audience is the academic community involved in the study of invasions and outbreaks of forest insect pests and advisory to the 'Slow-the-Spread' campaign of USDA forest service to help mitigate the damage caused by the ongoing gypsy moth invasion. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This project has three goals: (1) Characterize post-invasion synchronization among gypsy moth populations, (2) Investigate the role of trophic interactions in synchronization (3) Examine how habitat heterogeneity leads to differences in gypsy moth dynamics and synchronization. Building on results from last year were documented that certain xeric forest types have significantly more frequent outbreaks others. Our theoretical model discussing this phenomenon has been accepted for publication in Ecology. The postdoctoral fellow on the project, Dr Tomas de-Camino-Beck, leads the development of a new statistical method for estimating spread rates from historical quarantine data. The method involves wombling of the surface of the waiting times to species establishment to generate a field of speed vectors that describe local invasion spread across a landscape. We used a theoretical example and empirical data on the gypsy moth invasion of the USA to show how local rates of spread can be calculated and subsequently correlated with local habitat features. We also showed that this heterogeneity in spread rates can serve to increase the overall speed of range expansion. A manuscript detailing these results is under consideration for publication in Ecology. We continued the field studies of fixed-quadrat sites across the invasion front, from Pennsylvania through West-Virginia and Virginia. There, we conducted censuses of small mammal predation, egg mass abundances and acorn productions. These field measurements represented year three of a planned four years of study. As such, it is too early to start analyzing the data.
Publications
- Tobin, P.C., C. Robinet, D.M. Johnson, S.L. Whitmire, O.N. Bjornstad, and A.M. Liebhold. 2009. The role of Allee effects in gypsy moth, Lymantria dispar (L.), invasions. Population Ecology 51:373-384. http://dx.doi.org/10.1007/s10144-009-0144-6.
- Kelly, D., W.D. Koenig, and A.M. Liebhold. 2008. An intercontinental comparison of the dynamic behavior of mast seeding communities. Population Ecology 50:329-342.
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Progress 09/01/07 to 08/31/08
Outputs
OUTPUTS: In addition to disseminating the research to the academic community through peer-reviewed publications, our findings were communicated through a number of seminars and national and international meetings: Liebhold, A., O. Bjornstad, D. Johnson, K. Haynes, C. Robinet. 2008. "Spatial synchrony in forest insect outbreaks: Why is it so ubiquitous" presented in symposium, "Insect outbreaks revisited" at XXIII International Congress of Entomology July 6-12, 2008, Durban, South Africa; Liebhold, A., O. Bjornstad, D. Johnson, K. Haynes, C. Robinet-Makdoud. 2008. Spatial dynamics of gypsy moth outbreaks in North America. presented at 23rd Annual Landscape Ecology Symposium, Madison, Wisconsin, April 6-10, 2008; Liebhold, A. "Spatial dynamics of forest insect outbreaks", Dept. of Ecology & Evolution Seminar, University of Toronto, Toronto, Canada, Jan. 25, 2008. PARTICIPANTS: Ottar N. Bjornstad (PI) led the Penn State University-based portion of the project and supervised theoretical model development and statistical analyses. Andrew M. Liebhold (co-PI) and Patrick C. Tobin (co-PI) jointly led the USDA Forest Service portion of the project including curating the historical data and analyzing invasion speeds. Dr. Tomas de-Camino-Beck was a postdoctoral fellow jointly supervised by ONB and AML. The field work was carried out in part by AML with help from staff at the Northeastern Branch of the Forest service, and in part ONB with help from graduate students Angela Luis and Lawrence Chien. TARGET AUDIENCES: The target audience is in part the academic community involved in the study of invasions and outbreaks of forest insect pests, and in part advisory to the Slow-the-Spread campaign of USDA forest service to help mitigate the damage caused by the ongoing gypsy moth invasion. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This project has three goals: (1) Characterize post-invasion synchronization among gypsy moth populations, (2)Investigate the role of trophic interactions in synchronization(3) Examine how habitat heterogeneity leads to differences in gypsy moth dynamics and synchronization. Building on results from last year were documented that certain xeric forest types (notably Oak-Pine) have significantly more frequent outbreaks (with an inter-outbreak period around 5 years) than more mesic forest types (such as Oak-Hickory; that have inter-outbreak periods around 10 years), we developed a theoretical two-patch model that allow forest specific heterogeneities in densities of generalist predators. This model showed that such heterogeneities can account for the differences in dynamics. A paper detailing the analysis is currently in revision for Ecology. We further used the model to understand the role of generalist natural enemies in generating the Allee effect (inverse density-dependence at low densities) which we documented in last years analysis of historical data. We found that there is a possible role for such predators but it is unlikely to be the sole explanation. We continued the field studies of fixed-quadrat sites across the invasion front, from Pennsylvania through West-Virginia and Virginia. There we conducted small mammal predation censuses and measured pupal predation rates. We further censused egg mass abundances and acorn productions. These field measurements represents year two of a planned four years of study. As such, it is too early to start analyzing the data. We hired a new postdoctoral fellow on the project: Dr Tomas de-Camino-Beck who has since intiated two new activities on measuring landscape-specific rates on spread and using Markov logistic models to predict outbreaks. These activites are particularly relevant for goals 1 and 3. Finally a theoretical model to study how rates of synchronization depends on local dynamics was developed. This study was published in a special issue of Population Ecology.
Publications
- Bjornstad, O.N., A.M. Liebhold, and D.M. Johnson. 2008. Transient synchronization following invasion: revisiting Moran's model and a case study. Population Ecology. 50:379-389. doi: 10.1007/s10144-008-0105-5
- Satake, A. and O.N. Bjornstad. 2008. A resource budget model to explain intraspecific variation in mast reproductive dynamics. Ecological research. 23:3-10.
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Progress 09/01/06 to 08/31/07
Outputs
OUTPUTS: Several presentations were given at technical meetings: Liebhold, A., and P. Tobin "Biological information as the basis for strategies to exclude alien forest pest species" presented in "Sanidad Forestal" ("Forest Health") symposium at Segundo Congreso Latinoamericano IUFRO - La Serena, Chile, October 23-27, 2006. Liebhold, A. "Larch budmoth population cycles and climate change", Centre for Ecological and Evolutionary Synthesis, University of Oslo Oslo, Norway, April 20, 2006. Liebhold, A., O. Bjornstad, D. Johnson. "Forest Insect Outbreaks through Space and Time", international workshop, "Birch Forest Moth Dynamics and Environmental Change", Svanhovd, Norway Aug. 14-17, 2007. Liebhold A.M., O.N. Bjornstad & D.M. Johnson: "Role of natural enemies in the synchronization of forest insect outbreaks" IUFRO Conference, "Natural enemies and other multi-scale influences on forest insects", September 9-14, 2007, Vienna, Austria.Liebhold, A, O. Bjornstad, D. Johnson. "Spatial
Dynamics of a Forest Insect Invasion: The Conquest of North America by the Gypsy Moth", Dept. of Biology, University of Louisiana, Lafayette, LA, Nov. 8, 2007. Bjornstad, O.N., A.M. Liebhold, C. Robinet, P. Tobin and D. Johnson. 2007. "Forest Insect outbreaks: synchronization and spatiotemporal dynamics in the gypsy moth", 23rd Symposium of the Society of Population Ecology, Sapporo, Japan.
PARTICIPANTS: Ottar N. Bjornstad (PI) led the Penn State University-based portion of the project and supervised theoretical model development and statistical analyses. Andrew M. Liebhold (co-PI) and Patrick C. Tobin (co-PI) jointly led the USDA Forest Service portion of the project including curating the historical data and analyzing invasion speeds. Derek Johnson was a postdoctoral fellow jointly supervised by ONB and AML. Johnson is now an assistant professor at the University of Louisiana. The field work was carried out in part by AML with help from staff at the Northern Research Station of the Forest service, and in part ONB with help from graduate student Angela Luis.
TARGET AUDIENCES: The target audience is in part the academic community involved in the study of invasions and outbreaks of forest insect pests, and in part advisory to the gypsy moth "Slow-the-Spread" program of USDA forest service to help mitigate the damage caused by the ongoing gypsy moth invasion.
Impacts
Significant progress was made towards both goals of the project. Relative to goals 1 and 2 ("Characterize post-invasion synchronization among gypsy moth populations along the invasion front"), we digitized and started the analysis of historical gypsy moth pheromone trap data collected over ~5 million ha, and analysis of historical defoliation maps, to characterize rates of synchronization and how synchrony varies with forest types. We found that certain xeric forest types (notably Oak-Pine) have significantly more frequent outbreaks (with an inter-outbreak period around 5 years) than more mesic forest types (such as Oak-Hickory) that have inter-outbreak periods around 10 years. We developed theoretical models for the interaction between the insect and its' natural enemies to quantify the role of pathogens and generalist predators in these habitat-specific outbreak patterns. We further analyzed the historical data on invasion speeds to reveal that spatial variation in
the strength of the Allee effect (inverse density-dependence at low densities), result in significant geographic variation in gypsy moth invasion rates. Together these various statistical and theoretical results will have important impact on the planning of where and when to focus management for decreased spread. Relative to goal 3 ("Examine how habitat heterogeneity leads to differences in gypsy moth dynamics and synchronization"), we implemented fixed-quadrat study sites across the invasion front, from Pennsylvania through West-Virginia to Virginia. We conducted small mammal predation censuses and measured pupal predation rates. We further censused egg mass abundances and put out mast traps to measure acorn food resources for the small mammals. These field measurements represents year one of a planned four years of study. As such, it is too early to start analyzing the data. Results of this research provides new insight into the processes responsible for generating forest insect
outbreaks over large geographical regions. As such this work provides critical information ultimately leading to more effective approaches to predicting and managing forest insect outbreaks.
Publications
- Tobin, P. C., S. Whitmire, D. M. Johnson, O. N. Bjornstad and A. M. Liebhold. 2007. Invasion speed is affected by geographic variation in the strength of Allee effects. Ecology Letters 10:36-43.
- Johnson, D. M., A. M. Liebhold, P. C. Tobin and O. N. Bjornstad. 2006. Allee effects and pulsed invasion by the gypsy moth. Nature 444: 361-363.
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