Dispersal is a nearly ubiquitous life history process that drives gene flow, community assembly, invasions, etc. Despite its importance, we know very little about the specifics of the process, how it varies within and among species, and how environmental factors affect this movement. Because dispersal can be extremely difficult to measure, much about this process is either generalized or ignored. To address this knowledge gap, our research entwines empirical field-based approaches with theory to understand the causes and consequences of dispersal for structuring plant populations and communities.
Plant movement & Landscape fragmentation
Anthropogenic fragmentation subdivides continuous swaths of habitat into patches that vary in size and distance from each other. This heterogeneous environment can be difficult for organisms to traverse if inhospitable land is created between patches. I am interested in determining how well organisms move in patchy landscapes, and what traits play a role in this movement. A common solution to connecting patchy habitat is to build corridors, or thin strips of suitable habitat, between patches. While working with the Corridor Project I investigated the potential negative effects of corridors, and showed that corridors promote the spread of larger-bodied parasites that control their movement, but do not affect smaller parasites that are more sensitive to micro-environment conditions.
Determining how far plants disperse is one of the biggest challenges for understanding landscape connectivity. Due to the tiny nature of seeds, ecologists often use models to predict how far species move, but these predictions can be unsatisfactory as they involve simplifying assumptions regarding secondary movement and establishment. Starting in 2016, I will lead a newly funded research project (The Prairie Dispersal Project - check out more info here!) through the Minnesota LCCMR that leverages next generation sequencing technologies to quantify actual dispersal distances via pollen and seed of grassland species, which is now possible because of advances in sequencing technology. I have selected target species that vary in their pollen and seed dispersal traits in order to begin pinpointing traits that promote dispersal and connectivity. The measured dispersal information will parameterize landscape connectivity models that will be implemented by local conservation agencies to create a unique, targeted restoration program for Minnesota tallgrass prairie habitat.
Relevant publications
1. Sullivan, LL, Johnson, BL, Brudvig, LA, and Haddad, NM (2011). Can dispersal mode predict corridor effects on plant parasites? Ecology, 92(8):1559-1564.
2. Haddad, NM, Brudvig, LA, Damschen, EI, Evans, DM, Johnson, BL, Levey, DJ, Orrock, JL, Resasco, J, Sullivan, LL, Tewksbury, JJ, Wagner, SA, and Weldon, AJ (2014). Potential negative ecological effects of corridors. Conservation Biology, 28(5):1178-1187.
Determining how far plants disperse is one of the biggest challenges for understanding landscape connectivity. Due to the tiny nature of seeds, ecologists often use models to predict how far species move, but these predictions can be unsatisfactory as they involve simplifying assumptions regarding secondary movement and establishment. Starting in 2016, I will lead a newly funded research project (The Prairie Dispersal Project - check out more info here!) through the Minnesota LCCMR that leverages next generation sequencing technologies to quantify actual dispersal distances via pollen and seed of grassland species, which is now possible because of advances in sequencing technology. I have selected target species that vary in their pollen and seed dispersal traits in order to begin pinpointing traits that promote dispersal and connectivity. The measured dispersal information will parameterize landscape connectivity models that will be implemented by local conservation agencies to create a unique, targeted restoration program for Minnesota tallgrass prairie habitat.
Relevant publications
1. Sullivan, LL, Johnson, BL, Brudvig, LA, and Haddad, NM (2011). Can dispersal mode predict corridor effects on plant parasites? Ecology, 92(8):1559-1564.
2. Haddad, NM, Brudvig, LA, Damschen, EI, Evans, DM, Johnson, BL, Levey, DJ, Orrock, JL, Resasco, J, Sullivan, LL, Tewksbury, JJ, Wagner, SA, and Weldon, AJ (2014). Potential negative ecological effects of corridors. Conservation Biology, 28(5):1178-1187.
stoichiometric drivers of dispersal
Elemental resources such as nitrogen and phosphorus are necessary for organism growth, and the ratio of these resources (i.e.: the stoichiometry) can alter the composition and reproductive function of species within communities, which in turn has the potential to alter dispersal ability. As pools of these nutrients are increasing globally, understanding how multiple nutrients move on the landscape, and subsequently influence plant reproductive and dispersal traits is an important forefront in spatial ecology. I address this issue in multiple ways. I am investigating how resource limitation influences plant movement by altering dispersal traits using field nutrient addition experiments with the Nutrient Network. I am also collaborating with the Iowa State University Aerospace Engineering Department to investigate how seed morphology influences the kinematics and aerodynamics of seed flight. Finally, in order to understand more about how nutrients move on the landscape and how they affect receiving trophic levels, I participated in the Woodstoich III working group, where we synthesized current knowledge regarding coupled nutrient flows across ecosystem boundaries.
Relevant publications
1. Sitters, J, Atkinson, CL, Guelzow, N, Kelly, P, and Sullivan, LL (2015). Spatial stoichiometry: cross-ecosystem material flows and their impact on recipient ecosystems and organisms. Oikos, 124(7):920-930.
2. Harpole, WS, Sullivan, LL, Lind, EM, Firn, J ... and 29 authors (2016). Addition of multiple limiting resources reduces grassland diversity. Nature, 537:93-96. (link here)
Relevant publications
1. Sitters, J, Atkinson, CL, Guelzow, N, Kelly, P, and Sullivan, LL (2015). Spatial stoichiometry: cross-ecosystem material flows and their impact on recipient ecosystems and organisms. Oikos, 124(7):920-930.
2. Harpole, WS, Sullivan, LL, Lind, EM, Firn, J ... and 29 authors (2016). Addition of multiple limiting resources reduces grassland diversity. Nature, 537:93-96. (link here)
Feedbacks between population dynamics and invasion biology
Extirpation of native grazers and global increases in cattle grazing both alter herbivore abundance and distribution worldwide. While much is known about how herbivores influence plant population size and abundance, herbivore pressure on plant invasions is largely ignored in restoration ecology despite its critical importance on plant community assembly processes. To investigate this, a small coalition of Iowa State grad students and I restored a 4-acre prairie restoration in Ames, Iowa, where I specifically investigated how herbivores alter the movement of establishing native species. Herbivores decreased establishment and movement ability of the annual legume Chamaecrista fasciulata, while altering its community establishment context. We simultaneously used this restoration as an educational site where I worked with over 200 ISU students from multiple colleges on issues related to native ecosystem conservation.
As a postdoc with Dr. Allison Shaw at the University of Minnesota, I am developing mathematical models to explore some of the general mechanisms of invasion biology. Specifically, I investigated how internal population dynamics, including Allee Effects and density-dependent dispersal, induce oscillations in invasion speed. Additionally, I am coupling theory and empiricism by scaling up my empirical herbivore results to model the influence of multiple plant-herbivore interaction syndromes on plant invasion rate.
Relevant publications
1. Sullivan, LL, Danielson, BJ, and Harpole, WS (2016). Herbivores alter the population growth and spatial establishment of an early-establishing grassland species. PLOS ONE, 11(2):e0147715 (reprint)
2. Sullivan, LL, Li, B, Miller, TEX, Neubert, MG, and Shaw, AK (2017) Density dependence in demography and dispersal generates fluctuating invasion speeds. PNAS, 114(19)5053-5058 (link here)
As a postdoc with Dr. Allison Shaw at the University of Minnesota, I am developing mathematical models to explore some of the general mechanisms of invasion biology. Specifically, I investigated how internal population dynamics, including Allee Effects and density-dependent dispersal, induce oscillations in invasion speed. Additionally, I am coupling theory and empiricism by scaling up my empirical herbivore results to model the influence of multiple plant-herbivore interaction syndromes on plant invasion rate.
Relevant publications
1. Sullivan, LL, Danielson, BJ, and Harpole, WS (2016). Herbivores alter the population growth and spatial establishment of an early-establishing grassland species. PLOS ONE, 11(2):e0147715 (reprint)
2. Sullivan, LL, Li, B, Miller, TEX, Neubert, MG, and Shaw, AK (2017) Density dependence in demography and dispersal generates fluctuating invasion speeds. PNAS, 114(19)5053-5058 (link here)