Research Projects
The consequences of post-dispersal seed predation for rare, common and exotic species survival in remnant and restored prairies.
Period: March 1, 2020 - Present
Contact: Prairie Fork
Organization: University of Missouri Prairie Fork Trust, Missouri Department of Conservation, National Fish and Wildlife Foundation
Funding Source: PFCA
Objectives: Project Principal Investigator: Lauren Sullivan
Team Members: Maya Parker-Smith (graduate student, MU), 1 undergrad student (TBD)
Institution and/or Affiliation: University of Missouri, Division of Biological Sciences
Relationship of the proposal to the long-term goals of PFCA and/or to current project emphasis areas.
PFCA Goals Justification
Emphasis Area: Techniques, especially use of fire, to suppress the growth of warm-season grasses in order to encourage forb development within existing prairies. This project will elucidate the role that post-dispersal seed predation by animals (small mammals and insects) play in altering the survival and germination of both rare and exotic species in prairie systems at PFCA. This
information will help determine why many restored prairie systems tend to become grass dominated.
Emphasis Area: Control and management of exotic plant species. This project will be specifically informative for understanding why some species are able to create new recruits via seed and some cannot. This will provide information for the control of invasive species and the recruitment of rare forbs, as it will determine the natural
processes that are either helping or hindering germination from seed.
Emphasis Area: Indirect information on prairie fauna and insects. Through the hypotheses being tested here, we will experimentally determine how small mammals and insects alter the survival and germination rates of rare and exotic species at PFCA. While we will not have direct information about these specific non-plant communities, we can determine their general effects on
the plant community.
Long-term Goal: Re-establishment and maintenance of natural biological communities and service as an outdoor laboratory that advances science and engages students in active learning. This project addresses the long-term goals of PFCA by providing baseline knowledge necessary to understanding the role of post-seeding, natural biological processes in the creation of high quality restorations that are both forb-rich and free of noxious invasive species. Additionally, this project will engage both undergraduate and graduate students in restoration
ecology research at PFCA, thereby encouraging authentic research and active learning on site.
Objectives
Our overall objective is to understand the fate of seeds after they have fallen to the soil - either through the initial seeding of a restoration, or from maternal plants in the aboveground community. Our initial work from 2019 at PFCA and Tucker Prairie indicate that many thousands of seeds fall to the ground through natural processes each year. However, there is still a significant mismatch between the seeds captured through our methods, and the aboveground plant community that exists in these prairies (Wynne et al. in prep). One likely source of seed loss is predation by small mammals and insects (e.g. Howe & Brown 2000; Blaney & Kotanen 2001; Clark & Wilson 2003; Pufal & Klein 2013). Therefore, we will experimentally determine the role that small mammals and insects play regarding seed predation and seed death on both rare, common and exotic species at PFCA and Tucker Prairie. We hypothesize that small mammals and insects will have increased effects of seed predation on native over exotic species, as they have evolved with these seeds as a food source. We also hypothesize that rare species will be more likely to be consumed than common species, thus seed predation plays a role in their rarity.
Justification
It is commonly known that restored prairies tend to be less diverse than their remnant counterparts (Martin et al. 2005; Barak et al. 2017), and often fall short of restoration goals (Hallett et al. 2013). Specifically, diversity differences occur mostly through the loss of forbs, with warm- season grasses becoming increasingly abundant (Baer et al. 2002). For those species that appear in remnants but are difficult to establish in restorations, the problem tends to lie in some aspect of their seed either plant species are difficult to collect seed from, or the seeds do not germinate with any regularity (Newbold et al. 2019). The reverse can be true for many exotic species that
tend to dominate restored prairie systems. Individuals often produce a high abundance of seed, and this high propagule pressure allows for the successful invasion of these exotics (Lockwood et al. 2009). One unifying factor that could play a role in controlling the successful establishment of these native and exotic species by seed is post-dispersal seed predation (Orrock et al. 2008). If granivores such as small mammals or insects are preferentially consuming seeds, then the resulting differences could alter the composition of restored prairies toward high dominance by exotic species or warm season grasses. While we have evidence to show that at PFCA many seeds enter the system, we do not know the fate of those seeds. There are very few studies that examine the role of post-dispersal seed predation in prairie systems (but see: Clark & Wilson 2003; Pufal & Klein 2013), and none that we know of that look at these effects across a wide range of species (both native and exotic and across functional group). Thus it is imperative we understand how the animal components of grasslands alter the potential germination of rare, common and exotic species within prairie systems to determine if these factors are bottle necks for the germination of rare species, or promoters of exotic ones. We aim to address this knowledge gap by experimentally determining the rates of post-dispersal seed predation of rare, common and exotic species, and how these rates differ between remnant and restored prairies with varying restoration ages.
Expected benefits and outcomes:
This project has many expected benefits, as it will enhance both the specific research area of prairie restoration, and the mission of PFCA. First, the project will greatly improve the current PFCA project the Sullivan lab is working on (funded 2019) by rounding out the unanswered questions that arose from our seed rain work. While we have learned a great deal about the number and identity of the seeds that fall throughout the growing season at PFCA, we do not understand
the fate of all seeds that fall into the system. By determining the amount of post-dispersal seed predation on rare, common and exotic species at PFCA and Tucker Prairie, we would gain insight into how likely seeds of different functional groups (e.g. grass vs forb), and provenance (i.e. native vs exotic) are to survive to germination. These results will directly affect the mission of PFCA, as it will help managers learn if certain types of seeds are particularly susceptible to attack by animals. This would help managers at PFCA understand a potential reason for low germination of rare species, and a potential cause for why warm season grasses tend to push out native forbs as the restoration process proceeds.
Additionally, we will help advance the mission of PFCA by providing an educational environment where people can learn about the importance of native lands conservation in an active, outdoor setting. To do this, we will work with Amber Edwards to present the results of our work to various PFCA audiences through on-site outreach programs. Additionally, we will train one graduate student and one undergraduate students in restoration ecology research on site, therefore increasing the educational value of PFCA. Since this work connects to our previous PFCA grant, these students will be able to learn first-hand how the process of science works, and how one question leads to another in order to more fully understand a system.
Background and rationale:
Creating diverse prairie restorations that have a high forb to grass ratio and a high C-value is the goal for many land managers interested in grassland communities (e.g. Newbold et al. 2019). However, restorations tend to fall short of this goal (Hallett et al. 2013). While we have demonstrated in our previous research at PFCA that many seeds fall into restored and remnant prairies (Fig. 1), there is a disconnect between the seeds that we captured and the mature plants in
the aboveground community that are able to produce seed (analysis ongoing, but there are clear missing species in the seed rain that are found in the aboveground cover). It is necessary to understand what is happening to these seeds, and if in fact granivores are consuming them.
This critical gap has important consequences for understanding how to create highly functioning restored prairies that depend entirely on seed rain for promoting diversity. Not only is this information missing from PFCA, but from prairie systems in general. If the seeds of some species are not able to survive to germination, then they will not be able to form viable populations within restored prairie communities. Therefore, we propose to experimentally determine the rates at which seeds of rare, common and exotic species are removed by small mammal and insect granivores.
Figure 1. Seed rain patterns in a remnant (Tucker Prairie) and chronosequence of reconstructed prairies located at PFCA. Seed rain data for the remnant in 1980 was obtained from Rabinowitz and Rapp (1980). We are in the
process of completing our identification of seeds from our samples from 2019. Figure created by Katherine Wynne.
Methods:
We will use the same sites we used for our previous PFCA-funded research project for this project in order to match our seed rain results to our findings of post-dispersal seed consumption. We will conduct these experiments at Tucker Prairie - a 64ha remnant prairie that has never been plowed (Kucera 1961), and three restoration units within PFCA - restored in 2004 (16 year old restoration), 2012 and 2013 (6 and 7 year old restorations), and 2016 (4 year old restoration). This chronosequence represents a typical trajectory of restored prairies at PFCA, in that the plant communities tend to fall into three categories: early, medium and late successional restorations as quantified in Newbold et al. (2019).
Question: What is the role of post-dispersal seed predation by small mammal and insect on the removal of rare and exotic seeds at PFCA and Tucker Prairie? For our manipulative experiment, we will select 18 species as our target species 6 exotic, 6 rare and 6 common. Species will be determined based on the cover and seed rain data collected from the sites in 2019. Rare species will be those that were found in low abundance (<5%) of the cover data and low capture rate in the seed traps (e.g. Liatris pychnostachia, Silphium laciniatum), common species will be those found in high abundance (>50%) of the cover data and high capture rates in the seed traps (e.g. Chamaecrista fasciculata, Sorghastrum nutans, Eryngium yuccifiolium), and exotic species will be those that are common to both the cover and seed rain traps but are not native to the region (e.g. Lespedeza cuneata, Eriochloa villosa). Note: we are happy to consider species of interest to the PFCA management team, especially for rare species. When possible, we will attempt to look at both forbs and grasses within each category.
To determine how the rates of post-dispersal seed predation vary across granivore type and species, we will employ a common method used by seed removal studies that examine post-
dispersal seed predation by small mammals and insects (Craig et al. 2011; Pufal & Klein 2013). We will create seed caches (often called seed cafeterias) in a nested design that either allows both small mammals and insects access to seeds, just insects, or neither of the granivores. We will use small hardware cloth to exclude small mammals, and a fine mesh to exclude both mammals and insects. Within these caches we will mix twenty seeds of an individual species (one species per tray) with sand and place them at our 10 transects at each of the sites for 48 hours. We will split the species in half randomly and run the trials in two consecutive events in order to save money and time creating seed caches. We will place these trays out at two different times during the season: late spring/early summer, and late fall - to match up with the peaks of seed dispersal we measured from our seed rain traps (Fig. 1). Once the caches have been collected, we will count the number of seeds remaining in each cache. This way we can determine the total amount of post- dispersal seed predation pressure on these species (the percent of seeds left when both granivores have access), and the predation pressure by insects (the percent of seeds left when only insects have access) and small mammals (the percent of seeds left when both granivores have access the percent of seeds left when only insects have access) separately, as well as seed loss due to abiotic wind blowing (the percent of seeds left when neither granivores have access). We will analyze this data using mixed effects models, where the dependent variable is seed removal rate, and the fixed effects are the herbivore types and an additional additive factor for species type (rare vs common vs exotic for one test, and functional group for another) and for site. We will have a random effect for transect.
Schedule and Duration:
In June of 2020, we will create the seed caches and prepare the seeds by counting out lots of 20 seeds. We will run our seed trials at PFCA and Tucker Prairie in early July and early September. This should take about 1-1.5 weeks each assuming all goes well. We will attempt to have the first set of seed caches counted by the time we put out the second trial, and will have the second set of seed trials counted by the end of 2020. We will begin work to publish this data after the counting is completed.
Information Transfer:
We anticipate completing one publication in a peer reviewed journal from our findings.
Additionally, we will present our work at either the local St Louis Ecology and Evolution Conference (SLEEC) in the fall of 2020 as a poster or at a research symposium sponsored by the Missouri Botanical Garden in fall 2020. We will also present on our work and the importance of seed dispersal and post-dispersal seed predation for PFCA-sponsored outreach events when possible.
Previous funding:
In 2019, PI Sullivan was funded to conduct an examination of the seed rain at PFCA across a chronosequence of restoration, and at Tucker Prairie. This work has been going
extremely well, and will result in at least 2 peer-reviewed publications (we originally anticipated one publication). The samples take time to go through, but they should be completed by the summer of 2020. This project has been taken over by graduate student Katherine Wynne, who is now using it for a dissertation chapter. She will be presenting on this work at two conferences early in 2020, one local (the MNRC conference) and one international (The Frugivore and Seed Dispersal Conference), and will potentially be presenting on this work at the Ecological Society of America Conference in August 2020. She is also using this work as a springboard to apply for more money from the National Science Foundation, and the Missouri Native Plant Society.
Literature Cited
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3. Blaney, C.S. & Kotanen, P.M. (2001). Post-dispersal losses to seed predators: An experimental comparison of native and exotic old field plants. Can. J. Bot., 79, 284292
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13. Pufal, G. & Klein, A.M. (2013). Post-dispersal seed predation of three grassland species in a plant diversity experiment. J. Plant Ecol., 6, 468479