the role of plant dispersal on ecosystem function

The role of plant dispersal on ecosystem function

Luka Negoita, PhD candidate

SU Biology

Background

• The physical environment is traditionally considered the primary driver of community assembly• “Everything is everywhere, but, the environment

selects” – Becking and Beijerinck

• Seed-addition studies actually suggest otherwise for plants

• Indeed, plant communities tend to be dispersal limited (everything is noteverywhere!)

Background

• Plants are important drivers of ecosystem function, so does dispersal limitation also have ecosystem-level consequences?

• Could dispersal limitation affect the composition of traits that drive ecosystem function?

• Evolutionary and physiological tradeoffs suggest why functional traits and dispersal traits may be linked (e.g., competition-colonization tradeoffs).

Hypothesis and goals

Hypothesis:

– Dispersal limitation has ecosystem-level effects by driving the composition of functional traits

Research goals:

– Assess the relative role of dispersal in driving the composition of functional traits and resulting ecosystem processes

– Test associations between functional traits and dispersal ability

• 30 islands

• 1 to 67 ha in area

• 48 to 201 plant species on each island

• Used available trait data to quantify the composition of each island

• (SLA, LDMC, Leaf N, Vegetative Height)

• Used a landscape measure metric to quantify isolation of each island in GIS

Prelim study on Maine Islands

• Found significant patterns of functional trait variation across isolation

• These patterns are at least in part due to the association of functional traits with dispersal traits

• Effect of spatial isolation was much stronger than island area or elevation

Prelim study on Maine Islands

The next step is to conduct a controlled experiment

Framework

• It is important to understand where dispersal comes into the community assembly process and what other factors may also be important

• I chose to control for the effect of the physical environment since this is typically the focus of studies in community assembly

Species Interactions

Soil nutrient cycling Soil biotic activity Plant productivity

Dispersal Limitation

Ecosystem Function

Functional Trait Effects

Ecosystem Function




I propose an experiment that explicitly quantifies each of these steps to directly test the link between dispersal and ecosystem function.


Ecosystem Function




1 hectare> 50 m

Mow

Old-field community = [All potential colonists]

Maintain a one ha mown site within at least three old-field plant communities in NY state.Regional pool: All species found at each site.Use a plot-sampling protocol to record the abundance of species in the regional pool as a covariate.


Ecosystem Function




1 hectare> 50 m

Mow

= [All potential colonists]

Old-field plant communities will provide an ideal study system for testing the role of dispersal on ecosystem function because they harbor a diverse composition of fast-growing herbaceous species, making it feasible for me to test my questions in the short time-frame of a PhD project.


Old-field community

Ecosystem Function





Randomly place at least 20 plots containing seed-free soil within this mown area.Dispersal Limitation:inverse proportion of regional pool species that colonize each plot. This accounts for other factors affecting dispersal such as wind direction

= [All potential colonists]

> 50 m

Ecosystem Function





Each plot consists of two subplots. In one subplot record, but remove, germinating species. This eliminates the effect of species interactions such as competition, effectively acting as a seed trap

= [All potential colonists]60 cm

= [What actually gets there]

Ecosystem Function





I will not explicitly measure species interactions in this study, but will account for them by recording the relative abundance and composition of species in the adjacent paired plot, where I allow species to accumulate and grow.



= [Relative abundance of eachspecies (biomass)]

Ecosystem Function





Measure functional traits related to the leaf economics spectrum, growth rate, and life history from all species that make up at least 80% of cover in plots at each sites using standardized protocols.




Ecosystem Function




Collect soil samples throughout the two-year duration of this experiment to quantify nutrient cycling (mineralization, availability), biotic activity (respiration, decomposition), and primary productivity (biomass at end of experiment)





Analysis

Will use a hierarchical Bayesian approach

This will allow me to:

– Incorporate random effects (site, plot, species)

– Simultaneously partitioning the influence of parameters

– Provide direct statements on the probability and relative effect of parameters, allowing me to answer the following questions:

Will be able to answer:

• How well does dispersal limitation predict the relative composition of functional traits in communities?

• How well does dispersal limitation predict the ecosystem function of each plot?

• How much of ecosystem function can be predicted by functional composition rather than diversity alone?

• How well does arrival probability (dispersal ability) predict a species’ functional characteristics?

Why should you care?

• Understanding associations between dispersal ability and functional traits can address aspects of the competition-colonization tradeoff hypothesis

• A link between dispersal and ecosystem function suggests that historical contingency during plant community development may affect the successional trajectory of communities through changes in soil properties


• Results may provide the foundation for generating an ecosystem-level theory of island biogeography

• No effects of dispersal limitation on functional composition or ecosystem function would support the traditional view of dispersal as a random process, and in this case random with respect to functional traits


• Results will have important implications for understanding the ecosystem consequences of habitat fragmentation

• Results may inform habitat restoration and management practices

• Range-shifts due to climate change may also lead to ecosystem shifts based on dispersal ability

AcknowledgementsCommittee:

Jason Fridley, Mark Lomolino, Doug Frank, Mark Ritchie

Fridley Lab:

• Andrew Siefert

• Mason Heberling

• Insu Jo

• Elise Hinman

• Kelsey Martinez

• Mara McPartland

Maine Natural History Observatory

Other Collaborators:Glen Mittelhauser, Joseph Craine, Evan Weiher

the role of plant dispersal on ecosystem function

Science

role of plant dispersal

dispersal ability

plant species

plant communities

relative role of dispersal

composition of traits

ecosystemlevel effects

ecosystemlevel consequences