The Role of Plant Dispersal on Ecosystem Function

1. The role of plant dispersal on
ecosystem function
Luka Negoita, PhD candidate
SU Biology

2. 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 not
everywhere!)

3. 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).

4. 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

5. • 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

6. • 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

7. The next step is to conduct a
controlled experiment

8. 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

9. Species Interactions
Soil nutrient cycling
Soil biotic activity
Plant productivity
Dispersal Limitation
Ecosystem
Function
Functional Trait Effects

10. Ecosystem
Function
Dispersal Limitation
Species Interactions
Functional Trait Effects
I propose an experiment
that explicitly quantifies
each of these steps to
directly test the link
between dispersal and
ecosystem function.
Soil nutrient cycling
Soil biotic activity
Plant productivity

11. Ecosystem
Function
Dispersal Limitation
Species Interactions
Soil nutrient cycling
Soil biotic activity
Plant productivity
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.
Functional Trait Effects

12. Ecosystem
Function
Dispersal Limitation
Species Interactions
Soil nutrient cycling
Soil biotic activity
Plant productivity
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.
Functional Trait Effects
Old-field
community

13. Ecosystem
Function
Dispersal Limitation
Species Interactions
Functional Trait Effects
Soil nutrient cycling
Soil biotic activity
Plant productivity
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

14. Ecosystem
Function
Dispersal Limitation
Species Interactions
Functional Trait Effects
Soil nutrient cycling
Soil biotic activity
Plant productivity
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]

15. Ecosystem
Function
Dispersal Limitation
Species Interactions
Functional Trait Effects
Soil nutrient cycling
Soil biotic activity
Plant productivity
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.
= [All potential colonists]60 cm
= [What actually gets there]
= [Relative abundance of each
species (biomass)]

16. Ecosystem
Function
Dispersal Limitation
Species Interactions
Functional Trait Effects
Soil nutrient cycling
Soil biotic activity
Plant productivity
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.
= [All potential colonists]60 cm
= [What actually gets there]
= [Relative abundance of each
species (biomass)]

17. Ecosystem
Function
Dispersal Limitation
Species Interactions
Soil nutrient cycling
Soil biotic activity
Plant productivity
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)
= [All potential colonists]60 cm
= [What actually gets there]
= [Relative abundance of each
species (biomass)]
Functional Trait Effects

18. 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:

19. 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?

20. 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

21. Why should you care?
• 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

22. Why should you care?
• 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

23. Acknowledgements
Committee:
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