Predicting Pollen Transfer Using Plant-Pollinator Interaction Webs
Predicting Pollen Transfer Using Plant-Pollinator Interaction Webs
Karen GoodellDepartment of Evolution, Ecology and Organismal Biology,
The Ohio State Universitywith
Neal Williams and Daniela MitevaDepartment of Biology, Bryn Mawr College
Plant-pollinator webs• Quantitative plant-visitor web
– Use food-web analysis to derive metrics for comparing communities
• Pollen transport webs– Identify potential pollinators of plants– Identify additional resources of pollinators– Extend information about visitors to include historical (short-term) visits
Memmott 1999. Ecol. Let.
Applications of pollinator interaction webs
• Restoration– Compare web structure with intact habitats similar to target
habitat– Compare function of the pollinator community to that in intact
habitat– E.g.: Restoration of British hay meadows (Forup & Memmott,
2005)• Constructed insect visitation and pollen transport webs for intact
and restored meadows• Inferred pollinator function from pollen transport webs
Applications of plant-pollinator webs
• Conservation– Identify important pollinators of rare plants– Identify resources required by these pollinator species– E.g., Gibson et al. 2006
• Identified important pollinators of three rare plant species• Used pollen transport patterns to rank pollinators by their
effectiveness• Identified resources used by these pollinators from pollen transport
webs
• Agriculture– Associate pollinator community structure with pollinator services
to crop plants– Identify important non-crop resources used by pollinators
Relationship to pollination patterns?
• Plant pollinator webs and pollen transport webs consider interactions at the species level
• But patterns of pollination reflect movements and choices of individuals
• Most visitor species are generalists– Average species-level foraging patterns may differ from
individual-level foraging – Floral constancy– Spatially restricted foraging
• Can individual-level data derived from plant-pollinator web contribute to understanding pollination patterns from web data?
Research questions
• Is generality of visitors correlated with patterns of pollen deposition on stigmas across plant species?– More generalized visitor species deposit more
heterospecific pollen• Does consideration of pollen transport web
improve predictions of pollen deposition in a plant community?– Higher diversity of pollen transported means higher
diversity of pollen transferred
Visitation, transport, deposition
• Build visitation web• Examine pollens deposited on stigmas
– Function of visitor diversity– Function of visitor generality
Visitors
Plants
Restored Eastern US Prairie
Pollinator and stigmatic data
• Flower and Pollinator survey– 1 ha plot– Counted all flowers of 8 dominant
plant species– Individually netted and preserved
insect visitors to plants over 1 day– 90 min collection per plant species– Pinned and identified all visitors
• Stigmatic pollen loads– Collected stigmas following 1 day of
open pollination (n = 25 per plant species)
– Counted and identified all grains on stigmas
Flower species surveyed
Carduus acanthoides Heliopsis helianthoides Rudbeckia serotina Nepeta cataria
Monarda fistulosaPhysalis longifoliavar. subglabrataPycnanthemum tenuifolium Solanum carolinense
Pollen transport data
• Dabbed insects with a ca. 25 mm2 cube of glycerin gel stained with fuchsin.
• Melted the gel onto a microscope slide• Counted and identified the pollen using a
reference collection• Constructed a matrix of individuals by
frequencies of pollens on their bodies
Monard
aHeli
opsis
Carduu
sPyc
nanth
emum
Physa
lisRud
beck
iaSola
num
Nepeta
0
1000
2000
3000
4000
5000
6000
Num
ber f
lora
l uni
ts p
er h
a
Plant species
Community structure
Apiform
es
Other H
ym.
Lepid
opter
a
Diptera
0
50
100
150
200
250
300
350
Num
ber o
f ind
ivid
uals
Visitor taxa
67 visitor species 486 visitor specimens
38 bee species 17 wasp species9 Lepidoptera species4 fly species23 Singletons (4.7%)12 Doubletons (2.5%)
8 plant species
Do more generalized visitor species carry higher diversity of pollen?
1 2 3 4 5 6 72.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Num
ber o
f pol
len
spec
ies
trans
porte
d
Number of host species
• No • Species-level
foraging patterns poor predictors of individual-level pollen transport
• Shown for subset of species n > 4
0.0 0.5 1.0 1.5 2.0
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Mea
n pr
opor
tion
corr
ect p
olle
n
H of floral hosts
Hylaeus affinis
Do more generalized visitor species carry less correct pollen?
• No.• n.s. trend for
species with external pollen transport
• Shown for subset of visitor species n > 4)
• H = Shannon-Weiner diversity index
Colletes latitarsus, Physalis specialist
Does low pollen fidelity of visitors mean higher pollen diversity on stigmas?
• No• Marginally significant
negative correlation when Physalisexcluded
• Outlier is Physalis, which has aspecialist pollinator
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.00
0.05
0.10
0.15
0.20
0.25
Mea
n H
of s
tigm
atic
pol
lens
Mean H of bee body pollens
Physalis
Carduus
Heliopsis
Monarda
NepetaPycnanthemum
Rudbeckia
Solanum
• Compare observed diversity of pollen deposited to
– Diversity plants used by visitor species to that plant– Diversity of pollens transported by visitors caught on that plant– Number of pollen grains not considered because not comparable
among plant species
• Compare observed proportion of conspecific pollen deposited to that predicted by three null models
– Species-level visitation fidelity– Species-level pollen transport patterns– Individual-level pollen fidelity
Predicting diversity of stigmatic pollen loads
Visitor fidelity model
Species-level visitor fidelity
Proportion of i pollen on stigma of i =( )( )∑
∑ ×
ji
ijji
NPN
,
,,
Ni,j = number of visitors of species j collected on plant iPj,i = proportion bee species j collected on plant i
Species-level visitor fidelity
Plant
A
B
C
Visitor sp.
1
2
3
Number of visitsA B
10 0
5 5
0 10
1
0.333
0
Percent visits toA B
( )( )∑
∑ ×
ji
ijji
NPN
,
,,
0
0.333
0.5
= (10 x 1) + (5 x 0.3333)/15 = 0.89Proportion of A pollen on stigmas of A
=
=
Assumptions• All pollen on body has equal probability to land on a
stigma– No pollen layering– No grooming– No effects of pollen placement
• Species-level visitation patterns reflect individual foraging patterns– Constancy well-documented in eusocial bees– Spatially restricted foraging likely in small species
• Flowers receive adequate numbers of visits for stigmas to reflect average visitation patterns
• Effects of floral morphology minimal; plant species behave similarly
Pollen fidelity
Individual pollen fidelity model
Proportion of i pollen on stigma of i =
Ni,j = number of visitors of species j collected on plant iBj,i = Mean proportion of pollen i carried on bodies of visitor species j
( )( )∑
∑ ×
ji
ijji
NBN
,
,,
Weights visitors to a focal plant by their pollen fidelity rather than species-level visitation fidelity
Individual pollen fidelity
Plant
A
B
C
Visitor sp.
1
2
3
Number of visitsA B
10 0
5 5
0 10
Proportion pollen carriedA B
1
0.90
0.1
0
0.80
0.75
( )( )∑
∑ ×
ji
ijji
NBN
,
,,Proportion of A pollen on stigmas of A
= = (10 x 1) + (5 x 0.9)/15 = 0.97
If foragers tend to be constant this model will increase the predicted proportion of conspecific pollen on stigmas.
Ni,jBi,j
Assumptions• All pollen on body has equal probability to land on a
stigma• Species-level visitation patterns reflect individual
foraging patterns• Flowers receive adequate numbers of visits for stigmas
to reflect average visitation patterns• Effects of floral morphology minimal; plant species
behave similarly• Pollinator pool limited to those caught on focal plant
Pollen transport
Species-level pollen transport
Proportion of i pollen on stigma of i =( )
( )∑∑
×
××
jij
ijij
NTNDT
,
j,,
Tj,i = Proportion of visitors j transporting pollen iDi,j = Mean proportion pollen i carried on bodies of visitor species jNj = Number of bees of species j in total sample
Related to measure of pollinator importance for a plant speciesPI = Tj,i x Dj,I (Ne’eman, Dafni & Potts 1999)
Considers as potential pollinators all individuals transporting pollen of focal species
Pollen Transport
Plant
A
B
C
Visitor sp.
1
2
3
Number of visitsA B
10 0
5 5
0 10
Prop. pollen carried* Prop indiv. transportingA B A B
1
0.50
0.1
0
0.30
0.45
= [(1 x 1 x 10) + (0.9 x 0.5 x 10) + (0.1 X 0.1 x 10)]/(10 + 9 + 0)= 0.82
Proportion of A pollen on stigmas of A)
=
*Means for all individuals carrying that pollen
( )( )∑
∑×
××
jij
ijij
NTNDT
,
j,,
1.0 0.2
0.9 1.0
0.1 0.6
Tj,iDi,jNj
Assumptions• All pollen on body in fully dynamic pool with equal
probability to land on the stigma• Pollen on body independent of current host• Flowers receive adequate numbers of visits for stigmas
to reflect average visitation patterns• Effects of floral morphology minimal; plant species
behave similarly• Pollinator pool limited to those caught on focal plant
Physa
lisNep
eta
Solanu
mMon
arda
Pycna
nthem
um
Heliop
sis
Rudbe
ckia
Carduu
s
0.00.10.20.30.40.50.60.70.80.91.0
Prop
ortio
n of
con
spec
ific
polle
n on
stig
ma
ObservedSpecies-level visitor fidelityIndividual-level pollen fidelitySepcies-level pollen transport
Pollen deposited on stigmas
• Fit of models tested with log-likelihood G-test for each plant sp.
• No model fit best for all species of plant
• Pollen fidelity model decent fit for 2 of 3 Asteraceae
• Pollen transport model least predictive
***
Individual foraging patterns: pollen on Apis bodies
• 2-d NMS on pollen data
• Apis collected on different hosts group by pollens collected
• MRPP detected significant variation among host-plant groups in pollens carried.
-1.5 -1.0 -0.5 0.0 0.5 1.0-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Rud
Car
Mon
Nep
Sol
HelA
xis
2
Axis 1
NepetaCarduusMonardaMean of Apis
21.4% of variation
68.5
% o
f var
iatio
n
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5-1.5
-1.0
-0.5
0.0
0.5
1.0A
xis
3
Axis 2
Individuals Means Heliopsis Monarda Carduus Nepetaall Augochlorellapollens
Pyc
Monarda
Hel
Rud Solanum
Carduus
Nepeta
Augochlorella aurata pollen on bodies
• 3-d NMS on pollen data
• MRPP indicates significant clustering of visitors by host plant
• Within group variance larger for some species
34.7% of variation
31.2
% o
f var
iatio
n
Heliopsis
CarduusMonarda
Nepeta
Individual foraging patterns differ from species average?
• Apis mellifera Yes• Bombus griseocolis No• Augochlorella aurata Yes• Halictus ligatus No• Lasioglossum admirandum No
Represent species caught on >1 plant species for which n > 4 per plant species
Pollen on B. griseocolis• Similar suites of
pollens collected– Carduus a major
component for all individuals regardless of host plant
– Little Monardatransported
– Monarda primarily a nectar source?
– Complementarity of resources discourages individual specialization
Physalis Rudbeckia Carduus Monarda Solanum Heliopsis0.0
0.2
0.4
0.6
0.8
1.0
Mea
n pr
opor
tion
of p
olle
n on
bod
y
Pollen species
Collected on Carduus Collected on Monarda
Conclusions• Pollen visitation webs poorly predict pollen deposition • Species-level pollen transport patterns add little
predictive power at community level• Individual pollen fidelity shows some promise in
predicting pollen transfer for certain species– Pollen deposition influenced by floral morphology– Simple flowers like Asteraceae work best
• Some evidence for individual differences in foraging choices in some species, but not in others
• Suggest caution in inferring pollinator function from visitation and pollen transport webs
Future directions• Examine spatial patterns of plant species that
could influence constancy– Degree of clumping– Clustering of more than one species
• Compare pollen transport patterns among visitor types– bees of different sizes and social structures– Insect orders
• Investigate predictive power of pollen deposition models within plant species
Acknowledgements
Collaborators: T’ai Roulston, Bob MinckleyStudents: Sarah Letson, Amy Seese
Identification: Sam Droege, John WenzelFunding & logistical support:
Blandy Experimental FarmNSF (REU program)
OSU-Newark (Student assistantship grants)
Structure of the interaction web
Measure Value SD range
Mean # plants/visitor sp. 1.71 1.46 1 - 7
Linkage Density 1.71
Connectance 0.24 = 128/(67 x 8)
Mean # visitor spp./plant sp.
16 7.51 4 - 28
Proportion of plant species’ pollen
transported1.0
Carduus-Carduus Monarda-Monarda Carduus-Monarda0.0
0.5
1.0
1.5
2.0
2.5
3.0
Mea
n pa
irwis
e Eu
clid
ean
dist
ance
Host group comparison
• No significant grouping of B. griseocolis individuals based on host plant
• MRPP based on Euclidean distances (log10) A = 0.036, P>0.05
Bombus griseocolis
n = 55 n = 21 n=77
Pairwise distances betweenpollens carried by individuals
pollen on bodies all bees NMS euclidean logs
Axis 1
Axi
s 2
Host12345678
Explaining pollen transport:species or floral host?
• MRPP of all bees by pollen transported – Significant clustering by species– Clustering by host stronger
Top Related