This study examined the within-season dynamics of plant-flower visitor interactions in Mediterranean alpine grasslands over the flowering season. The researchers analyzed temporal subnetworks from early, mid, and late season and found higher than expected species turnover between subnetworks. They also found more shared interactions than expected when species were present in both subnetworks, indicating fidelity of interactions. Analysis of the cumulative network identified modular structures associated with temporal variation in activity over the season, contrary to hypotheses that most interactions would overlap in a short period. Phenology plays an important role in shaping the modular structure of plant-flower visitor networks over the flowering season in these alpine grasslands.

1. Disintegrating a network: within-season
dynamics of plant-flower visitor interactions
Javier Morente, Carlos Lara-Romero, Concepción Ornosa & José M. Iriondo
30th SCAPE meeting
October 13-16, 2016, Abisko

2. Introduction
 Plant-flower visitor networks:
 Data comprising the whole flowering season
 Whole view with a single set of descriptors
Burkle et al. (2013) Science

3. Introduction
 Temporal integration provides a synthetic but limited
view:
 Cannot assess within-season structural dynamics
(Rasmussen et. al. 2013)
 Does not inform if recorded interactions concur in time
(Olesen et al. 2008)
 Competing or complementary interactions?
 Does not inform about missing interactions (Olesen et al.
2011)
 Lack of temporal synchrony or morphological
incompatibilities?
 Temporal integration constrains functional assessments
of the network

4. Aim
 To explore within-season temporal dynamics of plant-
flower visitor interactions.
 To assess the effect of phenology on cumulative
network structure

5. Study system
 Mediterranean alpine grasslands
 Short summer vegetative period between snow seasons
aggravated by mid-summer droughts.
 Baseline reference case to study the temporal dynamics
of plant-flower visitor networks.

6. Hypotheses
 Flowering period in Mediterranean alpine grassland
would be short and the flowering peak of most plant
species would coincide within a short period of time.
Consequently, most interactions of the network would
simultaneously be overlapping in this period

7. Hypotheses
 Temporal replacement of species would be
constrained
 The short vegetative period would prevent the
formation of modules of plants and flower visitors
associated to temporal variation in the interactions.

8. Methods
Study sites
 Mediterranean alpine pastures of Sierra de Guadarrama
(Central Spain).
 Two mountain peaks: Nevero and Peñalara (>2100m a.s.l.)
Pico del Nevero
Pico Peñalara

9. Methods
Experimental design
 Two 60x100m plots in each mountain
 Contacts recorded through walks along line transects
 13 June – 28 July: 10-11 censuses per plot
 160 hours per site (two teams)
100
m
60
m

10. Methods
Cumulative
network
Early stage subnetwork
Late stage subnetwork
Mid stage subnetwork
Dynamic perspective of the network

11. Methods
Data analysis
 Three time-aggregated subnetworks
 Beta diversity analysis (Baselga, 2010, 2012) for species
activity (plants and flower visitors in separate analysis)
 Dissimilarity of interactions (Poisot 2012)
 Cumulative quantitative bipartite networks for each
site
 Modularity analysis: QuaBiMo (Dormann and Strauss,
2014)
 Assessment of activity of each module through time

12. Cumulative network and temporal
subnetworks
Species richness, number of interactions and total number of interactions obtained in Peñalara (PEN) and
Nevero (NEV) study sites.
PEN NEV
Metrics Early Mid Late Cumulative Early Mid Late Cumulative
Plant species 11 9 12 17 7 12 11 16
Animal species 65 46 59 103 65 56 66 115
Number of
Interactions 138 115 148 315 121 106 160 340
Number of visits 1082 1017 1179 3278 707 616 938 2261

13. Turnover beta diversity was greater than
expected both in plants and flower visitors
Within-season beta-diversity of plant and flower visitor assemblages at Nevero and Peñalara study
sites (Early, Mid and Late stage subnetworks compared).
βSOR βSIM βSNE Z βSOR Z βSIM Z βSNE
Plant species assemblages
Nevero 0.67* 0.39* 0.28* 2.11 2.19 -2.21
Peñalara 0.64* 0.35* 0.29 2.24 1.98 -1.75
Flower visitors assemblages
Nevero 0.73* 0.55* 0.18* 7.47 6.96 -6.39
Peñalara 0.71* 0.48* 0.23* 6.44 5.82 -5.26
ΒSOR: overall beta diversity, βSIM: turnover beta diversity, βNES: nestedness beta diversity. Z prefix
indicates beta diversity values standardized by a null model. *Value departs from null expectations
(Z greater than 1.96 or less than -1.96, α= 0.05)

14. Shared interactions were greater than
expected through fidelity of interactions
when same species were present
Within-season variation of species interactions at Nevero and Peñalara study sites (Early vs.
Mid, Mid vs. Late).
IS INT INP Z IS Z INT Z INP
Early vs. Mid
Nevero 14* 154 48 2.42 -1.36 -1.28
Peñalara 37* 112 60* 3.42 -0.91 -3.60
Mid vs Late
Nevero 33* 123 78* 2.22 0.83 -2.91
Peñalara 39* 94 81* 2.49 0.79 -2.90
IS: number of shared interactions at different times, INT: number of non-shared interactions due to
species turnover, INP: number of non-shared interactions due to changes in species preferences (both
species present in the two sub-networks compared). The Z prefix indicates number of interactions
standardized by a null model. *Value departs from null expectations (Z greater than 1.96 or less than -
1.96, α= 0.05)

15. Flowering periods hardly overlapped in the
mid flowering season

16. Flower visitor patterns varied through time

17. Significant modules in cumulative network
Distribution of plants and number of flower-visitors of the modules identified for NEV and PEN study sites.
NEV PEN
Modules Modules
NEV 1 NEV 2 NEV 3 NEV 4 NEV 5 PEN 1 PEN 2 PEN 3
Plant species assemblages
armcae bisint sedbre Solvir linsax genlut gagnev eupwil
adehis jascri sedcan - lentod jascri hiesp senpyr
leualp silcil - - pinvah jurhum leualp solvir
jurhum hiesp - - - cytoro bisint silcil
cytoro - - - - thypra ransp adehis
senpyr - - - - - armcae sedbre
Flower-visitors assemblages
Bombus 1 2 - - - 2 - -
Bees 9 5 - - 2 6 6 2
Small bees 3 3 - 1 2 2 3 -
Wasp 2 - 2 1 - 2 - 3
Hoverflies 5 1 5 3 - 1 3 9
Bee flies 1 - 3 - - 2 - -
Big flies 5 - - 2 - 4 - 5
Flies 8 1 - - 1 1 2 3
Butterflies 17 5 1 - - 19 3 4
Beetles 9 - - 2 - - 9 3
Others 11 2 - - - 1 3 5

18. Temporal variation in activity of network
modules

19. Conclusions on hypotheses
 The flowering peak of most plant species would
coincide within a short period of time. Consequently,
most interactions of the network would simultaneously
be overlapping in this period.
 Temporal replacement of species would be
constrained
 The short vegetative period would prevent the
formation of modules of plants and flower visitors
associated to temporal variation in the interactions.
 Phenology seems to play an important role in shaping
the modular structure of cumulative networks.

20. Thank you!

21. Baselga 2010
 Nestedness component
 Temporal species turnover

22. Poisot 2012
Non-shared interactions between species that are not present in both subnetworks.
Non-shared interactions between species present in both subnetworks due changes in
preferences
Interactions shared between the two subnetworks