Disintegrating a network: within-season

dynamics of plant-flower visitor interactions

Javier Morente, Carlos Lara-Romero, Concepción Ornosa & José M. Iriondo

30th SCAPE meetingOctober 13-16, 2016, Abisko

Introduction

Plant-flower visitor networks:

Data comprising the whole flowering season

Whole view with a single set of descriptors

Burkle et al. (2013) Science

Introduction

Temporal integration provides a synthetic but limitedview:

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 morphologicalincompatibilities?

Temporal integration constrains functional assessmentsof the network

Aim

To explore within-season temporal dynamics of plant-

flower visitor interactions.

To assess the effect of phenology on cumulative

network structure

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.

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

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.

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

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)

100m

60m

Methods

Cumulativenetwork

Early stage subnetwork

Late stage subnetwork

Mid stage subnetwork

Dynamic perspective of the network

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

Cumulative network and temporal

subnetworks

Species richness, number of interactions and total number of interactions obtained in Peñalara (PEN) andNevero (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

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)

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)

Flowering periods hardly overlapped in the

mid flowering season

Flower visitor patterns varied through time

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

Temporal variation in activity of network

modules

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.

Thank you!

Baselga 2010

Nestedness component

Temporal species turnover

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 preferencesInteractions shared between the two subnetworks