LETTER Flowering synchrony drives reproductive success in a wind-
Elizabeth E. Crone,
Synchronised and quasi-periodic production of seeds by plant populations, known as masting, is
implicated in many ecological processes, but how it arises remains poorly understood. Flowering
and pollination dynamics are hypothesised to provide the mechanistic link for the observed rela-
tionship between weather and population-level seed production. We report the ﬁrst experimental
test of the phenological synchrony hypotheses as a driver of pollen limitation in mast seeding oaks
(Quercus ilex). Higher ﬂowering synchrony yielded greater pollination efﬁciency, which resulted in
2-fold greater seed set in highly synchronised oaks compared to asynchronous individuals. Pollen
addition removed the negative effect of asynchronous ﬂowering on seed set. Because phenological
synchrony operates through environmental variation, this result suggests that oak masting is syn-
chronised by exogenous rather than endogenous factors. It also points to a mechanism by which
changes in ﬂowering phenology can affect plant reproduction of mast-seeding plants, with subse-
quent implications for community dynamics.
Flowering phenology, ﬂowering synchrony, mast seeding, pollen addition, wind pollination.
Ecology Letters (2020)
Synchronous and highly variable seed production among
years by a population of perennial plants, or masting, is impli-
cated in many important ecological processes, from macronu-
trient cycles to resource pulses that have cascading effects on
plant and animal population dynamics, and disease risk in
humans (Ostfeld and Keesing, 2000; Bogdziewicz et al., 2016;
Clark et al., 2019). Several hypotheses have been proposed to
explain the proximate drivers of masting, yet there have been
few experimental tests of underlying theory (Bogdziewicz
et al., 2020a). To date, few manipulative studies have experi-
mentally tested putative proximate drivers of masting (Crone
and Rapp, 2014). This lack of studies has prevented the con-
ﬁrmation of causal links, thereby precluding meaningful pre-
dictions about the consequences of changing environments for
plant reproductive patterns and global vegetation dynamics.
Proximately, masting arises by combining two processes:
interannual variability in seed production, and synchronisation
among individuals (Pearse et al., 2016). These two processes are
believed to be the consequence of external factors, such as
resource availability and environmental cues, internal resource
dynamics of plants and pollination success (Crone and Rapp,
2014; Bogdziewicz et al., 2020a). The importance of resource
dynamics as a driver of interannual variability of seed produc-
tion is supported by a number of modelling studies (Rees et al.,
2002; Crone et al., 2005; Bogdziewicz et al., 2018; Schermer
et al., 2019), and also by limited number of resource-manipula-
tion experiments (Crone et al., 2009; Smaill et al., 2011;
Miyazaki et al., 2014). Resource dynamics alone, however, can-
not account for the high synchrony in seed set among plants
within a region, since each plant could presumably maintain its
own unique schedule of high and low seed production years
(Satake and Iwasa, 2000; Rees et al., 2002).
Pollen limitation is an effective method of synchronising
individual plants because processes that prevent ﬂowers from
developing are generally more effective at creating synchrony
than those that affect resource gain (Rees et al., 2002; Crone
and Rapp, 2014; Bogdziewicz et al., 2018). However, pollen
limitation can maintain synchrony of interannual variation in
seed set in at least two ways that differ fundamentally in how
they operate, although they are not mutually exclusive. Pollen
coupling is an endogenous process in which pollination suc-
cess increases with ﬂowering plant density, reinforcing annual
variation in ﬂower production (Kelly et al., 2001; Satake and
Iwasa, 2002). In contrast, a pollination Moran effect is an
exogenous, density independent, synchronising mechanism in
which pollination efﬁciency is driven by environmental factors
(Pearse et al., 2015b; Pesendorfer et al., 2016).
Recently, Koenig et al. (2015) formulated a hypothesis for a
mechanism underlying the pollination Moran effect, propos-
ing that weather is linked to seed production by its effect on
ﬂowering synchrony and associated pollination efﬁciency. The
phenology synchrony hypothesis posits that interannual differ-
ences in spring weather determine the onset of ﬂowering for
each plant. In years when weather conditions result in asyn-
chronous ﬂowering, low ﬂowering synchrony decreases pollen
availability and increases pollen limitation. In contrast, in
Department of Systematic Zoology, Faculty of Biology, Adam Mickiewicz
Department of Forest and Soil Sciences, Institute of Forest Ecology, Univer-
sity of Natural Resources and Life Sciences, Vienna, Austria
Department of Biology, Tufts University, Medford, MA, USA
INDEHESA, Forest Research Group, University of Extremadura, Plasencia,
*Correspondence: E-mail: firstname.lastname@example.org
©2020 John Wiley & Sons Ltd.
Ecology Letters, (2020) doi: 10.1111/ele.13609
years when plants ﬂower in synchrony with a high number of
other individuals, pollination failure is limited. Recently,
Pearse et al. (2015) showed that pollen addition in Quercus
lobata reduces female ﬂower abortion rates, increasing seed
set and that this effect was limited to a subset of years. This
study demonstrated that pollen limitation varies between years
–a key assumption of theoretical models –but did not test
the potential drivers of this variation. Here, we expand on this
work and report the ﬁrst experimental evaluation of pheno-
logical synchrony hypothesis as drivers of pollen limitation in
mast seeding trees.
We tested the phenological synchrony hypothesis using a
pollen addition experiment in Holm oak (Quercus ilex). In this
experiment, we compared effects of pollen supplementation
on trees that varied in their ﬂowering synchrony with con-
speciﬁc trees. We hypothesised that pollen addition would
reverse the effects of spatial isolation and asynchronous ﬂow-
ering on reproductive success. The experiment therefore
explicitly tests the causal link between ﬂowering synchrony
and variation in reproductive success in a masting plant:
poorly synchronised ﬂowering in certain years limits reproduc-
tive success of individual plants, leading to intermittent failure
and, by extension, to mast years. We also tested whether
effects of pollen supplementation differed with spatial isola-
tion of trees as a broad test for density dependence. Finally,
to better understand the dynamics of resource and pollen limi-
tation in this system, we compared the effects of seed set in
1 year on ﬂowering in the next, and quantiﬁed the relative
contributions of differences in ﬂower production and matura-
tion to differences in seed production among individual trees.
Study system and site
We conducted our study in Malpartida de Plasencia, Extrema-
dura, located c. 200 km west of Madrid in Spain. Pollen sup-
plementation experiments were conducted on Las Carboneras
dehesa (39°56’29.2"N, 5°58’47.1"W), an oak savannah agroe-
cosystem resulting from the human use of Mediterranean for-
ests over centuries (Fig. S1). Tree clearing has produced
landscapes with oaks interspersed within a grassland matrix,
which are mainly used for ranching. Our site is occupied
solely by the broadleaved evergreen Holm oak (Quercus ilex
L.), the most widely distributed tree species in the Iberian
Peninsula. It inhabits a wide range of habitats but predomi-
nates in dry Mediterranean regions with strong summer
droughts. Q.ilex budburst takes place in late March and early
April. Flowering usually occurs in April–May and acorns
grow throughout the summer until early autumn. Past correla-
tive studies found that the duration of the pollen season, used
as an index of ﬂowering synchrony, correlated negatively with
the acorn production, indicating that phenological synchrony
potentially plays vital role in shaping the interannual variation
in crop size in Q.ilex (Bogdziewicz et al., 2017). In this sys-
tem, summer drought often leads to severe pre-mature acorn
abscission (Espelta et al., 2008; Bogdziewicz et al., 2017),
which modulates the relationship between phenological syn-
chrony and acorn production.
We conducted the pollen supplementation experiment with a
population of 81 marked Q.ilex trees in 2018 and 2019
(Fig. S1 & Fig. S2). At each plant, we selected two branches
facing south, and haphazardly assigned one branch to pollen-
supplementation and one to be a control. Previous work has
shown that within-plant comparisons may lead to overestima-
tion of pollen limitation when pollen-supplemented ﬂowers
compete for resources with control ﬂowers (Knight et al.,
2006). We attempted to minimise this effect by choosing
branches that were separated by at least 5 m of vascular tis-
sue. Because trees are often modular in their carbohydrate use
(Hoch, 2005; Han and Kabeya, 2017), these distant branches
are less likely to compete for resources than neighbouring
ﬂowers on smaller plants (Pearse et al., 2015b). Experimental
studies performing defoliation, ﬂower removal, branch gird-
ling and stable isotope analysis have reported that separate
branches behave as if autonomous for fruit maturation in at
least some trees species (Obeso, 1998; Hasegawa et al., 2003;
Sala et al., 2012). On pollen supplementation branches, we
individually marked three shoots and hand-pollinated ﬂowers
(c. 2000 over the course of two years, median per shoot =3,
min =1, max =39) with a mix of conspeciﬁc pollen collected
from at least ﬁve local trees from outside the experimental
population. We added pollen when ﬂowers were receptive,
that is when their stigmas were swollen and yellowish. Flowers
on each shoot received pollen supplementation twice with a
2–3-day break between additions. On control branches, we
marked three shoots and handled them in similar ways, but
did not apply hand-pollination. We visited all trees every 2–
3 days, starting during the ﬁrst week of ﬂowering. At each
visit, we counted all female ﬂowers on marked shoots, and
scored ﬂowering phenology at the tree level by examining the
catkin stage (0 –not active; 1–up to 50% of the crown active;
3–over 50% of the crown active; 4 –spent). We used male
ﬂowering as the measure of phenology because it was rela-
tively easy to quantify objectively on a large scale. The sur-
veys were continued until all trees ﬁnished shedding pollen.
We evaluated seed set on the marked shoots twice: in early
June to evaluate the effects of pollen addition before drought-
induced acorn abortion, and in mid-September, to evaluate
the cumulative effects of pollen addition and drought on seed
We measured acorn production of individual trees in mid-
September by means of visual surveys in which two observers
(MB and RB) counted as many acorns as they could on each
tree in a 30-s period from two different orientations (south
and north). This acorn count method has been found to pro-
vide a good index of acorn availability under most conditions
(Koenig et al., 1994). The counts of acorns for each tree were
added together for the analysis. We measured diameter at
breast height of all trees in the experimental population in
2019 (mean =53.23, SD =8.33).
We quantiﬁed ﬂowering synchrony as the mean pairwise over-
lap in ﬂowering phenology among all individuals within the
©2020 John Wiley & Sons Ltd.
2M. Bogdziewicz et al. Letter
experimental population. We deﬁne ﬂowering here as the time
during which plants are shedding pollen. Flowering synchrony
between each pair of plants was calculated using the number
of days both individuals were ﬂowering divided by the num-
ber of days either individual was available for mating (see
Ison et al., 2014) in the mateable R package version 0.3.1
(Wagenius et al., 2020). To evaluate the effects of plant den-
sity on pollen limitation, we calculated local density of ﬂower-
ing plants, that is, the number of conspeciﬁcs within a 50-m
radius (Fig. S1). This cut-off was based on past studies relat-
ing seed production to local plants density in oaks (Knapp
et al., 2001). Because the spatial scale at which density can
affect pollen limitation in trees is essentially unknown (Koenig
et al., 2017), we repeated this analysis using other cut-offs
(10–70 m, with a 10-m step). Choice of cutoff distance did
not alter the conclusions and is not discussed further.
To evaluate the effect of ﬂowering synchrony, conspeciﬁc
density and pollen addition on seed set, we built a generalised
linear mixed model (GLMM) with a binomial error distribu-
tion, logit link and tree ID as a random intercept. The
response variable was seed set, expressed as the proportion of
ﬂowers that developed to acorns censused in June. As is stan-
dard in binomial GLMMs, the analysis was based on counts
of successes and failures, not calculated proportions. The
model included tree-level ﬂowering synchrony (as described in
the previous paragraph) and density in an interaction with
treatment (pollen addition or control). We also included year
and tree diameter at breast height as covariates. We detected
overdispersion, and accounted for it by including an observa-
tion-level random intercept (Zuur et al., 2009). We arrived at
the ﬁnal model by removing non-signiﬁcant interaction terms.
We quantiﬁed the relative importance of ﬂower production
and post-ﬂowering processes (pollination and seed abortion)
for reproductive success of individual trees. This analysis used
a log-link, negative binomial GLMM, with tree ID as a ran-
dom intercept. The response variable was the tree-level visual
acorn count, noting that the log-link plays a similar role to log-
transformation. Fixed factors were ﬂower abundance and the
proportion of ﬂowers that successfully matured to acorns at the
branch level. We also included tree diameter at breast height as
covariate. For this analysis, the proportion of matured ﬂowers
was calculated based only on control branches. We z-standard-
ised predictors to allow direct comparisons of effect sizes. All
statistics were run in R version 4.0.0. (R Core Team 2020), and
GLMMs were implemented via glmmTMB package 1.0.1.
(Brooks et al., 2017). Model checking revealed no temporal or
spatial autocorrelation of residuals. Because all our tests were
evaluations of continuous predictors or factors with two levels,
we evaluated statistical signiﬁcance using the p-values from the
In 2018, the ﬂowering season started April 22nd and lasted until
May 2nd. In 2019, ﬂowering onset was almost a month earlier
and started March 27th and ﬁnished April 26th (Fig. 1). In the
later and shorter 2018 season, ﬂowering was highly synchronised
in most trees (mean synchrony SD: 0.49 0.13), whereas in
2019 ﬂowering synchrony was lower (0.41 0.12, LMM with
tree ID as random intercept: v
=17.03, P<0.001). Temperature
in the early-ﬂowering season (2019) was higher than in the late-
ﬂowering season (2018; mean daily temperature in January-
March in 2018: 9.2 °C vs. 2019: 11.4 °C).
The proportion of ﬂowers that developed into acorns was
signiﬁcantly affected by ﬂowering synchrony, suggesting
effects of among-tree variation in synchrony on pollen limita-
tion. In this statistical model, there was a signiﬁcant interac-
tion of ﬂowering synchrony and pollen addition (bSE:
5.13 1.43, z=3.59, P<0.001). Overlap in ﬂowering phe-
nology increased seed set of control branches (regression
slope: bSE: 2.53 1.15, z=2.20, P=0.03), but decreased
seed set of pollen-supplemented branches (regression slope:
bSE: 2.65 1.21, z=2.19, P=0.03). Asynchronous
trees were severely pollen limited (seed set c. 23%) which was
relaxed after pollen supplementation (seed set ~69%)
(Fig. 2). Seed set of well-synchronised trees did not differ
between treatments, suggesting that some other factor become
more limiting in such plants. Seed set was higher in 2019
(47%) compared to 2018 (37%) (logit-scale group difference,
bSE: 0.40 0.21, z=1.96, P=0.05), while tree DBH had
no effect (regression slope, bSE =0.006 0.02, z=0.43,
P=0.71). The interaction term of tree density and treatment
was not statistically signiﬁcant (P=0.49) and was removed
from the ﬁnal model. Conspeciﬁc tree density was not a statis-
tically signiﬁcant predictor of seed set (regression slope:
bSE =0.02 0.06, z=0.32, P=0.75).
Tree-level reproductive success (i.e. acorn crop size) was gen-
erally larger in trees that produced more ﬂowers (regression
slope, bSE =0.27 0.07, z=3.44, P<0.001), and had
higher acorn maturation rates (i.e. the proportion of ﬂowers
that reached full maturity) (bSE =0.24 0.07, z=3.09,
P<0.001). The effect sizes were comparable for both predic-
tors (Fig. 3). DBH had no effect on crop size, possibly because
of relatively small among-tree variation in size (regression slope,
bSE =0.02 0.07, z=0.28, P=0.78).
Our study demonstrates the causal link between ﬂowering syn-
chrony and seed set of masting trees, as proposed by the pheno-
logical synchrony hypothesis. Natural variation in ﬂowering
synchrony resulted in pollen limitation for asynchronous trees,
reducing seed set to half the seed set of synchronous trees.
Experimental pollen addition reversed this pollen limitation,
resulting in high pollination success, even in asynchronous
trees. Conspeciﬁc density, another potential driver of pollen
availability, did not correlate with pollination success. Thus,
this research provides the ﬁrst experimental evidence that pollen
limitation due to asynchronous ﬂowering reduces seed set, a key
assumption of the phenological synchrony hypothesis. This
hypothesis integrates environmental conditions and pollen
dynamics, and therefore brings together the two major factors
thought to inﬂuence synchrony of interannual variation in seed
production in species which gain an economy of scale from
wind pollination efﬁciency (Kelly & Sork 2002; Koenig et al.,
2015). In addition, the results support the notion that phenolog-
ical synchrony of ﬂowering, rather than density dependence,
was the driver of pollen limitation in our study.
©2020 John Wiley & Sons Ltd.
Interannual variation in masting is synchronised in popula-
tions thousands of kilometres distant –a pattern that is
strongly linked to synchrony in regional weather patterns
(Koenig and Knops, 1998; Vacchiano et al., 2017; LaMon-
tagne et al., 2020). Weather can synchronise seed production
through at least two mechanisms: (1) environmental cues that
induce changes in plant physiology and subsequently regulate
ﬂower production and maturation (Kelly et al., 2013), and (2)
direct abiotic effects on population-wide pollen limitation
(Pearse et al., 2016; Pesendorfer et al., 2016; Bogdziewicz
et al., 2020a). Our study provides unique experimental sup-
port for the latter, indicating that ﬂowering synchrony effects
of weather regulate pollen limitation in mast-seeding oaks.
The importance of phenological synchrony in mast seeding is
interesting because changes in the timing of ﬂowering and
leaf-out phenology are among the most conspicuous ﬁnger-
prints of climate change in temperate forests (Fu et al., 2015,
2019; Renner and Zohner, 2018). Most of these studies focus
on changes in the average or onset of phenological events,
with less emphasis on changes in the length of ﬂowering peri-
ods or changes in variation among individuals within popula-
tions (Zohner et al., 2018). Our results suggest that the nature
of changes in ﬂowering phenology can be a critical component
to patterns of mast-seeding in trees, with subsequent cascad-
ing effects on consumer communities (Ostfeld and Keesing,
2000; Touzot et al. 2020).
Flower production was a key determinant of crop size in Q.
ilex, along with seed set. Therefore, pollination alone is not
Figure 1 Flowering onset and ﬂowering synchrony during the study years. Flowering synchrony between each pair of plants was based on the number of
days both individuals were ﬂowering divided by the number of days either individual was ﬂowering. Spatial distribution of differently synchronised trees is
given in Figure S2.
Figure 2 Asynchronous trees are pollen limited, which is removed by pollen supplementation (a). Tree spatial isolation had no effect on pollen limitation
(b). The lines are based on signiﬁcant GLMM predictions, and the shading indicates the 95% conﬁdence intervals. Pollination success is the ﬂower to
acorn transition rate, and points are the per-branch, per-year means of 81 Quercus ilex trees.
©2020 John Wiley & Sons Ltd.
4M. Bogdziewicz et al. Letter
sufﬁcient to explain mast seeding. Understanding factors con-
trolling interannual variation in ﬂower production is a neces-
sary next research step. Interannual variation in ﬂower
production can be a product of large seasonal deviations from
mean weather values, which trigger changes in ﬂowering gene
expression and associated hormone synthesis responsible for
initiating bud formation and ﬂower induction (weather cuing
hypothesis; Kelly et al., 2013; Satake et al., 2019). Alterna-
tively, the resource budget hypothesis predicts that seed pro-
duction depletes resources, limiting allocation to ﬂowering in
the following year (Isagi et al., 1997; Sala et al., 2012). These
hypotheses are not mutually exclusive in that resource levels
can control gene expression and hormone secretion at the
same time (Miyazaki et al., 2014). Previously, we ﬁt resource
budget models to a time series of Q.ilex seed production pat-
terns (Bogdziewicz et al., 2019). This analysis indicated that
resource depletion was not important in determining interan-
nual variation in Q.ilex crop size. Our short-term data from
this study also indicate a positive correlation between crop
size in 1 year and ﬂower production in the following year
(Online Appendix, Figure S3); we would expect the opposite
pattern if reproduction strongly depleted stored resources. It
would be fascinating to manipulate hormonal levels in plant
organs, perhaps in combination with experimental ﬂower
removal, to explicitly evaluate hormonal cueing vs. resource
depletion as mechanisms of supra-annual reproduction within
individual plants (Turnbull et al., 2012). Oaks are ‘fruit matu-
ration’ species, in which fruit abortion is expected to be key
driver of masting variation Compared to oaks, interannual
variation in ﬂower production should be much stronger in
‘ﬂowering masting’ species in which annual variability in seed-
ing is primarily driven by differences in ﬂower production
(e.g. Fagus,Chionochloa; Kelly et al., 2001; Abe et al., 2016).
Our results are consistent with models of mast seeding that
implicate pollen limitation as a factor that synchronises seed set
(Crone and Rapp, 2014; Pearse et al., 2016; Pesendorfer et al.,
2016). Regardless of speciﬁc assumptions, nearly all models of
mast-seeding require a mechanism for coupling seed production
of nearby plants (Satake and Iwasa, 2000; Lyles et al., 2015;
Noble et al., 2018). Interestingly, the spatial scales of coupling
seem to differ dramatically among systems (Koenig and Ashley,
2003; Noble et al., 2018). Pollination synchrony has the poten-
tial to be such a mechanism, and further exploration of the spa-
tial scales of factors that determine both ﬂowering synchrony
and pollen dispersal could be a valuable avenue for future
research. So far, studies of oaks in California imply that pheno-
logical synchrony can be an important factor synchronising
masting at local spatial scales (Koenig et al., 2017), and that the
effective pollen transfer is mostly local (Knapp et al., 2001; Sork
et al., 2002). Another broad implication of our results is that a
single season with pollen limitation does not necessarily reduce
plant ﬁtness. In fact, if seed failure in some years allows plants
to reproduce more in the next year, then pollination failure
could help synchronise reproduction and increase plant ﬁtness.
Thus, pollen limitation could have evolved as a mechanism to
synchronise reproduction and enhance overall ﬁtness through
mast-seeding and its associated economies of scale, that is
decreased seed predation and increased pollination efﬁciency in
mast years (Bogdziewicz et al., 2020b, 2020c).
Pollen addition increased seed set in asynchronous oaks more
strongly than in synchronous oaks (c. 70% vs. c. 50% respec-
tively). This difference indicates that, in addition to pollen limita-
tion, synchrony is correlated with another factor limiting seed
set. Flowering onset of asynchronous trees was delayed com-
pared to synchronous ones (Online Appendix, Figure S4). One
hypothesis is that early trees suffered more folivore damage,
Figure 3 Acorn production is determined by ﬂower abundance and their maturation rate. (a) Average number of ﬂowers, successfully pollinated ﬂowers and
matured acorns. (b) The lines at (b) and (c) are based on signiﬁcant GLMM predictions, and the shading indicates the 95% conﬁdence intervals. Points are
the per-branch, per-year observations of 81 Quercus ilex trees.
©2020 John Wiley & Sons Ltd.
which could decrease their photosynthetic capacity and limit seed
set. In support of this hypothesis, in one past study, Quercus
lobata individuals with earlier budburst suffered more leaf dam-
age, which reduced their seed production (Pearse et al., 2015a).
Past experiments in our study system indicated that insect her-
bivory can decrease Q.ilex seed set by half (Canelo et al., 2018).
Early trees gain the advantage of reduced pollen limitation, but
may suffer reduced seed set due to other factors, such as her-
bivory. The relationship between plant phenology and plant–foli-
vore interactions is increasingly of interest, because climate
warming can shift the phenology of plants and their folivores
(Singer and Parmesan, 2010). These shifts in phenology may also
prove crucial to our understanding of masting dynamics.
The capacity of future forests to support biodiversity and deli-
ver ecosystem services will depend on the ability of seed produc-
tion to allow plant ranges to track climate change (LaDeau and
Clark, 2001; Ib
nez et al., 2009; McDowell et al., 2020). How-
ever, fecundity is the only major demographic process that lacks
ﬁeld-based estimates in models of global vegetation change
(McDowell et al., 2020). The sensitive dependence of pollination
effects on synchrony implies complex interactions among phenol-
ogy, pollination and herbivory. This complexity is daunting in
the context of predicting effects of climate change on plant fecun-
dity, and points to the importance of actions to mitigate climate
change. Our study is an important step towards process-based
understanding of links between climate and plant fecundity, that
can subsequently be incorporated into broader ecosystem-scale
models to aid predictions of vegetation dynamics.
I dedicate this work to my beloved father (M.B.). We thank
Dave Kelly and two Anonymous Reviewers for their construc-
tive comments on the earlier version of the text. We thank
Agnieszka Amborska-Bogdziewicz for invaluable help during
ﬁeld work. The study was supported by the Polish National
Science Centre grants Sonatina no. 2017/24/C/NZ8/00151
(MB), and the MICNN project AGL2014-54739-R (RB).
CONFLICT OF INTEREST
The authors declare no conﬂict of interests.
All authors designed the study. MB and RB ran the experi-
ments. MB analysed the data and drafter the manuscript. All
authors contributed critically to the interpretation of the
results and text revisions.
The peer review history for this article is available at https://
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Additional supporting information may be found online in
the Supporting Information section at the end of the article.
Editor, Richard Ostfeld
Manuscript received 8 July 2020
First decision made 16 August 2020
Manuscript accepted 24 August 2020
©2020 John Wiley & Sons Ltd.