Electronic Supplementary Material to:
Management-driven evolution in a domesticated ecosystem
Vigdis Vandvik1*, Joachim P. Töpper1,6, Zoë Cook2, Matthew I. Daws2, Einar Heegaard3,
Inger E. Måren4 & Liv Guri Velle1,5
1
Department of Biology, University of Bergen, Bergen, Norway.
2
Royal Botanic Gardens Kew, Wakehurst Place, West Sussex, UK.
3
Norwegian Forest and Landscape Institute, Fana, Norway.
4
Department of Geography, University of Bergen, Bergen, Norway.
5
Norwegian Institute for Agricultural and Environmental Research, Fureneset Norway.
6
Faculty of Engineering and Science, Sogn og Fjordane University College, PO Box 133,
6851 Sogndal, Norway
*
Correspondence: vigdis.vandvik@bio.uib.no
1
ESM file 1
Additional methodological information
Methods
Gradients. The study was conducted in Calluna populations along two geographical
gradients that span similar climatic variability but differ in land-use and fire history. The
latitudinal gradient spans 10ºN (58°4'N – 69°4'N) within coastal Calluna vulgaris L.
(hereafter referred to as Calluna) heaths that have been exposed to traditional heathland
management, involving high-frequency burning, for millennia. The altitudinal gradient spans
1000 m in altitude (10 – 1020 metres above sea level) from the anthropogenic coastal heaths
into natural pine forests and boreal and low-alpine heaths where burning is not part of the
traditional land-use, and where fire has therefore been historically much less frequent, or even
absent since the last glaciation (Fig. 1, Table S1).
Fire history. We searched the literature for palaeoecological microfossil analyses from
Norway reporting C14 dated charcoal records from peat or soil samples within heathlands,
moorlands, and open forests; the habitats in which Calluna grows [21]. From the coastal
heathland region five review papers [9, 11, 13-15] summarise >70 independent fossil records
documenting initial anthropogenic heathland establishment c. 6000-4500 cal. BP [11] in
south-west Norway, and later northwards [9, 13, 15]. In these records, heathland
establishment is paralleled by a sharp increase in charcoal dust, and continuous charcoal
records over time since the heathland establishment suggest high-frequency burning has been
part of the management regime throughout the history of the coastal heathlands (see Fig 1).
The temporal resolution of these studies vary, but both historical data [9, 10] and some of the
finer-resolution palaeoecological records [e.g., 11, 13] suggest that burn intervals of managed
coastal heathlands typically do not exceed 2-3 decades. From areas outside the anthropogenic
2
coastal heathland region, fossil charcoal records are generally not continuous, and dating of
charcoal particles in soils can be used to infer timing (and hence frequency) of individual past
fires [23]. From boreal forests outside the anthropogenic coastal heathland area 12
independently dated fire histories [22-25] suggest that natural fire frequency is relatively low,
especially in oceanic climates (several sites are fire-free since the last glaciation, median time
since fire >200 years, Fig, 1). These data indicate that fire frequencies differ sharply (by 1-3
orders of magnitude) between the anthropogenic coastal heathlands and the other habitats in
which Calluna occurs.
Seed sampling. Calluna seed material was collected between Oct 20th and Nov 4th 2007 from
11 heathland populations (i = 1,…, m) along these two gradients. The latitudinal gradient
(58°4'N to 69°4'N) comprised anthropogenic coastal heathland sites at Lista, Fedje, Møre,
Smøla, Bodø and Tromsø, and the altitudinal gradient (10 to 1020 m a.s.l.) spanned from
anthropogenic Calluna heath sites at the coast to boreal heath sites without any known fire
history in the mountains; Lygra, Gullbotn, Kvamskogen, Vøringsfossen and Ustaoset (Fig. 1,
Table S1). At each site, infructescences of 15 individual plants, spatially separated by at least
15 m, were harvested and thereafter dried at 20°C for two days before the seeds were
separated from the remaining debris. The samples from the Vøringsfossen site (altitudinal
gradient; 800 m a.s.l.) had been exposed to heavy arthropod seed predation and did not
contain enough live seeds for analysis. The seeds from the other 10 sites were stored in paper
bags at 15% relative humidity and 15°C for 5 months before being used in the germination
experiments.
Seed germination. A smoke solution experiment was conducted to test explicitly for
germination responses to smoke, following [4]. We used a standard Themeda smoke solution
obtained from the Research Centre for Plant Growth and Development, University of
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KwaZulu Natal, South Africa, courtesy of Johannes van Staden. This solution has been shown
to stimulate germination of a wide range of smoke-responsive species [e.g., 4, 5, 6].
In these experiments, approximately 1 ml of smoke solution was applied to two layers of
Fischer Scientific filter paper in Petri dishes (Sterilin 50 mm diameter, shallow Petri dishes,
single vent). Additional solution was added to the plates when they were drying, ca. every 10
days. Controls contained filter paper moisturised with distilled water that were treated in the
same manner. Previous work on temperature responses in these populations revealed that
germination rates and percentages peaked at 20ºC, with a light requirement but no
stratification requirement [26, see also very similar results from the UK in 18, 21]. We
therefore selected 20ºC for our germination trials. The plates were kept in incubators at 20°C
with a diurnal cycle of 16 hours of light and 8 hours of darkness. Germination was defined as
radicle emergence of ≥0.5 mm and was scored at least weekly for 60 days. Germinated and
decomposing seeds were removed from the dishes when scoring.
A dose response experiment was conducted to establish the relationship between the
concentration of smoke solution and germination response. The range tested was 1:50000 –
1:5000000, and the experiment was carried out on three replicate petri dishes from plants
from four populations spanning the two climate gradients (Latitudinal: Lista, Tromsø;
Altitudinal: Lygra, Gullbotn). The germination trial lasted for 46 days. For each population
the final germination percentages and time to mean germination (MTG) of the different
smoke solutions were compared to their respective controls with generalized linear models
using binomial distribution with logit link and Gaussian distribution with identity link,
respectively. For all populations but Lista, the final germination percentages increased with
increasing concentration until 1:500000, after which they did not change further with
concentration (Table S2). As for the Lista sample, already the control scored a final
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germination percentage of 95%, hence giving no room for any further increase. MTG was,
however, reduced by four to nine days under the smoke treatments in this population as well
as in Lygra and Gullbotn. For MTG, the highest smoke concentrations yielded somewhat
weaker effects and Tromsø showed no smoke response at all. Disregarding Lista for
germination percentages and Tromsø for MTG, only the 1:500000 smoke solutions yielded a
significant increase in germination percentages as well as a significant reduction in MTG for
all populations. The main experiment therefore used a 1:500000 dilution.
In the main smoke solution experiment seeds from 10 maternal plants from each of the 11
populations (j = 1, …, ni) were germinated at 20ºC with and without the addition of smoke
water. For the Møre and Kvamskogen populations seeds of several individuals were either
dead or eaten, resulting in only five and eight maternal plants from these populations,
respectively. For each individual/treatment combination, three replicates (k = 1,…, nij) of 22
seeds each were sown in petri dishes.. Germination was scored at least weekly for 60 days (t =
1, …, nijk) and germinated and decomposing seeds were removed from the dishes when
scoring.
Generalized Linear Mixed Model. A Bayesian inference was sought for the assessment of
seed germination. The sampling scheme dictates a Generalized Linear Mixed Model which
we solved by an Integrated Nested Laplace approximation [INLA; 27]. We assume binomial
distribution with germination of seeds (y|η ~Bin(n,p)) on petri-dishes, with trials (n) counting
22 seeds in each and the probability of germination (p) linked to the linear predictor (η) by a
logit link (logit(p) = η). The GLMM models consist of a linear predictor (η) with a fixed
effects part and random contributions. The random contribution accounts for the nested
experimental design, thereby avoiding potential pseudo-replication problems resulting from
spatial and temporal dependencies in the data. The effects of explanatory variables on
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germination along time in the 10 populations were assessed by models with the following
structure:
logit(pijkt) = ηijkt
ηijkt = β0 + f (timeijkt x treatmentijkt x geographyijkt) + b0i + b0ij + b0ijk + bijkt
were β and f (.) are fixed effects to be estimated for interpretation, time is number of days
since incubator experiment was initiated, treatment is smoke vs. control and geography is the
geographical position of the maternal populations. The b's are random contributions by the
i’th population, the j’th individual, and k’th replication, i.e. replicates within maternal plants
within populations. The residual random contribution (bijkt) is included to handle both overdispersion and an autoregressive AR-1 process. The INLA procedure works by setting up a
latent Gaussian field x = {η, β, fi(b0i), fij(b0ij), fijk(b0ijk), fijkt(bijkt)}, were we assume a broad
Gaussian distribution for priors of the fixed effects, and a Normal distribution assumption
follows the random contributors f (.) ~N(0,τ-1), were τ is the precision as inverted standard
deviation. The precisions here are regarded as hyperparameters and are assigned a Gamma
prior distribution, τ ~Gamma(1,0.001). The output statistics include the posterior distribution
of the intercept, and the coefficients for combinations of time, treatment and geography
(Figures S1 and S2). In addition, we receive posterior distributions of the precisions for
population, individual, replication, residuals, and the correlation between residuals (Figure S3
and S4). The details of the results reveal a considerable difference at the level of individuals,
as well as a considerable temporal correlation of the residuals. The posterior distributions for
the fitted values are also computed and used for graphical presentation of the model results.
The specification of the fixed effect of the models was performed using a backwards
6
elimination. Elements which included 0 (no effect) within the 95% credible interval were
omitted. All analyses were performed in R 2.15.2 [28].
References
See main document for a full reference list.
Author Contributions The study was conceived by VV and IEM, with inputs from MID and
LGV. Laboratory experiments were set up by JPS and carried out by ZC under the
supervision of MID. Historical data were collated by LGV. Statistical analyses were designed
by EH and carried out by EH and JPS. The manuscript was written by VV with input from all
authors.
Acknowledgements. We thank Birte Töpper, Liv Sigrid Nilsen, Unn Tveraabakk and Alf
Jakob Nilsen for assistance with seed-collection, Peter Emil Kaland for permission to modlfy
and use the example pollen diagram, and Christian Aasebø and Beate Helle for assistance
with Figure 1. Mons Kvamme the European Heathland Network, and the Ecological and
Environmental Change Research Group at the University of Bergen are acknowledged for
valuable contributions during discussions of this work.
7
Table S1. Geographic and climatic characteristics of the sampled Calluna vulgaris
populations. M.a.s.l. = metres above sea level. Temperatures given are mean annual
temperatures.
Population
Code
Longitude
Latitude
Altitude Temperature
(m.a.s.l) (°C)
Latitudinal gradient
Lista
A
6°48'E
58°40'N
5
7.3
Fedje
B
4°49'E
60°47'N
3
7.2
Møre
C
6°10'E
62°20'N
20
6.5
Smøla
D
8°40'E
63°17'N
10
6.1
Bodø
E
14°24'E
67°17'N
20
4.5
Tromsø
F
18°55'E
69°38'N
5
2.7
Altitudinal gradient
Lygra
a
5°50'E
60°42'N
10
7.3
Gullbotn
b
5°44'E
60°26'N
300
4.9
Kvamskogen
c
5°58'E
60°23'N
500
3.6
Vøringsfossen d
7°16'E
60°25'N
800
-
Ustaoset
8°20'E
60°29'N
1020
-0.6
e
8
Table S2. Final germination percentages (germ%) and time to mean germination (MTG) in
the dose response experiment investigating the germination response of four populations
(Lista and Tromsø along the latitudinal gradient as well as Lygra and Gullbotn along the
altitudinal gradient) to smoke solution concentrations from 1:50000 – 1:5000000. Asterisks
indicate whether or not the means of the smoke treatments were significantly different from
the control in a generalized linear model (***P < 0.001, **P < 0.01, *P < 0.05, NSP > 0.05).
Model
Site
df
control
germ%
Lista
Tromsø
Lygra
Gullbotn
14
14
14
14
95
26
83
56
MTG
(days)
Lista
Tromsø
Lygra
Gullbotn
14
14
14
14
18
32
27
24
smoke smoke smoke
(5*10-6) (3*10-6) (1*10-6)
98 NS 100 NS 98 NS
59 *** 56 *** 66 ***
100 **
83 NS 88 NS
71 NS
80 ** 74 *
13 ***
30 NS
20 **
18 **
13 **
30 NS
22 *
17 **
12 ***
30 NS
22 *
15 ***
smoke smoke
(5*10-6) (3*10-5)
100 NS 94 NS
80 *** 79 ***
95 *
95 *
86 *** 84 **
13 ***
31 NS
20 **
18 **
12 ***
30 NS
19 ***
21 NS
smoke
(5*10-4)
97 NS
85 ***
95 *
78 **
14 **
30 NS
25 NS
20 *
9
Figure S1. The posterior marginal distributions for the fixed effects of the GLMM model for
latitude. The posterior distributions of the models parameters are used for Table 1 and Table
2. The posterior distribution for the fitted values (Fig. 2) was obtained directly from the INLA
procedure.
10
Figure S2. The posterior marginal distributions for the fixed effects of the GLMM model for
altitude. The posterior distributions of the models parameters are used for Table 1 and Table
2. The posterior distribution for the fitted values (Fig. 2) was obtained directly from the INLA
procedure.
11
Figure S3. The posterior precisions related to the random contributions of the GLMM model
for latitude.
Figure S4. The posterior precisions related to the random contributions of the GLMM model
for altitude.
12