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Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
- 297 -
APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
INCREASED POLLINATOR ACTIVITY IN URBAN GARDENS
WITH MORE NATIVE FLORA
FUKASE, J.1 – SIMONS, A.M.2*
1Institute of Environmental Science, Carleton University, Ottawa, ON, K1S 5B6, Canada
2Department of Biology, Carleton University, Ottawa, ON, K1S 5B6, Canada
(phone: +1-613-859-1135; fax: +1-613-520-3539)
*Corresponding author
e-mail: andrew_simons@carleton.ca
(Received 7th Jun 2015; accepted 19th Dec 2015)
Abstract. Declining pollinator abundance has become a major global environmental concern. Almost
90% of flowering plants rely on animal pollinators for reproduction, and negative effects of pollinator
declines on crop production have been shown. Urbanization is at least partially responsible for pollinator
declines, and public programs have been developed to encourage pollinator-friendly gardens. Here, in an
observational study, we investigate the relationship between pollinator activity and the proportion of
native species in unmanipulated private gardens in an urban area. Pollinator activity in each of ten
gardens was recorded at nine times throughout the growing season. Pollinator frequency differed among
gardens, and visitation was positively associated with percent area planted with native species, after
correcting for effects of time of year, plant density and total garden area. The effect of proportion native
plant area on pollinator activity differed among pollinator guilds, and was particularly strong for bumble
bees and large bees. The observation of heightened pollinator activity with increasing native area in this
correlational study suggests that cultivating native plant species should be encouraged in urban gardens.
We discuss that, although such observational studies have the advantage of realism, they cannot
determine underlying causal factors driving the observed correlation.
Keywords: exotic plant species; native flora; pollinator decline; urbanization
Introduction
The decline of domesticated and wild insect pollinators has become a global
environmental concern (Potts et al., 2010; Stokstad, 2006; Thomann et al., 2013), and a
high priority in conservation efforts (Gallai et al., 2009; Withgott, 1999). For example,
several Bombus species are in serious decline across North America (Cameron et al.,
2011; Colla et al., 2012), Ireland (Fitzpatrick et al., 2007), and declines are occurring in
parallel in Britain and the Netherlands (Biesmeijer et al., 2006). Habitat lost to human
activity including urbanization is considered to be a major cause of pollinator decline
(Connor et al., 2002; Matteson and Langellotto, 2011; Vanbergen et al., 2013),
prompting a movement for pollinator friendly gardens, often encouraging the cultivation
of native flowering plant species. However, the effectiveness of the relative
“nativeness” of gardens in promoting pollinator activity is still unresolved. Here, in an
observational study, we investigate whether the proportion of native plants in urban
gardens affects pollinator activity, and thus whether the inclusion of native flora should
be considered in the development of programs to promote pollinator conservation.
Both managed and wild insect pollinators, such as honey bees (Apis sp.) and
bumblebees (Bombus sp.), play ecologically and economically crucial roles in both
natural and human-altered environments (Ashman et al., 2004; Gallai et al., 2009; Klein
et al., 2007; Potts et al., 2010). Close to 90% of all flowering plants are pollinated by
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
- 298 -
APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
animals (Ollerton et al., 2011), and 35% of global food production depends, at least in
part, on animal pollinators (Klein et al., 2007). The demand for agricultural products
requiring animal pollinators has increased with population increases in recent decades
(Aizen and Harder, 2009; Calderone, 2012), and the estimated annual value of
pollination services provided by insect pollinators in the United States reached $15.1
billion in 2009 (Calderone, 2012). Negative effects of pollinator decline on global crop
production and reproduction of wild flowers has been documented (Aizen and
Feinsinger, 1994; Biesmeijer et al., 2006; Gallai et al., 2009).
Much research aims to investigate and explain the causes of pollinator decline. There
are several possible causes, and there is growing consensus that declines are
multifactorial (Bryden et al., 2013; Vanbergen et al., 2013) and include habitat loss and
fragmentation through intensification of land use (Aizen and Feinsinger, 1994; Connor
et al., 2002); competition with invasive pollinator species (Thomson, 2004); diseases
such as Varroa destructor mite infection (Finley et al., 1996) and the Israeli acute
paralysis virus (Cox-Foster et al., 2007); exposure to pesticides (Brittain et al., 2010),
and reduced floral diversity as a result of invasive plant species (Dietzsch et al., 2011;
Koutika et al., 2011; Simons, 2003).
Potential pollinator habitat is limited by available green space in urban areas.
However, the use of private gardens is increasingly being recognized for its potential
contribution to pollinator conservation through the provision of habitat with a high
diversity of flowering plants (Comba et al., 1999; Goddard et al., 2010; Matteson and
Langellotto, 2011). The effectiveness of urban gardens in pollinator conservation is
expected to depend on the composition of the garden (McFrederick and LeBuhn, 2006).
Specifically, the selection of particular plant species can account for much of the
activity of insect pollinators such as bumblebees (Goulson et al., 2008; Thomson,
2004). Conservation programs provide information on how to create a “pollinator
friendly” garden, often encouraging the cultivation of native plant species rather than
non-native ornamentals and invasive species (Mysliwy, 2014). However, knowledge of
the effectiveness of planting native species in attracting diverse and abundant insect
pollinators is still needed. Existing studies (Corbet et al., 2001; Frankie et al., 2005;
Tuell et al., 2008) were designed specifically to examine pollinator attraction using
prescribed flower choices, and no study to date examines pollinator attraction and
degree of garden nativeness in unmanipulated gardens.
In this study we ask whether the degree of nativeness influences pollinator attraction
in intact gardens by monitoring pollinator foraging activity in ten urban gardens with
different compositions of flowerbed area, plant density and the proportion of area
planted with native flora. We address several questions; two basic to pollination, and
two more focused on effects of nativeness: 1) whether pollinator abundance changes
through the growing season and/or in response to ambient temperature; 2) whether the
effect of time of year on pollinator activity differs among pollinator type or “guild”; 3)
whether the proportion of garden area planted with native species (as well as plant
density and total garden area) affects pollinator activity; 4) because pollinators may
differ in their degree of host range specialization, whether the effect of nativeness on
visitation frequency differs among pollinator guilds.
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
- 299 -
APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
Material and methods
Measures of garden variables
The ten gardens for the study were selected with the assistance of the Backyard
Habitat Program established by the Canadian Wildlife Federation. The gardens were
located in two main municipal districts separated by a distance of 12km within the
greater Ottawa, ON region: three in Centretown and seven in Lincoln Fields. Gardens
within each area were selected on the basis of the feasibility of sampling every area
within a two-day window for dates throughout the season. Two properties had distinct
back and front gardens, and these were considered separate based on differences in
floral composition. In each garden, floral area, plant density, and the area planted with
native species were measured in mid-May (Table 1). Floral area was measured as the
total area of flowerbeds. Some gardens had two to several flowerbeds, whereas a few
had a single large flowerbed. Plant were identified to species, and density was estimated
as the count of individual stems divided by the flowerbed area. In gardens that were
large and densely planted, a randomized 1 m2-quadrat sampling technique was applied.
A “proportion native area” value was calculated for each garden as the proportion of
total flowerbed area sown with native species. These proportions (p) were transformed
as arcsine (p^0.5) to improve normality. To reduce sampling error in estimates of
pollinator activity in large gardens, two plots were established for the six gardens >
50m2, and means of measurement values across plots were used in analyses. To avoid
random selection of anomalous plot areas, plot location was selected subjectively, based
on representative flora and density of flowering plants.
Table 1. Characteristics of the ten selected study gardens in Ottawa, ON. Total area
represents the cultivated area within the garden.
Garden
Location
Total area
(m2)
Plant
density
(stems/m2)
Native
flower area
(m2)
Proportion
native area
1
LF
145. 81
47
45.97
0.315
2
LF
144.74
106
27.30
0.189
3
LF
32.50
21
6.52
0.201
4
LF
70.86
57
17.02
0.240
5
LF
29.93
71
3.73
0.125
6
LF
53.39
229
2.81
0.526
7
LF
25.85
10
0.08
0.030
8
CT
68.07
17
1.17
0.172
9
CT
39.15
30
0.46
0.118
10
CT
52.27
20
1.36
0.260
LF= Lincoln Fields, CT= Centretown
Measures of pollinator frequency
Pollinator activity was observed in each garden plot on nine dates spanning July 3rd
to September 13th. Because pollinator activity is influenced by temperature,
observations were conducted only if the temperature was between 15°C and 30°C, and
were postponed in cases of severe rainfall. Observations of gardens in Lincoln Fields
and Centretown were conducted on consecutive days due to time constraints.
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
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APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
Observations were made between 8:30 and 17:30, and the order in which gardens were
visited within each area was randomized for each day. Summary weather conditions
(temperature and sun index) were recorded for each observation. At each plot, two 10-
minute observations were conducted, and the mean value of the two observations was
used to calculate pollinator frequency (pollinators per minute).
All flower visitors initially present and all new visitors observed foraging within the
plot were monitored, although not all flower-visiting insects are effective pollinators
(Schemske et al., 1978). Potential pollinators were photographed rather than collected
for identification during observation, and were categorized into nine guilds: bumblebee
(Bombus sp.), honey bee (Apis sp.), small bee (halictid and colletid bees), large bee
(megachilid, and andrenid bees), small fly (syrphid flies), large fly (calliphorid and
bombyliid flies), wasp (vespids), butterfly (lepidopterans), and other invertebrates (e.g.
coleopterans), and counted. Events were scored as pollinator activity only if physical
contact was made with the flower; those pollinators merely traversing the plot were
ignored. This sampling method may overestimate true pollinator activity, but it does
not lead to bias across plots because all observations were made by a single researcher
(Hennig and Ghazoul, 2012).
Statistical analyses
Second-degree polynomial (quadratic) regression was first performed to assess
seasonal change in frequency of overall pollinator visitation. The residuals from this
quadratic fit were then used to ask whether there is also an effect of temperature on
pollinator activity independent of time of year. To account for overall changes in
pollinator activity through the season, “residual pollinator activity” from this quadratic
fit was used as the response variable in analyses as noted below. To ask whether the
change in pollinator activity through the season differs among pollinator guilds, we used
a mixed-model ANOVA where pollinator guild is a fixed effect, and day and the
interaction are random effects.
A preliminary one-way ANOVA was conducted to test for variation in the frequency
of total pollinator visitation among gardens (where the response variable is residual
pollinator activity, above), followed by a post-hoc Tukey test. To address the main
question of the effect of native plants on pollinator activity, multiple regression was
used to simultaneously examine the effect of proportion native, plant density and flower
area on residual pollinator activity to account for possible covariation among predictor
variables. Finally, ANCOVA was used to ask whether the effect of proportion native
flora differs among pollinator guilds, where proportion native, plant density, total area
are continuous, and pollinator guild is categorical. All analyses were performed using
SPSS 18.0 or JMP 10.0.
Results
A total of 1699 pollinators were recorded over the observation period. Although it
explains less than 10% of the variance, quadratic regression shows a highly significant
change in pollinator abundance through time (R2=0.087, F141=6.70, P= 0.002).
Therefore, to correct for the effect of time of year, these residuals were used as
pollinator frequency values in the following analyses. (Linear regression would not be
an appropriate analysis of pollinator abundance vs. time of year, because pollinator
abundance is lowest at both ends of the season.) Using the residuals from this quadratic
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
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APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
fit in a linear regression (there is no apparent nonlinear effect of temperature) shows no
independent effect of temperature on pollinator activity after correcting for time of year
(R2=0.015, F142=2.21, P=0.14).
Much variation was observed among pollinator guilds in average frequencies of
visitation (Figure 1), with small bees showing highest frequencies, followed by
bumblebees, with lowest frequencies observed for butterflies. Furthermore, the relative
abundance of pollinator guilds differed across dates (Figure 2): bumblebee and
honeybee abundance increased mid to late season while small bees were common in
early summer and persisted throughout the summer. Large bees and dipteran pollinators
appeared early in the observation period although their frequencies were generally
lower than that of bumblebees, honeybees and small bees. This pattern is confirmed by
the significant interaction between pollinator guild and time of year (Table 2).
Table 2. Mixed-effects ANOVA results for effect of pollinator guild and time of year on total
pollinator frequency. Guild is a fixed, whereas Day and the interaction terms are random
effects. Because different pollinator guilds may appear at different times during the season,
Day was treated as a categorical effect.
Effects
df
Mean square
F
P
Pollinator guild
8
267.23
14.47
<0.001
Day
8
46.07
2.50
0.020
Pollinator guild*Day
64
18.46
1.93
<0.001
0
100
200
300
400
500
600
700
Pollinatorabundance
Pollinatorguild
Figure 1. The total abundance of each of the nine pollinator guilds observed in urban garden
plots in Ottawa, ON. Values are from counts conducted for two, ten-minute periods for each
plot on nine occasions from the beginning of July through mid September.
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
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APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
0
50
100
150
200
250
300
350
Other
Wasp
Bu erfly
Largefly
Smallfly
Largebee
(>10mm)
Smallbee
(<10mm)
Honeybee
Bumblebee
Pollinatorabundance
Date
Figure 2. The abundance of each of the nine defined pollinator guilds across the nine
observation dates. Values represent total counts conducted for two, ten-minute periods for each
plot from the beginning of July through mid September.
A one-way ANOVA shows that there was a highly significant difference in the
frequency of (residual) pollinator visitation among gardens (F9,134; P<0.001). A post-hoc
Tukey test further reveals that differences in the average frequency of pollinator
visitation was largely attributable to differences between two subsets; a group of four
(6, 7, 8, 9) and two (3 & 4) gardens (Table 3).
Table 3. Post-Hoc Tukey HSD test from one-way ANOVA for differences among gardens in
pollinator activity. For the Tukey HSD column, values not sharing a letter are significantly
different.
Pollinator activity
(frequency)
Garden #
Transformed
proportion native area
Tukey HSD
1.375
4
12.04
a
1.544
3
10.05
a b
0.928
1
15.83
a b c
0.909
2
9.45
a b c d
0.769
10
1.30
a b c d
0.400
5
6.24
b c d
0.313
9
0.59
c d
0.209
6
2.63
d
0.144
7
0.15
d
0.297
8
0.86
d
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
- 303 -
APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
Multiple regression (Table 4) including proportion native area, plant density and total
area (R2=0.251) confirmed a highly significant independent effect of proportion native
plant area on residual pollinator activity. The independent effect of plant density was
also significant, with no evidence for an effect of total area. There are no qualitative
differences in results if pollination activity is used as the response variable instead of
the residuals from the quadratic regression of pollinator activity on time of year.
Table 4. Multiple regression of proportion native area, plant density, and total planted area
on pollinator activity. Proportion native area was arcsine-squareroot transformed, and
pollinator activity was corrected for time of year (see text).
Effects
Estimate
SE Estimate
T-ratio
P
Intercept
-6.924
2.12
-3.27
0.001
Proportion native area
38.21
6.61
5.78
<0.001
Plant density
-0.033
0.01
-2.51
0.013
Total area
-0.042
0.03
-1.48
0.141
Although the slopes of the relationships between activity and proportion native area
have positive values for all pollinator guilds (Figure 3), analysis of covariance
(ANCOVA) shows that the effect of proportion native area on activity differs among
pollinator guilds (Table 5): a significant interaction between pollinator guild and the
degree of garden nativeness exists (Table 6).
1
10
100
0 0.1 0.2 0.3 0.4 0.5 0.6
Propor onna vearea(arcsinp0.5transformed)
Allpollinators
Largebee
Bumblebee
Honeybee
Smallbee
Smallfly
Largefly
Bu erfly
Wasp
Other
Log10pollinatorac vity
Figure 3. Relationship between observed activity for each of the pollinator guilds and the
proportion of urban garden area planted with native plants. The category “All pollinators” is
the total abundance at each garden for all plotted pollinator guilds. Pollinator activity is
plotted on a log10 scale to allow visualization of low-abundance pollinators, and is based on
counts conducted for two, ten-minute periods for each plot on nine occasions during the
growing season
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
- 304 -
APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
Table 5. ANCOVA results including interaction between pollinator guild and proportion
native area in gardens. Model R2=0.224; F19d,1276=19.35; P<0.001. For individual
interaction effect sizes, see Table 6.
Effects
df
SS
F
P
Proportion native
area
1
446.89
48.66
<0.001
Plant density
1
84.17
9.16
=0.003
Total area
1
29.29
3.19
=0.074
Pollinator guild
8
2137.86
29.10
<0.001
Pollinator guild*
proportion native
area
8
610.87
8.31
<0.001
Table 6. Coefficients for each pollinator guild x proportion native plant interaction effect
from the ANCOVA model (Table 5). Note that all slope values for pollinator guild vs.
proportion native area are positive; coefficients represent difference from mean effect.
Interaction term (all
X Proportion native)
Effect
coefficient
T-ratio
P
Bublebee
9.83
7.54
<0.001
Honeybee
1.65
1.27
0.206
Small bee
-0.53
-0.4
0.686
Large bee
-1.078
-0.83
0.408
Small fly
-2.88
-2.21
0.027
Large fly
-1.73
-1.33
0.185
Butterfly
-3.24
-2.48
0.013
Wasp
0.11
0.08
0.935
Discussion
Programs meant to combat declining pollinator abundance by
encouraging the planting of native species in urban gardens are widespread. However,
empirical evidence for the success of this approach is equivocal (Bergerot et al., 2010;
Hanley et al., 2014; Matteson and Langellotto, 2011). A complicating factor in
assessing the efficacy of native gardens is that the effect of native flora may differ
among plant species, and relative frequencies of pollinators may change through time.
We thus took the approach of sampling several pollinator guilds, and at several times
throughout the growing season. As expected, the overall frequency of pollinator
visitation changed through time, presumably both reflecting pollinator phenology and
changes in ambient temperature that affect the activities of insects (Bergman et al.,
1996); the interaction effect between pollinator guild and time of year suggests that
pollinator guilds have asynchronous life cycles (Ginsberg, 1983), perhaps timed to
coincide with the availability of resources that they depend on (Tuell et al., 2008).
The present results suggest that gardens with higher proportion native flora exhibit
elevated pollinator activity, and that the various pollinator guilds contribute differently
to this overall effect. In agreement with previous work (Smith et al., 2006), we found
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
- 305 -
APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
no relationship between total garden area and pollinator abundance, although we found
an effect of plant density on pollinator activity. However, the main result showing an
effect of native flora on pollinator activity persists after controlling for both plant
density and total cultivated area.
Because pollinator activity is corrected for time of year, and because proportion
native area is arcsine-squareroot transformed prior to analysis, the biological
interpretation of the coefficients from the multiple regression is not straightforward.
However, back-transforming the regression predictor equation suggests that the effect of
proportion native area is strong: the expectation is for one additional pollinator per
minute for an increase of about 20% in the area cultivated with native plants.
An observational study of the effects of native flora has the advantage that the
species and range of native flora are known a priori to reflect realistic choices of
gardeners. However, like all observational studies, causation cannot be drawn from the
observed relationships. For example, no attempt is made to manipulate gardens to
represent a random sample of native and non-native species. Thus, the relationship
between proportion native area and pollinator activity is more cautiously interpreted as
valid for the particular flora cultivated by gardeners in the study. Neither could we
control the range in the predictor variable; proportion native area. Although a
manipulation experiment could theoretically include a range from 0 to 100%, the
present study included gardens composed of from 3% to 53% native area (Table 1).
Furthermore, we cannot control for the effect of individual gardeners. It is conceivable
that the most skilled gardeners plant a higher proportion native species–even after
correcting for density and total garden area–which somehow results in higher pollinator
activity.
An observational study does not experimentally control the choices of native and
non-native flora with respect to their timing of flowering. Because peak abundance of
the various pollinator guilds does not coincide, results may be explained by the
influence of particular plant species (Goulson et al., 2008; Hanley et al., 2014), perhaps
because of their flowering phenology and the resulting seasonal availability of floral
rewards. It is possible that gardens with greater proportion native area provided
resources more continuously than gardens dominated by non-native species. For
example, Asclepias incarnata (swamp milkweed) has been shown to be a native flower
highly attractive to North American bumblebees (Tuell et al., 2008), and its presence
likely influenced pollinator visitation to the gardens where it was abundant in this study
(see Appendix). Also, because plant phenology interacts with environmental variation
(Hughes and Simons, 2014), patterns of visitation are expected to differ among years.
Many native flowers adapted to local conditions bloom in the late summer in eastern
North America (Tuell et al., 2008), whereas many non-native plants had finished
flowering by the end of the observation period. This difference may help explain the
effect of native area on pollinator activity, specifically through increases in the
frequency of bumblebees and large bees. Some species of large univoltine solitary bees
(andrenids and megachilids) appear either early or late in the summer (Ginsberg, 1983),
and late species are known to specialize on late-blooming Solidago spp. (Ginsberg,
1983). Small bees–which did not show a strong preference for native flowers–appeared
early in the season when the abundance of native flowers was low in comparison to later
in the summer. Flower morphology may also contribute to the effect of native flora on
pollinator activity. For example, syrphid flies were frequently found foraging on native
umbelliferous flowers, which are characterized by shallow corollas that allow access to
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
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APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
both pollen and nectar (Colley and Luna, 2000), and there were few common non-native
umbelliferous flowers in the gardens. Much debate surrounds the effect of native flora
on lepidopterans; (Bergerot et al., 2010; Burghardt et al., 2009; Matteson and
Langellotto, 2011; Tallamy and Shropshire, 2009); however the low abundance of
butterflies observed in this study precludes any inferences here.
Pollinator diversity observed here is not meant to be representative of the pollinator
composition in the Ottawa area. First, bee species may vary in abundance and
richness among years (Dupont et al., 2009; McFrederick and LeBuhn, 2006). Second,
the landscape matrix surrounding gardens (Hennig and Ghazoul, 2012) and the
proximity of sites of reproduction (nests/hives etc.) to gardens (Greenleaf et al., 2007)
may influence pollinator activity on a more local scale. It should also be noted that
our response variable is pollinator activity, and not pollination success. Any useful
extrapolation from this study must thus assume that pollinator activity is positively
associated with pollination.
A commonly cited mechanism underlying the benefits of native flora is the
coevolutionary history of plants and their pollinators: exotic flowers may be either less
accessible and/or attractive to native insect pollinators (Comba et al., 1999; Corbet et
al., 2001). It has been pointed out that, in the context of coevolution, a comparison of
native and exotic plant species does not satisfactorily address mechanisms underlying
pollinator attraction, and a more relevant consideration is the shared biogeographic
distribution of plants and their pollinators (Hanley et al., 2014). This insight, however,
is complicated by the fact that shared biogeography at the species scale does not
necessarily imply an expectation of coevolution, because intraspecific genetic
population differentiation in plant life history traits including flowering phenology is
common (Wagner and Simons, 2009), and plant traits involved in pollination are
expected to evolve in response to uncertainty in pollinator availability (Burd et al.,
2009; Simons, 2011; Thomann et al., 2013).
In conclusion, this study has shown a positive relationship between pollinator
activity and proportion of a garden planted with native flowers. Observational studies
such as this can provide insight into effects that occur over realistic ranges of
independent variables (here, cultivation decisions taken freely by real gardeners), but
trade-off this realism for the ability to ascertain underlying causes of the relationship.
Even if, as suggested by our data, the increase in pollinator activity is dependent on the
particular flora chosen and effects differ among pollinator guilds, programs that
encourage the cultivation of native flora are expected to succeed in increasing pollinator
activity in general, assuming that the gardeners’ choices of plant species in this study
are a representative sample of choices in the general gardening public. Although the
mechanisms underlying the relationship between degree of nativeness and pollinator
activity must still be worked out, this study demonstrates that this relationship exists.
Acknowledgements. The authors thank K. Henein and P. Hennesey for comment, and the participating
homeowners in Ottawa for property access. This research was supported by a Natural Sciences and
Engineering Research Council (of Canada) Discovery Grant to AMS.
Fukase – Simons: Increased pollinator activity in urban gardens with more native flora
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APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 14(1): 297-310.
http://www.aloki.hu ● ISSN 1589 1623 (Print) ● ISSN 1785 0037 (Online)
DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
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APPENDIX
Appendix 1. List of Ontario native flowers cultivated in the study gardens.
Blooming
Season
Common name
Scientific name
Observed pollinator
type
Spring
Largeflower bellwort
Uvularia grandiflora
Marsh violet
Viola palustris
Virginia bluebells
Mertensia virginica
Columbine
Aquilegia canadensis
Dutchman's breeches
Dicentra cucullaria
Wild bleeding heart
Dicentra eximia
Celandine poppy
Stylophorum diphyllum
White trillium
Trillium grandiflorum
Late spring
Canada anemone
Anemone canadensis
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DOI: http://dx.doi.org/10.15666/aeer/1401_297310
2016, ALÖKI Kft., Budapest, Hungary
Early summer
Foxglove beard-tongue
Penstemon digitalis
Hairy beard-tongue
Penstemon hirsutus
Wild geranium
Geranium maculatum
Small bees
Pale corydalis
Corydalis sempervirens
Early-mid
summer
Harebell
Campanula rotundifolia
Small bees
Mid summer
Beebalm
Monarda didyma
Bumblebees, small
and large bees
Yerrow
Achillea millefolium
Black-eyed Susan
Rudbeckia hirta
Large flies, others
Cup-plant
Silphium perfoliatum
Giant hyssop
Agastache foeniculum
Bumblebees,
Spiderwort
Tradescantia ohioensis
Bumblebees, small
bees
Purple coneflower
Echinacea purpurea
Bumblebees, large
flies, others
Lanceleaf tickseed
Coreopsis lanceolata
Turtlehead
Chelone glabra
Bumblebees
Small and large bees,
Swamp wilkweed
Asclepias incarnata
Bumblebees, honey
bees, small and large
bees, wasps,
butterflies, others
Butterfly weed
Asclepias tuberosa
Butterfly
Blue vervain
Verbena hastata
Tall meadow-rue
Thalictrum pubescens
Daisy fleabane
Erigeron annuus
Boneset
Eupatorium perfoliatum
Wild mint
Mentha arvensis
Evening-primrose
Oenothera biennis
Mid-late
summer
Pearly everlasting
Anaphalis margaritacea
False sunflower
Heliopsis helianthoides
Bumblebees,
Joe pye weed
Eupatorium purpureum
Bumblebees, small
bees
Late summer
New England aster
Aster novae-angliae
Bumblebees, small
flies
White wood aster
Eurybia divaricata
Smooth blue aster
Symphyotrichum laeve
Bumblebees, small
bees, small flies
Obedient plant
Physostegia virginiana
Bumblebees, large
bees, small bees
Canada goldenrod
Solidago canadensis
Bumblebees, small
flies,
Zigzag goldenrod
Solidago flexicaulis
Bumblebees
Gray goldenrod
Solidago nemoralis
Stiff goldenrod
Solidago rigida
Observed pollinator type is identified based on casual observation, thus not conclusive.
