Importance of urban green areas connectivity for the conservation of pollinators

doi:10.21203/rs.3.rs-1415794/v2

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Importance of urban green areas connectivity for the conservation of pollinators

https://doi.org/10.21203/rs.3.rs-1415794/v2

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published 06 Nov, 2023

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Urbanization is one of the main processes generating large changes on the Earth's surface. The remaining green spaces within cities can be of utmost importance for pollinator conservation. Through a systematic literature review, we evaluate how the connectivity of urban green areas (parks, gardens, squares, among others) in different cities can affect the richness and abundance of pollinators. We utilize a connectivity metric using satellite images corresponding to 241 urban green areas obtained from 20 published works. The green areas were classified in urban, peri-urban and non-urban according to their percentage of impervious surface estimated in each image. The metric relates the connectivity of green areas contained within images with a radius of 500 meters immersed within a city. Our study shows the richness and abundance of pollinators is positively correlated with the connectivity of green areas in sites with different degrees of urbanization, mainly in urban and peri-urban sites. Our results emphasize the importance of green spaces to maintain the pollinator’s community in cities, and suggest that proper design and/or management could improve conditions for these important insects.

Urbanization

Fragmentation

Bees

Pollinators

Floral resources

Systematic literature review

The Earth’s surface is undergoing a critical transition from natural to urban and agricultural areas (Ellis et al. 2010; Potts et al. 2010). While the areas occupied by natural ecosystems are suffering reductions due to anthropogenic activities (e.g., expansion of agricultural frontiers), cities and urban settlements are growing and getting more industrialized over years (United Nations 2018). It is expected that by 2030 urban land will increase by 1.2 million km² (Seto et al. 2012). Furthermore, in the last decades the urban expansion rate has been considerably higher than the population growth rate, indicating that the urban area already exceeds what is needed to sustain population growth (Liu et al. 2020). As a result of this process, urban land expands over natural environments generating principally negative impacts on biodiversity. Regarding pollinators, these global changes affect flower-bee interactions with negative impacts on the pollination of native plants and/or crops (Harrison & Winfree 2015), mentioning introduction of exotic (non-native and/or managed) plant/pollinator species, fragmentation of semi-natural ecosystems (and the consequent isolation of the remaining areas), urban warming and environmental contaminants as specific urban drivers that directly affect plant–pollinator interactions.

Urban landscapes are a mosaic of impervious and pervious surfaces, which may include semi-natural habitats with different sizes and degrees of disturbance (Sattler et al. 2010). The remnants of these semi-natural habitats (green areas) that persist immersed in the urban matrix are regarded as biodiversity reservoirs (Seto et al. 2012; Gardiner et al. 2013; Baldock et al. 2015; Hall et al. 2017). Moreover, public parks and residential gardens can be considered green areas as well, since they provide food, shelter and/or nesting sites to different wild bees and others pollinators (Matteson et al. 2008; Banaszak-Cibicka & Zmihorski 2012), and allow the establishment and survival of wild plant populations (Threlfall et al. 2015). The proximity and connectivity of these urban green areas allow the movement of pollinators and the gene flow of their populations and of the plant partners.

Landscape connectivity is defined as the degree to which the landscape facilitates or impedes movements between resource patches (Taylor et al. 1993). In particular, the degree of structural connectivity presented by green areas (public parks, private gardens, squares, orchards) that are immersed in the urban matrix can provide information regarding the ecological functioning and the natural process that take place there. For example, a high degree of structural connectivity between green areas can greatly influence the movement of animals and dispersion of plant fruits/seeds/propagules (Uroy et al. 2019). It is also expected that the increase in connectivity of urban green areas could benefit the pollinator community and the ecosystem service they provide (Turo & Gardiner 2019).

Pollination service is a vital process to hold plant communities (Ashman et al. 2004) and ensure food production (Klein et al. 2007; Ricketts et al. 2008). Perhaps a future research direction is the link between landscape connectivity and the delivery of ecosystem services. Although pollinating insects have been at the center of research in recent years, little is known about their composition within cities. For example, richness, abundance, and/or composition of the different groups of pollinators are variable in cities. Some studies have found a negative relationship between pollinator richness and degree of urbanization (Hernandez et al. 2009; Bates et al. 2011), in others a maximum richness of certain groups has been observed at medium levels of urbanization (Fortel et al. 2014; Banaszak-Cibicka et al. 2018), while another study found no significant relationship between both variables (Amado De Santis & Chacoff 2020). These parameters could vary due to the irregular distribution of green areas within urbanized areas (Hülsmann et al. 2015; Kaluza et al. 2016; Theodorou et al. 2017; Yang et al. 2020). On the other hand, the size of the green areas is directly linked to the amount of resources, thus influencing the presence of pollinators (Ayers & Rehan 2021). Quistberg et al. (2016) suggested that the size of a green area is positively related to the abundance and richness of wild bees it harbors. Likewise, the degree of connectivity or isolation of green areas present within a city could influence the variability of these results.

In agroecosystems, another type of anthropogenic ecosystem, Steffan-Dewenter (2003) found a positive relationship between the richness of solitary bees and size of the semi-natural habitats immersed in the agricultural matrix. In addition, the author observed that the connectivity among these habitats positively influenced the number of solitary bee brood cells built per nest, showing the importance of the proximity among the semi-natural habitats for the flow of animals in agroecosystems (Potts et al. 2016; Theodorou et al. 2020). Pollinators in urban landscapes could present similar responses to those occurring in agricultural ones (Potts et al. 2016; Yang et al. 2020) and, therefore, the configuration of green areas (size and connectivity among these areas) within the urban matrix could be decisive for the establishment, maintenance and dispersion of pollinator communities (Baldock et al. 2019). Recently, Gathof et al. (2022) showed that urbanization and 3D connectivity (which combines area sizes, distances among areas, and building heights) significantly affected the taxonomic and functional composition of wild bee and hoverfly communities in Berlin. However, the composition of pollinator and plant communities in natural, agricultural and urban systems are usually different (Banaszak-Cibicka et al. 2018; Nakamura & Kudo 2019; Persson et al. 2020), and for that reason, ecological processes can differ too.

We performed a meta-study to estimate how the connectivity and relative area occupied by urban green areas in different cities around the world can affect pollinator richness and abundance. Our hypothesis is that the relative position of green areas within the urban landscape affects richness and abundance of pollinators. We predict that (i) richness and abundance will decline as urbanization increases; and (ii) richness and abundance of pollinators will increase along with connectivity of green areas in an urbanization gradient.

Bibliographic search

We performed a comprehensive literature search in the Scopus web database, using the string: "wild bee" OR "wild bees" OR “pollinator” OR “pollinators” AND "urban area" OR "urban garden" OR “urbanization” OR "community garden". Initially our search query returned 2393 potential papers (last accessed 14^th July 2020). Considering that the great majority of the publications were recent, we narrowed the search to the last 6 years, keeping the publications between January 1 2014 and July 14, 2020, with which we obtained 1896 potential papers. The papers were filtered by reading the summary, materials and methods, results and supplementary material if necessary. For a work to be considered valid for our systematic review, it had to contain data (richness and/or abundance) of pollinators from at least three sites (hereinafter: urban green area [UGA]) and present geographic coordinates or the name of each UGA used (for example, Munich Botanical Garden or 48°9'49.95"N and 11°30'3.56"E), to be able to be geolocated by Google Earth Pro (Google Earth 7.1.5.1557, 2015). Therefore, UGAs were those sites provided in each scientific work analyzed, whose geographic coordinates were provided and also presented data on the richness and/or abundance of pollinators. Further, we collected information of pollinator guild studied (bees, butterflies, flies, etc.) and data collection method (pan-traps, trap nests, direct observation, etc.) to include them in the analysis as variables. Finally, we indicated the continent where the study was carried out (see Electronic supplementary material 1: Tables S1, S2).

Landscape classification and connectivity

For each selected article, each of the UGAs was geolocated using Google Earth Pro. For each one, a circular portion of the image with a radius of 500 meters was delimited, containing the UGA in the center (Fig. 1; we assumed that georeferenced points indicated the UGA center). The use of this radius length is appropriate for pollinators, and it has been used in previous studies (Banaszak-Cibicka & Zmihorski 2012; Hülsmann et al. 2015; Kaluza et al. 2016; Monasterolo et al. 2022). Furthermore, Osborne et al. (2008) noted that while some bees and bumblebees can cover large foraging distances, these bees locally forage within a range of 500 meters. On the other hand, a recent study indicates that urbanization favored small-sized wild bees (Gathof et al. 2022) and considering that body size is directly related to foraging distance (Greenleaf et al. 2007), it is expected that their displacement could be shorter among urban green areas. Next, for each UGA, all other green areas (parks, gardens, etc.) greater than 0.2 ha contained within the area delimited by this radius were enclosed with polygons and their areas were measured (ha), using the Google Earth Pro tools. Thus, the total green area associated with each UGA was estimated as the sum of these green areas, and the percentage occupied by green areas ([total green area / 500 meter-radius-area]*100) was calculated. Moreover, the size of each UGA was used to calculate the relative area that each one occupies within the radius of 500 meters (Relative Area= area of UGA/ 500 meter radius area).

Then, to standardize and unify criteria, all the UGAs considered were classified according to their degree of urbanization (estimated as the percentage of impervious surface: (100-[percentage occupied by green areas]). This classification allowed to assign to each circular portion of the 500-meter image containing UGA one of the following three anthropogenic landscape categories: a) Urban (>70% of impervious surface); b) Peri-urban (30-70% of impervious surface); and c) Non-urban (<30% of impervious surface; this category includes cultivated areas and natural or semi-natural areas) (modified from Fortel et al. 2014). We assumed that these three anthropogenic categories represent different degrees of urbanization, being urban sites, those with high urbanization; peri-urban sites, those with intermediate levels of urbanization; and non-urban sites, those with lower populational density.

To estimate the connectivity of UGAs among green areas analyzed in each image with a radius of 500 meters, we measured using Google Earth Pro tools the minimum distances among focal UGA and their associated green areas within the radius of 500 meters (Fig. 1). With these data and the sizes of all green areas, a measure of connectivity was calculated for each UGA. This estimate reports the connectivity of the UGA with the associated green areas (for example, UGAs with closer green areas will have higher connectivity than those with remote green areas). We use the estimation considered by Steffan-Dewenter (2003), and modified from Hanski & Thomas (1994):

Connectivity = Σe^-dij Aj,

where Aj is the area of green area j (in ha) and d_ij represents the distance (in km) between UGA i and green area j. Connectivity could take values between zero and infinity. The increase in connectivity corresponds to more connected (or less isolated) sites.

Data analyses

Two generalized linear mixed models (GLMMs) were built to assess how connectivity and the relative area occupied by UGAs in each image with a radius of 500 m (explanatory variables) affect pollinator richness and abundance (response variables) in each anthropogenic landscape (Table 1). Connectivity, relative area of each UGA and the anthropogenic landscape classification (urban, peri-urban and non-urban) were included in each model as fixed factors (Table 1). Previously, it was verified that connectivity and relative area variables were not or low correlated (Spearman’s correlation: r=0.387, p>0.05). To build the GLMMs, the glmer function from the lme4 package was used, with a Negative Binomial distribution for both response variables due to the overdispersion of data. For all models, study identity and data collection method (pan traps, net, direct observations, nest traps, emergency traps, bait traps) were considered as nested random factors (Table 1). Connectivity variable was rescaled using the log₁₀ function. The goodness-of-fit of each model was evaluated using the plotQQunif and plotResiduals functions of the DHARMa package (Hartig & Hartig 2017, Electronic supplementary material 2: Fig. S1 and Fig. S2). All models included the interaction between connectivity and anthropogenic landscapes.

Finally, multiple comparison contrast tests were performed, one for richness and one for abundance of pollinators, in order to observe the differences between arithmetic means of each anthropogenic landscape (urban, peri-urban, non-urban). For this, the glht function of multcomp package was used (R Development Core Team 2013), using the GLMMs constructed above (Table 1) and degree of urbanization as fixed factor in both cases.

Table 1

Models used for the analysis. Response variables: richness and abundance of pollinators. Random variables: study identity (author) and data collection method (capture). These last two variables were nested. Fixed factors: Connectivity, anthropogenic landscape or degree of urbanization (DegUrbanization) and relative area occupied by each UGA in the radius of 500 meters (RelativeArea).

Model	Formula
a) Pollinator richness	richness~(1\|author/capture)+Connectivity:DegUrbanization+ DegUrbanization +RelativeArea
b) Pollinator abundance	abundance~(1\|author/capture)+Connectivity:DegUrbanization+DegUrbanization +RelativeArea

As a result of applying our inclusion criteria, 20 publications that contained a total of 241 UGAs in the three anthropogenic landscapes (94 urban, 91 peri-urban and 56 non-urban) were obtained. Of them, 214 UGAs presented data on pollinator richness, and 207 on pollinator abundance (Electronic supplementary material 1, Table S2). Of the 20 studies evaluated, 12 (60%) were performed in Europe, five (25%) in America (3 in North America and 2 in South America) and three (15%) in Asia.

GLMM for pollinator richness

The pollinator richness and the connectivity showed a positive and highly significant relationship throughout the three anthropogenic environments (Table 2a, Fig. 2a). On the other hand, no relationship was found between the pollinator richness and the relative area of UGAs. The results obtained from the multiple comparisons among the three different anthropogenic landscapes analyzed regarding pollinator richness was significantly higher in non-urban sites than peri-urban ones (Z=-2.885; p value=0.0106) and urban ones (Z=-4.357; p value=<0.001), while there was no significant differences between urban and peri-urban landscapes (Fig. 3a, and Electronic supplementary material 2: Table S4).

Table 2

GLMMs outputs. Models used to compare a) richness and b) abundance of pollinators with the anthropogenic landscapes or degree of urbanization (Urban, Peri-urban and Non-urban): Connectivity and the relative area occupied by each UGA in the radius of 500 meters (Relative area). Statistically significant values are in bold.

a)Pollinator richness	Estimate	Standar error	Z value	Probability (>\|z\|)	Significance
Intercept	2.024223	0.30777	7.285	3.21e-12	*******
Peri-urban	-1.05880	0.36700	-2.885	0.00391	**
Urban	-1.27286	0.29212	-4.357	1.32e-05	**
Relative area	0.05020	0.02779	1.806	0.07086
Connectivity:non-urban	0.15521	0.07029	2.208	0.02723	*
Connectivity:peri-urban	0.52232	0.10064	5.190	2.10e-07	*******
Connectivity:urban	0.58628	0.08421	6.962	3.36e-12	*******

b) Pollinator abundance	Estimate	Standar error	Z value	Probability (>\|z\|)	Significance
Intercept	5.10138	0.52773	9.667	<2e-16	*******
Peri-urban	-1.76820	0.71019	-2.490	0.01278	*
Urban	-2.21220	0.55518	-3.985	6.76e-05	*******
Relative area	0.61875	0.36862	1.679	0.09324
Connectivity:non-urban	-0.03733	0.13721	-0.272	0.78556
Connectivity:peri-urban	0.55811	0.19461	2.868	0.00413	**
Connectivity:urban	0.67847	0.15347	4.421	9.83e-06	*******

Significance codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

GLMM for pollinator abundance

Pollinator abundance showed a positive and statistically significant association with the connectivity in urban and peri-urban sites, while it was not significant in non-urban sites (Table 2b, Fig. 2b). In the same way as for pollinator richness, no significant relationship was found between the abundance of pollinators and the relative area of UGAs (Table 2b). The results obtained from the multiple comparisons among the different anthropogenic landscapes regarding abundance (Fig. 3b) was significantly higher in non-urban sites than in peri-urban ones (Z=2.490; p value=0.0336) and urban ones (Z=-3.985; p value<0.001), while there were no significant differences between urban and peri-urban landscapes (Fig. 3b, Electronic supplementary material 2: Table S4). Urban and peri-urban landscapes had lesser pollinator abundance than the non-urban sites (Fig. 3b).

Importance of green areas connectivity

Using data available in the literature combined with landscape analysis we found that, as we predicted, the connectivity among green areas within the urban landscape is positively related to the richness and abundance of pollinators. Our results show urban green areas host a greater diversity and abundance of pollinators when they are closer to each other (i.e., more connected). Thus, the proximity of green spaces could be promoting and facilitating the movement of urban pollinators among them.

Fenoglio et al. (2020) reported negative effects of urbanization for arthropods in cities and attribute it, in part, to the loss of habitable area and low habitat connectivity. Regardless of connectivity, non-urban sites presented higher pollinator richness than urban and peri-urban sites. These results are partially opposite to those reported by Baldock et al. (2015), who did not register differences in the diversity of pollinators in urban, agricultural and natural sites. However, such differences may be due to the use of different methodologies and criteria to classify the sampling sites. On the other hand, these authors found different responses for several taxonomic groups (bees, flies, hoverflies), with bee species richness higher and fly abundance (except hoverflies) lower in urban sites (Baldock et al. 2015). In our study, most of the analyzed papers included bees as the only or one of the main taxa, and we found a greater richness of these insects in non-urban sites (Geslin et al. 2016; Kratschmer et al. 2018; Sobreiro et al. 2019; Birdshire et al. 2020, among others). Ecological changes (e.g., extended phenology of flowering, availability of nesting sites, increased temperatures) produced by urbanization could generate positive, negative, or null effects on the pollinator communities. For example, Duchenne et al. (2020) classified wild bees as “winners or losers” from urbanization depending on several factors like sociability, nesting substrate and breadth of diet.

Different taxonomic groups of pollinators could be differentially affected by connectivity depending on their dispersal abilities. Hence, less mobile organisms could be more influenced to local scale (e.g., host plants for larvae butterflies) and more mobile organisms (bees, bumblebees, syrphids) to landscape scale (e.g., green areas connectivity) (Braaker et al. 2014). Thus, large bees with high foraging areas might be more affected by landscape connectivity than flies. However, some flies Syrphid species are considered highly mobile groups (Schweiger et al. 2007). On the other hand, butterflies have a relatively short lifespan as adults and moderate dispersal abilities (Soga & Koike 2013). Therefore, it would be reasonable to think that cities with more connected green areas would be beneficial for all insect pollinators regardless their dispersal distances, while those sites with more distant green areas would be disadvantageous for smaller pollinators with low dispersal.

Pollinator richness

Our results showed that landscapes with more connected green areas (i.e., less isolated), are harboring a greater richness of pollinators in all landscapes, regardless of their level of urbanization. This relationship was even more pronounced in urban sites than peri-urban and non-urban ones, which could indicate that landscape connectivity as a maintainer of pollinator richness becomes more useful in environments with a high degree of urbanization, regardless of the size of the green area. This suggests that, beyond the size of the green areas, it is important that they are connected to each other to allow the flow of pollinators between such green spaces.

It is important to highlight that there are more factors that influence the presence of pollinators within the cities, such as the surrounding landscape, temperature, and humidity, among others (Ayers & Rehan, 2021). For example, the impervious surface (roads, buildings, among others) could be generating physical barriers within the landscape and mainly among the vegetation patches, limiting the diversity of pollinators capable of living in such sites, such as those with greater flight ranges or greater body size. Thus, it becomes relevant to consider the connectivity of green areas to evaluate the quality of different anthropogenic landscapes, as well as other landscape variables such as environmental heterogeneity and fragmentation (Ayers & Rehan 2021). On the other hand, we did not analyze the different taxa separately, and the community present in each environment may vary according to their functional traits and life histories (flight ranges, body size, time of emergence, among others) (Luder et al. 2018; Wenzel et al. 2020). Although the general trend of the pollinator community is to increase with increasing connectivity, some taxonomic groups could respond with different magnitude to these variables, or to the urbanization gradient (Baldock et al. 2015).

Pollinator abundance

The abundance of pollinators increases with the connectivity of green areas in urban and peri-urban sites (Plascencia & Philpott 2017, but see Cohen et al. 2020), but no relationship was found in non-urban sites. In the same way as for pollinator richness, the abundance of pollinators is higher in non-urban sites compared to urban and peri-urban ones. This result contrasts with those reported by Zaninotto et al. (2021), who studied the general composition of floral visitors of two focal plant species; these authors observed a greater abundance of pollinators in urban environments compared to rural ones. They attributed such results to the greater dominance of social species (Apis mellifera and Bombus pascorum) in urban sites. In our study we included other taxonomic groups of pollinators in addition to bees (as syrphids, other flies, butterflies). Persson et al. (2020) showed that hoverflies and wild bees respond differently to urbanization, being urban hoverfly assemblages a subset of rural ones, and the solitary bee species richness higher in urban than in rural gardens. However, Desaegher et al. (2018) mentioned Syrphidae as an “urbanoneutral” family. On the other hand, in a review of urban diurnal Lepidoptera, Ramírez-Restrepo & MacGregor-Fors (2017) showed that most studies revealed a negative impact of urbanization intensity on richness and abundance of butterflies.

Generally, within the cities there exists a more homogenized fauna mainly composed by a small subset of cosmopolitan species adapted to urban conditions (Patitucci et al. 2011). These synanthropic species (generally, exotic and dominant) are associated with human settlements (Nuorteva 1963) and can reach high population densities (e.g., Musca domestica [Muscidae], Eristalis tenax [Syrphidae], among others). Also, urbanization is positively correlated with increased prevalence of exotic, social bees (e.g., Apis mellifera and Bombus spp.) and native, solitary (e.g., Anthidium manicatum [Megachilidae]) bees (Fitch et al. 2019). In an urban context, these synanthropic species could be responsible for the increase in the abundance of pollinators. So, in the same way as for pollinator richness, regardless of size, good connectivity between green areas is a fundamental requirement to maintain high abundances of pollinators and allow their movement between these spaces.

Resources for pollinators

Although urban settlements are disturbed and heterogeneous landscapes, they offer nesting sites and floral resources (primarily ornamental and exotic species, but several native species are also present) for pollinators (Matteson et al. 2008; Fortel et al. 2014; Hülsmann et al. al. 2015). In our study we did not include floral diversity as a variable because less than 10% of the studied work reported this data. However, we understand that this variable could influence our results. As a result of a SPIPOLL protocol (Photographic monitoring of pollinating insects, a citizen science project from the Museum national d’Histoire naturelle (MNHN)) carried out in France, floral morphology was the main driver of the 46 most frequent flower-feeding insect families (Desaegher et al. 2018). In addition, the distribution of floral resources could be driving the distribution of pollinators throughout cities (Krahner & Greil, 2020) since they represent an abundant and constant resource over time due to the presence of ornamental plants in gardens and private squares (Garbuzov et al. 2017; Corcos et al. 2019).

Study limitation

A possible limitation of our work is that only a radius of 500 meters was considered. We carried out a systematic review of published works in which the sampled sites were already established. We tried to use larger radii (750 and 1000 meters), even though delimited areas for higher radii from many UGAs overlapped, so we had to rule out sites, and little information remained. In addition, although it is known that the feeding distances of pollinating insects can exceed this working radius, the literature suggests that, in urban environments, the distances traveled to feed are smaller than in natural environments (López-Uribe et al. 2008). For example, foraging ranges of some bumblebees species within urban environments do not exceed 500 meters (Osborne et al. 2008). On the other hand, the movement of pollinators not only depends on the spatial distance that separates patches of vegetation (green areas), but also on the presence of restrictions imposed by physical barriers such as buildings and other vertical constructions (Peralta et al. 2011), which limits the movement of individuals.

The connectivity of green areas in urban environments could be a useful, accessible and simple tool, and it could be considered a key factor for urban planning. As we show in this study, the more connected green areas in a city, the greater its pollinator diversity, and it is expected that other groups of organisms present responses similar to those of pollinators (Fenoglio et al. 2020).

Finally, most of the studies analyzed were conducted in Europe and North America, and only a handful in South America and Asia (continents with a high rate of urbanization and densely populated cities). We believe that more studies of this type are necessary to detect general patterns that may be applicable to most urban centers. Our study summarizes and analyzes central aspects of urban ecology considered recently, and it hints at the aspects on which we should focus and those places where information is still lacking.

Acknowledgments

HJM. and JPT are affiliated with CONICET. SG thanks CONICET for her doctoral scholarships. RGV thanks ANPCyT for her postdoctoral scholarship (PICT 2016-0764).

Author contributions

SG and HJM were responsible for the conception and design of the study. RGV and JPT carried out the bibliographic search and selection. SG carried out the georeferencing and measurements of the work. SG and HJM performed the statistical analyses. SG and HJM made the first draft of the work and all the authors commented on the previous versions and approved the final manuscript.

Funding

This work was supported by grants PICT 2015-2523 provided to JPT and PICT 2017-3336, PIP-2020 and Neotropical Grassland Conservancy provided to HJM.

Ethics approval

Not Applicable.

Consent to participate

Not Applicable.

Consent for publication

All authors have contributed to and approved the manuscript’s content. The materials within this manuscript are neither published nor being considered for publication elsewhere.

Conflict of interest

The authors declare that they have no conflict of interest.

Data availability

The data can be found in the Dryad open source repository.

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Importance of urban green areas connectivity for the conservation of pollinators

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