Pollinator Preference Research Articles

Population structure and natural selection across a flower color polymorphism in the desert plant Encelia farinosa.

Clines-or the geographic sorting of phenotypes across continual space-provide an opportunity to understand the interaction of dispersal, selection, and history in structuring polymorphisms. In this study, we combine field-sampling, genetics, climatic analyses, and machine learning to understand a flower color polymorphism in the wide-ranging desert annual Encelia farinosa. We find evidence for replicated transitions in disk floret color from brown to yellow across spatial scales, with the most prominent cline stretching ~100 km from southwestern United States into México. Because population structure across the cline is minimal, selection is more likely than drift to have an important role in determining cline width. Given that the cline aligns with a climatic transition but there is no evidence for pollinator preference for flower color, we hypothesize that floret color likely varies as a function of climatic conditions.

Rootstock Effects on Tomato Fruit Composition and Pollinator Preferences in Tomato

Food security is threatened by climate change and associated abiotic stresses that affect the flowering stage and the biochemistry of flowers and fruits. In tomato, managed insect pollination and grafting elite tomato varieties onto robust rootstocks are widely practiced commercially to enhance tomato crop profitability, particularly under suboptimal conditions. However, little is known about rootstock–pollinator interactions and their impact on the chemical composition of fruit. In this study, a commercial tomato F1 hybrid (Solanum lycopersicum L.) was self-grafted and grafted onto a set of experimental rootstocks and cultivated under optimal and saline (75 mM NaCl) conditions in the presence of managed bumblebee pollinators (Bombus terrestris). The number of visits (VN) and total visiting time (TVT) by pollinators to different grafted plants were monitored through an RFID (radio-frequency identification) tracking system, while targeted metabolites (hormones, sugars, and organic and amino acids) and mineral composition were analyzed in the fruit juice by UHPLC-MS and ICP-OES, respectively. Pollinator foraging decisions were influenced by the rootstocks genotype and salinity treatment. Experimental rootstocks predominantly increased pollinator attraction compared to the self-grafted variety. Interestingly, the pollinator parameters were positively associated with the concentration of abscisic acid, salicylic acid, malate and fumarate, and tyrosine in salinized fruits. Moreover, a high accumulation of sodium was detected in the fruits of the plants most visited by pollinators, while rootstock genotype-specific responses were found for nitrogen and potassium concentrations. In addition to the known effect on yield, these findings underscore the synergic interactions between rootstocks, pollinators, and environmental stressors on tomato fruit composition.

Stable pollinator communities in different white clover populations suggest potential win-win scenarios for crop yield and biodiversity

Compared to monocultures, intercropping systems offer many agronomic benefits, including higher yield stability. In this study, we assessed whether cropping systems that are beneficial for yield stability are also beneficial for pollinator communities and whether the effect is modulated by the landscape type. Using a replicated block design in one heterogeneous and one homogeneous agricultural landscape, we studied the pollinator communities in eight populations (i.e., genotypes) of white clover (Trifolium repens) grown as a monoculture or as a two-species mixture (together with perennial ryegrass, Lolium perenne) or three-species mixture (together with perennial ryegrass and chicory, Cichorium intybus). We recorded 1486 honey bees and 1254 wild pollinators belonging to 46 species. Bumble bees were the most abundant wild pollinators (49.6 %), followed by hover flies (23.4 %), and non-Bombus wild bees (21.5 %). Lepidoptera accounted for only 5.4 % of the wild pollinators. We found a higher species richness and abundance of wild pollinators in monocultures than in two-species mixtures, but white clover population did not influence pollinators. Moreover, species richness and abundance were also higher in the homogeneous landscape than in the heterogenous one. Most species were foraging on white clover. However, 18 species (39.1 %, n = 18/46) were recorded foraging on chicory and/or weeds, and ten of these wild pollinator species were never recorded on white clover. Our study highlights that diverse pollinator communities require both abundant floral resources and diverse plant communities, that their needs are not in conflict with the goal of achieving yield stability, and that the landscape type can modulate the effect of the cropping system. Moreover, the lack of pollinator preference for different white clover populations suggests that farmers can select mixtures that enhance yield stability without negatively affecting pollinator communities. Overall, these results highlight that intercropping systems comprising several plant species and plant genotypes can guarantee yield stability without compromising the pollinator community, showing that win-win situations for farmers and biodiversity are possible.

Economic foraging in a floral marketplace: asymmetrically dominated decoy effects in bumblebees.

While most models of decision-making assume that individuals assign options absolute values, animals often assess options comparatively, violating principles of economic rationality. Such 'irrational' preferences are especially common when two rewards vary along multiple dimensions of quality and a third, 'decoy' option is available. Bumblebees are models of decision-making, yet whether they are subject to decoy effects is unknown. We addressed this question using bumblebees (Bombus impatiens) choosing between flowers that varied in their nectar concentration and reward rate. We first gave bees a choice between two flower types, one higher in concentration and the other higher in reward rate. Bees were then given a choice between these flowers and either a 'concentration' or 'rate' decoy, designed to be asymmetrically dominated on each axis. The rate decoy increased bees' preference in the expected direction, while the concentration decoy did not. In a second experiment, we manipulated choices along two single reward dimensions to test whether this discrepancy was explained by differences in how concentration versus reward rate were evaluated. We found that low-concentration decoys increased bees' preference for the medium option as predicted, whereas low-rate decoys had no effect. Our results suggest that both low- and high-value flowers can influence pollinator preferences in ways previously unconsidered.

Short Communication: Habitat preferences of epiphytic orchids and potential pollinators in Sumber Pawon Forest, Kediri District, East Java, Indonesia

Abstract. Putra SRT, Trisnawati I. 2024. Short Communication: Habitat preferences of epiphytic orchids and potential pollinators in Sumber Pawon Forest, Kediri District, East Java, Indonesia. Biodiversitas 25: 2780-2787. Sumber Pawon Forest, a unique and biodiverse ecosystem in Kediri, Indonesia, is home to approximately 30,000 orchids (family Orchidaceae), which can grow terrestrial or as epiphytes. A diversity of different taxa has been recorded as orchid pollinators. The distribution of epiphytic orchids in this forest is determined by habitat preferences including vertical distribution zone and host tree's characteristics. This research, conducted in the captivating Sumber Pawon Forest, aims to determine habitat preferences influencing the abundance of epiphytic orchids and provide a review of potential epiphytic orchid pollinators. The data were collected by systematic sampling method. Analysis of epiphytic orchids' habitat preferences was done using the ordination method. The study found 3 epiphytic orchids and 5 species of host trees, revealing new insights into their distribution. Epiphytic orchids include Cymbidium sp., Dendrobium crumenatum, and Rhynchostylis retusa. The host trees include Alstonia scholaris, Artocarpus elasticus, Bischofia javanica, Ficus elastica, and Samanea saman. Epiphytic orchids were mainly found in zone 4 rather than in zone 5. The characteristics of host trees, which are preferentially selected by epiphytic orchids, include tree height (ranging from 28.65 to 33.65 m), large DBH (ranging from 165.61 to 175.80 m), and closed canopy cover (ranging from 51 to 75%). One of the pollinator taxa (named Hymenoptera) was found to pollinate epiphytic orchid species, adding to our understanding of their ecological interactions.

Pollinator-assisted plant phenotyping, selection, and breeding for crop resilience to abiotic stresses.

Food security is threatened by climate change, with heat and drought being the main stresses affecting crop physiology and ecosystem services, such as plant-pollinator interactions. We hypothesize that tracking and ranking pollinators' preferences for flowers under environmental pressure could be used as a marker of plant quality for agricultural breeding to increase crop stress tolerance. Despite increasing relevance of flowers as the most stress sensitive organs, phenotyping platforms aim at identifying traits of resilience by assessing the plant physiological status through remote sensing-assisted vegetative indexes, but find strong bottlenecks in quantifying flower traits and in accurate genotype-to-phenotype prediction. However, as the transport of photoassimilates from leaves (sources) to flowers (sinks) is reduced in low-resilient plants, flowers are better indicators than leaves of plant well-being. Indeed, the chemical composition and amount of pollen and nectar that flowers produce, which ultimately serve as food resources for pollinators, change in response to environmental cues. Therefore, pollinators' preferences could be used as a measure of functional source-to-sink relationships for breeding decisions. To achieve this challenging goal, we propose to develop a pollinator-assisted phenotyping and selection platform for automated quantification of Genotype × Environment × Pollinator interactions through an insect geo-positioning system. Pollinator-assisted selection can be validated by metabolic, transcriptomic, and ionomic traits, and mapping of candidate genes, linking floral and leaf traits, pollinator preferences, plant resilience, and crop productivity. This radical new approach can change the current paradigm of plant phenotyping and find new paths for crop redomestication and breeding assisted by ecological decisions.

Polyploidy‐induced floral changes lead to unexpected pollinator behavior in Arabidopsis arenosa

The paradox between the ubiquity of polyploid lineages in plants and the early obstacles to the establishment of polyploids is a long‐studied yet unresolved question in evolutionary biology. It is assumed that to successfully persist after emergence, newly formed polyploids need to display certain fitness advantages and show a certain extent of reproductive isolation with their diploid progenitors. In this study, we tested whether immediate floral changes following polyploidization can improve pollinator visitation and enable pollinator preference leading to assortative mating, i.e. build a premating reproductive barrier between diploids and polyploids. For this purpose, we generated synthetic tetraploids of Arabidopsis arenosa and measured insect visitor behavior on diploids and synthetic tetraploids. We found that the increased floral size that accompanied polyploidization did not lead to a measurable increase in visitor preference, with insects visiting diploid and tetraploid plants at equal frequency. Despite this observation, tetraploids set more fruits than diploids, suggesting a positive impact of polyploidization on pollen transfer via other means. In addition, polyploidization did not lead to assortative mating but instead promoted interploidy pollen exchange, since visitors preferentially switched between cytotypes rather than preferring one. Consistent with this switching behavior, most of the progeny from tetraploid plants were triploid. Our data suggest that polyploidization has an immediate impact on mating in plants, but in a more complex way than has been assumed previously.

Intensive pasture management alters the composition and structure of plant-pollinator interactions in Sibiu, Romania.

Land management change towards intensive grazing has been shown to alter plant and pollinator communities and the structure of plant-pollinator interactions in different ways across the world. Land-use intensification in Eastern Europe is shifting highly diverse, traditionally managed hay meadows towards intensive pastures, but few studies have examined how this influences plant-pollinator networks. We hypothesized that the effects of intensive grazing on networks will depend on how plant communities and their floral traits change. We investigated plant and pollinator diversity and composition and the structure of plant-pollinator interactions near Sibiu, Romania at sites that were traditionally managed as hay meadows or intensive pastures. We quantified the identity and abundance of flowering plants, and used transect walks to observe pollinator genera interacting with flowering plant species. We evaluated the effects of management on diversity, composition and several indices of network structure. Pollinator but not plant diversity declined in pastures and both plant and pollinator taxonomic composition shifted. Functional diversity and composition remained unchanged, with rather specialized flowers having been found to dominate in both hay meadows and pastures. Apis mellifera was found to be the most abundant pollinator. Its foraging preferences played a crucial role in shaping plant-pollinator network structure. Apis mellifera thus preferred the highly abundant Dorycnium herbaceum in hay meadows, leading to hay meadows networks with lower Shannon diversity and interaction evenness. In pastures, however, it preferred less abundant and more generalized flower resources. With pollinators being overall less abundant and more generalized in pastures, we found that niche overlap between plants was higher. With both hay meadows and pastures being dominated by plant species with similar floral traits, shifts in pollinator preferences seem to have driven the observed changes in plant-pollinator interaction networks. We thus conclude that the effects of grazing on pollinators and their interactions are likely to depend on the traits of plant species present in different management types as well as on the effects of grazing on plant community composition. We thereby highlight the need for better understanding how floral abundance shapes pollinator visitation rates and how floral traits may influence this relationship.

Complex floral traits shape pollinator attraction to flowering plants in urban greenspaces

Urban greenspaces are recognized as a benefit to pollinator conservation. Selective planting of attractive flowering plants can improve the conservation value of urban greenspaces. However, the functional traits of flowering plants that moderate pollinator preference merits further study. We analyzed 98 ornamental plants and spontaneous plant species for ten categories of floral and plant traits across twelve parks or campus greenspaces in Wuhan, a megacity located in central China. Our results revealed that: (1) Plant species vary enormously in their pollinator visitation rate. (2) For Lepidoptera, the number of individuals to the plot was lower for disk/bowl-shaped flowers than other flower shapes, and it was negatively corelated with corolla tube length. The number of Diptera individuals to the plot was higher for white, red/pink and yellow/orange flowers than blue/violet flowers. (3) Honeybees preferred exotic annual/biennial herbaceous species, with disk/bowl and flag flowers. Solitary bees preferred horizontal, lip or flag flowers. Diptera most frequently visited upward-facing, yellow/orange flower heads and Lepidoptera preferred horizontal, funnel-shaped flowers or flower heads. Blue/violet flowers and a diverse floral orientation were preferred by most pollinator groups. We recommend planting native woody plants (Nandina domestica, Thymus quinquecostatus, Lagerstroemia indica, and Tamarix austromongolica) and attractive exotic plants (Centaurea cyanus, Borago officinalis, Portulaca grandiflora, and Echinacea purpurea) to support multiple pollinator groups. As preferences differ among pollinators, increasing the species richness of flowering plants is conducive to promote overall pollinator diversity.

Beneath the blooms: Unearthing the effect of rhizospheric bacteria on floral signals and pollinator preferences.

The relationship between plants and pollinators is known to be influenced by ecological interactions with other community members. While most research has focused on aboveground communities affecting plant-pollinator interactions, it is increasingly recognized that soil-dwelling organisms can directly or indirectly impact these interactions. Although studies have examined the effects of arbuscular mycorrhizal fungi on floral traits, there is a gap in research regarding similar effects associated with plant growth-promoting rhizobacteria (PGPR), particularly concerning floral scent. Our study aimed to investigate the influence of the PGPR Bacillus amyloliquefaciens on the floral traits of wild (Solanum habrochaites, Solanum pimpinellifoliumand Solanum peruvianum) and cultivated tomato (Solanum lycopersicum), as well as the impact of microbially-driven changes in floral scent on the foraging behaviour of the stingless bee Melipona quadrifasciata. Our findings revealed that inoculating tomatoes with PGPR led to an increased number of flowers and enhanced overall floral volatile emission. Additionally, we observed higher flower biomass and pollen levels in all species, except S. peruvianum. Importantly, these changes in volatile emissions influenced the foraging behaviour of M. quadrifasciata significantly. Our results highlight the impact of beneficial soil microbes on plant-pollinator interactions, shedding light on the multiple effects that plant-microbial interactions can have on aboveground organisms.

Bumblebee responses to variation in pollinator-attracting traits of Vicia faba flowers.

Adaptations that attract pollinators to flowers are central to the reproductive success of insect-pollinated plants, including crops. Understanding the influence of these non-rewarding traits on pollinator preference is important for our future food security by maintaining sufficient crop pollination. We have identified substantial variation in flower shape, petal size, corolla-tube length, petal spot size and floral volatile compounds among a panel of 30 genetically distinct lines of Vicia faba. Using this variation, we found that Bombus terrestris was able to distinguish between natural variation in petal spot size, floral volatile emissions and corolla-tube length. Foragers showed some innate preference for spotted flowers over non-spotted flowers and preferred shorter corolla-tube lengths over longer tubes. Our results suggest that some floral traits may have significant potential to enhance pollinator attraction to V. faba crops, particularly if paired with optimised rewards.

Summer grazing change fitness in a Tibetan lotus

It is believed that grazing has an effect on the functioning and performance of flowers, as well as their association with pollinator preferences and plant reproduction. However, the effects of grazing time on nectar secretion and pollen removal are still not fully understood. We hypothesized that seasonal grazing influences pollinator visitation and pollen removal by altering above-ground biomass and nectar secretion. In this study, we conducted field experiments to measure above-ground biomass, flower number per capitulum and capitulum number per plant, nectar volume and concentration, pollinator visitation of male- and female-phase flowers, pollen removal (e.g., number of pollens exported and deposition on a pollinator body and stigma), seed set ratio, and seed number between summer and winter grazing pastures of Saussurea stella. Our findings demonstrated that summer grazing reduced the above-ground biomass, nectar secretion, and pollinator visitation of male-phase flowers, thereby decreasing pollen export. There was a positive correlation between nectar secretion and above-ground biomass, as well as between pollinator visitation and nectar secretion, the number of pollens exported, and pollinator visitation of male-phase flowers. Experiments involving the removal of leaves revealed that a decrease in above-ground biomass was associated with a decrease in nectar secretion, pollinator visitation of male-phase flowers, and pollen removal. However, plants growing in summer and winter grazing pastures had comparable nectar secretion, pollinator visitation of female-phase flowers, seed number, and seed set ratio. Our results suggested that seasonal grazing influences nectar rewards, pollinator preferences, pollen removal, and male fitness. These findings would shed new light on the influence of herbivores on plant-pollinator interactions in the Tibetan meadow.

Innate preferences of Eristalis tenax L. (Syrphidae) for flower colour, size and symmetry are more intricate than the simple additive model

Abstract Plants have evolved complex flowers that differ in visual traits such as colour, size and shape, to attract pollinators. However, pollinators seem to respond differently to individual traits. Our objective was to unravel the effect of individual traits and their interplay in forming pollinator preferences. We measured the preferences of naive drone flies, Eristalis tenax (Syrphidae), for artificial flowers differing in colour, size and flower symmetry, in controlled conditions to untangle the effects of individual traits on pollinator behaviour. Eristalis tenax showed the highest selectivity for colour, followed by size, and only moderate selectivity in relationship to flower symmetry. Flower colour interacted with flower size, in that yellow colour was generally preferred, particularly when the flowers were large in comparison to other forms. Our results suggest that preferences for flower traits are structured, which might suggest that there have been different evolutionary pressures on individual floral traits.

Intraspecific variation of scent and its impact on pollinators' preferences.

Floral scents shape plant-pollinator interactions. Although populations of the same species can vary in their floral scent, little is known about how this variation affects pollinator visitation. In this study, we compare the scents emitted by buzz-pollinated Solanum rostratum (Solanaceae) in two areas of its distribution (Mexico and USA) and investigate how these differences in scent affect pollinator preferences and attraction. We determined the variation of floral volatile compounds using hexane extraction followed by gas chromatography coupled with spectrometry. We also performed a field cage multiple-choice bioassay and a Y-tube behavioural bioassay using Bombus impatiens. We recorded 13 volatile compounds in floral extracts for plants from both ranges that varied qualitative and semi-quantitatively among populations. We found that in the field cage experiment, bumble bees visited plants from the US populations more frequently than plants from Mexican populations. However, bees showed no difference in preference between extracts from Mexican or US flowers. We conclude that although bees show differential visitation to whole plants of different regions, variation in floral extract alone does not translate into differences in preference by B. impatiens. The potential effects of variation in floral scent on the other native bee pollinators remain to be assessed.

Indirect interactions between pollinators drive interaction rewiring through space

AbstractIn recent years, an extended body of literature has focused on the importance of either temporal or spatial dynamics in shaping the structure of interacting plant and pollinator communities. This improvement from a previously static and aggregated perspective has allowed us to understand many of the ecological processes that shape community assembly. However, fewer are the studies that have simultaneously focused on spatial and temporal dynamics, and even fewer are those that collect data across different habitat types to assess the generality of their findings. Here, we used a dataset collected weekly throughout the full flowering season for two consecutive years and within two contrasting habitat types in N and SW Spain: a mountain grassland area and the understory of sparse pine forests. We evaluated species and interaction persistence through space and time, pollinator fidelity, and turnover patterns in interaction composition while providing a potential mechanistic explanation for the patterns observed. Our results show that although species generalization does not explain species or interaction persistence, moderately generalist species are those showing the greatest fidelity to the subset of plant species they visit through space and time. Further, we find that interaction turnover through time is mostly driven by changes in species composition, while through space it is mostly driven by interaction rewiring resulting from indirect competitive interactions between pollinator species. Our results help to shed light on the potential mechanisms driving community assembly patterns beyond niche or neutral processes by adding within‐trophic‐level interactions that can modify pollinator preferences.

Variation and Natural Heritability of Blueberry Floral Volatiles.

Vaccinium corymbosum (highbush blueberry) in British Columbia relies on honeybee pollination for a reliable fruit set. As floral volatiles may help explain pollinator preference for blueberry, we surveyed components of variation for volatiles using gas chromatography-mass spectrometry (GC/MS). Principal component analysis of GC chromatogram peaks revealed a grouping of cultivars by a biosynthetic pathway that also corresponds with their known pedigree. To identify genetic variance, we identified 34 chemicals with adequate sample sizes. We estimated "natural heritability" (using uncontrolled crosses in natural environments) in two ways: (1) as "clonal repeatability," which is equivalent to broad-sense heritability and is an upper bound for narrow-sense heritability, and (2) "marker-based heritability," which serves as a lower bound for narrow-sense heritability. Both methods indicate that heritability is relatively low, ca. 15%, and variable among traits. This is expected as the floral volatile release is changeable and dependent on environmental conditions. It might be possible to use highly heritable volatiles for breeding.

The Movement Ecology of Mutualism (CSEE/ESA 2022, OOS17)

The Movement Ecology of Mutualism (<scp>CSEE</scp>/<scp>ESA</scp> 2022, <scp>OOS17</scp>)

Ecological Separation in an Ongoing Speciation Event

There are many factors that contribute to speciation events. Pollination is often seen as the biggest driver of speciation particularly when pollinators discriminate against certain traits. This discrimination of pollinators is driven by a variety of plant morphological traits, possibly leading specific pollinators to have a strong plant preference. However, phenological characteristics can serve an important role in separating species. For instance, if two plants differ in flowering time then there will be reproductive isolation between them, which then leads to potential speciation. These biotic and phenotypic influences can act together to rapidly diversify plant lineages. Studying these differences between pollinator preference and phenological differences can be important for predicting gene flow and how speciation events may start to occur. We tested for differences in phenological patterns by completing a series of experiments using two subspecies of rabbitbrush; germination trials, multiple observational field trials, and chemical analysis. This study will provide an understanding of the ongoing diversification events of rabbitbrush. Thereby, contributing to a more general and deeper understanding of how ecological roles, between pollinator and plant, contribute to evolution. It also may answer questions about what makes a species a species or subspecies. The specific focus of this paper will be on germination phenological characters.

Maintenance of andromonoecy in an autogamous species: Superior male function in male flowers of the endangered Sagittaria guayanensis

Andromonoecy is a rare sexual system in plants. The function of additional male flowers in andromonoecious species has been widely discussed; however, few studies have taken offspring fitness into account. In addition, little is known about the mechanisms that maintain andromonoecy in autogamous species. In this study, we compared morphology, pollinator preference, pollen production and export, siring ability, natural siring success, hundred seed dry weight, and seed germination rates between male and hermaphroditic flowers in an endangered autogamous andromonoecious species, Sagittaria guayanensis. Male flowers, which are larger than hermaphroditic flowers, required fewer resources to produce. Pollinators visited male flowers more frequently than they visited hermaphroditic flowers. In addition, pollen production and export were higher in male flowers. Hand pollination demonstrated that siring ability did not differ between flower type. However, the natural siring success of male flowers was triple that of hermaphroditic flowers. The seeds sired by male flowers performed better than those sired by hermaphroditic flowers, with greater dry weight and higher germination rate. In conclusion, male flowers may be superior pollen donors for outcrossing. The maintenance of andromonoecy in S. guayanensis may result from the better performance of male flowers in male function compared to that of hermaphroditic flowers.

Local and Landscape Factors Influence Plant-Pollinator Networks and Bee Foraging Behavior across an Urban Corridor

Given widespread concerns over human-mediated bee declines in abundance and species richness, conservation efforts are increasingly focused on maintaining natural habitats to support bee diversity in otherwise resource-poor environments. However, natural habitat patches can vary in composition, impacting landscape-level heterogeneity and affecting plant-pollinator interactions. Plant-pollinator networks, especially those based on pollen loads, can provide valuable insight into mutualistic relationships, such as revealing the degree of pollination specialization in a community; yet, local and landscape drivers of these network indices remain understudied within urbanizing landscapes. Beyond networks, analyzing pollen collection can reveal key information about species-level pollen preferences, providing plant restoration information for urban ecosystems. Through bee collection, vegetation surveys, and pollen load identification across ~350 km of urban habitat, we studied the impact of local and landscape-level management on plant-pollinator networks. We also quantified pollinator preferences for plants within urban grasslands. Bees exhibited higher foraging specialization with increasing habitat heterogeneity and visited fewer flowering species (decreased generality) with increasing semi-natural habitat cover. We also found strong pollinator species-specific flower foraging preferences, particularly for Asteraceae plants. We posit that maintaining native forbs and supporting landscape-level natural habitat cover and heterogeneity can provide pollinators with critical food resources across urbanizing ecosystems.