Large Pollinators Research Articles

Wild native insects are efficient pollinators of mangoes in the Northern Territory of Australia

Mango is an economically important fruit crop in tropical regions, including parts of Australia. However, the contribution of native flower visitors to mango pollination and fruit set is currently understudied. We studied cv. Kensington Pride (KP) in the Northern Territory (NT) of Australia to assess the overall contribution of insect pollinators to fruit set through pollinator exclusion treatments – open pollination, total pollinator exclusion and large pollinator exclusion (>5 mm). We also compared diurnal patterns in insect visitation with mango phenology and determined the pollination effectiveness and efficiency of flower visitors based on visitation rates, foraging behaviour and pollen deposition. At 45 days after the first pollinator survey, the number of fruits per panicle in open and large pollinator exclusion treatments was not significantly different from one another, despite large pollinator exclusion panicles receiving less than half of the number of insect visitations. Furthermore, open and large pollinator exclusion treatments had 28- and 30-times higher numbers of fruits per panicle than the total pollinator exclusion treatment, respectively, showing the importance of insect pollination. The native stingless bee Tetragonula mellipes was the most frequent visitor (7906 visits, 62.7 %), followed by a hover fly Mesembrius bengalensis (2404 visits, 19.1 %). Tetragonula mellipes had the highest mango pollen loads on their bodies and deposited more pollen grains on stigmas per visit than other flower visitors, and contributed 75.5 % to the mango pollination services, about 4.5 times more than the next most important pollinator (M. bengalensis: 16.8 %). Our results suggest that T. mellipes efficiently pollinate mango flowers in the NT when wild colonies are abundant in the native vegetation adjacent to the crop. Placing T. mellipes hives in the centre of larger mango orchards may increase pollination services and potentially farm productivity by ensuring good pollination towards the centre of orchard blocks.

Forest pollinator richness declines with distance into burned areas

The effects of prescribed fire on forest pollinator communities are complex and incompletely understood. One of the least-studied questions concerns how these organisms are affected by the size, or spatial scale, of fire. We sought to address this by sampling bees (Hymenoptera: Apoidea), butterflies (Lepidoptera), and hover flies (Diptera: Syrphidae) at different distances along 500 m transects into forests burned every three years in the southeastern United States. We found combined pollinator richness to decline significantly with distance, being about 23.9 % lower near the centers of burn units than near the edges, and this did not change with time since fire. These patterns held true when small and large pollinators were analyzed separately, as well as for the richness of bees and butterflies (but not hover flies), and regardless of bee nesting guild. We found no relationship between the abundance of all pollinators and distance. However, the abundance of small pollinators decreased with distance whereas that of large pollinators increased. A competing model provided no support for the alternative hypothesis that the observed effects of distance can be explained by the length of road edges nearby as opposed to distance from unburned habitat. The richness and abundance of all pollinators combined and most taxonomic groups and species analyzed separately increased with increasing canopy openness as well as with increasing plant richness. Although pollinator richness declined with distance into large burns and small species appear to be particularly sensitive, we also found the richness and abundance of pollinators to decrease with time since fire. Our results show that fire can improve local conditions for pollinators but that unburned habitats serve as important refugia or sources of flowers following fire, underscoring the importance of pyrodiversity in managed landscapes.

High Pollination Deficit and Strong Dependence on Honeybees in Pollination of Korla Fragrant Pear, Pyrus sinkiangensis.

Pollination deficits can compromise fruit yield and quality and have been reported in several fruit crops. It is unknown whether there is a pollination deficit in the production of Korla fragrant pear, Pyrus sinkiangensis, in China, and if so, whether this deficit can be mitigated by the use of managed honeybees (Apis mellifera). We assessed insect communities, flower visitation, pollination deficit and honeybee contribution to pear pollination in Korla fragrant pear orchards in Xinjiang, China. Insect communities were monitored using colored pan traps, and pollination deficit was assessed by comparing fruit set with open pollination to that with hand pollination in orchards without beehives from 2018 to 2021. The contribution of honeybees to pollination was assessed by comparing flower visitation, fruit set and fruit quality in pear orchards with and without beehives in 2020 and 2021. In orchards without beehives, wild bees (72%) were the dominant pollinator group in pan traps, followed by honeybees (15%), moths, hoverflies, butterflies and wasps (Vespidae). Fruit set in these orchards was much lower with open pollination (8 ± 2%) than with hand pollination (74 ± 4%). When comparing pollination in orchards with and without beehives in 2020 and 2021, we found that honeybees were responsible for most of the flower visits in orchards with (96%) and without beehives (66%). Wild bees were responsible for 1% and 6% of flower visits in orchards with and without beehives, respectively. Fruit set was significantly higher in orchards with beehives (38 ± 9%) than in orchards without beehives (12 ± 3%), while fruit set and sugar content were positively associated with pollinator visitation rate. The findings reveal a large pollination deficit in Korla fragrant pear orchards, and show that this deficit can be mitigated using managed honeybees.

Stigmas arrangement, reproductive system, and maternal reproductive success in two species of Stigmaphyllon (Malpighiaceae): does pollinator size matter?

Most species of Neotropical Malpighiaceae are pollinated by oil-collecting bees of diverse sizes, but the effect of pollinator size on their reproductive success has still not been addressed in the literature. We performed a comparative description of stigma arrangements, analyzing the reproductive system and reproductive success and assessing pollinator sizes in Stigmaphyllon bonariense and Stigmaphyllon jatrophifolium. We collected flowers in three natural populations, conducting pollinator censuses and captures and performing manipulative experiments to determine the plants breeding system. We analyzed the morphology of stigmas and their receptivity and calculated the perimeter of the triangle formed by the stigmas (ST). Pollinator sizes, potential area for pollen transfer (PAPT), and the frequency of visits were also calculated. Stigma arrangement resulted in inverted triangles, and the ST was smaller in S. jatrophifolium than in S. bonariense. The overlap between ST and PAPT suggests that pollinators of all sizes were efficient in pollinating S. jatrophifolium, whereas only large and very large pollinators where efficient in S. bonariense. Moreover, very large pollinators had the highest visit frequencies. Our results indicated that both species are obligate xenogamous, pollinator-dependent, and present pollen limitation. We observed an increase in reproductive success related to the marked turnover in pollinator assemblage throughout the flowering season. These findings suggest that fruit and seed sets vary according to the context of the pollinators and that large pollinators would have the best performance.

Criteria to select vegetal species for restoration of plant-pollinator interactions in agricultural landscapes of the Pampa grassland (Argentina)

Ecological functions, including pollination services, can be successfully restored in degraded ecosystems. In this study we propose a procedure for selection of target species to be employed in the restoration of plant-pollinator interactions in agricultural landscapes, which is illustrated by a case study located in the Tandilia System, in the Southern Pampa grasslands of Argentina. Based on information from a large pollination network dataset of 12 hills, composed of 172 pollinators and 96 plants (metaweb), we identified the plant species playing a major role in the maintenance of pollination mutualisms. We obtained a ranking of interaction frequency for each of the 96 plant species of the metaweb, and selected native plants that received more than 100 individual flower visitors. The targeted species were evaluated using ten criteria related to ecological, technical and cultural characteristics, and then ranked according to their suitability for use in restoration projects (species rank, SR). From the total number of plant species (96) registered for all sampled hills, we identified a total of 24 plant species that represented 90% of the total interactions and 25% of the plant species recorded in the metaweb. Six of the 24 selected species were excluded since they were non-native, leaving 18 targeted native plant species. The SR value ranged between 2.68 and 8, with a mean of 4.63 ± 1.40. Two genera presented the highest SR values (Eryngium sp. and Baccharis sp.), and are recognized as potential candidates for restoration of other ecosystems. A rank that evaluates plant species capable of rehabilitating plant-pollinator interactions will form a solid basis for planning restoration projects, which are crucial for biodiversity rehabilitation and conservation.

Empidine dance flies pollinate the woodland geranium as effectively as bees.

Most flowering plants species rely on insects for pollination, a successful mutualism allowing them to reproduce over wide areas while flower-visitors are rewarded with food. This association is so conspicuous in the case of bees that other groups of potential pollinators, especially flies, have long been underestimated. However, visitors are not always pollinators. While the importance of flies in plant-visitor networks is now acknowledged, their pollination effectiveness has hardly been investigated. In this study, we assessed the pollination effectiveness of Geranium sylvaticum flower-visitors using single-visit seed set experiments, in a subalpine meadow where flies are predominant. We found that: (i) empidine dance flies were the most frequent visitors of G. sylvaticum; (ii) a single-visit by an empidine dance fly produced the same average number of seeds as a visit by a bee; (iii) large pollinators were more efficient than small pollinators irrespective of their identity. As a conclusion, large empidines were the main pollinators of G. sylvaticum. Considering the high diversity and abundance of flower-visiting fly species, such results showing their ability to be as effective pollinators as bees should encourage further studies to develop a better understanding on their role in plant-pollinator networks.

First record of the genus <i>Spilomyia</i> (Diptera, Syrphidae) from the Oriental region

Spilomyia manicata (Rondani, 1865) is reported as a new genus and species record from India and the Oriental region. A brief diagnosis, images, and comparison with allied species are provided to scientifically validate this new faunal record from the Indian subcontinent and to facilitate its prompt identification. The species shows rare distribution across its range, and various factors pose a threat to the existence of this large pollinator species. Therefore, the documentation of this species assumes significance for devising conservation strategies and sustainable management.

Pollination of Granadilla (Passiflora ligularis) Benefits From Large Wild Insects.

The contribution of wild pollinators to food production has recently been assessed for many crops, although it remains unclear for several tropical crops. Granadilla (Passiflora ligularis Juss), a crop native to the tropical Andes, is one such crop where a gap exists regarding comprehensive knowledge about its pollination system. In a field experiment in the Colombian Andes, we 1) describe flower visitors in terms of visit quantity (visitation rate) and quality (touches of flower-reproductive structures), 2) assess the pollination system by comparing fruit set and fruit weight per flower in three pollination treatments: pollinator exclusion, open pollination, and supplementary pollination, and 3) evaluate pollination deficits (difference between open and supplementary pollination) in relation to pollinator density. We observed 12 bee species visiting granadilla flowers, with Apis mellifera Linnaeus being the most frequent species. However, large bees such as Xylocopa lachnea Moure and Epicharis rustica Olivier touched stigmata and anthers more often. Fruit set and fruit weight per flower were significantly lower in the pollinator exclusion treatment compared to open and supplementary pollination, while the latter treatments showed nonsignificant differences. Pollination deficit significantly decreased with the increasing density of large bees and wasps. Our results illustrate the high dependency of granadilla on wild pollinating insects and highlight the crucial role of large insects to granadilla production. This stresses the need to maintain or increase the density of large pollinators in granadilla production areas, which in turn will necessitate better knowledge on their ecological requirements to inform landscape planning and population-management programs.

Response to Comment on "Cognition-mediated evolution of low-quality floral nectars".

Pyke and Waser claim that our virtual pollination ecology model makes unrealistic assumptions and fails to predict observed nectar concentrations of bat flowers and negative correlations between pollinator body size and sugar concentration. In their comment, crucial model features are misrepresented, misunderstood, or ignored. Sensitivity to the supply/demand ratio explains both the equilibrium concentrations and the selection for lower concentrations by larger pollinators.

The impact of honey bee colony quality on crop yield and farmers’ profit in apples and pears

Despite global interest in the role of pollinators for food production, their impact on farmers’ profit, which determines farmers’ livelihood and land-use decisions, is unclear. Although average values of pollinator benefits are generally assumed, there is potential for large spatial variation among crop species and varieties or among pollinator management strategies, even within the same region and year. We studied how quality of honey bee colonies used for pollination services, which included artificial feeding during winter and pathogen control, affect flower visitation, fruit production, and farmers’ profit in the main apple and pear producing region of Argentina (Patagonia). For apple, high-quality colonies exhibited flower-visitation rates 130% greater than conventional colonies. Indeed, high-quality colonies increased fruit set by 15% (increasing production quantity), seed set and fruit sugar content, and subsequently farmeŕs profits by 70%. For pear, colony quality only affected fruit weight of the Abate Fetel variety, but not that of the Packham’s Triumph variety. Fruits were ∼20% heavier in farms deploying high quality colonies but did not contribute to increase farmers’ profits to the extent that it did for apple. In contrast to studies conducted elsewhere, we did not observe any wild pollinators visiting apple or pear flowers, highlighting the fragility of this conventionally intensified crop production system. We found that such orchard systems can suffer large pollinator deficits affecting farmers’ profit. Given that A. mellifera was the only flower visitor, we could estimate the impact of improving colony management on farmer’s profit without the influence of other pollinators. Our study also shows that variations within pome crops, i.e. apples and varieties of pears, in pollinator benefits can be very large, and that the assumption of global average values to guide local recommendations can be misleading.

The role of ants, birds and bats for ecosystem functions and yield in oil palm plantations.

One of the world's most important and rapidly expanding crops, oil palm, is associated with low levels of biodiversity. Changes in predator communities might alter ecosystem services and subsequently sustainable management but these links have received little attention to date. Here, for the first time, we manipulated ant and flying vertebrate (birds and bats) access to oil palms in six smallholder plantations in Sumatra (Indonesia) and measured effects on arthropod communities, related ecosystem functions (herbivory, predation, decomposition and pollination) and crop yield. Arthropod predators increased in response to reductions in ant and bird access, but the overall effect of experimental manipulations on ecosystem functions was minimal. Similarly, effects on yield were not significant. We conclude that ecosystem functions and productivity in oil palm are, under current levels of low pest pressure and large pollinator populations, robust to large reductions of major predators.

Stigma Sensitivity and the Duration of Temporary Closure Are Affected by Pollinator Identity in Mazus miquelii (Phrymaceae), a Species with Bilobed Stigma.

A sensitive bilobed stigma is thought to assure reproduction, avoid selfing and promote outcrossing. In addition, it may also play a role in pollinator selection since only pollinators with the appropriate body size can trigger this mechanism. However, no experimental study has investigated how the sensitive stigma responds to different pollinators and its potential effects on pollination. Mazus miquelii (Phrymaceae), a plant with a bilobed stigma was studied to investigate the relationship between stigma behaviors and its multiple insect pollinators. The reaction time of stigma closure after touched, duration of temporary closure, and factors determining permanent closure of the stigma were studied when flowers were exposed to different visitors and conducted with hand pollination. Manual stimulation was also used to detect the potential differences in stigmas when touched with different degrees of external forces. Results indicated that, compared to pollinators with a small body size, larger pollinators transferred more pollen grains to the stigma, causing a rapid stigma response and resulting in a higher percentage of permanent closures. Duration of temporary closure was negatively correlated with the speed of stigma closure; a stigma that closed more rapidly reopened more slowly. Manual stimulation showed that reaction time of stigma closure was likely a response to external mechanical forces. Hand pollination treatments revealed that the permanent closure of a stigma was determined by the size of stigmatic pollen load. For large pollinators, the speedy reaction of the stigma might help to reduce pollen loss, enhance pollen germination and avoid obstructing pollen export. Stigmas showed low sensitivity when touched by inferior pollinators, which may have increased the possibility of pollen deposition by subsequent visits. Therefore, the stigma behavior in M. miquelii is likely a mechanism of pollinator selection to maximize pollination success.

Effects of experimentally simulated pollinator decline on recruitment in two European herbs

Summary Pollinator decline causes great concern because reduced pollinator availability may negatively affect plants' seed production and in turn influence seedling recruitment and densities of plant populations. We used a novel experimental approach that simulates pollinator decline to assess the effects of a 4‐year reduction in pollinator availability on reproduction and recruitment in two common European herbs, Centaurea jacea and Leucanthemum vulgare. The experiment strongly reduced visitation rates (by 59%) and seed set (by 23%) in Leucanthemum, but this did not cause reduced seedling recruitment, suggesting that other factors, such as water availability or the existence of a seed bank, are important for recruitment in this population of Leucanthemum. The experiment also significantly reduced visitation rates to Centaurea (by 33%), but did not affect seed set or seedling recruitment. In this species, however, seed set increased with visitation rates and local recruitment increased with seed production, indicating that a consistent pollinator decline may negatively affect Centaurea population densities. Synthesis. Our experiment reduced pollinator availability without artificially affecting quality components of the pollination process. Therefore, this approach may represent a realistic simulation of a pollinator decline. To our knowledge, this is the first study that uses an experimental reduction in pollinator visitation to assess its effects on population recruitment in plants. This study shows that a large pollinator decline may affect population densities, but only in populations where seedling recruitment is limited by seed production. Our results also highlight the importance of going beyond visitation rates and seed production to study the impact of pollinator decline on plant populations.

Reproductive biology and colour polymorphism in the food-deceptive Iris lutescens (Iridaceae)

Among the diversity of pollination strategies, food deception is intriguing because of the lack of rewards offered for the pollination services. Floral food deception has been frequently recorded in orchids; however, there is little evidence for food deception outside the Orchidaceae. One putative non-orchid candidate is the Mediterranean Iris lutescens, which displays an heritable polymorphism for flower colour, with yellow and purple morphs. Colour polymorphism is frequently thought to be maintained by negative frequency-dependent selection, where rare morphs are visited more frequently than common ones. Here, we present data on reproductive biology and pollination ecology of the species in the light of the deceptive pollination strategy and the maintenance of flower colour polymorphism. There was no difference in sex allocation and flowering phenology between morphs, with a blooming period early in spring. Both colour morphs are equally self-incompatible and they depend on insects for seed production. The most common visitors with pollen loads are small and large Apoids. These were observed foraging for non-existent nectar (rather than pollen) on Iris flowers. Most of them appear to learn to avoid Iris flowers as classically observed for rewardless species, and there was no evidence of an advantage for the rare morph. Instead, we found that in some populations, large bee pollinators appeared to prefer the most common morph (positive frequency-dependent selection). Iris lutescens appears to be a hitherto neglected but relevant candidate to investigate deceptive reproductive strategy and selective pressures in generalist plants.

Do French beans (<i>Phaseolus vulgaris</i> L.) grown in proximity to Mt Kenya forest- Kenya- experience pollination deficit?

Yields of commercially important crops in Kenya are often far below their potential. Amongst the possible reasons for such low yields may be the ecosystem degradation that can be expected to have negative impacts on pollinator presence in cropland, and the consequent food security issue for smallholder farmers who depend on these crops for their livelihood. Our study was carried out to assess the potential pollination deficit of French beans (Phaseolus vulgaris L.), a major export vegetable crop in Kenya grown by small-scale farmers. Sufficient pollination of French beans likely results in high seed set and uniform heavier green pods. Such pods get the highest grade while malformed pods are unmarketable, reducing family income. We hypothesized that pollination success was linked to the abundance and diversity of large pollinators, itself associated with the proximity to natural habitats. Flower visitors to French beans were sampled in 2011 and 2012 in ten farmer-managed plots, five within 200 m from the edge of Mt. Kenya forest and five farther away, more than 1000 m. Each plot measured 760 m2 and was planted at the same time, with the “Julia” variety. Flowers were observed for 2 h in each plot once weekly for three weeks at peak flowering from 0900-1100 h in the morning and 1200 – 1400 h in the afternoon on alternate days. Honey bees (Apis mellifera) were the most abundant visitors of French bean flowers followed by carpenter bees (Xylocopa spp.) and leafcutter bees (Megachile spp.). Significantly higher numbers of leafcutter bees were recorded on farms far to the forest. There was no significant difference in honeybee abundance among the study sites, probably because apiaries and wild colonies are located across the landscape. French bean yield was significantly correlated with the mean abundance of carpenter bees in 2011. This suggests the possible occurrence of pollination deficit in French beans where the density of carpenter bees is insufficient, which was reflected by the high variability of yields in the farmland. We advocate that area-wide management and conservation of carpenter bees should be initiated to support French bean farming in the area.

Unravelling the role of mate density and sex ratio in competition for pollen

Mate density and sex ratio are commonly used concepts in pollination biology, but are not always clearly distinguished. Here we propose that mate density should only capture the number of male‐phase flowers in a defined area and ignore female‐phase flowers. Sex ratio is the ratio of male and female‐phase flowers in a defined area and captures female–female competition. We use a spatially explicit simulation model to quantify the effect of variation in mate density and sex ratio for plant–pollinator systems characterized by combinations of high or low rates of pollen loss and deposition from pollinator to stigma and then assess the size of pollination neighbourhoods. In efficient systems with relatively little pollen loss, female–female competition is of overriding importance. In contrast, in wasteful systems with high pollen loss rates, mate density becomes the dominant factor and sex ratio is no longer consequential. These patterns were observed at both landscape and local scales. Systems with low deposition and low pollen loss rates are associated with large pollination neighbourhoods, which decline with increasing deposition and pollen loss rates. These results show that mate density and sex ratio should carefully be distinguished and highlight the complex way in which pollen loss interacts with deposition rate, which has not previously been appreciated.

Temporal variation in pollen dispersal and breeding structure in a bee-pollinated Neotropical tree.

Variation among flowering seasons in the time of flowering, synchrony and length of flowering, and fluctuations in the abundance of pollinators may cause a variation in pollen dispersal distance. In this study, we analyzed the temporal variation in pollen dispersal and breeding structure in the Neotropical tree species Tabebuia aurea (Bignoniaceae) and evaluated pollen dispersal between a population inside the reserve and a patch of isolated individuals on the edge of the reserve, and tested the hypothesis that isolated individuals are sinking for pollen. All adult trees (260) within a population of 40 ha and 9 isolated individuals on the edge of the reserve were sampled, and from these adults, 21 open-pollinated progeny arrays were analyzed in 2 flowering seasons (309 seeds in 2004 and 328 in 2005). Genetic analyses were based on the polymorphism at 10 microsatellite loci. A high proportion of self-pollination found in both flowering seasons indicated a mixed-mating system. The mean pollen dispersal distance differed significantly between the two flowering seasons (307.78 m in 2004 and 396.26 m in 2005). Maximum pollen dispersal was 2608 m, but most pollination events (65%) occurred at distances <300 m. Our results also showed that isolated individuals are sinking for pollen, with high pollen flow between the population inside the reserve and individuals on the edge. These results are most likely due to the large pollinator species, which can potentially fly long distances, and also due to temporal variation in individual fecundity and contribution to pollen dispersal.

Is Pollination at Risk? Current Threats to and Conservation of Bees

Insect pollination is an ecosystem service with high economic value that is mainly provided by bees. However, feral bees and managed honeybees are threatened globally by several anthropogenic factors such as changes in agricultural practices, loss of unimproved grasslands, urbanization, and spread of pathogens. These factors have led to the extinction of many native bees, to a reduction in the number of managed honeybee colonies, and put the nutritional bases for bees at risk. Chronic exposure to insecticides, even when they are appropriately used, may affect the foraging behavior of honeybees, which in turn weakens a colony and makes it more susceptible for diseases. Honeybees suffer from parasites like the Varroa mite, and from several viral and bacterial pathogens, which need to be controlled with great efforts. Climate changes represent future threats that will probably impact native bee populations as well as apicultural practices. Coordinated actions are needed to prevent the global loss of large pollinator populations. Especially the maintenance of plant and bee diversity is very important – as well as basic research on the causes for honeybee colony losses. Together, policy, science, and economy should have a crucial interest in conserving the global pollination service of bees.

STABILITY AND FLUCTUATIONS IN A THREE SPECIES SYSTEM: A PLANT WITH TWO VERY DIFFERENT POLLINATORS

We present a multi-species model of one plant with two nectivore pollinators. This system has mutualism between the plant and the pollinators, and competition for food between pollinators. Both pollinators are different: the large pollinator can consume all the nectar offered by the plant in each visit; it permits the genetic interchange between plants from different patches, so, it avoids self-fertilization problems. The small pollinator consumes only a fraction of the flower nectar but the seeds produced by its pollination are less successful. The model gives different dynamics depending on both the differences between the pollinators' growth rates and the inbreeding effect. Stronger oscillations occur when the growth rates are very different. Paradoxically, a high inbreeding causes an increment in populations. The three species system is biologically stable and the asymmetry between pollinator species results in different roles that enhance the global stability and persistence of the system.

A simple model of bipartite cooperation for ecological and organizational networks

In theoretical ecology, simple stochastic models that satisfy two basic conditions about the distribution of niche values and feeding ranges have proved successful in reproducing the overall structural properties of real food webs, using species richness and connectance as the only input parameters. Recently, more detailed models have incorporated higher levels of constraint in order to reproduce the actual links observed in real food webs. Here, building on previous stochastic models of consumer-resource interactions between species, we propose a highly parsimonious model that can reproduce the overall bipartite structure of cooperative partner-partner interactions, as exemplified by plant-animal mutualistic networks. Our stochastic model of bipartite cooperation uses simple specialization and interaction rules, and only requires three empirical input parameters. We test the bipartite cooperation model on ten large pollination data sets that have been compiled in the literature, and find that it successfully replicates the degree distribution, nestedness and modularity of the empirical networks. These properties are regarded as key to understanding cooperation in mutualistic networks. We also apply our model to an extensive data set of two classes of company engaged in joint production in the garment industry. Using the same metrics, we find that the network of manufacturer-contractor interactions exhibits similar structural patterns to plant-animal pollination networks. This surprising correspondence between ecological and organizational networks suggests that the simple rules of cooperation that generate bipartite networks may be generic, and could prove relevant in many different domains, ranging from biological systems to human society.