Direct And Indirect Ecological Impacts Of Nonnative Bees Biology Essay

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Animal pollination plays an important role in the reproduction and fruit set of many cultivated, flowering crop plants and wild plant communities. Bees comprise an estimated 25,000-30,000 species worldwide, all obligate flower visitors. Animal pollination is effected by many different species ranging from vertebrates (e.g., bats) to invertebrates such as insects and intensity or quality of pollination may be affected if pollinator species change. Introduction of non-native (exotic) pollinators might have an impact on both native plants and pollinator communities. Thus, the introduction of non-native bees may cause direct and indirect ecological impacts.

1. Introduction

The flowering plants (angiosperms), comprise approximately one-sixth of the total number of described species (250,000 species) and insects about two-thirds. These groups thus dominate the flora and fauna of Earth's terrestrial habitats, and interactions between them are dominant components of all terrestrial ecosystems (Buchmann and Nabhan, 1996). One of the most ecologically important of these interactions is that between flowering plants and pollinator insects (Klein et al., 2007). Most of these flowering plants - in some studies estimates are as high as 90% (Kearns et al., 1998) - including many important agricultural species, are pollinated by animals, mainly insects (Daily, 1997); the rest of the angiosperms rely on abiotic agents such as wind or water. Animal pollination plays an important role in the reproduction and fruit set of many cultivated, flowering crop plants (Nabhan and Buchmann, 1997, Kearns et al., 1998, Westerkamp and Gottsberger, 2000) and wild plant communities (Kearns and Inouye, 1997, Larson and Barrett, 2000, Ashman et al., 2004, Kremen et al., 2007). It contributes to the maintenance of plant diversity, in terms of species number, genetic variation and richness of functional groups (Fontaine et al., 2005, Ashworth et al., 2009).

Flowering plants form a mutualistic relationship with their flower-visiting pollinators. Mutualisms are defined as interspecific interactions between two participants, in which partners gain a net benefit (Bronstein, 1994). A competition interaction is one of the well-known instances of ecological and evolutionary consequences of species diversity within mutualistic interactions (Jason and Bruna, 2000, Stanton, 2003, Palmer et al., 2003). When mutualists share the same resource, competition for access to the resources or services its partners provide may be frequent (e.g., competition between pollinators for floral resources) and is important for understanding the mechanisms underlying host use by multiple species (Palmer et al., 2003)

Pollination is defined as the transfer of pollen from the anther (the male part of a flower) to a stigma (female part of a flower) of the same or different flower, thus enabling fertilization to take place (Lovatt, 1997). Self-pollination occurs when the anther and stigma are from the same flower, from different flowers on the same plant, or from flowers on different plants of the same cultivar (Mauseth, 2009) . Cross-pollination is the transfer of pollen from one cultivar to the flower of a different cultivar of the same species. Bees are the main pollinating group in many climate zones and in most geographic regions (Michener, 2000). Bees comprise an estimated 25,000-30,000 species worldwide, all obligate flower visitors. Adding these species to other obligate or facultative pollinators such as flies, butterflies and moths, beetles, and birds, the total number of flower-visiting species worldwide is estimated to be nearly 300,000 (Kearns et al., 1998).

Pollinators are one of the important ecosystem elements and are well known to provide key ecosystem services, specifically pollination, to both natural and agro-ecosystems. An ecosystem is a unit of interdependent organisms that interact with each other and with abiotic factors. Ecosystems are considered functional groups composed of elements (structures) and processes (functions). The ecosystem structures are the biotic components (biological species), which can be organized according to the functions they have in the system (i.e. their trophic level). The ecosystem processes, or functions, refers to mechanistic processes such as decomposition, productivity and nitrogen fixation (De Marco and Coelho, 2004). Ecosystem services are natural functions that benefit human populations (Daily, 1999). These services include soil formation, nutrient cycling, gas regulation, climate regulation, biological control pollination as well as recreation and cultural. Hence, understanding the interaction of pollinators is important to improve our understanding of ecosystem services and functions.

Insect pollinators are thought to contribute between 15% and 30% of the human food supply (Greenleaf and Kremen, 2006) and bees are documented to be the most important pollinating taxo (Potts et al., 2006). However, the bulk of the world's staple foods are wind-pollinated, anemophilous (self-pollinated) or propagated vegetatively (Allsopp et al., 2008). The value of honeybee (Apis mellifera) pollination in the US ranges from $1.6 to $5.7 billion a year (Vergara, 2008), and increased to reach $14.6 billion in 2000 (Morse and Calderone, 2003); in Europe it is estimated to be worth approximately €4.25 billion, and pollination by other taxa worth around €0.75 billion (Potts et al., 2006). For global agriculture, the estimated value is around $200 billion (Kearns et al., 1998).

Animal pollination is effected by many different species ranging from vertebrates (e.g., bats) to invertebrates such as insects and intensity or quality of pollination may be affected if pollinator species change. It is widely documented that pollinators and the services they provide are under increasing threat from anthropogenic sources (Kremen and Ricketts, 2000, Kevan, 2001). Some of the most important threats recognized include: fragmentation of habitat, habitat isolation, agrochemicals, agricultural intensification, parasites, diseases, climate change, introduced non-native plants and competition with managed pollinators (Potts et al., 2006). Threats to managed pollinators such as honeybees are also recognized and some studies reported significant losses due to disease and competition between managed honeybees and Africanised honeybees (Kearns et al., 1998).

Introduction of non-native (exotic) pollinators such as the honeybee, will affect both native plant and pollinator communities. Such effects may be positive or negative for the communities' species. If the efficiency of exotic pollinators, in term of pollen transportation, is more than it in the native pollinator, then native and exotic plants will subsequently increase their fruit and seeds production compared with native plants not pollinated by the exotic species. On the other hand, if the efficiency of native pollinators is higher than the exotic pollinator in pollinating a specific plant, then this may reduce seed set (Whittaker, 2007).

Honeybees are thought to use less than a third of the available flowering species and substantially fewer species are in use in an intensive manner (Butz Huryn, 1997). Therefore, there are variable impacts of foraging by honeybees depending on the plants used, and subsequently on native fauna that use the same resources. If a minor proportion of pollen or nectar are consumed by honeybees, minimal effects on floral and fauna can be expected; if they consume a substantial amount of these resources, impacts may be more significant (Paton, 1993) (figure 1).

Figure 1. The variable impacts of honeybee foraging on native flora and fauna. Thicker arrows represent a potential for stronger effects (Butz Huryn, 1997).

Some studies assumed that nectar and pollen feeders, especially bees (Hymenoptera: Apoidea) are strongly affected by interspecific competition for the high-quality food resources provided by the floral community to attract pollinators (Eickwort and Ginsberg, 1980, Plowright and Laverty, 1984). It is thought that, on oceanic islands, the impact of the introduced honeybee upon native pollinators might have been more severe, and that most likely because native pollinator faunas on oceanic islands lack social bee species, which are frequently abundant pollinators on the continent (Kato et al., 1999). However, even in Europe, where A. mellifera is a native species, species richness and abundance of wild bees might have affected by invasion impacts of high local densities of A. Mellifera (Walther-Hellwig et al., 2006).

An increase in competitive effects may occur after: (i) the introduction of new competitors, (ii) changes in environmental conditions, and (iii) increased abundance of a competitor. The introduction of non-native pollinators may cause direct and indirect ecological impacts. The direct impacts include competition for floral and nesting resources with native organisms; indirect impacts include the transmission of parasites and/or pathogens to native organisms, and changes in pollination systems of native and exotic floral communities (Nagamitsu et al.).

2. Direct impacts of honeybees:


Competition between honeybees and wild bees (interspecific competition) is thought to be a key factor in structuring foraging communities on flowers (Corbet et al., 1995, Denno et al., 1995). Thus, honeybees may compete with native bees for resources, leading to reduced species diversity of pollinators, especially when resources are limited. Interference competition occurs when an organism physically excludes another from an access to food sources. Exploitative competition occurs when reduction of resources by one organism leads it to deprive others of the benefits to be gained from those resources (Denno et al., 1995).

2. 1. 1. Interference competition

While most studies support the fact that interference competition by aggressive exclusion does not frequently occur between honeybees and native insects during foraging (Jha and Vandermeer, 2009), an extremely rare study reported aggression behaviour by Apis toward other bees (Butz Huryn, 1997). However, interference by honeybees during robbing has been recognized under certain conditions. In Japan, Sakagami (1959) reports aggressive interactions between introduced A. mellifera and native Apis cerana during the flower dearth period of autumn since all the A. cerana workers were expelled within 2 days by A. mellifera. A. cerana frequently attacks A. mellifera, but A. melliferas was found to be more resistant to hive robbing than A. cerana. This interaction is widely cited to be evidence for interspecific aggression by honeybees by many authors, and it may the behaviour responsible for the reduction in population size seen for A. cerana in Japan (Butz Huryn, 1997). Aggressive behaviour of some other species of bees such as stingless bees has been recognized. For example, Johnson (1981) studied the aggressive defence of two stingless bee species, Trigona silverstriana and Trigona corvin,g and found that T. silverstriana had almost completely excluded T. corving within three hours of the start of the experiment.

2. 1. 2. Exploitative competition

The introduced honeybee is an example of a species that can compete with native bees for floral resources. Honeybees Apis mellifera might competitively displace native pollinators from both floral resources and geographic areas (Roubik, 1978). Nevertheless, the degree to which this introduced species modifies native communities remains debatable, reflecting ongoing uncertainty over the results of the resource competition as a mechanism responsible for population changes of native pollinators (Thomson, 2004).

Honeybees begin foraging at lower temperatures than most other pollinators and have first use of most floral resource. This behaviour in foraging activity gives the introduced honeybee an advantage in any competitive interaction, particularly if floral resources are available mainly in the morning before temperature rises (Roubik, 1978). For some plants, honeybees can remove up to 30-90% of the nectar and pollen from flowers before native bees start foraging (Lindenmayer, 2005).

Several studies have indicated that introduced honeybees decrease the foraging success of native pollinators as a result of competition for resources. For example, Ginsburg (1983) in New York suggested that interspecific competition between honeybees and native bees affects the distribution of foragers on flower clusters of various sizes, and was greater in the spring. Paton (1993) also found interspecific competition between honeybees and Australian native bees and reported that native bees spend twice as long collecting food in the absence of honeybees, implying that the net effect of introducing honeybees might be to increase the numbers of native bees working flowers at one time. Moreover, Roubik et al. (1986) have documented a direct competition for pollen or nectar between African honeybees and native stingless bees in Panama. Thomson (2004) in California demonstrated negative effects of non-native honeybees on native bumblebees. She found that proximity to honeybee hives significantly reduced the foraging rates and reproductive success of Bombus occidentalis colonies. Thomson (2006) found significant niche overlap between foraging preferences of native bumblebees and introduced honeybees, which was as high as 80- 90% during periods of resource scarcity. Schaffer et al (1979) studied competition among three species of bees (Apis mellifera, Bombus sonorus, and Xylocopa arizonensis) on several habitats of Agave schottii in Arizona. They found that abundance of Apis was greatest at the most productive habitat, Bombus at intermediate stands and Xylocopa at the least productive habitat. (Benest, 1976) studied foraging by honeybees and three species of bumblebees in France. Data show bees of the same species foraged together on one flowers, but bees avoided mixed-species foraging on the same flower, and honeybees are more tolerant of joint foraging than are bumblebees. Paini et al. (2005) have performed a replicated Before-After Control-Impact (BACI) experiment to study the putative impact of feral honeybees on an undescribed species of Australian solitary bee (Megachile sp. M323/F367), and they found a large resource overlap occurred between the two species.


Although the above studies show that honeybees have substantial overlap in resource use with some native pollinators, it is hard to confirm the importance of resource competition as a limiting process for population changes without evidence of population-level changes in natural habitats. Yet, no clear evidence has been found of long-term declines of native bees due to competition with non-native honeybees in natural habitats (Roubik and Wolda, 2001). This may be due to the difficulty of carrying out convincing studies of competition between such mobile organisms. The only way to clearly examine the effect of competition for floral resources as the limiting factor for the abundance of natives is by artificially manipulating the introduced bee species, and the population size of native species is then noted. If there is a significant increase in the population size in the absence of exotic bees, then competition is occurring. This task is very hard to accomplish (Goulson, 2003).

An alternative technique is to study the correlation between patterns of diversity of native bees and abundance of exotic bees without manipulating their distribution. Kato et al. (1999) studied oceanic islands in the northwest Pacific, and found that honeybees were dominant and native bees were rare or absent on islands. Aizen & Feinsinger (1994) related the fragmentation of forests in Argentina with a decline in native pollinators and an increase in honeybee populations. Thomson (2004) in California found that proximity to honeybee hives significantly reduced reproductive success of Bombus occidentalis colonies. Pleasants (1981) reported negative correlations between Apis and bumblebee abundance. Not all studies, however, support this hypothesis. For example, Steffan-Dewenter and Tscharntke (2000) demonstrated that there is no significant correlation between interspecific competition by honeybees and the abundance and species richness of wild bees. Minckley et al. (2003) also reported no negative impact of number of honeybees on species richness and abundance of all native bees in the deserts of North America.

Therefore, drawing conclusions from these studies is problematic due to the conflicting results, and the lack of indisputable evidence that introduced bees have had a significant impact, via competition, on a population of native pollinators.

Although the different assessments by which competition between honeybees and native bees can be measured, such as floral resource overlap, visitation rates and nest sites, are indirect and might not result in a detrimental impact on native bees being detected, investigating these indirect measurements of competition is nevertheless valuable, as they indicate the potential for competition between honeybees and native bees. The only way to determine a negative impact unequivocally, however, is by assessing direct measurements such as individual survival, fecundity or population numbers (Paini, 2004) (Fig. 2).

Figure 2. Shows the different measurements that have to be assessed to determine whether competition is occurring between honeybees and native bees. Although all these measurements can used to determine competitive incidence, only measurements 4a - c can cause a negative impact on native bees, whereas measurements 1-3 have either no impact or a negative impact on native bees (Paini, 2004).

Mechanisms for avoiding interspecific competition

Many authors concur that the response of wild bees to the presence of honey bees may differ among different species of wild bees and they use different mechanisms for competition avoidance (Pleasants, 1981, Eickwort and Ginsberg, 1980, Walther-Hellwig et al., 2006) .

Environmental Heterogeneity and Trade-Offs.

Results from previous experiments suggest that resource partitioning among species may be a common foraging strategy that lessen interspecific competition for resources and that facilitates the subordinate species to coexistence (Brown and Wilson, 1956, Pianka, 1973, Friedlaender et al., 2009, Bowers, 1982). And competitors may partition their resources in at least three levels of variation: spatial, temporal, and/or floral. For example, (Mayfield, 1998) showed experimentally that each one of the two main insect visitors of Chapmannia floridana plant was found to forage on different vegetation densities and sites. In an experiment to determine whether resource utilisation by 2 species of bumblebees is altered by the presence of the other species, (Inouye, 1978) reported that each bumblebee species significantly foraged on a different flower species.(Heinrich, 1976) found that patterns of resource utilization in the guild of bumblebees were associated with differences in the tongue length. Flowers with short corolla were visited mainly by short-tongued bumblebees and less visited by long-tongued one and those with deep corolla were visited primarily by long-tongued bumblebees. Moreover, (Graham and Jones, 1996) found that ,among 2 species of bumblebees, the larger one Bombus appositus were more frequently visiting Delphinium barbeyi while the smaller one, B. flavifrons, preferred Aconitum columbianum. B. appositus gained more nectar from their preferred plant while there was no significant difference in nectar gained for foraging B. flavifrons on either plant. Therefore, they suggested that B. flavifrons were competitively displaced from the other floral resource by B. appositus. (Morse, 1977) demonstrated that Bombus ternarius workers avoided competition with B. Terricola by shifting their foraging location to a distal part of flower clusters. Furthermore, (Ginsberg, 1983) have found that bees species tend to partition the available floral resources, mainly by foraging at different periods of the season.

Patch Dynamics and Competition-Colonization Trade-Offs.

Patch dynamics, in which new patches of a limiting resource are continually being created (e.g. adding new floral resource into territorial habitat, or opining new flowers, in local habitat), are likely to facilitate coexistence within competing species (Kotler et al., 1993, Stanton et al., 2002, Palmer et al., 2003). This may result from differential abilities among species to explore the new resources. For example (Roubik, 1980) suggested that the relatively larger body size of Africanized honeybee allow them to discover new resource sooner than that of the social stingless bees, Trigona spp. (Nagamitsu and Inoue, 1997) found a differentiation, among aggressive social bees, in the ability for finding new resource in, the more aggressive bees discover new baits slower than the less aggressive species. Furthermore, in a study of comparative foraging behaviour of six stingless bee species (Hubbell and Johnson, 1978) also found that the rapidity to discover new food was different among species, and it was as follow: Trigona fulviventris > T. silvestriana > T. testaceicornis > T. Frontalis > T. buyssoni > T. Fuscipennis.

Effects of introduced species on plant pollination and plant productivity:

Many plants that reproduce sexually relay on animals for cross-fertilisation. To achieve successful cross-fertilisation, a plant must receive an adequate pollinator visits, quantitatively and qualitatively. For successful pollination, Pollinator visits should ideally lead to removal and deposition of a viable, compatible and a sufficient quantity of pollen grains at the proper period of pollination, i. e., the period of stigmatic receptivity. Removal and deposition pollen, in the animal-pollinated plants rely, mostly, on the foraging behaviours of the pollinator (e.g. visitation rate, handling time).

Despite the fact that few studies have been concerned with the impacts of the competition between the animal pollinators on plant reproductive success (Paton, 1993, Carmo et al., 2004), data from several studies, cited above, reported that honeybees have impacts on the foraging behaviours and/or population of other pollinators. Therefore, changing in the foraging behaviours or population size due to presence of the competitor may, in turn, affect pollination and fertilization by modifying plant-pollinator interactions and consequently plant reproduction success. For example (Irwin and Alison, 1999) found that depleting floral resource by a nectar-robbing bumble bee, Bombus occidentalis, may change the behaviour of legitimate pollinators, and subsequently, the pollination and fertilization of Ipomopsis aggregate plant. (McDade and Sharon, 1980) also, reported that nectar robbers have adverse effects on fruit and seed set levels, by damaging plant reproductive structures. Moreover, (Reddy, 1992) found that pollination and fruit set of 70% of the flowers of Vitex negundo were affected by wasps visitation. (Roubik, 1982) revealed that Robber bees, Trigona ferricauda aggressively deter sole pollinator of Pavonia dasypetala, the Hermit Hummingbird, leading that to reduce their visitation, and thus, reducing sedd production of the plant. (Paton, 1993) reported that increasing number of honeybees competitively excludes the more effective pollinator, honeyeaters, from patches of Callistemon leading to remarkably decreased fruit production. (Carmo et al., 2004) reported that introduce honeybees have a detrimental effect on fruit and seed production of a Trigona ferricauda tree although the plant's attractiveness or affecting resource availability to its native pollinator, Eufriesea nigrohirta, did not affected.

3. Indirect impacts of honeybees:


Introduced pathogens have been recognized as a significant threat to biodiversity, and are associated with the extinction or dramatic decline of various wildlife populations (Altizer et al., 2003). In eusocial insect colonies, the vigour of the pathogen depends on both the ability to infect and spread between insects within a colony and on the ability to spread to new individuals in other colonies. Vertical transmission is thought to be the most important way of pathogen infection of new colonies (Fries and Camazine, 2001). Horizontal transmission of pathogens can occur through a number of routes such as: contact between individuals (or between individuals and infectious materials) during robbing, contact between infected and uninfected individuals from different colonies during foraging, contact with infectious material from the environment, such as flowers (Fries and Camazine, 2001). Due to the behaviours of bees foraging, pollinators could run the risk of acquiring infections if pathogens can be horizontally transmitted through shared use of flowers (Durrer and Schmid-Hempel, 1994).

Species introduced to new regions are likely to transport many pathogens (Torchin et al., 2003). Consequently, for example, the honeybee diseases chalkbrood, caused by the fungus Ascosphaera apis, foulbrood, caused by the bacteria Paenibacillus larvae, the microsporidian Nosema apis, and the mite Varroa destructor now occur throughout the world (Goka et al., 2000, Goulson, 2003) discovered that the commercially introduced colonies of European bumblebees are infested with a European race of the endoparasitic mite Locustacarus buchneri. Small hive beetles, Aethina tumida, are reported to have been transported into California, North America with the transport of honeybee hives, where they serves as a potential threat to native bumblebees colonies (Evans et al., 2000). Furthermore, as reviewed by Goulson (2003), the parasitic nematode and three mite species hosted by bumblebees in New Zealand are thought to have come from the U.K. with the imported bees. In Europe, bumblebees (Bombus. pascuorum) has been infected by a honeybee pathogen, deformed wing virus (DWV), raising the concern of transmission of viruses from introduced honeybees to native bumblebees and the serious threat this may pose to bumblebee populations (Genersch et al., 2006). On the other hand, not all of the honeybees and other bee diseases are cross-infective. For instance, in the case of Nosema species, Nosema apis infects honeybees but not bumblebees, while Nosema bombi does not infect honeybees but is a pathogen for bumblebees (Koppert Biological Systems, 2006). Also, the understanding of the susceptibility of native bees to the parasites and pathogens that have been transmitted by non-native bees is still weak (Goulson, 2003).

Table II. Evidence of pathogen/parasite transmission from non-native Bombus and Apis species imported for commercial crop pollination.

4. Conclusion and future perspectives

Honeybees have been shown to display a competitive interaction with several bee species for floral resources such as nectar and pollen. Interspecific competition interactions with honeybees have an effect on foraging success of native pollinators. Honeybees might also competitively displace native pollinators from both floral resources and geographic areas. In addition, honeybees do not use interference competition during foraging, although robbing behaviour may take place under certain condition. Although, species richness and abundance of wild bees might have been affected by the invasion of A. mellifera, there is no incontrovertible evidence, however, to indicate that the introduction of honeybees has caused decreased population sizes or extinction of any native pollinators.

Despite the fact that parasites and pathogens are one of the causes of pollinators decline worldwide, and that introduced bees may transmit pathogens to native pollinators, susceptibility of native bees to the parasites and pathogens that have been transmitted by non-native bees is still ambiguous. Yet, there is no clear evidence that enemies carried by introduced bees have impacted native bee populations. In contrast, Donovan (1980) concluded that introduced bees (leafcutting bees) are attacked by native bee enemies, but that the converse was not reported. However, the absence of experimental evidence does not necessarily mean that populations or ecosystem processes are not affected by introduced species.


In this study I will test the hypothesis that introduced honeybees affect wild pollinators, pollination and plant reproduction by modifying foraging behaviour of wild pollinators through the competition, to understand the community ecology, and its Impacts on ecosystem function and community structure.

Objectives of the work

The overall purpose of this study is to determine the competitive impacts of honeybees on wild pollinators, practically, bumblebees; potential (impact) consequences this may have on the functioning of pollination and plant productivity. A variety of experimental approaches will be used to identify the effects of honeybees on native bee abundance and foraging behaviours and the dynamic of plant pollination.

Other possibilities:

Examine whether honeybees can transmit pathogens and/or parasites to bumblebees and vice versa. This goal will be achieved by monitoring the bees before and after interact with each other. Visual test and some molecular techniques, i.e., RT-PCR may be used for this purpose.

A number of diagnostic techniques will be used to determine the presence of pathogens or parasites

transmission pathogens

For nosema, you usually just do a visual test

A number of diagnostic measures are available to determine the presence

and extent of varroa infestations

focus on the introduction of pathogens by commercial bees into an established population of wild bumble bees, and the subsequent horizontal transmission of infection among foraging workers.

monitored wild bumble bee populations near greenhouses for evidence of pathogen

examine bees before and after interact with each other

transmission from commercial hives would infect

Visual test and some molecular techniques may be used in this purpose


In this study I will use bees manipulation greenhouse experiments and field experimental approaches to answer the following questions:

How do honeybees interact with wild bees, particularly bumblebees?

Do honeybees competitively affect bumblebees foraging behaviours.

Does experimental increase in the density of honeybee colonies will affect bumblebees foraging behaviours?

Does the competition outcome purely due to inter-specific competition, or intra-specific competition between bumblebees do involved?

As a factor may influence the outcome of competition, does competition between floral resources traits affect the interaction between honeybees and bumblebees?

Will competition interaction between pollinators affect plant-pollinator interaction? And in turn, affect pollination and seed set.

Does proximity to honeybee hives affect wild bees' abundance and foraging behaviours?

Dose the proximity to the hives affect pollination services provide by bumblebees?

Proposed methods

I will include the following measurements to test the impacts of honeybees on bumblebees foraging behaviours and abundance , as these measurements should be affected as a result of competition (ref1, ref2, ref3, ref4, ref5 , , )

Visitation rates = the total number of pollinators observed per a given observation period. I will consider a flower to have visited if a bee will be seen to collect pollen and/or nectar. Measurements of visitation rates can give valuable insight into the interaction between pollinators; and amongst pollinators, plants and subsequent seed set.

Handling time = the time spent visiting individual flowers. I will measure handling time by direct observation using stopwatch or by filming the bees with a video camera while speaking into the camera tape.

Forager abundances. The mean number of forager per flower, instead of the mean number of foraging per square metre at each patch point will be used in analyses of forager abundance. Thus abundance here is not comparable to population size but is a measure of activities of bees at each patch point. (Bee (Hymenoptera: Apoidea) Diversity and Abundance on Cranberry in Southeastern Massachusetts ) I will use data from Apis and Bombus forager abundances to test for a negative correlation between the numbers of Apis and Bombus observe.

Richness and abundance of forager at patch level. pan traps

Forager density = (forager abundance)/ (patch size)

Patch size = mean number of flowers in a patch

Pollen deposition.

Air temperature at the period of observations and general weather conditions will be considered.

To achieve different assessments of competitive impacts, I will perform two series of experiments. In the first series of experiments will be conducted in a greenhouse to assess for effects of honeybees density on the bumblebees foraging behaviours based on resource overlap. The second first series of experiments, a field experiments, will be performed to assess the competitive impacts based on correlations between the abundance of competitor pollinators, Apis and Bombus.

Resource overlap experiments:

It has been suggested that Resource utilization by one pollinator may change the visitation pattern of the other pollinator(Strauss and Irwin, 2004, Irwin and Brody, 1999). For the competitive impacts, based on resource overlap, manipulative greenhouse experiments and 'Before-After Control-Impact (BACI)' studies in a greenhouse, to determine whether honeybees do substantially impact upon bumblebees, will be performed. I will study the foraging behaviours of bumblebees before and after introducing Apis nucleus hives. Then I will gradually increase the Apis populations in the addition treatment by adding new Apis nucleus hives with bumblebees held constant.

Resource overlap and avability measurements:

I will quantify availability of floral resources by measuring the number of the flowers at each patch. Overlap in plant use between Apis and Bombus will be quantified based on observations of plant visits by Apis and Bombus using a percent similarity index (after .. .........) as follow: PS=100Ã-Σ min(Ai,Bi), where Ai and Bi are the proportions of all Apis and all Bombus, respectively, observed visiting species i. PS is an index indicating the degree of overlap use, with 100 representing complete overlap in plant use.

Test for intra-specific competition:

To examine the contribution of intraspecific competition within bumblebees to the changes in their foraging behaviours as a result of the competition with honeybees, I will compare the foraging pattern of bumblebees with gradually increased number of bumblebee hives, without honeybees, with their foraging behaviours when compete with honeybees. This experiment is to ascertain whether the intra-specific competition within bumblebees has a significant force in inter-specific competition with honeybees.

Correlation experiments:

For the competitive impacts, based on correlations between the abundance of Apis and Bombus, I will test whether proximity to Apis hives will lead to a corresponding change in Bombus foraging behaviours and forager numbers. I will monitor numbers of Apis and Bombus foragers in a set of floral patches placed along a distance gradient from the Apis hives site in four different directions to reduce the bias of environmental variation, such as wind direction). Since Apis workers have been documented, in general, to forage within a 1-km radius of the hive (Eickwort and Ginsberg 1980 ref↓) , I will locate the patches at varying distances from the Apis hives with maximum distance 1000 m away. One floral patch will locate at each of five distances away from Apis site in four different directions, for a total of twenty floral patches.

Pollen deposition:

One of the consequences of the presence of honeybees is that plants may not receive adequate quantity of pollen to set seed (.....A consequence of both fragmentation and the presence of introduced honeybees is that plants may not be receiving). To determine whether competition between pollinators influences delivering pollination services, pollen grain deposition as a measure of this ecosystem service will be used. Pollen grain deposition was measured by randomly collecting styles from the flowers either from greenhouse or from field experiments, stigmas will be removed from the flowers with a fine forceps. The pollen grains on the stigmas will then stained with basic fuchsin gelatin by press them into fuchsin gelatin previously melted on a glass slide to squash the stigmas and cover with a cover slip. The number of pollen grains will be counted using a compound microscope.

Species sampling

Cluster of pan traps with different colours, matching the colours of the flowers in the plant used in the study will be used, so that the trapped insects are likely to be a visitor to these plants. Pan trap will be placed near each floral patch point. The pans will be filled with water, a few drops of a detergent to reduce surface tension and a small amount of salt to act as a preservative. The traps will be held approximately 0.5 m above the ground. When possible, traps will be emptied every two days. Insects in the traps will be placed in containers containing 70% alcohol for later counting and identification. A cluster of traps will be placed at each floral patch point for a total of twenty clusters. Data from these traps will be used for analysis richness and abundance of bumblebees at the patch level.