How Relationships within the Pollination Network Affect Pollination Efficiency and Seed Abundance

Abstract

Honeybee colony collapse disorder is a pressing ecological concern. The conservation of Apis-mellifera is emphasized due to their pollination services; crop yields are dependent on their efficacy as pollinators. Addressing the weaning population of honeybees has brought efforts in increasing the numbers of managed honeybees to compensate for loss or lack of natural presence. Augmenting a population may seem like a solution but it’s temporal. Managed honeybees themselves are declining. Apis-mellifera is but a single factor within the pollination network. Examining pollination requires linking relationships between its abiotic and biotic components. This mini-review will provide an observation on pollination network beyond Apis-mellifera.

Introduction

General estimates predicting the decline of animal-mediated pollination exists based on the resources that have been or currently exploited in unsustainable rates. From a global perspective, 35% of worldwide crop production, and that includes at least 800 cultivated plants depends on animal pollination1. Pollinators are responsible to a certain degree for the food that we consume, and roughly one-third of our food relies on bee-pollinated crops. Measures like sustainable intensification maybe a solution to prevent pollinator-decline, nonetheless any demand in agricultural intensification results into increase input even if methods for sustainability are applied. A miniscule change in landscape configuration (e.g. expansion) can manipulate pollinator behavior, such as variations in foraging patterns that can lead to a decrease in floral fidelity and reduction in seed counts. The distinction between landscape fragmentation and habitat loss should also be noted. When studies fall short on mentioning which independent variable (i.e. landscape fragmentation or habitat loss) caused a certain outcome, the integrity of the research lessens when singling out independent factors for causation are overlooked. Shaping one component within a pollination network may shift relational patterns between pollinators, plants, and their habitation, leading to a shortage in agricultural output, and thus isolating and analyzing each event is key to also connecting their results with each another.

This paper examines six studies that have compartmentalized interactions between landscape and pollination, agriculture and pollination, and plant and pollinators in non-hydroponic systems. In an attempt to link these associations, this paper observes plant biodiversity, pollinator behaviors, and landscape dynamics in relation to its effect on pollination network relationships and seed abundance, as well as agricultural crop yields. Bee abundance has a strong correlation with wildflower plantings, and isolated patches of small crop developments have entirely dissimilar effect on patches connected with corridors, and at the same time agricultural crop yields are dependent on these pollinators. Though all research falls under the umbrella of pollination, there is little tangible nexus that joins these relationships together. Comprehending the general scope of agricultural ecosystems is important for effectively managing farms, conserving managed and wild pollinators, and generating a sustainable amount of crop harvest.

Pollination Services with Non-Apis mellifera

Humans derive resources and benefit in many ways from ecosystems, and collectively these benefits are known as ecosystem services. Detritivores such as earthworms and dung beetles feed on organic waste and decomposing plants and animals. By breaking down decaying organisms, decomposers save humans valuable time from managing areas worldwide with unwanted detritus. Like detritivores, pollinators provide ecosystem services. Most pollinators are aerial animals (i.e. birds, bees, butterflies, etc.) that fly from flower to flower. Once a pollinator lands on the petals, pollen grains are attached to the stamen and dislodged via movement as the pollinator scrounges for nourishment. And in the next flower visitation, if the pollen is posited on a viable species, it will be transferred to the female reproductive organs starting at the stigma, eventually fertilizing the egg within the ovule. More seed sets results into higher agricultural output.

There is a positive correlation between pollination service and pollinator diversity. Up to 39 out of the 57 major crops have been reported to have an increase in fruit or seed quality or quantity when exposed to more diverse pollinator communities2. According to Brittain’s experiment, removing the presence of non-Apis bees on Apis melifera (western honeybees) within an isolated almond orchard triggered changes in the foraging patterns of western honeybees. 

Generally, almond trees are planted in alternating rows of two or more varieties. Achieving an optimal fruit set requires that pollen must be transmitted between varying rows in almond trees of a separate variety2. When non-Apis bees are temporarily removed from five open orchards, western honeybees sought out almond trees in the same row of the same variety instead of travelling to trees in parallel rows of a separate variety. In turn, this behavior reduces the efficiency of western honeybees as pollinators. The transference of pollen is cut due to limited bee visitations. Brittain’s findings conclude that wealth in pollinator diversity can synergistically increase pollination service through species interactions.

Studies like Brittain opens up the emphasis on pollinator diversity inclusive of non-Apis bees and other invertebrate pollinators. Additionally, Allen-Wardell echoes “moths, flies, wasps, bees, beetles, butterflies, and other invertebrates are critically important for ensuring the effective pollination of both cultivated and wild plants3.” Sustaining successful pollination requires observation on the overall pollinator population. For instance, butterflies have mutual relationships with flowers as much as honeybees. Over time, these mutual relationships develop into a coevolution. The long tubular mouth or proboscis of butterflies guarantees them an entry into the rattlesnake plant’s flowers minute and elongated openings. Bees would have to squeeze in the canal-like formation to retrieve their nutrition, pollen. Unlike bees, butterflies do not need to exert as much effort retrieving their food. Pollination service stretches beyond managed honeybees as pollinators.

Interspecies and Plant-Pollinator Interactions

Horticultural practices in farms such as pollination management include releasing and adding managed honeybees to increase the number of pollinators. However, augmenting the population is not guaranteed to improve crop quality or yield. Outdoor agriculture accounts for many unpredictable factors in pollination networks, and thus farmers should thoroughly examine for interspecific interactions between pollinators before deciding to proliferate the quantity of pollinators. Fundamentally, the fecundity of plants is based on floral fidelity between plant-pollinator relationships, and floral fidelity can be disturbed if pollinators acquire a new way of rummaging for food4.

Similar to Brittain’s research, Brosi temporarily removed a single pollinator species within a functioning pollination network. Unlike Brittain’s methods, Brosi has conducted his experiments using field manipulations in subalpine meadows and not almond orchards, and the species disconnected from the environment is Bombus (bumblebees) and not Apis-mellifera. The study compares a control to a manipulated setting where the most abundant Bombus species is removed. Brosi’s assessment does not dwell on synergistic interactions between varying pollinator-to-pollinator exchange. Rather, the focus is targeted on floral fidelity and plant reproductive function.

When the majority of bumblebees are extracted from the meadow, the remaining pollinators have extended their foraging strategies and thus showed less floral fidelity to particular plant species. The amount of conspecific pollen that is released by individuals decreased as a result in the reduction of floral fidelity4. Keeping a record track of what types of pollinator species exist within the targeted area can be used to test pollinator-to-pollinator interactions, and whether particular interactions are competitive, predatory, symbiotic, mutualistic, parasitic, or of commensalism. Integrating this in pollination management would give overviews if some pollinator species should be taken out or added.

As seen in the studies of Brosi and Brittain, the reproductive function of plants relies on capable pollinators accurately exchanging conspecific pollen between female and male interspecies. Conversely, pollinators also depend on plants for maintaining their own health. The nutrition pollinators consume stems from nectar and pollen they scrounge on floras. Pollinators must maintain constant energy throughout the day, which supports their travelling short to long distances based on availability of food resources5. Williams remark that there have been studies in Europe where wildflower plantings promote wild bee abundance, and there is evidence in North America but little is documented, and hence Williams’s research checks for a variety of wildflower mixes in Florida, Michigan, and California and their impact on wild bee wealth. In each site, six plots are placed, with one being a control. There is an annual basic, annual diverse, perennial basic, perennial diverse, and a mixed of both annual and perennial. In Florida, mixes containing perennial and annuals, including the annual-perennial mix attract the most bumblebees. Perennial mixes attract more bees in Michigan than annual or annual-perennial mixes5. And in California, all types of mixes relatively attract bees. Assessing which type of wildflower mixtures are best for bees will help farmers to establish a stable habitat for pollinators.

Measuring Agricultural Output

Understandably, farmers emphasize a great deal on agricultural production, and generated crop yields. Nevertheless, output would critically decrease if conservation of pollinators were not properly addressed. Discovering a correlation pattern in yearly crop loss and pollinator population without being involved in long-term and on-site case studies is the primary goal of Aizen. The data is already available, and it encompasses 87 important crops based on production and cultivated area gathered from the FAO (Food and Agriculture Organization of the United Nations) from 1961 to 20066. The research utilizes these datasets to quantify the total effect of pollinators on global agricultural production and crop production diversity. The variables assessed are compensation and deficit, the former measures the loss in production and the latter measures the input to mitigate or offset the loss in production. Their results present that there would be 3% to 8% direct crop reduction in the absence of animal pollinators, with developing worlds being more affected6.

The effect on crop production diversity is minimal. The model evidently displays that preserving pollinator abundance is imperative. Fruits and vegetables are regularly being exported and imported in-and-out of United States. As an example, India is the second largest producer of potatoes, a crop that depends on pollination. Potatoes are common in the American diet, and are often listed in most fast-food menu as French fries. From the data Aizen has analyzed, agricultural harvests from developing countries are more susceptible to the dearth of pollinators. The absence of pollinator is overall, an issue of conservation that will affect the majority of agriculture if not moderated soon.

Landscape Fragmentation

When accounting for variables that shape pollination, two central variables come to mind: plant and pollinator. Landscape is not usually accounted as a variable, or even for that matter its contour and form. And in investigations that have measured this variable’s influence on pollination, still, most of them have not separated the terms “habitat loss” and “fragmentation” correctly. These terms are occasionally swapped around due to their shared context consisting of reduction in relation to an area. Though reduction is exhibited by both definitions, the type of reduction is what separates habitat loss from fragmentation and vice-versa. Habitat loss specifies in noting the deficit in land composition and the outcome of biodiversity from this loss, whilst fragmentation demarcates the effects of land configuration but not necessarily a loss in habitat7.

Hadley reviews published work from 1989 to 2009, and only six out of the 303 studies have achieved in separating the effects of fragmentation from habitat loss. From the six-targeted research on fragmentation, the review emphasizes on appropriately tackling fragmentation first and understanding mismatches in spatial scales when it comes to landscapes observed versus landscapes with actual ecological developments of interest. Landscape configuration controls pollinator movements, and isolating landscape configuration as its own independent variable would allow for more clarified research in farming protocols and complex landscapes.

Conclusion

Pollination network is an ecosystem that requires active maintenance and sustainable practices. This review associates six studies focusing on varying independent variables that influence pollination (i.e. landscape and pollination, agriculture and pollination, and plant and pollinators). There are indefinitely more variables that play an integral role in pollination, and like landscape fragmentation or terrestrial patches of farmland, these minute subtleties are weaved into the overall outcome of pollination. Furthermore, this review mainly applies to soil-grown plants in open fields. Other systems of farming may or may not be applicable to the research results surmised in this review. Even if hydroponic environments are not considered, these papers still address pollination as part of the larger biota, and not localized to those areas of observation.

References

1. Nicholls, C. I. & Altieri, M. A. Plant biodiversity enhances bees and other insect pollinators in agroecosystems. A review. Agron. Sustain. Dev. 33, 257-274, doi:10.1007/s13593-012-0092-y (2013).

2. Brittain, C., Williams, N., Kremen, C. & Klein, A. M. Synergistic effects of non-Apis bees and honey bees for pollination services. Proc. R. Soc. B-Biol. Sci. 280, 7, doi:10.1098/rspb.2012.2767 (2013).

3. Allen-Wardell, G. et al. The potential consequences of pollinator declines on the conservation of biodiversity and stability of food crop yields. Conserv. Biol. 12, 8-17 (1998).

4. Brosi, B. J. & Briggs, H. M. Single pollinator species losses reduce floral fidelity and plant reproductive function. Proc. Natl. Acad. Sci. U. S. A. 110, 13044-13048, doi:10.1073/pnas.1307438110 (2013).

5. Williams, N. M. et al. Native wildflower plantings support wild bee abundance and diversity in agricultural landscapes across the United States. Ecol. Appl. 25, 2119-2131, doi:10.1890/14-1748.1.sm (2015).

6. Aizen, M. A., Garibaldi, L. A., Cunningham, S. A. & Klein, A. M. How much does agriculture depend on pollinators? Lessons from long-term trends in crop production. Ann. Bot. 103, 1579-1588, doi:10.1093/aob/mcp076 (2009).

7. Hadley, A. S. & Betts, M. G. The effects of landscape fragmentation on pollination dynamics: absence of evidence not evidence of absence. Biol. Rev. 87, 526-544, doi:10.1111/j.1469-185X.2011.00205.x (2012).

 

 

License

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