The Importance of Pollinator Behaviour and Heterospecific Pollen Deposition to Crop Pollination Service Delivery

Abstract

<p>Different pollinator taxa are needed to pollinate and increase the production of approximately 75% of the leading global food crops. As cropping systems are expanding rapidly, there is an urgent need to better understand pollinator behaviour, interactions between pollinators and pollination service delivery in these systems. This thesis investigates the behaviour and efficacy of pollinators that visit Australian food crops with a focus on almond (<i>Prunus dulcis</i> Mill.), blackberry (Rubus fruticosus L.), blueberry (<i>Vaccinium virgatum</i> Aiton and <i>Vaccinium corymbosum</i> L. interspecific hybrid), and raspberry (<i>Rubus idaeus</i> L.) as model crop species. First, I undertook a systematic review of published empirical literature to synthesise what is known about the interactions and competitive effects of the western honey bee (<i>Apis mellifera</i> L.) on other flower visiting taxa. Second, I observed the foraging behaviour of birds in berry crops, and investigated the efficacy of the brown honeyeater, <i>Lichmera indistincta</i> in pollinating blueberry flowers. Third, I investigated the timing, identity and quantity of pollen collection associated with almond floral abundance and spatial location of individual honey bee hives by analysing pollen samples collected across a flowering season. Fourth, I examined how variations in protected cropping structures (fully netted, partially netted and open orchard blocks), blueberry floral abundance, plant richness in remnant vegetation, and stigma location within blueberry orchard blocks, influence the amount and composition of pollen deposited on blueberry stigmas. Finally, I investigated how multiple visits by one pollinator species or mixed species to the same flower and pollinator species abundance, affect conspecific and heterospecific pollen deposition on blackberry, blueberry and raspberry stigmas.</p> <p>I found that most articles published to date about competition between pollinator species used indirect interactions (when there is no physical contact/encounter between individuals) to infer results. Resource competition and niche overlap between honey bees and other species were the most common metrics included in these studies. Further, while niche overlap is often a proxy for competition, the majority of these studies did not measure resource availability using methods such as floral availability, nectar production/volumes and sugar concentration, or amount of pollen available. The behaviour of honey bees varied with respect to the direction of interactions reported, with honey bees acting both as aggressors and displacing other species, as well as being displaced and impacted by other aggressors. The results of bird observations demonstrated that some bird species may act as both flower visitors and pest control agents in raspberry and blueberry orchards. One species, the brown honeyeater (<i>L. indistincta</i>) was an effective pollinator depositing conspecific pollen grains on blueberry stigmas. The study on honey bee collection of pollen from almond orchards, demonstrated that a large proportion of hives collected non-almond pollen in addition to almond pollen. The weight of almond pollen collected by the hives at each sampling time was positively related to the number of concurrently open almond flowers. However, non-almond pollen richness and abundance was not related to the number of almond flowers but had a positive relationship with the weight of almond pollen collected. There was no relationship between the distance among hives and identity of pollen collected. Yet, three plant families in the study area were found to account for a high percentage of the non-almond pollen collected: Euphorbiaceae, Fabaceae and Asteraceae.</p> <p>Conspecific pollen flow in blueberry orchards was reduced by up to 81% under netting and 36% by partial netting. On blueberry stigmas, we identified a total of 31 morphospecies of non blueberry pollen from 20 plant families. There was no relationship between blueberry stigmatic pollen loads and blueberry floral abundance. Moreover, the composition of non-blueberry pollen on stigmas differed between blueberry blocks under different netting categories. However, there was no relationship between the plant species present in the surrounding remnant vegetation and the composition of non-blueberry pollen on blueberry stigmas. Stigmas located at the edge of the blocks also received a greater amount of both conspecific and heterospecific pollen grains than those within the middle of blocks.</p> <p>Finally, after analysing berry stigmas that received multiple visits, I found that the abundance of conspecific pollen was related to pollinator species and visit number. Stingless bees deposited greater amounts of pollen when compared to honey bees or mixed visits, and the amount of pollen increased following each successive visit. Heterospecific pollen deposition was not related to pollinator species and was only related to visit number in blueberry. Honey bees and mixed visits also resulted in the deposition of a higher richness of pollen morphotypes in blueberry flowers, but only in blackberry flowers was increasing pollen deposition associated with the number of visits.</p> <p>This thesis demonstrates the importance of understanding the behaviours and outcomes of interactions among different species. Moreover, knowledge of crop and non-crop pollen use by different pollinators can inform management practices that support pollinators during crop flowering periods. Modern agricultural practices may impact pollen flow and consequently pollination service delivery. This may be detrimental to the fruit yield and quality of some varieties of pollinator dependent crops, particularly those that are self-incompatible. In conclusion, greater understanding of pollinator behaviour, efficacy and plant-pollinator interactions are required to enhance pollination service delivery and improve global food security.</p>