L5 Pollination II

L5 Pollination II

1. 1. BACKGROUND

   • a. Importance of pollinator services
     • Approximately 90% of flowering plants (angiosperm) depend on animals for pollination services
     • 15-30% of human food production depends on pollination relationships
     • 84% of crops in EC depend on insect pollination
     • Annual economic value of pollination (2000):
   • b. Pollination by wild bees
     • (Greenleaf & Kremen 2006)
     • Sunflower crop system, California
       • Seed production is worth $26 million (2002) – important economic crop
         • Dependent upon insect pollinators
           • Pollination-limited i.e. if insects aren’t present then they cannot set as much seed
             • What are the relative contributions of:
               • ii. Honey bees (in particular) – they are artificially brought into the system in the crop fields
               • i. Wild bees
               • iii. Their interactions

2. 3. A GLOBAL POLLINATION CRISIS?

   • a. Background
     • Major declines in honeybees:
       • USA: 1970s: >4 million colonies
       • 2006: 2.4 million colonies
       • Similar declines in Europe
     • Causes:
       • Africanised (‘killer’) honey bees (Apis mellifera scutellata)
       • Varroa mites
       • Pesticides
       • Climate change
     • Allen-Wardell et al. 1998: pollinator decline threatens human food supply
       • 1998 Sao Paulo Declaration – convention produced the declaration so that countries around the world would do something about the issue
         • However, they didn’t realise it was just for HBs, but other pollinating species were under threat
           • Wild pollinators – also in decline?
   • b. One of the first studies to try and gain a better understanding…
     • (Biesmeiker et al. 2006)
       • Two (non-honeybee) pollinator groups in two countries
         • i. Native bees
         • ii. Hoverflies (Syrphidae)
         • Carried out within England, based in Leeds
           • As we have a huge database on all organisms in terms of where they occur and when they were recorded - 1m records in 10km squares
             • Carried out a simple comparison in terms of distribution – number of species before and after a critical watershed date (1980)
               • Some variability in data
                 • Data in the south was good
                 • Comprehensiveness of the data declines further north - caused some limitations
                 • Mapped data and found in wild bees – most squares show different shades of red with few areas of green i.e. mostly decline
                   • Whereas hoverflies were mixed
           • Compared with data from the Netherlands
             • Found similar patterns
               • Both show a genuine decline in species richness (no necessarily abundance) in bees within both areas, whereas hoverfly patterns a more mixed (as shown below)
                 • Possible causes of decline in richness...
                   • Habitat loss
                   • Pesticides
                   • Parasites/disease
                   • Alien pollinators
                   • Fire/overgrazing
                   • Climate change

3. 2. WILD BEES IMPROVE POLLINATION AND SEED SET

   • a. Can aid either...
     • Directly
     • Indirectly
       • Honey bee is 3x more likely to move from male to female flowers after interacting with wild bee compared to honey bee
       • Wild bee abundance and diversity increases 5x pollination efficiency by honey bees
       • This was quantified by looking at the honeybee efficiency of pollination in relation to the abundance of wild bees and the species diversity of wild bees
         • The results suggest the presence of wild bees had a net positive effect on the efficiency of pollination by honeybees on this particular crop
     • Idea is that wild bees disturb honeybees in pollination and make them more likely to move onto a different flower – which is good as it is more likely to carry pollen between different flowers
   • b. Magnitude of effect is variable between fields
     • However the effect spatially is highly variable
       • Each one of the towers is a separate field they studied
         • The different sections on the diagramrepresent honey bee, wild bee and enhancement
           • The diagram is enormously variable between different fields – some have nearly 100% down to 10%
             • Even within that, the relative contribution to the total is variable between the categories
               • E.g. sometimes entirely down the honey bees, sometime wild bee pollination is not important
       • This raises the question – what is driving the relative contribution of the different components to the total?
         • They therefore showed...
           • Effect of local natural habitat
             • The direct effect of the wild bees on the whole pollination service and the enhanced effect was all related to the amount of natural (or semi-natural) habitat within the immediate area of the field being studied
               • I.e. within a 3km radius of the field
                 • Therefore, the more natural the habitat available within the vicinity, the greater the effect of wild bees directly and enhancing effect
                   • This makes sense, as the honey bees are provided with their artificial nesting site (hives) whereas the wild bees have to find their own nest as well as other resources
                     • Meaning lack of habitat = compromised wild be contribution
   • c. Pollination by wild bees
     • (Greenleaf & Kremen, 2006)
     • Conclusions
       • Sunflower crop pollination enhanced by...
         • Abundance and diversity of wild bees
         • Amount of ‘natural’ habitat in close proximity
       • Economic value of sunflower pollination ($million)...
         • Direct, by honey bees: 13.8
         • Direct, by wild bees: 1.9
         • Indirect, of wild bees on honey bees: 10.9 (doubles the effect of having honey bees by themselves when considered with direct effects)

4. 4. DISRUPTION OF POLLINATOR MUTUALISMS

   • a. Habitat fragmentation
     • Aizen & Feinsinger (1994)
       • I. Experiment
         • Looks into pollination of two trees in tropical forest
           • Chaco Serrand (sub-tropical, dry) forest, NW Argentina
             • Diversity of insect visitors to 2 tree species in different circumstances/landscapes:
               • Large fragments
               • Small fragments
               • In both cases there was a decline in the taxa of species visiting the trees
                 • To fully understand the results, you must know that:
                   • Apis mellifera (introduced spp) =
                     • 82% of visits
                     • 44% to C. austral
               • Continuous forest
       • ii. Results
         • Visitation rates
           • (visits x 10,000 / inflorescence / min)
             • If you break down data and look at visitation rate of firstly all insects, then honey bees and all but honey bees you can see that:
               • Data is flat for all insects
                 • No variation between sites
               • There is an increase in honey bee visitation with decreasing patch size
                 • Whereas a decrease in visitation of all other insects with decreasing patch size
               • THEREFORE, habitat fragmentation...
                 • Facilitates access by honey bees
                   • Adverse effect on native pollinators
                 • Complementary effects to balance out overall visitation
                 • EXPLANATION...
                   • Honey bees outcompete native bees
                     • Occupying a vacant niche
   • b. Invasive species
     • Blancafort & Gomez (2005)
       • Seed set reduced in areas infested by Argentine ants
     • Lach (2008)
       • Argentine ants (Linepithema humile):
         • Attracted to floral nectar of Protea
           • Visit flowers more frequently than native species
             • Major effect on flower-visiting arthropod assemblage
               • Honey bees spent 75% less time on flowers with Argentine ants present
                 • BUT no effect on pollination (Proteas tend to be pollen limited)
   • c. Introduced species
     • Goulson (2003)
       • Deliberately introduced for the pollination service they provide
         • Potential impacts....
           • Competition with native pollinators for floral resources
           • Competition with native species for nest sites
             • Depletion of resources
             • Deterrence of competitors
             • Competitive advantages of honeybees and bumblebees...
               • i. Diurnal and seasonal activity pattern (particularly bumble bees) – have longer seasons, they also get up earlier and the morning and forage till much later
               • iv. Social versus solitary species – sharing of information of resources etc.
               • ii. Foraging distances
               • iii. Body size, tongue length
             • Possible effects on native species
               • i. Modify foraging behaviour (plant species, habitats)
               • ii. Population-level (competitive exclusion/displacement)
           • Transmission of natural enemies (e.g. pathogens) to native species
           • Changes to seed set of native plants (up to down)
           • Pollination of exotic/alien (invasive) weeds
             • Stout et al. (2002)
               • Tasmania
                 • Honey bees introduced 180 years ago (now x10 abundance of native fauna)
                   • Tree lupin, Lupinus arboreus, (a ‘sleeper-weed’?)
                     • A plant species under normal circumstances won’t be do much, but will take off when it is released from the constraints of pollinator limitation
                       • Requires insect pollination
   • d. Climate change
     • i. Will climate change un-couple the seasonal phonologies of plants and their pollinators?
       • E.G. A pollinator visits plant A, B and C, with all three plants being dependent on it
         • The lines represent the pattern of seasonal activity
           • If the pollinator is present throughout the season, it could visit plant A, B then C
             • If the pollinator is present throughout the season, it could visit plant A, B then C
               • Whereas the entire life cycle of the plant species is covered by the pollinator
                 • An imposed climate change will advance the season for each of the plant species (i.e. cause it to occur earlier for all plants)
                   • The degree of advancement is different for the different species
                   • This shows that there are gaps in the continuity of pollination
       • ii. Memmott, Vraze et al (2007)
         • 19th century, Illinois prairie/forest dataset
           • Historical data on 15,000 interactions between 429 plant species and 1420 pollinator species
             • Also: first and last dates for flowering and pollinators
               • Used experimental data on plants to model response to 3-5° warming
                 • 17-50% of pollinators will suffer disruption of food supply
                   • Curtailment of season > no food > gaps
                     • iii. Burkle et al. (2013)
                       • Revisited Robertson’s sites in 2009-10:
                         • Subset: 26 forbs (herbaceous plant species) & 109 bee species
                           • Interactions retained – 24%
                             • Interactions lost because of bee species lost – 34%
                               • Interactions lost for other reasons e.g. phenology, change in abundance, landscapes – 42%
                                 • REFEREMCE NOTES FOR FINAL DETAILS AND CONCLUSION

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