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Reduced bird visits lower seed set of Banksia robur in fragmented heathland

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Final presentation for my Special Research Project over the summer of 2013-14. This project investigated habitat fragmentation effects on pollination and reproductive success by comparing plant-pollinator interactions between Banksia robur populations in heathland at Noosa National Park and Fraser Island, Queensland, Australia.

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Reduced bird visits lower seed set of Banksia robur in fragmented heathland

  1. 1. Reduced bird visits lower seed set of Banksia robur in fragmented heathland Rachele Wilson
  2. 2. Introduction: scope and purpose  How relationship between plant and pollinator is affected by habitat fragmentation  Focus on a coastal heath species – Banksia robur (Swamp Banksia) Image source: (above) http://www.texas-wildlife.org/program-areas/category/property-rights (below) http://www.anhs.com.au/images/
  3. 3. Previous research  Visits decline faster in:  tropical > temperate  vertebrates (birds, bats) > invertebrates  Seed/fruit set decline greater in self- incompatible plants  Focus on herbs and trees, forest and grassland  Few coastal studies, despite urbanisation Image source: (above) Ricketts et al. 2008; (below) Montero-Castaño and Vila 2012
  4. 4. Coastal heathland  Sandy, low nutrient soils  Habitat for threatened species  Historically cleared  sand mining, agriculture, development (~2 million ha)  endangered south of Noosa Eastern Ground Parrot (Pezoporus wallicus) Wallum Sedge Frog (Litoria olongburensis) Image sources: (parrot) http://www.environment.nsw.gov.au/threatenedspeciesapp/profile.aspx?id=10608# (sedge frog) http://www.wildlife.org.au/projects/researchgrants/wallumsedgefrog.html
  5. 5. Research question “Do pollinator behaviour and reproductive success of B. robur differ between intact and fragmented coastal heath?” Plant- pollinator interactions Banksia robur Fragmented vs. intact habitat
  6. 6. Methods: site selection  Two coastal heath sites (intact and fragmented)  Five replicate plots (20 × 5 m) per site  At least three flowering plants per plot West of Dilli Village, Fraser Island (Intact) East Weyba Section, Noosa N.P. (Fragmented)
  7. 7. Observations  40 × 20 min observations  morning and afternoon  twice per plot  Bird species – foraging behaviour  duration  movement between B. robur flower spikes  number of visits Images: background – visiting P. nigra; inset – observers. Courtesy of Marvin Scheiffer
  8. 8. Sampling  216 samples  up to 25 fruits per plot  Seed set  calculated as = follicles per fruit (one seed per follicle) (a) (b) (c) (a) B. robur fruit with closed follicles; (b) with open follicles; and (c), left – winged seed, centre – separator, and right – seedless wing.
  9. 9. Species Intact Fragmented Total (a) White-cheeked Honeyeater (Phylidonyris nigra) 349 26 375 (b) Lewin’s Honeyeater (Meliphaga lewinii) 0 6 6 (c) Noisy Friarbird (Philemon corniculatus) 0 2 2 (d) Red-browed Finch (Neochmia temporalis) 1 0 1 Total 350 34 384 (a) (b) (c) (d) Results: bird species observed Image credits (a,b,d): David & Diane Armbrust, http://www.anhs.com.au/images/ (c): David Cook, http://www.flickr.com/photos/kookr/2877951061/
  10. 10. Visitation rate 0 2 4 6 8 10 12 14 16 18 20 Intact Fragmented Meannumbervisits/20min Site  Frequency of bird visits to flower spikes was significantly lower in fragmented coastal heath Mann-Whitney U Test (U(39) = 106, Z = -2.923, p = 0.010).  10 × more visits in intact habitat
  11. 11. Duration of visits  Mean duration of bird visits was similar between sites Mann-Whitney U Test (U(383) = 6 174.5, Z = 0.363, p = 0.716). 0 10 20 30 40 50 60 Intact Fragmented Meandurationofvisit(sec) Site
  12. 12. Movement between flowers  Visitor travel between flower spikes was similar across sites Independent Samples T-Test (t(9.5) = 2.247, p = .050). 0 5 10 15 20 25 30 35 40 45 Intact Fragmented Meanpercentvisitswithinter-flower travel(%)
  13. 13. Average seed set  Seed set was significantly reduced in fruits from fragmented sites Independent Samples T-Test (t(213) = 3.249, p = 0.001). 0 10 20 30 40 50 60 70 Intact Fragmented Meanseedsetperfruit Site
  14. 14. Discussion: reduced visits  Less visits in fragmented population, e.g. B. goodii, B. cuneata  perceived decline in nesting or foraging resources  competition with aggressive edge species  Forage in nearby woodland  P. nigra dual habitat Image source: (above) http://upload.wikimedia.org/wikipedia/commons/1/13/Noisy-Miner-juvenile.jpg (below) http://farm7.static.flickr.com/6068/6158449973_74676438f7.jpg
  15. 15. Lower fertility  22% reduction in average seed set  changes in pollinator activity  disruption to pollination services  limited seed production
  16. 16. Lower fertility  Similar to that found in other fragmented ecosystems:  tropical forest 20%  grassland 16%  Risk to demographic turnover:  Low seed set  low % survival seedlings  E.g. up to 80% seedling mortality from kwongan fragments
  17. 17. Alternative explanations  Smaller plant population size and low density in fragmented site  ‘inbreeding’  poor pollen quality  fewer seeds  E.g. B. sphaerocarpa  Physiological stress on plants (e.g. drier conditions)  less resources, less output
  18. 18. Conclusion  Pollen limitation due to habitat fragmentation  reduced bird visits lower seed set of B. robur in fragmented heathland  Potential risk to long-term viability of population  Larger studies needed to assess risk
  19. 19. Questions?  Special thanks to: Prof Helen Wallace Ilee Sannholm Marvin Scheiffer Laura Simmons Dr David Walton Image (right) courtesy of Laura Simmons

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