Seed Dispersal & Germination by Native vs. Exotic Avian Frugivores in Forests of Hawaiʻi Island
Koa Matsuoka (1), Rebecca Ostertag(1) , Patrick Hart(1), Bryce Masuda (2), University of Hawaiʻi at Hilo, San Diego Zoo Global
- - As the last extant frugivores in Hawaiʻi, ensuring the survival and population stability of the ʻōmaʻo, ʻalalā and puaiohi plays an integral part in managing seed dispersal function in Hawaiʻi’s forest ecosystems.
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- - Recent management strategies by state and federal agencies have proposed utilizing ʻōmaʻo reintroductions as a means to refill the empty niche left by the localized extinctions of both bird species.
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- - In addition, the recent reintroduction of ʻAlalā introduction to the wild provides the opportunity to study their effects on seed dispersal function by examining the seed species in their diet.
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- - Lastly, it is important to examine the seed dispersal effects that ʻōmaʻo and exotic frugivores, such as the Japanese white-eye (Zosterops japonicus) and red billed leothrix (Leiothrix lutea), have on the plant community structure to better understand changes that Hawaiian forests may undergo in the absence of Hawaiʻi’s native frugivores.
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- - Stabilizing populations of native frugivores and utilizing reintroductions as a method to restore functioning populations could have the potential to save thousands of dollars in restoration costs and help restore the quality of Hawaiiʻs natural and cultural resources.
Introduction
- - As the last extant frugivores in Hawaiʻi, ensuring the survival and population stability of the ʻōmaʻo, ʻalalā and puaiohi plays an integral part in managing seed dispersal function in Hawaiʻi’s forest ecosystems.
-
- - Recent management strategies by state and federal agencies have proposed utilizing ʻōmaʻo reintroductions as a means to refill the empty niche left by the localized extinctions of both bird species.
-
- - In addition, the recent reintroduction of ʻAlalā introduction to the wild provides the opportunity to study their effects on seed dispersal function by examining the seed species in their diet.
-
- - Lastly, it is important to examine the seed dispersal effects that ʻōmaʻo and exotic frugivores, such as the Japanese white-eye (Zosterops japonicus) and red billed leothrix (Leiothrix lutea), have on the plant community structure to better understand changes that Hawaiian forests may undergo in the absence of Hawaiʻi’s native frugivores.
-
- - Stabilizing populations of native frugivores and utilizing reintroductions as a method to restore functioning populations could have the potential to save thousands of dollars in restoration costs and help restore the quality of Hawaiiʻs natural and cultural resources.
Species
- ʻAlalā (Corvus hawaiiensis)
- Status: Critically Endangered
- Population: 11 individuals in wild, ~120 in captivity
- Range: Endemic to Hawaiʻi Island
- ‘Ōmaʻo (Myadestes obscurus):
- Status: Vulnerable (IUCN)
- Population: ~170,000 individuals
- Range: Endemic to Hawaiʻi Island
- Puaiohi (Myadestes palmeri)
- Status: Critically Endangered (IUCN)
- Population: ~ 500 Individuals
- Range: Endemic to Kauaʻi
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- Japanese white-eye (Zosterops japonicus)
- Status: Least concern
- Population: Common
- Range: All main Hawaiian Islands
- Red billed leothrix (Leothrix lutea)
- Status: Least concern
- Population: Common
- Range: All main Hawaiian islands
Study Site
Fig. 1 Current and former range of ʻōmaʻo on Hawaiʻi island and location of study site for mist netting ʻōmaʻo, Japanese white-eye and red billed leothrix.
Fig. 2 The four forest fragments are where seed rain and 3 of the 5 frugivores (ʻōmaʻo, Japanese white-eye and red billed leothrix) in this study are mist netted for fecal extraction. The study site is located in the Upper Waiākea Forest Reserve along Powerline Road near mile marker 21 off Saddle Road (Daniel K. Inouye Highway). The forest are naturally fragmented by 1855 or 1880 Mauna Loa eruption. These forest fragments are known as "kīpuka".
Site & Species
Species
- ʻAlalā (Corvus hawaiiensis)
- Status: Critically Endangered
- Population: 11 individuals in wild, ~120 in captivity
- Range: Endemic to Hawaiʻi Island
- ‘Ōmaʻo (Myadestes obscurus):
- Status: Vulnerable (IUCN)
- Population: ~170,000 individuals
- Range: Endemic to Hawaiʻi Island
- Puaiohi (Myadestes palmeri)
- Status: Critically Endangered (IUCN)
- Population: ~ 500 Individuals
- Range: Endemic to Kauaʻi
-
- Japanese white-eye (Zosterops japonicus)
- Status: Least concern
- Population: Common
- Range: All main Hawaiian Islands
- Red billed leothrix (Leothrix lutea)
- Status: Least concern
- Population: Common
- Range: All main Hawaiian islands
Study Site
Fig. 1 Current and former range of ʻōmaʻo on Hawaiʻi island and location of study site for mist netting ʻōmaʻo, Japanese white-eye and red billed leothrix.
Fig. 2 The four forest fragments are where seed rain and 3 of the 5 frugivores (ʻōmaʻo, Japanese white-eye and red billed leothrix) in this study are mist netted for fecal extraction. The study site is located in the Upper Waiākea Forest Reserve along Powerline Road near mile marker 21 off Saddle Road (Daniel K. Inouye Highway). The forest are naturally fragmented by 1855 or 1880 Mauna Loa eruption. These forest fragments are known as "kīpuka".
Questions
- 1. In a naturally fragmented forest system, in what capacity and where are avian dispersed plant species commonly being dispersed (interior, edge or extior matrix)?
- 2. Is the diet diversity and abundance of fruiting plant seeds found in fecal samples of native avian frugivores different from exotic frugivores.
- 3. Are there differences between the germination rates and percentages of seeds passed through the guts of native birds, exotic birds and controls?
Hypotheses:
(H1): The interior of the forest fragment harbors higher densities of fruiting plants therefore, a higher proportion of fruiting plant seeds will be dispersed closer to conspecifics in the interior.
(H2): The larger gape size of ‘alalā and ʻōmaʻo allows the consumption of a wider size range and larger abundance of fruiting plants therefore, the seed diversity and abundance of seeds in native frugivore feces will be higher than smaller exotic frugivores.
(H3): Gut passage through birds increases the germination potential of fruiting plant seeds, therefore, seeds passed through the guts of native and exotic birds will have higher germination rates and percentages than their corresponding controls.
(H4): Seeds with gut-passage through native frugivores (‘ōmaʻo, puaiohi,ʻalalā) will have higher germination rates and percentages than seeds passed through the guts of exotic frugivores (Japanese white-eyes and red billed leothrix).
Fecal Collection
- ʻŌmaʻo, Japanese white-eye and red billed leothrix:
- 1. Caught in mist nets and usually defecate in holding bags
- 2. If not, placed in holding box for max of 10 mins. or until defecation
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- Captive ʻAlalā and Puaiohi:
- 1. Birds are fed fresh fruit from area around facility
- 2. Fecal collected from platforms under favored perches
- Wild ʻAlalā:
- 1. Fecal collected from platform under feeders where birds defecate
- 2. Seeds identified to species or genus level using seed reference library
Germination Trials
- 1. Seeds sterlized in 10% bleach solution for 5 minutes
- 2. Washed and place in 3:1 sand to vermiculite growth media
- 3. Placed in greenhouse with timed irrigation and monitored weekly
- 4. Germination Percentage = Seeds germinated / Total # of seeds
- 5. Germination Rate = Germination/Time (days since sowing)
Seed Rain
- 1. 1m diameter mesh basket with silkscreen
- 2. Hung above fruited plant understory to deduce avian dispersed seeds
- 3. Changed and examined monthly for seeds moved by avian frugivores
- 4. Distributed evenly on interior, edge and lava matrix of forest fragments
Methods
Fecal Collection
- ʻŌmaʻo, Japanese white-eye and red billed leothrix:
- 1. Caught in mist nets and usually defecate in holding bags
- 2. If not, placed in holding box for max of 10 mins. or until defecation
-
- Captive ʻAlalā and Puaiohi:
- 1. Birds are fed fresh fruit from area around facility
- 2. Fecal collected from platforms under favored perches
- Wild ʻAlalā:
- 1. Fecal collected from platform under feeders where birds defecate
- 2. Seeds identified to species or genus level using seed reference library
Germination Trials
- 1. Seeds sterlized in 10% bleach solution for 5 minutes
- 2. Washed and place in 3:1 sand to vermiculite growth media
- 3. Placed in greenhouse with timed irrigation and monitored weekly
- 4. Germination Percentage = Seeds germinated / Total # of seeds
- 5. Germination Rate = Germination/Time (days since sowing)
Seed Rain
- 1. 1m diameter mesh basket with silkscreen
- 2. Hung above fruited plant understory to deduce avian dispersed seeds
- 3. Changed and examined monthly for seeds moved by avian frugivores
- 4. Distributed evenly on interior, edge and lava matrix of forest fragments
- Fig. 1 Seed abundance in ʻōmaʻo fecal samples significantly higher than exotic frugivores
- Fig. 2 Shannon Diversity of seeds in ʻōmaʻo fecal samples are significantly higher than other exotic frugivores
Prelim. Results
- Fig. 1 Seed abundance in ʻōmaʻo fecal samples significantly higher than exotic frugivores
- Fig. 2 Shannon Diversity of seeds in ʻōmaʻo fecal samples are significantly higher than other exotic frugivores
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