Abstract
Despite being abundant in urban gardens, the Canary Island dragon tree Dracaena draco is close to extinction in the wild. It tends to produce relatively large fruits, which limits the pool of vertebrates that might disperse its seeds. We aimed to shed light on the seed dispersal system of this plant by studying its fruit size in relation to the feeding behavior of its present dispersers, and to discuss on possible differences with the past dispersal system, when large-sized dispersers were abundant. Besides fruit and seed characterization, we performed experiments on seedling emergence (using the characterized seeds), and field observations of the fruit handling behavior of frugivorous birds. Seed removal by granivores beneath and outside the dragon tree canopies was assessed through a field experiment. An additional seedling emergence experiment tested the effect of pulp removal from around the seed (using seeds contained within the fruits and manually depulped seeds). A feeding experiment was carried out with captive individuals of the Canary endemic white-tailed pigeon Columba junoniae –a large frugivore that occasionally consumes D. draco fruits– to test if its gut treatment influences seed viability. Small fruits produced seeds unable to germinate, while most seedling emergence was recorded only for seeds from large fruits. Our observations suggest that the only passerine species able to swallow large fruits is the medium-size passerine Turdus merula, whereas small passerines tended to pluck the pulp without aiding seed dispersal. Nonetheless, Sylvia atricapilla –the largest among the group of small passerines– occasionally transported fruits away from parent plants to consume the pulp, resulting in seed dispersal without any digestive treatment. This behavior indicates S. atricapilla might be occasionally a legitimate disperser of D. draco, since our experiments suggest that seed transport away from parent trees and pulp removal enhance both post-dispersal seed survival and seedling emergence. Lastly, the pigeons used in the experiment regurgitated mostly viable seeds, suggesting the legitimacy of C. junoniae as seed disperser for D. draco. Therefore, although D. draco likely had more seed dispersers in the past, we identified at least two bird species that can still disperse its seeds nowadays.
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Claims 9
Claim · model-written summary
Small fruits yielded seeds unable to germinate.
- Taxon
- Dracaena draco
Dracaena dracot0 - Outcome
- seeds unable to germinatee0
- Qualifier
- Small fruitse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Dracaena draco”
e0“Small fruits produced seeds unable to germinate”
Claim · model-written summary
Most seedling emergence came from large fruits.
- Taxon
- Dracaena dracoDracaena dracot0
- Material
- seeds from large fruitse0
- Outcome
- seedling emergencee0
- Direction
- moste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Dracaena draco”
e0“most seedling emergence was recorded only for seeds from large fruits”
Claim · model-written summary
Turdus merula appeared to be the only passerine able to swallow large fruits.
- Taxon
- Dracaena dracoDracaena dracot0
- Interactor
- Turdus merula
Turdus merulae0herbivore - Outcome
- able to swallow large fruitse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Dracaena draco”
e0“the only passerine species able to swallow large fruits is the medium-size passerine Turdus merula”
Claim · model-written summary
Small passerines tended to remove pulp without dispersing seeds.
- Taxon
- Dracaena dracoDracaena dracot0
- Interactor
- small passerinese0herbivore
- Outcome
- pluck the pulp without aiding seed dispersale0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Dracaena draco”
e0“small passerines tended to pluck the pulp without aiding seed dispersal”
Claim · model-written summary
Sylvia atricapilla occasionally carried fruits away and dispersed seeds without digestion.
- Taxon
- Dracaena dracoDracaena dracot0
- Interactor
- Sylvia atricapilla
Sylvia atricapillae0herbivore - Outcome
- seed dispersal without any digestive treatmente0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Dracaena draco”
e0“Sylvia atricapilla –the largest among the group of small passerines– occasionally transported fruits away from parent plants to consume the pulp, resulting in seed dispersal without any digestive treatment”
Claim · model-written summary
Transport away from parent trees enhanced postdispersal seed survival.
- Taxon
- Dracaena dracoDracaena dracot0
- Treatment
- seed transport away from parent treese0
- Outcome
- post-dispersal seed survivale0
- Direction
- enhancee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Dracaena draco”
e0“seed transport away from parent trees and pulp removal enhance both post-dispersal seed survival and seedling emergence”
Claim · model-written summary
Pulp removal enhanced seedling emergence.
- Taxon
- Dracaena dracoDracaena dracot0
- Treatment
- pulp removale0
- Outcome
- seedling emergencee0
- Direction
- enhancee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Dracaena draco”
e0“seed transport away from parent trees and pulp removal enhance both post-dispersal seed survival and seedling emergence”
Claim · model-written summary
Pigeons regurgitated mostly viable seeds.
- Taxon
- Dracaena dracoDracaena dracot0
- Interactor
- pigeonsColumbidaee0herbivore
- Outcome
- regurgitated mostly viable seedse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Dracaena draco”
e0“the pigeons used in the experiment regurgitated mostly viable seeds”
Claim · model-written summary
The authors identified at least two extant bird dispersers.
- Taxon
- Dracaena dracoDracaena dracot0
- Outcome
- bird species that can still disperse its seedse0
- Value
- at least twoe0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we identified at least two bird species that can still disperse its seeds nowadays”
t0“Dracaena draco”