Cassowary frugivory, seed defleshing and fruit fly infestation
influence the transition from seed to seedling in the rare Australian
rainforest tree, Ryparosa sp. nov.1 (Achariaceae).
Bruce L. Webber and Ian E. Woodrow, School of Botany, The University of Melbourne, Vic.3010, Australia. Email: firstname.lastname@example.org
Functional Plant Biology, 2004, 31: 505-516
The rare Australian rainforest tree Ryparosa sp. nov. 1 aff. javanica (sensu Webber & Curtis, BW-017; Achariaceae) has
large fleshy fruits that undergo a distinctive colour change during ripening.
Fruit seem highly suited to frugivore interactions with large ground-dwelling
avian or marsupial frugivores, a role primarily filled by the endangered
cassowary. We found that fruits had chemical defence traits that closely
paralleled morphological ripening signals. Young fruit seeds had amongst
the highest concentrations of plant tissue cyanogens ever recorded (some
in excess of 12 mg g-1dw), yet the flesh of ripe fruits had negligible
cyanogen defence. A seed treatment trial found that cassowary gut passage
significantly improved germination from 4% to 92%, and we were not able
to replicate this result with simulated treatments. While high levels
of fruit fly larval infestation accounted for reduced seed viability,
this predation was apparently reduced by cassowary gut passage. Post-germination
seedling traits such as haustorial cryptocotylar cotyledons and epigeal
germination may increase the chance of survival for established seedlings.
We conclude that the range of traits seen in Ryparosa recruitment
is particularly suited to interactions with frugivores and survival in
a rainforest ecosystem.
Comment from New Scientist (2004) 182:16