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Plantules
Une étude a été menée par Baraloto (2001) sur les graines et plantules de nombreuses espèces de Guyane française.
Données
Données par espèce.
Résumé
Differences in distribution among plant species across environmental gradients
are often assumed to be due to tradeoffs in organismal traits, individual performance,
or both. In this thesis, I investigated how tradeoffs among neotropical tree
species might lead to differences in their distribution in contrasting environments,
linking the three levels at which tradeoffs migh occur: organismal traits,
individual performance and population structure.
I first conducted a survey of traits for seeds and seedlings of 202 tree
species at Paracou, French Guiana, and found that taxa with larger seeds generally
had seedlings with hypogeal cotyledons and taproots. While larger-seeded taxa
were associated with larger seedlings, they also had lower maximum relative
growth rates and lower specific leaf area. I then studied differences among
a total of 31 species differing in seed size and seedling morphology, examining
performance response to multiple environmental variables at fines spatial scales.
At the seed-seedling stage, no tradeoffs occured for survival or growth across
a wide range of conditions; larger seeds performed better in all environments.
In contrast, species-environment interactions for the relative growth rates
of older seedlings resulted in a shift in the performance hierarchy between
soil types and light environments. However, this tradeoff did not reflect the
tradeoffs in traits observed among seedlings. Established seedlings more than
one year in age did not exhibit tradeoffs in growth. Moreover, traits related
to initial performance, such as seed size, were not associated with growth
rates over a two-year period. The lack of tradeoffs I found for individual
performance was consistent with the few differences in distribution of juveniles
that I observed in a 1.5 hectare permanent plot census. For all 15 species
studied, juveniles coexisted across environmental gradients without partitioning
microhabitats.
These results suggest that competitive hierarchies during regeneration are
not strong forces influencing seedling community structure in neotropical forests.
The early structuring of these communities may be largery determined by life
history tradeoffs related to seed size, independent of environment. In contrast,
subsequent growth of juveniles appear to be uncoupled from initial survival
because species-environment interactions occur that are governed by morphological
tradeoffs unrelated to seed size.
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Dernière mise à jour le
28/02/2011
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