Functional redundancy and complementarities of seed dispersal by the last neotropical megafrugivores.

BACKGROUND: Functional redundancy has been debated largely in ecology and conservation, yet we lack detailed empirical studies on the roles of functionally similar species in ecosystem function. Large bodied frugivores may disperse similar plant species and have strong impact on plant recruitment in tropical forests. The two largest frugivores in the neotropics, tapirs (Tapirus terrestris) and muriquis (Brachyteles arachnoides) are potential candidates for functional redundancy on seed dispersal effectiveness. Here we provide a comparison of the quantitative, qualitative and spatial effects on seed dispersal by these megafrugivores in a continuous Brazilian Atlantic forest. METHODOLOGY/PRINCIPAL FINDINGS: We found a low overlap of plant species dispersed by both muriquis and tapirs. A group of 35 muriquis occupied an area of 850 ha and dispersed 5 times more plant species, and 13 times more seeds than 22 tapirs living in the same area. Muriquis dispersed 2.4 times more seeds in any random position than tapirs. This can be explained mainly because seed deposition by muriquis leaves less empty space than tapirs. However, tapirs are able to disperse larger seeds than muriquis and move them into sites not reached by primates, such as large forest gaps, open areas and fragments nearby. Based on published information we found 302 plant species that are dispersed by at least one of these megafrugivores in the Brazilian Atlantic forest. CONCLUSIONS/SIGNIFICANCE: Our study showed that both megafrugivores play complementary rather than redundant roles as seed dispersers. Although tapirs disperse fewer seeds and species than muriquis, they disperse larger-seeded species and in places not used by primates. The selective extinction of these megafrugivores will change the spatial seed rain they generate and may have negative effects on the recruitment of several plant species, particularly those with large seeds that have muriquis and tapirs as the last living seed dispersers.

[Responses of mesophyllic conductance in leaves of 4 dominant subtropical forest tree species to moderate high temperature].

By using CO2 exchange system and chlorophyll fluorescence method, the magnitude of mesophyllic conductance (g(m)), namely the CO2 transfer conductance from intercellular space to chloroplast, in the leaves of four dominant subtropical forest tree species under moderate high temperature (38 degrees C) was studied. The results revealed that sun or early-successional species Schima superba had a higher g(m) than mesophytic and shade-tolerant species, such as Castanopsis hystrix, C. fissa and Cryptocarya concinna, and the leaves under full direct light had a higher g(m) than those under shade. The average g(m) of the four test trees from 25 degrees C to 38 degrees C was 1.59 +/- 0.27, and the responses of g(m) to temperature were dependant on the tree species and their leaf type (sun or shade leaves). Because the diffusion of CO2 in water was only about 1.25, g(m) might be controlled by a protein-related process besides temperature. Moderate high temperature could increase the g(m) value, resulting in the increase of CO2 concentration and carboxylation rate in chloroplasts. Comparing with that of S. superba, the carboxylation rate of C. hystrix, C. fissa and C. concinna was significantly increased by moderate high temperature, regardless of under full direct light or shading, indicating that moderate high temperature would favor the succession of mid- and late-successional species.

[Quantitative relationships of intra- and interspecific competition in Cryptocarya concinna].

The monsoon evergreen broad-leaved forest (MEBF) in Dinghushan Nature Reserve (DNR) has been considered as a zonal vegetation in lower subtropical China, with a history of more than 400 years. In this paper, the intra- and interspecific competition intensity in Cryptocarya concinna, one of the constructive species in MEBF in DNR was quantitatively analyzed by Hegyi single-tree competition index model. The results showed that the intraspecific competition intensity in C. concinna decreased gradually with increasing tree diameter. For C. concinna, its intraspecific competition was weaker than its interspecific competition with Aporosa yunnanensis. The competition intensity of interspecific competition with C. concinna followed the order of A. yunnanensis > Schima superba > Gironniera subaequalis > Acmena acuminatissima > Castanopsis chinensis > Syzygium rehderianum > Pygeum topengii > Blastus cochinchinensis > Sarcosperma laurinum > Pterospermum lanceaefolium > Cryptocarya chinensis. The relationship of the DBH of objective tree and the competition intensity between competitive tree and objective tree in the whole forest and C. concinna population nearly conformed to power function, while that between other competitive tree and the objective C. concinna tree conformed to logarithm function. There was a significantly negative correlation between the competition intensity and the DBH of objective tree.