Dispersal spectrum of four forest types along an altitudinal range of the Brazilian Atlantic Rainforest

Abstract

In ecological communities, the proportion of plant species with different dispersal syndromes is known as the dispersal spectrum, which can result from different selective pressures such as climate. This is because variations in temperature, humidity, atmospheric pressure and precipitation result in distinct flora and fauna among different sites. If climate conditions along an altitudinal range act as a strong direct or indirect selective pressure on dispersal syndromes, the dispersal spectrum among plant communities in different altitudes should be distinct. We organized the dispersal syndromes in five hierarchical levels according to the levels of detail in diaspore morphology and, consequently, different degrees of specificity to the dispersers. Then we identified, within each hierarchical level, the syndromes of tree species of four forest types of the Atlantic Rainforest along a 1200 m altitudinal range in Southeast Brazil. Among 327 species, we found two syndromes in the most general hierarchical level (abiotic and biotic dispersal), three in the following level (wind, self and animal), three in the intermediate level (barochory, autochory and endozoochory), two in the forth level (mammal and bird), and 12 syndromes in the most specific level, all of which were related to the morphology of diaspores dispersed by wind, autochory, mammals and birds. The dispersal spectrum in the five hierarchical levels was similar among the four forest types. Overall, the majority of species is dispersed by biotic agents, considered here as animals and the parent plant itself. Within biotic agents, the most important are animals, specifically birds. Most bird-dispersed species present drupoid diaspores. Our results indicate that the selective pressures on dispersal syndromes originated from climate conditions that vary with altitude are not strong, hence resulting in the same dispersal spectrum among the forest types.