INTERSPECIFIC SEGREGATION IN A TROPICAL RAIN FOREST AT BAWANGLING NATURE RESERVE, HAINAN ISLAND
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ABSTRACT:
With the aid of GIS software (ArcView), a distribution map of all trees with DBH¡Ý1cm from a tropical rain forest community at Bawangling National Nature Reserve in Hainan Island was drawn. The nearest neighbours of each individual and the distances between every individual-neighbour pairs were obtained by using ArcView¡¯s nearest-neighbor extension module (Jeff Jenness¡¯s Nearest Features v.3.5). Based on this, the spatial pattern and interspecific segregation in the multi-species community was studied with a subtable method of a N¡ÁN nearest-neighbor contingency table. Distribution pattern was measured by a revised Clark-Evans index (CE) and the often-used ¦Ö2 method. Pielou¡¯s coefficient of segregation (S) was adopted to measure the segregated degree between two species: When 0.7¡ÜS¡Ü1, two species are positively segregated; -1¡ÜS¡Ü-0.7, negatively segregated; otherwise they are random neighbors. In order to solve zero cell problems, each zero cell will be added by 0.001. This will not change the polarity of segregation and the zero denominators will be avoided in Pielou¡¯s equation. Pairwise segregation was shown in a constellation diagram in which solid lines stand for positive segregation while dash lines for negative segregation and different shapes mean different mean DBH. The results firstly indicated that some species pairs are positively segregated (23.3%) and a few pairs are negatively segregated (2.4%). In contrast, the segregation relations between most of the species are random (74.3%). Our results agree with Pielou¡¯s opinion that negative segregation is rare in a mature plant community. Secondly, most understory trees (mean DBH<15cm) are positively segregated between each other, few negatively segregated. No negative segregation occurs between large arbors (mean DBH¡Ý65cm). Segregation relations between understory trees and large arbors are complicated. Third, most species will not be negatively segregated with others. Some will not be positively segregated with others. Two species have both positive and negative segregated relationship, while only one species has neither positive nor negative segregation with all other species. The results also indicated that interspecific segregation is closely related to their distribution pattern. Proportion of positive segregation between clumped species and other species (31.4%) is much larger than that of random species (16.7%) or uniform species (20.0%). Proportion of negative segregation between clumped species and other species (1.3%) is less than that of random (3.3%) or uniform species (2.4%). Clumped¨Cclumped species pair tends to be more positive segregated (43.1%) than that of other species pairs. Both clumped¨Cuniform and random¨Crandom species pairs are more likely to be negative segregated, with a proportion of 5.6% and 4.8% respectively. Whatever the species distribution or the pairwise relative distribution is, the proportion of random neighbor pairs is the largest.
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STATISTICS
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