蚂蚁对澜沧舞花姜种子散布及种苗空间分布格局的影响

 在野外系统观测了澜沧舞花姜（Globba lancangensis）18个果实共216粒种子的散布过程。共有10种蚂蚁参与了澜沧舞花姜的种子散布，距离为0.01～3.35 m，平均距离(0.47±0.03) m（平均值±SE，n=216）。其中最重要的３种蚂蚁是横纹齿猛蚁（Odontoponera transversa）、大头蚁(Pheidole sp.)和黄足厚结猛蚁(Pachycondyla luteipes)，其出现频率分别为61%、50%和28%，散布的平均距离分别为(0.60±0.09) m、(0.20±0.01) m和(0.32±0.05) m。从总体上看,蚂蚁促进了种子的分散，降低了种子的聚集程度。横纹齿猛蚁对于种子上的油质体最为敏感，对人工去除了油质体的种子不搬运，对种子散布距离较远，暗示了其与澜沧舞花姜之间可能存在更紧密的互惠关系。野外样方调查结果表明，在3种舞花姜属植物中，以种子繁殖为主的澜沧舞花姜种苗之间的平均最近距离为(36.8±1.45) cm（平均值±SE，n=74），显著大于以珠芽繁殖为主的毛舞花姜（Globba barthiri）的(29.8±2.70) m（n=34）（t73,33=2.11，p=0.037）和异果舞花姜（Globba racemosa）的(28.7±3.16) cm（n=32）（t73,31=2.33，p=0.022）；澜沧舞花姜的种苗聚集程度（Z=-1.70±0.19）显著小于毛舞花姜（Z=-2.58±0.37，t73,33=2.36，p=0.020）和异果舞花姜（Z=-3.28±0.53）（t73,31=3.54，p=0.001）。这说明相对于毛舞花姜和异果舞花姜，蚂蚁对种子的散布作用显著增加了澜沧舞花姜种苗间的平均最近距离，降低了居群的聚集度。

THE ROLE OF ANTS IN SEED DISPERSAL OF GLOBBA LANCANGENSIS AND THE SPATIAL DISTRIBUTION OF ITS SEEDLINGS

Seed dispersal is a key process determining the spatial pattern of plant populations. Myrmecochory is a term referring to a plant-ant mutualism in which ants disperse plant seeds while using the nutritionally valuable elaiosomes as food. In this study, our goal was to understand how ants affect seed dispersal and seedling distribution patterns of a myrmecochorous plant, Globba lancangensis. G. lancangensis is a small perennial herb of Zingiberaceae mainly distributed in southwest Yunnan Province. It propagates primarily by seeds but also by a small number of bulbils. There are 31.2±2.13 (Mean±SE, n=32) seeds in each fruit. The seeds are 2-3 mm in length and bear a white-colored elaiosome. We conducted an observational study on the seed dispersal of G. lancangensis in October 2002 in its natural habitat in Xishuangbanna, Yunnan Province of China (21°59′ N, 100°16′ E; 1 180 m asl; annual mean temperature, 18.3 ℃; annual mean rainfall, 1 339 mm). A total of ten species of ants were identified that transported the seeds of G. lancangensis and their activities were recorded. The mean dispersal distance of seeds was （0.47±0.03） m (n=216), ranging from 0.01 m to 3.35 m. Odontoponera transversa, Pheidole sp. and Pachycondyla luteipes were the most important seed dispersing ant species, occurring 61%, 50% and 28% of the time, respectively, with mean dispersal distances of (0.60±0.09) m, (0.20±0.01) m and (0.32±0.05) m, respectively. As a whole, ants promoted a decrease in the degree of aggregation of G. lancangensis seeds. Ants of Pheidole sp. collected a total of 43% of the seeds of G. lancangensis but consumed most of the seeds collected, suggesting that Pheidole sp. is a seed harvester ant　O. transversa did not remove seeds with artificially removed elaiosomes and appeared to be the most sensitive ant species to seed elaiosomes. Overall, O. transversa made the most significant contribution to seed dispersal, as demonstrated by the highest visiting frequency (61%) and the greatest mean dispersal distance (0.60±0.09) m of all ants. These results imply that a tight mutualism exists between O. transversa and G. lancangensis. To understand whether ants influence the spatial pattern of seedlings, we compared the spatial distribution of seedlings of G. lancangensis in its natural habitat with that of two other species in the Globba genus, G. barthei and G. racemosa; the latter two species propagate mainly by bulbils which are dispersed by abiotic means. Nine 25 m×25 m plots, three plots for each species, were established and the location of every Globba seedling inside the plots was recorded. The mean distance to the nearest neighbor of G. lancangensis was significantly higher than both G. barthei ((36.8±1.45) cm vs. (29.8±2.70) cm, Mean±SE; t73,33=2.11, p=0.037) and G. racemosa ((36.8±1.45) cm vs. (28.7±3.16) cm, t73,31=2.33, p=0.022). We used Z-values to describe the degree of aggregation of the populations of the three species. The Z-value of G. lancangensis (-1.70±0.19, Mean±SE) was significantly larger than the Z-value of both G. barthei (-2.58±0.37, t73,33=2.36, p=0.020) and G. racemosa (-3.28±0.53, t73,31=3.54, p=0.001), indicating that G. lancangensis was significantly less aggregated. These results suggest that ants make a significant contribution to dispersing G. lancangensis seedlings by increasing the distance to its nearest neighbor and decreasing the degree of aggregation in its natural habitat.