Supercolonial ants are among the largest cooperative units in nature, attaining extremely high densities. How these densities feed back into their population growth rates and how abundance and extrinsic factors interact to affect their population dynamics remain open questions. We studied how local worker abundance and extrinsic factors (rain, tree density) affect population growth rate and spread in the invasive big-headed ant, which is disrupting a keystone mutualism between acacia trees and native ants in parts of East Africa. We measured temporal changes in big-headed ant (BHA) abundance and rates of spread over 20 months along eight transects, extending from areas behind the front with high BHA abundances to areas at the invasion front with low BHA abundances. We used models that account for negative density dependence and incorporated extrinsic factors to determine what variables best explain variation in local population growth rates. Population growth rates declined with abundance, however, the strength of density dependence decreased with abundance. We suggest that weaker density dependence at higher ant abundances may be due to the beneficial effect of cooperative behavior that partially counteracts resource limitation. Rainfall and tree density had minor effects on ant population dynamics. BHA spread near 50 m/year, more than previous studies reported and comparable to rates of spread of other supercolonial ants. Although we did not detect declines in abundance in areas invaded a long time ago (> 10 years), continued monitoring of abundance at invaded sites may help to better understand the widespread collapse of many invasive ants.

超殖民地蚂蚁是自然界中最大的合作单位之一，密度极高。这些密度如何反馈到其人口增长率以及丰度和外部因素如何相互作用以影响其人口动态仍是悬而未决的问题。我们研究了当地工人的丰富度和外部因素（雨水，树木密度）如何影响人口增长率并在侵入性大头蚁中传播，这正在破坏东非部分地区的相思树与本地蚂蚁之间的关键共生关系。我们测量了八头样大头蚁（BHA）丰度的时间变化和在20个月内的扩散速率，从BHA丰度高的前部后面区域扩展到BHA丰度低的入侵前部区域。我们使用模型说明负密度依赖性，并结合外部因素来确定哪些变量最能解释当地人口增长率的变化。人口增长率随着数量的增加而下降，但是密度依赖性的强度随着数量的增加而下降。我们建议，在较高的蚂蚁丰度下较弱的密度依赖性可能是由于合作行为的有益效果部分抵消了资源限制。降雨和树木密度对蚂蚁种群动态影响较小。BHA的扩散速度接近50 m /年，比以前的研究报告要多，并且与其他超殖民地蚂蚁的扩散速度相当。尽管我们没有发现很久以前（> 10年）入侵地区的丰度下降，