In 1977 ecologists Stephen Hubbell and Leslie Johnson recorded a dramatic example of how social interactions can produce and enforce regular spacing in a population. They studied competition and nest spacing in populations of stingless bees in tropical dry forests in Costa Rica. Though these bees do no sting, rival colonies of some species fight fiercely over potential nesting sites.
Stingless bees are abundant in tropical and subtropical environments, where they gather nectar and pollen from a wide variety of flowers. They generally nest in trees and live in colonies made up of hundreds to thousands of workers. Hubbell and Johnson observed that some species of stingless bees are highly aggressive to members of their species from other colonies, while other species are not. Aggressive species usually forage in groups and feed mainly on flowers that occur in high-density clumps. Nonaggressive species feed singly or in small groups and on more widely distributed flowers.
Hubbell and Johnson studied several species of stingless bees to determine whether there is a relationship between aggressiveness and patterns of colony distribution. They predicted that the colonies of aggressive species would show regular distributions, while those of nonaggressive species would show random or closely grouped (clumped) distribution. They concentrated their studies on a thirteen-hectare tract of tropical dry forest that contained numerous nests of nine species of stingless bees.
Though Hubbell and Johnson were interested in how bee behavior might affect colony distributions, they recognized that the availability of potential nest sites for colonies could also affect distributions.So as one of the first steps in their study, they mapped the distributions of trees suitable for nesting. They found that potential nest trees were distributed randomly through the study area. They also found that the number of potential nest sites was much greater than the number of bee colonies. What did these measurements show the researchers? The number of colonies in the study area was not limited by availability of suitable trees, and a clumped or regular distribution of colonies was not due to an underlying clumped or regular distribution of potential nest sites.
Hubbell and Johnson mapped the nests of five of the nine species of stingless bees accurately, and the nests of four of these species were distributed regularly. All four species with regular nest distributions were highly aggressive to bees from other colonies of their own species. The fifth species was not aggressive, and its nests were randomly distributed over the study area.
The researchers also studied the process by which the aggressive species establish new colonies. Their observations provide insights into the mechanisms that establish and maintain the regular nest distribution of these species. Aggressive species apparently mark prospective nest sites with pheromones, chemical substances secreted by some animals for communication with other members of their species. The pheromone secreted by these stingless bees attracts and aggregates members of their colony to the prospective nest site; however, it also attracts workers from other nests.
If workers from two different colonies arrive at the prospective nest at the same time, they may fight for possession. Fights may be escalated into protracted battles.The researchers observed battles over a nest tree that lasted for two weeks. Each dawn, fifteen to thirty workers from two competing colonies arrived at the contested nest site. The workers from the two colonies faced off in two swarms and displayed and fought with each other. In the displays, pairs of bees faced each other, slowly flew vertically to a height of about three meters, and then grappled each other to the ground. When the two bees hit the ground, they separated, faced off, and performed another aerial display. Bees did not appear to be injured in these fights, which were apparently ritualized. The two swarms abandoned the battle at about 8 or 9 A.M. each morning, only to re-form and begin again the next day just after dawn. While this contest over an unoccupied nest site produced no obvious mortality, fights over occupied nests sometimes kill over 1,000 bees in a single battle.
1977年，生态学家Stephen Hubbell和Leslie Johnson记录了一个有关社会交互作用如何能在种群中产生并维持一个规则的空间分布。他们在Costa Rica的热带旱地森林中研究了无刺蜜蜂种群中的竞争关系和巢穴间距。尽管这些蜜蜂不叮人，一些种类的敌对群体间会为了潜在筑巢位置激烈斗争。 无刺蜜蜂在热带和亚热带环境中广泛存在。它们从各种各样的花上收集花蜜和花粉。它们一般栖居在树上，群居生活，群体由几百到几千工蜂组成。Hubbell和Johnson观察到，一些种类的无刺蜜蜂对于来自其他群体的本物种蜜蜂具体很强的攻击性，但其他种类的蜜蜂则不然。攻击性物种通常集体出动觅食，主要以密集的花丛为食。无攻击性的物种通常单独觅食，或以小团体形式觅食，它们主要以分散的花为食。 Hubbell和Johnson研究了几种无刺蜜蜂来确定攻击性和群体分布之间是否存在联系。他们预测攻击性物种的群体将呈现规则分布，而无攻击性物种的群体将呈现随机分布或集群分布。他们把研究集中于热带旱地森林中一个13公顷的地带，这个地带中包含了9种无刺蜜蜂众多的巢穴。 尽管Hubbell和Johnson对蜜蜂的行为怎样影响群体分布很感兴趣，他们意识到潜在筑巢位置的可获得性也会影响群体的分布。因此在他们研究的第一步，他们绘制了适合筑巢的树的分布图。他们发现潜在筑巢的树在研究区域内是随机分布的。他们还发现潜在筑巢位置的数量比蜜蜂群体的数量要多得多。这些测量结果说明什么呢？研究区域的蜜蜂群体数量并不受可获得的适宜的树的限制，蜂群集群分布或规则分布不是由于潜在筑巢位置的集群分布或规则分布。 Hubbell和Johnson精确绘制了9种无刺蜜蜂中5种蜜蜂的巢穴，其中4种蜜蜂的巢穴是规则分布的。这4种巢穴规则分布的物种都对来自其他群体的本物种蜜蜂具有高度攻击性。第五个物种不具有攻击性，它们的巢穴在研究区域是随机分布的。 研究者们也研究了攻击性物种建立新群体的过程。他们的观察洞悉了这些物种建立和维持巢穴规则分布的机制。攻击性物种显然是利用信息素来标记可能的巢穴地点，信息素是一些动物分泌出来用于和同种类其他成员交换信息的化学物质。这些无刺蜜蜂分泌的信息素吸引并召集同群的成员前往可能的筑巢地点，然而，信息素也会吸引其他群体的工蜂。 如果两个来自不同群体的工蜂在同一时刻到达可能筑巢地点，它们会为争夺占有权而开战。战斗可能会升级为持久战。研究者曾观察到围绕一棵筑巢树的战争持续了两周。每天黎明时分，来自竞争双方的15-30只工蜂到达争夺巢穴的地点，分成两拨，互相斗殴。在对阵过程中，成对的蜜蜂面对面，慢慢垂直飞到3米左右的高度，然后互相扭打落到地上。当两只蜜蜂掉到地上后，它们会分开，重新对峙，再次表演一遍空中炫耀行为。蜜蜂们在这样的争斗中并没有受伤，这些争斗显然只是形式化的。对阵双方在每天上午8点或9点偃旗息鼓 ，第二天破晓时卷土重来。尽管这种对未被占领的巢穴的争夺不会造成明显的伤亡，但对已占领巢穴的争夺有时在单场战争中就死掉1000多只蜜蜂。