No abstract

Ant communities in Vermont and New York woods were sampled in four time periods to determine species composition, relative abundances, and nest locations in space. The Vermont community was richer, containing more species and higher nest densities than New York. Both communities followed the geometric distribution of species abundances, suggesting that a single resource was mediating competition. The resource most clearly implicated was suitable nest sites, principally pre-formed plant cavities. Nonrandom species associations, underdispersion in every season, and the occurrence of incipient nests overwintering aboveground all implicated shortage of such cavities. Furthermore, microhabitat differences which produce suitable nest sites occur over a very small scale in these communities.

Slavemaking ants are of great interest to biologists because of their highly specialized lifestyle. Slavemakers rely on the presence of heterospecific ''slaves'' to perform routine chores such as foraging and brood care. While we have considerable information on the behavior of these ants, mostly gleaned from laboratory studies, we know very little of their basic ecology. Here we report data collected over 20 yr in three geographic sites on the occurrence, spatial pattern, nest site use, and demography of two slavemaker species and three of the host species they enslave; all are small ants in the tribe Formicoxenini. We found geographic and temporal variation with respect to the interaction between social parasites and their hosts. The slavemaker Protomognathus americanus occurred in each geographic site, and in each its most common host was Leptothorax longispinosus; the other known hosts of this slavemaker, L. curvispinosus and L. ambiguus were less abundant. In a West Virginia site, slavemaker nests were smaller than in New York and Vermont sites. Additional data from West Virginia showed that the slavemaker is strongly constrained by its hosts there, but we found little impact of the parasite on its hosts. By contrast, in the New York site, we found strong evidence that the majority host was affected by the slavemaker: host nests showed important life history shifts between neighborhoods containing slavemakers vs. those that were parasite-free. Furthermore, the slavemaker was able to subjugate large host nests there and had large slave pools. In a third site in Vermont, parasite and host demography reflected their interaction weakly. We discovered a second slavemaking species there, and both parasites were preferentially found in areas of high host density. However, we uncovered no demographic or spatial evidence that slavemakers affected their hosts in Vermont. Likewise, we found no evidence in any site of demographic responses by the minority hosts to the presence of slavemakers. Thus our results imply that host-parasite interactions varied among host species and among geographic locales. The slavemaker system therefore is amenable to analysis in terms of parasite-host coevolution.

Colony structure and reproductive investment were studied in a population of Myrmica punctiventris. This species undergoes a seasonal cycle of polydomy. A colony overwinters in entirety but fractionates into two or more nest sites during the active season and then coalesces in the fall. Colony boundaries were determined by integrating data on spatial pattern, behavioral compatability, and genetic relatedness as revealed by protein electrophoresis. Colonies contained at most one queen. Consequently, a colony consisted of one queenright nest and one or more queenless nests. Furthermore, estimates of relatedness were fully consistent, with queens being single mated. M. punctiventris therefore has a colony genetic structure that conforms to the classical explanation of the maintenance of worker sterility by kin selection. Kin selection theory predicts that workers would favor a female-biased allocation ratio while selection on queens would favor equal investment in males and females. We predicted that in polydomous populations, queenless nests would rear more female reproductives from diploid larvae than queenright nests. There was a significant difference between queenright and queenless nests in sexual allocation; queenless nests allocated energy to reproductive females whereas queenright nests did not. At neither the nest nor colony levels did worker number limit sexual production. We also found that nests tended to rear either males or females but when colony reproduction was summed over nests, the sexes were more equally represented. The difference in allocation ratios between queenless and queenright nests was attributed solely to queen presence/absence. Our work shows that polydomy provides an opportunity for workers to evade queen control and thereby to sexualize brood.

Investigations of time budgets reveal that for many animals a surprising proportion of their active time is spent in inactivity. The question of why these beasts are often idle is investigated by examining their foraging behavior in a model which does not utilize optimization criteria. If an organism's goal is to stay alive, one satisfactory strategy is a thermostat feeding process whereby the animal initiates foraging when it perceives hunger and ceases when it becomes satiated. The simple model is formulated as a Markov chain and analyzed for three cases. Results from each case predict that for many combinations of activity levels and resource spectra, the time spent looking for food is smaller than the time spent not foraging, and laziness may result. Simple decision rules as well as optimization schemes are therefore useful for studying some types of foraging behavior.