Dr. Walter R. Tschinkel
Robert O. Lawton Distinguished Professor of Biological Science;
Smith, J. J., B. F. Platt, G. A. Ludvigson, and J. R. Thomasson. 2011. Ant-nest ichnofossils in honeycomb calcretes, Neogene Ogallala Formation, High Plains region of western Kansas, U.S.A., Paleogeology, Paleoclimatology, Paleoecology 308:383-394. This publication presents Daimoniobarax tschinkeli, a new species of fossil ant nest named for Dr. Walter R. Tschinkel.
The Fire Ants by Walter R. Tschinkel (Harvard University/Belknap Press, 2006)
Research and Professional Interests:
Ants are among the most important organisms found in mid- to low-latitude terrestrial ecosystems, often playing keystone roles. Their success is due largely to their highly social way of life; they live in colonies ranging in size from a few dozen to several hundred million individuals. In many ways, ant colonies function like superorganisms—tasks and physiological roles (including reproduction) are divided among the queen and several types and ages of workers. My research recognizes the organism-like nature of ant colonies: each colony most commonly begins life as a single individual and goes through a process of growth, development, and death; specific colony functions are carried out by specialized classes of workers, larvae, or sexual individuals; competition takes place among colonies, just as it does among individuals of nonsocial animals; nourishment must be taken in by colonies, distributed, and allocated among colony members and colony functions; colonies must produce specialized sexual individuals (propagules) for reproducing themselves, and these must leave the colony, mate, and found new colonies.
Current and past research projects follow several major themes.
(1) Sociogenesis (parts are ongoing): Just as an organism results from the growth of a zygote through the rules and interactions of embryogenesis, so the mature ant colony is produced from the single, mated queen through the rules and interactions of sociogenesis. Just as the differences among mature organisms reflect the differences in their rules of embryogeny, so the differences among the mature colonies of species of ants reflect the differences in their rules of sociogenesis. Describing and unraveling the rules of sociogenesis is one of the broad goals of our research. Actual projects have included: (a) a description of the changes in fire-ant worker size and size distribution (polymorphism) as colonies grow; (b) changes in the patterns of labor distribution as colonies grow; (c) the social regulation of egg-laying rate in fire-ant queens; (d) the rules by which workers feed larvae; (e) the manner in which the size- and age-based division of labor among fire-ant workers translates into a force of sociogenesis; (f) most recently, how harvester ant colonies allocate labor to foraging as they grow and pass through the annual cycle.
(2) Colony reproduction: A second major theme focuses on ecological and evolutionary aspects of colony reproduction. Whereas newly mated fire-ant queens typically found colonies alone, they often cooperate with other newly mated queens during this period. Because workers will kill all but one of the queens in such associations, it is a puzzle that queens choose to associate. The puzzle is compounded by the existence of brood-raiding—workers from incipient colonies steal brood from other such colonies, who steal it back, until one colony is victorious. Workers then all coalesce in the winning nest, abandoning their mothers. We have been attempting to solve these evolutionary puzzles, as well as to link these colony-level phenomena to population-level outcomes.
While trying to determine whether colonies whose queens have died are able to replace them, we discovered a new mode of colony founding. Fire ant colonies overwinter a small number of sexual reproductives, and these depart on mating flights during the very early spring. The function of these overwintered queens is to seek out orphaned colonies, enter them, and take over as functioning queens. This is an essentially parasitic mode of colony founding, because the new queen is unrelated to the workers who will rear her offspring. We have estimated the proportion of mature colonies that are headed by such replacement queens in both S. invicta and S. geminata.
(3) Population dynamics among colonies (partly ongoing): Relatively little work has been done on the dynamics of populations of colonies. With Dr. Eldridge Adams (University of Connecticut), we established long-term mapped plots that yielded data on the "birth," death, spacing, and movement of over 1000 fire ant colonies. This long-term study was coupled with determinations of territory size and study of territorial defense, giving insight into how the behavior of colonies results in the characteristics of populations and how the characteristics of neighborhoods feed back on territory area, colony size, and fitness. We are currently experimenting with the effects of neighborhood density on the territory area and forager density of focal colonies.
A fire-ant territory: boundaries shown by tape, colony by blue flag.
In 2010, I established a long-term study of a population of Florida harvester ants, mapping (with GPS) the location and condition of over 300 colonies. The site is visited several times a year, and any changes noted and mapped. As with the fire-ant study, the births, deaths, and moves yield a picture of population interactions as well as size-related colony longevity and behavior.
A section of the mapped Florida harvester ant population on Google Earth. Colonies move about once a year, resulting in different map locations.
(4) The natural history of other ant species (ongoing): We have an ongoing interest in the biology of several other species of Florida ants, including the Florida harvester ant (Pogonomyrmex badius), the winter-active Prenolepis imparis, several arboreal species, and any other species that strike us as "neat." These studies often follow the same themes established with the fire-ant research described above, e.g. the sociogenesis of harvester-ant colonies, but include many other aspects of natural history. Most recently, we have worked on the local fungus-gardening ant Trachymyrmex septentrionalis, asking whether the workers know what substrate is best for their fungus gardens. Another example is Dorymyrmex mariae, a multiple-queen species that shows an enormous seasonal expansion and contraction, existing as a single nest in winter and expanding to up to 60 nests in summer. Most recently, we investigated the seasonal life histories of the trap-jawed Odontomachus brunneus and are currently investigating the piney flatwoods most abundant ant, Pheidole morrisi.
(5) Arboreal ant ecology (completed): The discovery that the arboreal ant Crematogaster ashmeadi is the main food of the endangered red-cockaded woodpecker led to a collaborative study (with Dr. Frances C. James of this department) of the ecosystem processes that link recurrent ground fires in the longleaf pine ecosystem with the well-being of the red-cockaded woodpecker, the cycling of nutrients, changes in the ground-cover vegetation, and the abundance of arboreal ants. This long-term project consisted of a large experiment in which three different prescribed fire treatments were applied to about 60,000 acres of the Apalachicola National Forest and the effects on woodpeckers, vegetation, nutrients, ants, and other insects were monitored.
(6) Allometry and the evolution and development of fire ant species (ongoing): Division of labor among the workers of ant colonies is based on worker age, but in a minority of species it is also based on worker body size (which varies greatly), a phenomenon referred to as polymorphism. The shape of a number of worker body parts changes as workers become larger. These shape changes are assumed to be associated with functional changes, which in turn are associated with division of labor by body size. We have determined the growth rules that change body shape in S. invicta, and because we have strong indication that these rules apply across fire-ant species, we are continuing with allometric studies of all of the fire-ant species we can acquire. These studies will tell us both how worker polymorphism evolves within a genus and how it develops.
(7) Ecological disturbance, native ants, and fire ants (ongoing): Ever since S. invicta landed on the shores of Mobile Bay, the belief has been strong that S. invicta suppresses native ant populations through competition, but our recent studies and those of Joshua King suggest otherwise. Our results show that, instead, ecological disturbance suppresses native ant populations while simultaneously favoring S. invicta, a specialist in exploiting ecological disturbance. Our large field experiments have shown that fire ants do not compete with cooccurring ants in pasture. Our continuing experiments in more natural flatwoods habitats are testing the effects of both disturbance and fire ants on native ants. (The photo shows plowing of treatment plots, a disturbance that favors fire ants.) Future experiments will determine exactly what features of disturbance favor fire ants and harm native ants. Current projects are focused on the role that newly mated ant queens play in assembling ant communities through habitat selection.
(8) The organization of foraging in fire ant colonies (ongoing): In ant colonies, foraging is regulated at the colony level such that the number and type of foragers that arrive on a food find are appropriate to the value of the food, its amount, its distance from the nest, and the colony's nutritional needs. Although a good deal is known about how recruitment works at the level of the individual forager, little is known about this process at the colony level. We are characterizing the allocation of workers to foraging in relation to colony size and territory size and are determining how these foragers are distributed and recruited throughout the foraging territory by means of underground foraging tunnels.
(9) The nest architecture of ground-nesting ants (ongoing): The development of methods that allow subterranean ant nests to be filled with casting material (dental plaster, wax, or liquid metal) has spurred our study of the nest architecture of ants. Because this is a pioneering study, the majority of the work consists of making casts of the nests of as many species as possible (like the one in the photo of the nest of the Florida harvester ant) and including the full range of nest sizes within each species. This work produces both an inventory of the diversity of architectures and a developmental sequence within each species. The casts produced in this study are objects of great beauty and interest and represent an intersection of science and art.
(10) The fairy circles of the Namib Desert (ongoing): The eastern margin of the Namib Desert of Namibia, Africa is home to a mysterious phenomenon in which the grassy vegetation is punctuated by tens of thousands of evenly spaced barren spots surrounded by taller grass. The origin of these circles is unknown, although many hypotheses have been offered. Using satellite images and visits on the ground, I am describing the range of variation of fairy circles and estimating their life span.
Fairy circles in the Namib Desert.
Adams, E. S., and W. R. Tschinkel. 2001. Mechanisms of population regulation in the fire ant Solenopsis invicta: an experimental study. J. Anim. Ecol. 70: 355-369. (full text, PDF)
Haight, K. L., and W. R. Tschinkel. 2003. Patterns of venom synthesis and use in the fire ant, Solenopsis invicta. Toxicon 42:673-682. (full text, PDF)
Lubertazzi, D., and W. R. Tschinkel. 2003. Ant community change across a ground vegetation gradient in north Florida's longleaf pine flatwoods. J. Insect Sci. 3, article number 21 (17 pages). (full text, PDF)
Tschinkel, W. R., A. S. Mikheyev, and S. R. Storz. 2003. Allometry of workersin the fire ant, Solenopsis invicta. J. Insect Sci. 3, article number 2 (11 pages). (full text, PDF)
Tschinkel, W. R. 2004. The nest architecture of the Florida harvester ant, Pogonomyrmex badius. J. Insect Sci. 4, article number 21 (19 pages). (full text, PDF)
Seal, J. N., and W. R. Tschinkel. 2006. Colony productivity of the fungus-gardening ant, Trachymyrmex septentrionalis McCook, in a Florida pine forest (Hymenoptera: Formicidae). Ann. Entomol. Soc. Am. 99: 673-682. (full text, PDF)
King, J. R., and W. R. Tschinkel. 2006. Experimental evidence that the introduced fire ant, Solenopsis invicta, does not competitively suppress co-occurring ants in a disturbed habitat. J. Anim. Ecol. 75: 13701378. (full text, PDF)
Tschinkel, W. R. 2006. The Fire Ants. Belknap/Harvard University Press. 730 pp. (2007 Pulitzer Prize nominee)
Smith, C. R., and W. R. Tschinkel. 2007. The adaptive nature of non-food collection for the Florida harvester ant, Pogonomyrmex badius. Ecol. Entomol. 32: 105-112. (full text, PDF)
Laskis, K. O., and W. R. Tschinkel. 2009. The seasonal natural history of the ant, Dolichoderus mariae (Hymenoptera: Formicidae) in northern Florida. J. Insect Sci. 9:2. (full text, PDF)
Tschinkel, W. R. 2010. The foraging tunnel system of the Namibian termite, Baucaliotermes hainesi. J. Insect Sci. 10:65. (full text, PDF)
Tschinkel, W. R. 2010. Methods for casting subterranean ant nests. J. Insect Sci. 10:88. (full text, PDF)
King, J. R., and W. R. Tschinkel. 2008. Experimental evidence that human impacts drive fire ant invasions and ecological change. Proc. Natl. Acad. Sci. USA 105:20339-20343. (full text, PDF)