The Impact of the Leaf Cutter Ant Atta Colombica on the Energy Flow of a Tropical West Forest Author(s): Ariel E. Lugo, Edward G. Farnworth, Douglas Pool, Patricio Jerez, Glen Kaufman Source: Ecology, Vol. 54, No. 6 (Nov., 1973), pp. 1292-1301 Published by: Ecological Society of America Stable URL: http://www.jstor.org/stable/1934191 Accessed: 21/07/2010 10:41 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=esa. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. http://www.jstor.org THE IMPACT OF THE LEAF CUTTER ANT A TTA COLOMBICA ON THE ENERGY FLOW OF A TROPICAL WET FOREST' ARIEL E. LUGO Department of Botany, Universityof Florida, Gainesville, FL 32601 EDWARD G. FARNWORTH Department of Entomology and Nematology, Universityof Florida DOUGLAS POOL Department of Agronomy, Universityof Florida PATRICIO JEREZ Department of Botany, Universityof Florida and GLEN KAUFMAN Universal Plant Breeding Services, Ltd., Box 50, Caistor, London, England Abstract. The patterns,quantity, and activities associated with the leaf-cuttingof Atta colombica were studiedAugust 20-27, 1971, in a lowland tropicalwet forestat Osa Peninsula, Costa Rica (Lat. 08'42'N Long. 83029'W). The study nest had an area of 44.8 m2 and covered1.4 ha of forestfloor. Daily, on a m2of forestfloor, the studynest had inputs of 10.17 leaf fragmentswith an area of 0.0108 M2, a weightof 0.0813 g, an ash content of 0.0039 g, and a potentialenergy of 0.3455 Kcalories. The ants returnto the forestfloor 0.0525 g of refusewith a potentialenergy of 0.0764 Kcalories and an ash contentof 0.0212 g/m2 day. It was calculatedthat the leaf-cuttingactivity of ants reducedthe grossproduction of the forestby 1.76 Kcal/m2*day but acceleratednet productionby at least 1.80 Kcal/m2. day throughthe returnof ash rich in phosphorusto the forestfloor. The size of the Atta nest may be determinedby the balance of the energyinput to the nest and the cost of ob- taining,carrying (concentrating), and distributingthe potentialenergy into the nest. Of a workforce of 12,000 ants/M2of trail,75% were not carryingleaves and were assumedto be doingtrail maintenancework. Rainfalland litterfall were the main obstaclesof leaf trans- port,which was about70% efficient. The ant's energyallocation for maintenance,which limitsgrowth, and the establishment of reward feedbacksto theirenergy producers have implicationsfor man's urban system development. INTRODUCTION (Weber 1966) and the foraging activities of ants Scatteredon the floor of many tropical forestsone (Cherrett 1968a, Harris 1969, Rockwood 1971). E. 0. frequentlyfinds trails teeming with traffic,reminis- Wilson (1971) has reviewed the literature on social insects. cent of the freewaysof our major cities. The traffic This study that one observes, however, is not of cars but of a involves the quantificationof the im- pact of leaf multitude of ant and termite species, working and cuttingon the energy flow of the sur- rounding survivingin the forest. One of these species is the forest,and observationsrelated to activities associated leaf cutterant Atta colombica, which belongs to the withleaf cuttingand transport.An energy flow tribe Attini,a group of fungus-growingants of the diagram is presentedin the discussion, showing the major new world (Weber 1966, 1969). Because of their energy relations of an Atta nest. It is hoped that this conspicuous trails covered with ants carryinggreen study will encourage investigatorsin leaf fragments,these ants have attracted the atten- this field to perfectand quantifythe energydiagram tion of many biologists. Studies have been oriented for this important component of the forest com- towardbehavior and plant-animalinteractions (Mark- munity. ham 1966, Hodgson 1955, Parsons 1968, Martin METHODS 1970, Martin and associates 1969a-b, Martin and Martin 1970), the natural history of leaf cutters Study area '-ReceivedFebruary 10, 1972; acceptedFebruary 14, The study took place on the Osa Peninsula, 1973. Puntarenas Province, in southwestCosta Rica, C.A. Autumn 1973 LEAF CUTTER ANTS AFFECT ENERGY FLOW 1293 we collected 200 leaf fragmentsfrom ants on the trails and made the following determinations: leaf area, wet and dry weight, ash content, and caloric value. The caloric values were determined with a Parr Bomb CalorimeterModel 1241. We obtained the total nest input by plottingthe VR-f rate of leaf-fragmentflow over the study period, 2 determiningthe area under that curve, and multi- plying the total number of fragmentsentering the nest by their mean weight, ash weight, and caloric value. Results were expressed on an area basis (Fig. 1). Efficiencyof transportand program of leaf cutting An estimateof the efficiencyof leaf transporton the lengthytrails leading to the nest was made on the morningof 25 August. Counts were made of frag- ment-carryingants leaving the treesand those arriving FIG. 1. Scale drawingof the studynest and other at the nest. All treesalong a discretetrail were moni- ant activitiesin the vicinity.Trail areas in m2: Trail tored, so that all the trafficof ants could be ac- I-130.9, Trail II-244.0, Trail III-307.3, Trail IV- counted for. The ratio of ants arrivingat the nest 179.8, Trail V-72.3. These values include the canopy area of treesbeing cut; the total area of trailswithout to ants leaving the tree was considered a measure the canopies was 32.3 m2. The centralnest areas was of leaf transportsuccess. 10.0 m2and the total refusepile 2.5 M2. The total area We investigated the cycles of leaf cutting by whereants were active was 946.8 m2and the surrounding examiningtrees periodically during the day for cutting area of forestconsidered as the ant's immediatehabitat activity. In addition, the morningwave of workers (enclosedby the solid line) was 14,025M2. Solid dots = abandonedant nest; the X = an activenest. Tree identifi- leaving the nest and moving into trees was followed cations: 1 = Trema micrantha (capulin blanco); 2 = Inga and timed for rate of movementand commencement sp. (guavo); 3 = Brosimum tiles (baco); 4 = Brosium of leaf cutting. sapiifolium (morillo); 5 = Goethalsia meiantha (guacimo blanco); 6 = Sapium jamaicenses (olive); 7 = Virola sp. Ratio of non-carryingto leaf-carryingants and (frutadorada); questionmarks = two treesof the same speciesthat could not be identifiedand one treeon Trail ant biomass IV that was overlooked. The tree at the nest was A 5 X 10 cm framewas used for countingthe ants Terminalia lucida (guayabon). All trees, except the with and without leaves traveling along Trail 2 on nest tree,were softwoods. 26 August. We conducted the inventoryby placing the frame over 10 spots along a transectevery hour (lat. 08'42'N long. 83029'W). This area is a tropical between 0730 and 1600. At the end of the experi- wet forest characterized by an annual rainfall of ment 400 ants were collected for biomass deter- minations. 4200 mm, an annual mean temperatureof 26.30 C, and a brief dry season from January to March Rate of refuse deposition (Holdridge et al. 1971). A large Atta nest (Fig. 1) was observed for 7 days (20-27 Aug. 1971) while Refuse from the nest's internalprocesses was de- the ants on the to side the authors participated in the summer tropical posited by forestfloor one of the nest (Fig. 1). We measured the rate of deposi- biology course (No. 71-6) sponsored by the Or- tion by placing a plastic sheet under this area, and ganization of Tropical Studies, Inc. collecting and weighing the refuse accumulation at various time intervals. Leaf imports into the nest To estimate the amount of leaf fragmentsenter- Other observations ing the nest,we monitoredthe five trailscoming into Throughoutthe studyall authorsspent many hours the nest for a 50-hour period for 1/2-hintervals dur- observing and measuring the behavior and ac- ing the day and at hourly intervals at night, since tivitiesof ants on the trails,nest, and trees. In addi- leaf cutting was essentiallyzero at night. All leaf tion, the observationsand experiences of other OTS fragmentscarried during a 5-minute interval were studentsaided us in clarifyingsome of the mecha- counted. Every 3 hours duringperiods of leaf cutting, nisms operatingin this nest. 1294 ARIEL E. LUGO ET AL. Ecology, Vol. 54, No. 6 Trail. Aug.2123,1971 600 57 6 600As 516 Trail2 Aug21 23.1911 480 410 400 38X 84 g/hr 288 28.8g/hr. 200 19.2 EL 19?2 E. 20 96 9.6 12 6 12 6 12 6 12 6 12 12 6 12 6 12 6 1? 6 12 PM AM PM AM PM AM PM AM Timeof Day Timeof Day the TraiI3.AUg.2123,12 AUT.2Ti23219T1Trail4. Trail 56 Tcnrte dttgm 5hmtlecb009gel480 fa e;toa 4050 ,384mliy 384 288 g/hr.288V r Eg/r 280 1 200 21 200 1 1-r 128 600~~~~~~~~~~1 626 ~~~~57~~~~~19 60 127C ~~96 .1999 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~~~~ ~ ~~~ ~~~~ 12 6 12 6 12 6 12 6 12 12 6 12 6 12 6 6 12 PM AM PM AM PM AM PM AM limeof Day TimeofDay 5 000 TraH5.
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