Ant Diversity Between Two Methods of Coffee Farming in the San Luis Valley Jo Anna Leachman Berea College, Department of Biology Abstract Due to herbaceous, fungal, or insectivorous pests, coffee farms are sometimes treated with chemicals throughout the year to eliminate these problems. However, this can impact beneficial insects, like predaceous ants. Using tuna and honey as bait, I captured ants on the ground of three organic and three inorganic coffee farms. I also measured the amount of ground vegetat ion at each site. I found a significantly higher diversity of both total and predaceous ant species on organic farms p < 0.001, p < 0.005. The amount of ground vegetation on organic farms was also significantly higher p < 0.0001. Resumen Debido a los i nsectos y los hongos, las fincas de cafÃ© estÃ¡n a veces siendo tratadas con quÃmicos durante todo el aÃ±o por estos problemas. Sin embargo, esto puede afectar a los insectos beneficiosos, como a las hormigas que comen los malos insectos. Uso de atÃºn y miel c omo carnada, capture hormigas en la tierra de tres fincas orgÃ¡nicas y tres fincas que usan quÃmicos. TambiÃ©n , medÃ la cantidad de vegetaciÃ³n de la tierra de cada finca. Encontre una diferencia significativa de total hormigas en las fincas orgÃ¡nicas p < 0.001 y tambiÃ©n una diferencia significativa de hormigas rapaz p < 0.005. La vegetaciÃ³n en la tierra es significativa mas en las fincas orgÃ¡nicas p < 0.0001. La cantidad de vegetaciÃ³n en la tierra afecta la diversidad de especies de fincas de cafÃ©. M as estudios miran en la dieta de las hormigas, la vegetaciÃ³n de la tierra, y la diversidad de los malos insectos es necesario para comprender mejor esta interacciÃ³n. Introduction In Latin America, coffee Coffea arabica is an important export crop, accou nting for 44% of the area of permanent cropland Perfect et al. 1996. In Central America approximately 750,00 ha of land are in coffee production Perfecto et al. 1996. Like most agricultural crops, coffee is commonly treated with chemicals to avoid fung al, herbaceous, or herbivorous pests. This elimination of pests inevitably results in a loss of species diversity on coffee farms, specifically arthropods Vober 1999. Therefore, the loss of arthropods also results in a decrease of the order Hymenoptera, which includes ants. In the Neotropics ants have been considered to be the most important pests of crops Hanson 1995. Among a variety of crops they have been found to be detrimental as herbivores, have mutualisms with Homopteran pests, and also interfer e with harvests Hanson 1995. For example, the morphological species Solenopsis found in this study
has been described to sting fiercely, eat tips of young shoots, and protect Homoptera Hanson 1995. Also, in Costa Rica a mealy bug that is a vector for d isease in pineapple is protected by Solenopsis and Pheidole a morphological species also found in this study Hanson 1995. Despite the bad rep ants have received, species do exist that are beneficial to agricultural crops as important pest predators R isch 1983 and Hason 1995. Ants forage on vegetation, and among their collections of food are known to include herbivores found on plants Holldobler and Wilson 1990. In Cuba Pheidole was used to reduce populations of the sweet potato weevil Hanson 1995 , and in Mexico ants reduced the number of both arthropod individuals and species in plots of corn and squash Holldobler and Wilson 1990. Although Solenopsis is also described as a seed predator, it is more dependent on insect prey and honeydew Holldobl er and Wilson 1990. Another morphological species found in this study, Ectatomma preys on cotton boll weevils Hogue 1993. Ants can also be beneficial by foraging on unwanted plants. For example, in Mexico and Central America the lowest biomass of weeds and their seeds was found where Solenopsis occurred Holldobler and Wilson 1990. The use of herbicides, therefore, may eliminate vegetation that may sustain beneficial arthropod species. Past studies have shown a decrease in arthropod species on coffee farms treated with pesticides Vober 1999, but none have focused specifically on ants. This project was done in the San Luis Valley of Guanacaste, Costa Rica, to test ant species diversity and the amount of ground vegetation in coffee farms treated with p esticides any type of anti herbivore, weed, or fungal chemicals versus those untreated. The foraging habits of each morphological species was also studied in literature to determine, along with the habits, which were predaceous to identify potentially be neficial ants. Materials and Methods The project was conducted from mid October to mid November, 2000 in the San Luis Valley of Puntarenas, Costa Rica. Six available coffee farms were selected; three that use no chemical treatments organic and three th at do inorganic. The three inorganic farms were located in Finca la Bella of San Luis Arriba, a co op of approximately seven family farms. The farms of SeÃ±ores Gilberto, Milton, and Oldemar were used. Two of the organic coffee farms were located in San L uis Arriba, and were owned by SeÃ±or Vargas and the other by SeÃ±or Camora. The third organic farm was in San Luis Abajo and was owned by SeÃ±or Ramirez. Two farms were sampled a day, one in the morning and one in the afternoon. Trappings were alternated at each farm between morning 0800 1200 hrs and afternoon 1300 1700 hrs. All farms were, in the end, sampled twice in the morning and twice in the afternoon. A total of three transects were completed during each sampling period, and no rows in one samplin g period were repeatedly used.
A transect was begun by walking approximately ten meters between coffee rows and placing an ant trap on the ground. Each transect consisted of ten ant traps; an ant trap every ten meters. The traps were made of wax paper cut into 5 x 7.5 cm rectangles, folded, stapled, and contained small amounts of tuna and honey. Due to the short length of rows, this sometimes required entry into parallel rows of coffee to lay down ten traps, resulting in up to three rows of coffee being sampled in one transect. A total of 270 traps were used. After lying down a transect, approximately ten minutes passed before walking along the transect and to co llect traps that had the presence of one or more ants on or in the trap. Every ten minutes this was repeated until the transect was checked five times or all envelopes were collected. Each envelope was stapled in consecutive order on a notecard and its pic k up time recorded. The pick up time was recorded as 1 5, depending on which check it was picked up. The notecard was then put in a plastic bag with alcohol to preserve the ants. All ants were identified to morphological species and given a letter. The sev en morphological species were identified to sub family and genus using the keys in Hanson and Gauld 1995 and Holldobler and Wilson 1990 and the foraging habits of each were determined using Hanson and Gauld 1995. Ground vegetation was also sampled at each farm. A 0.5m x 0.5m grid divided into 25 5 x 5 even squares constructed of PVC pipe and string strung through drilled holes was used. At each farm the grid was placed arbitrarily meaning I picked a random number of paces from 10 20 between each site on the ground at twelve different sites. Squares with vegetation protruding through them were counted and a ratio of vegetation was recorded. Diversity values were found using a Shannon Wiener diversity index, and a modified t test was used to test for differences Zar 1984. A Paired Sign Test was used to test for difference in the number of captures of the two most prominent genera over time Zar 1984. The number of captures during each check were graphed Fig. 2 and 3. To test difference in the number captured of the two most prominent morphological species a Chi square test was used Ambrose and Ambrose 1995. The difference of amounts of ground vegetation between the organic and inorganic coffee farms was tested after transforming the data arc sin using a two way ANOVA Zar 1984. Results A total of 720 traps were used and 528 collected with ants. Among the three organic coffee farms four sub families and seven genera were captured, and in the inorganic coffee farms three sub families and fou r genera were captured Table 1. Of these five predaceous genera two sub families were captured in the organic coffee farms, and three predaceous genera two sub families were captured in the inorganic coffee farms Table 1. The ant fauna of the organ ic coffee farms HÂ¹ = 0.4095 was significantly more diverse than the inorganic HÂ¹ = 0.2441 modified t test, p < 0.001.
Also, the predaceous ant fauna of the organic coffee farms HÂ¹ = 0.2590 was significantly more diverse than the inorganic HÂ¹ = 0.1 608 modified t test, p < 0.005. The Paired Sign Test found no significant difference in the number of captures over time between the two farming methods for either morphological species, Pheidole or Solenopsis p = 0.50 and p = 0. 3750, respectively. Also, there was no difference in the total number of Pheidole or Solenopsis captured mean = .779 an d 2.571 respectively, df = 1. T he ground vegetation differed significantly between the two farming methods inorganic mean 4.111, S.D. + 4.990, Organic me an 18.750, S.D. + 7.591 Figure 1, ANOVA, p < 0.0001. Discussion Past studies have shown that there is a positive correlation between ground vegetation diversity and arthropod diversity in coffee farms Perfect et al. 1996. My study supports this findi ng with the decrease in ant diversity between the organic farms with the greater amount of ground vegetation and the inorganic farms with significantly lower ground vegetation, assuming that less vegetation also means less diversity. The decrease in bo th vegetation and arthropods is also a decrease in the food resources of species who are omnivorous, generalized scavengers, predaceous, or forage specifically on the ground and low growing vegetation. Six of the seven morphological species, Pheidole, Sole nopsis, Amblyopone, Hypoponera, Ectatomma, and Dolichoderus found in this study have one form of the aforementioned eating habits Hanson 1995. Therefore it is possible that the loss of vegetation has impacted the diversity of ants on the studied coffee f arms. On chemically treated farms some predaceous species may not be supported with the lack of both ground vegetation and herbivores of ground vegetation. Hanson 1995 lists Ectatomma sp., Pheidole sp., and Solenopsis sp. as specific pest predators, and each genus is represented in both organic and inorganic coffee farms Table 1. However, Amblyopone sp. and Hypoponera sp. are described only as predaceous and were captured only in the organic farms Longino and Hanson 1995, Table 1. The presence of mo re ground vegetation and possibly herbivores in the organic coffee farms may allow a greater resource base to support higher ant diversity. Torres 1984 explains that Â€agricultural land antsÂ utilize the habitat in different ways e.g. different diets th at allow species to coexist. However, by limiting the resources for survival through eliminating weeds along with the herbivores of those weeds may have reduced already restrained microhabitats. This may explain why three of the four genera with the fewest captures exist only in the organic coffee farms. This may also explain why, even though there are fewer genera in the inorganic coffee farms, there were not significantly more captures of the prominent genera than the organic coffee farms. Without the veg etation their levels of fitness could not be enhanced.
Longino and Hanson 1995 describe Hypoponera, Brachymyrmex, Solenopsis, and Pheidole as being common and/or variable in their habitats. This may explain the prominence of Solenopsis and Pheidole, but not the infrequency of Hypoponera and Brachymyrmex. Possibly it is because the foraging habits of Hypoponera and Brachymyrmex are more specific to predation and extrafloral nectaries, respectively Table 1. Since Pheidole and Solenopsis have generalized foraging habits not only larger communities can be supported, but they can also be sustained by alternative resources when one is lacking. However, there being no difference in the number of captures of the two most prominent morphological species between farming methods suggests that their levels of fitness could not be enhanced. Since Hypoponera and Brachymyrmex were captured so few times but are described as being common suggests that these two morphological species may need to be further studied. In a habitat such as an organic farm with the resources to support communities of these morphological species, why were so few caught? It is also questionable why there was such a low frequency of Ectatomma and Dolichoderus captures since both have a very gene ral foraging habit. Possibly it is because neither were described as common, but it would be interesting to know why two generalist species are more prominent than two others. The morphological species Amblyopone was not described as being common and its foraging habit described as only predaceous Table 1. Therefore it can be expected that it would be caught infrequently, and like all other species show a decrease from organic to inorganic coffee farms. Of the two most common ant genera, the initial che ck on the organic farms had the higher number of captures but after this the number of captures become similar Figures 2 and 3. This suggests that the ants may be more responsive on organic coffee farms, but the lack of significance explains that this ca n only be a trend. It may have been possible that the traps were placed, overall, in closer proximity to populations in organic coffee farms. Acknowledgements I would like to thank SeÃ±or Gilberto, SeÃ±or Milton, SeÃ±or Oldemar, SeÃ±or Vargas, SeÃ±or Camora , and SeÃ±or Ramirez for the use of their farms and sometimes restraining their pets from eating my traps. Also, my host family who supported my endeavors. Thanks to Andrew Rodstrom, Mike Wise, and Tim Kuhman for helping with revisions, and Mauricio Garcia for help with my final revision and statistical assistance. Literature Cited Ambrose, H.W. III and K.P. Ambrose. 1995. A handbook of biological investigation. 5 th ed. Hunter Textbooks, Winston Salem, North Carolina.
Hanson, P.E. 1995. Economic import ance of Hymenoptera. In P.E. Hanson and I.D. G auld Eds, pp 89 101. The Hymenoptera of Costa Rica. Oxford University Press, New York. HÃ¶lldobler, Bert and Edward O. Wilson. 1990. The ants. Harvard University press, Cambridge, Massachusetts. Hogue, C.L . 1993. Latin America insects and entomology. University of California Press, Berkeley. Risch, S. 1983. Corn. In D.H. Jazen. Costa Rican natural history. University of Chicago Press, Chicago. Longino, J.T. and P.E. Hanson. 1995. The ants Formicida e. In P.E. Hanson and I.D. Gauld Eds, pp. 588 620. The Hymenoptera of Costa Rica. Oxford University Press, new York. Perfecto, I., R.A. Rica, R. Greenberg, M.E. Van der Voort. 1996. Shade coffee: a dissappearing refuge for biodiversity. BioScience 468: 598 608. Romero, Hernan and Klaus Jaffe. 1989. A comparison of methods of sampling ants Hymenoptera, Formicidae in savannas. Biotropica 214: 348 352. Torres, Juan A. 1984. Niches and coexistence of ant communities in Puerto Rico: repeated patterns. Biotropica 164: 284 295. Vober, Emily. 1999. A comparison or arthropod diversity and species richness between herbicide treated and herbicide free coffee plantation in the Guanacaste Province Costa Rica. Monteverde, Costa Rica. Zar , J.H. 1984. Biostatistical analysis. 2 nd ed. Prentice Hall, New Jersey.
Table 1. Number of captures of each morphological species in both organic and inorganic coffee farms , and the foraging habits of each as described in both Longino and Hanson 199 5 and Hanson 1995. Genus Organic Inorganic Foraging habits Myrmicinae Pheidole 199 217 Generalized scavengers, predaceous, and frequent extrafloral nectaries Solenopsis 34 22 Generalized omnivores, scavengers, predaceous, and forage on low vegetation or ground Formicinae Brachymyrmex 11 0 Extrafloral nectarines Ponerinae Amblyopone 1 0 Predaceous Hypoponera 8 0 Predaceous Ectatomma 1 3 Forage on ground and vegetation, extrafloral nectarines, and predaceous Dolichoderinae Dolichoderus 18 14 Generalized scavengers, extrafloral nectarines total 272 256