1 Azteca ants inhabiting Cecropia trees are moving up in elevation in Monteverde Meghan R. Garfink Department of Environmental Science and Policy University of California, Davis UCEAP Tropical Biodiversity and Conservation Spring 2019 7 June 2019 ABSTRACT Global c limate change impacts ecological relationships of all taxa and kingdoms, yet little has been documented of the impact on insects. This study documents the changing elevation al range of four Azteca ant species in Cecropia trees in the Monteverde cloud forest. In Monteverde, Costa Rica, many species of Cecropia form a mutualism with Azteca in which ants receive nutrients in exchange for protection of the tree. Data was collected in May 2019 and compared to similar studies done in 1989 (Longino) , 2003 (Mazzei) , 2008 (Loope) , and 2016 (Jensen) . Since 1989, maximum elevational range of Azteca increased by 132 meters . Average elevation of all species of Azteca and Cecropia h ave increased significantly since 1989 as well. One species of Cecropia, C . polyphlebia, contained Azteca at 1500 m, despite historically not harboring Azteca . This data indicates that Azteca are moving upslope and inhabiting different species of Cecropia in Monteverde, potentially due to climate change. Hormigas Azteca que habitan en rboles de Cecropia en Monteverde se estn desplazando hacia arriba en elevacin RESUMEN El cambio climtico global afecta las relaciones ecolgicas de todos los taxones y reinos, sin embargo, el impacto en los insectos ha sido poco documentado. Este estudio documenta el cambio del rango de elevacin de cuatro especies de hormigas Azteca que viven en rboles de Cecropia en el bosque nuboso de Monteverde . En Monteverde, muchas especies de Cecropia tienen una relacin mutualista con Azteca, en el que las hormigas reciben nutrientes y casa a cambio de proteger el rbol hospedero. Recopil datos en mayo de 2019 y los compar con estudios similares realizados en 1989 (Longino), 2003 (Mazzei), 2008 (Loope) y 2016 (Jensen). Desde 1989, el rango de elevacin mxima de Azteca ha aumentado 132 metros. La elevacin promedio de todas las especies de Azteca y Cecropia tambin ha aumentado significativamente desde 1989. Encontr hormigas Azteca en C. polyphlebia a 1500 m, a pesar de que histricamente no albergaba a Azteca . Estos datos indican que las hormigas estn utilizando rboles en elevaciones ms altas y habitando diferentes especies de Cecropia en Monteverde, potencialmente debido a cambios en el clima.
Elevational range of Azteca and Cecropia Garfink 2 Climate change is affecting species distributions and ecological interactions globally (Welch 2017) . Often , these i nteractions are mutualisms, where both species benefit from the relationship . Mu tualisms can be obligate, when one organism cannot survive without the other, or facultative, where both species are not dependent on each o ther to survive (Jorgensen et al. 2008) . Many observed changes i n ecological relationships have been correlated to climate change, including the m utualism between Azteca ants and Cecropia trees in Monteverde, Costa Rica ( Mazzei 2003, Loope 2008, Jensen 2016) . Cecropia are native to lowland, and mid elevation cloud forests in the American tropics. They grow alongside forests, forest edges, pastures, and residential areas (Longino 1991). Eighty percent of Cecropia are myrmecophytic: plant s which lives in a mutualistic relationship with ants (Berg et al. 2005) . In this mutualism, ants protect against herbivores and kill vine ends that begin to attach to the Cecropia trunk. Cecropia provide shelter and food from glycogenrich Mullerian bodies found on the stems of Cecropia leaves (Janzen 1969). Azteca in this mutu alism are obligate and therefore cannot survive without nesting in Cecropia wood (Berg et al. 2005) . The four species of Azteca found in Monteverde are A. constructor, A. xanthrochroa, A. alfari, and A. coeruleipennis (Longino 1989). There are four species of Cecropia found in the Monteverde area: C. peltata, C. obtusifolia , C. insignis , and C. polyphlebia (also known as C. angustifolia ) (Longino 1989). C. peltata is found on the Pacific slope in lower elevations . C. insignis can be found in lowland regions of the Caribbean slope and C. obtusifolia can be found in midelevations on both s lopes . Typically, nonmyrmecophytic Cecropia ( C. polyphlebia ) is found at higher elevations where it can survive without the ant mutualism (Zuchowski 2007) . Azteca are limited by cold, wet environments (Longino 1991). For this reason, C. polyphlebia historically do not partner with Azteca . I nstead , C. polyphlebia relies on secondary compounds to defend from predators (Longino 1989, 1991, Jensen 2016). For over 30 ye ars, noncontinuous data has been collected in Monteverde comparing Cecropia and Azteca ranges at varying elevations: a primary study from 1989 (Longino on Azteca and Cecropia ), and replicate studies in 2003 (Mazzei on Azteca ), 2008 (Loope on Azteca and Cecropia ), and 2016 (Jensen on Azteca and Cecropia ). Comp aring these studies, trends show that Azteca are moving up in elevation in Monteverde over the past 30 years. While there is no known cause for these changes, many studies on ecological interactions have been attributed to climate change. To track elevational shifts in Monteverde, I asked the questions (1) what is the current distribution of Azteca and Cecropia, and (2) how does this compare to previous studies ? To answer this, I surveyed Azteca and Cecropia at varying altitudes in Monteverde and compa red the results to previous work. MATERIALS AND METHODS I collected s amples of Cecropia and Azteca from 10001800 m on the Caribbean and Pacific slopes in Monteverde, Costa Rica between 6 May 2019 and 19 May 2019. I sampled along trails near the San Luis Valley ( 10001200 m .a.s.l.), San Gerardo ( Caribbean slope, 11001300 m ), La Calandr a ( 12001300 m ), Cerro P lano (14001500 m), Bajo del Tigre Reserve (1400 m ), the Estacin Biolgica forest (around 15001600 m), and Cerro Amigos ( 16001800
Elevational range of Azteca and Cecropia Garfink 3 m). I identified Cecropia in the field with the help of plant expert and Monteverde local, Eladio Cruz , and with additional assistance from the Tropical Plants of Costa Rica (Zuchowski 2007) . In the appendix of this paper there are images and notes of Cecropia that I identified for future reference. Also included are tables of my collected data, satellite imagery of the locations surveyed, and the averages, maximums, minimums, and sample sizes from past data. I measured t ree height with a Nikon Forestry Pro laser range finder . I then calculated tree height accuracy a s +/ 0.37 m by taking the same measurement from one tree 10 times and calculating the standard deviation. I recorded the diameter at breast height with a tape measurer for each tree . Altitude was recorded at each sample with an Oregon Scientific altimeter. I knocked on Cecropia trunks and used an extenda ble tree trimmer to observe ant activity . If present, 3 4 ants were collected u sing an aspirator and placed in ethanol for preservation. Ant spe cies were identified in lab with the help of University of Utah professor and ant expert, John Longino. I classified a nt s with setae on the hind tibia as A. alfari . Ants with a flat, shelf like metanotal groove, were identified as A. coeruleipennis . Other ants were classified as either A. xanthrocroa or A. constructor . Physical and ecological differences (such as nesting in Cecropia ) between the two species are insignific ant (Longino pers. comm. 2019) , so A. xanthrocroa and A. constructor were combined into the group A. xanthrocroa/constructor for statistical analysis. I produced box plots of the elevational ranges of Azteca and Cecropia in Microsoft Excel. I also made scatter plots with reg ression lines of the average elevations of all Azteca and Cecropia species per year. A scatter plot and linear regression of maximum elevational height for all Azteca by year was also produced . R ESULTS Sixty one Cecropia were sampled between 1000 m and 1800 m. Of the 61 trees, 37 were C. obtusifolia, four were C. peltata, 19 were C. polyphlebia, and one was C. insignis . Fortytwo trees of Cecropia contained Azteca . Of the 42 samples, 36 were identified as A. xanthrocroa/constructor , 5 were A. alfari , and 1 was A. coeruleipennis. No trees contained more than one species of ant, except for six individual C. obtusifolia tree s which were also being harvested by leaf cutter ants. Azteca spp. were found throughout the sampling area below 1532 m. A. xanthrocroa/constructor had the largest range: 1035 1532 m. A. alfari was found between 1037 m and 1240 m . One A. coeruleipennis was identified and found at 1087 m ( Fig. 1) . C. obtusifolia was most common throughout the survey. C. obtusifolia was found above 1035 m and below 1532 m. C. peltata was found between 10851239 m. One C. insignis was sampled along the distribution and was found at 1238 m on the Caribbean slope . C. polyphlebia was found at higher elevations, yet had the largest range of 564 meters ( from 12381802 m ) ( Fig. 2) . Five C. polyphlebia samples contained A. xanthrocroa/constructor .
Elevational range of Azteca and Cecropia Garfink 4 Fig. 1: Elevational ranges of Azteca ants by species in 2019. Average altitude per species is represented by the horizontal b lack line s . Minimum and maximum altitude per species is represented through the vertical black lines. ( A. xanthrocroa N=35, A. alfari N=5, A. coeruleipennis N=1). Fig. 2: Elevational ranges of Cecropia trees by species in 2019. Average altitude per species is represented through the horizontal black lin e s . Maximum and minimum altitude per species is represented through vertical black lines. ( C. obtusifolia N=35, C. peltata N=4, C. polyphlebia N=19, C. in signis N=1)
Elevational range of Azteca and Cecropia Garfink 5 In c omparison with previous studies, the average elevation of A. xanthrocroa/constructor has increased by 172.5 m sin ce the original 1989 study by Longino (F ig. 3). A. coeruleipennis has increased by 251 m (F ig. 4) . A. alfari ha s increased by 271 m, the most since 1989 (F ig . 5). Average elevation of C. obtusifolia has increased 172 m since 1989 (Fig. 6) and C. peltata has increased 283.5 m (Fig. 7). All documented Cecropia and Azteca have increased average elevational range since 1989. Maximum elevation of all Azteca measured in Monteverde is 1532 m, 132 m higher than in 1989 (Fig. 8). The relationship between year and altitudinal height is stro ngly correlated and increasing (R2 = 0.983) (Fig. 8). Fig. 3: Average elevational height in mete rs of Azteca xanthrocroa/constructor in 1989 (Longino), 2003 (Mazzei), 2008 (Loope), 2016 (Jensen), and 2019 (Garfink). Fig 4: Average elevational height in meters of Azteca coeruleipennis in 1989 (Longino), 2003 (Mazzei), 2008 (Loope), 2016 (Jensen), and 2019 (Garfink).
Elevational range of Azteca and Cecropia Garfink 6 Fig. 5: Average elevational height in meters of Azteca alfari in 1989 (Longino), 2003 (Mazzei), 2008 (Loope), 2016 (Jensen), and 2019 (Garfink). Fig. 6: Average elevational height in meters of C. obtusifolia in 1989 (Longino), 2003 (Mazzei), 2008 (Loope), 2016 (Jensen), and 2019 (Garfink).
Elevational range of Azteca and Cecropia Garfink 7 Fig. 7: Average elevational height in meters of C. peltata in 1989 (Longino), 2003 (Mazzei), 2008 (Loope), 2016 (Jensen), and 2019 (Garfink). Fig. 8: Maximum altitude in meters of Cecropia inhabiting Azteca spp. in Monteverde in 1989 (Longino), 2003 (Mazzei), 2008 (Loope), 2016 (Jensen), and 2019 (Garfink).
Elevational range of Azteca and Cecropia Garfink 8 D ISCUSSION There is a clear increase in the elevational distribution of Azteca in Cecropia in Monteverde over the past thirty years . While the elevational height difference from 2016 to 2019 is small, the re is a strong overall trend in average elevation in all species of Azteca that occupy Cecropia in Monteverde . There are four possible explanations for how Azteca and Cecropia are distributed: (1) habitat characteristics determine Azteca distribution, (2) habitat characteristics determine Cecropia distribution, (3) Azteca influences Cecropia distribution, (4) Cecropia influences Azteca distribution (Longino 1991). In all possible explanations, c limate is a leading contributor to distribution. Temperature, rainfall, and seasonality in explanations 1 and 2 can disturb Azteca / Cecropia habitats and thus alter their distributions. Cold, wet environments typically determine the upper limit for Azteca range (Longino 1991). Increasing annual temperature and decreasing cloud cover in high elevations of the cloud forest could create new inhabitable trees for Azteca who were previously limited by heavy rains . Explanations 3 and 4 show how ecological relationships can change due to succession and chemical defense alterations (Longino 1991). Changes in atmospheric composition (particularly higher levels of CO2) can influence plant metabolism and decrease the production of s econdary compounds (Alnsour et al 2015). A lack of secondary compounds in C. polyphlebia due to changes in atmospheric composition could explain in the presence of Azteca at high elevations . It is also possible that Azteca are experiencing high levels of competition at lower elevations . If new inhabitable Cecropia are available at higher elevations due to changing temperature and weather patterns, it is possible that Azteca could shift range to relieve competitive pressures . It could be argued that Cecrop ia and Azteca are going up in elevational range due to urbanization and deforestation in the Santa Elena and Cerro Plano area of Monteverde (since Cecropia are commonly found on forest edges and pastures). If land in Monteverde was being deforested for roa d building or farming construction, it is likely that Cecropia would be shifting range ( with Azteca following ) . This, however, is not the case. Monteverde has significantly decreased deforestation since the late 1970â€™s (Pounds 1991). The Monteverde Conservation League has planted hundreds of thousands of trees to serve as windbreaks, corridors, and habitat (Nadkarni et al . 2000). For this reason, it is unlikely that the Azteca are moving in elevation due to deforestation and road building. The year 2019 was drier than most in Costa Rica due to the El Nio phenomenon which brings dry, high pressure air to the Tropics. This, however did not impact the results of this study since the upwards trend of Azteca elevational range has been occurring over the past 30 years (or more) , not just in 2019. Earth â€™s annual average temperature has increased 0.8C since preindustrial times ( NASA 2010) . The Intergovernmental Panel on Climate Change (IPCC 2014) expects global temperatures to rise an additional 2.3 2.9C by 2100 under â€œbusiness as usualâ€ conditions (IPCC 2014) . Models predict a 600 m upslope trend in temperature isotherms in the next few decades in tropical mountain ranges (Smith et al. 2014). A shift this large could be detrimental to ant species in Cost a Rica , s ince many tropical ant species hav e ranges of 600 m in total (Smith et al. 2014). Research on invertebrate species could lead to a better understanding of the impact of climate change. I would suggest that future studies barcode Azteca found in Cecropia to make identification easier for future projects. Identifying Azteca is notoriously difficult and using barcoding would give a clear, definite, identification for tracking species ranges. Gathering GPS
Elevational range of Azteca and Cecropia Garfink 9 information at each Cecropia would also make tracking Cecropia and Azteca colonies easier. Future studies should also take note on the presence or absence of vines/other invading plant species on Cecropia . I found that most Cecropia in the Cerro Amigos area without Azteca had dying leaves and were c overed in vines. Since C. polyphlebia in the 1500 m range were found contain ing Azteca , further research could potentially study the presence or absence of secondary compounds in these trees which usually protect from vines and predators. Continuing with studies on the changing elevational range of Azteca and Cecropia could help solidify triggers for the range shifts and prevent further changes. A CKNOWLEDGEMENTS I would like to thank my primary advisory, Emilia Triana , for her endless support and e ncouragement during my research. Emi was always there to help me with paper editing, drive me to far away Cecropia trees, and laugh at me as I tried to suck up Azteca with my broken aspirator. I would also like to thank Frank Joyce , my secondary advisor and excellent professor, for encouraging and pushing me to produce my best work (and for wheeze laughing at my jokes) . I would also like to thank Eladio Cruz for his immaculate plant knowledge, and Jack Longino for his time and patience in teaching me how to identify ants. Finally, thank you to my classmates at EAP for listening to me frantically talk about Azteca during all hours of the day (especially those who heard it at 5am in the study room). Thank you. LITERATURE CITED Alnsour , M.; and LudwigMuller, J . 2015. â€œ Potential effects of climate change on plant primary and secondary metabolism and its influence on plant ecological interactions.â€ Journal of Endocytobiosis and Cell Research , vol. 26, pp. 9099 Berg, C.C.; Rosselli , P. F.; and Davidson, D.W. 2005. â€œCecropiaâ€ Flora Neotropica.â€ New York Botanical Garden Press , vol. 94, pp. 1â€“230. Haber, W.A.; Zuchowski, W.; and Bello, E . 1996. An Introduction to Cloud Forest Trees . P. 53. Heikkinen, N . â€œClimate Change Could Alter Interactions among Speciesâ€. Scientific American. July 5, 2016. Web. IPCC, 2014. â€œ Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change â€ [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp. Janzen, D. H. â€œAllelopathy by Myrmecophytes: The Ant Azteca as an Allelopathic Agent of Cecropia.â€ Ecology , vol. 50, no. 1, 1969, pp. 147â€“153. Jensen, I . 2016. â€œ Climate change and elevational range shif ts by mutualistic Azteca (Hymenoptera: Formicidae) and Cecropia (Urticaceae) in Monteverde, Costa Rica. â€ CIEE Tropical Biodiversity and Conservation Spring 2016. Jorgensen, S.E.; Fath, B.D. 2008. â€œ Encyclopedia of Ecology.â€ Web. â€œKey to Costa Rica Azteca Workersâ€. AntWiki. N.p. April 8, 2016. Web. Longino, J.T. 1989. â€œGeographic Variation and Community Structure in an Ant Plant Mutualism: Azteca and Cecropia in Costa Rica.â€ Biotropica, Vol. 21, No. 2, pp. 126132.
Elevational range of Azteca and Cecropia Garfink 10 Longino, J.T. 1991. â€œTaxonomy of Cecropia inhabiting Azteca antsâ€. Journal of Natural History, Vol. 25, pp. 15711602 Loope, G . 2008. â€œ Range change in Cecropia and Azteca : the effects of climate change on mutualistic partners in Monteverde, Costa Rica. â€ CIEE Tropical Biodiversity and Conservation Spring 2008. Mazzei, P . 2003. â€œ Effect of climate change on four species of Azteca in Monteverde, Puntarenas, Costa Rica. â€ CIEE Tropical Biodiversity and Conservation Fall 2003. Pounds, J.A., M.P.L. Fogden, and J.H. Campbell. 1999. Biological response to climate change on a tropical mountain. Nature 398: 611615. Smith, A.M.; Hallwachs, W.; and Janzen, D.H. 2014 â€œDiversity and phylogenetic community structure of ants along a Costa Rican elevational gradient.â€ Ecography, Vol. 37, pp. 720731. Welch, C . â€œHalf of All Species Are on the Move And Weâ€™re Feeling Itâ€. National Geographic. April 27, 2017. Web. â€œWorld of Change: Global Temperaturesâ€. NASA Earth Observatory. N.P. December 2010. Web. Zuchowski, W . 2007. Tropical Plants of Costa Rica: A Guide to Native and Exotic Flora. P. 4548 A PPENDIX Locations of land surveyed:
Elevational range of Azteca and Cecropia Garfink 11
Elevational range of Azteca and Cecropia Garfink 12
Elevational range of Azteca and Cecropia Garfink 13 Descriptions of Cecropia identified (E ladio Cruz pers. comm. 2019, Zuchowski 2007) : Cecropia insignis Leaves: large, large/thick lobes . Each leaf has 10 lobes or less Inflorescences: medium length (6 18cm) Location : mostly on wet Atlantic slope Other notes: fallen leaves tend not to curl up
Elevational range of Azteca and Cecropia Garfink 14 Cecropia obtusifolia Leaves: Typically have 10 or more lobes. Secondary veins are more spread apart than polyphlebia . Inflorescences: long and skinny. Typically, more than 50cm long Location : found on both slopes. Moist, wet habitat Other notes: most likely to be confused with C. polyphlebia
Elevational range of Azteca and Cecropia Garfink 15 Cecropia peltata Leaves: white underside . Leaf has 11 lobes or less Inflorescences: short , fat fruit spikes (4 10cm long) Location: mostly dry, low elevations Other notes: most likely to be confused with C. insignis
Elevational range of Azteca and Cecropia Garfink 16 C. polyphlebia (C. angustifolia) Leaves: venation is closer together than C. obtusifolia. Secondary veins and new leaf bracts are reddish in color. Leaves have 10 or more lobes Inflorescences: fruit spikes are short and resemble a sea urchin Location : on both slopes (Pacific and Caribbean) in elevations higher than 1200m. Often found without Azteca ants. Other notes: most likely to be confused with C. obtusifolia
Elevational range of Azteca and Cecropia Garfink 17 Mean, max, min altitude (meters), and total number found of Azteca and Cecropia in 2019, 2016, 2008, 2003, and 1989. Garfink 2019 Mean altitude (meters) Max altitude (meters) Min altitude (meters) Total number found A. xanthrocroa/A. constructor 1336.5 1532 1035 36 A. coeruleipennis 1087 1087 1087 1 A. alfari 1187 1240 1037 5 C. obtusifolia 1313 1532 1035 37 C. peltata 1143.5 1239 1085 4 C. insignis 1238 1238 1238 1 C. polyphlebia 1562 1802 1238 19 Jensen 2016 Mean altitude (meters) Max altitude (meters) Min altitude (meters) Total number found A. xanthrocroa/A. constructor 1309 1530 765 55 A. coeruleipennis 873 1430 720 14 A. alfari 959 1300 725 7 C. obtusifolia /C. angustifolia hybrid 1398 1770 940 35 C. obtusifolia 1261 1530 865 44 C. peltata 821 1100 720 19 Loope 2008 Mean altitude (meters) Max altitude (meters) Min altitude (meters) Total number found A. xanthrocroa/A. constructor 1211 1450 815 79 A. coeruleipennis 793 975 720 22 A. alfari 1016 1280 725 15 C. obtusifolia/C. angustifolia hybrid 1259 1610 890 34 C. obtusifolia 1179 1450 725 60 C. peltata 835 1135 720 31 Mazzei 2003 Mean altitude (meters) Max altitude (meters) Min altitude (meters) Total number found A. xanthrocroa/A. constructor 1235.5 1450 925 51 A. coeruleipennis 840 980 745 10 A. alfari 997 1310 780 19 Longino 1989 Mean altitude (meters) Max altitude (meters) Min altitude (meters) Total number found
Elevational range of Azteca and Cecropia Garfink 18 A. xanthrocroa/A. constructor 1164 1400 860 46 A. coeruleipennis 836 940 730 20 A. alfari 916 1240 750 27 C. obtusifolia 1140 1400 770 57 C. peltata 860 1250 730 40
Elevational range of Azteca and Cecropia Garfink 19 Data ( Garfink 2019) :