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1 Range change in Cecropia and Azteca : the effects of climate change on mutualistic partners in Monteverde, Costa Rica Garrison Loope Department of Geology, Oberlin College Abstract The effects of climate change on the fauna of the M onteverde area has been well documented for vertebr ate taxa such as birds, anurans, Norops spp, (Pounds 1999) and bats (LaVal 2004), but like the rest of the world little work has been done on the effects of climate change on invertebrates. This study examines the altitudinal ranges of the four species of Azteca and the three species of Cecropia living between 1500 and 700m in an area from Monteverde-Cerro Plano to San Luis. The current ranges of species are compared t o elevations from a 1985 survey by John Longino (Longino 1989) and a 20 03 survey by Mazzei (2003). In the last 23 years two species, A. xanthochroa, and A. alfari, are shown to have moved significantly up slope with a change in mean elevation of 103m, and 100m ( P= .0018, and .0348). A. constructor shows no evidence for upslope movement but it increased its relative population size threefold over that report ed by Longino (1989). The lowermost Azteca A. coeruleipennis has not shifted with climate change but its distribution may be restricted by the range of C. peltata. The two ant-housing Cecropia species did not have significant changes in means, but the upper of the two, C. obtusifolia, did show an extension of its range upslope as well as an increase in hybrids bet ween it and the uppermost non-ant-housing species C. angustifolia. These data are unique in showing the effect of clim ate change on invertebrate populations. Although the impact of climate change on invertebra tes throughout the world has been poorly studied, t his study suggests that they can be heavily impacted by climate change. Resumen Los efectos del cambio climtico en los animals de la regin de Monteverde est bien estudiado para los vertebrados como aves, ranas, Norops spp, (Pounds 1999) y marcielagos (LaVal 2004), per o como en todo el mundo hay pocos trabajos sobre los efect os del cambio climtico en invertebrados. Este est udio busca los alcances de altitud de cuatro especies d e Azteca y tres especes de Cecropia que viven entre 1500 y 700m en un area de Monteverde-Cerro Plano a San L uis. Comparo los alcances actuales de las especies a los altitudes con una inspeccin por John Longino e n 1985 (Longino 1989) y un inspeccin por Mazzei (2003). En los vientitres aos pasados dos especes A. xanthochroa y A. alfari se movieron hacia arriba con cambios en altitud de 103m y 100m (P=.0018, y 0348). A. constructor no see movio hacia arriba pero hubo un aumento relativo en la poblacion de tres ve ces desde el reportaje de Longino (1989). El Azteca de mas baja distribucion, A. coeruleipennis, no he cambiado su alcance pero es posible que haya una coneccin con el alcance de C. peltata que restringe el alcance de A. coeruleipennis Los dos especes de Cecropia que tienen hormigas no cambiaron sus altitudes med ias, pero la especie ms alta de los dos, C. obtusifolia aument su lmite superior, tambien hubo ms hibr idos entre este y C. angustifolia, un arbl que no contiene hormigas. Esta informacin es unic a por qu es evidencia de un efecto del cambio climtico en poblaciones de invertebratdos. Aunque no hay mucha informacin sobre de el impacto del cambio climtico en invertebrados, este estudio sug iere que el cambio climtico tiene mucho impacto en los invertebrados. Introduction
2 It is now well established that the average global temperature has been increasing over the last 100 years (IPCC 4th Assessment Report, 2007). Global temperatures ros e an average of 0.74 C in the last century, which makes the last 50 years the warmest 50-year period since 1300. There has been heterogeneity in climate change, in that some areas have been impacted more than others. The areas wit h the most warming tend to be polar and temperate (IPCC, 2007). The tropics have exper ienced relatively little warming, but high levels of climatic specificity in tropical spe cies (Ghalambor et al. 2006) may make them more vulnerable to climate change. Recent cli mate change has been shown to have far reaching biological effects including shifts in ranges upslope or to higher latitudes, destabilization of ecosystems, and changes in pheno logy, such as the timing of migrations, breeding, flowering, and length of the growing season (Walther et al. 2002). Pounds et al. (1999) linked elevated sea surface te mperatures to drying in the cloud forest at Monteverde, Costa Rica by showing that the zone with temperatures critical for cloud formation rises with rising sea surface temperature s. Monteverde is an ideal place to study shifts in range because it has experienced pe rceived drying as well as increased seasonality and includes seven Holdridge Life Zones in a relatively small area (Pounds et al. 1999). In Monteverde climate change has been im plicated in population declines in Norops spp and anurans as well as the up-slope migration o f many avian species (Pounds et al. 1999) as well as several species of bats (La Val 2004). While many of these species are important pollinat ors and dispersers, little work has been done on the impact of climate change on in terspecies relationships. The relationship between Azteca and Cecropia is the most conspicuous ant-plant relationship in the neotropics (Longino 1989,1991a and b). Cecropia spp are pioneer trees common in pastures and along roads throughout the neotropi cs. Janzen (1969) showed that the relationship was mutualistic; Cecropia provide domatia in their hollow internodes and carbohydrates in their Mllerian bodies, while Azteca protect Cecropia from herbivery and remove climbers (Longino 1991a). In the Monteve rde area there are three species of Cecropia and four species of Azteca all restricted to narrow altitudinal bands (Longi no 1989). Although all four species of Azteca are obligate Cecropia -ants, one species of Cecropia never have ant partners and the other two are facu ltative ant-partners but almost always contain colonies of Azteca (Longino 1989). Although the altitudinal distribut ion between individual species of Azteca and Cecropia are correlated, none have speciesspecific partners and all species of Azteca were able to inhabit all species of antCecropia in controlled experiments (Longino 1989). Past studies on Cecropia and Azteca in Monteverde suggest that climate change is having a complex effect on both genera. Mazzei (20 03) showed that three of the four species of Azteca in Monteverde had moved up-slope since 1985. Cern ac (2005) found that since 1985 the average range of C. obtusifolia moved up 73.8m into the range of C. angustifolia (formerly C. polyphlebia ) enlarging the zone of hybridization between the species. This report examines Cecropia and Azteca along an altitudinal and moisture gradient from 700-1500m. I compare my data to histo ric ranges from 1985 (Longino 1989 on both Azteca and Cecropia ) and 2003 (Mazzei on Azteca ). My time span of 23 years is comparable to studies done by Pounds (1999 ) and should be sufficient for fast growing pioneer species and their mutualistic partn ers to show adjustment in range to a change in climate.
3 Materials and Methods I collected samples of Azteca and Cecropia over an approximately 9km transect from 720-1610m along roads and trails from La Estac in Biolgica de Monteverde through the Monteverde-Cerro Plano area, down throu gh the San Luis Valley, ending just below the town of San Luis. I attempted to collect samples from at least 15 trees in each 100m segment of my range in order to keep an even d istribution. This study covers the same area sampled by Longino (1989) and Mazzei (200 3) which should facilitate comparisons. I collected Azteca by using a long tree trimmer to cut leaves I collected four to 8 ants from leaves or trunks using an aspir ator and placed them in vials with alcohol for later identification under a microscope For identification I used photos and descriptions found on John Longinos website (http: //academic.evergreen.edu/ projects/ants/) and in Longino (1991a and b). Ant s were identified using characteristics such as placement and length of setae, color, and s hape and height of petiole. I sampled every tree that I could reach with the tree trimmer except for trees less than 2m tall because I found that they only rarely contained ant s. I counted the secondary veins on the longest lobe of four leaves from each Cecropia sp in order to identify the species. I considered Cecropia with a mean number of secondary veins less than 25 and short inflorescences as C. peltata trees with between 25 and 35 secondary veins, lon g inflorescences, and ants as C. obtusifolia trees with over 35 secondary veins, short inflorescences, and no ants as C. angustifolia and trees displaying some characters of both C. obtusifolia and C. angustifolia as hybrids. This system was developed using information from Longinos website. For each tree i n the field I recorded the number of secondary veins, sample number for ant vial, diamet er at breast height, and elevation using a Casio Protrek Twin Sensor Altimeter. Results I sampled a total of 138 Cecropia trees. Of the trees sampled a total of 114 had Azteca and two trees had two species of Azteca C. peltata were common in the lower elevations up to 900m, C. obtusifolia was present throughout the transect but was most common from 1000 to 1400m, C. angustifolia was common above 1350m although occasionally present at lower elevations, and hybri ds were scattered between 900 and 1610m but were most common above 1350m (figure 1). A. xanthochroa was found to be a high elevation species common from 1050 to 1450m, A. constructor was the most common and widespread species representing 44.8% of total Azteca population sampled (Table 1) and was most common from 950 to 1350m, A. alfari was the least common species and occurred scattered across a range from 1280m all the way to the lower limit of the study, and A. coeruleipennis was the lowest species and was common up to 900m but quickly disappeared above 900m (figure 1). Figure 2 shows the changes in mean elevation fro m 1985 (Longino 1989) to 2003 (Mazzei) to 2008. It shows that in 23 years two sp ecies, A. xanthochroa, and A. alfari, moved significantly up slope with a change in mean elevation of 103m, and 100m (onevariable t-test, P = .0018, and .035). A. constructor, C. obtusifolia, and C. angustifolia have not moved significantly with only a change in means of -9m, 39m and -25m (P= 0.738, 0.190, 0.264) and A. coeruleipennis has moved down significantly with a change
4 in mean of -43m since 1985 (P= .033). Each species of Azteca occupied every species of Cecropia in its range (except C. angustifolia a non-ant species), and Chi2 goodness of fit tests showed that no species of ant had a preferenc e for a specific species of tree in its range (X2, P; A. coeruleipennis = 0.561, 0.454, A. alfari = .018, 0.892, A. constructor = 0.385, 0.535). It was also noted that A. constructor increased greatly in its relative abundance from 15.1% in 1989 to 28.8% in 2003 to 44 .8% in 2008 (table 1). Species Ranges 2008 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700A. a l fari A. co erule i p en nis A. co nstruc t o r A x antho ch roa C. p el t ata C. o b tusifolia H y bridElevation (m)Figure 1. shows the 2008 distribution of the four species of Azteca and the two species of anthousing Cecropia in the Monteverde area. Mean, standard deviation and range are shown for each species. For A. coeruleipennis and C. peltata the lowest samples are less than one standard deviation from the mean because only the upper part of the ranges are in the study area
5 Species Mean Elevation Comparisons700 800 900 1000 1100 1200 1300 1400A. xa nt hoc h roa A. const rc t or A. coer u le i pe n nis A. alf ar i C obtus i fol i a C. pe l tataElevation (m) Figure 2. compares the mean elevations for all species over 2 3 years using data from this study, Longino (1989), and Mazzei (2003). Table 1. Elevation data from 2008 (Loope), 2003 (Mazzei), a nd 1985 (Longino 1989) for all species of Azteca and ant-housing Cecropia in the Monteverde area. nrrr n nn nrrr r rrrr n nn nrrr rrr n nn nrrr r
6 Discussion Azteca and Cecropia spp. in my survey follow the same general pattern of relative altitudinal preferences as in the past (Longino, 19 89; Mazzei, 2003). A. xanthochroa and A. constructor are still largely high elevation species, A. coeruleipennis is still strictly low elevation and A. alfari is still a low to mid elevation species. C. peltata still is found in the lowest driest areas and C angustifolia still dominates in the highest elevations, and grades continuously into C. obtusifolia which is nearly ubiquitous across the study area. In comparison with 1985 I found that A. xanthochroa and A. alfari had shifted their altitudinal distribution up slope significant ly. This agrees with Mazzei (2003) although he could not statistically show that A. alfari had moved up because of his small sample size (n= 10). A constructor did not show an upslope shift, however. The failure of A. constructor to shift upslope with perceived drying can be expla ined by its broad tolerance for climate. Of all the Azteca present in the study area A. constructor is the only one that is know to thrive in both dry and wet forests (Longino 1991b). Also, although its mean elevation has not changed, A. constructor has become much more widespread and has increased its relative abundance by nearly three times in 23 years (Table 1). This could represent selection for gene ralist species in response to a more variable and more seasonal climate. Mazzei found t hat A. constructor had moved up significantly which is in direct opposition to my d ata. It is not that Mazzei found more A. constructor at higher elevations but that he did not find it c ommonly between 850 and 1100m. It is possible that this is due to Mazzeis smaller sample size, but also he does not report the evenness of his sampling. It is pos sible that because of the particular geographical layout of the study area Mazzei collec ted more samples from 1200-1400m than from 900-1100m thus skewing his results. Acce ss to areas from 1300 to 1400m is very easy because of the large relatively flat area at this altitude. From 1200 to 900m the slopes are steep so the sampling area is likely sma ller and the roads fewer. This study showed that A. coeruleipennis actually moved down slope since 1985 but this is most likely an artifact of my sampling of lower elevations. I sampled six trees with A. coeruleipennis below Longinos lowest site 730m. Because A. coeruleipennis is found down to the coast, more samples at lower elev ations would decrease species mean elevation. Mazzei (2003) agrees that A. coeruleipennis has not moved up in elevation since 1985 and his lowest sample was even higher th an Longinos. A. coeruleipennis like its cousins A. xanthochroa and A. alfari is a climate specialist so it would be expected to be affected b y climate change. It is also possible that climate change is having different effects at different altitudes. The higher area where the upper three species live has experienced a reduction of the windy misty season due to a decreased frequency of days cool enough to condense moisture into mist (Pounds 1999). This increase in seasonality and consecutiv e dry days has been implicated in many range shifts in the Monteverde area. The lower premontane moist forest that A. coeruleipennis inhabits never experienced seasonal mist inputs so is unlikely to feel the effect of Pounds rising cloudbank hypothesis. It is also possible that A. coeruleipennis is not only a dry forest specialist, but also a Cecropia specialist. Its range nearly always mirrors the ra nge of C. peltata Although it is known to inhabit other species of Cecropia, it nearly always nests in C. peltata (Longino 1991b). This study shows that A. coeruleipennis has no preference for C.
7 peltata but even if they do not preferentially select C. peltata species specific adaptations could allow A. coeruliepennis to out-compete other species of Azteca in forests dominated by C. peltata. Even though C peltata is present up to 1100m it is only dominant up to about 900m, which is the upper limit of the range of A. coeruleipennis If indeed A. coeruleipennis is linked with C. peltata then because C. peltata shows no sign of moving upslope A. coeruleipennis is restricted to the lower elevations. Neither species of ant-housing Cecropia have showed significant shifts in mean ranges, possibly because they have longer generation times or are less well dispersed than ants. However, C. obtusifolia is expanding its range upslope into the range of C. angustifolia, which is creating a larger hybrid zone. This is ha ppening faster than the lower part of range is retreating upslope, which leaves little ch ange in the mean elevation. This could be due to a lag created by long-lived individuals i n the lower part of the range. The mutualism between Azteca and Cecropia causes a change in one partner to affect the other. The range changes, population ex pansions, and increases in hybrids are likely to have complex affects on the fitness of Azteca and Cecropia For instance Scalley (1993) showed that C. angustifolia produces more toxic secondary compounds to deter herbivores. This means that the hybrid zone has a mix of different herbivore defenses. Expansion of the hybridization zone is l ikely to have a detrimental effect on the plants ability to deter herbivores. Ants that start to colonize these upper hybrids will be exposed to different selection pressures than th eir lower relatives which may produce divergence. Also, the four species of Azteca have different levels of aggression (Longino 1991a). If A. alfari increases its range it could increase herbivery on the trees it inhabits because it is much less aggressive than the ants it would replace. More research is needed find the true effects of climate change on t his interesting ant-plant mutualism. In conclusion it appears that climate change is ha ving a complex affect on Azteca and Cecropia populations in the Monteverde area. Azteca seem to be more affected than Cecropia possibly because they have shorter generations, ar e better dispersed, or are more sensitive than their hosts. Climate change ap pears to be affecting ranges of Azteca and Cecropia separately with the possible exception of the A. coeruleipennis C. peltata interaction. These results along with Mazzei (200 3) support the findings of Pounds (1999) and add arthropods, whose responses to clima te change have long been neglected, to the growing list of taxa known to be affected by climate change in the Monteverde area. If climate change has an effect on arthropod s in Monteverde, it is likely that arthropods are being affected throughout the world. More work on climate change and arthropods is clearly needed as they are the most s pecies rich taxon on the planet, and a threat to them is an assault on biodiversity itself Acknowledgments I would like to thank Alan and Karen Masters for an swering my questions at any time of day, as well as all the kind citizens of the San Luis Valley for lettin g me collect ants on their property and giving me r ides up the hill when they thought I was going to die on th e road. Literature Cited
8 Cernac, Joy. 2005. Altitudinal Range Change in a Pacific Cecropia-Azteca Mutualism CIEE Fall. Monteverde, Costa Rica. Ghalambor, C.K., Huey, R.B., Martin, P.R., Tewksbur y, J.J., and Wang, G. 2006. Are mountain passes higher in the tropics? Janzens hyp othesis revisited Integr. Comp. Biol. 46, 517. Intergovernmental Panel on Climate Change. 2007. C limate Change Assessment Report 2007: the scientific basis Janzen, D. H. 1969. Alleopathy by Myrmecophytes: t he ant Azteca as an alleopathic agent of Cecropia Ecology 50: 147-150. LaVal, Richard. 2004. Impact of Global Warming a nd Locally Changing Climate on Tropical Cloud Forest Bats Journal of Mammalogy 85(2): 237-244. Longino, John. 1989. Geographical Variation and C ommunity Structure in an Ant-Plant Mutualism: Azteca and Cecropia in Costa Rica Biotropica 21(2): 126-132. Longino, John. 1991a. Azteca ants in Cecropia Trees: Taxonomy, Colony Structure, and Behaviour Pages 271-288 in C. Huxley and D. Cutler editors. Ant-plant interactions. Oxford University Press, Oxford, U.K. Longino, John. 1991b. Taxonomy of Cecropiainhabiting Azteca ants Journal of Natural History 25, 1571-1602. Longino, John. 2000. Myrmecophytes in N. M. Nadk arni and N. T. Wheelwright (Editors). Monteverde: ecology and conservation of a tropical cloud forest. 291293. Oxford University Press, New York, New York. Longino, John. 2007. http://academic.evergreen.edu/ projects/ants/ Mazzei, Paul. 2003. Effect of Climate Change on Fo ur Species of Azteca in Monteverde, Puntarenas, Costa Rica CIEE Fall. Monteverde, Cost a Rica. Pounds, J.A., M. P. L. Fogden, and J. H. Campbell. 1999. Biological Responces to Climate Change on a Tropical Mountain Nature 398 : 611-615. Scalley, Michelle. 2003. Defence Tradeoffs and its effects on herbivores in two species of Cecropia EAP Fall. Monteverde, Costa Rica. Walther, G., E. Post, A. Menzel, C. Parmesan, T. J. C. Beebee, J. Fromentin, O. HoeghGuldberg, and F. Bairlein. 2002. Ecological Respon ses to Recent Climate Change Nature 416: 389-395.
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Cambio de rango en Cecropia y azteca: los efectos del cambio climtico sobre los socios mutualistas en Monteverde, Costa Rica
Range change in Cecropia and Azteca: the effects of climate change on mutualistic partners in Monteverde, Costa Rica
The effects of climate change on the fauna of the Monteverde area has been well documented for vertebrate taxa such as birds, anurans, Norops spp, (Pounds 1999) and bats (LaVal 2004), but like the rest of the world little work has been done on the effects of climate change on invertebrates. This study examines the altitudinal ranges of the four species of Azteca and the three species of Cecropia living between 1500 and 700m in an area from Monteverde-Cerro Plano to San Luis. The current ranges of species are compared to elevations from a 1985 survey by John Longino (Longino 1989) and a 2003 survey by Mazzei (2003). In the last 23 years two species, A. xanthochroa, and A. alfari, are shown to have moved significantly up slope with a change in mean elevation of 103m, and 100m (P= .0018, and .0348). A. constructor shows no evidence for upslope movement but it increased its relative population size threefold over that reported by Longino (1989). The lowermost Azteca, A. coeruleipennis, has not shifted with climate change but its distribution may be restricted by the range of C. peltata. The two ant-housing Cecropia species did not have significant changes in means, but the upper of the two, C.obtusifolia, did show an extension of its range upslope as well as an increase in hybrids between it and the uppermost non-ant-housing species C. angustifolia. These data are unique in showing the effect of climate change on invertebrate populations. Although the impact of climate change on invertebrates throughout the world has been poorly studied, this study suggests that they can be heavily impacted by climate change.
Existen documentos sobre los efectos del cambio climtico en los animales de la zona de Monteverde especialmente los vertebrados como las aves, las ranas, Norops spp, (Pounds 1999) y los murcilagos (LaVal 2004), pero al igual que el resto del mundo hay pocos trabajos que se han hecho sobre los efectos del cambio climtico en los invertebrados. Este estudio examina la distribucin altitudinal de las cuatro especies de azteca y las tres especies de Cecropia que viven entre los 1500 y 700 metros en una area desde Monteverde-Cerro Plano hasta San Luis.
Text in English.
Plant species diversity--Costa Rica--Puntarenas--Monteverde Zone
Species diversity--Costa Rica--Puntarenas--Monteverde Zone
Azteca (Insects)--Climatic factors
Cloud forest ecology--Costa Rica
Diversidad de especies de plantas--Costa Rica--Puntarenas--Zona de Monteverde
Diversidad de especies--Costa Rica--Puntarenas--Zona de Monteverde
Ecologa del bosque nuboso--Costa Rica
Tropical Ecology 2008
Ecologa Tropical 2008
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