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Schmitt, Patricia A.
Los efectos alelopticos sobre la hojarasca en invertebrados Dicksonia gigantea (Polypodiopsida: Dicksoniaceae) y Cyathea caracasana var. meridensis (Polypodiopsida: Cyatheaceae)
Allelopathic effects on leaf litter invertebrates under Dicksonia gigantea (Polypodiopsida: Dicksoniaceae) and Cyathea caracasana var. meridensis (Polypodiopsida: Cyatheaceae)
Allelopathic chemical release may affect many aspects of plant and soil ecology, including community composition, diversity, and richness (Ferguson 2003). The effects of allelopathic chemicals in tree ferns D.
gigantea and C. caracasana var. meridensis on the biodiversity of leaf litter invertebrate communities were examined in the Monteverde Cloud Forest. In total, 15 sites were surveyed, where a paired sample of one
tree fern and one non-fern tree were collected, filtered and invertebrates were analyzed to morphospecies. When examining the local communities under tree fern and non-fern trees, no significant difference in N, S, H', Smarg and E was found. However, there was a significant difference in the H' of tree fern and non-fern trees (Modified T-Test, t = -2.52, p < 0.05, df = 2075), as well as observed differences in N, S, Smarg and E, on the metacommunity level. All indices were found to be higher under non-fern trees. Seven invertebrate species were also observed having a 20 % change in abundance, suggesting that certain
species may be more affected by the presence or absence of allelopathic chemicals. These include springtails (Order Collembola), one spider morpho species (Order Arachnida), one beetle morpho species \(Order Coleoptera), insect larvae (Class Insecta), silverfish (Order Zygentoma), angel insects (Order
Zoraptera), and caterpillars (Order Lepidoptera). Allelopathic effects on bottom-up trophic level interactions are a plausible explanation as to why changes in the abundance, richness and diversity of leaf litter invertebrates may occur under tree ferns.
La liberacin de las sustancias qumicas alelopticas pueden afectar muchos aspectos de las plantas y la ecologa del suelo, incluso la composicin de una comunidad, su diversidad, y su riqueza (Ferguson 2003). Los efectos de los productos qumicos alelopticos en los helechos del rbol D. gigantea y C. caracasana var. meridensis en la biodiversidad de las comunidades de invertebrados de la hojarasca fueron examinados en el Bosque Nuboso de Monteverde.
Text in English.
Basura del bosque
Tropical Ecology 2007
Ecologa Tropical 2007
t Monteverde Institute : Tropical Ecology
Allelopathic effects on leaf litter invertebrates u nder Dicksonia gigantea (Polypodiopsida: Dicksoniaceae) and Cyathea caracasana var. meridensis (Polypodiopsida: Cyatheaceae) Patricia A. Schmitt Department of Biology, Northeastern University ABSTRACT Allelopathic chemical release may affect many aspec ts of plant and soil ecology, including community composition, diversity, and richness (Ferguson 2003 ). The effects of allelopathic chemicals in tree ferns D. gigantea and C. caracasana var. meridensis on the biodiversity of leaf litter invertebrate co mmunities were examined in the Monteverde Cloud Forest. In total, 15 sites were surveyed, where a paired sample of on e tree fern and one non-fern tree were collected, fil tered and invertebrates were analyzed to morphospec ies. When examining the local communities under tree fer n and non-fern trees, no significant difference in N, S, H', Smarg and E was found. However, there was a sig nificant difference in the H' of tree fern and nonfern trees (Modified T-Test, t = -2.52, p < 0.05, df = 2 075), as well as observed differences in N, S, Smar g and E, on the metacommunity level. All indices were fou nd to be higher under non-fern trees. Seven invertebrate species were also observed having a 20 % change in abundance, suggesting that certain species may be more affected by the presence or abs ence of allelopathic chemicals. These include springtails (Order Collembola), one spider morpho s pecies (Order Arachnida), one beetle morpho species \(Order Coleoptera), insect larvae (Class Insecta), silverfish (Order Zygentoma), angel insects (Order Zoraptera), and caterpillars (Order Lepidoptera). A llelopathic effects on bottom-up trophic level interactions are a plausible explanation as to why changes in the abundance, richness and diversity of leaf litter invertebrates may occur under tree ferns. RESUMEN La liberaciÂ—n de sustancias quÂ’micas alelopÂ‡ticas p uede afectar muchos aspectos de las plantas y la ecologÂ’a del suelo, incluso la composiciÂ—n de una c omunidad, su diversidad, y su riqueza (Ferguson 200 3). Los efectos de productos quÂ’micos alelopÂ‡ticas en h elechos de Â‡rbol D. gigantea y C. caracasana var. meridensis en la biodiversidad de las comunidades de inverteb rados de la hojarasca fueron examinados en el Bosque de Nuboso de Monteverde. En total, 15 sit ios fueron contemplados, donde se tomÂ— una muestra pareada de un helecho de Â‡rbol y un Â‡rbol de no hel echo se filtro la muestra y los invertebrados fuero n analizados a morfoespecies. Examinando las comunida des locales bajo el helecho arborecente y otros Â‡rboles, ninguna diferencia significativa en N, S, H', Smarg y E fue encontradas. Sin embargo, habÂ’a u na diferencia significativa en el H' de helecho arbore cente y otros Â‡rboles (T-prueba Modificada, t =-2.5 2, p <0.05, df = 2075), asÂ’ se como observÂ— diferencias en N, S, Smarg y E, en el nivel de metacomunidad. Todos los Â’ndices fueron mÂ‡s altos bajo Â‡rboles de no helecho. Siete especies invertebrados tambiÂŽn tuvieron un cambio del 20 % de la abundancia, sugiriendo que ciertas espec ies puedan ser mÂ‡s afectadas por la presencia o ausencia de productos quÂ’micos a lelopÂ‡ticas. Âƒstos incluyen organismos del springta ils Collembola, una morfoespecie de la araÂ–a (Piden Ara chnida), la morfoespecie de escarabajo 1 (Coleoptera), larvas de insecto (Clase Insecta), (O rden Zygentoma), los insectos de Â‡ngel (Orden Zoraptera), y las orugas (Orden Lepidoptera). Los e fectos de alelopÂ‡ticas en los niveles trÂ—ficos bajo s son una explicaciÂ—n plausible en cuanto a por quÂŽ los c ambios de la abundancia, riqueza y diversidad de invertebrados de hojarasca pueden ocurrir bajo los helechos arborescentes.
INTRODUCTION Cyatheaceae and Dicksoniaceae are two tree fern fam ilies that are found in great abundance in Monteverde Cloud Forest Reserve and ar e notorious for possessing secondary metabolites that are used as a means of d efense (GÂ—mez 1983, Rojas 1999). These light gap pioneers have phenolic acid concent rated in their fronds and roots, which reportedly have potential for allelopathic effects (Bell 1979). Allelopathy is the release of chemicals from dead or live plant material via leac hing, root exudation, volatilization, or residue decomposition. Allelopathic chemical releas e may affect many aspects of plant and soil ecology including plant community composit ion, diversity, and richness, as well as plant succession and productivity (Ferguson 2003 ). The amount and strength of the exudates produced are correlated with plant species plant age, temperature, light, and soil microorganisms present (Bell 1979). The concentrati on of the inhibitor in the exudates is a determining factor of whether or not the chemical s will inhibit or stimulate plant growth (Evenari 1949). Plants often produce these allelopa thic compounds to reduce competition for limited resources by inhibiting the growth and development of other species. In moist environments, tree ferns release allelopathic chemi cals via leaching from senescent leaves by rainfall or decomposition of dead leaves, further preventing the growth of cohabiting plants (Wagner & Long 1991). Although the role of secondary metabolites as a de terminant of plant populations is debated, the significance of these compounds is more widely accepted as a regulatory factor in soil biotic interactions and nutrient cyc ling (Northup et al. 1995, Wardle & Lavalle 1997). Through the effects of allelopathic chemicals on soil chemistry and vegetation composition, these compounds can induce changes in ecosystem functioning (Wardle et al. 1998). These changes may directly or indirectly affect the structure and composition of the surrounding leaf-litter inverteb rate community, as the effects of secondary metabolites are generally considerably st ronger on soil invertebrates in the same ecosystem than they are on direct plant-plant interactions (Wardle et al. 1998). Outright mortality of individuals may be one direct effect on invertebrate communities, as some invertebrates may be more vulnerable to phe nolic compounds at varying concentrations. Invertebrate communities may be ind irectly affected by individuals preferentially living under trees that do not posse ss allelopathic chemicals, as a result of decreased litter quality under tree ferns. Invertebrates play an important role in their surro unding environment through their involvement in soil aeration, nutrient minera lization, interactions with lower trophic level organisms, litter decomposition rates and oth er ecosystem services (Boyce 2005). As a result, their presence largely influences the composition of other plant species and the functioning of the microhabitat as a whole. As allelopathic chemicals are more commonly being used in agriculture as growth regula tors and natural pesticides, it is imperative to examine how the micro and macro inver tebrate community structure and function are both indirectly and directly impacted by the presence of allelopathic exudates (Boyce 2005). The tree ferns Dicksonia gigantea (Dicksoniaceae) and Cyathea caracasana var. meridensis (Cyatheaceae) have potent allelochemicals that have a documented effect on nearby angiosperm communities, making them excellent candidates for the study of possible effects on inv ertebrates of leaf litter (Heckendorn & Saeman 2003). Because of the strength of their alle lopathic properties, I will investigate
the leaf litter communities under both D. gigantea and C. caracasana var. meridensis as well as non-fern trees, to see if the phenolic comp ounds directly or indirectly influence the abundance, richness and diversity of soil inver tebrates in the Monteverde Cloud Forest. MATERIALS and METHODS Study Site Leaf litter collections were taken in lower montane wet forest on the property of EstaciÂ—n BiolÂ—gica de Monteverde, Costa Rica on Sendero Prin cipal and Sendero Cariblancos at an elevation of 1500-1600 m between April 11-May 4, 2007 (Figure 1). Data Collection To reduce the number of factors that may influence the composition of leaf litter invertebrates, and thereby isolate the effects of t ree fern allelochemicals, leaf litter collections were made under 15 pairs of trees (one D. gigantea or C. caracasana var. meridensis and one non-fern tree) of similar sizes (6 to 23 c m in DBH), in close proximity ( 7 m away from one another), and under similar cond itions of slope, light, wind, and precipitation. The height of all tree fe rns were measured to ensure that the trunk was between 2 and 8 m tall, fitting the physi cal description of D. gigantea and C. caracasana var. meridensis (Rojas 1999). Samples were taken every other day using a composit e method, in which approximately 6 to 7 large handfuls were collected along the base of each tree trunk. The leaf litter under each tree was mixed separately in a large cardboard box, and from the mixture, 1.5 L were sub-sampled and put into plasti c bags. The contents of each bag were placed into Berlese funnels that were equipped with 75W light bulbs and sieves made of 1 x 1cm mesh, allowing macro and micro invertebrate s to separate from bulky leaf litter and fall into the vials (Southwood 1966) (Appendix A). Each sample was allowed to sit for a total of 24 hours. The extracted arthropods were preserved in a soluti on of ethanol and were examined a day after collection under a dissecting microscope. All individuals were identified to morphospecies. Invertebrate community samples were kept for future reference of morphospecies identification. Abundanc e, richness, diversity and evenness of invertebrate communities for each tree were calc ulated. Species represented by 20 individuals in either the tree fern or non-fern sam ple, with 20% difference in total abundance between both communities, were identified to the lowest taxonomic level possible, in order to further research their role a nd function in leaf litter communities. Statistical Analysis A modified t-test on the total diversity (Shannon-W einer index, H') of leaf litter invertebrates under tree ferns and non-fern trees w as performed to determine whether or not there was a significant difference between the two communities Sign tests were used on the 15 paired trees to determine if abundance, r ichness, index of richness (Marglef's index), H', or evenness differed in arthropod commu nities under tree ferns and non-fern trees.
RESULTS Thirty leaf litter samples from 15 sampling areas, consisting of 15 pairs of tree ferns and non-fern trees, were collected and analyzed during a 25-day period. In total, 2128 individual invertebrates were accounted for and 146 morpho species were identified. I found no significant difference in the abundance of macroand micro-invertebrates in the local communities of tree ferns and non-fern trees (Sign test, p > 0.05, n = 15; 5 pluses, 9 minuses). There was no significant difference in sp ecies richness of macroand microinvertebrates between the two local communities (Si gn test, p > 0.05, n = 15; 5 pluses, 8 minuses). There was no significant difference in di versity between the two local communities (Sign test, p > 0.05, n = 15; 6 pluses, 8 minuses). There was no significant difference in evenness between the two local commun ities (Sign test, p > 0.05, n = 15; 6 pluses, 7 minuses). Lastly, there was no significan t difference in the index of richness (Smarg) between the local communities of tree ferns and non-fern trees, totaling 4 out of 15 positives (Sign test, p > 0.05, n = 15; 4 pluses 10 minuses). The two communities were further analyzed on the lo cal level by comparing the means of each index. The mean abundance of macroa nd micro-invertebrates of tree ferns and non-fern trees were 64.8 39.8 and 77.0 52.8 respectively (Figure 2). The mean species richness of macroand micro-invertebr ates of tree ferns and non-fern trees were 20.6 9.7 and 24.2 3.3 respectively (Figure 3). The mean diversity of macroand micro-invertebrates of tree ferns and non-fern tree s were 2.467 0.485 and 2.548 0.657 respectively (Figure 4). The mean evenness of macro and micro-invertebrates for tree ferns and non-fern trees were 0.872 0.081 and 0.8 79 0.066 respectively (Figure 5). Lastly, the mean index of richness (Smarg) for macr oand micro-invertebrates of tree ferns and non-fern trees were 4.78 1.57 and 5.39 0.56 respectively (Figure 6). "! #! $! %! &! '! (! )! *! "!! +,--./-,01203/-,0.+,-!"##$%&'&() Figure 2. Mean abundance (N) of leaf litter inverte brates under tree ferns and non-fern trees for 15 sites. There was no significant differ ence between the two communities (Sign test, p > 0.05, n = 15; 5 pluses, 9 minuses). Stand ard error values are shown.
! & "! "& #! #& $! +,--./-,01203/-,0.+,-!"##$%&'&() Figure 3. Mean species richness (S) of leaf litter invertebrates under Tree ferns and NonTree ferns for 15 sites. There was no significant d ifference between the two communities (Sign test, p > 0.05, n = 15; 5 pluses, 8 minuses). Standard error values are shown. #4# #4$ #4% #4& #4' #4( #4) +,--./-,01203/-,0.+,-!"##$%&'&() Figure 4. Mean diversity (H') of leaf litter invert ebrates under Tree ferns and Non-Tree ferns for 15 sites. There was no significant difference b etween the two communities (Sign test, p > 0.05, n = 15; 6 pluses, 8 minuses). Standard erro r values are shown.
!4)# !4)$ !4)% !4)& !4)' !4)( !4)) !4)* !4*! +,--./-,01203/-,0.+,-!"##$%&'&() Figure 5. Mean evenness (E) of leaf litter inverteb rates under Tree ferns and Non-Tree ferns for 15 sites. There was no significant difference b etween the two communities (Sign test, p > 0.05, n = 15; 6 pluses, 7 minuses). Standard erro r values are shown. # $ % & ( +,--./-,01203+,--./-,0 !"##$%&'&() Figure 6. Mean index of richness (Smarg) of leaf li tter invertebrates under Tree ferns and Non-Tree ferns for 15 sites. There was no significa nt difference between the two communities (Sign test, p > 0.05, n = 15; 4 pluses 10 minuses). Standard error values are shown. When comparing total abundance, species ric hness, diversity, evenness and index of richness of macroand micro-invertebrates in a met acommunity level, many differences are apparent. The total abundance of invertebrates for the tree fern metacommunity was 973 individuals in comparison to 1155 individuals from the non-fern tree metacommunity, showing that non-fern trees had a greater abundance of invertebrates. In terms of species richness, out of a total of 146 morphospecies, the tree fern metacommunity harbored 110
species while non-fern tree metacommunity had 121 m orphospecies, showing non-fern trees had a higher species richness. The index of richnes s (Smarg) for the tree fern metacommunity was 15.8 in comparison to the metacom munity of non-fern trees, which was calculated to be 17.0, showing that the Smarg f or the non-fern tree metacommunity was greater. When looking at diversity on a metacommuni ty level, there was a significant difference between tree ferns and non-fern trees, w ith an H' value of 3.48 and 3.65 respectively (Modified T-Test, t = -2.52, p < 0.05, df = 2075). In terms of overall metacommunity evenness, the invertebrates under tre e ferns had an index of 0.74 in comparison to non-fern trees, which had an evenness index of 0.76, showing that the metacommunity under non-fern trees was overall, mor e even. When comparing the total abundance of inve rtebrates in the leaf litter under the tree ferns D. gigantea and C. caracasana var. meridensis and non-fern trees on the metacommunity level, seven species were observed ha ving a 20% change in number. These species were considered to be most affected b y the presence or absence of allelopathic chemicals. Five morpho species showed a proportionally higher abundance of individuals under non-fern trees. "*" "% #$ )# ) $% ( #%$ #' %( $$ %" ## #$ &! "!! "&! #!! #&! $!! 5,6-,7 8299-:;29<= >?,@0AB<@9 5,6-,7 C,?@6-, 5,6-,7 829-2?B-,<= F--B95,6-,7 G2,@9J-,M@HE *+(,&() -"'./012$%3.%,(0456 +,--./-,0 1203+,--./-,0 Figure 7. Species having the greatest difference in total abundance when comparing leaf litter invertebrates under tree ferns and non-fern trees. In order to be considered as undergoing a significant change, each species had t o have 20 individuals in the leaf litter under tree ferns or non-fern trees, and there must be a 20% increase or decrease in abundance between the two communities. The numbers above each bar represent the total abundance of each labeled species in the given micr ohabitat.
These individuals include Springtails (Order Collem bola), which had a 21% increase, one spider morphospecies (Order Arachnida), which had a 51% increase, one beetle morphospecies (Order Coleoptera), which had a 46% increase, insect larvae (Class Insecta), which had an 80% increase, and Silverfish (Order Z ygentoma), which had a 69% increase. The two remaining species that were observed having 20% change in abundance, also had a proportionally lower number of individuals in the leaf litter under non-fern trees. These individuals include angel insects (Order Zoraptera) which were observed having a 49% decrease, and caterpillars (Order Lepidoptera), whi ch were observed having a 54% decrease under non-fern trees (Sturm 2003)(Figure 7). DISCUSSION In this experiment, the differences observed in com munity structure and composition between the leaf litter under tree fern and non-fer n trees are striking. My findings support previous studies showing that tree ferns exhibit al lelopathic effects (Bell 1979) and do, in fact, influence invertebrate communities (Wardle et al 1998). Leaf litter invertebrate metacommunities showed a significant difference in H' as well as observed differences in N, S, Smarg and E all of which were higher under non-fern trees. Trophic interactions and the importance of saprophytic microflora and fu ngi can help explain these results. In a study of herbivory in boreal forests, the presenc e of allelochemicals was shown to contribute to a decline in ecosystem performance th rough adversely affecting other biotic components (Wardle et al 1998). In this experiment, the secondary metabolites exuded by D. giantea and C. caracasana var. meridensis were overall unfavorable to invertebrates present in the same community. One subset of organisms that may have been directly affected by secondary metabolites is soil microflora. Soil microflora pla y important roles as detritivores and decomposers and greatly influence all other ecosyst em functions. Detritivores and decomposers are very much regulated by litter quali ty, which can be strongly influenced by the presence of certain chemicals like phenolic acid, found in tree ferns. The exuded allelopathic chemicals likely produced poor litter quality, making the leaf litter undesirable for microbes and soil animals. This fur ther affects the decomposition rate of dead plant material, which is the primary energy ba se of the leaf litter food web (Chen & Wise 1999). Examining this from a bottom-up approac h, allelopathic chemicals under tree ferns can be seen to decrease the productivity and effectiveness of detritus-based food webs, in which organisms that depend on soil m icrobes and fungi at higher trophic levels may be negatively impacted. As a result, it is likely that the degradation of the microbe and fungi community resulted in a decline o f the abundance, richness and diversity of soil invertebrates. Likewise, inverteb rates may have been directly impacted by allelopathic chemicals, by avoiding areas under tree ferns where secondary metabolites were present, leading to low species ri chness and diversity. Regardless of whether allelopathic chemicals impact communities i ndirectly or directly, their presence has certainly resulted in lower N, S, H', Smarg and E for invertebrate metacommunities under tree ferns. Despite the differences between tree fern and non-f ern trees at the metacommunity level, there was no significant diffe rence in the N, S, Smarg, H' or E of invertebrate communities under tree fern and non-fe rn trees at the local level. These
results may be attributed to the scale of compariso n. When analyzing these two distinct communities at the local level, the sample sizes ar e much smaller than those used for the metacommunity comparison. In approximately 50% of t he samples analyzed, N, S, Smarg, H', and E were higher in the leaf litter of non-fern trees. Although there were no significant differences between local means of all of these indices, a slight trend was apparent. Therefore, examination at the local level may fail to produce significant evidence for allelopathy as a determinant of biodiv ersity due simply to small sample sizes. Upon examining the invertebrate communities under tree ferns and non-fern trees, I was able to see that each tree had a highly uniqu e assemblage. Certain species appeared to be more affected by the presence of secondary me tabolites in tree ferns. Springtails (Order Collembola), some of the most conspicuous li fe forms in soil and leaf litter (Chen & Wise 1999, Jacot 1936), had a greater abundance i n non-fern tree leaf litter. Their decline in tree fern leaf litter may be attributed to their involvement in detritus-based food webs. As fungivores, springtails actively seek out microscopic patches occupied by fungal species that are associated with high-qualit y litter (Kliromonas, Widden & Deslandes 1992). Therefore, allelopathic chemicals that degrade leaf litter quality, like those produced by tree ferns, would actively decrea se the abundance of certain invertebrates. The decreased abundance of silverfis h (Order Zygentoma) under tree ferns may also be explained by poor leaf litter quality, since silverfish and springtails share similar primitive characteristics. A high abundance of springtails has also been corre lated with a high abundance of coleopterans and arachnids (Chen & Wise 1999), evid enced in this study by increased numbers of one spider morphospecies and one beetle morphospecies under non-fern trees. Field observations indicate that collembolan s comprise a major proportion of the diet of ground-dwelling spiders and beetles (Chen a nd Wise 1999). As a result, some species of beetles and spiders preferentially selec t habitats where their primary food sources are abundant, such as under non-fern trees. Insect larvae (Class Insecta) were also seen to hav e an increased abundance under non-fern trees. This can be attributed to the direc t effects allelopathic compounds may have on larvae. Because larvae are developing insec ts, a large proportion of their energy is put into growing. Therefore, they may have less energy to defend themselves against harsh abiotic conditions and predators. Because ins ect larvae are vulnerable during development, they may be unable to deal with the pr esence of secondary metabolites under tree ferns. Therefore, insect larvae beneath the leaf litter of allelopathic tree ferns may have low survival rates and subsequently low ab undances. Both caterpillars (Order Lepidoptera) and angel in sects (Order Zoraptera) had higher abundances in leaf litter under tree ferns, contradicting the prediction that allelopathic chemicals negatively influence the abu ndance of micro and macro fauna. However, these insects lack direct associations wit h D. gigantea and C. caracasana var. meridensis and may have been randomly located under only a fe w tree ferns. Since angel insects are commonly found in colonies of 15 to 20, they are likely to be abundant when present (Engel 2003). This was observed for both sp ecies, in which the majority of observed individuals was found at 3 or 4 sites. Overall, the differences in abundance, richness, a nd diversity of leaf litter invertebrates under D. gigantea C. caracasana var. meridensis and non-fern trees illustrate the importance of biological interaction s in ecosystems. On a metacommunity
level, allelopathic tree ferns and their secondary metabolites have an impact on the structure, function, and composition of organisms i n their surrounding environment. However, current field research associated with all elopathy is lacking, while use of allelopathic compounds as natural herbicides and pe sticides are becoming more widespread. Thus, future investigation of allelopa thic plants in their natural setting is necessary to fully comprehend their effects on biol ogical interactions and protect leaf litter and soil biodiversity. ACKNOWLEDGEMENTS I would like to thank two of the most inspirational mentors and professors I have been lucky enough to encounter, Alan & Karen Masters, for all of their h elp and support and teaching me everything I needed to know from square one all the way on up. I would lik e to thank the EstaciÂ—n BiolÂ—gica de Monteverde for providing me with a beautiful place to do this expe riment and for hot showers, which were few and far between elsewhere. Many more thanks to Tom McFarlan d for spending countless hours making my Berlese funnels, saving me hours of unnecessary work. Thank s to Cam Pennington for answering all of my thousands of questions and providing help in every way possible, making the entire research process ru n a little bit smoother. My fellow lab rats, thank you for making 6 hour blocks of looking under a microsc ope the most entertaining part of my day. Lastly, an ov erwhelmingly large thank you to Danielle, Amy & Meeta for constant laughs, unlimited support, study ing with me till 4 am, showing me your top notch da nce moves and being amazing friends. You've made every second worth while. LITERATURE CITED Bell, S. & L. Klikoff. 1979. Allelopathic and autop athic relationships among the ferns Polystichum acrostichoides Polypodium vulgare and Onoclea sensibilis American Midland Naturalist 102 (1): 168-171 Boyce, R.L. 2005. "Life under your feet: Measuring soil invertebrate diversity." Teaching Issues and Experiments in Ecology (TIEE) Ecological Society of America. 7 April 2007. . Chen, B & D. Wise. 1999. Bottom-up limitation of pr edaceous arthropods in a detritus-based terrestrial food web. Ecology 80 (3): 761-772 Engel, M. 2003. Zoraptera. In: Encyclopedia of Inse cts V. Resh & R. CardÂŽ, eds. Academic Press, Boston, MA, pp. 1201-1203 Ferguson, J.J. and B. Rathinasabapathi. 2003. Allel opathy: how plants suppress other plants. Universit y of Florida: Horticultural Sciences Department. "Germinator inhibitors." (Evenari, M. 1949, in Bell S. & L. Klikoff 1979)" GÂ—mez, L.D. 1983. Cyatheaceae and Dicksoniaceae (Ra bos de Mico, Tree Ferns). In: Costa Rican Natural History D.H. Janzen, ed. The University of Chicago Press, Chicago, IL, pp. 225-228 Heckendorn, K. & M. Saeman. 2003. Tree fern (Dickso niaceae and Cyathaceae) allelopathy in the Monteverde Cloud Forest. CIEE Fall 2003: 58-74 Jacot, A. 1936. Soil structure and soil biology. Ec ology 17 (3): 359-379 Klironomas, J., P. Widden & I. Deslandes. 1992. Fee ding preferences of the collembolan Folsomia candida in relation to microfungal successions of decaying litter. Functional Ecology 9: 528-536 Rojas, A. 1999. Costa Rica: Arborescent Ferns, pp. 128. Instituto Nacional de Biodiversidad (INBio), Santo Domingo, Costa Rica. Southwood, T.R.E. Ecological Methods, pp. 184-187. Chapman & Hall, London, Paris. Sturm, H. 2003. Zygentoma. In: Encyclopedia of Inse cts V. Resh & R. CardÂŽ, eds. Academic Press, Boston, MA, pp. 1201-1203 Wagner, H. and K. Long. 1991. Allelopathic effects of Osmunda cinnamomea on three species of Dryopteris. American Fern Journal 81(4): 134-138 Wardle, D., M.C. Nilsson, C. Gallet & O. Zackrisson 1998. An ecosystem-level perspective of allelopat hy. Bio. Rev. 73: 305-319
Wardle, D. & P. Lavelle. 1997. Linkages between soi l biota, plant litter quality and decomposition. In : Driven by Nature, Plant Litter Quality and Decompos ition G. Cadisch & K. Giller, eds. CAB International, Wallingford, pp. 107-124
QuickTime and a decompressor are needed to see this picture. Figure 1. Trail map of the Monteverde Cloud Forest behind EstaciÂ—n Biologica de Monteverde, Costa Rica. Sampling areas along S. Pri ncipal and S. Cariblancos are symbolically marked ().
APPENDIX A: Two versions of a Berlese funnel apparatus: Version 1 (top) allows for greater depth of leaf litter but requires a lon ger exposure time for drying (48-72 hours). Version 2 (bottom) holds a smaller volume o f leaf litter but the exposure time is shorter (24 hours).