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Estructura de los artrpodos del suelo y las comunidades de plantas en los claros del bosque y un bosque contino en Monteverde, Costa Rica
Structure of soil arthropod and plant communities in light gaps and continuous forest in Monteverde, Costa Rica
Several studies have confirmed that higher plant community richness facilitates greater arthropod community richness. The purpose of this study is to examine how plant community structure in continuous forest and light gaps impact soil arthropod community structure. In this study plant surveys were conducted for twenty plots, ten located in continuous forest and ten located within a forest gap. Along with plant surveys, a soil sample from each plot was collected in order to obtain soil dwelling arthropods. Arthropods were extracted from the soil first using a Burlese funnel, and then manually picked out of the soil. After all arthropods were obtained, they were identified to order and when possible to family. It was hypothesized that there would be a correlation between plant community structure and soil arthropod community structure, as well as a difference in diversity in continuous forest and forest gaps. The richness, evenness, and Smarg were calculated for plants in closed forest and in forest gap (H1' = 2.892, H2' = 2.406, t = 4.72, p < 0.0005). In addition, the richness, evenness and Smarg were calculated for soil arthropods in closed forest and in forest gap (H1' = 2.052, H2'= 1.896, t = 1.44, p = 0.10). There was no difference between soil arthropod diversity in continuous forest and forest gap and plant diversity did vary between continuous forest and forest gap. Regression analyses were also conducted, and the results suggest that there is no correlation between plant and soil arthropod community composition. However, there were obvious trends derived from the regressions that should be taken into consideration for future studies.
Algunos estudios han confirmado que una gran riqueza en las comunidades de plantas facilita una gran diversidad en la comunidad de artrpodos. El propsito de este estudio es examinar cmo la estructura de la comunidad de plantas en un bosque continuo y en los claros del bosque impacta a la comunidad de artrpodos del suelo. En este estudio se llevaron a cabo encuestas sobre plantas en 20 parcelas, diez ubicadas en el bosque continuo y diez ubicadas en los claros del bosque. Junto con las encuestas sobre plantas, tambin se llevaron a cabo encuestas sobre el suelo para obtener una muestra de los artrpodos que se encuentran en el mismo.
Text in English.
Arthropod surveys--Costa Rica--Monteverde-- Biological Station
Species diversity--Costa Rica--Puntarenas--Monteverde Zone
Cloud forest ecology--Costa Rica
Encuestas de Artrpodos--Costa Rica--Monteverde--Estacin biolgica
Diversidad de especies--Costa Rica--Puntarenas--Zona de Monteverde
Ecologa del bosque nuboso--Costa Rica
Tropical Ecology 2008
Ecologa Tropical 2008
t Monteverde Institute : Tropical Ecology
Structure of soil arthropod and plant communities in light gaps and continuous forest in Monteverde, Costa Rica Lauren Breza Department of Ecology and Evolutionary Biology, Uni versity of Tennessee ABSTRACT Several studies have confirmed that higher plant co mmunity richness facilitates greater arthropod community richness. The purpose of this study is t o examine how plant community structure in continuo us forest and light gaps impact soil arthropod communi ty structure. In this study plant surveys were conducted for twenty plots, ten located in continuo us forest and ten located within a forest gap. Alo ng with plant surveys, a soil sample from each plot was col lected in order to obtain soil dwelling arthropods. Arthropods were extracted from the soil first using a Burlese funnel, and then manually picked out of the soil. After all arthropods were obtained, they wer e identified to order and when possible to family. It was hypothesized that there would be a correlation betw een plant community structure and soil arthropod community structure, as well as a difference in div ersity in continuous forest and forest gaps. The r ichness, evenness, and Smarg were calculated for plants in c losed forest and in forest gap (H1' = 2.892, H2' = 2.406, t = 4.72, p < 0.0005). In addition, the richness, evenness and Smarg were calculated for soil arthrop ods in closed forest and in forest gap (H1' = 2.052, H2'= 1.896, t = 1.44, p = 0.10). There was no differ ence between soil arthropod diversity in continuous fore st and forest gap and plant diversity did vary betw een continuous forest and forest gap. Regression analy ses were also conducted, and the results suggest th at there is no correlation between plant and soil arth ropod community composition. However, there were obvious trends derived from the regressions that sh ould be taken into consideration for future studies RESUMEN Algunos estudios han confirmado que una gran riquez a en las comunidades de plantas facilita una gran diversidad en la comunidad de artrpodos. El propsito de este estudio es examinar como la estructura de la comunidad de plantas en un bosque continuo y en claros de bosque impacta la comunidad de artrpodos del suelo. En este estudio se muestr earon plantas en 20 parcelas, diez ubicadas en el b osque y diez ubicadas en claros de bosque. A lo largo de las plantas se tomaron muestras de suelo para obte ner una muestra de los artrpodos que se encuentran en el mismo. Artrpodos fueron extrados del suelo utilizando embudos Burlese, y luego extrados manua lmente del sustrato. Despus de que se obtuvieron todos los artrpodos, se identificaron a nivel de orden o familia en los que fue posible. La hiptes is del estudio es que existe una correlacin entre la estr uctura de la comunidad de plantas y la estructura d e la comunidad de artrpodos, as como la diferencia en diversidad entre el bosque continuo y claros de bos que. La riqueza, equidad y Smarg fueron calculados para bosque cerrado y claros de bosque (H1' = 2.892, H2' = 2.406, t = 4.72, p < 0.0005). Adems se calcul lo mismo para los artrpodos del sustrato en bosque cerrado y claros de bosque (H1' = 2.052, H2'= 1.896, t = 1.44, p = 0.10). No hay diferencia e ntre la diversidad de artrpodos del suelo entre el bosque cerrado y los claros de bosque, mientras que la diversidad de plantas si vara entre estos. No hay correlacin en cuanto a la composicin de la comun idad de plantas y artrpodos; sin embargo, existen tend encias obvias que pueden ser tomadas en consideraci n para futuros estudios.
INTRODUCTION Knowing and understating the relationships that soi l dwelling arthropods have within a community is essential to understanding the process es of any food web. A majority of soil arthropods usually fall into the category of d etritivores, organisms that play a crucial role in the decomposition of detritus, however othe r trophic levels are found in the soil as well (predators, herbivores, and parasites) (Sieman n 1998). Detritus is made up of dead organic material, which generally includes dead fal len leaves and the dead branches, stems, and roots of plants which can be found above or below ground (Whittaker 1975). With out these organisms, dead organic matter would continue to build up into unfathomable amounts. By taking part in the decomp osition processes, along with microbes and carrion feeders, detritivores are comp leting the necessary sequence of energy flow through a food web. It has been found through several studies that ener gy flow through ecosystems is controlled by a combination of top-down and bottomup interactions (Httenschwiler 2005, Siemann et al. 1999). Top-down interactions are facilitated by the top trophic level, where as bottom-up interactions are initiate d by plants, the primary producers. Both processes are a crucial part of any ecosystem, but each ecosystem is highly variable in which process, top-down or bottom-up, is the dom inating force. In tropical premontane forests the soil is mostly c omprised of nutrient poor clay and sand. All of the nutrients found in tropical r ainforests reside within the canopy and only a thin layer of rich decaying organic matter i s found on the forest floor. Depending on the type of forest, whether it is pristine conti nuous forest or secondary growth facilitated by a tree fall gap, the types of succes sion found in a tropical forest will determine the types of flora and fauna species foun d there. Succession is the process by which one type of forest age gives way to the next stage until a stable climax is reached. The modern view of succession says that only by bot tom up interactions drive succession, however studies have shown that ecological successi on is driven by both bottom-up and top-down interactions (Schmitz 2006). Within the s uccesssional process of forest regeneration it is important to know what kind of i mpact both top-down and bottom-up interactions have on the species richness. In general, it has been established that fauna dive rsity will increase with plant diversity (Lagerlf et. al. 1993, Siemann 1998 Ward el et. al. 1999). Previous studies have also found that detritivore communities are po sitively correlated with an increase in plant species in old fields (Siemann et al. 1999). Though this is significant for old fields, it leaves plausible opportunities to investigate wh ether or not detritivore diversity is positively correlated with an increase in plant spe cies in other ecosystems. This same study also acknowledges that arthropod diversity (h erbivores, predators, parasites, and detritivores) increases in diversity with an increa se in succession. The purpose of this study is to investigate whether or not plant species richness and abundance, in both continuous forest systems an d in naturally disturbed areas like forest gaps, impact the soil arthropod community co mposition and abundance. It was hypothesized that there would be a correlation betw een soil dwelling arthropods and plant community structure. I predicted that soil dwellin g arthropods would be positively correlated in species richness and abundance with p lant species richness and abundance. It was also hypothesized that overall species richn ess of plants and soil arthropods would
be different in different types of forest growth. I predicted that there would be the greatest diversity in pristine closed forest and le ss diverse in naturally disturbed forest. METHODS This study was conducted in the premontane wet fore st of la Estacin Biolgia de Monteverde, Puntarenas, Costa Rica. Four 30 m tran sects were marked, two within continuous forest and two in a naturally disturbed area (light gap). On each transect five randomly selected 1 m x 1 m quadrates were placed. In each quadrate a plant survey was conducted by counting the abundance of each species present within the 1 m x 1 m quadrate. Any unidentifiable plant species was col lected. In addition to plant surveys, 0.5 L of soil was collected from each quadrate to d etermine the type and abundance of soil dwelling arthropods. At each quadrate, the Br aun-Blanquet cover classes were used to estimate the canopy coverage (1 = 1%Â–5%; 2 = 6%Â– 25%;. 3 = 26%Â–50%; 4 = 51%Â– 75%; and 5 = > 75%). The collected soil was taken back to the biological station and placed in Burlese funnels for a maximum of two days to collect soil d welling arthropods. The soil was then hand processed for 30 minutes per soil sample. The arthropods were stored in containers with 95% ethanol and were identified to order, if p ossible family. Collected unidenfiable plant species were taken back to the biological sta tion, pressed in a plant press, and then identified. Statistical Analysis The Shannon-Weiner index for diversity was calculat ed along with evenness and Margalef's index in order to compare plant diversit y in a closed forest system and an open forest system. These same statistics were conducte d for soil arthropod diversity in both the closed forest system and an open forest system. Regression analyses were conducted to examine if there were any relations between the following: the number of arthropod taxa and the number of plant taxa; the arthropod ab undance and the number of plant taxa; the number of arthropod taxa and plant abundance, a nd finally the arthropod taxa and plant abundance. Then Chi squared tests were performed to determine if there was any difference between sites in arthropod abundance, number of arthropod t axa, plant abundance and the number of plant taxa and finally the degree of canopy cove rage. RESULTS In this study it was observed that the largest taxo n of soil dwelling arthropods were coleopterans (beetles) and members of the fami ly Formicidae (ants). The large numbers in Coleopteran abundance is not abnormal be cause Coleoptera is the largest order of insects. The large numbers of individuals from the family Formicidae are not representative of the abundance in soil habitats; t hese numbers are derived from only two plots out of 20. In the continuous forest the plan ts with the highest abundance was Icanthaceae I, Monstera adensoni and Begonia involucrata In the forest gap the plants that dominated in abundance were Unknown 32, Pouzolia perasitica and Viola
stipularis In both continuous forest and forest gaps Begonia involucrata was extremely common; this plant is a succulent understory plant that has a wide distribution and is found anywhere in primary and secondary forest, for est edges, and along side trails (Zuchowski). Because of B. involucrata's ability to survive and persist in various habitats, it is not unusual that this was one of th e most common plants in both forest systems. The results of the Shannon-Wiener test showed that the closed forest (H' = 2.892) is more diverse in plants than open naturally distu rbed forest (H' = 2.406) (t = 4.72, p < 0005) (Appendix, Table 2). However, there were no differences indicating that soil arthropod communities are more diverse in closed fo rest (H' = 2.085) or in naturally disturbed forest (H' = 1.945) (t = 1.22, p = 0.10) (Appendix, Table 1). The regression analyses showed that there were no statistically si gnificant relationships between plant diversity and abundance and soil arthropod diversit y and abundance (Fig. 1). In spite of this, there are obvious trends that suggest that th ere could be a significant correlation with further investigation. (A) B) n nr
(C) (C) nrrr n nrrr
(D) FIGURE 1. Closed circles represent plots found in c losed forest and open circles represent plots found in naturally disturbed areas. The solid lines are the regression lines for closed circles and the dashed lines are the regressions for open circles. a) A strong trend between the number of plant taxa and the number of arthropod taxa in both closed and open forest (R2 = 0.029, F = 0.55, df = 1, 18, p = 0.46). b) When arthropod abundance was correlated with plant abund ance there was not a significantly strong correlati on to suggest any pattern (R2 = 0.074, F = 0.134, df = 1, 18, p = 0.7185). c) Shows a correlation between th e number of arthropod taxa and plant abundance, but t he correlation is not strong enough to pursue furth er investigation (R2 = 0.049, 0.925, df = 1, 18, p = 0 .349). d) a visible correlation within an open fore st system, but not in the closed forest system (R2 = 0 .077, f = 1.496, df = 1, 18, p = 0.2370). The Chi squared analyses showed that arthropod abun dance (c2 = 53.8, p < 0.0005) and plant abundance (c2 = 71.9, p < 0.0005) are impacted by the amount of canopy coverage. The Chi squared test also determined that canopy co verage does not affect the number of arthropod taxa (c2 = 5.07, p = 0.27) and the number of plant taxa i n a premontane wet forest (c2 = 2.57, p = 0.63). nr
(A) r (B) r
(C) (D) r r
FIGURE 2. Frequency distributions of (A) number of plant taxa and amount of canopy coverage, (B) number of arthropod taxa and amount of canopy cover age, (C) plant abundance and the amount of canopy coverage (D) and arthropod abundance and canopy cov erage. DISCUSSION It is not surprising that continuous forest has a h igher diversity of plant species than a naturally disturbed forest area; it is a wid ely accepted idea that forest age is an indicator of the amount of flora diversity (Siemann et al. 1999). In this study it was determined that there was a higher amount of divers ity found in the continuous forest system than in the younger forest gap. However, it is interesting to note that there was not a different in the diversity between soil arthr opods in continuous forest and naturally disturbed areas. Several succession studies have s hown that arthropod diversity in general increases with forest age. These studies i ncluded herbivores, predators, parasites, and detritivores. Even thought the overall arthrop od diversity changes, it has been found that the largest of arthropods that change are herb ivores that colonize individual plants rather in the soil. Detritivores in previous studi es are shown to not change in diversity or relative abundance (Schmitz 2006, Seimann et al. 19 99) One aspect that is critical for future studies exam ining soil arthropod diversity in light gaps, it is important to take note of which p ioneer plant species use chemical defenses to deter soil dwelling herbivores. In the premontane wet forest of Monteverde there are several species of plants that use alkalo ids and other toxins to make themselves less desirable to herbivores, of these plants the s pecies Bocconia frutescens (Papaveraceae) has been shown to have chemicals tha t are the most effective at deterring soil arthropods, specifically brine shrimp (Veldman et al. 2007). Canopy coverage is factor that plays an important r ole in limiting resources such as light, moisture, and subcanopy temperatures. Th e amount of coverage impacts plant and soil arthropod abundance. It is not surprising that with greater canopy coverage, the abundance of plants decreases (Figure 2c, p < 0.000 5); resources are limited and the plants with the greatest advantage will succeed in growth. However, in the frequency distribution of soil arthropod abundance and canopy coverage, it appears that there is an optimal amount of canopy coverage, which peaks at c lass 3 (26-50% of coverage) (Figure 2d, p < 0.0005). This could be due to bottom-up in teractions; bottom-up limitations, in this case canopy coverage, are the determinant fact or in the amount of leaf litter that will make its way to the forest floor. Canopy coverage is a resulting variable of how productive the canopy elements are, and up to 90% o f the aboveground net primary productivity (soon to become leaf litter) enters th e detritus food web in forest ecosystems (Chen and Wise 1999). Depending on what the optima l conditions are for soil arthropods thrive, it is possible that a certain level of ligh t is needed as well as a specific amount of detritus. A study conducted by Siemann (1999) documented that increased plant productivity increases the total arthropod abundanc e and species richness, as well as species richness and abundance of each trophic grou p within an old-field ecosystem. Detritivores, herbivores, parasites, and predators were shown to have been greater in
plots with higher levels of modern methods of ferti lization. This study suggests that the diversity and composition of plants control the div ersity of consumers through both bottom-up and top-down interactions. However, in t his study the data indicates that there is no correlation between plant abundance and richn ess to soil arthropod abundance and richness. Overall the hypotheses were not supported by the da ta; the prediction that plant diversity is greater in continuous forest than in g ap forest was supported. However, the results did not support the prediction that soil ar thropod diversity would be greater in continuous forest rather than in gap forest. Thoug h many studies have concluded that detritivore diversity and abundance are not correla ted with plant richness and abundance, they have been shown to increase in diversity with increased plant productivity. A second study examining this trend (especially in a tropical forest) would provide more insight into the plant-detritivore relationship, wh ich is usually overlooked in many cases. ACKNOWLEDGEMENTS First and foremost I would like to thank my parents Pam Breza and Jim Breza for being supportive of my love and appreciation of biology. Without them I would have never respected the Earth that I love to study. I would like to thank both of my grandparents, Jesse Poore and Sandy Sartin; they made funding my trip to Costa Rica possible. Thank you Allan and Karen Masters for teaching me the kno wledge I used to conduct this experiment. Thanks you Tania Chavarra for providi ng me all the guidance through the good and difficult times of data collection and sta tistical analyses. Thank you Willow Zuchowski and Bill Haber for helping me identify th e eighty or so plant species. Thank you Pablo Allen for letting me know that I didnÂ’t a ctually identify a new species of beetle and that it was just an odd looking beetle larvae, and thank you Moncho Caldern for always providing me with project supplies. You guy s are the greatest TA's on earth! Last but not least I would like to say thank you to all off my fellow students; my experience in Costa Rica would be dull with out eve ry single one of you!
LITERATURE CITED Chen, B. and D. H. Wise. 1999. Bottom-Up Limitation of Predaceous Arthropods in a Detritus-Based Terrestrial Food Web. Ecology 80(3): 761-772 Httenschwiler, S., P. Gasser, C.B. Soil Animals Al ter Plant Litter Diversity Effects on Decomposition. 2005. Proceedings of the National A cademy of Sciences of the United States of America 102(5): 1519-1524 Lagerlf, J., H. Wallin. 1993. The abundance of art hropods along two field margins with different types of vegetation composition: an expe rimental study. Agriculture, Ecosystems and Environment 43: 141-154 Siemann, E. 1998. Experimental Tests of Effects of Plant Productivity and Diversity on Grassland. Ecology 79(6): 2057-2070 Siemann, E, J. Haarstad and D. Tilman. 1999. Dynami cs of plant and arthropod diversity during old fied succession. Ecography 22 : 406-414. Schmitz, O. J., E. L. Kalies and M. G. Booth. 2006. Alternative Dynamic Regimes and Trophic Control of Plant Succession. Ecosystems 9: 659-672. Veldman, J. W., K. G. Murray, A. L. Hull, J. M. Gar cia, W. S. Mungall, G. B. Rotman, M. P. Plosz and L. K. McNamara. 2007. Chemical Def ense and the Persistence of Plant Seeds in the Soil of a Tropical Cloud Forest BIOTROPICA 39(1): 87Â–93 Wardle, D.A., K.I. Bonner, G.M. Barker, G.W. Yeates K.S. Nicholson, R.D Bardgett, R.N., Watson, A. Ghani. 1999. Plant Removals in Pe rennial Grassland: Vegetation Dynamics, Decomposers, Soil Biodiversity ,and Ecosystem. Ecological Monographs 69(4): 535-568 Whittaker, R. H. Production. 1975. Communities and Ecosystems MacMillan Publishing, New York. Pages 218-119. Zuchowski, W. 2005. Special Habitats: Tropical Mont ane Cloud Forests. A Guide to Tropical Plants of Costa Rica David Featherstone, ed. Distribuidores Zona Tropical, S.A., Miami. Page 187
APPENDIX r #r$$ r #r$$ rrrr rrrr rr rrr !r!"#$rrr% &rr' &$$(rr)$(rr *$ !r+r!$#r#(r ,!-r+.#!! r-rr!$#rr+-#$ //-r!!r#r.r0($!r#! /#r r!rr1!2!3! r$!rr1!2!3! $r1!2!3! '#r-1!2!3! '##!r1!2!3! '!rr!!1!2!3! '!r1!2!3! r$#!r1!2!3! #!!1!2!3!n $-1!2!3! 1!2!3! $r./#rr1!2!3! r1!2!3! r1!2!3! r&1!2!3! r41!2!3! r*1!2!3! r51!2!3! r,1!23!6! 7! r TABLE 1. List of all plant taxa found in the contin uous forest transects
%" r #r$$ r #r$$ !r!"#"rrr8 #r!r) &$-!r!rr+ &! rr0 &$)!#rr-!r &$$(rr)$(rr ,!-r+! r-rr!$#r+-#r. #!r-!"!+-#r. ##$r#r+#r!r9 #-.r!r1!rr-rr r!rr1!2!3!n $r1!2!3! %r1!2!3! 'r#-r1!2!3! '!rrr1!2!3! :-r!rr! $#r1!2!3! :#$r$# !r1!2!3! ;-!$((r!!n1!2!3! r/#r(/#r1!2!3! -r!r!r/#r1!2!3! #!!r$r!/#$-1!2!3!n #rr$$#rr1!2!3! #r1!2!3! 1!2!3!n $<#rrr1!2!3! r:6!rr(! r;6#r$#r r=r!-r$! TABLE 2. List of all plant taxa found in the gap fo rest transects
" %" r #r$$ r #r$$ rnr #rrr rr r#-(#r #-(#r&r &r4#rn 4#r4r 4r5-r 5/$#r-r 5-rr -r%r -!r r!r r %r r!r TABLE 3. List of all arthropod taxa found in contin uous and gap forest transects