Edge effects on understory Rubiaceae communities in lower montane moist forest at Monteverde, Costa Rica Jenna Halsey Department of Environmental Sciences, Indiana University ABSTRACT Understory plants are important to tropical forest structure as the y support diverse communities of frugivorous birds, insects, and mammals. The biodiversity in understory communities is becoming increasingly altered as fragmentation of forests exposes more land to edge effects. Rubiaceae is a common understory fruiting plant family that can be found in forest fragments in tropical and subtropical regions. This study examined the effects of distance from a pasture edge on the abundance and species richness of Rubiaceae. I tested a total of ten transects that ran 68 m d eep into the forest fragment. Each transect contained four 2x2 m 2 plots, and each plot was placed 20 meters apart. I took a census of Rubiaceae species in each plot and calculated the abundance and species richness. I tested for a significant gradient of abundance and species diversity across all plots, per transect. I found a strongly consistent correlation between abundance and species diversity and thus concluded that distance from the edge had a profound effect on Rubiaceae. I also tested the effect s that distance from the pasture edge had on the overall composition of Rubiaceae in the forest. I found that the composition of the plot nearest to the edge differed to a great extent from the farthest plot. Thus, edges also have a great effect on Rubia ceae composition. The effects of edges on crucial understory plants, such as Rubiaceae, are important to tropical and subtropical conservation and management. RESUMEN Las plantas del sotobosque son importantes para la estructura del bosque tropical ya que sostienen comunidades diversas de aves frugÃvoras,, de insectos y de mamÃferos. La biodiversidad en comunidades del sotobosque se altera cada dÃa mÃ¡s debido a que la fragmentaciÃ³n de bosques expone mÃ¡s Ã¡rea a los efectos de borde. La famil i a Rubiaceae es un grupo comÃºn de plantas frutales del sotobosque que se pueden encontrar en fragmentos de bosque en regiones tropicales y subtropicales. Se examinaron los efectos de la distancia a la orilla de un potrero en la riqueza de especies y abundancia de ru biÃ¡ceas. Se examinÃ³ un total de diez transeptos que se adentraban 68 m en el fragmento de bosque. Cada transepto contenÃa cuatro parcelas de 2x2 m 2 y cada parcela se colocÃ³ a 20 m de la distancia de la siguiente parcela. Se registrÃ³ el nÃºmero de especies de Rubiaceae en cada parcela y se calculÃ³ la riqueza de especies y la abundancia. Se analizÃ³ la presencia de un gradiente significativo de abundancia y diversidad de especies en todos los transeptos de cada parcela. EncontrÃ© una fuerte correlaciÃ³n entre la diversidad de especies y la abundancia y por eso concluÃ que la distancia a la orilla tuvo un efecto profundo en las rubiÃ¡ceas. TambiÃ©n probÃ© los efectos que la distancia a la orilla del potrero tuvo en la composiciÃ³n general de rubiÃ¡ceas en el bosq ue. EncontrÃ© que la composiciÃ³n de la parcela mÃ¡s cercana a la orilla era muy diferente a la composiciÃ³n de la parcela mÃ¡s lejana; de esta manera, las orillas tambiÃ©n tienen un gran efecto en la composiciÃ³n de las rubiÃ¡ceas. Los efectos de orilla en plan tas cruciales del sotobosque, tal como las rubiÃ¡ceas, son importantes para la conservaciÃ³n y la administraciÃ³n de Ã¡reas tropicales y subtropicales.
INTRODUCTION The tropics are home to nearly 50% of described species in the world and an even larger num ber of undescribed species Dirzo and Raven, 2003. Over the last century approximately 350 million hectares of secondary and primary forests have been degraded ITTO, 2002 and the conversion rate of tropical forests into disturbed habitats is greater th an 1.2% annually Laurance and Bierregaard, 1997. Since land use and cover change are becoming increasingly common, studies on the effects of forest fragmentation on the ecology of plants and animals are especially important to management of remnant fore sts Laurance and Bierregard, 1997, Davies, 2001. Habitat fragmentation creates new edges around the core forest and exposes a vast perimeter of forest to changes in light, air temperature, soil moisture, and humidity Gehlhausen, S.M., 2000. The under story environment is characterized by low light, high humidity, low wind, and moderate temperature, which vary greatly from the windy, sunny, hot, and dry edges of a forest. The introduction of these edge effects may alter the composition of understory co mmunities. For instance, shade tolerant understory plants may be out competed by pioneers that grow rapidly in the presence of increased light availability. Also, understory communities may desiccate in the absence of canopy, which would maintain moistur e and protect against wind and high temperatures. Since many species of insects, birds, and mammals have diets that are restricted to the understory, the alteration of fruiting and flowering plants may have far reaching effects Gentry and Emmons, 1987. Rubiaceae is one of the largest flowering plant families, consisting of about 7,000 species. Most of the family is concentrated in the topics and subtropics, and the majority of species are trees or shrubs Heywood, 1993. Rubiaceae is abundant in the u nderstory environment and may be disturbed by increased light, temperature, wind, and evaporation found in edge environments Stiles, 1993. The aim of this study was to investigate how edge effects impacts understory Rubiaceae. I asked two primary questi ons: Is there an effect of distance from the edge on abundance and species richness of Rubiaceae and How does the composition of Rubiaceae change as distance from the edge increases? I predict that as you move further away from the edge of the forest, the abundance and species richness of Rubiaceae would increase. Additionally, the composition of plots closest to the edge would vary greatly from the plots furthest from the edge. I suggest abiotic changes along the forest edge will disrupt the optimal env ironment for Rubiaceae, pushing the community further back into the forest. METHODS This study was conducted where primary tropical lower montane moist forest met open pasturelands between altitudes of 1500 m and 1600 m in Monteverde, Costa Rica. I exa mined ten 68 m transects separated by at least 100 m between each transect. I took a census of Rubiaceae species richness and diversity in four 2x2 m 2 plots positioned at intervals along each transect. The first plot was situated 0 2 m where open pastu re abutted remnant forest. I collected individual Rubiaceae plants in each plot and created a
library of pressed leaves, digital photos, and made notes on each individual. With the help of local botanists, I identified each plant to species. RESULTS In order to look at the effects of distance from the edge on the abundance and species richness of Rubiaceae, I compared the number of individuals N and the total number of species S for each plot, per transect Fig 1, Fig 2. 0 2 4 6 8 10 12 14 16 Plot A Plot B Plot C Plot D Plot Cumulative S FIG 1. Edge effects on cumulative Rubiaceae species richness as distance increases from the edge. Plot A 0 2 m from edge; Plot B 22 24 m; Plot C 44 46 m; Plot D 66 68m. 0 10 20 30 40 50 60 Plot A Plot B Plot C Plot D Plot Cumulative N FIG 2. Edge effects on cumulative abundance of Rubiaceae as distance increases from the edge. Plot A 0 2 m from edge; Plot B 22 24 m; Plot C 44 46 m; Plot D 66 68m I ran a Friedman test across each plot per transect and found a significant gradient of both abundance P <. 05 and species ric hness P < .05 as distance from the edge increased Table 1, Fig. 1, Fig 2. I found the plot closest to the edge contained the lowest abundance and species richness, and the plots furthest from the edge contained the highest abundance and species richne ss.
TABLE 1. Results of Friedman Test for Rubiaceae abundance N and species diversity S between each plot per transect. The Mean Rank N shows plot D was ranked highest in abundance. Rubiaceae plants than Plot A DF=3. Mean Rank S shows species ri chness in plot D is ranked highest in species richness and Plot A was ranked lowest DF=3. Plot Distance from Edge Mean Rank N Mean Rank S A 0 2 m 1.3 1.4 B 22 24 m 2.15 2.05 C 44 46 m 2.95 3.1 D 66 68 m 3.6 3.45 I also calculated a Sorenson s index of each plot across transects 1 10 to determine which communities are most similar. The results show that plot sets A&B and C&D were significantly similar Table 2. It also indicates that abundance is less similar in between plots A&C, B&C, and B &D, and least similar in set A&D where the distance between the plots are greatest. TABLE 2. Sorenson s Index values C s between each set of plots across all ten transects. Set A&B have greatest C s value and show greatest similarity between plots. 0 2 M 22 24 M 44 46 M 66 68 M A B C D A 0.32 0.16 0.15 B 0.15 0.14 C 0.19 D I found that Psychotria valeriana, Psychotria monteverdensis , and Posqueria latifolia were common throughout all plots. The common species also followed the abu ndance gradient as distance from the pasture edge increased, so did the number of individuals. Psychotria monteverdensis was especially prevalent across all plots and transects. Furthermore, the majority of rare species were restricted to Plot D and a fe w were present in Plot C. TABLE 3. Species abundance per plot. Common and rare species composition . Species Plot A Plot B Plot C Plot D Posqueria latifolia* 1 2 1 2 Psychotria monteverdensis* 1 2 3 7 Psychotria valeriana* 2 13 24 24 Chione syl vicola 0 0 2 2 Psychotria uliginosa 0 0 2 1
Palicourea albocaerulea 1 1 0 0 Faramea multiflora 0 0 1 1 Psychotria eurycarpa 0 2 1 1 Coussarea austin smithii 0 0 0 1 Palicourea padifolia 0 0 0 1 Faramea ovalis 0 0 6 3 Hoffmannia laxa 0 0 5 0 Randia "bullpin" 0 0 0 3 Psychotria goldmanii 0 0 0 1 Randia matidae 0 0 0 1 Psychotria aggregata 0 0 0 1 TOTAL 5 20 45 49 * Represents common species found across all plots DISCUSSION Edge effects seem to be significantly impacting not only abundance but also species richness of understory Rubiaceae, an important understory plant family in Monteverde, Costa Rica. Plots located closest to the edge 0 24 m had consistently fewer individuals and species than plots furthest from the edge 44 68 m. Fig.1 a nd Fig. 2 clearly show a consistent correlation of richness and abundance across a gradient. This was confirmed through testing a comparison of each plot in all ten transects. The results support a strong effect of distance on Rubiaceae abundance and spe cies richness. This was further reinforced by comparing similarities of each plot across all transects Sorenson s Quantitative Index. Plot set A&D had the greatest difference in distance and were least similar across all plots and transects. This fur ther supports that distance from the edge has a profound effects on Rubiaceae abundance. It may be that the harsh edge conditions such as intense light, heat, and wind create a suboptimal environment for Rubiaceae seedlings, thus limiting their habitat to the core forest. A compounding factor may be that the seeds are not being dispersed near the pasture edge; birds that normally disperse Rubiaceae may have moved further back as a result of edge presence. This may hold true for the declination of species richness as well. The composition of the plots show that common species persist throughout all plots and rare species were only found farthest from the edge. It may be that common species, such as Psychotria monteverdensis and Psychotria valeriana are a ble to adapt better to abiotic changes or have more general dispersers that visit edges more frequently. Another possibility is that the common species are common throughout the region Monteverde, thus increasing the probability that they will be found on the edge. The alteration of understory fruiting plants may have strong repercussions on biodiversity. For example, the ecology of frugivorous birds may be disrupted, as their main food source is restricted to the core forest Stiles, 1980. Evidence o f edge effects on important plant communities such as Rubiaceae could aid in future management decisions. A larger area of core forest and a smaller edge perimeter would offer optimal for conservation efforts.
ACKNOWLEDGMENTS First and foremost, I wou ld like to thank Karen Masters for her time, ultimate patience, advice, direction, and supreme fudge recipe. I would also like to thank Bill and Willow Zuchowski for taking the time to share their precious knowledge of Rubiacaeae. Many thanks to Ma r jorie Arguedas for the permission to tromp through private pastures and forest. Thanks to Ollie for having the patience to guide me through statistical analyses and Maria for help along the way. I would like to thank Javier for his gentle guidance, Spanish tr anslation, and a kitchen for cooking arroz con leche. A special thanks goes out to those students who frequently stood on my plant press so that I may successfully tighten the straps I couldn t have done it without you. LITERATURE CITED Davies, K.F., C . Gascon, AND C.R . Margules. 2001. Habitat Fragmentation. Consequences, Management, and Future Research Priorities. SoulÃ¨, M.E., Orians, G.H. Conservation Biology. Research Priorities for the Next Decade, pp.81 92. Island Press, Washington, D.C. Dirzo , R. and Raven, P.H. 2003 Global state of biodiversity and loss. Annu. Rev. Environ. Resources 28, 137 167. In Tropical forests in a changing environment. Wright, S.J., TRENDS in Ecology and Evolution. 2005 Vol. 20 No. 1 Gehlhausen, S.M., M.W. Schw artz, AND C.K. Augspurger. 2000. Vegetation and microclimatic edge effects in two mixed mesophytic forest fragments. Plant Ecology 147: 21 35. Gentry, A.H. AND L.H. Emmons. 1987. Geographical Variation in Fertility, Phenology, and Composition of the Un derstory of Neotropical Forests. Biotropica 29: 286 297. Gilbert, L.E. 1980. Food web organization and the conservation of neotropical diversity. In: SouleÂ´ , M.E., Wilcox, A.B. Eds., Conservation Biology. Sinauer Associates, Sunderland, pp. 11 33. Galetti M., C.P , Alves Costa, AND E. Cazetta. 2003. Effects of forest fragmentation, anthropgenic edges and fruit colour on the consumption of ornithocoric fruits. Biological Conservation:111. 269 273. Heywood, V.H. 1993. Flowering Plants of The World. Oxford University Press. New York, N.Y. Laurance, W.F.AND J.R.O., Bierregaard. 1997. Tropical Forest Remnants Ecology, Management, and Conservation of Fragmented Communities. Chicago University Press, Chicago. AS SEEN IN : Galetti M., C.P , Alv es Costa, AND E. Cazetta. 2003. Effects of forest fragmentation, anthropgenic edges and fruit colour on the consumption of ornithocoric fruits. Biological Conservation:111. 269 273. Stiles, F.G., 1980. Evolutionary implications of habitat relations betwe en permanent and winter resident land birds in Costa Rica. In: Keast, A., Morton, E.S. Eds., Migrant Birds in the Neotropics:Ecology, Behavior, Distribution and
Conservation. Smithsonian,Washington, DC, pp. 421 435. Galetti M., C.P , Alves Costa, AN D E. Cazetta. 2003. Effects of forest fragmentation, anthropgenic edges and fruit colour on the consumption of ornithocoric fruits. Biological Conservation:111. 269 273. Wright, S.J. 2005. TRENDS in Ecology and Evolution. Vol. 20 No. 10
APPENDIX A TRANSECT PLOT Species Number of Individuals 1 A 0 0 B Posqueria latifolia 1 C Psychotria monteverdensis 2 Psychotria valeriana 2 D Psychotria monteverdensis 3 Chione sylvicola 1 Psychotria valeriana 2 2 A Palic ourea albocaerulea 1 Psychotria monteverdensis 1 Psychotria valeriana 1 B Psychotria valeriana 4 Psychotria monteverdensis 1 C Posqueria latifolia 1 D Psychotria valeriana 2 3 A 0 0 B 0 0 C Psychotria valeriana 3 D Psychotria val eriana 5 Psychotria eurycarpa 1 Psychotria monteverdensis 1 4 A 0 0 B 0 0 C Posqueria latifolia 1 Psychotria valeriana 1 Psychotria monteverdensis 1 Faramea ovalis 1 D Psychotria valeriana 5 Posqueria latifolia 1 Coussarea austin smithii 1 5 A 0 0
B Posqueria latifolia 1 C Faramea ovalis 4 Hoffmannia laxa 1 D Psychotria valeriana 1 Randia "bullpin" 1 Psychotria goldmanii 1 6 A 0 0 B Psychotria valeriana 2 Palicourea albocaerulea 1 C Psychotr ia valeriana 2 Psychotria uliginosa 1 D Psychotria valeriana 5 Chione sylvicola 1 Faramea ovalis 1 Randia matidae 1 7 A 0 0 B Psychotria valeriana 3 C Psychotria valeriana 7 Hoffmanii laxa 2 D Hoffmanii laxa 6 Randia "bullpi n" 1 Psychotria aggregata 1 8 A 0 0 B Psychotria eurycarpa 1 Psychotria valeriana 2 C Psychotria valeriana 2 Psychotria eurycarpa 1 Faramea ovalis 1 Psychotria uliginosa 1 D Psychotria valeriana 2 Faramea ovalis 1 Psychotri a monteverdensis 3 9 A 0 0 B Psychotria valeriana 1
Psychotria uliginosa 1 C Psychotria valeriana 3 Hoffmanii laxa 2 Chione sylvicola 1 D Faramea ovalis 1 Psychotria valeriana 1 Psychotria uliginosa 1 Psychotria monteverdensis 2 Posqueria latifolia 1 10 A Psychotria valeriana 1 B Psychotria valeriana 1 Psychotria uliginosa 1 C Psychotria valeriana 4 Chione sylvicola 1 Coussarea austin smithii 1 D Psychotria monteverdensis 3 Posqueria latifolia 1 Ra ndia "bullpin" 1 Chione sylvicola 1