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Diversity of macroinvertebrate feeding guilds along a stream order continuum in San Luis Valley, Costa Rica

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Title:
Diversity of macroinvertebrate feeding guilds along a stream order continuum in San Luis Valley, Costa Rica
Translated Title:
Diversidad de los gremios de alimentación de macroinvertebrados a lo largo de una quebrada con flujo continuo en el Valle de San Luis, Costa Rica ( )
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Schrautemeier, Tim
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Invertebrates   ( lcsh )
Species diversity   ( lcsh )
Costa Rica--Puntarenas--Monteverde Zone--San Luis   ( lcsh )
Invertebrados
Diversidad de especies
Costa Rica--Puntarenas--Zona de Monteverde--San Luis
Tropical Ecology Spring 2010
Ecología Tropical Primavera 2010
Genre:
Reports   ( lcsh )
Reports

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Abstract:
Under the surface of streams, there is dominance and compositional variance among biological communities, which normally goes unobserved. The River Continuum Concept (RCC) describes shifts in biological communities caused by shifts in abiotic factors along a longitudinal gradient of a river system. Macroinvertebrates, which are influenced by the RCC, were collected and identified from 18 sites along 3.6 km of the Rio San Luis. The Morisita Index of Similarity and cluster analysis showed a difference in upper and lower reaches of the river. Canopy cover and feeding guild composition were strongly correlated. Different families showed higher dominance with and without the presence of canopy. The RCC was supported by the stream tests, however, changes in biodiversity, composition, and abundance occurred in a much shorter distance than predicted.
Abstract:
Bajo la superficie de las quebradas, hay una dominancia y variación composicional entre las comunidades biológicas, que normalmente no se nota. El Concepto de Continuidad del Río (CCR) describe cambios en las comunidades biológicas causados por los cambios en los factores abióticos a lo largo de un gradiente longitudinal de un sistema ripario. Los macroinvertebrados, que están influidos por el CCR, fueron colectados e identificados en 18 sitios a lo largo de 3.6 km en el río San Luis. El índice de similaridad de Morisita y un análisis agrupado muestran diferencias en las partes altas y bajas del río. La cobertura del dosel y la composición de los gremios alimenticios están altamente correlacionadas. Diferentes familias muestran una alta dominancia en lugares con y sin cobertura del dosel. El CCR está apoyado por las pruebas de flujo, sin embargo, los cambios en la biodiversidad, la composición y la abundancia ocurrió en una distancia mucho más corta de lo previsto.
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Diversity of Macroinvertebrate Feeding Guilds Along a Stream Order Continuum in San Luis Valley, Costa Rica Tim Schrautemeier Department of Biology, University of Missouri Columbia ABSTRACT Under the surface of streams, there is dominance and compos itional variance among biological communities, which normally goes unobserved. The River Continuum Concept (RCC) describes shifts in biological communities caused by shifts in abiotic factors along a longitudinal gradient of a river system. Macroinvertebra tes, which are influenced by the RCC, were collected and identified from 18 sites along 3.6 km of the Rio San Luis. The Morisita Index of Similarity and cluster analysis showed a difference in upper and lower reaches of the river. Canopy cover and feeding guild composition were strongly correlated. Different families showed higher dominance with and without the presence of canopy. The RCC was supported by the stream tests, however, changes in biodiversity, composition, and abundance occurred in a much short er distance than predicted. RESUMEN Bajo la superficie de quebradas, hay una dominancia y variacin composicional entre las comunidades biolgicas, que normalmente no se nota. El Concepto de Continuidad del Ro (CCR) describe cambios en las comunidade s biolgicas causados por cambios en factores abiticos a lo largo de un gradiente longitudinal de un sistema ripario. Macroinvertebrados, los cuales son influenciados por el CCR, fueron colectados e identificados en 18 sitios a lo largo de 3.6 km en el r o San Luis. El ndice de similaridad de Morisita y un anlisis agrupado muestra diferencias en las partes altas y bajas del ro. La cobertura del dosel y la composicin de los gremios alimenticios estn altamente correlacionados. Diferentes familias mu estran una alta dominancia en lugares con y sin cobertura del dosel. El CCR esta soportado por las pruebas del ro, sin embargo, cambios en la biodiversidad, composicin y abundancia ocurren a una menor distancia de la predicha. INTRODUCTION As a river flows, there are significant shifts in biodiversity not visible to the common viewer. The RCC was developed by Vannote et al. (1980) to provide a framework for integrating predictable and observable biological features of flowing water systems. This concep t proposes understanding of biological dynamics with consideration of river systems gradient of physical features formed by natural drainage networks (Vannote et al. 1980). The RCC considers longitudinal variation in aquatic communities and physicals chang es downstream. As a river flows from headwaters through downstream reaches, a variety of abiotic factors change including canopy cover and substrate. Biological communities adapt to these conditions along this longitudinal gradient (Sedell et al. 1989). Aquatic macroinvertebrates are abundant, diverse, and play a central role in many stream ecosystems and are used in many studies (Clarke et al. 2008). Morphological and

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behavioral adaptations of macroinvertebrates reflect shifts in types and locations of f ood resources with stream size (Vannote et al. 1980). Changes in macroinvertebrate feeding guilds indicate shifts in food resources caused by changes in stream size. The RCC suggests that as physical structure of a river changes from headwaters to mouth, t here will be a change in relative importance of allochthonous (energy formed external to a river) versus autochthonous (river generated) resources to consumers (March & Pringle 2003). Vannote et al. (1980) describes that shifts from heterotrophic to autotr ophic organisms is mostly dependent upon the degree of shading present. Headwater streams are greatly influenced by riparian vegetation, which reduces autotrophic production by shading and contributes large amounts of allochthonous organic matter. As relat ive dominance of various food resource categories change, there often is a corresponding shift in the ratios of different functional feeding groups down the continuum (Hauer & Lambert 1996). The RCC has been well studied over long distances in the tropics ; however, the purpose of this experiment is to see how the trends in feeding guilds change over a shorter distance. According to Holdridge life zones, the encompassing area of the study was conducted in premontane wet forest. In this life zone, the San Lu is Valley is believed too be more seasonal than other areas of this particular life zone (Nadkarni & Wheelwright 2000). The goal is to study the variation and sensitivity to minor changes of feeding guilds along a small distance (3.6 km) of the Ro San Lui s, which flows in a premontane wet forest. I hypothesize that the general trends of the RCC will hold true, however, the scale at which feeding guilds change will be much shorter than predicted. METHODS STUDY SITE The study site was the Quebrada Alondra located in the San Luis Valley, Costa Rica approximately 52 longitude and 49 latitude. The river flows out of the Monteverde Reserve into Ro San Luis, and is known to be pristine. The first site was located approximately 20 m from the San Luis waterfall 17 additional sites ranging from 957 1217 m were located with a GPS every 200 meters down stream from the first site totaling 3.6 km. All sampling took place April 13 through April 26, between 8 am and 4 pm. ABIOTIC WATER QUALITY MEASUREMENTS Substrate and canopy cover were abiotic factors used to describe physical features. I visually tested and assigned numerical percentages to canopy cover and created five distinct groups for substrate; Rock/Sand/Leaf, Rock, Rock/Sand, Rock/Grass, Rock/Algae MACROIN VERTEBRATE COLLECTION AND SAMPLING To collect macroinvertebrates, I used a 12 inch benthic macroinvertebrate collection sieve and a pair of tweezers. I placed the sieve in the water and scraped the rocks, sand, or debris in front of the sieve to dislodge t he macroinvertebrates, which were then caught in the sieve. Macroinvertebrates collected were preserved using 95% ethanol. Collection took place until 100 individuals were collected or after 60 minutes of sampling. The

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average time at each site was 38 minu tes. Identification of macroinvertebrates to their respected families was conducted in the lab with the use of a stereoscope and a macroinvertebrate identification guide. I used Morisita Index of Similarity to determine the percent similarity between sites based on family richness and abundance. Hierarchical cluster analysis was constructed from the similarity percentages, grouping the sites with the most similar macroinvertebrate assemblages (Krebs 1999). I used regression analysis to compare certain fami lies, (Baetidae, Hydropsychidae, Ptilodactylidae, and Leptophebiidae), abundances downstream. Collection and analysis was conducted according to Burnett (2009). RESULTS A total of 1,809 macroinvertebrates from 27 families were identified (Appendix 1). Ephemeroptera was the most abundant order with 890 individuals identified, the family Baetidae comprising 550 of these. Species diversity decreases as the river flows away from the waterfall (Fig. 1). Site 1 consisted of 16 different species of macroinver tebrates, where as, Site 18 only consisted of 9. The hierarchal cluster analysis shows Site 9 to be the least similar considering abundance and diversity of macroinvertebrates, followed by Site 4. Two larger groups were formed, compromising of either the u pper or lower half of sites. This is also represented by a shift in presence of canopy cover (Table 1). Both Site 9 and 4 consisted of the highest predatory feeding guild contributing to the divide of the two groups (Table 2). At least, four families incre ase or decrease downstream, that play a role in the diversity in the stream composition (families Baetidae, Hydropsychidae (Fig. 3), Ptilodactylidae, and Leptophebiidae (Fig.4). FIGURE 1. Number of macroinvertebrate species at si tes downstream (Site 1 being closest to the waterfall of Ro San Luis and Site 18 being farthest)

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FIGURE 2. Cluster chart of site similarity in Ro San Luis according to the Morisita Index of Similarity using macroinvertebrate richness and abundance. Numbers correlate with those of the sites. (1 being closest to the waterfall and 18 being farthest). TABLE 1 Abiotic factors quantified, number of macroinvertebrates (N), and species shared (S) for each site in Ro San Luis Site # Macroinvertebrates Species (N) Substrate Canopy (%) 1 106 16 Rock/Sand/Leaf 0 2 108 15 Rock/Sand/Leaf 95 3 104 16 Rock/Sand/Leaf 40 4 110 15 Roc k/Sand/Leaf 60 5 107 12 Rock/Sand/Leaf 70 6 107 13 Rock 0 7 80 13 Rock/Sand/Leaf 0 8 41 10 Rock/Sand 5 9 98 11 Rock/Sand 10 10 98 9 Rock/Sand 5 11 101 12 Rock/Sand/Leaf 10 12 104 10 Rock/Sand/Leaf 15 13 104 13 Rock 0 14 111 10 Rock/ Grass 0 15 1 11 9 Rock/ Grass 0 16 102 11 Rock/Algae 0 17 107 7 Rock/Algae 0 18 110 9 Rock/Algae 0

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TABLE 2: Percent R elative abundance of macroinvertebrate functional feeding groups at each site. FIGURE 3. Abundance shift of two families downstream. Ephemeroptera: Baetidae shows a significant increase (see dashed line ) and Tricoptera: Hydropsychidae shows a significant decrease (see solid line) along Ro San Luis. Site Filter Collector Gather Collector Predator Scraper Shredder 1 15.1 25.5 47.2 10.4 1.9 2 29.6 14.8 41.7 3.7 10.2 3 32.7 14.4 33.7 3.8 15.4 4 10.1 12.8 60.6 2.8 13.8 5 28.0 46.7 21.5 0.9 2.8 6 20.6 54.2 21.5 1.9 1.9 7 34.2 32.9 30.4 1.3 1.3 8 22.0 31.7 31.7 9.8 4.9 9 6.2 27.8 61.9 2.1 2.1 10 1.0 72.4 19.4 7.1 0 11 12.9 49.5 31.7 5.0 1.0 12 7.7 72.1 7.7 12.5 0 13 3.8 53.8 30.8 8.7 2.9 14 1.8 69.4 16.2 11.7 0.9 1 5 0.9 73.9 17.1 8.1 0.0 16 5.9 57.8 24.5 10.8 1.0 17 0 46.7 37.4 15.9 0 18 0.9 60.9 20.9 17.3 0

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FIGURE 4. Abundance shift of two families downstream. Ephemeroptera: Leptophebiidae shows a significant increase (see solid line ) and Coleoptera: Ptilodactylidae shows a significant decrease (see dashed line) along Ro San Luis DISCUSSION There is a significant decrease in diversity as flow of the continuum moves away from headwaters to further stream reaches. Sedell et al. (198 9) showed that most dramatic and predictable ecological changes occur between small streams and intermediate sized rivers or within the first 200 km of river length. This study has shown that there can be significant changes in diversity and abundance in j ust a short distance. This is not suggesting that the addition of organisms, rather it is showing a change in dominant organisms of a river, such as macroinvertebrates, over a short distance in response to abiotic factors. Cluster analysis has shown simi larities in sites that have been broken into upper and lower reaches of the stream, most apparent at Site 9 (Fig. 2). This is a result of different abiotic factors that influence the composition of stream diversity. Canopy cover changed drastically when co ntinuing downstream. Upper reaches towards headwaters were well shaded and almost consisted of full canopy, whereas lower reaches had no canopy at all. This trend may only have relevance to the river studied, however, Vannote et al. (1980) stated that cano py cover would decrease downstream. This shift in canopy cover had a significant influence in macroinvertebrate functional feeding guilds. The functional feeding guilds of macroinvertebrates show an increase of scraper and gather collector guilds with a de crease in filter collector and shredder downstream. Scrapers feed on organic matter that adheres to surfaces and gather collectors feed on deposited organic matter, which is characteristic of the absence of canopy cover. Filter collectors feed on suspended organic matter and shredders feed on living or decomposing vascular tissue, which is characteristic of presence of canopy cover near headwaters. This supports

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the prediction of Vannote et al. (1980), that importance of riparian vegetation near headwaters to autochthonous production in further stream reaches. Species diversity and abundance can vary among particular species, and their sensitivity to abiotic factors may also play a part in the river continuum. Plecoptera is absent in Site 9 but present at e very other site. Site 9 also consisted of the highest percentage of predators. These results may be due to niche partitioning of predators, in which this particular family was out competed. Homogenous sites offer higher diversity due to consistency of suit able habitat; however, heterogeneous sites offer a higher variety of niches for macroinvertebrates (Principe 2008). Hydropsychidae of Tricoptera also had significant trends, however this is a case in which this family may have restricted distributions alon g a river continuum (Mackay & Wiggins 1979). Species belonging to orders such as Ephemeroptera, Plecoptera and Tricoptera are all sensitive taxa that have significant trends in this experiment (Harding et al. 1999). Sensitive taxa are good biological indic ators when determining water quality or other trends in stream ecology. In conclusion, this experiment has shown significant trends when following a river downstream. The RCC can be used when comparing communities longitudinally down a continuum. The lan dscape along the river shifted from higher presence of canopy to none at all. Canopy cover influenced trends in macroinvertebrate feeding guilds by influencing food resources. These trends effects on diversity and abundance are supported by the RCC, althou gh predicted trends were shown to occur in only 3.6 km instead of hundreds of kilometers. ACKNOWLEDGEMENTS I would like to thank my advisor, Pablo Allen, for all of his persistence and guidance throughout the duration of this project. His eagerness has inspired me to work hard and look forward to similar tasks in the future. Secondly, I thank the other members of the CIEE staff for helping me with miscellaneous questions and for the retrieval of supplies. I would like to thank Dan Paul for his support an d advice while formulating the experiment. I would like to thank my home stay family for their hospitality and patience while conducting my experiment. I would like to thank Geovanny for allowing me to continuously have access to the trails of the waterfal l of San Luis. Finally, I would like to thank my parents for their inspiration and giving me all their support while allowing me to explore my future and having them there whenever I needed them along the way. _____________________________________________ ___________________________ LITERATURE CITED Allan, D.J. 1995. Stream Ecology: Structure and Function of Running Waters. Chapman and Hall, London. Burnett, A.S. 2009. The Effect of Land Use on Stream Water Quality in San Luis and Caitas. CIEE Fall 200 9, Monteverde, Costa Rica. Clarke, A., R.M. Nally, N. Bond, and P.S. Lake. 2008. Macroinvertebrate Diversity in Headwater Streams: A Review. Freshwater Biology. 53: 1707 1721. Cummins, K.W., and M.J. Klug. 1979. Feeding Ecology of Stream Invertebrates. Annu. Rev. Ecol. Syst. 10: 147 172. Harding, J.S. 1999. Changes in Agricultural Intensity and River Health Along a River Continuum. Freshwater Biology. 42: 345 357.

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Hauer, R.F., and G.A. Lambert. 1996. Methods in Stream Ecology. Academic Press Inc, San Diego, California. Krebs, C.J. 1999. Ecological Methodology. Addison Welsey Educational Publishers, Menlo Park Mackay, R.J., and G.B. Wiggins. 1979. Ecology Diversity in Trichoptera. Annu. Rev. Entomol. 24: 185 208. March, J.G., and C.M. Pringl e. 2003. Food Web Structure and Basal Resource Utilization along a Tropical Island Stream Continuum, Puerto Rico. Biotropica. 35: 84 93. Montgomery, D.R. 1999. Process Domains and The River Continuum. Journal of the American Water Resources Associat ion. 35: 397 410 Nadkarni, N.M., and N.T. Wheelwright. 2000. Monteverde: Ecology and Conservation of a Tropical Cloud Forest. Oxford University Press, New York. Principe, R.E. 2008. Taxonomic and Size Structures of Aquatic Macroinvertebrate Assemblages in Different Habitats of Tropical Streams, Costa Rica. Zoological Studies 47: 525 534. Sedell, J.R., J.E. Richey, and F.J. Swanson. 1989. The River Continuum Concept: A Basis for the Expected Ecosystem Behavior of Very Large Rivers. Can. Spec. Fis h. Aquat. Sci. 106 Vannote, F.L., W.G. Minshall, K.W. Cummins, J.R. Sedell, and C.E. Cushing. 1980. The River Continuum Concept. Can. J. Fish. Aquat. Sci. 37: 130 137.

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APPENDIX APPENDIX 1. Total number and distribution of macroinvertebrates iden tified at each of the 18 sites studied in the Ro San Luis in the San Luis Valley, Costa Rica. Order/ Family 1 2 3 4 5 6 7 8 9 Site 10 11 12 13 14 15 16 17 18 Totals Coleoptera 8 15 17 22 6 6 3 2 3 8 11 11 4 5 3 2 7 133 Coleoptera sp 01 1 1 1 3 Elmidae 6 6 3 7 3 4 1 7 11 7 3 5 2 2 7 74 Psephenidae 1 1 2 Ptilodactylidae 2 9 13 14 3 2 1 2 2 1 3 1 1 54 Diptera 3 1 2 1 7 Simuliidae 2 2 Tabanidae 1 1 Tipulidae 1 2 1 4 Ephemeroptera 31 15 16 8 48 56 26 17 28 78 48 77 57 87 86 68 65 79 890 Baetidae 16 10 1 16 21 16 5 15 32 28 55 33 71 72 53 48 58 550 Euthyplociidae 1 1 2 Heptageniidae 2 1 3 Leptohyphidae 5 11 7 31 33 9 8 12 39 15 9 16 3 5 4 2 209 Leptophebiidae 10 4 1 1 1 1 1 4 1 7 5 13 8 13 9 11 17 19 126 Hemiptera 4 1 43 1 2 4 9 52 4 17 1 3 2 5 1 3 152 Naucoridae 4 1 43 1 2 4 9 52 4 17 1 3 2 5 1 3 152 Lepidoptera 1 2 1 4 Pyralidae 1 2 1 4 Megaloptera 1 3 9 3 1 6 6 1 2 3 3 1 8 4 5 6 5 5 72 Corydalidae 1 3 9 3 1 6 6 1 2 3 3 1 8 4 5 6 5 5 72 Odonata 7 9 7 6 4 7 8 1 6 11 6 5 1 1 2 3 1 85 Calopterygidae 3 1 2 2 1 9 Coenagrionidae 1 1 2 Corduleg astridae 1 1 4 3 2 6 6 1 5 10 6 5 1 1 2 3 1 58 Megapodegrionidae 2 1 3 Platysticitidae 4 3 2 2 11 Polythoridae 1 1 2 Plecoptera 37 32 19 14 16 7 6 2 1 4 5 13 11 12 12 31 14 236 Perlidae 37 32 19 14 16 7 6 2 1 4 5 13 11 12 12 31 14 236 Tricoptera 14 32 34 11 31 23 27 9 6 1 15 9 7 2 2 6 1 230 Hydrobiosidae 1 2 1 3 1 8 Hydropsychidae 10 32 33 10 30 22 26 8 6 1 12 7 1 2 1 201 Philopotamidae 4 1 1 1 2 1 10 Polycentropodidae 1 1 1 3 4 10 Rhyacophilidae 1 1 Total 106 108 104 110 107 107 80 41 98 98 101 104 104 111 111 102 107 110 1809

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APPENDIX 2. Appendix showing the results from the Morisita Index of Similarity in terms of percent similarity bet ween each of the 18 sites based on the richness and abundance of macroinvertebrate families (below diagonal line) and number of shared families (above diagonal line). Site Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1 X 11 10 11 11 10 11 9 9 8 11 8 10 10 8 10 7 9 2 0.836 X 12 11 10 9 10 8 8 7 9 7 9 9 7 8 7 7 3 0.618 0.891 X 10 10 10 10 9 8 7 9 8 11 9 8 9 6 7 4 0.416 0.419 0.427 X 9 9 12 8 10 7 10 7 9 9 7 9 6 8 5 0.622 0.718 0.809 0.352 X 10 10 9 8 8 11 9 11 10 9 9 7 8 6 0.505 0.541 0.678 0.31 5 0.951 X 10 9 8 9 10 8 10 10 8 9 7 8 7 0.557 0.759 0.81 0.381 0.865 0.847 X 9 10 8 11 8 10 10 8 10 7 9 8 0.498 0.533 0.629 0.727 0.777 0.791 0.777 X 8 8 9 8 10 9 7 9 6 7 9 0.227 0.154 0.161 0.85 0.306 0.367 0.383 0.724 X 7 8 6 8 8 6 7 5 6 10 0.359 0.1 71 0.253 0.196 0.696 0.841 0.549 0.634 0.418 X 8 7 8 8 7 7 6 7 11 0.549 0.464 0.439 0.555 0.71 0.806 0.781 0.853 0.669 0.769 X 9 11 10 9 10 7 9 12 0.506 0.362 0.201 0.113 0.507 0.601 0.58 0.469 0.315 0.721 0.777 X 10 8 8 8 6 7 13 0.677 0.45 0.361 0.273 0.64 0.747 0.623 0.603 0.362 0.809 0.859 0.853 X 10 9 10 7 8 14 0.485 0.321 0.129 0.088 0.39 0.477 0.489 0.367 0.3 0.645 0.676 0.963 0.784 X 8 9 7 8 15 0.483 0.316 0.129 0.069 0.401 0.491 0.485 0.347 0.278 0.656 0.67 0.961 0.789 0.997 X 7 6 7 16 0.568 0 .362 0.166 0.166 0.426 0.522 0.526 0.44 0.36 0.679 0.749 0.96 0.87 0.975 0.969 X 7 9 17 0.763 0.531 0.265 0.175 0.433 0.452 0.486 0.376 0.242 0.554 0.638 0.862 0.829 0.898 0.891 0.931 X 7 18 0.581 0.37 0.151 0.131 0.397 0.48 0.492 0.404 0.305 0.639 0.713 0.967 0.844 0.976 0.967 0.985 0.944 X

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APPENDIX 3. Table representing functional feeding groups of each family. Order Family Feeding Guild Coleoptera Elmidae Gather Collector Coleoptera Psephenidae Scraper Coleoptera Ptilodactylidae Shredder Diptera Simuliidae Filter Collector Diptera Tabanidae Predator Diptera Tipulidae Shredder Ephemeroptera Baetidae Gather Collector Ephemeroptera Euthyplociidae Shredder Ephemeroptera Heptageniidae Scraper Ephemeroptera Leptohyphidae Gather Collector Ephemer optera Leptophebiidae Scraper Hemiptera Navcoridae Predator Lepidoptera Pyralidae Scraper Megaloptera Corydalidae Predator Odonata Calopterygidae Predator Odonata Coenagrionidae Predator Odonata Cordulegastridae Predator Odonata Megapodegrionidae Pr edator Odonata Platysticitidae Predator Odonata Polythoridae Predator Plecoptera Perlidae Predator Tricoptera Hydrobiosidae Predator Tricoptera Hydropsychidae Filter Collector Tricoptera Philopotamidae Filter Collector Tricoptera Polycentropodidae F ilter Collector Tricoptera Rhyacophilidae Predator


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Diversidad de los gremios de alimentacin de macroinvertebrados a lo largo de una quebrada con flujo continuo en el Valle de San Luis, Costa Rica
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Diversity of macroinvertebrate feeding guilds along a stream order continuum in San Luis Valley, Costa Rica
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Under the surface of streams, there is dominance and compositional variance among biological communities, which normally goes unobserved. The River Continuum Concept (RCC) describes shifts in biological communities caused by shifts in abiotic factors along a longitudinal gradient of a river system.
Macroinvertebrates, which are influenced by the RCC, were collected and identified from 18 sites along 3.6 km of the Rio San Luis. The Morisita Index of Similarity and cluster analysis showed a difference in upper and lower reaches of the river. Canopy cover and feeding guild composition were strongly correlated. Different families showed higher dominance with and without the presence of canopy. The RCC was supported by the stream tests, however, changes in biodiversity, composition, and abundance occurred in a
much shorter distance than predicted.
Bajo la superficie de las quebradas, hay una dominancia y variacin composicional entre las comunidades biolgicas, que normalmente no se nota. El Concepto de Continuidad del Ro (CCR) describe cambios en las comunidades biolgicas causados por los cambios en los factores abiticos a lo largo de un gradiente longitudinal de un sistema ripario. Los macroinvertebrados, que estn influidos por el CCR, fueron colectados e identificados en 18 sitios a lo largo de 3.6 km en el ro San Luis. El ndice de similaridad de Morisita y un anlisis agrupado muestran diferencias en las partes altas y bajas del ro. La cobertura del dosel y la composicin de los gremios alimenticios estn altamente correlacionadas. Diferentes familias muestran una alta dominancia en lugares con y sin cobertura del dosel. El CCR est apoyado por las pruebas de flujo, sin embargo, los cambios en la biodiversidad, la composicin y la abundancia ocurri en una distancia mucho ms corta de lo previsto.
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