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Milici, Valerie, R.
Composicin de la comunidad de invertebrados terrestres como indicador de la regeneracin forestal
Terrestrial invertebrate community composition as an indicator of forest regeneration
Forest regeneration will play an important role in the future of tropical biodiversity, as much has been lost to deforestation and continues to be degraded. Terrestrial arthropod composition in a community could be an indicator of succession level as arthropods are a highly diverse phylum and their short generation periods allow communities to adapt to changes much faster than plants or animals. This study tests the changes in community composition of terrestrial arthropods along a successional gradient. Pitfall traps were placed in four sites of varying regeneration, from farmland to old growth. It was found that abundance, species richness, and diversity increased as site age increased. Old growth had higher abundance of Arachnida and Coleoptera, 15-year had higher abundance of Orthoptera and moderate abundance of all other orders, 5-year had overall low abundance, and farmland had high abundance of Hymenoptera coupled with low abundance in every other category. Through this, it was determined that terrestrial arthropod composition does change along a successional gradient and that terrestrial arthropod community composition can be used as a tool to assess succession level.
La regeneracin de los bosques desempea un papel importante en el futuro de la biodiversidad tropical. Hasta ahora hay mucho bosque que se ha perdido a causa de la deforestacin y contina siendo degradada al da de hoy. La composicin de las comunidades de artrpodos terrestres puede ser un mejor indicador de los niveles de sucesin porque los artrpodos son un filo muy diverso y sus periodos cortos de generaciones permiten que las comunidades se adapten a los cambios ms rpidamente que las plantas u otros animales. Este estudio examina los cambios de la composicin de las comunidades de artrpodos por un gradiente de sucesiones. Puse trampas pitfall en cuatro sitios diferentes de regeneracin, desde el pasto hasta el bosque primario. Encontr que la abundancia, la riqueza de especies, y la diversidad aumentaron con la edad del bosque. El bosque primario tenia abundancias ms altas de Coleoptera y Arachnida, el bosque que tena 15 aos de edad tena una abundancia ms alta de Orthoptera y abundancias promedias de los otros Ordenes, el rea de 5 aos de regeneracin tenan abundancias bajas de todos los artrpodos, y el rea de pasto tenia abundancias altas de Hymenoptera y abundancias bajas de todas las otras categoras. Determine que podemos usar la composicin de las comunidades de artrpodos terrestres para entender los niveles de sucesin.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone--San Luis
Diversidad de especies
Regeneracin del bosque
Costa Rica--Puntarenas--Zona de Monteverde-San Luis
Tropical Ecology Spring 2011
Ecologa Tropical Primavera 2011
t Monteverde Institute : Tropical Ecology
Terrestrial invertebrate community composition as an indicator of forest regeneration Valerie R. Milici Department of Biology, Indiana University ABSTRACT Forest regeneration will play an important role in the future of tropical biodiversity, as much has been lost to deforestation and continues to be degraded. Terrestrial arthropod composition in a community could be an indicator of succession level as arthr opods are a highly diverse phylum and their short generation periods allow communities to adapt to changes much faster than plants or animals. This study tests the changes in community composition of terrestrial arthropods along a successional gradient. Pi tfall traps were placed in four sites of varying regeneration, from farmland to old growth. It was found that abundance, species richness, and diversity increased as site age increased. Old growth had higher abundance of Arachnida and Coleoptera, 15 year h ad higher abundance of Orthoptera and moderate abundance of all other orders, 5 year had overall low abundance, and farmland had high abundance of Hymenoptera coupled with low abundance in every other category. Through this, it was determined that terrestr ial arthropod composition does change along a successional gradient and that terrestrial arthropod community composition can be used as a tool to assess succession level. RESUMEN La regeneracin de bosques ser una parte importante en el futuro de la cub ierta forestal. Hasta ahora hay mucho bosque que estn perdidos a causa de deforestacin y continua la degradacin de bosques hoy. La composicin de comunidades de artrpodos terrestres puede ser una indicador mejor de niveles de sucesin porque artrpodos son un filo muy diverso y sus cortos periodos de generaciones permiten que las comunidades adaptan a cambios mas rpido que plantas o otros animales. Este estudio examine los cambios a la composicin de comunidades de artrpodos por un gradiente de sucesi ones. Puse trampas pitfall en cuatro sitios de regeneracin diferentes, desde pasto a bosque primario. Encontre que abundancia, la riqueza de especies, y diversidad aumentaron con edad de bosque. Bosque primario tenia abundancias mas altas de Coleoptera y Arachnida, el bosque que tenia 15 aos de edad tenia una abundancia mas alta de Orthoptera y abundancias promedias de los otros Ordenes, el rea de 5 aos de regeneracin tenan abundancias bajas de todos los artrpodos, y el rea de pasto tenia abundancia s altas de Hymenoptera y abundancias bajas de todos los otros categoras. Determine que podemos usar la composicin de comunidades de artrpodos terrestres como entender niveles de sucesin. INTRODUCTION T ROPICAL FOREST HABIT ATS have the highest biodiversity on the planet, but also the highest rate of degradation (Lewis 2008) This threat is driven by high population growth and the resulting demand for land and resources (Lewis 2008). Roughly 350 million hectares have been deforested and 500 million more hectares are degraded (Lamb et al. 2005). This deforestation and its recovery have unknown effects on biodiversity, ecosystem, and community interactions (Lewis 2008). Although ecologically important at a global scale Costa Rica experien ced the fifth highest rate of deforestation worldwide between 1976 and 1980, with 3.2% forest lost/year (FAO 1990). Much of this forest loss was due to clearing land for cattle and agriculture (Nygren 1995).
Due to pressure from countries concerned by the rapid rate of deforestation, the Costa Rican government began taking steps to preserve forest by creating national parks (Persson & Munasinghe 1995). Costa Rican conservation programs now currently protect more than 12% of the country as national parks (Ny gren 1995). Although Costa Rica has made great strides in conservation, there is still much room for improvement as biodiversity continues to be threatened (Snchez Azofeifa et al. 2001). It is not just biodiversity, but many economic benefits such as bio prospecting and tropical hardwood harvesting, that are threatened by this deforestation and degradation. Therefore there are both intrinsic and economic benefits to reforestation. However, not all successional forests are created equal. Various factors ca n affect regeneration rate: degree of fragmentation, proximity to forest, residual seed bank composition, and previous use of the land (Lamb et al. 2005). Guariguata & Dupuy (1997) found that land compacted from logging took 80 years to reach the status of the logged forest and even longer to regain species richness. Additionally, tropical grasslands tend to persist although surrounded by forest (Lamb et al. 2005). A loss of topsoil from erosion, as can be caused by agricultural practices (Holt & Coventry 1 990), can also hamper regeneration from decreased soil nutrients. It seems that there are thresholds an ecosystem can cross, making natural regeneration difficult (Lamb et al. 2005). Succession age is therefore not a good indicator of level of regeneratio n because so many factors affect regeneration rate (Lamb et al 2005). Instead terrestrial arthropods could be an accurate representation of the ecosystem (Kremen et al. 1993). Terrestrial arthropods serve a diverse array of functions to an e cosystem in nutrient cycling as both predators and prey (Kremen et al 1 993). They are the most species rich phylum and due to short life cycles, respond to environmental changes more quickly than both plants and vertebrates, and are therefore the best early indicator s of environmental change (Kremen et al 1993). Past studies have shown that the diversity of forest floor arthropods changes along a successional gradient (Niemel et al 1996). It was found that clear cut land received new species rapid ly and that over t ime, abundance of species varied more than species richness (Niemel et al. 1996). The goal of this experiment was to determine whether the diversity and composition of terrestrial arthropods could be used as an indicator of forest succession. Terrestrial arthropods were collected at four sites along a successional gradient to determine how community composition changes over time. I hypothesized that diversity will increase over a successional gradient and that there will be a difference in abundance among species within this gradient. This will help establish a baseline of the composition expected at pre early mid succession, and primary forest and provide a guideline for determining stage of forest succession for a given neotropical forest regeneration plot. MATERIALS AND METHODS Study Site ). San Luis is surrounded by premontane moist forest, which is highly seasonal with a pronounced wet and dry season. It receives between 1200 2200 mm of rainfall each year and has a mean annual temperature between 17 24 C. The forest that surrounds San Luis is composed of mainly evergreen species (Haber 2000). There were four site types; th e first were fields that are currently being cultivated (Site 0). These fields were located on organic coffee farms. Site 0 was open and exposed to the sun; the fields had no plant cover other than coffee and banana plants. The second site type is
early re generation (Site 5); these fields had been fallow for five years. Site 5 had a few sporadic trees no higher than 3 meters, and low level plant cover. There was a riverbed to the side of Site 5 and a windbreak on the other separating it from the pasture. Th e third site represents mid succession (Site 15), and had been left to fallow fifteen years ago. Site 15 had previously been pasture and was surrounded by pasture, but located close to intact primary forest. Site 15 was composed of fragments of regeneratio n; the trees were small with a low (~10 m), mostly closed canopy. The fourth site is an old growth forest sample (Site O.G). This was located on a hillside behind a cattle farm. This forest patch was continuous and surrounded San Luis. This site had a high er and more closed canopy than the other sites. It also had larger and more numerous trees. Data Collection Data was collected over a ten day period, from April 24 th to May 4 th 2011. 200 ml pitfall traps were placed in each site. Site 15 had 15 pitfall traps, Site 0 and Old growth had 14 pitfall traps, and Site 5 had 12 pitfall traps. Traps were between 5 and 100 meters apart depend on possible placement sites, as some areas were too rocky to dig deep enough to place traps. Traps were checked and reset e very other day and insect abundance and species per trap were recorded. Insects were identified to order and then separated into morpho species within orders. For analysis of all data from one pitfall trap was grouped as one sample, for a total of 55 sampl es. RESULTS Data Summary A summary of data collection can be seen in Table 1. A total of 3,073 terrestrial arthropods were collected, which were separated into 12 orders and 62 morpho species. It can be seen how many individuals from each family were c ollected at each site. Averages for comparison between sites were not calculated from this table.
T ABLE 1. Compilation of all terrestrial arthropods along a regeneration gradient in San Luis, Costa Rica. There were four sites; 0 = farmland, 5 = young growth, 15 = early regeneration forest, O.G = old growth. Table 1 Provides number of individuals from each order sampled at each site. Also gives total number of arthropods counted at each site, total number of individuals from a given order sampled across sites, and number of morpho species found for each order. Site Order 0 5 15 O.G Total Morpho Species Arachnida 46 46 258 396 746 8 Blattodea 9 23 118 81 231 4 Chilopoda 2 2 2 3 9 2 Coleoptera 19 16 33 263 331 16 Dermaptera 1 10 3 14 1 Diptera 13 90 19 53 175 4 Hymenoptera 595 36 327 21 979 10 Isopoda 3 28 71 77 179 1 Lepidoptera 2 7 3 12 4 Orthoptera 12 16 219 101 348 6 Staphy linid 9 16 18 43 5 Worm 3 1 2 6 1 Total 704 275 1075 1019 3073 62 Abundance and Diversity Abundance varied significantly between sites (One way ANOVA, F = 5.533, df = 3, P = 0.0023; Fig. 1). Site 5 had the lowest average number of individuals per trap (30.5) followed by Site 0 (50.4). Both Sites 15 and O.G. had similar averages (73.73 and 72.78, respectively). F IGURE 1. Average ( SE) number of terrestrial arthropods collected over 10 days per pitfall trap along a successional gradient in San Luis, Costa Rica (May 2011) Those not connected by the same letter have significantly different abundances
Species richness was calculated as the average number of species per trap per site. It can be seen that species richness increases with sites age and there is a large jump in richness from 5 to 15 years. A comparison between sites showed a significant d ifference in species richness (One way ANOVA, F = 28.38, df = 3, p <0.0001; Fig. 2). The two older sites are about twice as species rich as the younger sites. Diversity was calculated using the Shannon Weiner index. Diversity increased between site 0 and site 5 and then remained relatively constant (Fig. 3). There is a significant difference between diversity and site age (One way ANOVA, F = 4.98, df = 3, p = 0.0043). The diversity of site 0 is the lowest, 0.95; the next three sites have about a 1.74 fold increase. F IGURE 2. Average ( SE) number of species per pitfall trap per site along a successional gradient in San Luis, Costa Rica collected over 10 days in May 2011. Points not connected by the 0.05)
Composition Comparisons Average abundance of the five most common orders (Table 1) per trap was calculated and compared. The orders compared were Arachnida, Hymenoptera, Coleoptera, Blattodea, and Or thoptera. Each order showed a significant difference in abundance between Site ages, but where the orders were most or least abundant varied between orders. Average Arachnid abundance varied significantly with site age (One way ANOVA, F = 13.14, df = 3, p < 0.0001). Arachnid abundance increased with age (Fig. 4), as abundance was low in both Sites 0 and 5, and then increased dramatically for Sites 15 and old growth. Sites 0 and 5 were significantly different from Sites 15 and old growth, but not different from each other each other. Hymenoptera showed an opposite relationship from Arachnida (Fig. 4). They were most numerous at site 0 and showed a general tren d towards lower abundance at older sites. There was a significant difference between abundance and site age (One way ANOVA, F = 10.38, df = 3, p which had aver age hymenoptera abundances of 3.00 and 1.5, respectively. Site 15, however, did not vary significantly from either site and had an average abundance of 21.8 hymenoptera per trap. F IGURE 3. Average ( SE). Shannon Weiner index diversities of terrestrial arthropods per pitfall trap across regeneration gradient in San Luis, Costa Rica (May 2011). There is an increase in diversity between site 0 and site 5, and then diversity levels off. Significant diffe rences in diversity are given different letters.
Abundance of Coleoptera was low for the first three sites and then increased dramatically for the old growth site (Fig. 5) and had a significant relationship with site age (One way ANOVA, F = 18.45, df = 3, p < 0.0001). Coleoptera individuals are about 9 times more abundant in old growth fields than any other site. When comparing abundances site by site, there is a significant difference between the old growth site and the three younger sites, while there is no difference between the three younger sites (Tukey HSD test, p < 0.05). Blattodea abundance changed between sites in a general trend of increased abundance with increased site age (Fig. 5). There is a relationship between age and Blattodea abundance (One way ANOVA, F = 8.82, df = 3, p < 0.0001). Site 15 had the highest average abundance, growth site had an average abundance of 5.8 and was significantly higher than site 0. Site 5 was similar to both sites 0 and old growth, and different from site 15. Site age is a significant factor in Orthoptera abundance and they show an increase in abundance as site age increases, but abundance peaks at site 15 (One way ANOVA, F = 17.78, p < growth site has the second highest abundance, 7.21, and is significantly different from sites 15 and 0, but not site 5. Site 5, was only significantly differe nt from site 15, but similar to old growth and site 0. The old growth was significantly lower than both sites 15 and old growth. F IGURE 4. The average ( SD) abundances of Hymenoptera and Arachnida per pitfall trap each Site. Samples were collected along a successional gradient over 10 days in San Luis, Costa Rica (May 2011). Site 0 is farmland, 5 is young growth, 15 is early growth forest, and Old growth is old growth forest. 5 0 5 10 15 20 25 30 35 40 45 50 20 10 0 10 20 30 40 50 60 70 80 0 5 15 Old growth Arachnida Hymenoptera Years Regrowth Hymenoptera Arachnida
DISCUSSION There is a general trend towards more abundance, richness, and diversity as a site ages. This suggests that as fields progress in regeneration, there should be an increase in the number of terrestrial arthropods. Though Site 0 had a higher abun dance than Site 5, this may be explained by the fact that Site 0 is located on an organic farm. This is consistent with findings by Asteraki et al. ( 2003 ) that abundance of arthropods was higher in organically managed plots A likely reason that organic fi elds facilitate more insects is the absence of chemical use. Also, it is important to note that the majority of the abundance is due to the high number of Hymenoptera typically found in each cup and that every Hymenoptera found at Site 0 was an ant. Ants a re both social organisms (Hoyt 1996) and certain species such as Solenopsis invicta are prevalent in pastures (Apperson & Powell 1984). Therefore, abundance does not amount to diversity or a necessarily healthy environment. As expected, species richness increased dramatically between younger and older sites. The main increase occurred between Site 5 and Site 15. This suggests that between 5 and 15 years of regeneration, a major change occurs that allows for the accumulation of many more species. Then aft er this change, richness stabilizes. This change that increases arthropod richness is most likely an increase in species richness of plants (Asteraki et al 2003). Diversity too, increased with age. There was an increase from Site 0 to Site 5 and after the initial increase, diversity stabilized. This is consistent with the results of species richness and the summary in Table 1. Species richness increased along the regeneration gradient, as did evenness. As the fields aged, there were a similar number of ind ividuals found per order and fewer extreme outliers as well as more species overall. These factors all lead to an increase in diversity. This is consistent with and supports my hypothesis. Results show that a high abundance of Arachnida and Coleoptera could potentially be used as indicators of old growth forest in the premontane moist life zone. Both orders showed a dramatic increase as site age progressed and were the most abundant orders found in old growth F IGURE 5. A comparison of the average abundances of the orders Coleoptera, Blattodea, and Orthoptera caught in pitfall traps along a successional gradient ( SE). Samples were taken over a 10 day period in San Luis, Costa Rica (May 2011). Site 0 is farmland, 5 is young growth, 15 is early successional forest, and Old growth is old growth forest. 0 2 4 6 8 10 12 14 16 18 5 0 5 10 15 20 25 30 35 40 0 5 15 Old growth Blattodea Coleoptera/Orthoptera Years Regrowth Coleoptera Orthoptera Blattodea
sites. Arachnids are predators (Anderson 20 03) and Asteraki et al. (2003) found that most Coleoptera species in regeneration were predators, so this suggests that old growth forests might be abundant in predators. This could be explained by the higher overall richness and abundance found in older r egeneration sites. The higher richness of both plants and insects (Asteraki et al. 2003) could help to support the higher trophic level of the predators and represent an overall rich and resource abundant community (Hairston & Hairston 1993). It appears that high abundances of Orthoptera have potential to be used as indicators for early secondary forest, the status of Site 15. High abundances of Orthoptera are might good indicators, as Orthoptera abundances in Site 15 were significantly higher than every other site. There was also moderate abundance of every order except Coleoptera at Site 15. This implies that early succession could be a transitional environment in which many orders are present from both early regeneration and late succession, but not man y in high abundances because it is not an ideal environment for many species. The two younger sites, 0 and 5, have no real trends other than general low abundance. This implies that there may be no specific order indicative of younger regeneration sites. However, lack of abundance could potentially be used to define sites that are still in their first stages of succession. However, in all cases, more research must be done. These findings should be tested across more sites of the same age, and across more site factors such as altitude and life zone to see if they hold true for a more general area. With more comprehensive data, more set guidelines for determining the health and regeneration of forests can be created. Conclusions Many factors impact speed of regeneration. Therefore, age of regeneration is not necessarily an accurate indicator of level of succession (Lamb et al. 2005). Instead terrestrial arthropods can be used as indicators of level of succession because they are both highly diverse and res pond to environmental changes rapidly (Kremen et al. 1993). Data support the hypothesis; terrestrial arthropod diversity increases across a successional gradient and there are patterns in community composition. Coleoptera and Arachnida were abundant in old growth and Orthoptera abundance high for early successional forest. These patterns could be used as a guideline for the identification of succession level, but more data is needed for this to be fully supported. This has important implications for conserv ation biology as it provides a new methodology for determining relative site health. As different types of sites appear to have different compositions, scientists can lay pitfall traps in multiple sites instead of intensive tree sampling to determine regen eration stage. This can both save time and help pinpoint the sites that might be in the best position to be conserved so that conservation funds can be allocated to the best places. ACKNOWLEDGEMENTS Thanks to Pablo Allen for all of his advice statistical help, and psychological guidance, Moncho Calderon and Gisella Fernandez for supplies, Mario Picado Perez and Raul Leitn Araya for letting me use their land as study sites, my familia tica for their wonderful support and food, Nathan Sellers an d Isa Betancourt for their help in ide ntifying and separating insects, t he University of Georgia Ecolodge medkit. And thanks to the sloths for sparing my soul.
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