No. 7
Caribbean Naturalist
2014
Potential Impacts of the Invasive Grass Megathyrsus maximus (Poaceae) on Ground-dwelling Arthropods in a Caribbean Dry Forest Lorna M. Moreno, Elvia Meléndez-Ackerman, Christopher Cheleuitte, Lourdes Lastra, Ricardo Rodriguez, and Julissa Rojas-Sandoval
The Caribbean Naturalist . . .
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Cover Photograph: Mona Island site invaded by African grass Megathrysus maximus. Photograph © Julissa Rojas-Sandoval.
Board of Editors
CARIBBEAN NATURALIST
James D. Ackerman, Department of Biology, University of Puerto Rico at Río Piedras, USA Alfonso Aguilar-Perera, Department of Marine Biology, Universidad Autónoma de Yucatán, Mexico Wayne J. Arendt, International Institute of Tropical Forestry, Luquillo, Puerto Rico, USA Rüdiger Bieler, Field Museum of Natural History, Chicago, IL, USA Leo Douglas, Department of Geography/Geology, University of the West Indies, Mona, Jamaica Robert Erdman, Department of Biological Sciences, Florida Gulf Coast University, Fort Myers, FL, USA Keith Goldfarb, Eagle Hill Institute, Steuben, ME, USA ... Editor-in-Chief Grizelle González, International Institute of Tropical Forestry, San Juan, Puerto Rico, USA Gary R. Graves, Department of Vertebrate Zoology, Smithsonian Institution, Washington, DC, USA S. Blair Hedges, Department of Biology, Pennsylvania State University, University Park, PA, USA Julia A. Horrocks, Dept. of Biological and Chemical Sciences, Univ. of the West Indies, Cave Hill Campus, Barbados Scott Jones, Smithsonian Institution, Caribbean Coral Reef Ecosystems, Carrie Bow Cay, Belize Heather Judkins, Department of Biological Sciences, University of South Florida, St. Petersburg, FL, USA Craig A. Layman, Department of Biological Sciences,Florida International University, North Miami, FL, USA John Leavengood, Department of Entomology, University of Kentucky, Lexington, KY, USA Antonio A. Mignucci-Giannoni, Manatee Conservation Center, Inter American University, Bayamón, Puerto Rico, USA Gregg Moore, Department of Biological Sciences, Jackson Estuarine Laboratory, University of New Hampshire, Durham, NH, USA Robert Powell, Department of Biological Sciences, Avila University, Kansas City, MO, USA Chris Rimmer, Vermont Center for Ecostudies, Norwich, VT, USA Armando Rodríguez-Durán, Dean for Research, Inter American University, Bayamón, Puerto Rico, USA Noris Salazar Allen, Smithsonian Tropical Research Institute, Panama Inés Sastre de Jesus, Biology Department, University of Puerto Rico at Mayagüez, USA J. Angel Soto-Centeno, American Museum of Natural History, Division of Mammalogy, New York, NY, USA Christopher Starr, Department of Life Sciences, University of the West Indies, St. Augustine, Trinidad and Tobago David W. Steadman, Florida Museum of Natural History, Gainesville, FL, USA Kathleen Sullivan Sealey, Department of Biology, University of Miami, Coral Gables, FL, USA Jarrod M. Thaxton, Department of Biology, University of Puerto at Mayagüez, USA Jason M. Townsend, Department of Wildlife, Fish and Conservation Biology, University of California-Davis, USA ... Managing Editor Jill Weber, Eagle Hill Institute, Steuben, ME, USA ... Production Editor Byron Wilson, Department of Life Sciences, University of the West Indies at Mona, Kingston, Jamaica Graham A. J. Worthy, Department of Biology, University of Central Florida, Orlando, FL, USA Joseph M. Wunderle, International Institute of Tropical Forestry, University of Puerto Rico at Río Píedras, USA The Caribbean Naturalist (ISSN # 2326-7119) is published by the Eagle Hill Institute, PO Box 9, 59 Eagle Hill Road, Steuben, ME 04680-0009. Phone 207-546-2821, FAX 207-546-3042. E-mail:
[email protected]. Webpage: www.eaglehill.us/cana. Copyright © 2014, all rights reserved. Periodical postage paid in Steuben, ME and additional mailing offices. Published quarterly. Special issue proposals are welcome. On-line secure subscription ordering: rate per year for Caribbean subscribers - $15 regular, $10 students, $60 organizations; for Non-Caribbean subscribers - $20 regular, $15 students, $80 organizations. Journal subscription exchanges are considered. Authors: submission guidelines are available at www.eaglehill.us/cana. Co-published journals: The Northeastern Naturalist (ISSN 1092-6194 [print], ISSN 1938-5307 [online]) and the Southeastern Naturalist (ISSN 1528-7092 [print], ISSN 1938-5412 [online]), journals with separate Boards of Editors. The Eagle Hill Institute is a tax exempt 501(c)(3) nonprofit corporation of the State of Maine (Federal ID # 010379899).
2014 2014
Caribbean Naturalist CARIBBEAN NATURALIST L.M. Moreno, et al.
No. 7 No. 7:1–15
Potential Impacts of the Invasive Grass Megathyrsus maximus (Poaceae) on Ground-dwelling Arthropods in a Caribbean Dry Forest Lorna M. Moreno1, Elvia Meléndez-Ackerman1,*, Christopher Cheleuitte2, Lourdes Lastra1, Ricardo Rodriguez3, and Julissa Rojas-Sandoval4,5 Abstract - Invasive species are important drivers of biodiversity loss and community changes worldwide. The African grass Megathyrsus maximus (Guinea Grass), introduced on Mona Island in the last century, has established extensive stands, but information about its effect on natural ground-dwelling communities is lacking. Ground-dwelling organisms play an important role in ecosystem function, and their diversity and distribution may be influenced by plant community composition. In this study, we tested if the presence of Guinea Grass on Mona Island was related to differences in species richness, composition, and abundance of ground-dwelling arthropods. To that effect, we established pitfall traps in two invaded sites and two non-invaded sites for five continuous days. Areas invaded by Guinea Grass had lessdiverse ground-dwelling arthropods communities than areas where this exotic grass was absent. Abundances of Collembola and Acari (mites) were particularly lower at invaded sites relative to non-invaded ones, suggesting that invasion by M. maximus has the potential to alter ground-dwelling arthropods communities in somewhat predictable ways.
Introduction Exotic species are one of the primary threats to global biodiversity (Brooks and Pyke 2002, D’Antonio and Vitousek 1992). Species invasions not only can increase competitive interactions among species, but also can change environmental conditions and resources available to natural communities (Chapin et al. 2000). It has been suggested that interdependence between the aboveground vegetation and ground-dwelling communities may result in reduced richness and abundance of vegetation species and ground-dwelling biota following plant invasions (Brown and Rice 2000, Sammon and Wilkins 2005, Verloove 2006). However, most of the studies on the impacts of plant invasions has focused on aboveground flora and fauna effects, leaving this hypothesis rather understudied (Wolf and Klironomos 2005). Vegetation would provide resources for ground-dwelling communities in part through organic matter deposition that becomes available for decomposition. Department of Environmental Sciences and Institute for Tropical Ecosystems Studies, University of Puerto Rico, Río Piedras Campus, PO Box 21910, San Juan, PR 00931-1910, USA; 2College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA; 3Department of Biology, University of Puerto Rico at Humacao, Call Box 860, Humacao, PR 00792, USA; 4Center for Applied Tropical Ecology and Conservation, University of Puerto Rico, Río Piedras Campus, PO Box 23341, San Juan, PR 00931-3341 USA. 5Department of Botany, National Museum of Natural History, MRC-166 Smithsonian Institution, PO Box 37012, Washington, DC 20013, USA. *Corresponding author -
[email protected]. 1
Manuscript Editor: Grizelle González 1
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Caribbean Naturalist L.M. Moreno, et al.
No. 7
Thus, changes in aboveground plant biodiversity and abundance could impact ground fauna variability as well (Wardle 2004). To date, very few studies have assessed the effects of grass invasions on ground-dwelling arthropod communities with enough detail to make generalizations about the associations between above- and belowground biotic communities within the context of grass invasions (but see Flanders et al. 2006, Parr et al. 2010, Wolkovich et al. 2009). For example, in semiarid ecosystems in Texas and California (USA), invasive grasses have been associated with reductions in arthropod diversity (Flanders et al. 2006, Wolkovich et al. 2009). On the other hand, in a semiarid system in Utah (USA), a study has shown that effects of invasive grasses on diversity and abundance of soil biota may be modulated by the type of plant community that is invading, and the composition of plant species within this type of plant community (Belnap and Phillips 2001). As a result, depending on the original conditions of plant communities, increases in ground-dwelling and soil fauna abundance (and not necessarily reductions) are also possible upon grass invasions. For that semiarid system, Belnap and Phillips (2001) found lower richness, fewer fungi and invertebrates, and higher abundances of soil bacteria in areas invaded by the exotic grass Bromus tectorum L. (Drooping Brome) relative to non-invaded areas. In this study, we evaluated if the presence of the African grass Megathyrsus maximus (Jacq.) B.K. Simon & S.W.L. Jacobs (Guinea Grass) on Mona Island was associated with a lower diversity and abundance of ground-dwelling arthropods. Guinea Grass has been naturalized in many parts of the world (D’Antonio and Vitousek 1992), and currently is widely distributed in tropical zones in Central and South America (Williams and Baruch 2000). On Mona Island, the time of arrival of Guinea Grass is not well defined, but we know that the variety introduced was the common variety of Guinea Grass (Más and García-Molinari 2006). Wadsworth (1973) first reported that this grass species was introduced on this island in 1888, but Cintrón and Rogers (1991) suggested that it was introduced in the 1960s to support cattle activities. Currently, this exotic grass is spreading across Mona Island (Meléndez-Ackerman 2011, Rojas-Sandoval 2010) and forms extensive patches in the native vegetation association that has been classified as lowland dry limestone shrubland, which is the third-most abundant vegetation association on this island (Martinuzzi et al. 2008). Prior studies indicate that the presence of Guinea Grass on Mona Island is associated with significant changes in microclimatic conditions such as increases in soil temperature and light intensity in the understory and reduction in soil humidity (Rojas-Sandoval and MeléndezAckerman 2012a) and is also known to negatively affect the germination and establishment of a native and threatened cactus species by altering the microclimate in the understory (Rojas-Sandoval and Meléndez-Ackerman 2012b), and to lead to changes in vegetation complexity and abundance (Rojas-Sandoval et al. 2012). Considering these changes in vegetation and in microclimatic conditions in areas invaded by M. maximus on Mona Island, we hypothesized that species richness and abundance of ground-dwelling arthropods would also be reduced in grass-invaded areas relative to non-invaded areas. 2
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Field-Site Description Mona Island is located in the Caribbean Sea, between Puerto Rico and Hispaniola (18°05'N, 67°54'W; Fig. 1). The island is a limestone-dolomite platform covering an area of 55 km2 (Cintrón 1991). Mona Island has a mean annual temperature of 26.8 °C and a mean annual precipitation of 896 mm (Rojas-Sandoval and Meléndez-Ackerman 2011). The island has a variety of subtropical dry forest associations with many rare and protected species of plants and animals (Cintrón and Rogers 1991, Meléndez-Ackerman 2011). At our study sites, Guinea Grass was the dominant species at invaded areas (average plant density = 9 ramets/ m2; Rojas-Sandoval and Meléndez-Ackerman 2012a), while non-invaded areas were dominated by Croton species interspersed with small trees such as Plumeria obtusa L. (Singapore Plumeria), Reynosia uncinatata Urb. (Sloe), and Anthirrea acutata (DC.) Urban (Placa Chiquita) (Cintrón and Rogers 1991). Plant communities at our study sites have been classified as lowland dry limestone shrublands (Martinuzzi et al. 2008). Vegetation in this forest type is described as dense and shrubby due to the high incidence of xerophytic shrubs, globular and columnar cacti, and trees with low canopy heights (
