Orthopteran Diversity of the Cowling Arboretum and Mcknight Prairie In
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Orthopteran Diversity of the Cowling Arboretum and McKnight Prairie in Northfield, MN Alexander Forde Elisabeth Sederberg and Mark McKone 5 McKnight Prairie Carleton College. Northfield, MN Arb Prairie 4 Restorations Results and 3 Discussion A. The 2006 Orthoptera biodiversity survey for the Cowling Arboretum and Figure 1. Examples of per trap 2 McKnight Prairie found a total of 36 unique species across both sites Orthopterans from various (Figure 3). 29 species were collected at the arboretum while 20 species were C. taxonomic groups: 1 collected at McKnight Prairie. The higher absolute species number at the Average number of subfamilies arboretum can be mostly attributed to a greater number of katydid species A. a grasshopper (Acrididae) found there compared to McKnight. This difference in katydid diversity B. a katydid (Tettigonidae) 0 makes sense, since Tettigonids prefer more forested habitats (Capinera, 2004), C. a cricket (Gryllidae) of which there are none at McKnight. The Gryllidae and Acrididae identified were more consistent between locations, in terms of the absolute number of Figure 5. Average number of species in the groups, though there were important differences in the different groups of Orthopteran particular species represented within these families. taxa (shown in Figure 4) per trap In the pitfall trap experiment, there were significantly more Gomphocerinae B. at McKnight Prairie and the (U=30, P =0.002), and Raphidophoridae (U=43, P =0.037) observed per trap arboretum prairie restorations. at McKnight (Figure 4). The average number of Oecanthinae per trap was higher for the arboretum (U=49.5, P =0.088) and the average number of Error bars represent ± standard Oedipodinae was higher for McKnight (U=54, P =0.07), though these error relationships were only marginally significant (Figure 4). There were significantly more taxonomic groups represented in McKnight traps compared Introduction to Arboretum traps (t = 2.07, d.f.=22, P =0.049) (Figure 5). The higher number of total Orthopterans per trap at McKnight was marginally significant The order Orthoptera is a taxonomic division of insects that includes the species commonly referred to as grasshoppers, crickets and (t = 1.78, d.f.=22, P =0.087) (Figure 6). katydids (Figure 1). The Orthoptera of North America are relatively well-known compared to other insect orders, due to the large size of individuals and a low number of species in the region: ~1080 (Otte, 1981). The order Orthoptera is divided into two suborders, The data from the trap experiment are suggestive of several differences Caelifera which encompasses species known as grasshoppers and Ensifera which contains groups of species with a more broad range 16 McKnight between the Orthopteran assemblages of the prairie restorations of the of common names such as katydids, crickets, camel crickets, and mole crickets. Species from both suborders are known to both Prairie 14 Cowling Arboretum and the McKnight Prairie remnant. There appear to be produce audible calls by stridulating and to be able to “hear” these calls with eardrum like structures called tympana. In the United Arb Prairie Restorations more species and higher densities of Orthopterans at McKnight compared to States the greatest concentrations of Orthopteran species diversity and abundance can be found in the semi-desert of the southwest and 12 the arboretum prairie restorations. Additionally, the Orthopteran community in the tall and short grass prairies of the great plains region (Capinera, 2004). 10 composition appears very different between the locations. It is possible that the fact that sections of McKnight have never been tilled has allowed a more Orthopterans have been the subject of much research due to their economic and ecological significance (Otte, 1991) and their 8 diverse and prosperous prairie Orthopteran assemblage to persist there. suitability as model systems for basic questions about biology (Chapman, 1990). Special attention has been paid to the ecological per trap Gomphocerinae and Oedipodinae are much more abundant at McKnight, as roles of grasshoppers in grasslands, where they, along with grazing mammals can be considered the dominant herbivores (Otte, 1981). 6 observed by the trap data and also their much lower sweep net capture rate in In tallgrass prairies, grasshoppers have been found to influence nutrient cycling by affecting the amount of and type of decomposing 4 in the arboretum (A. Forde, pers. obs.). The great abundance and diversity of plant litter (Belovsky and Slade, 2000). Also, they have been observed to have an impact on the plant communities of prairies, 2 Oedipodinae at McKnight may be attributable to the drier sander conditions especially in terms of forb species (Whiles, 2006). Ritchie and Tilman (1995) found that excluding grasshoppers increased legume Average number of individuals there, rather than McKnight’s status as a remnant, though this remains to be abundance, while Belovsky and Slade (2000) observed an increase in plant abundance when they artificially increased grasshopper 0 confirmed. density in Palouse Prairie. Prairie orthopterans do not seem to significantly compete with other phyophagous insects (Evans, 1989) but they do have important effects on their many predators and parasites (Capinera, 2004) Future surveys and experiments pertaining to Orthopteran distributions should Figure 6. Average numbers of be conducted in McKnight Prairie and the Cowling Arboretum in order to In the summer of 2006, a biodiversity survey of the Orthoptera of the Carleton College Cowling Arboretum and McKnight Prairie was enhance our understanding of these insects and their ecological impacts. initiated due to the ecological importance and well-studied nature of this group. Orthopterans were collected opportunistically Orthopteran individuals Specifically, it it may be fruitful to explore the relationship between prairie throughout the summer and, additionally, a prairie-focused trapping experiment was conducted. captured per trap at McKnight succession and changing Orthopteran communities. Prairie and the arboretum prairie restorations. Error bars represent ± standard error Figure 2. Aspects of trap 2.5 experiment design McKnight Prairie Cowling Arboretum Prairie (Red diamonds represent Restorations individual pitfall traps) 2 A. Location of traps in the * * arboretum restorations 1.5 B. Location of traps in McKnight Prairie Figure 3. Species lists for Orthoptera of the Cowling Arboretum and McKnight 1 C. A pitfall trap at McKnight Prairie. Species in red are present in the arboretum but not at McKnight while species in blue are present at McKnight but not in the arboretum. 0.5 C. Average number of individuals per trap 0 Methods Conocephalinae Cyrtacanthacridinae Gomphocerinae Gryllinae Nemobiinae Oedipodinae Rhaphidophoridae Copiphorinae Oecanthinae 100m Study sites: Carleton College Cowling Arboretum covers 360 ha of land and includes a range of habitats such as restored tallgrass prairie and oak savannah, upland deciduous forest, floodplain deciduous forest, and coniferous forest. McKnight prairie is a 13 ha tallgrass prairie remnant Figure 4. Average number of References located 11 km from the arboretum. Both sites are located in Northfield MN, USA. individuals of different taxa Belovsky, G. E., and J. B. Slade. 2000. Insect herbivory accelerates nutrient cycling and increases plant Orthopteran biodiversity survey: Collection of Orthopteran insects at the Cowling Arboretum and Mcknight prairie began June 20th, 2006 and production. Proceedings of the National Academy of Sciences of the United States of America A. 97:14412-14417. th found in traps set at the ended September 11 , 2006. Various collecting methods were employed, such as pitfall traps consisting of buried deli containers with a 2 cm Capinera, J. L., R. D. Scott, and T. J. Walker. 2004. Field Guide to Grasshoppers, Katydids, and Crickets of the deep layer of 50% ethylene glycol in the bottom (Figure 2C), and directed searches based on insect calls. However, the most prominent Mcknight prairie remnant (Blue United States. Cornell University Press, Ithaca. collection method was beating through vegetation with sweep nets. Chapman, R. F., editor. 1990. Biology of Grasshoppers. John Wiley and Sons, New York. bars on left) (N=12) and in Evans, E. W. 1989. Interspecific Interactions among Phytophagous Insects of Tallgrass Prairie - an Experimental Prairie trap experiment: Twelve pitfall traps of the above description were established both at McKnight Prairie and in the prairie restorations Test. Ecology 70:435-444. of the Cowling Arboretum in early September 2006. McKnight prairie was divided into three equivalent regions, each of which received four traps set in the prairie Otte, D. 1981. The North American Grasshoppers: Volume 1. Harvard University Press, Cambridge. Otte, D. 1984. The North American Grasshoppers: Volume 2. Harvard University Press, Cambridge. B. traps (Figure 2B). Within the arboretum, three ~3 ha restorations of various ages were selected and each received four traps (Figure 2A). Due to restorations of the arboretum Ritchie, M. E., and D. Tilman. 1995. Responses of Legumes to Herbivores and Nutrients During Succession on a logistical limitations, the trapping periods for each location were not exactly the same. Traps at McKnight were put in place September 5th and Nitrogen-Poor Soil. Ecology 76:2648-2655. th th th (Red bars on right) (N=12). Whiles, M. R., and R. E. Charlton. 2006. The ecological significance of tallgrass