A Preliminary Assessment of the Ground-Dwelling Arthropod Community Composition in Six Common Dune Cover Types at Cape Cod National Seashore

2013 NORTHEASTERNNortheastern Naturalist NATURALIST 20(3):529–539Vol. 20, No. 3 B.C. Timm and K. McGarigal A Preliminary Assessment of the Ground-Dwelling Arthropod Community Composition in Six Common Dune Cover Types at Cape Cod National Seashore Brad C. Timm1,* and Kevin McGarigal1 Abstract - We provide a preliminary assessment of the ground-dwelling arthropod community composition in six common coastal dune ecosystem land cover-types at Cape Cod National Seashore. We captured 6815 individual arthropods representing 16 arthropod orders from 1008 terrestrial pitfall trap-nights. The most abundant orders were Hyme- noptera, Diptera, Araneae, and Isopoda (76.1%, 8.5%, 5.5%, and 3.3% of total captures, respectively). There were differences in ground-dwelling arthropod community composition among the three early-successional and the three later-successional cover types, with the latter having a greater overall arthropod diversity and higher capture rates for a number of the major arthropod taxa captured. Our report is among the first community- wide analyses of arthropod community composition in coastal dune ecosystems of the northeastern US. The results from this study should be viewed as a preliminary assessment given that: 1) we employed a single trapping method (i.e., pitfall traps); 2) traps were only open during the late-afternoon to early morning hours, and only during the summer months; and 3) captured arthropods were classified only to order. We hope our report will inspire additional research of coastal dune arthropod communities. Introduction In many terrestrial ecosystems, arthropods comprise the greatest faunal species diversity, biomass, and number of individuals (Gaston 1991, Ponder and Lunney 1999, Wilson 1985). Arthropods are critical to nutrient cycling and play vital roles as decomposers, pollinators, predators, and prey in natural ecosystems (Greenslade 1992, Wilson 1987). Although the importance and relative abundance of arthropods in many ecosystem types has been well established and accepted by ecologists, surprisingly few studies assessing arthropod community composition and habitat associations in coastal dune systems of North America have been conducted (for exceptions see Fork 2010, Heckscher and Bartlett 2004, Mattoni et al. 2000). Given arthropods’ importance to biodiversity, understanding arthropod community structure and habitat associations are essential to identify and prioritize areas for conservation actions, and to understand and project impacts of human- induced modifications to the natural environment (Kremen et al. 1993, Longcore 2003, Nakamura et al. 2007). In addition, because arthropods are a food source for many species (Hardy and Crnkovic 2006, Razeng and Watson 2012, Tahir et al. 2009, van Windergen et al. 1981, Vonshak et al. 2009), an improved understanding of arthropod abundance and habitat associations can provide insight 1Department of Environmental Conservation, University of Massachusetts-Amherst, Holdsworth Natural Resources Center, Amherst, MA 01003. *Corresponding author - [email protected]. 529 2013 Northeastern Naturalist Vol. 20, No. 3 B.C. Timm and K. McGarigal into habitat use and population dynamics of sympatric species. Finally, it has been suggested that terrestrial arthropod taxa may be very useful in ecosystem monitoring because they are diverse and abundant, they have rapid population growth rates and short generation times, and they are sensitive to minor changes in microclimate and microhabitat conditions (Andersen and Majer 2004, Mattoni et al. 2000, Schowalter 2006). Coastal dune faunal assemblages are typically dominated by arthropods (Gay- lard et al. 1995, sensu McLachlan 1991), many of which have evolved behavioral adaptations (Boomsma and Isaaks 1982, den Hollander and van Heerdt 1981) and exhibit habitat specificities (Maes and Bonte 2006, Schirmel and Buchholz 2011) that enable them to survive in ecosystems that are characterized by wide microcli- matic variability, high wind, and heavy salt loads. There has been some study of arthropod taxa in coastal dunes, (e.g., Araneae, Coleoptera, and Formicidae), but compared to other biota, arthropods have been understudied in these ecosystems. We report on a preliminary assessment of the community composition of ground-dwelling arthropods in a coastal dune ecosystem at Cape Cod National Seashore. Our study took place during the late afternoon to early morning from 20 June–21 September 2007. We assessed differences among six common land-cover types present in these dunes with respect to: 1) capture rates of the dominant (i.e., most abundantly captured) ground-dwelling arthropod orders throughout the study duration, and 2) the overall arthropod community composition (to the taxonomic level of order). Our goal is to enhance existing, yet limited knowledge of arthropod communities that are present in coastal dune ecosystems. The study was originally designed to assess ground-dwelling arthropod prey availability for two amphibian species (i.e., Anaxyrus fowleri Hinckley [Fowler’s Toad] and Scaphiopus holbrookii Harlan [Eastern Spadefoot]) present in the study landscape (Timm and McGarigal 2010). Methods Study area The study was conducted in the Province Lands, a vast dune ecosystem encom- passing approximately 1800 ha at the northern tip of Cape Cod, MA (≈42.05°N, 70.18°W1; Fig. 1). The topography is irregular with elevations ranging from ≈0–33 m above sea level, with a substrate comprised primarily of coarse-grained sand. Upland cover types throughout the study area vary spatially and include: non-vegetated (open sand) communities, Ammophila spp. (beachgrass) and Deschampsia flexuosa Trin (Wavy Hairgrass) grasslands, Hudsonia tomentosa Nutt (Woolly Beachheather)- and Arctostaphylos uva-ursi Spreng (Bearberry)- dominated heathlands, Cladonia spp. (reindeer lichen) patches, and deciduous and coniferous (predominantly Pinus rigida Mill [Pitch Pine]) shrublands and woodlands. The climate is mild with mean high temperatures ranging from 2.7 ºC in February to 25 ºC in August (NADP 2005). Mean annual precipitation is 110 cm with relatively little monthly variation (NADP 2005). 530 2013 Northeastern Naturalist Vol. 20, No. 3 B.C. Timm and K. McGarigal Field methods Arthropods were captured using terrestrial pitfall traps in six common cover types (hereafter habitats or habitat types) found throughout the study area—1) creeping Pitch Pine edge: the interface between ground-creeping Pitch Pine branches and open sand; 2) Pitch Pine interior: the interior portion of an individual Pitch Pine shrub with a relatively open understory and complete canopy coverage; 3) deciduous shrubland: a patch of individual to several sparse deciduous shrubs, primarily Quercus ilicifolia Wangenh (Bear Oak) and Prunus maritima Marshall (Beach Plum); 4) Woolly Beachheather; 5) open sand; and (6) reindeer lichen. Pitfall traps each consisted of a single 300-ml-capacity plastic cup (top di- ameter = 7.25 cm, height = 10 cm) buried so that the top was flush with the ground surface and filled to a depth of 2 cm with a dishwashing soap and water solution to prevent escape by captured invertebrates. Traps were placed in each of the six habitats and kept closed for a minimum of 48 h prior to trapping to minimize the capture of any organisms due to the initial disturbance of the substrate. During a single night each week from mid-June to late-September 2007 (14 weeks total), we opened four groups of three pitfall traps in each of the six habitat types for a total of 1008 trap nights (14 nights x 72 pitfall traps per sampling night). During each night of trapping, the three pitfall traps in each group were situated ≈1.0 m apart from one another within the same habitat type, and each group was located 50–500 m away from any other group in the same habitat type during a given trapping night. A new trapping site was selected for each weekly sample, with a total of 14 sample sites during the study period (Fig. 1). Traps were open from the late afternoon through early morning to coincide with foraging activity patterns of Fowler’s Toads and Eastern Spadefoots. During each weekly sampling event, traps were open for ≈18 h (from ≈1530–930), after which all traps were collected and brought back to the laboratory for examina- tion. Trap captures were sorted to order (with the exception of the Hymenoptera which were separated to family [Formicidae]). We pooled captures across all trap groups within each habitat type at each sample site for analysis (84 samples). Figure 1. Study area at Cape Cod National Seashore with the 14 weekly sampling loca- tions denoted by black dots in the subset map. 531 2013 Northeastern Naturalist Vol. 20, No. 3 B.C. Timm and K. McGarigal Analysis We conducted a Kruskal-Wallis one-way ANOVA to test for among-habitat differences in captures across all six habitat types for each taxon with ≥50 captures. We then conducted a posteriori pairwise comparisons (Siegel and Castellan 1988) to test for pairwise differences in capture rates of individual taxa between habitat types. We conducted a non-metric multidimensional scaling (NMDS) analysis to detect groupings of sample sites using captures across all arthropod taxa and a Bray-Curtis dissimilarity matrix. Prior to running the NMDS analysis, we removed all taxa that we deemed to be insufficiently sampled, which we defined as being present in less than five of the 84 samples; insufficiently sampled taxa included Chilopoda, Dermaptera, Gastropoda, Homoptera, Opiliones, and Pseudoscorpiones. We conducted all analyses in the R computing environment (R Development Core Team 2012) and defined statistical significance as P ≤ 0.05. Results We captured a total of 6815 individual arthropods across 16 orders and one family (Formicidae) (Table 1). Formicidae (ants) accounted for 76.1% of the captures, followed in abundance by Diptera (8.5%), Araneae (5.5%), and Isop- oda (3.3%;) (Table 1). Capture rates differed among habitat types for six of the seven taxa that had ≥50 captures (Table 2), which, when combined, accounted for ≈97.5% of all captures. There were a number of differences in the pairwise Table 1.

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