2013 SOUTHEASTERN NATURALIST 12(2):379–386 Relationships Between Carabid Beetle Communities and Forest Stand Parameters: Taxon Congruence or Habitat Association? Wade B. Worthen1,* and David C.G. Merriman1 Abstract - We sampled ground beetles (Coleoptera: Family Carabidae) at the Furman Forest in northeast Greenville County, SC, and compared species richness and community attributes with tree stand richness, diversity, and composition. Beetles were collected by pitfall trap 1 night/week for 9 weeks from June to August 2011 in 24 plots (200 m2) varying in tree abundance (11–131 trees/plot), mean tree size (6.5–26.0 cm DBH), species richness (2–13 species/plot), Simpson’s diversity (1.6–9.1/plot), and composition. We collected 286 carabids representing 13 genera and 26 species, including a new state record for South Carolina, Cyclotrachelus hypherpiformis. Carabid abundance, species richness, and diversity were unrelated to tree abundance, richness, or diversity. However, carabid abundance and richness were positively correlated with the abundance of Liriodendron tulipifera (Tulip Poplar), suggesting a preference for mesic habitats. Total carabid abundance and the abundance and dominance of Carabus goryi (the most abundant species) were also positively correlated with mean tree size (DBH), suggesting a preference for older stands. Carabid diversity, abundance, and community structure were associated with habitat type and stand age (as indicated by dominant canopy species and tree size) and not canopy tree species richness or diversity. Introduction Species diversity patterns in different taxa are often positively correlated. Such “cross-taxon congruence” is particularly useful for environmental monitoring and biodiversity studies, as diversity in one “indicator taxon” may correlate with environmental pollution, environmental or disturbance gradients, and/or total biodiversity (Hellawell 1986; Kremen 1992, 1994; Kremen et al. 1993; Noss 1990; Oliver and Beattie 1996). Taxon congruence can occur because of direct interactions among organisms. Through “bottom-up” relationships, increased plant or herbivore diversity can spur diversity in consumers and mutualists (Hunter and Price 1992, Murdoch et al. 1972, Schaffers et al. 2008, Siemann et al. 1998, Southwood et al. 1979). Likewise, through “top-down” forces, increased predator diversity may reduce competition at lower trophic levels and increase the diversity of resource taxa (Carpenter et al. 1985, Estes et al. 2011, Letnic et al. 2012, Paine 1966, Siemann et al. 1998). Congruence can also occur because diversity in different taxa respond in independent but parallel ways to the spatial distribution and size of habitat patches (sensu MacArthur and Wilson 1967), to the same environmental factors (such as temperature, light, water availability, or a pollutant), or to temporal, “successional” changes in the environment. 1Department of Biology, Furman University, Greenville, SC 29613. *Corresponding author - wade.worthen@furman.edu. 380 Southeastern Naturalist Vol. 12, No. 2 Ground beetles (Order: Coleoptera, Family: Carabidae) and canopy trees are likely candidates for congruent groups—they are both diverse and important components of forest ecosystems. In addition, because most of the >40,000 carabid species are generalist predators (Lövei and Sunderland 1996), their abundance and diversity might be driven by “bottom-up” forces—by the diversity and abundance of their invertebrate prey and the diversity of plants their prey consume. In addition, carabid abundance and diversity increases with leaf-litter depth (Koivula et al. 1999), soil moisture (Luff et al. 1989), and the presence of dead wood (Nitterus et al. 2007), which all may correlate with stand age and canopy tree diversity. Results testing for congruence between carabids and plants, however, have been mixed. Carabid diversity correlates with plant diversity across a grassland– plantation–forest continuum (Fahy and Gormally 1998), but not in grassland (Vessby et al. 2002) and alpine habitats (Finch and Löffler 2010). In a recent review, Koivula (2011) concluded that carabids were poor indicators of general biodiversity. Rather, because carabids may respond more directly to the structural diversity of plant communities (Brose 2003, Janssen et al. 2009, Sobek et al. 2009, Taboada et al. 2010), they may be better indicators of habitat type and environmental conditions. The purpose of this investigation was to test Koivula’s (2011) conclusions. We compared carabid diversity and community structure with tree stand diversity and composition across a range of natural forest types in the southern Appalachians to determine whether carabid communities respond to canopy tree diversity or habitat type and forest composition. Study Site This experiment was conducted at Furman Forest, a 600-ha tract on the eastern slope of Hogback Mountain in the northeast corner of Greenville County, SC, on the first ridge of the Blue Ridge Mountains (383811.84m E, 3894591.25m N). The forest consists of three adjoining 200-ha parcels owned by The Nature Conservancy (“Blue Wall Preserve”), The Spartanburg Water System, and the town of Tryon, NC, and includes two watersheds protected from the ridgeline. There are a variety of community types on site including the following: ravines with hemlock (Tsuga canadensis (L.) Carrière [Eastern Hemlock] and T. caroliniana Engelm. [Carolina Hemlock]); mature stands of Quercus montana Willd. (Chestnut Oak) and Carya spp. (hickory); mesic hardwood stands of Liriodendron tulipifera L. (Tulip Poplar) and Acer rubrum L. (Red Maple); dry ridge communities dominated by Quercus alba L. (White Oak), Q. rubra L. (Northern Red Oak), Q. falcata Michx. (Southern Red Oak), Q. coccinea Münchh. (Scarlet Oak), Q. velutina Lam. (Black Oak), and Pinus virginiana Mill. (Virginia Pine); and successional stands dominated by Virginia Pine and Liquidambar styraciflua L. (Sweetgum). Methods In 2008, a grid of sampling points was established across the site, with 100 m between points. Since then, trees have been sampled using circular plots with a 2013 W.B. Worthen and D.C.G. Merriman 381 radius of 8 m (area = 200 m2) centered on each point. The species and size (DBH) of each tree (>2.0 cm DBH) within each plot were recorded, and species richness and Simpson’s reciprocal index of diversity measurements (D = 1 / Σ[pi 2]) were calculated. For this study, we purposefully selected 24 points that maximized the range in tree species richness (2 to 13 species per point) and Simpson’s diversity (1.2 to 9.1). These points also ranged across several habitat types, from successional pine stands to mesic hardwoods to drier oak/pine ridge communities. A pitfall trap station was placed at each sampling point, consisting of two 0.95-L cans buried 1 m apart, and linked by a 0.15- x 1-m aluminum drift fence. Small holes (≈0.3 cm) were punched in the bottom of each can to prevent rainwater accumulation. No preservative was used, and the traps were checked after 24 hours to eliminate the effects of baiting that preservatives and the accumulation of dead beetles may cause. Although pitfall traps bias samples towards larger, more active species, they are a common and reliable method for comparing assemblages of carabids (Spence and Niemelä 1994). For nine weeks between 9 June–5 August 2011, each trap station (n = 24) was left open for one day per week, with eight different stations opened on each of three consecutive mornings each week. Cans were covered when not in use. Ground beetles were collected from open traps each morning after a 24-hr trapping period, euthanized with ethyl acetate, and identified using Arnett and Thomas (2001), Bousquet (2010), Ciegler (2000), and Freitag (1969). The abundance of each species, total carabid abundance, species richness, and Simpson’s diversity were computed for each point (pooling the data for both cans across all sampling dates). Spearman rank correlation analyses were used to describe the relationships between carabid communities and tree communities. Partial correlations were used to describe these relationships while controlling for variation in tree size. Results and Discussion A total of 286 ground beetles were collected from the pitfall traps, representing 13 genera and 26 species (Table 1), including a new state record for South Carolina, Cyclotrachelus hypherpiformis (Freitag). The communities were dominated by Carabus goryi Dejean, which accounted for more than 34% of all individuals. The four species of Carabus (39.3%) and the five species of Dicaelus (22.1%) accounted for over 60% of the individuals captured (Table 1). On initial inspection, there appear to be several significant relationships between canopy tree species richness and carabid communities. Curiously, tree species richness was negatively correlated with carabid species richness, carabid abundance, and the abundance of Carabus goryi (Table 2). There were also relationships with tree size; mean tree DBH was positively correlated with total carabid abundance and the abundance and dominance (% of total carabids) of Carabus goryi (Table 2). Because tree abundance and tree species richness were negatively correlated with mean tree DBH (plots with larger trees containing fewer individuals and species; Table 2), we hypothesized that the significant correlations between beetle parameters and tree abundance/richness might be 382 Southeastern Naturalist Vol. 12, No. 2 Table 1. The species of carabid beetles captured at Furman Forest, Greenville County, SC; number of individuals captured and % representation of each species and genus. Species n % by species % by genus Carabus goryi Dejean 97 34.04% 39.30% Carabus serratus Say 2 0.70% Carabus sylvosus Say 3 1.05% Carabus vinctus Weber 10 3.51% Chlaenius tomentosus (Say) 4 1.40% 1.40% Cicindela unipunctata Fabricius 32 11.23% 11.23% Cyclotrachelus hypherpiformis (Freitag) 3 1.05% 12.98% Cyclotrachelus sigillatus (Say) 34 11.93% Dicaelus dilatatus dilatatus Say 23 8.07% 22.10% Dicaelus elongatus Bonelli 1 0.35% Dicaelus politus Dejean 20 7.02% Dicaelus purpuratus Bonelli 4 1.40% Dicaelus teter Bonelli 15 5.26% Galerita bicolor Drury 2 0.70% 0.70% Harpalus pensylvanicus (DeGeer) 1 0.35% 1.05% Harpalus protractus Casey 2 0.70% Helluomorphoides nigripennis (Dejean) 2 0.70% 0.70% Pasimachus depressus (Fabricius) 1 0.35% 3.16% Pasimachus punctulatus Haldeman 8 2.81% Platynus decentis (Say) 2 0.70% 0.70% Poecilis lucublandus (Say) 2 0.70% 0.70% Pterostichus acutipes acutipes Barr 2 0.70% 3.50% Pterostichus adoxus (Say) 2 0.70% Pterostichus moestus (Say) 1 0.35% Pterostichus stygicus (Say) 5 1.75% Sphaeroderus stenostomus (Weber) 8 2.81% 2.81% Table 2. Spearman rank correlations between carabid community descriptors and forest stand parameters at Furman Forest, Greenville County, SC (DBH = diameter at breast height; ns = P > 0.05, * = P < 0.05, ** = P < 0.01, *** = P < 0.001; bold formatting = relationships that remain significant in partial correlations controlling for DBH (see text for values). One site had no beetles, so diversity and dominance sample sizes are reduced by 1. Tulip White Virginia Tree Tree Tree Tree Poplar Oak Pine DBH abundance richness diversity abundance abundance abundance Tree DBH -0.656*** -0.404* -0.150 ns 0.294 ns -0.406* -0.599** Carabid abundance 0.495* -0.351 ns -0.456* -0.320 ns 0.653*** -0.600** -0.513* (n = 24) Carabid richness 0.307 ns -0.339 ns -0.413* -0.248 ns 0.407* -0.480* -0.491* (n = 24) Carabid diversity 0.051 ns -0.121 ns -0.188 ns -0.110 ns 0.026 ns -0.048 ns -0.214 ns (n = 23) C. goryi abundance 0.711*** -0.658*** -0.465* -0.189 ns 0.514** -0.426* -0.569** (n = 24) C. goryi dominance 0.709*** -0.662*** -0.451* -0.158 ns 0.436* -0.287 ns -0.538** (n = 23) 2013 W.B. Worthen and D.C.G. Merriman 383 spurious. Indeed, when partial correlations were conducted that controlled for mean tree DBH, there were no statistically significant relationships between carabid community descriptors and tree abundance, richness, or diversity (P > 0.05). As such, after accounting for variation in tree size, there was no evidence for “cross-taxon congruence” between carabids and canopy trees. With respect to habitat type, total carabid abundance, carabid richness, and C. goryi abundance and dominance were positively correlated with the abundance of Tulip Poplar and negatively correlated with the abundance of White Oak and/or Virginia Pine (Table 2). In partial correlations holding mean tree DBH constant, the positive correlations between Tulip Poplar abundance and carabid abundance (r = 0.632, df = 21, P < 0.001), C. goryi abundance (r = 0.614, df = 21, P < 0.01), and C. goryi dominance (r = 0.499, df = 20, P < 0.05) remained significant, probably indicating a preference for mesic habitats over drier ridges. These results are consistent with previous research indicating that forest carabids prefer mesic deciduous stands (Fahy and Gormally 1998; Fuller et al. 2008; Magura et al. 2000, 2003; Taboada et al. 2010); perhaps because of their preference for higher soil moisture (Antvogel and Bonn 2001, Luff et al. 1989), more dead wood (Barton et al. 2009, Fuller et al. 2008, Nitterus et al. 2007) and deeper leaf litter (Antvogel and Bonn 2001; Fuller 2008; Koivula et al. 1999; Magura et al. 2000, 2005). Because these factors also correlate with stand age and successional stage, it is not surprising that forest carabid abundance and diversity also correlates with mean tree size (Tabaoda et al. 2010), as we found in our study. In addition, the compositional changes we found in C. goryi abundance and dominance with stand age (as indicated by mean tree DBH) confirmed the results of Jelaska et al. (2011), who found that the abundance and dominance of large Carabus species increased through successional time. Our results also contradict some studies, typically those where a broader range of habitats were examined. For example, carabid diversity declines with successional stage and tree size when grasslands or young successional stands are included (Butterfield 1997, Butterfield et al. 1995, da Silva et al. 2008, Magura et al. 2001, Niemelä et al. 1996, Silverman et al. 2008). This finding is probably the result of changes in community composition and a greater diversity of generalists that prefer open habitats relative to the number of specialized forest species (Butterfield et al. 1995, da Silva et al. 2008, Fuller 2008, McGeoch 1998, Silverman et al. 2008). There are also some discordant patterns regarding habitat preferences of the dominant species, C. goryi. In our study, C. goryi abundance was strongly correlated with mean tree DBH and the abundance of Tulip Poplar, suggesting a preference for older mesic stands. Silverman et al. (2008) also found that C. goryi was the most abundant species in forest sites in Ohio, but abundance was greater in ecotonal sites than in forest interior. In Michigan studies, Petrillo and Witter (2009) found that C. goryi was more abundant in more mesic Sugar Maple-American Beech sites than in drier Northern Red Oak-American Beech sites, but Liebherr and Mahar (1979) found that C. goryi was more abundant in drier White Oak sites than more mesic sites. These discrepancies might be a 384 Southeastern Naturalist Vol. 12, No. 2 function of C. goryi responding to other factors besides moisture and temperature levels—like leaf-litter depth, dead wood, and stand age—that might vary in different ways between the sites compared in each study. In conclusion, carabid beetle abundance and community structure, and the abundance and dominance of C. goryi, were related to the abundance of canopy dominants and stand age, probably as a consequence of preferring moist, mesic habitats with deep leaf litter and lots of dead wood. There was no evidence for taxon congruence between carabids and canopy trees, once differences in tree size were taken into account. This was a very small study, however, focusing on large beetles sampled over a short period. It is certainly possible that a larger, more extensive survey of all carabids might resolve a pattern of taxon congruence between these groups. Acknowledgments We thank The Nature Conservancy, Tryon Water District, and Spartanburg Water Commission for the use of Furman Forest. We thank Janet Ceigler for confirming and correcting our beetle identifications. We also thank Megan Aprill, Tara Smith, and Amelia Schulz for their assistance in the field. 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