Effects of invasive Amur honeysuckle (Lonicera maackii) and white-tailed deer (Odocoileus virginianus) on litter-dwelling arthropod communities.
|Abstract:||Litter-dwelling arthropods play crucial roles in litter decomposition and nutrient cycling, and changes in their diversity or abundance can affect these processes. Previous studies have outlined individual effects of invasive plants and overabundant ungulates on litter-dwelling arthropod communities but have paid little attention to whether invasive plants and ungulates interact to affect these arthropod communifies. We examined how invasive Amur honeysuckle (Lonicera maackii) and grazing by white-tailed deer (Odocoileus virginianus) affected diversity, abundance, and taxonomic composition of litter-dwelling arthropod communities in a deciduous forest in southwestern Ohio. We also examined whether deer or honeysuckle affected substrate composition and depth of litter. We found no significant effect of honeysuckle, deer, or their interaction on arthropod diversity, bur exclusion of deer increased total arthropod abundance and abundance of Araneae, and thereby affected taxonomic composition of the litter community. These effects were likely related to greater plant cover and less soil compaction in areas from which deer were excluded. Honeysuckle negatively affected Araneae abundance and positively affected Acari abundance, possibly revealing an indirect effect of Araneae on Acari. A honeysuckle x deer interaction on abundance of Acari was important only during the first year of our study. There were no differences in arthropod abundance between honeysuckle-absent and honeysuckle-removed plots, indicating rapid restoration of the litter community after honeysuckle removal. Neither honeysuckle nor deer affected composition or depth of litter. Our findings suggest that current management techniques that control the effects of honeysuckle and deer on native plant communities by separate measures may be sufficient to reduce impacts on litter-dwelling arthropods.|
Honeysuckle (Environmental aspects)
Arthropoda (Environmental aspects)
Invasive species (Environmental aspects)
Christopher, Cory C.
Cameron, Guy N.
|Publication:||Name: The American Midland Naturalist Publisher: University of Notre Dame, Department of Biological Sciences Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Earth sciences Copyright: COPYRIGHT 2012 University of Notre Dame, Department of Biological Sciences ISSN: 0003-0031|
|Issue:||Date: April, 2012 Source Volume: 167 Source Issue: 2|
|Geographic:||Geographic Scope: United States Geographic Code: 1USA United States|
Above-ground and below-ground food webs often have been studied separately, although connections between these food webs are being revealed (Wardle, 2002; Coleman et al., 2004; Bardgett and Wardle, 2010). One such connection is the linkage that litter-dwelling arthropods form between above-ground and below-ground food webs (Schmitz, 2010). Specifically, above-ground carnivores feed on litter-dwelling arthropods and, by feeding on plants, above-ground herbivores affect amount of litter available for litter-dwelling arthropods (Bardgett and Wardle, 2010; Schmitz, 2010). Together these linkages alter the amount of litter available to and broken down by litter-dwelling arthropods (e.g., litter-transformers, sensu Wardle, 2002). Diversity and abundance of litter-dwelling arthropods are affected directly by quality, microclimate, structure, and depth of leaf litter (Uetz, 1979; Bultman and Uetz, 1984; Badejo et al., 1998; Antvogel and Bonn, 2001), and by diversity, structure, and height of plants (Murdoch et al., 1972; Strong et al., 1984; Gibson, 1992; Samways et al., 1996; Kruess and Tscharntke, 2002). Changes to the structure of litter-dwelling arthropod communities alters the chemistry and mass loss of leaf litter during decomposition, which affects availability of soil nutrients, rates of nutrient cycling, and, ultimately, primary production (Seastedt and Crossley, 1984; Kim, 1993; Kremen et al., 1993; Lavelle, 1996; Bradford et al., 2002; Hunter et al., 2003). Thus, although land managers do not typically consider litter-dwelling arthropods in management plans, it is worthwhile to determine if current methods used to manage native communities (e.g., removal of invasive plants or exclusion of deer) have consequences for litter-dwelling arthropod communities because of their importance in ecosystem functions.
By changing structure and species composition of native plant communities, invasive exotic plants also may alter structure of communities of litter-dwelling arthropods and, hence, rates of decomposition of litter (Cuddington and Hastings, 2004; Ashton et al., 2005; Wolfe and Klironomos, 2005; Baiser et al., 2008). For example, invasion by Arundo donax (giant reed) along streams in San Francisco altered moisture of leaf litter, increased proportion of bare ground, and reduced availability of food resources for litter-dwelling arthropods (Herrera and Dudley, 2003). Similarly, invasive Tradescantia fluminensis (small-leaf spiderwort) altered community composition of litter-dwelling arthropods in New Zealand forests by increasing litter moisture and providing greater physical structure than native herbs (Standish, 2004).
Such impacts ofinvasive plants on litter-dwelling arthropods may be compounded by grazing by overabundant ungulates (Baiser et al., 2008). Foraging by moose (Alces alces) reduced cover of whortleberry (Vaccinium myrtillus), which lowered soil moisture and altered composition of carabid beetle communities (Melis et al., 2007). Similarly, overgrazing by red deer (Cervus elaphus; Baines et al., 1994), Sitka black-tailed deer (Odocoileus hemionus sitkensis; Allombert et al., 2005), and moose (Suominen et al., 1999a) reduced abundance of arthropods. Alternatively, moose positively affected abundance of litter arthropods (Suominen et al., 1999a; Suominen et al., 1999b) and caribou (Rangifer tarandus; Suominen et al., 2003).
Despite such evidence that invasive plants and overabundant ungulates may independently affect abundance and structure of litter-dwelling arthropod communities, little attention has been paid to whether these organisms may have interactive effects upon litter-dwelling organisms. Presence of interactive effects between invasive plants and overabundant ungulates would have important consequences for habitat managers because separate control measures on invasive plants and overabundant ungulates could have unintended consequences on litter-dwelling arthropods. Accordingly, we devised a field experiment to examine the independent and interactive effects of white-trailed deer (Odocoileus virginianus; hereafter, deer) and Amur honeysuckle (Loniceva maackii; hereafter, honeysuckle) on diversity, abundance, and taxonomic structure of litter-dwelling arthropods. Amur honeysuckle is an Asian shrub that has invaded more than 24 states in the eastern U.S. (Gorchov and Trisel, 2003). Once established, this invasive shrub reduces richness, abundance, growth, and reproduction of native herbaceous and woody vegetation (Gould and Gorchov, 2000; Collier et al., 2002; Gorchov and Trisel, 2003; Miller and Gorchov, 2004; Hartman and McCarthy, 2008). In addition, the dense canopy of honeysuckle may prevent fallen leaves from deciduous trees reaching the forest floor. Such effects on both understory vegetation and amount of leaf litter that reaches the ground could indirectly affect litter-dwelling arthropods by altering the structure of the leaf-litter on the forest floor (Hutchinson and Vankat, 1997; Buddle et al., 2004).
In addition to impacts from invasive honeysuckle, litter-dwelling arthropod communities may also be affected by grazing from overabundant white-tailed deer. White-tailed deer are the dominant large herbivore in the eastern U.S. Populations of deer in Ohio have increased from about 25,000 (0.24/[km.sup.2]) in 1970 to about 650,000 (6.3/[km.sup.2]) in 2009 [Nixon et al., 1970; Ohio Department of Natural Resources (www.dnr.state.oh.us)]. In southwestern Ohio, deer populations in some metro parks have reached 110/[km.sup.2] (Peek and Stahl, 1997). Browsing by overabundant deer decreases growth, reproduction, density, and diversity of native plants (Horsley et al., 2003; Rooney and Waller, 2003; Cote et al., 2004; McGraw and Fuerdi, 2005). Additionally, over-browsing by deer promotes the establishment of invasive species (Vellend, 2002; Myers et al., 2004; Baiser et al., 2008; Knight et al., 2009). By impacting composition and structure of native plant communities, deer also could affect the abundance and composition of litter-dwelling arthropod communities (Murdoch et al., 1972; Strong et al., 1984).
Several lines of evidence lead to our prediction that deer and honeysuckle have interactive effects on density, abundance, and community structure of litter-dwelling arthropods. First, white-tailed deer occur at higher densities in areas with than without Amur honeysuckle (Allan et al., 2010). Second, over-abundant deer facilitated success of invasive plant species in deciduous forests (Knight et al., 2009). Finally, the physical structure of Amur honeysuckle may protect tree seedlings from browsing by deer (Gorchov and Trisel, 2003; Cipollini et al., 2009). Our experimental design allowed us to explicitly test whether the presence of honeysuckle reduced effects of deer on litter-dwelling arthropods and also allowed us to measure individual impacts of honeysuckle and deer on these arthropod communities. We also examined whether honeysuckle or deer affected depth of leaf litter or composition of the litter layer and, hence, indirectly affected litter-dwelling arthropods by altering the habitat on the forest-floor (Bultman and Uetz, 1984; Antvogel and Bonn, 2001).
We conducted our experiment at the Cincinnati Nature Center, a 405-ha preserve in Mifford, Ohio. Our study site was located on a west-facing slope dominated by beech (Fagus grandifolia), Chinquapin oak (Quercus muehlenbergii), red oak (Q. rubra), shagbark hickory (Carya ovata), bitternut hickory (C. cordiformis), red maple (Acer rubrum), and sugar maple (A. saccharum). The understory of the northern portion of the study site was dominated by a dense stand of Amur honeysuckle, but the southern portion was uninvaded by honeysuckle. We occasionally found and removed honeysuckle seedlings in the uninvaded area, confirming that this area was suitable to honeysuckle invasion and represented an uninvaded control.
All experimental plots were located in the same contiguous forest and did not differ in aspect, slope (10%), or vegetation (other than presence of honeysuckle). In Apr. 2005, we positioned 12 (10 X 10 m) plots in the invaded northern portion of our study site in a 2 x 2 arrangement of Lonicera maackii present/removed and Odocoileus virginianus present/ excluded (n = 3 replicate plots of each treatment). Each invaded plot had approximately the same density of honeysuckle shrubs (8-10 shrubs/plot). Six additional plots were placed in a 1 X 2 arrangement in the uninvaded southern portion of the study site, approximately 75 m away with treatments of L. maackii absent and O. virginianus present/excluded (n = 3 replicates of each treatment). Deer were excluded with 2.4-m deer fencing (Benner's Gardens, Conshohocken, PA, www.bennersgardens.com) supported by 2.7-m steel fence posts. Deer were observed foraging in deer-present plots. Honeysuckle shrubs were removed by cutting them off at ground level and painting the stumps with 2% glyphosate two months prior to initiation of arthropod sampling. Glyphosate has no known effect on abundance or community composition of litter arthropods (Lindsay and French, 2004).
SAMPLING LEAF LITTER ARTHROPODS
Arthropods in leaf litter were sampled monthly from Jun. through Sep. 2005 and 2006, months during which we predicted that there would be the greatest arthropod biomass (Blair and Crossley, 1988; Perry et al., 1997), for a total of eight sampling periods. We sampled leaf litter from five arbitrarily chosen areas within each 10 x 10 m plot using a round 0.1 [m.sup.2] quadrat that was 15-cm tall. For each sample, we pushed the bottom edge of the quadrat into the ground to prevent escape of arthropods. To reduce amount of leaf litter removed from each plot during sampling, all litter collected from inside each quadrat was sifted through a large sieve (15-mm mesh), examined in the field for remaining arthropods, and replaced. All sieved litter was then transported to the lab and placed into Berlese-Tullgren funnels for separation. Specimens were preserved in 70% ethanol and were identified to order (Triplehorn and Johnson, 2005).
SUBSTRATE AND LEAF LITTER MEASUREMENTS
Total abundance of arthropods was higher in Jun. (2101.3 [+ or -] 79.3 [m.sup.2]) than in Jul. (1791.3 [+ or -] 70.4 [m.sup.2]), Aug. (1632.0 [+ or -] 75.2/[m.sup.2]), or Sep. (1283.3 [+ or -] 62.4.[m.sup.2]) 2005. Consequently, we concluded that sampling leaf litter during Jun. would provide the best assessment of whether leaf litter affected arthropod communities. We sampled substrate with a 1-m2 quadrat with string laced through a plastic frame to form a grid of 100 10 X 10-cm squares. This grid was placed at nine equally spaced locations arranged as a 3 X 3 grid in each plot in Jun. 2006 to measure the type and percent cover of substrate. We categorized substrate in each square as bare ground, leaves, woody debris, rock, vegetation, or mixed, and computed the percent of total cover occupied by each type of substrate within each grid. Mixed was ground sparsely covered with decomposing woody debris and leaf material but without a dominant or identifiable substrate. Including this category allowed us to be more conservative when designating a square as bare ground. We then arbitrarily selected four squares in each sample grid dominated by leaves to measure depth of litter from the ground to the upper-most leaf, for a total of 36 measurements (4 measurements in each of 9 substrate sample grids).
We also measured total annual leaf fall in each experimental plot because differences in leaf fall among experimental plots could have altered substrate composition and depth of leaf litter. We randomly placed four wire mesh baskets (50W x 50L x 20H cm) in each experimental plot beginning on 20 Sep. 2005 and 2006. We collected, dried, and weighed all leaves that fell into these baskets every other week until no overhead leaves were visible (after about 2 mo). Because leaf accumulation also could be affected by differences in wind penetrability into plots with different densities of honeysuckle (i.e., present, absent, and removed), we measured wind speed in autumn 2006 at breast height in ten random locations in each of these habitat types using a Kestrel 1000 hand-held wind meter (Nielsen Kellerman, Chester, PA). Wind speed did not differ between honeysuckle treatments (ANOVA, F2,27 = 1.09, P = 0.35).
To determine differences in arthropod diversity between treatment types, we calculated Shannon diversity indices for all orders of arthropods collected in each sample month (Jun., Jul., Aug., Sep.) in each plot for 2005 and 2006. Diversity values were normally distributed. We tested differences in diversity among treatments with a two-way repeated measures analysis of variance (ANOVA), with deer and honeysuckle treatments as interacting sources of variation (JMP IN, version 8.0, SAS Institute Inc., Cary, NC).
We computed total abundance of all arthropods for each sample month (Jun., Jul., Aug., Sep.) in each plot in 2005 and 2006. We were unable to normalize abundance of these data by transformations. Therefore, within each month sampled, we ranked each plot according to its abundance with lowest rank assigned to plots with lowest abundance and using average ranks in cases of ties. This technique approximates a non-parametric procedure (i.e., Kruskal-Wallis test) and provided tests of interactions (Conover and Iman, 1981). We then used a repeated measures two-way ANOVA to compare abundance of total arthropods among treatment types, with deer and honeysuckle treatments as interacting sources of variation. We also computed abundance of each arthropod order sampled (Appendix 1). Abundance for each of the five most abundant arthropod orders (Acari, Araneae, Collembola, Coleoptera, and Hymentoptera) was rank-ordered as above for total abundance. We analyzed abundance of each of these orders among treatments with separate repeated measures two-way ANOVA's. Tukey's HSD tests were used for all ANOVA post-hoc pair-wise comparisons (P < 0.05).
We used non-metric multidimensional scaling (NMDS) of untransformed counts of individuals in each arthropod order for 2005 and 2006 to determine differences in taxonomic composition of arthropods among treatment types (PC-ORD, version 4; MjM Software Design, Glenden Beach, OR, 1999; Clarke, 1993; McCune and Grace, 2002). For all NMDS tests, we used 40 runs with real data, 50 randomized runs, 100 maximum iterations, a stability criterion of 0.0005, and a dimensionality of two generated by an initial autopilot run that established the appropriate dimensionality (McCune and Grace, 2002). Sorensen's distance measurements were used for all NMDS analyses. We paired NMDS procedures with Multiple Response Permutation Procedures (MRPP), a nonparametric test of equitability between groups that provides an "A" value representing chance-corrected, within-group agreement (McCune and Grace, 2002).
We determined whether deer or honeysuckle altered composition of litter substrate by calculating the proportion of total substrate comprised by each substrate type and then normalized these data with an arcsine transformation (Zar, 1999) to meet assumptions of ANOVA. These data were compared for honeysuckle and deer treatments with a two-way ANOVA, allowing deer and honeysuckle factors to interact. Vegetation, rocks, and exposed root substrate types were omitted from these analyses because of insufficient occurrences (Table 3). Depth of leaf litter was compared among treatments with a nested ANOVA, with depth of litter nested within substrates. These data were compared with a two-way ANOVA, allowing deer and honeysuckle as sources of variation.
We compared differences in total annual leaf fall in each treatment and each year with a Kruskal-Wallis nonparametric analysis because transformations did not normalize these data. Since we had more than five groups in our experimental design, the statistic generated by this test was compared to the chi-square distribution, providing a conservative test of significance (Zar, 1999).
DIVERSITY AND ABUNDANCE
There were no significant effects of deer, honeysuckle, or the deer x honeysuckle interaction on diversity of arthropods (Fig. 1; Table 1). Total abundance of arthropods was significantly higher in deer-excluded plots (Table 1), but honeysuckle and the deer x honeysuckle interaction had no significant effect on total abundance (Fig. 2; Table 1). Acari were significantly more abundant in honeysuckle-present plots (Figs. 3a, b; Table 1). This effect included higher abundance on honeysuckle-removed plots likely because the short time since removal of honeysuckle was insufficient for abundance of Acari to decline to levels in honeysuckle-absent plots. Abundance of Acari was not significantly affected by deer (Figs. 3a, b; Table 1). Abundance of Acari was significantly affected by the deer X honeysuckle interaction because abundance was higher in deer-excluded plots when honeysuckle was removed, but was lower in deer-excluded plots when honeysuckle was present or absent (Figs. 3a, b; Table 1). Abundance of Araneae was significantly higher in deer-excluded plots and in honeysuckle-absent plots (Figs. 3c, d; Table 1), but the deer x honeysuckle interaction was not significant (Table 1). Deer, honeysuckle, or the deer x honeysuckle interaction did not significantly affect abundance of Coleoptera, Collembola, or Hymenoptera (Table 1).
[FIGURE 1 OMITTED]
Taxonomic composition of arthropod orders differed significantly between treatments (A = 0.18, P = 0.003; final stress = 17.35; Fig. 4). Two-dimension ordination separated honeysuckleabsent, deer excluded plots and honeysuckle-absent, deer-present plots from the other plots.
The deer x honeysuckle interaction on Acari (Figs. 3a, b; Table 1) was not evident in the 2-dimensional plot of community composition. This interaction would show a distinction in deer-excluded plots between honeysuckle-removed plots and the other honeysuckle treatments (absent, present). Comparison of these plots in Fig. 4 reveals that deer-excluded, honeysuckleabsent plots differed from the other honeysuckle treatment plots, which is likely a result of differences in abundance of total arthropods and Araneae and not abundance of Acari.
LEAF LITTER AND SUBSTRATE COMPOSITION
There was no effect of deer ([F.sub.1,9] = 0.002, P = 0.15), honeysuckle (F2,18 = 2.19, P = 0.15), or the deer x honeysuckle interaction ([F.sub.2,18] = 0.57, P = 0.10) on depth of leaf litter (Table 2). However, total annual leaf fall was greater in deer-present plots than in deer-excluded plots (2005: [chi square] = 3.27, df = 1, P = 0.07; 2006: [chi square] = 5.07, df= 1, P = 0.02). Honeysuckle did not significantly affect annual leaf fall (2005: [chi square] = 0.33, df = 2, P = 0.85; 2006: [chi square] = 3.56, df = 2, P = 0.17; Table 2). Percent cover of each substrate type was not affected significantly by deer (Bare ground, [F.sub.1,12] = 1.42, P = 0.26; Woody debris, [F.sub.1,12] = 2.01, P = 0.11; Leaves, [F.sub.1,12] = 1.11, P = 0.31; Mixed, [F.sub.1,12] = 0.11, P = 0.74) or honeysuckle (Bare ground, [F.sub.2,12] = 2.88, P = 0.10; Woody debris, [F.sub.2,12] = 0.43, P = 0.66; Leaves, [F.sub.2,12] = 0.34, P = 0.72; Mixed, [F.sub.2,12] = 1.29, P = 0.31) treatments (Table 3). There also was no significant deer x honeysuckle interaction on substrate cover (Bare ground, [F.sub.2,12] = 1.16, P = 0.35; Woody debris, [F.sub.2,12] = 0.13, P = 0.88; Leaves, [F.sub.2,12] = 0.87, P = 0.44; Mixed, [F.sub.2,12] = 2.36, P = 0.14; Table 3).
[FIGURE 2 OMITTED]
Presence of deer and honeysuckle significantly impacted community composition and abundance of litter dwelling arthropods but did not affect arthropod diversity. We also found a significant interaction of honeysuckle and deer on abundance of Acari. These findings are important for land managers faced with controlling the effects of these species in habitats where they co-occur.
[FIGURE 3 OMITTED]
Amur honeysuckle had contrasting effects on arthropod abundance. While total abundance of arthropods was not affected by honeysuckle, abundance of Acari was higher on plots with honeysuckle and abundance of Araneae was higher on plots without honeysuckle. Secretion of allelochemicals by honeysuckle leaves and roots (Cipollini et al., 2008; McEwan et al., 2009) may have lowered abundance of fungi and bacteria at the soil surface. This lower availability of sources of food could have affected abundance of prey in the litter layer and negatively affected Araneae. The positive effect of honeysuckle on Acari abundance could reflect an indirect effect of reduction of abundance of Araneae (Snyder and Wise, 2001; Rosenheim et al., 2004; Wise, 2004) or could be related to alterations in microclimate at the litter layer caused by the presence of a nearly continuous shrub layer.
[FIGURE 4 OMITTED]
The primary effect of deer on litter arthropods was to reduce their total abundance. In addition, abundance of Araneae also decreased on plots with deer present. Because percent substrate cover and depth of leaf litter did not vary among deer treatments, these differences in arthropod abundance did not result from changes in the structure or composition of the litter layer caused by grazing by deer. Alternatively, in a concurrent study in these same plots, we found that exclusion of deer reduced soil compaction and resulted in greater stem height and leaf number of Maianthemum racemosa (false Solomon's seal). This herb contributes the greatest amount of ground cover in these forests (Christopher and Cameron, in prep). Thus, lower total abundance of arthropods and lower abundance of Araneae in plots accessible to deer also could be related to lower plant cover (Baines et al., 1994; Rypstra and Carter, 1995; Dennis et al., 1997; Kruess and Tscharntke, 2002) or increased soil compaction (Watt et al., 2002). A mechanism for this reduction could have been lower availability of suitable microhabitats (e.g., soil crevices, reduced protective herb cover) for litter-dwelling organisms.
Taxonomic composition of litter-dwelling arthropods differed among experimental treatments, and these differences primarily were attributable to presence or absence of deer and absence of honeysuckle. As described above, total arthropod abundance and abundance of Araneae were higher in deer-excluded plots than in deer-present plots, and abundance of Araneae was higher in honeysuckle-absent plots than in the other honeysuckle treatments. These changes in abundance resulted in a change in taxonomic composition that distinguished honeysuckle-absent, deer excluded and honeysuckle-absent, deer present plots from the other plots (Fig. 4). The alteration in abundance of Araneae (e.g., lower abundance on deer-present plots and on honeysuckle-present plots) could have multi-trophic effects by modulating the impact of these macrofaunal predators on prey abundance (Moulder and Reichle, 1972; Rosenheim et al., 2004). Additionally, changes in abundance of Araneae affect the fungal decomposer system and thereby alter the rate of litter decomposition (Manley et al., 1976; Lawrence and Wise, 2000, 2004; Wise, 2004).
In spite of the short, 2 y duration of our study, we found no difference in arthropod diversity, total arthropod abundance, or abundance of the five most abundant orders between honeysuckle-removed and honeysuckle-absent plots. This result indicated that a short time since removal of honeysuckle shrubs was sufficient for the arthropod community to return to pre-honeysuckle conditions. An exception was higher abundance of Acari on honeysuckle-removed plots than on honeysuckle-absent or honeysuckle-present plots (Fig. 3a). However, this effect had diminished by the second year of our study (Fig. 3a), indicating that sufficient time had elapsed since our experiment began for abundance of Acari on honeysuckle-removed plots to return to levels seen on honeysuckle-absent plots. The rapid response by litter-dwelling organisms to removal of honeysuckle indicated that this control strategy by land managers can effectively return the community to pre-invasion levels. Since Araneae were more abundant on honeysuckle-absent plots, rapid return of these macrofaunal predators to pre-honeysuckle levels would be important not only to reestablish trophic links in the litter layer but also to modulate litter decomposition (Lawrence and Wise, 2004; Wise, 2004).
Although composition of the forest floor (e.g., depth and complexity of leaf litter) is an important variable influencing structure of litter arthropod communities (Uetz, 1979), we did not find an effect of deer or honeysuckle on these litter characteristics. However, annual leaf fall was lower in plots from which deer were excluded (Table 2). This result was most likely caused by fences that surrounded deer-exclusion plots. In these plots, leaves collected in litter traps would necessarily have come from directly above the plot, while in deer-present plots, litter traps could have caught leaves falling from directly above as well as those blowing into plots from trees that were not overhead. Considering that leaf fall was similar among honeysuckle treatments, it was not surprising that composition of litter substrate was unaffected by presence of honeysuckle. Additionally, wind speed in the shrub layer was also similar among treatments, and thus removal of honeysuckle shrubs did not increase scattering of leaves by wind. Although we observed leaves from overstory trees entangled in the canopy of honeysuckle shrubs, our results indicated that the canopy was not dense enough to prevent leaves from eventually reaching the ground.
The contribution of litter-dwelling arthropods to community processes such as litter decomposition and nutrient cycling are undeniably important (Kim, 1993; Kremen et al., 1993; Lawrence and Wise, 2002, 2004; Wall et al., 2007; Gessner et al., 2010). We demonstrated that total abundance of litter arthropods and abundance of Araneae were negatively impacted by overabundant ungulates and that abundance of Araneae and Acari were affected in different ways by presence of honeysuckle. We believe this is the first study to empirically show that grazing by deer may reduce abundance of litter-dwelling arthropods and that these effects are most likely not attributable to direct alterations in the leaf-litter layer. These effects upon litter-dwelling organisms altered the taxonomic composition of the litter-dwelling arthropod community and could add to the negative impacts of both deer and honeysuckle on native plant communities. In turn, the combination of these effects would have overall effects upon litter decomposition and nutrient cycling (Lawrence and Wise, 2000, 2004). The only deer x honeysuckle interaction that we detected was upon abundance of Acari, but the diminution of that interaction by the second year of our study indicated that it was likely not important. Our results have important implications for restoration of habitats impacted by honeysuckle and overabundant deer. Namely, management plans for these species need not explicitly consider how honeysuckle and deer interact to affect litter dwelling arthropod communities. In fact, our findings suggest that current management practices (e.g., culling deer herds, deer exclosures, removing honeysuckle) to reduce the negative effects of deer and honeysuckle on native plant communities also should increase abundance of total arthropods and abundance of Araneae. The lack of a negative effect of honeysuckle on litter organisms other than Araneae indicated that changes in microclimate associated with invasion by honeysuckle were unlikely to play a role. Additionally, the rapid return to pre-honeysuckle assemblages after removal of Amur honeysuckle also indicated that current control strategies would be viable in restoring assemblages of litter-dwelling organisms.
Acknowledgments.--We thank T. Culley, D. Gorehov, E. Maurer, and G. Uetz for providing assistance with our experimental design, implementation of our study, and interpretation of our results. We also thank D. Capella, A. Cooperman, E. Dame, G. Klein, J. Kleinhans, J. Lawrence, S. Puthoff, and D. Wright for field and laboratory assistance.
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SUBMITTED 7 MAY 2010
ACCEPTED 22 NOVEMBER 2011
CORY C. CHRISTOPHER (1) AND GUY N. CAMERON (2)
Department of Biological Sciences, University of Cincinnati, Cincinnati, Ohio 45221
(1) Present address: Education Department, Cincinnati Zoo and Botanical Garden, 3400 Vine Street, Cincinnati, Ohio 45220
(2) Corresponding author: e-mail: email@example.com; Telephone: (513) 556-9740; FAX: (513) 556-5299
APPENDIX 1. Abundance (number-[m.sup.2] [+ or -] 1 SE) of taxa collected in each treatment during 2005 and 2006. n = 60 [5 samples in each treatment, 3 replicates of each treatment. 4 mo of samples (Jun., Jul., Aug., Sep.)]. na = none captured. Taxonomy follows Triplehorn and Johnson, 2004 Treatment HS absent Year Class Order Deer excluded 2005 Arachnida Acari 111.3 [+ or -] 5.3 Araneae 108.0 [+ or -] 4.3 Chilopoda 7.3 [+ or -] 0.7 Diplopoda 14.7 [+ or -] 2.1 Opiliones 10.7 [+ or -] 1.8 Pseudoscorpiones 0.7 [+ or -] 0.2 Isopoda 22.0 [+ or -] 2.6 Hexapoda Blattodea na Coleoptera 40.7 [+ or -] 2.8 Collembola 267.3 [+ or -] 12.3 Diplura 2.0 [+ or -] 0.5 Diptera 22.7 [+ or -] 3.3 Hemiptera 14.7 [+ or -] 2.3 Hymenoptera 382.0 [+ or -] 37.7 Isoptera na Lepidoptera 2.7 [+ or -] 0.5 Neuroptera na Orthoptera 3.3 [+ or -] 0.8 Protura na Psocoptera 0.7 [+ or -] 0.2 Thysanoptera 4.7 [+ or -] 0.7 Trichoptera na 2006 Arachnida Acari 103.3 [+ or -] 7.0 Araneae 101.3 [+ or -] 4.7 Chilopoda 6.0 [+ or -] 1.0 Diplopoda 22.7 [+ or -] 2.6 Opiliones 6.0 [+ or -] 1.1 Pseudoscorpiones 3.3 [+ or -] 0.6 Isopoda 48.0 [+ or -] 6.7 Hexapoda Blattodea na Coleoptera 292.7 [+ or -] 19.9 Collembola 164.7 [+ or -] 7.2 Diplura na Diptera 26.7 [+ or -] 1.5 Hemiptera 17.3 [+ or -] 2.0 Hymenoptera 625.3 [+ or -] 65.0 Isoptera na Lepidoptera 2.7 [+ or -] 0.5 Neuroptera na Orthoptera 4.7 [+ or -] 0.9 Protura na Psocoptera 3.3 [+ or -] 0.6 Thysanoptera 10.7 [+ or -] 1.0 Tricoptera na Treatment HS absent Year Class Order Deer excluded 2005 Arachnida Acari Deer present Araneae Chilopoda 129.3 [+ or -] 8.5 Diplopoda 72.7 [+ or -] 2.7 Opiliones 6.0 [+ or -] 1.1 Pseudoscorpiones 32.0 [+ or -] 3.4 Isopoda 8.7 [+ or -] 1.2 2.0 [+ or -] 0.5 Hexapoda Blattodea 10.0 [+ or -] 1.7 Coleoptera Collembola 0.7 [+ or -] 0.2 Diplura 43.3 [+ or -] 3.4 Diptera 267.3 [+ or -] 13.2 Hemiptera 3.3 [+ or -] 0.6 Hymenoptera 19.3 [+ or -] 3.4 Isoptera 9.3 [+ or -] 1.7 Lepidoptera 335.3 [+ or -] 31.2 Neuroptera na Orthoptera 4.0 [+ or -] 0.5 Protura 0.7 [+ or -] 0.2 Psocoptera 2.0 [+ or -] 0.5 Thysanoptera 0.7 [+ or -] 0.2 Trichoptera 1.3 [+ or -] 0.2 6.0 [+ or -] 1.1 2006 Arachnida Acari 0.7 [+ or -] 0.2 Araneae Chilopoda 134.0 [+ or -] 6.1 Diplopoda 68.0 [+ or -] 3.1 Opiliones 10.0 [+ or -] 1.3 Pseudoscorpiones 19.3 [+ or -] 2.2 Isopoda 5.3 [+ or -] 0.5 3.3 [+ or -] 0.7 Hexapoda Blattodea 51.3 [+ or -] 7.7 Coleoptera Collembola na Diplura 136.7 [+ or -] 13.4 Diptera 206.7 [+ or -] 10.6 Hemiptera 0.7 [+ or -] 0.2 Hymenoptera 28.7 [+ or -] 2.6 Isoptera 12.7 [+ or -] 1.6 Lepidoptera 242.0 [+ or -] 29.6 Neuroptera na Orthoptera 6.0 [+ or -] 0.5 Protura na Psocoptera 1.3 [+ or -] 0.3 Thysanoptera 0.7 [+ or -] 0.2 Tricoptera 3.3 [+ or -] 0.7 12.0 [+ or -] 1.7 na Treatment HS present Year Class Order Deer excluded 2005 Arachnida Acari 184.0 [+ or -] 9.6 Araneae 88.0 [+ or -] 2.9 Chilopoda 9.3 [+ or -] 1.5 Diplopoda 38.0 [+ or -] 3.9 Opiliones 6.7 [+ or -] 0.5 Pseudoscorpiones 12.7 [+ or -] 2.0 Isopoda 52.7 [+ or -] 7.4 Hexapoda Blattodea na Coleoptera 75.3 [+ or -] 6.3 Collembola 325.3 [+ or -] 18.8 Diplura 2.0 [+ or -] 0.5 Diptera 14.0 [+ or -] 1.1 Hemiptera 22.0 [+ or -] 3.4 Hymenoptera 302.7 [+ or -] 1.9 Isoptera na Lepidoptera 0.7 [+ or -] 0.2 Neuroptera na Orthoptera 3.3 [+ or -] 0.3 Protura 0.7 [+ or -] 0.2 Psocoptera 2.7 [+ or -] 0.7 Thysanoptera 6.0 [+ or -] 0.6 Trichoptera na 2006 Arachnida Acari 294.7 [+ or -] 13.8 Araneae 54.7 [+ or -] 4.1 Chilopoda 17.3 [+ or -] 1.7 Diplopoda 41.3 [+ or -] 5.9 Opiliones 6.0 [+ or -] 1.3 Pseudoscorpiones 3.3 [+ or -] 0.7 Isopoda 72.7 [+ or -] 5.5 Hexapoda Blattodea na Coleoptera 96.0 [+ or -] 6.2 Collembola 440.0 [+ or -] 34.4 Diplura 0.7 [+ or -] 0.2 Diptera 36.0 [+ or -] 2.2 Hemiptera 11.3 [+ or -] 1.2 Hymenoptera 249.3 [+ or -] 15.3 Isoptera na Lepidoptera 2.0 [+ or -] 0.3 Neuroptera na Orthoptera 1.3 [+ or -] 0.3 Protura 1.3 [+ or -] 0.3 Psocoptera 3.3 [+ or -] 0.7 Thysanoptera 82.0 [+ or -] 18.6 Tricoptera na Treatment HS present Year Class Order Deer present 2005 Arachnida Acari 236.0 [+ or -] 12.7 Araneae 58.0 [+ or -] 3.4 Chilopoda 11.3 [+ or -] 1.8 Diplopoda 46.0 [+ or -] 3.1 Opiliones 6.7 [+ or -] .l.0 Pseudoscorpiones 11.3 [+ or -] 1.1 Isopoda 86.0 [+ or -] 7.0 Hexapoda Blattodea 1.3 [+ or -] 0.3 Coleoptera 52.7 [+ or -] 3.5 Collembola 360.7 [+ or -] 15.0 Diplura na Diptera 31.3 [+ or -] 3.8 Hemiptera 4.0 [+ or -] 0.6 Hymenoptera 233.3 [+ or -] 1.4 Isoptera na Lepidoptera 1.3 [+ or -] 0.3 Neuroptera na Orthoptera 1.3 [+ or -] 0.3 Protura 0.7 [+ or -] 0.2 Psocoptera 4.0 [+ or -] 0.8 Thysanoptera 6.7 [+ or -] 0.7 Trichoptera na 2006 Arachnida Acari 332.0 [+ or -] 23.2 Araneae 49.3 [+ or -] 2.9 Chilopoda 16.0 [+ or -] 1.6 Diplopoda 23.3 [+ or -] 3.6 Opiliones 3.3 [+ or -] 0.7 Pseudoscorpiones 2.0 [+ or -] 0.5 Isopoda 70.0 [+ or -] 7.4 Hexapoda Blattodea 1.3 [+ or -] 0.3 Coleoptera 88.0 [+ or -] 3.5 Collembola 325.3 [+ or -] 16.5 Diplura 0.7 [+ or -] 0.2 Diptera 30.7 [+ or -] 2.0 Hemiptera 11.3 [+ or -] 1.4 Hymenoptera 255.3 [+ or -] 2.9 Isoptera na Lepidoptera 5.3 [+ or -] - 1.0 Neuroptera na Orthoptera 3.3 [+ or -] 0.2 Protura na Psocoptera 2.0 [+ or -] 0.5 Thysanoptera 22.7 [+ or -] 2.9 Tricoptera na Treatment HS removed Year Class Order Deer excluded 2005 Arachnida Acari 330.7 [+ or -] 26.6 Araneae 68.7 [+ or -] 3.6 Chilopoda 18.7 [+ or -] 1.6 Diplopoda 23.3 [+ or -] 1.4 Opiliones 7.3 [+ or -] 1.2 Pseudoscorpiones 20.0 [+ or -] 2.3 Isopoda 53.3 [+ or -] 5.3 Hexapoda Blattodea 0.7 [+ or -] 0.2 Coleoptera 73.3 [+ or -] 2.6 Collembola 375.3 [+ or -] 12.2 Diplura 1.3 [+ or -] 0.3 Diptera 12.7 [+ or -] 1.4 Hemiptera 17.3 [+ or -] 1.6 Hymenoptera 470.7 [+ or -] 45.6 Isoptera 0.7 [+ or -] 0.2 Lepidoptera 2.7 [+ or -] 0.7 Neuroptera na Orthoptera 4.0 [+ or -] 0.8 Protura 1.3 [+ or -] 0.3 Psocoptera 2.7 [+ or -] 0.7 Thysanoptera 6.0 [+ or -] 0.8 Trichoptera na 2006 Arachnida Acari 360.7 [+ or -] 21.0 Araneae 66.7 [+ or -] 3.1 Chilopoda 14.0 [+ or -] 1.6 Diplopoda 51.3 [+ or -] 9.4 Opiliones 3.3 [+ or -] 0.7 Pseudoscorpiones 4.7 [+ or -] 0.8 Isopoda 73.3 [+ or -] 6.4 Hexapoda Blattodea 0.7 [+ or -] 0.2 Coleoptera 110.0 [+ or -] 0.3 Collembola 358.0 [+ or -] 2.4 Diplura na Diptera 28.0 [+ or -] 2.6 Hemiptera 12.7 [+ or -] 1.7 Hymenoptera 310.0 [+ or -] 28.6 Isoptera na Lepidoptera 4.0 [+ or -] 1.0 Neuroptera na Orthoptera 4.0 [+ or -] -0.8 Protura na Psocoptera 4.7 [+ or -] 0.8 Thysanoptera 16.0 [+ or -] 1.2 Tricoptera na Treatment HS removed Year Class Order Deer present 2005 Arachnida Acari 168.0 [+ or -] 14.4 Araneae 66.0 [+ or -] 3.9 Chilopoda 8.0 [+ or -] 1.4 Diplopoda 29.3 [+ or -] 2.9 Opiliones 6.0 [+ or -] 0.6 Pseudoscorpiones 12.0 [+ or -] 1.5 Isopoda 22.0 [+ or -] 2.2 Hexapoda Blattodea na Coleoptera 57.3 [+ or -] 4.5 Collembola 248.7 [+ or -] 17.6 Diplura 2.7 [+ or -] -0.5 Diptera 8.0 [+ or -] 1.4 Hemiptera 9.3 [+ or -] 1.4 Hymenoptera 218.0 [+ or -] 12.5 Isoptera 0.7 [+ or -] 0.2 Lepidoptera na Neuroptera na Orthoptera 3.3 [+ or -] 0.6 Protura 0.7 [+ or -] 0.2 Psocoptera 2.7 [+ or -] 0.7 Thysanoptera 2.7 [+ or -] 0.5 Trichoptera na 2006 Arachnida Acari 316.0 [+ or -] 16.7 Araneae 48.0 [+ or -] 2.9 Chilopoda 18.0 [+ or -] 2.0 Diplopoda 30.7 [+ or -] 3.5 Opiliones 4.7 [+ or -] 1.0 Pseudoscorpiones 5.3 [+ or -] 1.1 Isopoda 33 [+ or -] 4.3 Hexapoda Blattodea na Coleoptera 131.3 [+ or -] 10.8 Collembola 335.3 [+ or -] 26.9 Diplura 1.3 [+ or -] 0.3 Diptera 29.3 [+ or -] 2.7 Hemiptera 28.0 [+ or -] 3.6 Hymenoptera 307.3 [+ or -] 21.6 Isoptera na Lepidoptera 9.3 [+ or -] 1.3 Neuroptera na Orthoptera 1.3 [+ or -] 0.3 Protura na Psocoptera 5.3 [+ or -] 1.1 Thysanoptera 10.0 [+ or -] 1.1 Tricoptera na
TABLE 1.--Effects of white-tailed deer, Amur honeysuckle, and the deer X honeysuckle interaction on Shannon species diversity, total arthropod abundance, and abundance of the five most abundant orders from analyses by repeated measures ANOVA. Bold indicates significant effects Analysis of Effects F df P Diversity Deer 0.63 1.12 0.44 Honeysuckle 1.09 2.12 0.37 Deer X honeysuckle 0.11 2.12 0.90 Total arthropod Deer 4.56 1.12 0.05 abundance Honeysuckle 2.36 2.12 0.14 Deer X honeysuckle 1.03 2.12 0.39 Acari abundance Deer 0.68 1.12 0.43 Honeysuckle 29.25 2.12 <0.001# Deer X honeysuckle 6.45 2.12 0.01# Araneae Deer 13.73 1.12 0.003# abundance Honeysuckle 8.13 2.12 0.006# Deer X honeysuckle 0.45 2.12 0.65 Coleoptera Deer 0.78 1.12 0.40 abundance Honeysuckle 3.15 2.12 0.08 Deer X honeysuckle 0.10 2.12 0.91 Collembola Deer 0.37 1.12 0.88 abundance Honeysuckle 3.12 2.12 0.08 Deer X honeysuckle 0.83 2.12 0.46 Hymenoptera Deer 1.79 1.12 0.21 abundance Honeysuckle 0.20 2.12 0.82 Deer X honeysuckle 0.05 2.12 0.95 Note: Data in bold indicates significant effects is indicated with #. TABLE 2.-Mean ([+ or -] 1 SE) depth of leaf litter and annual leaf fall in Amur honeysuckle and white-tailed deer treatments Treatments Mean annual leaf fall (dry g/[m.sup.2]) Mean depth of leaf Honeysuckle Deer litter (mm) 2005 Absent Excluded 29.5 [+ or -] 1.6 354.9 [+ or -] 4.3 Absent Present 30.2 [+ or -] 1.3 389.2 [+ or -] 1.3 Present Excluded 31.4 [+ or -] 1.4 405.9 [+ or -] 42.3 Present Present 35.9 [+ or -] 1.3 468.1 [+ or -] 32.6 Removed Excluded 32.7 [+ or -] 1.1 420.8 [+ or -] 42.2 Removed Present 27.5 [+ or -] 1.2 461.9 [+ or -] 85.0 Mean annual leaf fall Treatments (dry g/[m.sup.2]) Honeysuckle 2006 Absent 375.9 [+ or -] 45.3 Absent 457.2 [+ or -] 14.5 Present 442.3 [+ or -] 38.1 Present 452.2 [+ or -] 9.3 Removed 328.7 [+ or -] 45.1 Removed 593.2 [+ or -] 57.8 TABLE 3.--Mean ([+ or -] 1 SE) percent cover for each type of substrate in Amur honeysuckle (HS) and white-tailed deer treatments. na = none present Treatments HS absent Substrate Deer excluded Deer present Bare 16.5 [+ or -] 2.8 29.5 [+ or -] 2.8 Rock 0.04 [+ or -] 0.04 na Woody 5.5 [+ or -] 1.8 6.2 [+ or -] 0.9 Leaves 72.8 [+ or -] 3.7 58.2 [+ or -] 3.6 Mixed 4.9 [+ or -] 0.9 5.6 [+ or -] 1.4 Vegetation 0.3 [+ or -] 0.2 0.6 [+ or -] 0.2 Exposed roots 0.04 [+ or -] 0.04 na Treatments HS present Substrate Deer excluded Deer present Bare 14.2 [+ or -] 2.7 11.0 [+ or -] 2.0 Rock 0.5 [+ or -] 0.2 0.5 [+ or -] 0.3 Woody 3.6 [+ or -] 1.0 8.3 [+ or -] 2.8 Leaves 69.5 [+ or -] 4.3 76.2 [+ or -] 4.2 Mixed 12.1 [+ or -] 2.0 3.9 [+ or -] 1.2 Vegetation na 0.04 [+ or -] 0.04 Exposed roots 0.2 [+ or -] 0.2 na Treatments HS removed Substrate Deer excluded Deer present Bare 10.3 [+ or -] -1.4 13.9 [+ or -] 2.7 Rock na 0.04 [+ or -] 0.04 Woody 5.6 [+ or -] 1.5 9.0 [+ or -] -2.1 Leaves 77.0 [+ or -] 3.0 64.7 [+ or -] 4.4 Mixed 7.0 [+ or -] 1.5 12.0 [+ or -] 2.6 Vegetation 0.04 [+ or -] 0.04 0.2 [+ or -] 0.1 Exposed roots na 0.2 [+ or -] 0.2
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