Implications of Food Web Interactions for Restoration of Missouri Ozark Glade Habitats Peter A
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Implications of Food Web Interactions for Restoration of Missouri Ozark Glade Habitats Peter A. Van Zandt,1,2 Eboni Collins,1 Jonathan B. Losos,1 and Jonathan M. Chase1 Abstract surveys across six Missouri glades indicated that lizard Ozark glades are gaps in forested areas that are domi- activity was minimal beyond 1 m from habitat structures. nated by grasses and forbs growing in rocky, nutrient-poor This activity pattern reduced grasshopper abundance by soil. Historically, these open, patchy habitats were main- 75% and plant damage by over 66% on Echinacea para- tained by natural and anthropogenic fire cycles that pro- doxa and Rudbeckia missouriensis near structures with hibited tree encroachment. However, because of decades lizards. A field transplant experiment demonstrated simi- of fire suppression, glades have become overgrown by lar reductions in grasshopper abundance and damage on fire-intolerant species such as Eastern red cedar (Junipe- two other glade endemic species, Aster oblongifolius and rus virginiana). Current restoration practices include cut- Schizachyrium scoparium. These results demonstrate that ting down invasive cedars and burning brush piles, which future glade restoration efforts might benefit from consid- represent habitat for Northern fence lizards (Sceloporus ering top-down effects of predators in facilitating native undulatus). Because Sceloporus actively consumes herbi- plant establishment. vores, we hypothesized that the presence of these lizards in and around brush piles might result in a trophic cas- Key words: biomanipulation, Sceloporus undulatus, tro- cade, whereby damage on native plants is reduced. Field phic cascade. Introduction introduced wolves filling the role of plant mutualists Restoration efforts commonly focus on manipulations and (Ripple & Beschta 2003). In other terrestrial systems, at- reinstatement of the bottom trophic level—plants. How- tempts at the biocontrol of crop pests have centered on ever, consumers of plants (herbivores), and consumers of increasing physical structure with the addition of mulch to those consumers (carnivores), can often have profound augment habitat for predators such as spiders (Riechert & effects on the growth rates, population dynamics, biodi- Bishop 1990; Brust 1994; Symondson et al. 2002). versity, and ecosystem functioning of plant communities In this study we examined the indirect effects of native (reviewed in Huntly 1991). Although the importance of insectivorous lizards (Sceloporus undulatus) on the herba- such food web effects is still debated, particularly in ter- ceous plant communities in actively restored Missouri restrial ecosystems (Strong 1992; Leibold et al. 1997; (U.S.A.) Ozark glades through their direct effects on her- Chase 2000; Chase et al. 2000; Polis et al. 2000; Schmitz bivorous insects. Glades are rocky outcrops contained et al. 2000; Shurin et al. 2002), it is apparent that an effec- within forested areas where poor abiotic conditions such tive restoration strategy needs to consider the entire com- as low soil moisture and acidic, nutrient-poor soils limit munity, including the effects of consumers in food webs plant productivity (Nelson 1987; Baskin & Baskin 2000). (Bevill et al. 1999; Howe et al. 2002; Ruhren & Handel These outcrops are the result of years of landform erosion, 2003). Indeed, the recognition of the importance of con- which allows the bedrock to break the surface of the sumers has already influenced restoration efforts in some glade’s thin soil. Glades resemble prairie communities of aquatic and terrestrial agricultural ecosystems. In aquatic the western United States and share many plant and ani- communities the addition of piscivorous (fish eating) fish mal genera with those systems (Nelson & Ladd 1980). In causes a decline in the abundance of zooplanktivorous fish, addition, many glade plant species are relictual and thus resulting in more grazers and less algae (Bergman endemic, and glade species are often typical of hotter and et al. 1999; Lathrop et al. 2002). Similar recommenda- drier conditions of desert areas (Baskin et al. 1995; Baskin tions have been made for riparian plant management with & Baskin 2000; McClain & Ebinger 2002). Historically, glades were maintained as herbaceous (grass and forb) communities in part by a regular fire cycle that excluded fire-sensitive species, including most trees (Templeton et al. 1 Department of Biology, Washington University, Campus Box 1137, St. Louis, MO 63130, U.S.A. 2001; Ware 2002). Fire suppression following European 2 Address correspondence to P. A. Van Zandt, email vanzandt@biology2. settlement has allowed native fire-sensitive trees to in- wustl.edu vade many of these glade habitats (Bergmann & Chaplin Ó 2005 Society for Ecological Restoration International 1992; Baskin & Baskin 2000; Ware 2002). Of particular 312 Restoration Ecology Vol. 13, No. 2, pp. 312–317 JUNE 2005 Fence Lizards and Glade Restoration concern is the Eastern red cedar (Juniperus virginiana), activity, grasshopper abundance, and plant damage in nat- because it further fragments glade habitats and forms dense ural glades, along with an experiment in which we planted stands that shade out glade endemic plants. glade plants at three different distances from cover objects Recently, Ozark glades have been targeted by restora- to simulate common restoration practices in a glade that is tion efforts. Restoration of glades typically requires sev- currently undergoing restoration. Our results indicate eral seasons of prescribed burns and physical removal of a potential role for predation in facilitating glade restora- cedar trees and saplings, combined with hand planting of tion efforts. This is particularly pertinent, because current glade endemics (Davis 1982). Often, because of high seed- glade restoration projects often remove brush piles and ling mortality and low germination success, transplantation other potential cover habitats. We conclude that future of juvenile plants is the most effective way of reestablish- restoration efforts would benefit by providing cover habi- ing glade species (J. C. Walker 2003, Tyson Research Cen- tats for lizards, which could facilitate plant establishment. ter, personal communication; Ruhren & Handel 2003). However, even juvenile plants that have been planted may not become successfully established if they are suffi- Methods ciently consumed by grasshoppers (Orthoptera: Acridi- dae) and other herbivorous insects. In Missouri Ozark Glade Sampling glades, leaf-chewing herbivores can cause substantial dam- To assess the natural patterns in herbivory which might be age (approximately 10–80%) to a wide variety of glade attributed to trophic cascades, we measured Sceloporus plants. For example, insect herbivory on the glade peren- activity, grasshopper density, and levels of herbivory on nial Liatris cylindracea has been shown to reduce fecun- three plant species in six recently restored glades in dity by as much as 83% and establishment of seedlings in southeastern Missouri. We collected data at two glades at the next season by over 50% (Kelly & Dyer 2002). Washington University’s Tyson Research Center (St. Louis Because grasshoppers and larval lepidopterans are the County) and four glades at Meramec State Park (Franklin most abundant groups of herbivorous insects (in terms of County). These glades are of similar size and consist of biomass; 80%) in glades (Chase, unpublished data; Kelly comparable plant communities occurring in thin, nutrient- & Dyer 2002), minimizing their impact can substantially poor soil over dolomitic limestone bedrock (Walker 1998; reduce herbivore damage in these communities. Baskin & Baskin 2000; Ware 2002). Restoration efforts We hypothesize that the restoration of Ozark glades will have recently (within the last 10–15 years) been initiated be enhanced by explicitly considering the predators and on all our study glades and consist of intensive manage- their concomitant food web interactions. That is, predators ment involving physical removal of Eastern red cedar of insects can reduce herbivore density in glade ecosys- trees, prescribed burns, and reseeding of native glade- tems, thereby reducing losses of plants to abundant grass- specific plants. hoppers and other chewing herbivores. One predator of To characterize lizard foraging patterns, we estimated grasshoppers that can be quite common in Ozark glades is Sceloporus activity weekly by repeatedly observing lizards the Northern fence lizard S. undulatus (hereafter, Scelopo- between 0800 and 1800 hr over a 10-week period in the rus). Sceloporus is usually restricted in its foraging to areas two glades at Tyson, and during a 1-day sampling transect on and around cover objects, such as downed logs, brush through the four Meramec glades. We estimated activity piles, and rock piles (Angert et al. 2002; James & by having one observer walk transects throughout each M’Closkey 2002). We focus on grasshopper abundance, glade, noting the presence and activity of all Sceloporus, because in Missouri, grasshoppers constitute a majority of and measuring the distance to the nearest cover object the summer and fall diet of Sceloporus (Marion 1970), with (e.g., downed logs, brush piles, bushes). The repeated ob- larval lepidopterans constituting a small fraction of the diet servations of lizard behavior at Tyson were made on the (DeMarco et al. 1985). Also, observations and experiments same lizard populations, and therefore are not indepen- in California meadows showed that Western fence lizards