Plant architecture affects periodical cicada oviposition behavior on native and non-native hosts. Oikos

Variation in plant quality provides a basis for oviposition site selection for a variety of insects. Of the plant traits that infl uence plant-insect interactions, plant architecture has received little attention despite its putative role in modulating oviposition behavior. In a common garden comprised of native and non-native plant species, we assessed how host plant architecture and identity infl uenced the oviposition behavior of 17-year periodical cicadas (Homoptera: Cicadidae: Magicicada ). On each host, we quantifi ed the availability of branches suitable for oviposition and compared those measures with the branches used by ovipositing cicadas. Using this approach, we determined how the structural attributes of plants (i.e. branch diameter, length and incline) aff ected oviposition site selection. We then related cicada oviposition preferences to off spring performance by quantifying egg hatching success. On each host species, cicadas selectively used broader and longer branches for oviposition, suggesting that branch architecture provides a basis for oviposition behavior irrespective of plant identity. Broader and longer branches were more abundant on native than on non-native hosts in our study, contributing to greater oviposition loads among the native species. Egg hatching success was similar among native and nonnative hosts. However, it is possible that the use of native plants for oviposition could enhance off spring output because native hosts generally contained more viable eggs per egg nest and more egg nests per plant. While previous accounts of cicada oviposition preferences have focused on diff erences in oviposition loads among hosts, our evaluation of within-host branch selection by ovipositing cicadas helps to clarify oviposition preferences at a higher resolution and demonstrates that plant architecture provides an important basis for oviposition behavior. Furthermore, because branch structure can diff er substantially among host species, our results suggest that periodical cicadas may be sensitive to the changes in plant composition that often result from non-native plant invasions

Response of host plants to periodical cicada oviposition damage

Abstract Insect oviposition on plants is widespread across many systems, but studies on the response of host plants to oviposition damage are lacking. Although patterns of oviposition vary spatially and temporally, ovipositing insects that exhibit outbreak characteristics may have strong eVects on host plants during peak abundance. Periodical cicadas (Magicicada spp.), in particular, may reduce the performance of host plants when they synchronously emerge in massive numbers to mate and oviposit on host plants. Here we provide the Wrst experimental manipulation of host plant use by periodical cicadas to evaluate the impact of cicada oviposition on plant performance across a diversity of host species within an ecologically relevant setting. Using a randomized block design, we established a plantation of three native and three exotic host plant species common to the successional forests in which cicadas occur. During the emergence of Brood X in 2004, we employed a highly eVective cicada exclusion treatment by netting half of the host plants within each block. We assessed multiple measures of host plant performance, including overall plant growth and the growth and reproduction of individual branches, across three growing seasons. Despite our thorough assessment of potential host plant responses to oviposition damage, cicada oviposition did not generally inhibit host plant performance. Oviposition densities on unnetted host plants were comparable to levels documented in other studies, reinforcing the ecological relevance of our results, which indicate that cicada oviposition damage did not generally reduce the performance of native or exotic host plants

Species evenness and invasion resistance of experimental grassland communities

Concern for biodiversity loss coupled with the accelerated rate of biological invasions has provoked much interest in assessing how native plant species diversity affects invasibility. Although experimental studies extensively document the effects of species richness on invader performance, the role of species evenness in such studies is rarely examined. Species evenness warrants more attention because the relative abundances of species can account for substantially more of the variance in plant community diversity and tend to change more rapidly and more frequently in response to disturbances than the absolute numbers of species. In this study, we experimentally manipulated species evenness within native prairie grassland mesocosms. We assessed how evenness affected primary productivity, light availability and the resistance of native communities to invasion. The primary productivity of native communities increased significantly with species evenness, and this increase in productivity was accompanied by significant decreases in light availability. However, evenness had no effect on native community resistance to invasion by three common exotic invasive species. In this study, niche complementarity provides a potential mechanism for the effects of evenness on productivity and light availability, but these effects apparently were not strong enough to alter the invasibility of the experimental communities. Our results suggest that species evenness enhances community productivity but provides no benefit to invasion resistance in otherwise functionally diverse communities

Appendix B. Bivariate plots of all (untransformed) measured variables included in the structural equation modeling (SEM).

Bivariate plots of all (untransformed) measured variables included in the structural equation modeling (SEM)

Appendix A. Classification, frequencies, and abundances of tree species.

Classification, frequencies, and abundances of tree species

Historical agriculture alters the effects of fire on understory plant beta diversity

fire, two prominent disturbances that are often coincident in terrestrial ecosystems. At three study locations spanning 450 km in the southeastern United States, we surveyed longleaf pine woodland understory plant communities across 232 remnant and post-agricultural sites with differing prescribed fire regimes. Our results demonstrate that agricultural legacies are a strong predictor of beta diversity, but the direction of this land-use effect differed among the three study locations. Further, although beta diversity increased with prescribed fire frequency at each study location, this effect was influenced by agricultural land-use history, such that positive fire effects were only documented among sites that lacked a history of agriculture at two of our three study locations. Our study not only highlights the role of historical agriculture in shaping beta diversity in a fire-maintained ecosystem but also illustrates how this effect can be contingent upon fire regime and geographic location. We suggest that interactions among historical and contemporary landuse activities may help to explain dissimilarities in plant communities among sites in human-dominated landscapes

Land-Use History and Contemporary Management Inform an Ecological Reference Model for Longleaf Pine Woodland Understory Plant Communities

<div><p>Ecological restoration is frequently guided by reference conditions describing a successfully restored ecosystem; however, the causes and magnitude of ecosystem degradation vary, making simple knowledge of reference conditions insufficient for prioritizing and guiding restoration. Ecological reference models provide further guidance by quantifying reference conditions, as well as conditions at degraded states that deviate from reference conditions. Many reference models remain qualitative, however, limiting their utility. We quantified and evaluated a reference model for southeastern U.S. longleaf pine woodland understory plant communities. We used regression trees to classify 232 longleaf pine woodland sites at three locations along the Atlantic coastal plain based on relationships between understory plant community composition, soils (which broadly structure these communities), and factors associated with understory degradation, including fire frequency, agricultural history, and tree basal area. To understand the spatial generality of this model, we classified all sites together and for each of three study locations separately. Both the regional and location-specific models produced quantifiable degradation gradients–i.e., progressive deviation from conditions at 38 reference sites, based on understory species composition, diversity and total cover, litter depth, and other attributes. Regionally, fire suppression was the most important degrading factor, followed by agricultural history, but at individual locations, agricultural history or tree basal area was most important. At one location, the influence of a degrading factor depended on soil attributes. We suggest that our regional model can help prioritize longleaf pine woodland restoration across our study region; however, due to substantial landscape-to-landscape variation, local management decisions should take into account additional factors (e.g., soil attributes). Our study demonstrates the utility of quantifying degraded states and provides a series of hypotheses for future experimental restoration work. More broadly, our work provides a framework for developing and evaluating reference models that incorporate multiple, interactive anthropogenic drivers of ecosystem degradation.</p></div

Geographic range of the longleaf pine ecosystem and map of study locations.

<p>Study locations (Fort Bragg [NC], 31°11' N, 79°15' W; Fort Stewart [GA], 31°56' N, 81°36' W; and Savannah River Site [SC], 33°20' N, 81°40' W) were in three different physiographic regions (sandhills, southern coastal plain, and Atlantic coastal plain, respectively <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086604#pone.0086604-Peet1" target="_blank">[26]</a>) allowing for creation and evaluation of an ecological reference model across a range of ecological settings. This model was based on data from 232 sites, which varied in their levels of degradation, with results subsequently compared to data from 38 reference sites.</p

Conceptual model of degradation for understory plant communities in longleaf pine woodlands.

<p>Understory degradation (deviation in community composition from reference site conditions) is predicted to increase with occurrence of agricultural history, increasing overstory density, and declining fire frequency. Note: not all combinations of model components are presented in this figure and, while depicted as a linear process in this conceptual diagram, nonlinearities may exist during restoration from degraded states. Model is based on <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086604#pone.0086604-Walker1" target="_blank">[8]</a>.</p