bluuebunny/crossref_metadata_2025_split huggingface dataset:
Can we detect ecosystem critical transitions and signals of changing resilience from paleo‐ecological records?
Authors: Taranu Zofia E. , Carpenter Stephen R. , Frossard Victor , Jenny Jean‐Philippe , Thomas Zoë , Vermaire Jesse C. , Perga Marie‐Elodie 
Published: October 2018

AbstractNonlinear responses to changing external pressures are increasingly studied in real‐world ecosystems. However, as many of the changes observed by ecologists extend beyond the monitoring record, the occurrence of critical transitions, where the system is pushed from one equilibrium state to another, remains difficult to detect. Paleo‐ecological records thus represent a unique opportunity to expand our temporal perspective to consider regime shifts and critical transitions, and whether such events are the exception rather than the rule. Yet, sediment core records can be affected by their own biases, such as sediment mixing or compression, with unknown consequences for the statistics commonly used to assess regime shifts, resilience, or critical transitions. To address this shortcoming, we developed a protocol to simulate paleolimnological records undergoing regime shifts or critical transitions to alternate states and tested, using both simulated and real core records, how mixing and compression affected our ability to detect past abrupt shifts. The smoothing that is built into paleolimnological data sets apparently interfered with the signal of rolling window indicators, especially autocorrelation. We thus turned to time‐varying autoregressions (online dynamic linear models, DLMs; and time‐varying autoregressive state‐space models, TVARSS) to evaluate the possibility of detecting regime shifts and critical transitions in simulated and real core records. For the real cores, we examined both varved (annually laminated sediments) and non‐varved cores, as the former have limited mixing issues. Our results show that state‐space models can be used to detect regime shifts and critical transitions in some paleolimnological data, especially when the signal‐to‐noise ratio is strong. However, if the records are noisy, the online DLM and TVARSS have limitations for detecting critical transitions in sediment records.
Associational susceptibility of a native shrub induced by context‐dependent attraction of an invasive herbivore
Authors: Lillian Sarah , Redak Richard A. , Daugherty Matthew P. 
Published: October 2018

AbstractIndirect interactions among native and invasive species are notoriously difficult to predict. Here, we apply theory from trait‐mediated indirect effects and plant–insect interactions to explain the outcomes of multiple invader interactions. The present study investigates the roles of herbivore preference and plant ontogeny in mediating associational effects among a southern California native shrub, Atriplex canescens, an invasive annual forb, Brassica tournefortii, and an invasive stink bug, Bagrada hilaris. Ba. hilaris have been observed to form dense aggregations on A. canescens in late spring following senescence of Br. tournefortii, with subsequent increased mortality of A. canescens. A manipulative experiment found Ba. hilaris recruited to A. canescens in approximately 70 times greater numbers when neighbored by Br. tournefortii than when alone. Ba. hilaris nymph production, while minimized experimentally, occurred only on Br. tournefortii, suggesting A. canescens is not of sufficient quality for Ba. hilaris reproduction. In greenhouse preference trials, Ba. hilaris exhibited an overall preference for Br. tournefortii over A. canescens; however, the magnitude of preference depended on ontogenetic stage of Br. tournefortii. Overall, our results suggest significant potential for associational susceptibility mediated by a combination of Ba. hilaris preference for reproductive Br. tournefortii, substantial aggregation of Ba. hilaris onto Br. tournefortii, and a marked decline in Ba. hilaris preference for Br. tournefortii with advancing ontogeny—triggering spillover onto neighboring plants. Our results demonstrate an important role for multiple invaders and phenologically driven trait changes in mediating associational susceptibility.
Evidence for scale‐dependent topographic controls on wildfire spread
Authors: Povak Nicholas A. , Hessburg Paul F. , Salter R. Brion 
Published: October 2018

AbstractWildfire ecosystems are thought to be self‐regulated through pattern–process interactions between ignition frequency and location, and patterns of burned and recovering vegetation. Yet, recent increases in the frequency of large wildfires call into question the application of self‐organization theory to landscape resilience. Topography represents a stable bottom‐up template upon which fire interacts as both a physical and an ecological process. However, it is unclear how topographic control changes geographically and across spatial scales. We analyzed fire perimeter and topography data from 16 Bailey ecoregions across the State of California to identify spatial correspondence between ecoregional fire event and topographic patch size distributions. We found both sets of distributions followed a power‐law form and were statistically similar across several orders of magnitude, for most ecoregions. As a direct test of topographic controls on fire event perimeters, we used a paired t‐test across ~11,000 fires to identify differences in topographic attributes at fire boundaries versus fire interiors. Statistical significance was determined using 500 iterations of a neutral landscape model. Level of topographic control varied significantly by ecoregion and across topographic features. For example, north–south aspect breaks, valley bottoms, and roads showed a consistently high degree of spatial control on wildfire perimeters. Topographic controls were most pronounced in mountainous ecoregions and were least influential in arid regions. Ridgetops provided a low‐level control across all ecoregions. Spatial control was strongest for small (100–102 ha) to medium (103–104 ha) fire sizes, suggesting that controls were scale‐dependent rather than scale‐invariant. Roads were the dominant control across all ecoregions; however, removing roads from the analyses had no significant effect on the overall role of topography on wildfire extinguishment in this analysis. This result suggested that certain topographic settings show strong spatial control on fire growth, despite the presence of roads. Our results support the observation that both bottom‐up and top‐down factors constrain fire sizes and that there are likely scaling regions within fire size distributions wherein the dominance of these spatial controls varies. Human influences on fire spread may either diminish or enhance the role of some bottom‐up and top‐down factors, adding further complexity.
Loss of biodiversity alters ecosystem function in freshwater streams: potential evidence from benthic macroinvertebrates
Authors: Cao Xiaofeng , Chai Liwei , Jiang Dalin , Wang Jie , Liu Yanqiu , Huang Yi 
Published: October 2018

AbstractParticular attention has been paid on the evidence that ecosystem function can be impacted by changes of biodiversity. However, how the loss of biodiversity alters the ecosystem function in aquatic ecosystems remains unclear. Here, the effects of benthic macroinvertebrate community structure on ecosystem function and the possibility of which being shifted by ecological threshold along the habitat condition gradient were examined by quantifying community structure and ecosystem function in streams of Lake Dianchi basin. The results demonstrated that the relative abundance of Oligochaete was significantly linear correlated with ecosystem multifunctions, especially N and P cycling functions, as well as the dominant taxon% and Gather‐Collectors% closely affected P cycling function and multifunctions, respectively, while no remarkable nonlinearities were observed. Besides, there was a distinct shift from sensitive taxa‐dominated healthy state to tolerant taxa‐dominated degraded state with an increase in habitat pressure. The nonlinear transition of benthic macroinvertebrate community structure in combination with altered ecosystem function clearly indicated the present of extinction threshold in the process of stream habitat degradation. The findings contribute to the growing evidence for fully understanding the implications of biodiversity loss in ecosystem function.
Release of hatchery adult steelhead for angler opportunity increases potential for interactions with endemic steelhead
Authors: Erdman Charles S. , Caudill Christopher C. , Naughton George P. , Jepson Michael A. 
Published: October 2018

AbstractTranslocation is often used to increase local abundance of fish and wildlife populations for conservation or harvest purposes, and effects of releases on recipient populations are context dependent. Release of non‐local animals intended for harvest can have negative demographic, genetic, and ecological risks to endemic populations when not harvested. In 2012–2014, we used radiotelemetry to monitor the fate and potential for interactions between non‐local hatchery‐origin adult summer‐run steelhead Oncorhynchus mykiss (n = 423) and Endangered Species Act (ESA)‐listed native winter‐run steelhead (WRS) in two tributaries of the Willamette River, Oregon, USA. Summer steelhead were recycled—collected, translocated downstream, and released—to provide additional angler opportunity as a part of a regional mitigation program. Overall, reported harvest rate of recycled steelhead was low (15%) and a majority of individuals (62%) were last recorded in the release tributary. Furthermore, 14% of radio‐tagged recycled steelhead were last detected outside the release tributary (i.e., strayed after release). Expanded estimates indicate the number of recycled summer‐run steelhead remaining in the South Santiam River exceeded the WRS spawning population size. Low reported harvest and straying and demographic estimates indicate the recycling program may have negative effects on endemic WRS. Translocation and hatchery supplementation are likely to remain important conservation and mitigation tools in the future, though these results highlight the importance of post‐release monitoring and considering both the risks and benefits of translocations to endemic populations and communities.
A long‐term perspective on microclimate and spring plant phenology in the Western Cascades
Authors: Ward Sarah E. , Schulze Mark , Roy Bitty 
Published: October 2018

AbstractPhenology—recurring seasonal events in an organism's life cycle—is largely driven by local climates <1 km2 (microclimates), and changes in phenology are frequently used to indicate a species’ or community response to climate change. Phenological shifts can result in trophic asynchrony, population declines of higher‐level consumers, and reduction of plant fitness. While timing of phenological events is often correlated with elevation, studies have shown that microclimates created by areas of heterogeneous topography can be decoupled from regional climate patterns and that the distribution of microclimates does not always follow the elevation gradient. To examine the interaction between regional weather patterns and microclimate, and the subsequent effect of microclimate on phenology, we conducted standardized weekly spring phenology surveys of 18 native forest plants at the H.J. Andrews Experimental Forest in the Western Cascades from 2009 to 2016. We saw a high degree of inter‐annual variability of microclimate within and across sites, resulting in a changing pattern of microclimate diversity across the landscape from year to year. Most importantly, we saw that years with regional conditions predicted by continued climate change showed a loss of diversity in both microclimate and phenological events, with a more rapid advancement in bud break occurring at higher elevation sites. This study highlights the importance of understanding the interactions between regional and local processes that determine microclimate conditions and how those conditions influence patterns of plant phenology within forest communities, across mountain landscapes and over time, with implications for the capacity of mountainous regions to buffer local communities against the effects of climate change.
Site conditions are more important than abundance for explaining plant invasion impacts on soil nitrogen cycling
Authors: Lee Marissa R. , Flory S. Luke , Phillips Richard P. , Wright Justin P. 
Published: October 2018

AbstractInvasive plant species can alter critical ecosystem processes including nitrogen transformations, but it is often difficult to anticipate where in an invaded landscape, these effects will occur. Our predictive ability lags because we lack a framework for understanding the multiple pathways through which environmental conditions mediate invader impacts. Here, we present a framework using structural equation modeling to evaluate the impact of an invasive grass, Microstegium vimineum (M.v.), on nitrogen cycling based on a series of invaded sites that varied in invader biomass and non‐M.v. understory biomass, tree basal area, light availability, and soil conditions. Unlike previous studies, we did not find an overall pattern of elevated nitrate concentrations or higher nitrification rates in M.v.‐invaded areas. We found that reference plot conditions mediated differences in mineralization between paired invaded and reference plots at each site through indirect (via M.v. biomass), direct, and interactive pathways; however, the strongest pathways were independent of M.v. biomass. For example, sites with low reference soil nitrate and high non‐M.v. understory biomass tended to have faster mineralization at 5–15 cm in invaded plots. These findings suggest that more attention to reference conditions is needed to understand the impact of invasive species on soil nitrogen cycling and other ecosystem processes and that the greatest impacts will not necessarily be where the invader is most abundant.
Unfolding long‐term Late Pleistocene–Holocene disturbances of forest communities in the southwestern Amazonian lowlands
Authors: Rossetti Dilce F. , Gribel Rogério , Toledo Peter M. , Tatumi Sonia H. , Yee Márcio , Tudela Diego R. G. , Munita Casimiro S. , de Souza Coelho Luiz 
Published: October 2018

AbstractLinking the distribution of plant species to geology has generally been biased by the over‐simplification of landscape evolution and the lack of understanding of complex geological processes. The Amazonian lowlands have forests in different successional stages, and a growing perception is that such heterogeneity results from long‐term environmental changes. This hypothesis is investigated by designing an analytical model based on past and present‐day vegetation and successions of the plant communities, combined with an advanced understanding of geological history. An area of southwestern Amazonia was selected for floristic inventories, and we interpreted the paleovegetation based on C/N and δ13C analyses of sedimentary organic matter. These data were examined in the context of the geological evolution on the basis of new sedimentological and chronological data. The topographically high Late Pleistocene deposits had continuous and highly diversified late‐successional terra firme forests as well as local fluvial paleolandforms of younger ages with less diversified campinarana forests. Late Pleistocene–Holocene terrains in intermediate elevations had terra firme forests, but shorter trees with lower basal areas and ecotonal forests appeared near the confines of the forest–savanna, while Holocene deposits recorded only seasonally flooded varzea forests. Several deposits of Late Pleistocene and Late Pleistocene–Holocene age recorded an expansion of C4 terrestrial plants before the establishment of the forest from ~20,000 cal yr BP to 7578 cal yr BP, which is not related to past arid episodes. We recorded forests with onsets at 6130–3533 cal yr BP, 3402–2800 cal yr BP, and 1624–964 cal yr BP to terra firme, varzea, and ecotonal forests, respectively. However, not all forests have reached maturity stages due to their location on terrains with a diverse history of terrace downcutting and deposition, which had a direct impact on local hydrology with the interaction of topographic gradients. The hydrology of the study area was also controlled by the distance from the main river valley. Capturing long‐term disturbances over this region of still pristine forests may help elucidate the potential mechanisms that also determine trends in tree growth and forest diversity in other Neotropical regions.
Legitimate visitors and nectar robbers of Aquilegia formosa have different effects on nectar bacterial communities
Authors: Zemenick Ash T. , Rosenheim Jay A. , Vannette Rachel L. 
Published: October 2018

AbstractMetacommunity structure is strongly influenced by dispersal between habitat patches. Dispersal mode (e.g., active or passively via vector, wind, or water) is recognized to influence metacommunity dynamics, but it is not well understood how within‐mode heterogeneity impacts dispersal and community assembly, particularly for microbial communities. Microbes often rely on flower visitors for dispersal among short‐lived floral nectar habitats, but it is unclear whether flower visitor guilds (e.g., legitimate visitors vs. larcenists) differentially influence nectar microbial diversity and community structure. We surveyed the community of legitimate nectar foragers and nectar robbers, which damage flowers to obtain floral rewards, of Aquilegia formosa. Then, we evaluated how manipulating access by legitimate nectar foragers, primary nectar robbers, and/or secondary nectar robbers influenced the diversity, species composition, and beta diversity of nectar bacteria within individual flowers. A taxonomically diverse insect community visited A. formosa, and visitors differentially influenced nectar bacterial community structure at within‐flower (local) and among‐flower (regional) scales. When legitimate nectar foragers were allowed to access A. formosa, we observed an increase in bacterial diversity and changes in bacterial species composition such that common nectar bacteria had higher relative abundances. In contrast, effects of natural and simulated robbing had little effect on bacterial alpha diversity, but simulated robbing decreased the relative abundance of common nectar bacteria, and natural nectar robbing events reduced beta diversity of nectar bacteria. This work highlights the importance of visitor identity on microbial diversity and species composition in flowers, and, more broadly, suggests that vectors can differentially influence metacommunity structure.
NDVI exhibits mixed success in predicting spatiotemporal variation in caribou summer forage quality and quantity
Authors: Johnson Heather E. , Gustine David D. , Golden Trevor S. , Adams Layne G. , Parrett Lincoln S. , Lenart Elizabeth A. , Barboza Perry S. 
Published: October 2018

AbstractThe satellite‐derived Normalized Difference Vegetation Index (NDVI) is commonly used by researchers and managers to represent ungulate forage conditions in landscapes across the globe, despite limited information about how it compares to empirical measurements of forage quality and quantity. The application of NDVI as a forage metric is particularly appealing for studying migratory caribou (Rangifer tarandus) in remote Arctic ecosystems, where field assessments are logistically and financially prohibitive, and climate‐mediated changes in vegetation have been hypothesized to influence population declines. To determine the utility of NDVI for adequately representing caribou forage conditions, we compared NDVI derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery to empirical measures of caribou forage biomass, nitrogen, digestible nitrogen, and digestible energy within the summer range of the Central Arctic Caribou Herd on the North Slope of Alaska. Specifically, we determined the strength of forage–NDVI relationships at the start of the growing season and across the summer, assessed the efficacy of NDVI variables for modeling spatiotemporal variation in field measurements of different forage components, and used long‐term MODIS data to estimate temporal changes in forage between 2000 and 2016. We found that NDVI values were weakly correlated with caribou forage quality at the start of the growing season and throughout the summer. Although linear models of forage–NDVI relationships performed poorly, NDVI variables (NDVI and the number of days from when NDVI reached its maximum value) were useful for modeling spatiotemporal variation in empirical measurements of forage components across the growing season, but only when we incorporated nonlinear forage–NDVI relationships and other habitat covariates. Phenological advances in the date of peak NDVI were associated with significant changes in forage conditions, particularly nitrogen, which exhibited earlier seasonal declines. Using long‐term MODIS data, predicted values of forage nitrogen declined between 2000 and 2016, driven by exceedingly low values in 2014 and 2015. Given our results, we caution the application of NDVI as a general (linear) proxy of caribou forage conditions across the growing season, and encourage practitioners to use NDVI variables to model spatiotemporal variation in specific forage conditions from empirical field data, accounting for nonlinear forage–NDVI relationships.
Mixed effects of an introduced ecosystem engineer on the foraging behavior and habitat selection of predators
Authors: Haram Linsey E. , Kinney Kaitlin A. , Sotka Erik E. , Byers James E. 
Published: October 2018

AbstractInvasive ecosystem engineers both positively and negatively affect their recipient ecosystems by generating novel habitats. Many studies have focused on alterations to ecosystem properties and to native species diversity and abundance caused by invasive engineers. However, relatively few studies have documented the extent to which behaviors of native species are affected. The red seaweedGracilaria vermiculophylla(Rhodophyta) invaded estuaries of the southeastern United States within the last few decades and now provides abundant aboveground vegetative cover on intertidal mudflats that were historically devoid of seaweeds. We hypothesized thatG. vermiculophyllawould affect the foraging behavior of native shorebirds positively for birds that target seaweed‐associated invertebrates or negatively for birds that target prey on or within the sediment now covered with seaweed. Visual surveys of mudflats >1 ha in size revealed that more shorebirds occurred on mudflats withG. vermiculophyllarelative to mudflats withoutG. vermiculophylla. This increased density was consistent across 7 of 8 species, with the one exception being the semipalmated ploverCharadrius semipalmatus. A regression‐based analysis indicated that while algal presence predicted shorebird density, densities of some bird species depended on sediment composition and infaunal invertebrate densities. At smaller spatial scales (200 m2and <1 m2), experimental removals and additions ofG. vermiculophyllaand focal observations showed strong variation in behavioral response toG. vermiculophyllaamong bird species. Birds preferentially foraged in bare mud (e.g.,C. semipalmatus), inG. vermiculophylla(e.g.,Arenaria interpres), or displayed no preference for either habitat (e.g.,Tringa semipalmata). Thus, while the presence of the invasive ecosystem engineer on a mudflat appeared to attract greater numbers of these predators, shorebird species differed in their behavioral responses at the smaller spatial scales that affect their foraging. Our research illuminates the need to account for species identity, individual behavior, and scale when predicting the impacts of invasive species on native communities.