01986nas a2200193   4500008004100000245012700041210006900168300001400237490000800251520130500259653002301564653003701587653003001624653003301654653002501687100001501712700001901727856004601746       2017                        eng d00aDensity mediates grasshopper performance in response to temperature manipulation and spider predation in tallgrass prairie0 aDensity mediates grasshopper performance in response to temperat  a261 - 2670 v1073 a<p>Species interactions are often context-dependent, where outcomes require an understanding of influences among multiple biotic and abiotic factors. However, it remains unclear how abiotic factors such as temperature combine with important biotic factors such as density-dependent food limitation and predation to influence species interactions. Using a native grassland - grasshopper - wolf spider model food chain in tallgrass prairie, we conducted a manipulative field experiment to examine how predator-prey interactions respond to manipulations of temperature, grasshopper density, and food chain length. We find that grasshopper performance responses to temperature and predator treatments were density dependent. At high densities, grasshopper survival decreased with increased temperature when no spiders were present. When spiders were present, grasshopper survival was reduced, and this effect was strongest in the cooled treatment. In contrast, grasshopper survival did not vary significantly with spider presence or among temperature treatments at low grasshopper densities. Our results indicate that context-dependent species interactions are common and highlight the importance of understanding how and when key biotic and abiotic factors combine to influence species interactions.</p>10adensity dependence10aKonza Prairie Biological Station10aPhoetaliotes nebrascensis10aRabidosa rabida; temperature10aSpecies interactions1 aLaws, A.N.1 aJoern, Anthony  uhttps://doi.org/10.1017/S000748531600089402673nas a2200181   4500008004100000245008000041210006900121490000600190520210100196100001702297700001902314700001702333700001502350700001902365700001502384700001702399856007502416       2017                        eng d00aTemporal variability in large grazer space use in an experimental landscape0 aTemporal variability in large grazer space use in an experimenta0 v83 aLand use, climate change, and their interaction each have great potential to affect grazing systems. With anticipated more frequent and extensive future drought, a more complete understanding of the mechanisms that determine large grazer landscape-level distribution under varying climatic conditions is integral to ecosystem management. Using an experimental setting with contrasting fire treatments, we describe the inter-annual variability of the effect of landscape topography and disturbance from prescribed spring fire on large grazer space use in years of variable resource availability. Using GPS telemetry, we investigated space use of plains bison (Bison bison bison) as they moved among watersheds managed with variable experimental burn treatments (1-, 2-, 4-, and 20-year burn intervals) during a seven-year period spanning years of average-to-above average forage production and severe drought. At the landscape scale, bison more strongly favored high-elevation and recently burned watersheds with watersheds burned for the first time in 2 or 4 yr consistently showing higher use relative to annually burned watersheds. In particular, watersheds burned for the first time in 4 yr were avoided to lesser extent than other more frequently burned watersheds during the dormant season. This management type also maintained coupling between bison space use and post-fire regrowth across post-drought growing season months, whereas watersheds with more frequent fire-return intervals attracted bison in only the first month post-fire. Hence, fire frequency played a role in maintaining the coupling of grazer and post-fire regrowth, the fire–grazer interaction, in response to drought-induced reduction in fuel loads. Moreover, bison avoided upland habitat in poor forage production years, when forage regrowth is less likely to occur in upland than in lowland habitats. Such quantified responses of bison to landscape features can aid future conservation management efforts and planning to sustain fire–grazer interactions and resulting spatial heterogeneity in grassland ecosystems.1 aRaynor, E.J.1 aJoern, Anthony1 aSkibbe, A.M.1 aSowers, M.1 aBriggs, J., M.1 aLaws, A.N.1 aGoodin, D.G.  uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecs2.167402079nas a2200205   4500008004100000245013700041210006900178300001500247490000600262520139700268653002501665653003301690653002301723100001501746700001701761700001701778700001501795700001901810856004401829       2014                        eng d00aEstimating canopy nitrogen content in a heterogeneous grassland with varying fire and grazing treatments: Konza Prairie, Kansas, USA0 aEstimating canopy nitrogen content in a heterogeneous grassland   a4430 -44530 v63 a<p>Quantitative, spatially explicit estimates of canopy nitrogen are essential for understanding the structure and function of natural and managed ecosystems. Methods for extracting nitrogen estimates via hyperspectral remote sensing have been an active area of research. Much of this research has been conducted either in the laboratory, or in relatively uniform canopies such as crops. Efforts to assess the feasibility of the use of hyperspectral analysis in heterogeneous canopies with diverse plant species and canopy structures have been less extensive. In this study, we use in situ and aircraft hyperspectral data to assess several empirical methods for extracting canopy nitrogen from a tallgrass prairie with varying fire and grazing treatments. The remote sensing data were collected four times between May and September in 2011, and were then coupled with the field-measured leaf nitrogen levels for empirical modeling of canopy nitrogen content based on first derivatives, continuum-removed reflectance and ratio-based indices in the 562&ndash;600 nm range. Results indicated that the best-performing model type varied between in situ and aircraft data in different months. However, models from the pooled samples over the growing season with acceptable accuracy suggested that these methods are robust with respect to canopy heterogeneity across spatial and temporal scales.</p>10aheterogeneous canopy10ahyperspectral remote sensing10anitrogen estimates1 aLing, B.H.1 aGoodin, D.G.1 aMohler, R.L.1 aLaws, A.N.1 aJoern, Anthony  uhttps://www.mdpi.com/2072-4292/6/5/4430