RESUMEN
Much interest lies in the identification of manageable habitat variables that affect key vital rates for species of concern. For ground-nesting birds, vegetation surrounding the nest may play an important role in mediating nest success by providing concealment from predators. Height of grasses surrounding the nest is thought to be a driver of nest survival in greater sage-grouse (Centrocercus urophasianus; sage-grouse), a species that has experienced widespread population declines throughout their range. However, a growing body of the literature has found that widely used field methods can produce misleading inference on the relationship between grass height and nest success. Specifically, it has been demonstrated that measuring concealment following nest fate (failure or hatch) introduces a temporal bias whereby successful nests are measured later in the season, on average, than failed nests. This sampling bias can produce inference suggesting a positive effect of grass height on nest survival, though the relationship arises due to the confounding effect of plant phenology, not an effect on predation risk. To test the generality of this finding for sage-grouse, we reanalyzed existing datasets comprising >800 sage-grouse nests from three independent studies across the range where there was a positive relationship found between grass height and nest survival, including two using methods now known to be biased. Correcting for phenology produced equivocal relationships between grass height and sage-grouse nest survival. Viewed in total, evidence for a ubiquitous biological effect of grass height on sage-grouse nest success across time and space is lacking. In light of these findings, a reevaluation of land management guidelines emphasizing specific grass height targets to promote nest success may be merited.
RESUMEN
Livestock grazing affects over 60% of the world's agricultural lands and can influence rangeland ecosystem services and the quantity and quality of wildlife habitat, resulting in changes in biodiversity. Concomitantly, livestock grazing has the potential to be detrimental to some wildlife species while benefiting other rangeland organisms. Many imperiled grouse species require rangeland landscapes that exhibit diverse vegetation structure and composition to complete their life cycle. However, because of declining populations and reduced distributions, grouse are increasingly becoming a worldwide conservation concern. Grouse, as a suite of upland gamebirds, are often considered an umbrella species for other wildlife and thus used as indicators of rangeland health. With a projected increase in demand for livestock products, better information will be required to mitigate the anthropogenic effects of livestock grazing on rangeland biodiversity. To address this need, we completed a data-driven and systematic review of the peer-reviewed literature to determine the current knowledge of the effects of livestock grazing on grouse populations (i.e., chick production and population indices) worldwide. Our meta-analysis revealed an overall negative effect of livestock grazing on grouse populations. Perhaps more importantly, we identified an information void regarding the effects of livestock grazing on the majority of grouse species. Additionally, the reported indirect effects of livestock grazing on grouse species were inconclusive and more reflective of differences in the experimental design of the available studies. Future studies designed to evaluate the direct and indirect effects of livestock grazing on wildlife should document (i) livestock type, (ii) timing and frequency of grazing, (iii) duration, and (iv) stocking rate. Much of this information was lacking in the available published studies we reviewed, but is essential when making comparisons between different livestock grazing management practices and their potential impacts on rangeland biodiversity.
RESUMEN
The upper temperature limits for germination and growth were determined for Metarhizium acridum (ARSEF 324, 3341 and 3609), M. robertsii (ARSEF 2575), M. anisopliae (ARSEF 5749), and Aspergillus nidulans (ATCC 10074). Most of the Metarhizium species germinated well at 35 and 36 degrees C; however, compared to 28 degrees C, the growth was very slow (except ARSEF 5749 from Mexico, which germinated at 35 degrees C, but did not grow at 34 or 36 degrees C). Germination was severely impaired at 38 and 40 degrees C for all Metarhizium species. ARSEF 324 conidia were the most thermotolerant. Based on radial growth measurements, however, none of the M. anisopliae or M. robertsii isolates grew (produced visible colonies) during 10 days at 38 degrees C. All Metarhizium species kept at 38 and 40 degrees C for 10 days resumed growth when transferred to 28 degrees C, and they all sporulated. When the plates were held 10 days at 42 degrees C, however, only the two M. acridum isolates (ARSEF 324 and 3609) grew after returning to 28 degrees C, but with some delay. Conidia germinated at restrictive temperatures, but the growth was impaired or discontinued soon after germination. Nevertheless, when transferred to a permissive temperature, they produced colonies and new conidia. In contrast, the thermophilic A. nidulans germinated and grew well at 42 degrees C, and therefore was much more thermotolerant than any of the Metarhizium spp. isolates.
