Phenological overlap of terrestrial and marine food resources did not reduce salmon consumption by Kodiak brown bears

Climate change is altering the predictability of timing of resource pulses and how consumers interact with them, resulting in phenomena placed under the trophic mismatch hypothesis (TMH). This occurs when a consumer fails to overlap and capitalize on availability of a key food resource pulse. Such changes to predator-prey interactions can alter nutrient transfer, destabilize food webs, and reduce species reproduction and survival. Brown bears (Ursus arctos) on the Kodiak Archipelago, Alaska, USA, have purportedly altered their foraging toward increased use of terrestrial resources under TMH. We examined how the extent of within- and across-year overlap between abundances of Pacific salmon (Oncorhynchus spp.) and berries altered salmon assimilation by brown bears on the Kodiak Archipelago during 2015–2017. We further examined whether salmon consumption differed with brown bear sex and age. We found no decrease in salmon assimilation in response to variation in terrestrial and marine food overlap across and within years. Overall salmon assimilation was high, representing over 60% of brown bear diets in 2015 and 2017, with lower (44%) consumption of salmon in 2016 corresponding with a 28% reduction in salmon abundance. Within years, monthly salmon assimilation was lower in June when salmon began to enter the system, then increased and remained similar during July–October, despite 0–71% within month overlap in peak salmon and berry availability. Older brown bears, particularly males, consumed more salmon than did females and younger bears. While the potential ecosystem impacts of TMH may pose a lesser threat to brown bears than previously reported, possible future declines in Pacific salmon abundance due to climate change may adversely affect North American coastal brown bear populations by reducing abundance of this important food source

Electron impact fragmentation of adenine: partial ionization cross sections for positive fragments

Using computer-controlled data acquisition we have measured mass spectra of positive ions for electron impact on adenine, with electron energies up to 100 eV. Ion yield curves for 50 ions have been obtained and normalized by comparing their sum to the average of calculated total ionization cross sections. Appearance energies have been determined for 37 ions; for 20 ions for the first time. All appearance energies are consistent with the fragmentation pathways identified in the literature. Second onset energies have been determined for 12 fragment ions (for 11 ions for the first time), indicating the occurrence of more than one fragmentation process e.g. for 39 u (C2HN+) and 70 u (C2H4N3+). Matching ion yield shapes (118–120 u, 107–108 u, 91–92 u, and 54–56 u) provide new evidence supporting closely related fragmentation pathways and are attributed to hydrogen rearrangement immediately preceding the fragmentation. We present the first measurement of the ion yield curve of the doubly charged parent ion (67.5 u), with an appearance energy of 23.5 ± 1.0 eV