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1. Assessing seasonal demographic covariation to understand environmental‐change impacts on a hibernating mammal

   https://doi.org/10.1111/ele.13459  

   Paniw, Maria; Childs, Dylan Z.; Armitage, Kenneth B.; Blumstein, Daniel T.; Martin, Julien G. A.; Oli, Madan K.; Ozgul, Arpat; Munch, ed., Stephan (January 2020, Ecology Letters)

   Abstract Natural populations are exposed to seasonal variation in environmental factors that simultaneously affect several demographic rates (survival, development and reproduction). The resulting covariation in these rates determines population dynamics, but accounting for its numerous biotic and abiotic drivers is a significant challenge. Here, we use a factor‐analytic approach to capture partially unobserved drivers of seasonal population dynamics. We use 40 years of individual‐based demography from yellow‐bellied marmots (Marmota flaviventer) to fit and project population models that account for seasonal demographic covariation using a latent variable. We show that this latent variable, by producing positive covariation among winter demographic rates, depicts a measure of environmental quality. Simultaneously, negative responses of winter survival and reproductive‐status change to declining environmental quality result in a higher risk of population quasi‐extinction, regardless of summer demography where recruitment takes place. We demonstrate how complex environmental processes can be summarized to understand population persistence in seasonal environments. 

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2. Is flight initiation distance associated with longer-term survival in yellow-bellied marmots, Marmota flaviventer?

   https://doi.org/10.1016/j.anbehav.2023.05.013  

   Blumstein, Daniel T; Sanchez, McKenna; Philson, Conner S; Bliard, Louis (August 2023, Animal Behaviour)

   The distance at which animals move away from threats, flight initiation distance (FID), is often used to study antipredator behaviour and risk assessment. Variation in FID is explained by a variety of internal and external biotic and physical factors, including anthropogenic activities. Most prior studies focused on unidentified individuals, so our understanding of the fitness consequences of FID is relatively limited. We asked whether consistent individual differences in variation in flight initiation distance is associated with variation in summer survival and/or winter survival in an individually marked population of yellow- bellied marmots. We found no clear association between flight initiation distance and summer sur- vival or winter survival. This suggests that FID decisions, while demonstrably optimizing current survival, may not have longer-term fitness consequences. Our results may be explained by the relatively modest repeatability of FID or it may have emerged from our attempt to explain longer-term measures of fitness. Future studies of the fitness consequences of personality traits should pay particular attention to the time interval between measuring the individuality of a trait and examining its fitness consequences. 

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3. Marmots do not consistently use their left eye to respond to an approaching threat but those that did fled sooner

   Blumstein, D. Diaz (January 2018, Current Zoology)

   In many vertebrates, the brain’s right hemisphere which is connected to the left visual field specializes in the processing of information about threats while the left hemisphere which is connected to the right visual field specializes in the processing of information about conspecifics. This is referred to as hemispheric lateralization. But individuals that are too predictable in their response to predators could have reduced survival and we may expect selection for somewhat unpredictable responses. We studied hemispheric lateralization in yellow-bellied marmots Marmota flaviventer, a social rodent that falls prey to a variety of terrestrial and aerial predators. We first asked if they have lateralized responses to a predatory threat. We then asked if the eye that they used to assess risk influenced their perceptions of risk. We recorded the direction marmots were initially looking and then walked toward them until they fled. We recorded the distance that they responded to our experimental approach by looking, the eye with which they looked at us, and the distance at which they fled (i.e., flight initiation distance; FID). We found that marmots had no eye preference with which they looked at an approaching threat. Furthermore, the population was not comprised of individuals that responded in consistent ways. However, we found that marmots that looked at the approaching person with their left eye had larger FIDs suggesting that risk assessment was influenced by the eye used to monitor the threat. These findings are consistent with selection to make prey less predictable for their predators, despite underlying lateralization. 

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4. OXYGEN AND CARBON ISOTOPES IN ADAMUSSIUM COLBECKI: δ13C PROXY FOR SEA-ICE PERSISTENCE?

   https://doi.org/doi: 10.1130/abs/2020AM-357341  

   Cronin, K.; Walker, S.E.; Gillikin, D.P.; Bowser, S.S. (October 2020, Geological Society of America Abstracts with Programs)

   null (Ed.)

   The Antarctic scallop Adamussium colbecki is a promising proxy for sea-ice persistence and can potentially resolve subannual seawater conditions characteristic of annual and multiannual sea ice. Alternating groups of widely- and narrowly-spaced striae (small ridges on valve surfaces) are thought to indicate seasonal growth differences: wide groups in summer, narrow groups in winter. Shell oxygen (δ18Os) and carbon (δ13Cs) in striae groups may therefore reflect seasonal seawater conditions. We expect lower δ18Os in wide summer striae groups under both annual and multiannual sea ice if glacial meltwater mixes through the water column. We also expect higher δ13Cs in wide striae groups under annual sea ice but not under multiannual sea ice, as phytoplankton blooms post seaice breakout enrich seawater δ13CDIC. Scallops were collected from two sites in western McMurdo Sound (Ross Sea) located ~30 km apart: Explorers Cove (EC) has multiannual sea ice and Bay of Sails (BOS) has annual sea ice. Adults were collected live by divers at 9–18 m depth in 2008 from EC and BOS. Additional juveniles (< 2 yrs) were collected from EC in 2016. Two adults each from EC and BOS and two 2016 juveniles were serially sampled for stable isotopes. δ13Cs decreases over ontogeny due to metabolic effects; the linear trend was removed to enable seasonal comparison. Detrended residuals are referred to as δ13Cs det. Mean δ18Os (~3.7‰) is not different in narrow and wide striae groups under either annual or multiannual sea ice, suggesting negligible glacial meltwater mixing at depth and minimal seasonal temperature change at both sites. δ18Os values are within expected equilibrium range and decrease over ontogeny, suggesting increased growth during warmer temperatures in older scallops. In contrast, mean δ13Cs det is ~1‰ higher in wide summer striae groups than narrow winter striae groups under annual sea ice at BOS, but not different between striae groups under multiannual sea ice in EC adults. δ13Cs det is also higher in wide summer striae groups from 2016 EC juveniles, however sea ice broke out at EC in 2015, so juveniles experienced annual-like sea-ice conditions. Seasonal differences in δ13Cs suggest that carbon isotopes coupled with striae width in A. colbecki may be a good proxy for sea-ice persistence in Antarctica both in modern and fossil assemblages. 

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5. Multi‐cohort survival of northern red oak seedlings at a northern hardwood forest transition

   https://doi.org/10.1002/ecs2.4949  

   Cleavitt, Natalie_L; Battles, John_J; Matthes, Jaclyn_Hatala; Wentzell‐Brehme, Sage (August 2024, Ecosphere)

   Abstract Global change has created less stable forest systems and given urgency to understanding limitations to the establishment of tree seedlings beyond current range boundaries. We quantified trends in 13 years of annual northern red oak (QURU) seedling survival data for 1733 marked individuals at a local species distribution boundary within the northern hardwood forest in New Hampshire, USA. Over the study period, the median distance of seedlings into the valley did not change, although there was a net gain of 89 plots (5 m²) occupied. For a subset of seedlings that were marked in their year of birth (N = 937), we examined relationships among terrain, vegetation community, and initial individual seedling traits, and evaluated their effects on time to seedling mortality using a parametric accelerated failure time model. The year of seedling germination had the largest effect on survival with increasing mortality rates for seedlings from more recent cohorts. Seedlings had longer survival times where oak seedling densities were lower, shrub cover was higher, and when the acorn remained attached. Additionally, survival time was increased in higher elevation plots, which were also located further into the valley. Interannual seedling survival (N = 1580) was strongly impacted by seedling condition in the previous year, particularly leaf number and amount of leaf damage. Most seedling deaths occurred over winter, and seedlings failed to break bud the following spring. Interannual variation in seasonal climate, particularly deep, heavy snowpack in 2019 followed by drought conditions in 2020, coincided with recent elevated mortality. Overall, the median survival time of 3–4 years and the rapid turnover of the oak seedling population currently limit ability for expansion, although the net gain of occupied plots and increase in survival at higher elevation plots with lower QURU densities present some mechanisms that could promote expansion if the current suboptimal understory conditions shift to favor QURU. 

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