Movement and selection by migratory ungulates in dynamic landscapes: plasticity and individual difference in a changing world

A fundamental aspect of many ecological systems is that they fluctuate in habitat quality through time. A common strategy among species is therefore to time reproduction, which is energetically expensive, to when resources are most abundant. A challenge for animals in adopting such a strategy is dealing with environmental change at intra- and inter-annual scales. Within years, migrating individuals can track areas of resource abundance throughout the season to increase energy intake. Alternatively, individuals may time reproduction to coincide with when resources are most abundant, at the cost of being able to track those resources spatially due to young that reduce movement capacity. For either strategy to be successful, individuals must deal with interannual changes in the timing of resource abundance, which threatens to decouple resources and consumers via trophic asynchrony. This is especially important in light of climate change which continues to advance the timing of spring events. Animals or populations can cope with this change in the timing of spring in two ways: individuals can be plastic to change and acclimate their behaviour to annual conditions, and/or populations can adapt if there are consistent differences among individuals in the timing of life-history behaviours that are transmissible across generations, resulting in selective pressures that result in an adaptive response. I tested these ideas in caribou (Rangifer tarandus) in Newfoundland and in migratory herbivores in Wyoming, USA. I demonstrate that caribou follow a gradient of melting snow to time their migrations, and as such give birth during the peak of resource availability (green-up). I then demonstrate that timing of migration and timing of parturition are plastic to timing of melting snow and are correlated. I tested for an effect of forage, conspecific density, and predation risk on calf mortality in two populations of caribou and found that avoidance of predators predicted calf survival in one of the two populations. Finally, I found that migratory ungulates in Wyoming had high repeatability in migration timing and were plastic to the timing of annual green-up. The results of my thesis are overall positive news for the conservation of migratory herbivores faced with changing environmental conditions in the Anthropocene

Collective Autoionization in Multiply-Excited Systems: A novel ionization process observed in Helium Nanodroplets

Free electron lasers (FELs) offer the unprecedented capability to study reaction dynamics and image the structure of complex systems. When multiple photons are absorbed in complex systems, a plasma-like state is formed where many atoms are ionized on a femtosecond timescale. If multiphoton absorption is resonantly-enhanced, the system becomes electronically-excited prior to plasma formation, with subsequent decay paths which have been scarcely investigated to date. Here, we show using helium nanodroplets as an example that these systems can decay by a new type of process, named collective autoionization. In addition, we show that this process is surprisingly efficient, leading to ion abundances much greater than that of direct single-photon ionization. This novel collective ionization process is expected to be important in many other complex systems, e.g. macromolecules and nanoparticles, exposed to high intensity radiation fields

Temporal aspects of polar bear occurrences at field camps in Wapusk National Park, Canada

Wapusk National Park, University of Manitoba, University of Saskatchewan, the Social Sciences and Humanities Research Council of Canada, Hudson Bay Helicopters, the Churchill Northern Studies Centre, and EarthRangers.Interaction between polar bears (Ursus maritimus) and people is a growing concern for both bear conservation and human safety in a warming Arctic climate. Consequently, the importance of monitoring temporal trends in the proximity of polar bears to people has become critical in managing human-polar bear conflicts. Such concerns are acute in Wapusk National Park in Manitoba, Canada on the Western Hudson Bay coast, where we deployed 18 camera traps at three remote field camps from 2010–2014 (~22,100 camera-days) to monitor the frequency and timing of bears’ visits to those facilities. Following seasonal breakup of Hudson Bay’s sea ice polar bear occurrences at these camps increased throughout the summer and into fall (low in May–July and increasing sharply through August–November and then approaching zero in December when Hudson Bay freezes). We quantified age and sex class and estimated body condition of bears visiting the camps: adult males were most prevalent at Nester One camp close to where adult males congregate at Cape Churchill, whereas the two camps farther south were visited more frequently by females with dependent young, likely traveling to and from a known maternal denning area. Few subadults were observed. As expected, body condition scores declined throughout the on-shore season. Our method of monitoring polar bear occurrence on shore is robust, cost-effective, and non-invasive, and so may provide an economical complement to data gathered through more conventional techniques

Matter-gravity interaction in a multiply warped braneworld,

The role of a bulk graviton in predicting the signature of extra dimensions through collider-based experiments is explored in the context of a multiply warped spacetime. In particular it is shown that in a doubly warped braneworld model, the presence of the sixth dimension, results in enhanced concentration of graviton Kaluza Klein (KK) modes compared to that obtained in the usual 5-dimensional Randall-Sundrum model. Also, the couplings of these massive graviton KK modes with the matter fields on the visible brane turn out to be appreciably larger than that in the corresponding 5- dimensional model. The significance of these results are discussed in the context of KK graviton search at the Large Hadron Collider (LHC).Comment: 13 pages, 2 table

Conceptual and methodological advances in habitat-selection modeling: guidelines for ecology and evolution

Habitat selection is a fundamental animal behavior that shapes a wide range of ecological processes, including animal movement, nutrient transfer, trophic dynamics and population distribution. Although habitat selection has been a focus of ecological studies for decades, technological, conceptual and methodological advances over the last 20 yr have led to a surge in studies addressing this process. Despite the substantial literature focused on quantifying the habitat-selection patterns of animals, there is a marked lack of guidance on best analytical practices. The conceptual foundations of the most commonly applied modeling frameworks can be confusing even to those well versed in their application. Furthermore, there has yet to be a synthesis of the advances made over the last 20 yr. Therefore, there is a need for both synthesis of the current state of knowledge on habitat selection, and guidance for those seeking to study this process. Here, we provide an approachable overview and synthesis of the literature on habitat-selection analyses (HSAs) conducted using selection functions, which are by far the most applied modeling framework for understanding the habitat-selection process. This review is purposefully non-technical and focused on understanding without heavy mathematical and statistical notation, which can confuse many practitioners. We offer an overview and history of HSAs, describing the tortuous conceptual path to our current understanding. Through this overview, we also aim to address the areas of greatest confusion in the literature. We synthesize the literature outlining the most exciting conceptual advances in the field of habitat-selection modeling, discussing the substantial ecological and evolutionary inference that can be made using contemporary techniques. We aim for this paper to provide clarity for those navigating the complex literature on HSAs while acting as a reference and best practices guide for practitioners

Two-Stage Rotational Disordering of a Molecular Crystal Surface: C60

We propose a two-stage mechanism for the rotational surface disordering phase transition of a molecular crystal, as realized in C$_{60}$ fullerite. Our study, based on Monte Carlo simulations, uncovers the existence of a new intermediate regime, between a low temperature ordered $(2 \times 2)$ state, and a high temperature $(1 \times 1)$ disordered phase. In the intermediate regime there is partial disorder, strongest for a subset of particularly frustrated surface molecules. These concepts and calculations provide a coherent understanding of experimental observations, with possible extension to other molecular crystal surfaces.Comment: 4 pages, 2 figure

Real-time dynamics of the formation of hydrated electrons upon irradiation of water clusters with extreme ultraviolet light

Free electrons in a polar liquid can form a bound state via interaction with the molecular environment. This so-called hydrated electron state in water is of fundamental importance e.g.~in cellular biology or radiation chemistry. Hydrated electrons are highly reactive radicals that can either directly interact with DNA or enzymes, or form highly excited hydrogen (H∗) after being captured by protons. Here, we investigate the formation of the hydrated electron in real-time employing XUV femtosecond pulses from a free electron laser, in this way observing the initial steps of the hydration process. Using time-resolved photoelectron spectroscopy we find formation timescales in the low picosecond range and resolve the prominent dynamics of forming excited hydrogen states