Although climate change is a global phenomenon, the Arctic is warming faster than any other region on earth. These climatic changes have driven rapid regional changes over the past half-century in both the physical landscape and the ecosystems therein. One such ecological interaction is between migratory shorebird survival and local insect emergence. Annually, tens of millions of migratory shorebirds travel to the Arctic to rear their young in the relative absence of predators, but in a relative abundance of food (insects). Over evolutionary time, these trophic levels have coupled: shorebird chicks tend to hatch during the period of highest terrestrial insect availability. However, climate change is currently uncoupling this food-web synchrony, creating potential for trophic mismatch. In the High Arctic near Utqiaġvik (formerly Barrow), Alaska, trophic mismatch between nesting shorebirds and their insect food base is already detectable. In this ecosystem, flies in the Family Chironomidae (non-biting midges) dominate the prey trophic level in the avian food web. We have found that the pre-emergence development of one particular midge, Trichotanypus alaskensis, defies conventional wisdom of the Family, as this species molts to an additional fifth larval instar prior to pupation and emergence (all other chironomids are known to have four larval instars). We discovered an Utqiaġvik midge that reproduces asexually, a species that was not documented in the 1970s. Utilizing controlled temperature rearings of Utqiaġvik midge larvae, we discovered that as temperatures rise, emerging chironomid adults are generally smaller in size. We have found that chironomid pre-emergence developmental rates follow a positive exponential relationship as temperatures increase, can vary by taxon, yet are consistent across field and lab settings for a given taxon. At Utqiaġvik in the 2010s, chironomid emergence occurs 8-12 days earlier than it did in the 1970s. These findings shape our understanding of trophic mismatch in this arctic food web. / Arctic Landscape Conservation Cooperative; NDSU Graduate School Dissertation Fellowship; U.S. National Fish and Wildlife Foundation; Environmental and Conservation Sciences Program; Department of Biological Sciences

There is ample evidence that climate change is impacting on phenology and it has been suggested that this may generate trophic mismatches. A key system for investigating phenology and trophic mismatch occurs in spring in temperate deciduous woodlands, where folivorous caterpillars and their predators, insectivorous passerines, are reliant upon ephemeral resources for reproductive success and survival. However, studies are primarily conducted within single-site, oak- (Quercus sp) dominated woodland and focus on a single caterpillar species, winter moth (Operophtera brumata), despite these passerines being habitat generalists with large geographic ranges. It remains to be seen whether insights gained from these studies can be generalised on the landscape scale across different habitats. In this thesis, I explore the extent to which geographic and habitat variation operates in this system and attempt to expand the system beyond a linear single-species food chain into a more biologically realistic multi-species food web. I also identify the most important environmental factors predicting the phenology of the passerines to allow better predictions of how their phenology could alter under future climate change scenarios. To address these questions, I established a novel 220km transect of Scotland incorporating 40 field sites that vary in elevation and the type of deciduous woodland habitat, monitoring six blue tit (Cyanistes caeruleus) nestboxes, tree and invertebrate phenology and abundance, at each site throughout the springs of 2014-16. Firstly, I assess how blue tit occupancy and productivity are affected by the variation in fine-scale woodland habitat, latitude, elevation and prey availability that exists along the transect (Chapter 2). I find that habitat variables strongly affect fledging success but not occupancy or clutch size, whilst occupancy exhibits biogeographic trends, revealing that the relationship between breeding decisions and outcomes differs among habitats and implies that it may be difficult to generalise results from one habitat to others. Next, I aim to identify the environmental aspects which play a role in regulating blue tit reproductive phenology by examining the ability of temperature, tree phenology, invertebrate prey abundance and photoperiod to predict nest initiation and laying dates (Chapter 3). I find that night-time temperature in early spring is the most important predictor of both nest initiation and lay date (slopes ~ -3days/°C) and I suggest that this supports the hypothesis that temperature acts as a constraint on timing rather than a cue. Invertebrate abundance is also a positive correlate of lay date, possibly allowing fine-tuning of timing. This knowledge provides clearer foundations from which to predict future phenological change and possible trophic mismatch in this system. There is the potential that the apparent effect of temperature on blue tit reproductive phenology is indirect and mediated by diet, which is largely undescribed in the period prior to breeding. Therefore, in Chapter 4 I examine how blue tit diet varies across habitat, geography and time, and whether there is a dietary cue utilised to initiate breeding phenology, using data from metabarcoding faeces collected from nestbox-roosting adults in early spring. Geographic variation in diet is substantial, with high site-to-site dietary turnover (β-diversity), as well as high turnover along the elevational and latitudinal gradients studied. Dietary α-diversity (richness) is unaffected by geographical variables, but increases over time, with significant pre-breeding dietary increases in Lepidoptera and Hemiptera signifying a possible cue. In addition, these data provide the most comprehensive next-generation insights into the diet of a wild bird to date and identify 432 prey taxa. Finally, I analyse how biogeographic and habitat variables affect the phenology, abundance and diversity of caterpillars (Chapter 5). Host tree species’ varied significantly in their likelihood of hosting a caterpillar, with oak and willow (Salix sp.) the most likely. Biogeography had less effect on the likelihood of caterpillar occurrence, but elevation delayed peak date by 3.7 days/100m increase. There was also support for the spring caterpillar peak being dominated by a few key species, with over half of all caterpillars identified being of just three of the 62 total species, including winter moth. These findings contribute to understanding how the temporal distribution of caterpillars varies across habitats on the landscape scale. Taken together, the findings of this thesis reveal considerable geographic and habitat variation throughout this system, in both the composition of the food web and the impacts on blue tit productivity, demonstrating why caution must be exercised when extrapolating findings from one location or habitat to others.

Studier visar att dagens elever känner oro inför framtiden och de klimatförändringar vår värld utsätts för. Skolverkets nationella kartläggning utav miljöundervisning i skolan visar dock att cirka hälften av de tillfrågade gymnasielärarna inte bedriver någon undervisning i ämnet. Denna studie beskriver en alternativ modell för undervisning i klimatfrågor. Elever ges genom modellering av ekosystem möjlighet att fördjupa sin förståelse kring klimatförändringar i samband med exploatering av topp-predatorer. Detta är ett realistiskt problem då en mängd studier visar att dagens ekosystem utsätts för en mängd stressfaktorer, med ursprung i klimatförändringar, och att exploatering av topp-predatorer kan leda till konsekvenser med artutdöende som följd. Modellen som används i undersökningen är en generell Lotka-Volterra-modell vilken fungerar som analytiskt verktyg. Skolverket betonar matematikens roll som ämnesöverskridande verktyg och modellekosystem ger elever möjlighet att använda matematiska kunskaper i ett verkligt scenario. I studien undersöks även hur pass stor exploatering topp-predatorer kan utsättas för i takt med ökade klimatförändringar. De undersökta områdena inbegriper tre- och fyr-artssystem i marina och terrestra miljöer. Resultaten visar att exploateringen måste minska i takt med ökade klimatorsakade förändringar i samtliga fall, undantag terrestra tre-artsystem som utsätts för förändrade interaktionsstyrkor. / Studies show that today's students are worried about the future and the increasing climate change. A survey made by the Swedish National Agency for Education about environmental education shows that approximately half of the surveyed secondary school teachers are not engaged in teaching in the field. This study describes an alternative model for teaching environmental issues. Students are by the modeling of ecosystem given an opportunity to deepen their understanding of climate change associated with the exploitation of top predators. This is a realistic problem, numerous studies show that today's ecosystems are exposed to a variety of stressors, with the origin of climate change, and the exploitation of top predators can lead to serious consequences with extinction as a result. The model used in this study is a generalized Lotka-Volterra model which works as an analytical tool. The Swedish National Agency for Education emphasizes the role of mathematics as interdisciplinary tools and model ecosystem gives students the opportunity to use math skills in a real scenario. The study also investigated how much exploitation top predators can be exposed to in line with increased climate change. The research sites include three-and four-species system of marine and terrestrial environments. The results show that the exploitation must be reduced in line with increased climate-caused changes in all cases, except terrestrial three-species system exposed to changes in interaction strengths.

There is concern that climate change may cause mismatches between timing of flowering and activity of pollinators (phenology). However, concluding that mismatches will occur, and have serious consequences for pollination services, requires assumptions that have not yet been tested. I begin by discussing a set of these assumptions, bringing past research into the context of mismatch. Briefly, the assumptions are that 1) dates of first-flowering or emergence (DFFE) correctly describe phenology (and therefore mismatch); 2) differences in DFFE represent the magnitude of mismatch; 3) advancement of DFFE will be the primary phenological change; 4) shifts will be random and independent for each species; 5) populations of plants and pollinators are “bottom-up” regulated by their mutualistic interactions; 6) all interactions are of similar strength and importance; 7) dispersal, and the spatial context of phenological mismatches can be ignored; and ecological processes including 8) phenotypic plasticity and adaptive evolution of phenology, 9) competition and facilitation, and 10) emergence of novel interactions, will not affect mismatches. I then describe novel experiments, which could help to account for some of these assumptions, clarifying the existence and impacts of mismatches. Next, I present an original field experiment on factors affecting seed set in an alpine meadow in the Coast Range of British Columbia, Canada. I found evidence contradicting the assumption that seed set is primarily limited by pollination. My data highlight the roles of phenology, temperature (degree-days above 15°C, and frost hours), and interactions with pollinators (mutualists) and seed-predators (floral antagonists) in driving patterns of seed set. Seed set of early and late-flowering species responded differently to a 400m elevation gradient, which might be explained by phenology of bumble bees. My data suggest that the consequences of mismatch may be smallest for plants that are fly-pollinated and self-fertile. Non-selfing, bee-pollinated species might be more prone to reproductive limitation through mismatch (affected by snowmelt and cumulative degree-days). Plants that are limited by seed-predators might be negatively affected by warming temperatures with fewer frost hours, and extreme events such as late-season frosts and hail storms can prevent plants from setting seed entirely. Overall, my work emphasizes the importance of complementing theory, data-driven simulations, and meta-analyses with experiments carried out in the field. / Graduate