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Improved estimation of temporal dynamics in the ASCAT backscatter-incidence angle relation using regularization
Get PDFThe relation between microwave backscatter and incidence angle estimated from observations of the Advanced Scatterometer (ASCAT) onboard the Metop satellites contains valuable information on the dynamics of vegetation water content and structure. The relation between backscatter and incidence angle (parameterized using so-called slope and curvature parameter) has been related to vegetation water dynamics in studies on the North American Grasslands and the Cerrado Savannah. The current approach to estimate time series of the slope and curvature parameters involves a kernel smoother, weighing observations according to their temporal distance to the day of interest. While this approach provides a robust representation of backscatter-incidence angle relation over longer time scales, it does not accurately capture the timing of short-term changes. To further improve the correspondence between backscatter-incidence angle relation and vegetation water dynamics, the timing of short-term changes should be preserved in the estimation of slope and curvature. This would allow slope and curvature to be reconciled with independent estimates of biogeophysical variables, and allow us to isolate high-frequency variations due to, for example, intercepted precipitation or soil moisture. Here, an alternative method is introduced to estimate the ASCAT backscatter-incidence angle relation using temporally constrained least squares. While the proposed method yields similar performance to the kernel smoother in aggregated statistics, this method retains the timing of short-term changes
Beneath the buzz: quantifying nest locations and densities of ground‐nesting wild bees (Hymenoptera: Anthophila)
Get PDFWild bees (Hymenoptera: Anthophila) are important pollinators and essential for maintaining ecosystem health. The majority of bee species are ground-nesting, and all bees spend most of their lifetime inside the nest. Still, most studies and monitoring schemes assess wild bees during flower visitation, allowing no conclusion about their nest sites. Methods for locating and assessing the ground nests of bees are currently limited, hindering scientific progress and conservation efforts.
To evaluate and improve methods for locating and assessing ground nests, we combined information from a literature review and our own empirical studies. Methods ranging from established field methods (visual nest observations and emergence traps) to new technological approaches (marking and tracking individuals) are compared in terms of success in catching nesting bees and identifying nest locations, time effort required to implement the methods, and limitations.
We provide guidelines and recommendations on the use of the different methods depending on the data requirements and study locations. We also present a novel emergence trap design and two newly developed marking methods, using a radioactive tracer substance and a retroreflective pigment, and show that these methods can be used to successfully locate and assess ground-nesting habitats of bees.
With this work, we address gaps in current research methods and aim to enhance the efficiency of field research that explicitly targets ground-nesting bees and their nest sites in various environments. By providing a comprehensive overview for researchers and practitioners, we demonstrate how to improve knowledge about the ecology and life history of ground-nesting bees and thus support efforts for their conservation
Fractured Britannia: the twilight of Roman Britain
No full textThis thesis provides an in-depth examination of the distribution of coinage and elite items of
Roman dress in later and sub-Roman Britain. Previous research has often sought to
distinguish various groups serving the Roman state, yet identifying these groups in the
archaeological record remains challenging. Both the military and the bureaucracy were
ranked as soldiers and used similar objects to denote their status. Furthermore, the local elite,
responsible for much of the day-to-day administration, began to adopt military fashions,
leading to an evolution of dress accessories throughout the fourth century.
Five extensive datasets (404 crossbow brooches, 1,334 belt fittings, 86 spurs, 454 penannular
brooches and 489,867 Roman coins) are collated and explored holistically, materials which
previously have only been studied in isolation. These datasets lend themselves to a big data
approach through systematic examination in combination as these objects, with their
prolonged lifespans, provide insights into social and political changes. Evidence suggests that
while some regions continued relatively unchanged into the fifth century, other parts of
Britain abandoned Roman forms of material culture as early as AD 375.
This evaluation of a broad range of material culture offers new perspectives on a critical
phase of the history of Britain, marked by the transition from a fully integrated Roman
diocese to smaller post-Roman polities. The study delves into how material culture and
specific forms of clothing were used to highlight status and identity within the later Roman
world. By evaluating methodologies and revising typologies, the thesis details the geographic
and site category distributions of various artefacts, pulling out key patterns in the data and
making huge datasets publicly available. Ultimately, the thesis provides a chronological and
geographic framework, analyses differential use of material across different site types and
compares these patterns to those on the continent, thereby shedding light on the
transformation of Roman Britain into the sub-Roman and early-medieval world
Unravelling the facilitation-competition continuum among ectomycorrhizal and saprotrophic fungi
Get PDFSoil fungal inter-guild interactions may impact ecosystem processes significantly. In particular, competition between ectomycorrhizal and saprotrophic fungi could reduce organic matter decomposition through the “Gadgil effect”. Whether fungal facilitative and competitive interactions predictably shift under moderate environmental stress, as hypothesised by the stress-gradient hypothesis (SGH), is still uncertain, particularly across multiple environmental resource gradients. Here, we quantified reciprocal interactions among fungal guilds in root tips and soil mycelia in 84 temperate forests of various tree compositions comprising a natural gradient of soil fertility and root carbon resources. The two resource gradients were negatively related. In keeping with SGH, we found that the typical interactions between fungal guilds were symmetrically positive at the lowest end of both gradients. These findings corroborate enhanced decomposition, indicating a facilitative effect generated by the ectomycorrhizal and saprotrophic fungal positive interactions. Inter-guild interactions varied with the spatial habitat and resource type gradient, with root carbon resources more strongly influencing root tip than soil mycelium communities. When both gradients were integrated, SGH held for the dominant gradient in the system. The premises of the “Gadgil effect” became apparent in the more fertile soils, but under higher C/N ratios, certain ectomycorrhizal groups, including taxa capable of mobilising nitrogen from complex organic substrates, exerted negative effects on saprotrophic fungi. Under lower soil pH and in drier, warmer climates resembling global change scenarios, soil fungal guilds positively influence each other. These interactions potentially aid in the preservation of soil biodiversity and the support of forest ecosystem function
A scoping review of evidence for the effects of seven global deer species on woody vegetation
Get PDFContext: Rapid expansion of deer (Cervidae) populations is a concern for forest ecosystems. Despite extensive reviews on how deer affect forests, variation in effects across deer species has received less attention. A lack of focus on species‐specific effects may lead to oversights and failure to achieve desired management outcomes. Methodology: We used a systematic approach to compile data on the extent to which the effects of seven deer species on woody vegetation have been studied. We focused on the six deer species present in Britain and Ireland, and elk (Cervus canadensis). Results: A total of 455 studies were included from across the globe. Red deer (Cervus elaphus) (n = 163) and elk (n = 158) were the most studied species, while Reeve's muntjac (Muntiacus reevesi) (n = 18) and Chinese water deer (Hydropotes inermis) (n = 5) were the least researched. Fifty‐four per cent of studies (n = 245) used fenced exclosures to assess deer impacts. Research mainly focused on defoliation via browsing and grazing (n = 424), while debarking (n = 44), defecation (n = 8) and trampling (n = 5) were less frequently studied. Vegetation density (n = 235), height (n = 189) and diversity (n = 135) were the most common metrics used, while fewer studies focused on vegetation mortality (n = 74), structural variability (n = 28) and condition (n = 15). Practical implication: While previous studies have often focused on the probability or severity of deer damage to woody vegetation, we identified key knowledge gaps on the ecological influence of such damage, with a species‐specific focus. Researchers should treat deer species as distinct entities and appreciate the differences in their body size, sociality, physiology and behaviour when studying their ecological effects. Where multiple deer species co‐occur, identifying relative local species abundance and differences among species foraging behaviours will help to determine how their interactions—whether additive, synergistic or antagonistic—affect ecosystem processes and vegetation dynamics
Hedge fund performance, classification with machine learning, and managerial implications
Get PDFPrior academic research on hedge funds focuses predominately on fund strategies in relation to market timing, stock picking, and performance persistence, among others. However, the hedge fund industry lacks a universal classification scheme for strategies, leading to potentially biased fund classifications and inaccurate expectations of hedge fund performance. This paper uses machine learning techniques to address this issue. First, it examines whether the reported fund strategies are consistent with their performance. Second, it examines the potential impact of hedge fund classification on managerial decision making. Our results suggest that for most reported strategies there is no alignment with fund performance. Classification matters in terms of abnormal returns and risk exposures, although the market factor remains consistently the most important exposure for most clusters and strategies. An important policy implication of our study is that the classification of hedge funds affects asset and portfolio allocation decisions, and the construction of the benchmarks against which performance is judged
Hydra-LSTM: a semi-shared machine learning architecture for prediction across watersheds
Get PDFLong Short Term Memory networks (LSTMs) are used to build single models that predict river discharge across many catchments. These models offer greater accuracy than
models trained on each catchment independently, if the same variables are used as inputs for each catchment. However, the same data is rarely available for all catchments. This prevents the use of variables available only in some catchments, such as historic river discharge or upstream discharge.
The only existing method that allows for optional variables requires all variables to be in the initial training of the model, limiting its transferability to new catchments. To address this limitation, we
develop the Hydra-LSTM. The Hydra-LSTM is able to use some variables across all catchments
to make predictions, and use further variables in other catchments where they are helpful and
available. This allows general training and the use of catchment-specific data. The bulk of the
model can be shared across catchments, maintaining the benefits of multi-catchment models to
generalize while also benefiting from the using bespoke data. We apply this methodology to 2
day-ahead river discharge prediction in the Western US, a small enough time step to expect our
models to be skilful and difficult enough to expect differences between models. We obtain more accurate quantile predictions than Multi-Catchment and Single-Catchment LSTMs while allowing forecasters to introduce and remove variables from their prediction set. We test the ability of the
Hydra-LSTM to incorporate catchment-specific data,
introducing historical river discharge as a catchment-specific input, outperforming other commonly used models
Harmony in political discourse? The impact of high-quality listening on speakers’ perceptions following political conversations
Get PDFConversations with people who hold opposite partisan attitudes can elicit defensiveness, reinforce extreme attitudes, and undermine relationships with those with opposing views. However, this might not be the case when speakers experience high-quality (attentive, understanding, and non-judgmental) listening from their conversation partners. We hypothesized that high-quality listening would increase speakers’ positive views toward, and their willingness to further interact with, others who hold politically opposed attitudes, and that these effects would be mediated by greater state openness. We conducted three experiments using different modalities to manipulate listening. In Study 1 (N = 379), participants recalled a conversation with an opposing political party member, with listening quality described as high-quality, low-quality, or control. Study 2 (N = 269) used imagined interactions, with participants reading vignettes describing either high-quality listening or a control condition. In Study 3 (preregistered; N = 741), participants watched a video of a listener modeling high-quality or moderate-quality listening and imagined themselves engaging in a similar interaction. Across studies, we found that high-quality listening consistently increased speakers’ state openness to politically opposed others but did not change political attitudes. We found inconsistent evidence for speakers’ increased willingness to engage in future interactions (meta-analytic effect: = 0.20, p = 0.015). However, we observed a consistent indirect effect of listening on positive attitudes and willingness for future interactions through increased openness