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A statistical framework for camera trap data analysis in ecological research
No full textThe Anthropocene is characterized by accelerating extinction rates of
many species, but at the same time other species are increasing their geographic
ranges and growing in population size. Some of these species that thrive in our
increasingly anthropogenic world are causing human wildlife interactions. Because
many of these interactions are perceived as negative and conflicting with human
interest, an evidence-based management aimed at conflict mitigation is
warranted. In this dissertation, I studied wild boar (Sus scrofa) in several areas,
where the species was actively managed, often through hunting. In addition, the
work in this dissertation focused on the optimal application of statistical
methodology to account for false-negatives on other common sources of bias in
assessing occupancy and abundance of wildlife.
Wild boar were studied using wildlife cameras, often referred to as camera
traps, which ensured that the species and its environment were minimally
disturbed. Photographs derived from these camera traps were annotated and
analysed using Bayesian hierarchical population models. Specifically, I applied
occupancy and N-mixture models, often in combination with statistical methods
that allowed the flexible modelling of spatial, temporal or spatiotemporal patterns
in occupancy or abundance. Through these results, I found that (i) African swine
fever (ASF), culling, and other ASF-related management actions led to strong
population declines of wild boar in the south of Belgium. Moreover, I report that
camera traps were a useful tool in the monitoring of wild boar population trends
during an ASF epidemic; (ii) Site-structured hierarchical models for the estimation
of animal abundance could only be used to produce reliable insights in relative
trends in abundance. Hence, they should not be used to obtain absolute
abundances; (iii) Hunting pressure did not appear to influence the space use of
wild boar in an agro-ecosystem. Non-lethal human disturbance on the other hand
appeared to have a stronger impact on wild boar space use; (iv) Trends and rankorder patterns between different camera-based estimators could often be
compared when the variability is large, but may not be compared when variability
is small; (v) Wild boar dynamically changed their space use across the diel cycle in an agro-ecosystem. However, the driving factors behind these changes
remained uncertain.
Following the results of my study, the lack in strong scientific knowledge
on the impacts of management actions on wild boar becomes apparent. Among
other things, it remains uncertain, or it depends on the area, whether hunting
and/or non-lethal human activities change the spatial behaviour of wild boar.
Furthermore, the statistical tools used to assess absolute animal abundances often
suffer from biases in real life settings. Thus, further work towards improving
abundance estimators for unmarked animal populations remains essential.Het Anthropoceen wordt gekenmerkt door het steeds sneller uitsterven
van diersoorten, tegelijkertijd zijn er enkele diersoorten wiens geografische
gebied en populatiegrootte toeneemt. Soorten die succesvol zijn in een wereld die
alsmaar meer door de mens beïnvloed is, leiden regelmatig tot dier-mens
interacties. Omdat veel van deze dier-mens interacties als negatief worden
ervaren en leiden tot conflicten met menselijke belangen is er nood aan een op
evidentie gebaseerd beheer van deze soorten. In deze thesis, heb ik het everzwijn
(Sus scrofa) bestudeerd in verscheidene gebieden, waar de soort onderworpen
was aan wildbeheer, vaak door middel van jacht. Daarnaast, focust deze thesis
zich op de optimale toepassing van statistische methoden, die gericht zijn op het
evalueren van de ruimtelijke verdeling en abundantie van wild en die tevens
corrigeren voor imperfecte detectie en andere bronnen van bias.
Het everzwijn werd bestudeerd aan de hand van wild camera’s, ook
cameravallen genaamd, wat ervoor zorgde dat de diersoorten en hun omgeving
minimaal verstoord werden. Specifiek, paste ik occupancy en N-mixture modellen
toe, vaak in combinatie met statistische methoden die het toelaten om spatiale,
temporele of spatio-temporele patronen in ruimtelijke verspreiding of abundantie
flexibel te modelleren. Aan de hand van mijn resultaten, vond ik dat (i) Afrikaanse
varkenspest (ASF), gerichte jacht en andere ASF-gerelateerde beheeracties leidde
tot een sterke populatieafname van het everzwijn in het zuiden van België.
Daarnaast, rapporteerde ik dat cameravallen nuttige middelen zijn in het
monitoren van everzwijn populaties tijdens een ASF epidemie; (ii) Hiërarchische
modellen voor het schatten van abundantie konden enkel gebruikt worden om
betrouwbare schatting van relatieve trends in abundantie te verkrijgen. Dus, ze
dienen niet gebruikt te worden om absolute abundantie mee te verkrijgen; (iii)
Jachtdruk leek geen impact te hebben op het ruimtegebruik van het everzwijn in
een agro-ecosysteem. Niet-lethale menselijke verstoring daarentegen leek het
ruimtegebruik van het everzwijn wel te beïnvloeden; (iv) Trends en rangorde
patronen tussen verschillende camera-gebaseerde schatters kunnen vaak direct
vergeleken worden als de variabiliteit groot is, maar niet wanneer deze gering is;
(v) Everzwijn veranderde zijn ruimtegebruik doorheen een 24-uur cyclus in een agro-ecosyteem. Hoewel, de drijvende factoren achter deze veranderingen
onduidelijk blijven.
Uit de resultaten van mijn studie leid ik af dat er een tekort is aan
wetenschappelijke kennis wat betreft de impact van wildbeheer op het ruimtelijke
gedrag van het everzwijn. Zo blijft het onduidelijk, of het hangt af van het gebied,
of jacht en/of niet-lethale menselijke activiteiten veranderingen in het
ruimtegebruik van het everzwijn veroorzaken. Verder zijn statistische methoden
gebruikt voor het schatten van absolute abundantie van dieren vaak onderworpen
aan verschillende vormen van bias. In de toekomst blijft het dus essentieel om
verder in te zetten op methodologische verbeteringen in het schatten van de
abundantie van ongemarkeerde dieren
Simulation-based assessment of the performance of hierarchical abundance estimators for camera trap surveys of unmarked species
No full textKnowledge on animal abundances is essential in ecology, but is complicated by low detectability of many species. This has led to a widespread use of hierarchical models (HMs) for species abundance, which are also commonly applied in the context of nature areas studied by camera traps (CTs). However, the best choice among these models is unclear, particularly based on how they perform in the face of complicating features of realistic populations, including: movements relative to sites, multiple detections of unmarked individuals within a single survey, and low detectability. We conducted a simulation-based comparison of three HMs (Royle-Nichols, binomial N-mixture and Poisson N-mixture model) by generating groups of unmarked individuals moving according to a bivariate Ornstein-Uhlenbeck process, monitored by CTs. Under a range of simulated scenarios, none of the HMs consistently yielded accurate abundances. Yet, the Poisson N-mixture model performed well when animals did move across sites, despite accidental double counting of individuals. Absolute abundances were better captured by Royle-Nichols and Poisson N-mixture models, while a binomial N-mixture model better estimated the actual number of individuals that used a site. The best performance of all HMs was observed when estimating relative trends in abundance, which were captured with similar accuracy across these models.MB is a PhD fellow funded by a BOF mandate at Hasselt University. TN gratefully acknowledges the Research Foundation – Flanders [Grant Number G0A4121N] and by the Internal Funds KU Leuven [project number
3M190682]. Te resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation—Flanders (FWO) and the Flemish Government.
We would like to express our gratitude towards Marc Kéry for his feedback on an early draf of our work. Furthermore, we are grateful for the valuable comments of two anonymous reviewers. Together, their feedback has
improved the clarity and quality of the pape
Impacts of zoning and landscape structure on the relative abundance of wild boar assessed through a Bayesian N-mixture model
No full textIncreasing human-wild boar interactions have led to damage to agricultural crops, traffic collisions and disease transmissions. Dividing natural areas in zones with differential hunting pressure is one of the currently adopted management strategies. However, the effectiveness of this approach is under debate. Hence, there is a need to better understand how to mitigate negative human-wild boar interactions effectively.Camera traps are cost-efficient, and non-invasive tools to monitor animal populations. N-mixture models can reliably estimate spatial variation in relative abundances when animals are imperfectly detected and/or cannot be individually identified. Thus, they are useful tools to infer the impacts of several factors on the land-use intensity of wild boar, based on camera trap data. In a nature area in central Belgium, we compare "summer" (April-September) land-use intensity of wild boar from 2018 until 2021 between three zones: a hunting free core zone, a winter hunting zone where hunting only takes place between November and March, and a year-round hunting zone. The latter is also close to the forest edge, agricultural crops and settlements. We compare spatial abundance models that capture these zone effects, or attractive effects of croplands, repulsive effects of hunting and repulsive effects of non-lethal human disturbances.We reveal between zone differences in wild boar land-use intensities across all summers. Additionally, we find that non-lethal human disturbance and croplands also explain variation in wild boar land-use intensity, but do not find negative associations with hunting locations. Our results suggest that the effects of zoning on wild boar land-use patterns are relevant in medium-sized natural areas. Moreover, we identify the need to install additional cameras outside of the managed area in order to assess the impacts of hunting in combination with non-lethal human activities on wild boar to mitigate negative human-wild boar interactions in the future.Research Foundation Flanders (FWO) [G0A4121N]; Flemish Government; BO
When and where? Day-night alterations in wild boar space use captured by a generalized additive mixed model
No full textWild boar (Sus scrofa), an abundant species across Europe, is often subjected to management in agro-ecosystems in order to control population size, or to scare them away from agricultural fields to safeguard crop yields. Wild boar management can benefit from a better understanding on changes in its space use across the diel cycle (i.e., diel space use) in relation to variable hunting pressures or other factors. Here, we estimate wild boar diel space use in an agro-ecosystem in central Belgium during four consecutive "growing seasons"(i.e., April-September). To achieve this, we fit generalized additive mixed models (GAMMs) to camera trap data of wild boar aggregated over 1-h periods. Our results reveal that wild boar are predominantly nocturnal in all of the hunting management zones in Meerdaal, with activity peaks around sunrise and sunset. Hunting events in our study area tend to take place around sunrise and sunset, while non -lethal human activities occur during sunlight hours. Our GAMM reveals that wild boar use different areas throughout the diel cycle. During the day, wild boar utilized areas in the centre of the forest, possibly to avoid human activities during daytime. During the night, they foraged near (or in) agricultural fields. A post hoc comparison of space use maps of wild boar in Meerdaal revealed that their diurnal and nocturnal space use were uncorrelated. We did not find sufficient evidence to prove that wild boar spatiotemporally avoid hunters. Finally, our work reveals the potential of GAMMs to model variation in space across 24-h periods from camera trap data, an application that will be useful to address a range of ecological questions. However, to test the robustness of this approach we advise that it should be compared against telemetry -based methods to derive diel space use.Funding
This work makes use of data and/or infrastructure provided by INBO and funded by Research Foundation-Flanders (FWO) as part of the Belgian contribution to LifeWatch. Martijn Bollen is a PhD fellow funded by a BOF mandate at Hasselt University. Thomas Neyens received funding from the FWO (G0A4121N) and from the Internal Funds KU Leuven (project number 3M190682). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
ACKNOWLEDGEMENTS
We are grateful to the Flemish Agency for Nature and Forest and the local nature conservation NGO ‘‘Vrienden van Heverleebos en Meerdaalwoud’’ to allow us to place camera traps on their properties. Further, we thank all volunteers and students that aided in the field or processed and annotated photographs. Our final word of gratitude goes to Donald Kramer, Oliver Keuling and Frederik Dalerum for providing us with valuable feedback, which has improved both the form and content of this article
Managing African Swine Fever: Assessing the Potential of Camera Traps in Monitoring Wild Boar Occupancy Trends in Infected and Non-infected Zones, Using Spatio-Temporal Statistical Models
No full textThe recent spreading of African swine fever (ASF) over the Eurasian continent has been acknowledged as a serious economic threat for the pork industry. Consequently, an extensive body of research focuses on the epidemiology and control of ASF. Nevertheless, little information is available on the combined effect of ASF and ASF-related control measures on wild boar (Sus scrofa) population abundances. This is crucial information given the role of the remaining wild boar that act as an important reservoir of the disease. Given the high potential of camera traps as a non-invasive method for ungulate trend estimation, we assess the effectiveness of ASF control measures using a camera trap network. In this study, we focus on a major ASF outbreak in 2018-2020 in the South of Belgium. This outbreak elicited a strong management response, both in terms of fencing off a large infected zone as well as an intensive culling regime. We apply a Bayesian multi-season site-occupancy model to wild boar detection/non-detection data. Our results show that (1) occupancy rates at the onset of our monitoring period reflect the ASF infection status; (2) ASF-induced mortality and culling efforts jointly lead to decreased occupancy over time; and (3) the estimated mean total extinction rate ranges between 22.44 and 91.35%, depending on the ASF infection status. Together, these results confirm the effectiveness of ASF control measures implemented in Wallonia (Belgium), which has regained its disease-free status in December 2020, as well as the usefulness of a camera trap network to monitor these effects.sponsorship: Funding MB and MF are PhD fellows, MB is funded by a BOF-mandate at Hasselt University, MF is funded by the Research Foundation Flanders (FWO) (grant number 11E3220N). The camera trapping infrastructure was provided and funded by the Public Service of Wallonia. Services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation Flanders (FWO) and the Flemish Government. Finally, the ecotope dataset, used in this work, is derived from the LifeWatch ecotope database, which is led by the Earth & Life Institute (UC Louvain) and funded by the Wallonia-Brussels Federation. (y)status: Publishe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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