Scalability of genetic biocontrols for eradicating invasive alien mammals

CRISPR-based gene drives offer novel solutions for controlling invasive alien species, which could ultimately extend eradication efforts to continental scales. Gene drives for suppressing invasive alien vertebrates are now under development. Using a landscape-scale individual-based model, we present the first estimates of times to eradication for long-lived alien mammals. We show that demography and life-history traits interact to determine the scalability of gene drives for vertebrate pest eradication. Notably, optimism around eradicating smaller-bodied pests (rodents and rabbits) with gene-drive technologies does not easily translate into eradication of larger-bodied alien species (cats and foxes).Aysegul Birand, Phillip Cassey, Joshua V. Ross, Paul Q. Thomas, Thomas A. A. Prows

Patrones globales en reproducción y mortalidad del conejo de monte y su impacto en la dinámica de poblaciones

Tesis descargada desde TESEOEl conejo de campo es un mamífero autóctono de la Península Ibérica que ha sido introducido por el ser humano en muchas partes del mundo para su caza, su carne o su pelaje entre otras causas. Mientras que en su área de distribución original, donde es una especie clave, se encuentra en declive, en otras regiones donde ha sido introducido el conejo es considerado como especie plaga. Esta doble problemática ha motivado numerosos estudios a nivel local para intentar paliar el declive o los efectos nocivos de este lagomorfo. Sin embargo, pocos autores han examinado la dinámica de poblaciones de la especie a nivel global. Nuestro objetivo fue utilizar una combinación de revisiones bibliográficas y modelos de simulación para estudiar los patrones de reproducción y mortalidad de los conejos en diferentes partes del mundo y el impacto de los mismos en la dinámica poblacional de la especie. De esta forma hemos podído investigar más a fondo los mecanismos y factores que generan los patrones de variabilidad intra y entre poblaciones de conejo de campo. Los resultados muestran que la amplia variabilidad espacio-temporal de los parámetros reproductivos del conejo está influenciados tanto por factores ambientales (como temperatura, precipitación o fotoperiodo) o características individuales (e. g. edad). Las tasas de supervivencia y epidemias también dependen de la edad y parecen estar relacionadas con factores climáticos, como la temperatura y la precipitación, entre otros. Incorporando dicha información en el modelo de simulación hemos observado que es muy probable que el cambio climático agrave el dualismo de control/conservación de esta especie a través de una simultánea disminución del periodo reproductor en la Península Ibérica y un aumento del mismo en zonas del norte y este europeo. Asimismo, se han examinado las interacciones entre los diferentes parámetros poblacionales y entre las causas de mortalidad (que son principalmente la predación, la mixomatosis y neumonía hemorrágica vírica). Estudios como este son necesarios para poder comprender mejor la dinámica poblacional de una especie y poder así actuar eficientemente para su conservación y/o su control

Recontamination Helps a Lot to Hunt a Rabbit

The Hunters and Rabbit game is played on a graph G where the Hunter player shoots at k vertices in every round while the Rabbit player occupies an unknown vertex and, if it is not shot, must move to a neighbouring vertex after each round. The Rabbit player wins if it can ensure that its position is never shot. The Hunter player wins otherwise. The hunter number h(G) of a graph G is the minimum integer k such that the Hunter player has a winning strategy (i.e., allowing him to win whatever be the strategy of the Rabbit player). This game has been studied in several graph classes, in particular in bipartite graphs (grids, trees, hypercubes...), but the computational complexity of computing h(G) remains open in general graphs and even in more restricted graph classes such as trees. To progress further in this study, we propose a notion of monotonicity (a well-studied and useful property in classical pursuit-evasion games such as Graph Searching games) for the Hunters and Rabbit game imposing that, roughly, a vertex that has already been shot "must not host the rabbit anymore". This allows us to obtain new results in various graph classes. More precisely, let the monotone hunter number mh(G) of a graph G be the minimum integer k such that the Hunter player has a monotone winning strategy. We show that pw(G) ? mh(G) ? pw(G)+1 for any graph G with pathwidth pw(G), which implies that computing mh(G), or even approximating mh(G) up to an additive constant, is NP-hard. Then, we show that mh(G) can be computed in polynomial time in split graphs, interval graphs, cographs and trees. These results go through structural characterisations which allow us to relate the monotone hunter number with the pathwidth in some of these graph classes. In all cases, this allows us to specify the hunter number or to show that there may be an arbitrary gap between h and mh, i.e., that monotonicity does not help. In particular, we show that, for every k ? 3, there exists a tree T with h(T) = 2 and mh(T) = k. We conclude by proving that computing h (resp., mh) is FPT parameterised by the minimum size of a vertex cover

Conservation Implications of Illegal Bird Trade and Disease Risk in Peru

Trade in wild-caught animals as pets is a global conservation and animal-welfare concern. Illegal and poorly-regulated legal wildlife trade can threaten biodiversity, spread infectious diseases, and result in considerable animal suffering and mortality. I used illegal wildlife trade in Peru, specifically native bird trade, as a case study to explore important aspects and consequences of the trade for domestic markets. With data collected from a five-year market survey and governmental seizure records, I applied a statistical modeling approach to investigate the influence of Peru’s legal export quota system on the country’s illegal domestic bird trade. I used an infectious-disease mathematical modeling approach to analyze how illegal harvest influenced disease dynamics in a wild parrot population. Finally, I used qualitative research methods to investigate the role of non-governmental organizations (NGOs) and their members’ philosophical perspectives toward wildlife in combating illegal trade. I found that Peru had a thriving illegal trade in native birds (mostly parrots) for domestic consumers; 150 species were recorded in markets and/or seizures with over 35,250 individuals offered for sale (2007–2011). Peru’s current legal export quota system did not influence avian abundance in markets, but historic export trade did. Because authorities frequently release confiscated birds without health evaluation, infectious pathogens may be introduced into wild populations. I determined that the hypothetical release of white-winged parakeets infected with Newcastle disease would provoke a disease outbreak with considerable mortality in a susceptible population. Higher rates of illegal harvest dampened the magnitude of the outbreak, but the combined effects of high harvest and disease-induced mortality may threaten population survival. According to interviewees, Peru’s government was considered lax in combating illegal wildlife trade and as such, many NGOs supplemented the government’s efforts. The five NGOs most dedicated to decreasing illegal wildlife-pet trade in Peru had strong, dual philosophical perspectives that prioritized both wildlife populations and individual wild animals. In conclusion, there is considerable avian trafficking for Peru’s domestic consumers that (1) is independent of Peru’s export market, (2) provides a mechanism to introduce harmful infectious diseases into wild population, and (3) is combated most by dual-perspective NGOs

Sarcoptic mange and the demography of the red fox, Vulpes vulpes

Vertebrate species are managed for many reasons, including their role as economically important predators or as carriers of disease. Successful management depends on the ability to predict the outcome of management actions on a species’ population dynamics. However, uncertainty in the models used to make such predictions can arise from multiple sources, including sampling error in vital rates, intraspecific demographic variation and unknown interspecific interactions. The red fox Vulpes vulpes provides a useful model organism for exploring such uncertainty, because management of this important predator and disease host is often ineffective, despite substantial sampling effort. By explicitly accounting for sampling error in survival and fecundity, confidence intervals for population growth rates were derived from published point estimates of red fox demographic data. Uncertainty in population growth rates was found to be high, requiring a quadrupling of sampling effort to halve the confidence intervals. Given the often poor justification for the choice of distribution used to model litter size, the influence of probability distributions on population model outcomes was tested. In this first comprehensive evaluation, estimates of quasi-extinction and disease control probabilities for three Canid species were found to be robust to litter size distribution choice. Demographic analyses of the red fox revealed a medium to fast life history speed and significant survival and fecundity contributions from juveniles to population growth. Intraspecific variation was detected within these spectra of demographic metrics: the first such demonstration for carnivores. Simulated data substitution between fox populations revealed that geographic proximity and similar levels of anthropogenic disturbance did not infer demographic similarity. Considering the sampling effort expended on the red fox, the species appears well-studied; yet, substantial limitations in data collection were identified. Compartment modelling of a sarcoptic mange outbreak in an urban fox population in Bristol, UK, revealed that disease transmission was frequency-dependent, consistent with contact rates being determined by social interactions rather than by population density. Individual-based modelling suggested that indirect transmission, genetic resistance and long-distance recolonisation were required to replicate the observed rapid spread of mange and subsequent population recovery. Thus, this first attempt to model mange dynamics in this canid provided novel insight into previously uncertain epidemiological and behavioural processes in the transmission of sarcoptic mange in the red fox

Further results on the Hunters and Rabbit game through monotonicity

Hunters and Rabbit game is played on a graph $G$ where the Hunter player shoots at $k$ vertices in every round while the Rabbit player occupies an unknown vertex and, if not shot, must move to a neighbouring vertex after each round. The Rabbit player wins if it can ensure that its position is never shot. The Hunter player wins otherwise. The hunter number $h(G)$ of a graph $G$ is the minimum integer $k$ such that the Hunter player has a winning strategy (i.e., allowing him to win whatever be the strategy of the Rabbit player). This game has been studied in several graph classes, in particular in bipartite graphs (grids, trees, hypercubes...), but the computational complexity of computing $h(G)$ remains open in general graphs and even in trees. To progress further, we propose a notion of monotonicity for the Hunters and Rabbit game imposing that, roughly, a vertex that has already been shot ``must not host the rabbit anymore''. This allows us to obtain new results in various graph classes. Let the monotone hunter number be denoted by $mh(G)$. We show that $pw(G) \leq mh(G) \leq pw(G)+1$ for any graph $G$ with pathwidth $pw(G)$, implying that computing $mh(G)$, or even approximating $mh(G)$ up to an additive constant, is NP-hard. Then, we show that $mh(G)$ can be computed in polynomial time in split graphs, interval graphs, cographs and trees. These results go through structural characterisations which allow us to relate the monotone hunter number with the pathwidth in some of these graph classes. In all cases, this allows us to specify the hunter number or to show that there may be an arbitrary gap between $h$ and $mh$, i.e., that monotonicity does not help. In particular, we show that, for every $k\geq 3$, there exists a tree $T$ with $h(T)=2$ and $mh(T)=k$. We conclude by proving that computing $h$ (resp., $mh$) is FPT parameterised by the minimum size of a vertex cover.Comment: A preliminary version appeared in MFCS 2023. Abstract shortened due to Arxiv submission requirement