Gradual and eruptive dynamics of rodent pests : outbreaks in house mice in Australia and common voles in Spain
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2021
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Las plagas de roedores son habituales en los cultivos de todo el mundo, causando grandes daños
económicos y problemas de salud por zoonosis. Este proyecto de tesis trabajó con dos plagas de
roedores: el ratón doméstico australiano y los topillos españoles por ser plagas que generan
pérdidas económicas en los cultivos, tener dinámicas de población complejas con influencia de
factores endógenos y exógenos, y la ausencia de un mecanismo explicativo causal. Para analizar
los brotes poblacionales de ratones domésticos en Australia se usaron datos de abundancia de la
plaga en tres sitios productores de trigo (Victoria, Sur de Australia y Queensland) junto con
variables climáticas y depredadores generalistas para identificar los factores causantes del
incremento poblacional. Para analizar las dinámicas se emplearon modelos estacionales y anuales
para comprender los factores que impulsan el aumento y la disminución de la población (fase de
brote y colapso). Se evaluaron los efectos de las variables climáticas en la tasa de crecimiento de
la población a través de sus efectos potenciales en el suelo, capacidad para cavar madrigueras, y
datos de abundancia relativa de aves para entender el papel de los depredadores y la existencia de
umbrales de escape. La tasa de aumento de las poblaciones de ratones en el sureste australiano
(Victoria y Sur de Australia) se explicó mejor por la baja evaporación en verano, las altas
precipitaciones acumuladas de invierno en los dos años anteriores al brote y un índice de
abundancia de los depredadores Nankeen kestrel (Walpeup) y Brown falcon (Sur de Australia)
durante el verano al otoño. En cuanto a Queensland los factores más importantes fueron las
precipitaciones de los dos años anteriores y factores denso-dependientes de las estaciones previas.
El rol de los depredadores no fue evidente. El colapso poblacional en el sureste australiano y en
Queensland se explicó por la abundancia poblacional de los ratones domésticos en la fase de brote
y la abundancia de depredadores. Por lo tanto, se evidenció que las poblaciones de ratones en
Australia presentan dos estructuras de brote diferentes: el sureste australiano se caracteriza por tener brotes de tipo eruptivo dependientes del clima y con umbrales de escape a los depredadores,
y brotes de tipo gradual en Queensland dependientes del clima y densidades previas de ratones
domésticos, lo cual influye en el tipo de manejo y predicción de estas plagas. Estos resultados son
útiles para predecir brotes futuros y reducir su impacto económico en los cultivos de trigo
australianos.
Los topillos en España son un ejemplo de una especie plaga que cada 3 o 4 años alcanza grandes
números en cultivos de alfalfa y cereales causando daños considerables en los cultivos. Para
analizar los brotes poblacionales se usó una serie de tiempo de 11 años de abundancia de topillos
en la región de Castilla y León (Zamora, Valladolid y Palencia), factores climáticos, abundancia
de competidores como el ratón de madera, ratón argelino y musaraña, y la abundancia de
comadrejas para examinar el papel de los depredadores. Para el análisis se emplearon modelos
estacionales y anuales para comprender los factores que impulsan el aumento y la disminución de
la población. La tasa de aumento de las poblaciones de ratones se explicó mejor por las altas
precipitaciones acumuladas (otoño a primavera) en los dos años previos al brote, la humedad de
primavera a verano y la abundancia de comadrejas en primavera. La tasa de disminución de la
población se explicó mejor por la abundancia en la temporada de brote (denso-dependencia) y la
precipitación en otoño. En conclusión, los brotes de topillos españoles fueron clasificados como
eruptivos, al depender no solo de factores exógenos como la precipitación y la humedad, si no de
un umbral de escape a las comadrejas en primavera. Estos resultados son útiles para predecir brotes
futuros y reducir el impacto económico de los topillos en los cultivos de alfalfa y cereales.
Abstract Rodent plagues are usual on crops around the world causing severe economic damage and health problems by zoonoses. The thesis project worked on two rodent plagues: Australian house mouse and Spanish voles which generate economic loss on crops. They have complex population dynamics with endogenous and exogenous influence factors, and an absence of a causal explanatory mechanism to predict their outbreaks. House mice in Australia are a plague with irregular population dynamics and cause considerable damage on cereal crop systems. We used a 20-year mouse mark-recapture dataset from Walpeup (Victoria), Roseworthy (South Australia) and Darling Downs (Queensland), and climatic and predator variables. We employed seasonal and annual models to understand the increase and decrease of the population through different drivers. In south-eastern Australia, the rate of increase was best explained by low evaporation in summer, high cumulative winter rainfall, and an index of abundance of the Nankeen kestrel (Walpeup), and the Brown falcon (Roseworthy) during summer to autumn. The Queensland mouse outbreaks were explained by spring to summer rainfall from two years before the plague, and previous mouse abundances. On the other hand, the South-eastern decline rate was explained by outbreak abundance and predators like the Barn owl to Walpeup and Swamp harrier to Roseworthy. The Queensland collapse was related to outbreak abundance (density-dependence) and Barn owl density. We conclude that South-eastern mouse dynamics can be defined as an eruptive dynamic caused by weather triggers that allow the population to obtain more and better resources avoiding being consumed by predators. Queensland outbreaks can be defined as gradual because they are generated by changes in rainfall and a strong density-dependence. These results are useful to explain and predict the outbreaks, understanding the mechanisms that cause the mice explosion on wheat production sites. 11 The common voles in Spain are an example of an irruptive species that every three or four years reaches plague numbers and causes considerable damage in cropping systems. We used an 11-year mark-recapture dataset from Castilla y León region (Zamora, Valladolid, and Palencia) and various climatic, competitors and predator variables, employing seasonal and annual models to understand the drivers of the population increase and decrease. We examine the climatic effects, interspecific competition (Wood mouse, Algerian mouse, and Shrew), and weasel’s abundance to examine the predators’ role. The rate of increase of vole populations was best explained by high cumulative rainfall (autumn to spring) in the two years prior to the outbreak, spring and summer humidity, and spring weasel’s abundance. The rate of population decline over winter was best explained by abundance in the peak season (density-dependence) and autumn precipitation. We conclude that the outbreaks of Spanish voles are classified as eruptive because depended on precipitation and humidity, an index of food supply and burrows, and weasel’s density. The results are useful to predict future outbreaks to reduce their economic impact on alfalfa and cereal crops.
Abstract Rodent plagues are usual on crops around the world causing severe economic damage and health problems by zoonoses. The thesis project worked on two rodent plagues: Australian house mouse and Spanish voles which generate economic loss on crops. They have complex population dynamics with endogenous and exogenous influence factors, and an absence of a causal explanatory mechanism to predict their outbreaks. House mice in Australia are a plague with irregular population dynamics and cause considerable damage on cereal crop systems. We used a 20-year mouse mark-recapture dataset from Walpeup (Victoria), Roseworthy (South Australia) and Darling Downs (Queensland), and climatic and predator variables. We employed seasonal and annual models to understand the increase and decrease of the population through different drivers. In south-eastern Australia, the rate of increase was best explained by low evaporation in summer, high cumulative winter rainfall, and an index of abundance of the Nankeen kestrel (Walpeup), and the Brown falcon (Roseworthy) during summer to autumn. The Queensland mouse outbreaks were explained by spring to summer rainfall from two years before the plague, and previous mouse abundances. On the other hand, the South-eastern decline rate was explained by outbreak abundance and predators like the Barn owl to Walpeup and Swamp harrier to Roseworthy. The Queensland collapse was related to outbreak abundance (density-dependence) and Barn owl density. We conclude that South-eastern mouse dynamics can be defined as an eruptive dynamic caused by weather triggers that allow the population to obtain more and better resources avoiding being consumed by predators. Queensland outbreaks can be defined as gradual because they are generated by changes in rainfall and a strong density-dependence. These results are useful to explain and predict the outbreaks, understanding the mechanisms that cause the mice explosion on wheat production sites. 11 The common voles in Spain are an example of an irruptive species that every three or four years reaches plague numbers and causes considerable damage in cropping systems. We used an 11-year mark-recapture dataset from Castilla y León region (Zamora, Valladolid, and Palencia) and various climatic, competitors and predator variables, employing seasonal and annual models to understand the drivers of the population increase and decrease. We examine the climatic effects, interspecific competition (Wood mouse, Algerian mouse, and Shrew), and weasel’s abundance to examine the predators’ role. The rate of increase of vole populations was best explained by high cumulative rainfall (autumn to spring) in the two years prior to the outbreak, spring and summer humidity, and spring weasel’s abundance. The rate of population decline over winter was best explained by abundance in the peak season (density-dependence) and autumn precipitation. We conclude that the outbreaks of Spanish voles are classified as eruptive because depended on precipitation and humidity, an index of food supply and burrows, and weasel’s density. The results are useful to predict future outbreaks to reduce their economic impact on alfalfa and cereal crops.
Description
Tesis (Doctor en Ciencias con mención en Ecología)--Pontificia Universidad Católica de Chile, 2021