Population dynamics of rice rats (a Hantavirus reservoir) in southern Chile: feedback structure and non‐linear effects of climatic oscillations

Abstract

Murú a, R., González, L. A. and Lima, M. 2003. Population dynamics of rice rats (a Hantavirus reservoir) in southern Chile: feedback structure and non-linear effects of climatic oscillations. -Oikos 102: 137-145.We studied a fluctuating population of the long-tail rice rat (Oligoryzomys longicaudatus), the main Hantavirus vector in southern Chile, and spanning 19 years of monitoring. We determined that a first-order feedback structure and non-linear effects of Antarctic Oscillation Index (AAOI) and Southern Oscillation Index (SOI) explain 96% of the variation in annual per capita population growth rates. One important result of this study is that first-order feedback structure captures the essential features of population dynamics of long-tailed rice rats. This regulatory structure suggests that rice rats are limited by food, space or predators and regulated by intra-specific competition. The first-order dynamics observed in long-tailed rice rats strongly suggests that Hantavirus have no harmful effects on survival or reproductive processes. Besides the non-linear climatic signature in population dynamics, the periodic event of bamboo-flowering and mast seeding strongly influence rice rats population growth rates. Because of this, bamboo flowering may be used as a signal for forecasting long-tail rice rats outbreaks and for implementing information and health policies to avoid human-rodent contacts in specific areas. The observed effects of the two large-scale climatic indexes that influence climatic variability along southern Pacific Ocean, the AAOI and the SOI, emphasizes the role of considering non-linear feedback structures and climatic forces for understanding small rodent population dynamics. Because long-tailed rice rats represent the major Hantavirus reservoir in southern Chile and Argentina, we need to gain an in-depth understanding of the structure and functioning of these small rodent populations in face of the potential consequences of global change and climatic fluctuations.

Spatio‐temporal rainfall patterns in Southern South America

“…Lara et al (2008) have recently shown that stream flow in the Rio Puelo in Northern Patagonia is significantly correlated with the AAO over 1948-2000 confirming the precipitation linkage. Murúa et al (2003) also found that the AAO correlates with fluctuations in the population density of a native mouse in south-central Chile, suggesting that the available food supply for these grain-eating rodents is controlled by precipitation. The influence of AAO on precipitation may possibly be explained by variations in the blocking activity over the Amundsen-Bellingshausen area west of the Antarctic Peninsula.…”

Non-linear dynamics in marine-phytoplankton population systems

“…climate) influence population processes (Royama 1992, Stenseth et al 2002. On the other hand, the existence of non-linearity in climatic forcing has been recently explored in terrestrial (Murúa et al 2003) and marine ecosystems (L. Ciannelli et al unpubl. ).…”

Precisando el “Impacto medioambiental en la incidencia del síndrome cardiopulmonar por Hantavirus en Chile”

“…Segundo, los autores postulan que el aumento en el número de casos (de SCPH) en esos años en la X Región sería (hipotéticamente) el resultado de una cascada trófica catalizada inicialmente por el Fenómeno del Niño (ENSO, por sus siglas en inglés) ocurrido 1 ó 2 años antes. Sin embargo, la dinámica poblacional de roedores (en particular de O. longicaudatus) en el Sur de Chile es entendida por procesos más complejos que no sólo consideran la incidencia de las precipitaciones derivadas de un fenómeno ENSO 6 . Y esto no necesariamente resulta en un aumento del número de casos de SCPH.…”