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Small mammals use plant species for gathering food resources and for shelter. Preferences for certain plant species are related to nutritional restrictions and behavioural patterns, which could be altered in the presence of an infectious disease. Several native small mammals are part of the wild cycle of the protozoan Trypanosoma cruzi, responsible for Chagas disease in humans. This is a vector-borne disease transmitted by insects of the subfamily Triatominae. We examined the effect of T. cruzi infection status on the use and preference patterns of shrub species by two native rodent species: Octodon degus and Phyllotis darwini. This study was conducted during four sampling years (2010-2013) in a hyper-endemic zone of Chagas disease located in a semiarid Mediterranean ecosystem. We captured individuals of 599 O.degus and 575 P. darwini (89% of the total captures), which were related to nine shrub species and examined for T. cruzi infection. In a community-level analysis, infected and non-infected O.degus used individual shrub species within the shrub community significantly non-randomly relative to their availability; the same pattern was detected for non-infected P. darwini individuals, whereas infected individuals used the shrub community according to the abundance of each shrub species. Examining individual preferences, both rodents showed a strong preference for Flourensia thurifera and Colliguaja odorifera regardless of their infection status. Preferences for specific shrub species were variable among years, showing a 'core' of preferred shrub species and variable levels of use of the remaining ones. Our results show that T. cruzi infection in wild small mammals can modify habitat use patterns and preferences for certain shrub species, probably affecting processes acting at community level. [ABSTRACT FROM AUTHOR]

Aim Biodiversity losses under the species level may have been severely underestimated in future global climate change scenarios. Therefore, it is important to characterize the diversity units at this level, as well as to understand their ecological responses to climatic forcings. We have chosen an endemic rodent from a highly endangered ecogeographic area as a model to look for distributional responses below the species level: Phyllotis darwini. Location The central Chile biodiversity hotspot: This area harbours a high number of endemic species, and it is known to have experienced vegetational displacements between two mountain systems during and after the Last Glacial Maximum. Methods We have characterized cryptic lineages inside P. darwini in a classic phylogeographic approach; those intraspecific lineages were considered as relevant units to construct distribution models at Last Glacial Maximum and at present, as border climatic conditions. Differences in distribution between border conditions for each lineage were interpreted as distributional responses to post-glacial climate change. Results The species is composed of two major phylogroups: one of them has a broad distribution not only across the valley but also in mountain ranges, whereas the other displays a disjunct distribution across both mountain ranges and always above 1500 m. The lineage distribution model under LGM climatic conditions suggests that both lineages were codistributed in the southern portion of P. darwini's current geographic range, mainly at the valley and at the coast. Main conclusions Present distribution of lineages in P. darwini is the consequence of a cryptic distributional response to climate change after LGM: post-glacial northward colonization, with strict altitudinal segregation of both phylogroups. [ABSTRACT FROM AUTHOR]

Several reports have described host species diversity and identity as the most important factors influencing disease risk, producing either dilution or amplification of the pathogen in a host community. Triatomine vectors, mammals and the protozoan Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) Chagas are involved in the wild cycle of Chagas disease, in which infection of mammals occurs by contamination of mucous membranes or skin abrasions with insect-infected faeces. We examined the extent to which host diversity and identity determine the infection level observed in vector populations (i.e. disease risk in humans). We recorded infection in triatomine colonies and on the coexisting host mammalian species in semi-arid Chile. Host diversity, and total and infected host species densities are used as predictor variables for disease risk. Disease risk did not correlate with host diversity changes. However, the densities of each infected rodent species were positively associated with disease risk. We suggest that the infected host density surrounding the vector colonies is a relevant variable for disease risk and should be considered to understand disease dynamics. It is crucial to pay attention on the spatial scale of analysis, considering the pattern of vector dispersal, when the relationship between host diversity and disease risk is studied. [ABSTRACT FROM AUTHOR]

Precipitation plays an important role in the dynamics of species found in arid and semiarid environments. However, population fluctuations generally are driven by a combination of multiple factors whose relative contribution may vary through time and among species. We monitored fluctuations of species in three trophic levels for >17 years at a semiarid community in north-central Chile. The region is strongly affected by the El Niño Southern Oscillation, resulting in high variation in rainfall that triggers dramatic changes in food resource availability, with strong effects on upper trophic levels. We focused our analyses on the role played by endogenous and exogenous (climatic) factors on the dynamics of two important rodent species in the community, Octodon degus and Phyllotis darwini. We documented population fluctuations of several orders of magnitude in response to wet and dry episodes of different strength and duration. P. darwini reached similar maximum densities, regardless of the duration of high-rainfall events, whereas 0. degus showed additive effects of multiple wet years. Time series diagnostic tools revealed oscillations with a 5-year periodicity in rainfall, which may be the cause of the same periodicity and a weak second-order signal observed in the rodent dynamics. However, the dynamics of both rodent species were dominated by strong first-order processes, suggesting an important role of direct density dependence. Intraspecific competition, expressed as the ratio of rodent density/rainfall (or food resources) explained more than two-thirds of the variation in the population rate, of change, whereas less than one-third was explained by lagged rainfall (or food resources). We detected no significant effects of predation. Our results contribute to a growing number of examples of dynamics governed by the combined effect of density dependence and climatic forcing. They also reveal strong bottom-up regulation that may be common in other arid environments. [ABSTRACT FROM AUTHOR]

We report on the foraging behavior of three small-mammal species over 2½ years using experimental foraging trays. Trays provisioned with oat seed were set out in the field at dawn and dusk, and the amount of seed consumed (with re-provisioning) was determined over three consecutive nights and days. Experiments simultaneously evaluated the role of lunar phase, season, and microhabitat (shrub vs. open); additionally, artificial exclosures (∼0.56 ha) were employed to evaluate the influence both of mammalian and avian predators and of a dominant competitor species, the large diurnal degu (Octodon degus). Other principal small mammals included Darwin's leaf-eared mouse (Phyliotis darwini) and the olive field mouse (Akodon olivaceus). Trays were enclosed by hardware- cloth cages with either small or large holes in the side to exclude avian consumers and provide selective access to all small mammals (large holes) or to exclude the largest species (small holes). Small-mammal population sizes varied, greatly throughout the study. Principal factors affecting seed consumption rates were population size, followed by season (winter > summer), and microhabitat (shrub > open).. The role of the latter factors was relatively minor in 1999 and 2000 but amplified greatly in the final year of study when small-mammal numbers increased five-fold. In contrast to earlier work at this site, predation had minimal direct effects on foraging activities, although significant effects of microhabitat, lunar phase, and season suggest the importance of perceived predator risk. Both Phyllotis and Akodon foraged more in the absence of degus, and two- and three-way interactions further supported an important role for competition in this system. [ABSTRACT FROM AUTHOR]

The leaf-eared mouse (Phyllotis darwini) undergoes periodical population irruptions in semiarid Chile associated with unusual rainfall driven by ENSO (El Nino/Southern Oscillation) disturbances. In this study, we estimated survival, immigration and recruitment between contiguous subpopulations in opposite-facing slopes of two creeks by means of probabilistic models. Population trajectories were similar in all four subpopulations. However, xeric-habitat subpopulations were larger than mesic-habitat subpopulations in the two creeks studied. On theother hand, survival showed strong temporal effects, but no habitat-type or life-stage effects. The most parsimonious models were those that included seasonal effects on survival rate. Number of births and immigrants were correlated with total population changes in both subpopulations at the El Cobre creek, but the two subpopulations at the El Grillo creek showed juvenile and adult mortality plus emigration asthe most important processes contributing to population change. Our study demonstrates spatiotemporal variability in population processes(survival, birth, immigration and recruitment) between neighboring subpopulations. [ABSTRACT FROM AUTHOR]