Browsing by Author "Lima, M"

Now showing 1 - 13 of 13
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    Demographic dynamics of a neotropical small rodent (Phyllotis darwini)
    (2001) Lima, M; Julliard, R; Stenseth, NC; Jaksic, FM
    1. The leaf-eared mouse (Phyllotis darwini) exhibits large numerical fluctuations associated with high- and low-rainfall years in semi-arid Chile. Using capture-mark-recapture (CMR) statistical modelling.. we provide a detailed description of the demographic variation in this species. We studied between-year and seasonal variation of demography, and tested for the relative importance of endogenous and exogenous factors as covariates of survival, recruitment, maturation and reproduction over a 12-year period.
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    Demography and population dynamics of South American fur seals
    (1997) Lima, M; Paez, E
    The demography and population dynamics of South American fur seals, Arctocephalus australis, at Isla de Lobos, Uruguay, were examined. Age-specific rates of survival of females were estimated during four harvest periods (1987, 1988, 1990, and 1991). The estimated continuous and finite rate of population growth (r = 0.021 and lambda = 1.021, respectively), obtained from an estimation of abundance of pups was about equal to the value obtained from a matrix model (lambda = 1.014). South American fur seals at Isla de Lobos had the highest rates of survival of adults between 1.5 and 2.5 years. Senescence in the age-specific rates of reproduction was determined. The high rates of survival of young females may be the most important life-history parameter in determining the rates of population growth, Fur seals, as other large mammals, appear to have life histories characterized by high rates of survival of adults and low effects of reproduction on growth rates of populations.
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    Demography and population dynamics of the mouse opossum (Thylamys elegans) in semi-arid Chile
    (2001) Lima, M; Stenseth, NC; Yoccoz, NG; Jaksic, FM
    Here, we present, to the authors' knowledge for the very first time for a small marsupial, a thorough analysis of the demography and population dynamics of the mouse opossum (Thylamys elegans) in western South America. We test the relative importance of feedback structure and climatic factors (rainfall and the Southern Oscillation Index) in explaining the temporal variation in the demography of the mouse opossum. The demographic information was incorporated into a stage-structured population dynamics model and the model's predictions were compared with observed patterns. The mouse opossum's capture rates showed seasonal (within-year) and between-year variability, with individuals having higher capture rates during late summer and autumn and lower capture rates during winter and spring. There was also a strong between-year effect on capture probabilities. The reproductive (the fraction of reproductively active individuals) and recruitment rates showed a clear seasonal and a between-year pattern of variation with the peak of reproductive activity occuring during winter and early spring. In addition, the fraction of reproductive individuals was positively related to annual rainfall, while population density and annual rainfall positively influenced the recruitment rate. The survival rates were negatively related to annual rainfall. The average finite population growth rate during the study period was estimated to be 1.011 +/- 0.0019 from capture-recapture estimates. While the annual growth rate estimated from the seasonal linear matrix models was 1.026, the subadult and adult survival and maturation rates represent between 54% (winter) and 81% (summer) of the impact on the annual growth rate.
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    El Nino events, precipitation patterns, and rodent outbreaks are statistically associated in semiarid Chile
    (1999) Lima, M; Marquet, PA; Jaksic, FM
    In the last two decades, several researchers have noted rodent population outbreaks in semiarid South America, in association with unusually high precipitation that seemingly concurs with Ei Nino events. To date, no studies have been conducted to determine the statistical relationships between ENSO (El Nino Southern Oscillation) events. increased precipitation, and rodent irruptions. Here we show that: 1) there is a statistical association between ENSO events and increased precipitation in the semiarid region of northern Chile, 2) the occurrence or rodent outbreaks in that region is statistically related with the precipitation levels of the same year; 3) the multi-annual patterns of the total annual precipitation levels and population abundance of those rodents Juring the summer are positively associated. The putative chain of effects seems to start with unusually high rainfall brought by ENSO to semiarid environments. which thus respond with increased primary productivity (herbage and seeds), which then fuels the rodent outbreaks.
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    El Nino-southern oscillation-driven rainfall variability and delayed density dependence cause rodent outbreaks in western South America: Linking demography and population dynamics
    (UNIV CHICAGO PRESS, 1999) Lima, M; Keymer, JE; Jaksic, FM
    It is well known that some rodent populations display dramatic density fluctuations in semiarid regions of western South America after the unusual rainfall levels associated with El Nino-southern oscillation (ENSO) disturbances. These correlated phenomena have led some ecologists to believe that rodent outbreaks are determined solely by density-independent factors (e.g., rainfall regime). However, demographic studies have detected strong delayed density-dependent effects in one of the most irruptive rodent species, the leaf-eared mouse Phyllotis darwini. We tested the effects of rainfall and delayed density-dependent factors by constructing a structured model based on demographic data estimated from a capture-mark-recapture study of this species in Chile. A model including both rainfall and delayed density-dependent effects predicts the observed population dynamics rather accurately over a 10-yr period. Interestingly, small changes in model parameters result in large changes in model dynamics, which strongly suggests that local variations in demographic features are important in explaining the asynchronous pattern in outbreak occurrences. These findings suggest that inextricably intertwined endogenous and exogenous forces cause rodent outbreaks in western South America. The former are characterized by delayed nonlinear feedbacks, whereas the latter are characterized by the positive effects of the El Nino phases and the negative effects of the La Nina phases of the ENSO disturbance.
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    Food web structure and climate effects on the dynamics of small mammals and owls in semi-arid Chile
    (2002) Lima, M; Stenseth, NC; Jaksic, FM
    Population dynamics of small mammals and predators in semi-arid Chile is positively correlated with rainfall associated with incursions of El Nino (El Nino Southern Oscillation: ENSO). However, the causal relationships between small mammal fluctuations, predator oscillations, and climatic disturbances are poorly understood. Here, we report time series models for three species of small mammal prey and two species of owl predators. The large differences in population fluctuations between the three small mammal species are related to differences in their respective feedback structures. The analyses reveal that per capita growth rate of the leaf-cared mouse is a decreasing function of log density and of log barn owl abundance together with a positive rainfall effect. In turn, per capita population growth rate (R-function) of the barn owl is a negative function of log barn owl abundance and a positive function leaf-eared mouse abundance, suggesting a predator-prey interaction. The dramatic population fluctuations exhibited by leaf-cared mouse (Phyllotis darwini) are caused by climate effects coupled with a complex food web architecture.
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    Numerical fluctuations in the northern short-tailed shrew: evidence of non-linear feedback signatures on population dynamics and demography
    (2002) Lima, M; Merritt, JF; Bozinovic, F
    1. We studied a fluctuating population of the northern short-tailed shrew (Blarina brevicauda) in the Appalachian Plateau Province of Pennsylvania, USA, spanning 21 years of monitoring. We analysed the pattern of annual temporal variation fitting both time-series models and capture-mark-recapture (CMR) statistical models for survival and recruitment rates.
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    Population dynamics of rice rats (a Hantavirus reservoir) in southern Chile
    (2003) Murúa, R; González, LA; Lima, M
    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.
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    Population dynamics of the yellow clam Mesodesma mactroides: recruitment variability, density-dependence and stochastic processes
    (2000) Lima, M; Brazeiro, A; Defeo, O
    Recruitment of benthic marine invertebrates varies greatly at different spatio-temporal scales. For instance, population dynamics of the yellow clam Mesodesma mactroides at Uruguay exhibit large temporal fluctuations, mainly associated with recruitment. We used data from an 8 yr long-term study to develop an age-structured model to show that density-dependent and density-independent forces acting together can jointly explain the population fluctuations in a sandy-beach bivalve population of the yellow clam Mesodesma mactroides. The pure density-dependent deterministic model parameterised with empirical values estimated during the 8 yr study predicted stable dynamics. The dynamics of the deterministic skeleton was markedly influenced by the addition of a relatively small amount of stochastic variability to fertility rates. The yellow clam population dynamics seem to be driven by the combined forces of density-dependent and density-independent factors operating together. A combination of (uncorrelated) stochasticity in reproductive rates and asymmetric intercohort interactions (density-dependent recruitment and density-dependent survival rates) seems to be the key process generating large variability in recruitment.
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    Population dynamics of three Neotropical small mammals: Time series models and the role of delayed density-dependence in population irruptions
    (1999) Lima, M; Jaksic, FM
    It is widely believed that only precipitation levels (through increased primary production) determine irruptions of small mammals in semi-arid areas of western South America. Nevertheless, density-dependent factors may also drive population fluctuations. To test statistically these putative effects we analysed 11 years of population records on three sympatric species of small mammals at two different habitat types in north central Chile. We applied the classical diagnostic tools of time series analysis (the autocorrelation function: ACF) to the observed time series of three neotropical small mammals. We also used simple linear autoregressive time series models to reconstruct the endogenous dynamics of these populations. The analysis strongly suggests that population fluctuations of the three species have an important density-dependent component, with the most irruptive species (Phyllotis darwini, Waterhouse 1837) displaying stronger second order population feedbacks than the other two (AKodon olivaceus, Waterhouse 1837 and Thylamys elegans, Waterhouse 1839). The latter two species showed direct density-dependent feedbacks. We hypothesize that the frequent population outbreaks of I? darwini land perhaps of other species) in semi-arid regions of western South America, may be the result of population-level (direct density-dependence) and community-level processes (delayed density-dependence), interacting with exogenous perturbations (rainfall and associated primary production).
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    Population rate of change in the leaf-eared mouse: The role of density-dependence, seasonality and rainfall
    (1999) Lima, M; Jaksic, FM
    We analysed statistically the influence of density-dependent regulation, seasonality and precipitation on the realized population rate of change of the Neotropical rodent Phyllotis darwini (Waterhouse 1837) at an intraannual rime scale. We used four years of continuous live trapping at a semiarid locality of north central Chile. Results showed that density-dependence, seasonal effects and precipitation were important factors influencing population growth rates in this species. An empirical population model including a sine function fur seasonal effects, a linear form for density-dependence, and precipitation was fitted to the full data set and to the data set with the first year removed (after an outbreak). The empirical model explained 33% and 48% of the variance in population growth. The natural rate of population increase, estimated from the empirical model, was r(max) = 2.51 or 5.06 years(-1). These estimates indicate a great potential for population increase and may explain the capability of this species to undergo large irruptions. We propose that merging empirical and theoretical modelling with field research is the most promising avenue to understand the outbreaks experienced by some rodent species in western South America.
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    Population variability among three small mammal species in the semiarid Neotropics: The role of density-dependent and density-independent factors
    (1998) Lima, M; Jaksic, FM
    We addressed the role of density-dependent (direct and delayed) and density-independent (precipitation) factors in shaping the dynamics of fluctuating populations of three small mammal species. Using a stepwise regression procedure, we tested the effects of nonlagged population density (log(10)N(t-1)), lagged population density (log(10)N(t-2)), and annual precipitation on the per capita rate of population change of Phyllotis darwini, Akodon olivaceus, and Thylamys elegans in two habitat types of a semiarid region of Chile. The most irruptive species (P. darwini) showed direct and delayed density-dependent effects in equatorial subpopulation, and only direct density-dependence in polar subpopulation. The per capita rates of population change of A. olivaceus showed direct density-dependent and precipitation effects in both habitats types, while T. elegans showed direct density-dependence and precipitation effects in the equatorial subpopulation but only a marginal effect of direct density-dependence in the polar subpopulation. The presence of delayed density-dependent strongly suggests the importance of biological interactions in shaping the dramatic irruptions exhibited by P. darwini.