Detecting and modelling delayed density-dependence in abundance time series of a small mammal (Didelphis aurita)

Growth-rate distributions of gut microbiota time series

Logarithmic growth-rates are fundamental observables for describing ecological systems and the characterization of their distributions with analytical techniques can greatly improve their comprehension. Here a neutral model based on a stochastic differential equation with demographic noise, which presents a closed form for these distributions, is used to describe the population dynamics of microbiota. Results show that this model can successfully reproduce the log-growth rate distribution of the considered abundance time-series. More significantly, it predicts its temporal dependence, by reproducing its kurtosis evolution when the time lag τ is increased. Furthermore, its typical shape for large τ is assessed, verifying that the distribution variance does not diverge with τ. The simulated processes generated by the calibrated stochastic equation and the analysis of each time-series, taken one by one, provided additional support for our approach. Alternatively, we tried to describe our dataset by using a logistic neutral model with an environmental stochastic term. Analytical and numerical results show that this model is not suited for describing the leptokurtic log-growth rates distribution found in our data. These results support an effective neutral model with demographic stochasticity for describing the considered microbiota.

Regime shift tipping point in hare population collapse associated with climatic and agricultural change during the very early 20th century

Animal populations at northern latitudes may have cyclical dynamics that are degraded by climate change leading to trophic cascade. Hare populations at more southerly latitudes are characterized by dramatic declines in abundance associated with agricultural intensification. We focus on the impact of historical climatic and agricultural change on a mid-latitude population of mountain hares, Lepus timidus hibernicus. Using game bag records from multiple sites throughout Ireland, the hare population index exhibited a distinct regime shift. Contrary to expectations, there was a dynamical structure typical of northern latitude hare populations from 1853 to 1908, during which numbers were stable but cyclic with a periodicity of 8 years. This regime was replaced by dynamics more typical of southern latitude hare populations from 1909 to 1970, in which cycles were lost and numbers declined dramatically. Destabilization of the autumn North Atlantic Oscillation (NAO) led to the collapse of similar cycles in the hare population, coincident with the onset of agricultural intensification (a shift from small-to-large farms) in the first half of the 20th century. Similar, but more recent regime shifts have been observed in Arctic ecosystems and attributed to anthropogenic climate change. The present study suggests such shifts may have occurred at lower latitudes more than a century ago during the very early 20th century. It seems likely that similar tipping points in the population collapse of other farmland species may have occurred similarly early but went undocumented. As northern systems are increasingly impacted by climate change and probable expansion of agriculture, the interaction of these processes is likely to disrupt the pulsed flow of resources from cyclic populations impacting ecosystem function.

The Program for Biodiversity Research in Brazil: The role of regional networks for biodiversity knowledge, dissemination, and conservation

The Program for Biodiversity Research (PPBio) is an innovative program designed to integrate all biodiversity research stakeholders. Operating since 2004, it has installed long-term ecological research sites throughout Brazil and its logic has been applied in some other southern-hemisphere countries. The program supports all aspects of research necessary to understand biodiversity and the processes that affect it. There are presently 161 sampling sites (see some of them at Supplementary Appendix), most of which use a standardized methodology that allows comparisons across biomes and through time. To date, there are about 1200 publications associated with PPBio that cover topics ranging from natural history to genetics and species distributions. Most of the field data and metadata are available through PPBio web sites or DataONE. Metadata is available for researchers that intend to explore the different faces of Brazilian biodiversity spatio-temporal variation, as well as for managers intending to improve conservation strategies. The Program also fostered, directly and indirectly, local technical capacity building, and supported the training of hundreds of undergraduate and graduate students. The main challenge is maintaining the long-term funding necessary to understand biodiversity patterns and processes under pressure from global environmental changes.

What are the main drivers of survival and recruitment in tropical forest marsupials? A 16-year study

Tropical forest marsupials exhibit large interannual variation in population sizes, with direct negative density dependence capturing the essential features of their dynamics. However, the demographic mechanisms underlying population growth rate and driving both survival and reproduction are still unclear. We used a 16-year capture-mark-recapture data set for five tropical forest marsupials to test for seasonal and interannual density dependence in survival and recruitment. Hypotheses regarding the effects of exogenous (rainfall and minimum temperature) factors on survival, recruitment, and reproductive parameters (fecundity, litter size, and proportion of reproductive females) were also tested. Population size negatively affected survival in three of five species. High population sizes in a given year reduced survival rates in the following year, with strong detrimental effects on males. Recruitment and proportion of reproductive females were highly dependent on weather variables, and were not affected by previous population sizes (except for Metachirus nudicaudatus). Fecundity (number of female offspring/female) was related negatively to population size only in the black-eared opossum (Didelphis aurita), while litter size was a relatively conservative parameter, largely independent of external conditions. Our analyses indicate that density-dependent survival is the mechanism that regulates population size of tropical forest marsupials, either through a reduction in survival or an increase in emigration rates. This general regulatory mechanism may be common to other marsupials in the Atlantic Forest and other tropical forests.

Marsupiais de florestas tropicais exibem grande variação interanual nos tamanhos populacionais, com dependência negativa e direta da densidade capturando a essência de sua dinâmica populacional. No entanto, os mecanismos demográficos subjacentes à taxa de crescimento populacional e determinantes da sobrevivência e reprodução ainda são incertos. Nós usamos 16 anos de dados de captura-marcação-recaptura de cinco espécies de marsupiais de florestas tropicais para avaliar a dependência de densidade sazonal e interanual na sobrevivência e recrutamento. Hipóteses sobre efeitos de fatores exógenos (pluviosidade e temperatura mínima) na sobrevivência, recrutamento e parâmetros reprodutivos (fecundidade, tamanho da ninhada e proporção de fêmeas reprodutivas) também foram testadas. O tamanho da população afetou negativamente a sobrevivência em três das cinco espécies. O tamanho populacional elevado em um ano reduziu as taxas de sobrevivência no ano seguinte, com efeitos mais negativos nos machos. Recrutamento e proporção de fêmeas reprodutivas foram dependentes das variáveis climáticas e não foram afetados pelos tamanhos populacionais anteriores (com exceção de Metachirus nudicaudatus). A fecundidade (número de filhotes fêmea/fêmea) foi relacionada negativamente ao tamanho da população do gambá-de-orelha-preta (Didelphis aurita), enquanto o tamanho da ninhada foi um parâmetro relativamente conservador e independente das condições externas. Nossas análises indicam que a sobrevivência dependente da densidade regula as populações de marsupiais em florestas tropicais, seja através da redução na sobrevivência ou no aumento da emigração. Esse mecanismo regulatório pode ser comum a outros marsupiais na Mata Atlântica e outras florestas tropicais.