Population Size In Years Research Articles

Morphological Traits Are Not Consistently Related to Population Size in Four Migratory Caribou Populations Across North America.

To develop effective management to maintain or restore populations of large herbivores, wildlife managers require sound empirical data on their variations in size and associated parameters. Many studies have highlighted links between morphological traits of individuals and population density; however, less attention has been devoted to whether or not morphological traits can reliably inform on population size in years when no population estimates are available. We evaluated the relationships between three morphological traits (hind foot length, body mass, and body fat) and population size interpolated over three decades, for four migratory caribou (Rangifer tarandus) herds in northern Canada and Alaska. Our sample included 8865 measurements of 4473 individuals. We used a Bayesian modeling approach to evaluate the relationships between morphology and population size across different sex and age classes, considering different temporal scales and, when possible, phases of population growth or decline. We found that morphological traits were not consistently linked to population size. Statistically significant relationships existed for some combinations of herd and age classes, but weak to absent relationships were more common. Our study suggests that morphological traits alone cannot replace data obtained from aerial surveys to approximate population size when population trends are unknown. We discuss the usefulness of morphological traits to explain population size, and recognize their role as complementary metrics to inform the management and conservation of large herbivores, but conclude that morphological data should not be used to predict population size without information on population trends.

Enigmatic Near‐Extirpation in a Boreal Toad Metapopulation in Northwestern Montana

ABSTRACTNorth America's protected lands harbor biodiversity and provide habitats where species threatened by a variety of stressors in other environments can thrive. Yet disease, climate change, and other threats are not limited by land management boundaries and can interact with conditions within protected landscapes to affect sensitive populations. We examined the population dynamics of a boreal toad (Anaxyrus boreas boreas) metapopulation at a wildlife refuge in northwestern Montana, USA, over a 16‐year period (2003–2018). We used robust design capture‐recapture models to estimate male population size, recruitment, and apparent survival over time and in relation to the amphibian chytrid fungus (Batrachochytrium dendrobatidis). We estimated female population size in years with sufficient captures. Finally, we examined trends in male and female toad body size and condition. We found no evidence of an effect of disease or time on male toad survival but detected a strong negative trend in recruitment of new males to the population. Estimates of male and female abundance decreased over time. Body size of males and females was inversely related to estimated population size, consistent with reduced recruitment to replace adults, but body condition of adult males was only weakly associated with abundance. Together, these results describe the demography of a near‐extirpation event, and point to dramatic decreases in the recruitment of new individuals to the breeding population as the cause of this decline. We surmise that processes related to the restoration of historical hydrology within the refuge adversely affected amphibian breeding habitat, and that these changes interacted with disease, life history, and other factors to restrict the recruitment of new individuals to the breeding population over time. Our results point to challenges in understanding and predicting factors that influence population change and highlight that current metrics for assessing population status can have limited predictive ability. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

Das postmalthusianische Zeitalter: Die Bevölkerungsentwicklung in Deutschland, 1815–1871

The study constructs new data series for population and vital rates in the German states between 1815 and 1871 and aggregates these to the national level. Major improvements in the data at state level include a broadening of the source material, the determination of population size in years between censuses on the basis of recorded natural increase, and a correction for improvement of population coverage across the censuses taken between the late 1810s and the 1830s. The resulting national series also show broader regional coverage than the earlier series constructed by Hoffmann (1965). The new series establish that the period from the late 1810s to the 1870s can be characterized as Germany’s post-Malthusian era: High population growth of 0.8 per cent p. a. could coexist with largely stable real wages in the long run, implying that expansion of demand for labour compensated for the negative effect of population growth on material welfare. Moreover, on the national level (not on the regional level) natural increase was positive in every single year during the period under study. Nevertheless, vital rates and the emigration rate remained vulnerable to fluctuations of grain production.

Spatial and temporal variation in the relative contribution of density dependence, climate variation and migration to fluctuations in the size of great tit populations

1. The aim of the present study is to model the stochastic variation in the size of five populations of great tit Parus major in the Netherlands, using a combination of individual-based demographic data and time series of population fluctuations. We will examine relative contribution of density-dependent effects, and variation in climate and winter food on local dynamics as well as on number of immigrants. 2. Annual changes in population size were strongly affected by temporal variation in number of recruits produced locally as well as by the number of immigrants. The number of individuals recruited from one breeding season to the next was mainly determined by the population size in year t, the beech crop index (BCI) in year t and the temperature during March-April in year t. The number of immigrating females in year t + 1 was also explained by the number of females present in the population in year t, the BCI in autumn year t and the temperature during April-May in year t. 3. By comparing predictions of the population model with the recorded number of females, the simultaneous modelling of local recruitment and immigration explained a large proportion of the annual variation in recorded population growth rates. 4. Environmental stochasticity especially caused by spring temperature and BCI did in general contribute more to annual fluctuations in population size than density-dependent effects. Similar effects of climate on local recruitment and immigration also caused covariation in temporal fluctuations of immigration and local production of recruits. 5. The effects of various variables in explaining fluctuations in population size were not independent, and the combined effect of the variables were generally non-additive. Thus, the effects of variables causing fluctuations in population size should not be considered separately because the total effect will be influenced by covariances among the explanatory variables. 6. Our results show that fluctuations in the environment affect local recruitment as well as annual fluctuations in the number of immigrants. This effect of environment on the interchange of individuals among populations is important for predicting effects of global climate change on the pattern of population fluctuations.

Demographic pressure, economic development, and social engineering: An assessment of fertility declines in the second half of the twentieth century.

Concerns over the prospects of explosive demographic growth led to concerted efforts to engineer fertility reductions in the developing world, while skeptics argued that economic development was the best way to hasten fertility decline. Now that fertility declines have occurred in many countries can either side claim victory? Or was demographic pressure simply self-regulated by links between mortality and fertility changes? Using country-level data and a methodology inspired by a series of seminal articles by Preston, I assess the impact of economic change on both fertility and mortality and the independent effect of mortality on fertility between the 1960s and the 1990s. Aggregating country-level estimates into six regional population projections from 1950 to 2000, I translate these impacts on demographic variables into population size impacts. Although economic development accounted poorly for either mortality or fertility changes, the prevailing population growth was not that different from the growth predicted had economic development alone influenced demographic trends. The main reason appears to be an association between mortality and fertility levels that offset the initial effects of mortality declines outpacing economic growth. Together, the effect of economic change on both mortality and fertility declines and the effect of mortality on fertility predicted reasonably well actual population size in year 2000, suggesting only a modest influence of any additional factor.

Index Numbers for Waterbird Populations. I. Review and Methodology

This paper reviews methods used to estimate bird population index numbers and proposes a new method. An index number for a year is defined as the ratio of the population size in the year to the population size in the base year. In the context of waterbird populations, the major problem with generating index numbers is the fact that, owing to missing observations at a subset of localities, the total population size in any year is unknown. We suggest a model-based approach to imputing missing observations so that the total population size at the localities may be estimated and used to produce a series of index numbers of the population sizes each year