Factors Driving Flowering Phenology and Reproductive Success in Silene acaulis and implications for response to climate change

Along with survival, successful reproduction is one of the key features of individual performance that is necessary for a species to survive, including in the face of environmental alterations. This study examined possible drivers of reproductive success in alpine cushion plant Silene acaulis, and the implications of reproductive patterns for long-term stability of populations in the face of climate change. First, I asked whether the timing of flowering in a long-lived alpine plant species influenced whether flowers successfully produced fruit, and whether that timing was correlated with the plant’s long-term seed production. I found that the timing of flowering did have an effect on long-term fruit set – plants that flowered earlier tended to produce more fruit per unit area overall. Secondly, I asked whether some individuals in the population consistently produce more fruit than others, and if trends in fruit production varied at the population level. I found that some individuals consistently produce more fruit than their neighbors, which suggests that some variation in fruit set within a population is due to individual differences (possibly genetic or microhabitat differences). I examined possible correlations between climate factors and fruit production. I used summer temperatures and precipitation as climate indicators, and found that both were negatively correlated with fruit set. I also found that variation in population fruit set was lower than expected, suggesting that disparate individual responses to environmental variation buffer population fruit set

A critical comparison of integral projection and matrix projection models for demographic analysis

Structured demographic models are among the most common and useful tools in population biology. However, the introduction of integral projection models (IPMs) has caused a profound shift in the way many demographic models are conceptualized. Some researchers have argued that IPMs, by explicitly representing demographic processes as continuous functions of state variables such as size, are more statistically efficient, biologically realistic, and accurate than classic matrix projection models, calling into question the usefulness of the many studies based on matrix models. Here, we evaluate how IPMs and matrix models differ, as well as the extent to which these differences matter for estimation of key model outputs, including population growth rates, sensitivity patterns, and life spans. First, we detail the steps in constructing and using each type of model. Second, we present a review of published demographic models, concentrating on size-based studies, which shows significant overlap in the way IPMs and matrix models are constructed and analyzed. Third, to assess the impact of various modeling decisions on demographic predictions, we ran a series of simulations based on size-based demographic data sets for five biologically diverse species. We found little evidence that discrete vital rate estimation is less accurate than continuous functions across a wide range of sample sizes or size classes (equivalently bin numbers or mesh points). Most model outputs quickly converged with modest class numbers (≥10), regardless of most other modeling decisions. Another surprising result was that the most commonly used method to discretize growth rates for IPM analyses can introduce substantial error into model outputs. Finally, we show that empirical sample sizes generally matter more than modeling approach for the accuracy of demographic outputs. Based on these results, we provide specific recommendations to those constructing and evaluating structured population models. Both our literature review and simulations question the treatment of IPMs as a clearly distinct modeling approach or one that is inherently more accurate than classic matrix models. Importantly, this suggests that matrix models, representing the vast majority of past demographic analyses available for comparative and conservation work, continue to be useful and important sources of demographic information.Support for this work was provided by NSF awards 1146489, 1242558, 1242355, 1353781, 1340024, 1753980, and 1753954, 1144807, 0841423, and 1144083. Support also came from USDA NIFA Postdoctoral Fellowship (award no. 2019-67012-29726/project accession no. 1019364) for R. K. Shriver; the Swiss Polar Institute of Food and Agriculture for N. I. Chardon; the ICREA under the ICREA Academia Programme for C. Linares; and SERDP contract RC-2512 and USDA National Institute of Food and Agriculture, Hatch project 1016746 for A .M. Louthan. This is Contribution no. 21-177-J from the Kansas Agricultural Experiment Station

Climate and synchrony with conspecifics determine the effects of flowering phenology on reproductive success in Silene acaulis

Changes in flowering phenology resulting from climate change could impact individual plant fitness and population viability. Flowering phenology can mediate plant reproductive success in several ways, including pollinator interactions, flowering synchrony with conspecifics, and timing of suitable abiotic conditions. We explored factors that control phenology and reproductive success for an alpine cushion plant, Silene acaulis, across two years and four sites, totaling 1,123 plants, in Colorado, USA. We investigated relationships between flowering time, flowering synchrony, and reproductive success with local abiotic conditions and pollinator behavior. Mean flowering phenology was strongly correlated with the timing of snowmelt across sites and years. Relative to mean flowering times, earlier flowering plants generally produced more flowers and experienced greater soil moisture during flowering but reduced synchrony with conspecifics. Fruit set tended to increase with greater soil moisture, synchrony during flowering, and earlier flowering times. Pollinator visitation increased with local Silene flower density. Earlier snowmelt and drier conditions later in the season favor earlier flowering, but these effects are partially counteracted by the positive effects of synchrony, perhaps because of changes in pollinator visitation. Overall, while both biotic and abiotic effects influence reproductive success, late-season drought may outweigh the benefits of flowering synchrony to increasingly favor earlier flowering

Federal Reserve Bank of Minneapolis Research Department Staff Report 472 On Financing Retirement with an Aging Population *

ABSTRACT A problem facing the United States is financing retirement consumption as its population ages. Policy analysts increasingly advocate switching to a savings-for-retirement system that does not rely on taxing workers' incomes, but are concerned about insufficient savings opportunities with limited government debt. This concern is unwarranted. First, there is more productive capital than commonly assumed in macroeconomic modeling. Second, if the policy reform subsumes the elimination of capital income taxes, then the value of business equity increases relative to the capital stock. We show how to devise a transition path from the current U.S. system to a savingsfor-retirement system that increases the welfare of all current and future cohorts, with estimates of future gains that are twice as large as those found with typically used macroeconomic models