Simple Trade-offs Research Articles

Effects of Phenology on Plant Community Assembly and Structure

Phenology—the timing of critical stages of growth and reproduction and the transitions between them—determines environmental conditions and biotic interactions. Hence, phenology is a key functional trait influencing organisms’ survival and fitness; however, the role of phenology in community assembly processes has been less considered. Here we review the importance of phenology in environmental and biotic filtering, structuring priority effects, and species coexistence in the context of the assembly of native communities, as well as in invasions and restoration. We highlight the complexity of the life-history aspect of phenology, which makes simple trade-offs—such as between growth timing and competitive ability—part of larger plant strategies shaped by a framework of risk, reward, and investment over multiple timescales. Embracing this complexity could yield insights into how phenology shapes communities.

Partial protection from fluctuating selection leads to evolution towards wider population size fluctuation and a novel mechanism of balancing selection.

When a population is partially protected from fluctuating selection, as when a seed bank is present, variance in fitness will be reduced and reproductive success of the population will be promoted. This study further investigates the effect of such a 'refuge' from fluctuating selection using a mathematical model that couples demographic and evolutionary dynamics. While alleles that cause smaller fluctuations in population density should be positively selected according to classical theoretic predictions, this study finds the opposite: alleles that increase the amplitude of population size fluctuation are positively selected if population density is weakly regulated. Under strong density regulation with a constant carrying capacity, long-term maintenance of polymorphism caused by the storage effect emerges. However, if the carrying capacity of the population is oscillating, mutant alleles whose fitness fluctuates in the same direction as population size are positively selected, eventually reaching fixation or intermediate frequencies that oscillate over time. This oscillatory polymorphism, which requires fitness fluctuations that can arise with simple trade-offs in life-history traits, is a novel form of balancing selection. These results highlight the importance of allowing joint demographic and population genetic changes in models, the failure of which prevents the discovery of novel eco-evolutionary dynamics.

Dynamics in a simple evolutionary-epidemiological model for the evolution of an initial asymptomatic infection stage

Pathogens exhibit a rich variety of life history strategies, shaped by natural selection. An important pathogen life history characteristic is the propensity to induce an asymptomatic yet productive (transmissive) stage at the beginning of an infection. This characteristic is subject to complex trade-offs, ranging from immunological considerations to population-level social processes. We aim to classify the evolutionary dynamics of such asymptomatic behavior of pathogens (hereafter "latency") in order to unify epidemiology and evolution for this life history strategy. We focus on a simple epidemiological model with two infectious stages, where hosts in the first stage can be partially or fully asymptomatic. Immunologically, there is a trade-off between transmission and progression in this first stage. For arbitrary trade-offs, we derive different conditions that guarantee either at least one evolutionarily stable strategy (ESS) at zero, some, or maximal latency of the first stage or, perhaps surprisingly, at least one unstable evolutionarily singular strategy. In this latter case, there is bistability between zero and nonzero (possibly maximal) latency. We then prove the uniqueness of interior evolutionarily singular strategies for power-law and exponential trade-offs: Thus, bistability is always between zero and maximal latency. Overall, previous multistage infection models can be summarized with a single model that includes evolutionary processes acting on latency. Since small changes in parameter values can lead to abrupt transitions in evolutionary dynamics, appropriate disease control strategies could have a substantial impact on the evolution of first-stage latency.

Defense with benefits? Ducking plants outperformed erect plants in the goldenrod Solidago gigantea in the absence of herbivory.

Despite the fact that herbivores can be highly detrimental to their host plants' fitness, plant populations often maintain genetic variation for resistance to their natural enemies. Investigating the various costs (e.g., allocation tradeoffs, autotoxicity, and ecological costs) that may prevent plants from evolving to their fullest potential resistance has been a productive strategy for shedding insight into the eco-evolutionary dynamics of plant-herbivore communities. Recent studies have shown that some individuals of goldenrod (Solidago spp.) evade apex-attacking herbivores by a temporary nodding of their stem (i.e., resistance-by-ducking). Although ducking provides an obvious fitness benefit to these individuals, nonducking (erect) morphs persist in goldenrod populations. In this study, I investigated potential costs of ducking in Solidago gigantea in terms of tradeoffs involving growth and reproduction in a common garden experiment using field-collected seeds. The S. gigantea population contained substantial genetic variation for stem morph, with 28% erect and 72% ducking stems. In the absence of herbivory, ducking plants were taller, had thicker stems, and produced an average of 20% more seeds than erect plants. This study suggests that resistance-by-ducking, instead of being costly, actually comes with additional, nondefense-related benefits. These results support the conclusion that the factors that constrain the evolution of resistance in plant populations are likely to be more subtle and complex than simple tradeoffs in resource allocation.

Optimizing nitrogen rates in the midwestern United States for maximum ecosystem value

The importance of corn production to the midwestern United States cannot be overestimated. However, high production requires high nitrogen fertilization, which carries costs to environmental services such as water quality. Therefore, a trade-off exists between the production of corn yield and water quality. We used the Groundwater Vulnerability Assessment for Shallow depths and Crop Environment Resource Synthesis-Maize models to investigate the nature of this trade-off while testing the Simple Analytic Framework trade-offs featured in this Special Feature. First, we estimated the current levels of yield and water quality production in northeastern Iowa and southern Minnesota at the 1-square-kilometer, county, and regional scales. We then constructed an efficiency frontier from optimized nitrogen application patterns to maximize the production of both yield and water quality. Results highlight the context dependency of this trade-off, but show room for increasing the production of both services to the benefit of all stakeholders. We discuss these results in the context of spatial scale, biophysical limitations to the production of services, and stakeholder outcomes given disparate power balances and biophysical contexts.

Testosterone levels correlate with the number of children in human males, but the direction of the relationship depends on paternal education

Most research shows that fatherhood is related to reduced testosterone (T) levels, but relationships between the number of children and T levels are not addressed. In humans, paternal care usually involves obtaining adequate resources to support children, which may require engaging in male–male competition and maintaining high T levels. We hypothesize that T levels in fathers should increase with increasing family size. In 78 Polish men, aged 30 to 77 years, the number of children was significantly correlated with paternal T levels, but the direction of this relationship was dependent on the fathers' education. In agreement with our hypothesis, in men with below-college education, T levels increased with increasing number of children. In contrast, in men with college education, the number of children was negatively related to paternal T levels. Drop in T levels throughout the day tended to be less pronounced the more children fathers had, irrespective of their educational level. Our results suggest that a hypothesis of simple trade-offs between mating and parenting effort may be too simplistic to explain changes in testosterone response to parenting in human males. In order to understand functional response of changes in T levels, it is crucial to account for family size and socioeconomic factors. However, due to the cross-sectional study design, we cannot exclude the possibility that T levels influenced reproductive behavior (rather than vice versa) and thus the number of children produced by men.

Flexicurity: In Pursuit of a Moving Target

Flexicurity – the contraction of flexibility and security – has in a short time become a political celebrity. In this article we trace back the genealogy of this celebrity. We begin by analysing the reasons behind the current celebration of flexicurity by the European Commission, and describe the European evolution of the concept. Then we take one step backwards and describe the conceptualisation and development of the Danish case of flexicurity, which is currently the most prominent real-life example of flexicurity in action. Our final step back in time takes us to the Dutch origins of the concept. With the near-universal celebration of flexicurity in both policy and academic circles there is a real risk of the concept becoming diluted, and eventually meaningless. In order to understand what flexicurity could and should mean we discuss various definitions of flexicurity, and arrive at a new understanding of flexicurity as an analytical concept. We suggest distinguishing between internal and external dimensions of flexibility and security, and arrive at two ideal models of either internal or external flexicurity. This distinction opens up for empirical enquiry combinations of flexibility and security that go beyond simple trade-offs and include virtuous and vicious circles between flexibility and security. The distinction also raises the issue of the difficulty in shifting from one balance of flexicurity towards another – and, thus, uncritically trying to imitate specific flexicurity examples.

TESTING OPTIMALITY WITH EXPERIMENTAL EVOLUTION: LYSIS TIME IN A BACTERIOPHAGE

Optimality models collapse the vagaries of genetics into simple trade-offs to calculate phenotypes expected to evolve by natural selection. Optimality approaches are commonly criticized for this neglect of genetic details, but resolution of this disagreement has been difficult. The importance of genetic details may be tested by experimental evolution of a trait for which an optimality model exists and in which genetic details can be studied. Here we evolved lysis time in bacteriophage T7, a virus of Escherichia coli. Lysis time is equivalent to the age of reproduction in an organism that reproduces once and then dies. Delaying lysis increases the number of offspring but slows generation time, and this trade-off renders the optimum sensitive to environmental conditions: earlier lysis is favored when bacterial hosts are dense, later lysis is favored when hosts are sparse. In experimental adaptations, T7 evolved close to the optimum in conditions favoring early lysis but not in conditions favoring late lysis. One of the late lysis adaptations exhibited no detectable phenotypic evolution despite genetic evolution; the other evolved only partly toward the expected optimum. Overall, the lysis time of the adapted phages remained closer to their starting values than predicted by the model. From the perspective of the optimality model, the experimental conditions were expected to select changes only along the postulated trade-off, but a trait outside the trade-off evolved as well. Evidence suggests that the model's failure ultimately stems from a violation of the trade-off, rather than a paucity of mutations.

Priority-setting decisions for new cancer drugs: a qualitative case study

Frameworks for legitimate and fair priority setting emphasise the importance of the rationales for priority setting decisions. However, priority setting rationales, in particular for new cancer drugs, are not well described. We describe the rationales used by a committee making funding decisions for new cancer drugs. We did a qualitative case study of a priority setting committee (Cancer Care Ontario Policy Advisory Committee for the New Drug Funding Program) by analysing documents, interviewing committee members, and observing committee meetings. We identified and described decisions and rationales related to 14 drugs in eight disease conditions over 3 years. Our main findings were that: priority setting existed in relation to resource mobilisation; clinical benefit was the primary factor in decisions; in the context of an expanding budget, rationales changed; rationales could change as costs for individual treatments increased; when all options were reasonable, groups funded a range of options and let patients decide; and priority setting rationales involve clusters of factors, not simple trade-offs. Observing priority-setting decisions and their rationales in actual practice reveals lessons not contained in theoretical accounts.

Size-Dependent Resource Allocation and Costs of Reproduction in Pinguicula Vulgaris (Lentibulariaceae)

1 Sexual reproduction, vegetative propagation and growth of Pinguicula vulgaris were monitored at two sites in Alberta, Canada during a single growing season. Seed number, biomass invested in growth, and vegetative propagation (gemmae production) were used as indices of resource allocation. Allocations to sexual reproduction, vegetative propagation and growth were analysed relative to allocation to the other two functions, plant size (winter bud mass), and site. 2 The effects of plant size on patterns of resource investment were not consistent. Allocation to growth varied negatively with plant size, particularly in large fruiting plants. In contrast, sexual reproduction and gemmae production varied positively with plant size: seed and fruit production increased allometrically, whereas allocation to gemmae was isometric. 3 In isolation from the effects of plant size, trade-offs occurred between sexual reproduction and vegetative functions (growth and gemmae production), whereas vegetative propagation and growth varied positively. Decreased gemmae production by fruiting plants, even after the effects of reproduction on growth had been accounted for, implied that: (1) reproduction affected vegetative propagation and growth independently; (2) growth was favoured over vegetative propagation; and (3) reproduction was more costly than indicated by simple trade-offs. Positive relations between growth and vegetative propagation probably arise because gemmae are in effect axillary buds on the over-wintering structure. 4 These allocation patterns, combined with threshold sizes for reproduction, suggest an emphasis on growth until a minimum size is reached. Beyond this threshold, resources not required to maintain size seem to be allocated to current reproduction. We suggest that resource allocation by P. vulgaris may reflect growth form and phenology as well as the relative probabilities of adult, gemmae and seedling survival. Plants of similar growth form and/or phenology, such as bulbor corm-forming species, probably employ similar strategies of resource allocation.

Telecommunications and economic development: Econometric analysis of the US experience

Investment in the telecommunications infrastructure can be justified because of the positive impact on economic development. Using statistical data for the 50 states of the USA, econometric analysis suggests that the influence of telecommunications is very strong when it is viewed as the only developmental input as well as when it is compared with other inputs such as education, energy and physical infrastructure. The multiple regression analysis provides a comparative perspective on resource inputs which has not been available in past research. The analysis also suggests that it is not a question of simple trade-offs between investment in one input with that of another. Instead, investment has to be made in multiple inputs including education, telecommunications and physical infrastructure.