Demographic Costs Research Articles

Microbial symbionts buffer hosts from the demographic costs of environmental stochasticity.

Species' persistence in increasingly variable climates will depend on resilience against the fitness costs of environmental stochasticity. Most organisms host microbiota that shield against stressors. Here, we test the hypothesis that, by limiting exposure to temporally variable stressors, microbial symbionts reduce hosts' demographic variance. We parameterized stochastic population models using data from a 14-year symbiont-removal experiment including seven grass species that host Epichloë fungal endophytes. Results provide novel evidence that symbiotic benefits arise not only through improved mean fitness, but also through dampened inter-annual variance. Hosts with "fast" life-history traits benefited most from symbiont-mediated demographic buffering. Under current climate conditions, contributions of demographic buffering were modest compared to benefits to mean fitness. However, simulations of increased stochasticity amplified benefits of demographic buffering and made it the more important pathway of host-symbiont mutualism. Microbial-mediated variance buffering is likely an important, yet cryptic, mechanism of resilience in an increasingly variable world.

Directional selection coupled with kin selection favors the establishment of senescence.

Conventional wisdom in evolutionary theory considers aging as a non-selected byproduct of natural selection. Based on this, conviction aging was regarded as an inevitable phenomenon. It was also thought that in the wild organisms tend to die from diseases, predation and other accidents before they could reach the time when senescence takes its course. Evidence has accumulated, however, that aging is not inevitable and there are organisms that show negative aging even. Furthermore, old age does play a role in the deaths of many different organisms in the wild also. The hypothesis of programmed aging posits that a limited lifespan can evolve as an adaptation (i.e., positively selected for) in its own right, partly because it can enhance evolvability by eliminating "outdated" genotypes. A major shortcoming of this idea is that non-aging sexual individuals that fail to pay the demographic cost of aging would be able to steal good genes by recombination from aging ones. Here, we show by a spatially explicit, individual-based simulation model that aging can positively be selected for if a sufficient degree of kin selection complements directional selection. Under such conditions, senescence enhances evolvability because the rate of aging and the rate of recombination play complementary roles. The selected aging rate is highest at zero recombination (clonal reproduction). In our model, increasing extrinsic mortality favors evolved aging by making up free space, thereby decreasing competition and increasing drift, even when selection is stabilizing and the level of aging is set by mutation-selection balance. Importantly, higher extrinsic mortality is not a substitute for evolved aging under directional selection either. Reduction of relatedness decreases the evolved level of aging; chance relatedness favors non-aging genotypes. The applicability of our results depends on empirical values of directional and kin selection in the wild. We found that aging can positively be selected for in a spatially explicit population model when sufficiently strong directional and kin selection prevail, even if reproduction is sexual. The view that there is a conceptual link between giving up clonal reproduction and evolving an aging genotype is supported by computational results.

Behavioral adjustments of endangered Barbary macaques (Macaca sylvanus) living at the edge of an agricultural landscape in Morocco.

Transition zones between natural and human-altered spaces are eroding in most terrestrial ecosystems. The persistence of animals in shared landscapes depends in part on their behavioral flexibility, which may involve being able to exploit human agricultural production. As a forest-dependent species, the Barbary macaque (Macaca sylvanus) is affected by the progressive conversion of forest-adjacent lands into crops. We explore how Barbary macaque behavior differs between groups living in a forest at the edge of agricultural zones (hereafter "disturbed groups") and groups inhabiting undisturbed forests (hereafter "natural groups"). We compare the diets, activity-budgets, home range sizes, daily path lengths, and sleeping site locations of the groups. We also quantify anthropogenic disturbances (i.e., rates of encounter with humans and dogs) and investigate relationships between such disturbances and the diets and activity budgets of macaques through multiple co-inertia analysis. Disturbed groups included high proportions of cultivated food items in their diet and encountered over 0.5/h anthropogenic disturbances. Activity-budgets differed between disturbed and natural groups and were mostly influenced by diets, not anthropogenic disturbances. Disturbed groups spent more time feeding and less time resting than natural ones. Patterns of space use differed markedly between groups, with disturbed groups displaying smaller home ranges, shorter daily path length, and much higher reutilization of sleeping sites than natural groups. This study highlights the dietary and behavioral flexibility of Barbary macaques living in human-altered environments. Their patterns of space use suggest a reduction in energy expenditure in the disturbed groups due to the inclusion of cultivated food items in their diet possibly leading to increased foraging efficiency. However, the high rates of anthropogenic encounters, including aggressive ones, are likely stressful and may potentially induce extra energy costs and lead to macaque injuries. This could result in demographic costs for crop-foraging groups, threatening the conservation of this endangered species.

Source-sink dynamics within a complex life history.

Source-sink patch dynamics occur when movement from sources stabilizes sinks by compensating for low local vital rates. The mechanisms underlying source-sink dynamics may be complicated in species that undergo transitions between discrete life stages, particularly when stages have overlapping habitat requirements and similar movement abilities. In these species, for example, the demographic effects of movement by one stage may augment or offset the effects of movement by another stage. We used a stream salamander system to investigate patch dynamics within this form of complex life history. Specifically, we tested the hypothesis that the salamander Gyrinophilus porphyriticus experiences source-sink dynamics in riffles and pools, the dominant geomorphic patch types in headwater streams. We estimated stage-specific survival probabilities in riffles and pools and stage-specific movement probabilities between the two patch types using 8 years of capture-recapture data on 4491 individuals, including premetamorphic larvae and postmetamorphic adults. We then incorporated survival and movement probabilities into a stage-structured, two-patch model to determine the demographic interactions between riffles and pools. Monthly survival probabilities of both stages were higher in pools than in riffles. Larvae were more likely to move from riffles to pools, but adults were more likely to move from pools to riffles, despite experiencing much lower survival in riffles. In simulations, eliminating interpatch movements by both stages indicated that riffles are sinks that rely on immigration from pools for stability. Allowing only larvae to move stabilized both patch types, but allowing only adults to move destabilized pools due to the demographic cost of adult emigration. These results indicated that larval movement not only stabilizes riffles, but also offsets the destabilizing effects of maladaptive adult movement. Similar patch dynamics may emerge in any structured population in which movement and local vital rates differ by age, size, or stage. Addressing these forms of internal demographic structure in patch dynamics analyses will help to refine and advance general understanding of spatial ecology.

Male harm suppresses female fitness, affecting the dynamics of adaptation and evolutionary rescue.

One of the most pressing questions we face as biologists is to understand how climate change will affect the evolutionary dynamics of natural populations and how these dynamics will in turn affect population recovery. Increasing evidence shows that sexual selection favors population viability and local adaptation. However, sexual selection can also foster sexual conflict and drive the evolution of male harm to females. Male harm is extraordinarily widespread and has the potential to suppress female fitness and compromise population growth, yet we currently ignore its net effects across taxa or its influence on local adaptation and evolutionary rescue. We conducted a comparative meta-analysis to quantify the impact of male harm on female fitness and found an overall negative effect of male harm on female fitness. Negative effects seem to depend on proxies of sexual selection, increasing inversely to the female relative size and in species with strong sperm competition. We then developed theoretical models to explore how male harm affects adaptation and evolutionary rescue. We show that, when sexual conflict depends on local adaptation, population decline is reduced, but at the cost of slowing down genetic adaptation. This trade-off suggests that eco-evolutionary feedback on sexual conflict can act like a double-edged sword, reducing extinction risk by buffering the demographic costs of climate change, but delaying genetic adaptation. However, variation in the mating system and male harm type can mitigate this trade-off. Our work shows that male harm has widespread negative effects on female fitness and productivity, identifies potential mechanistic factors underlying variability in such costs across taxa, and underscores how acknowledging the condition-dependence of male harm may be important to understand the demographic and evolutionary processes that impact how species adapt to environmental change.

The Demographic Costs of Sexually Antagonistic Selection in Partially Selfing Populations

AbstractWhen selection differs between the sexes, genes expressed by both males and females can experience sexually antagonistic (SA) selection, where beneficial alleles for one sex are deleterious for the other. Classic population genetics theory has been fundamental to understanding how and when SA genetic variation can be maintained by balancing selection, but these models have rarely considered the demographic consequences of coexisting alleles with deleterious fitness effects in each sex. In this article, we develop a stage-structured Mendelian matrix model and jointly analyze the evolutionary and demographic consequences of SA selection in obligately outcrossing (i.e., dioecious/gonochorous) and partially selfing hermaphrodite populations. We focus on identifying when SA polymorphisms are maintained by balancing selection and the population growth rate remains positive. Additionally, we analyze the effects of inbreeding depression manifesting at different life history stages and give an illustrative example of the potential for SA polymorphism in real populations using empirically estimated demographic rates for the hermaphroditic flowering plant Mimulus guttatus. Our results show that when population intrinsic growth rates approach 1, extinction occurs across large swathes of parameter space, favoring SA polymorphism or the fixation of male-beneficial alleles, and that inbreeding depression is a significant problem for maintaining SA polymorphism in partially selfing populations. Despite these demographic challenges, our example with M. guttatus appears to show that demographic rates observed in some real populations can sustain large regions of viable SA polymorphic space.

The expression of demographic costs of reproduction varies among coexisting plants with different life history traits

Abstract Demographic costs of reproduction in flowering plants should depend on life history and reproductive efforts, but how the expression of costs varies with life‐history traits is poorly understood. We experimentally increased and reduced reproductive effort (fruit production) to quantify demographic costs of reproduction in four coexisting species with contrasting growth forms (clonal vs. non‐clonal) and flower production (single‐ vs. multi‐flowered). We repeated the experiment for 3 years and measured the demographic rates the year after the treatment. In 2 years, we also quantified the costs of flower maintenance by contrasting the performance of non‐fruiting plants with intact flowers and plants with their flowers removed. Costs varied among species, in both magnitude and demographic rate affected. Costs of natural reproduction were expressed as reductions in size and fecundity next year, whereas increased reproduction additionally reduced sprouting probability. The magnitude of demographic costs of both reproduction and flower maintenance was highest in the non‐clonal, multi‐flowered species, and costs were more frequently detected in the two multi‐flowered species than in the single‐flowered ones. This may be explained by higher biomass allocation to reproductive parts and a longer flowering period in the former. Demographic costs of reproduction did not depend on clone size. Synthesis. These results document that demographic costs vary among coexisting species sharing similar niches and are associated with divergence in life‐history traits. Such trait‐dependent variation in costs may reduce competition among coexisting species and facilitate diversity.

Dissecting the costs of a facultative symbiosis in an isopod living with ants.

The balance between costs and benefits is expected to drive associations between species. While these balances are well understood for strict associations, we have no insights to which extent they determine facultative associations between species. Here, we quantified the costs of living in a facultative association, by studying the effects of red wood ants on the facultatively associated isopod Porcellio scaber. Porcellio scaber frequently occurred in and near hostile red wood ant nests and might outnumber obligate nest associates. The facultative association involved different costs for the isopod. We found that the density of the isopod decreases near the nest with higher ant traffic. Individuals in and near the nest were smaller than individuals further away from the nest. Smaller individuals were also found at sites with higher ant traffic. A higher proportion of wounded individuals was found closer to the nest and with higher ant traffic. We recorded pregnant females and juveniles in the nest suggesting that the life cycle can be completed inside the nests. Lab experiments showed that females died sooner and invested less in reproduction in presence of red wood ants. Porcellio scaber rarely provoked an aggression response, but large numbers were carried as prey to the nest. These preyed isopods were mainly dried out corpses. Our results showed that the ant association incurred several costs for a facultative associate. Consequently, red wood ant nests and their surrounding territory act as an alternative habitat where demographic costs are offset by a stable resource provisioning and protection.

Morphological defences and defence–cost trade‐offs in Daphnia in response to two co‐occurring invertebrate predators

Abstract Inducible morphological defences are crucial for understanding predator–prey interactions. Such defences have been mostly studied in a single‐predator context, ignoring the fact that prey organisms are often exposed to multiple predators. In deep peri‐Alpine European lakes, the keystone grazer Daphnia coexists with two cladoceran predators, Bythotrephes longimanus and Leptodora kindtii. Up to now, life history and morphological responses of Daphnia to these two predators have not been analysed systematically. We studied the responses of two life history (age at first reproduction, and offspring production) and five morphological traits (body size, body width, head size, spina size, and eye diameter) of eight Daphnia galeata clones to the presence of Bythotrephes and Leptodora in a common garden experiment. We compared each response trait between treatments using linear mixed models, and investigated the covariation between defence traits and demographic costs (neonate production) for the two predators. Our results show that the responses of Daphnia are predator‐ and trait‐specific. Daphnia developed a typical helmet and a larger eye only in the presence of Bythotrephes, not in the presence of Leptodora. In contrast, both predators induced larger body sizes and longer spines. Age at first reproduction was latest and demographic costs were highest in the Bythotrephes treatment, suggesting that the development of a helmet exceeds the costs of spina elongation. The responses of Daphnia clones revealed a defence‐cost trade‐off for helmet formation in the Bythotrephes, and for spina elongation in the Leptodora treatment. Hence, despite Bythotrephes and Leptodora being closely related co‐occurring predators, Daphnia responds with a unique combination of trait changes and defence‐cost trade‐offs to the two predators. The presence of predator‐specific clonal defence‐cost trade‐offs suggests that the presence of these invertebrate predators can drive different evolutionary processes in natural zooplankton communities. Disentangling the evolutionary ecology of phenotypic responses of prey species to co‐occurring predators will require multi‐trait, multi‐clone studies of induced antipredator defences.

Environmental variation and biotic interactions limit adaptation at ecological margins: lessons from rainforest Drosophila and European butterflies.

Models of local adaptation to spatially varying selection predict that maximum rates of evolution are determined by the interaction between increased adaptive potential owing to increased genetic variation, and the cost genetic variation brings by reducing population fitness. We discuss existing and new results from our laboratory assays and field transplants of rainforest Drosophila and UK butterflies along environmental gradients, which try to test these predictions in natural populations. Our data suggest that: (i) local adaptation along ecological gradients is not consistently observed in time and space, especially where biotic and abiotic interactions affect both gradient steepness and genetic variation in fitness; (ii) genetic variation in fitness observed in the laboratory is only sometimes visible to selection in the field, suggesting that demographic costs can remain high without increasing adaptive potential; and (iii) antagonistic interactions between species reduce local productivity, especially at ecological margins. Such antagonistic interactions steepen gradients and may increase the cost of adaptation by increasing its dimensionality. However, where biotic interactions do evolve, rapid range expansion can follow. Future research should test how the environmental sensitivity of genotypes determines their ecological exposure, and its effects on genetic variation in fitness, to predict the probability of evolutionary rescue at ecological margins. This article is part of the theme issue 'Species' ranges in the face of changing environments (Part II)'.

Competitive superiority of N-fixing cyanobacteria when fixed N is scarce: Reconsiderations based on a model with heterocyst differentiation

Some cyanobacteria fix nitrogen (N) with specialized cells (heterocysts). Resource competition theory and some evidence suggest that such cyanobacteria can dominate when the supply of available dissolved N is low relative to that of phosphorus (P). To probe this notion, a recently introduced mathematical model of cyanobacteria that differentiate heterocysts was paired with a model of non-fixing algal competitors. With sufficiently low abiotic loss rates, dominance by cyanobacteria was predicted at low N:P supply ratios, coexistence for intermediate ratios, and dominance by algae at high ratios. Heterocysts do not reproduce, so differentiation is demographically costly, and at abiotic loss rates exceeding about 0.18 d − 1, cyanobacteria are predicted to be competitively excluded for all N:P supply ratios examined. The demographic cost of heterocyst production is also predicted to impact competitive dynamics in the presence of herbivores. Cyanobacteria are highly susceptible to apparent competition from algae, even when they are the less-preferred food of herbivores. Algae dominate at highest and lowest N:P supply ratios, and cyanobacteria at intermediate ratios, with two non-contiguous intervals of coexistence. In addition to these unexpected results, this study illustrates how planktonic community processes could determine whether nitrogen fixation contributes significantly to planktonic nitrogen supply.

Stronger net selection on males across animals.

Sexual selection is considered the major driver for the evolution of sex differences. However, the eco-evolutionary dynamics of sexual selection and their role for a population's adaptive potential to respond to environmental change have only recently been explored. Theory predicts that sexual selection promotes adaptation at a low demographic cost only if sexual selection is aligned with natural selection and if net selection is stronger on males compared to females. We used a comparative approach to show that net selection is indeed stronger in males and provide preliminary support that this sex bias is associated with sexual selection. Given that both sexes share the vast majority of their genes, our findings corroborate the notion that the genome is often confronted with a more stressful environment when expressed in males. Collectively, our study supports one of the long-standing key assumptions required for sexual selection to bolster adaptation, and sexual selection may therefore enable some species to track environmental change more efficiently.

Context-dependent fitness costs of reproduction despite stable body mass costs in an Arctic herbivore.

The cost of reproduction on demographic rates is often assumed to operate through changing body condition. Several studies have found that reproduction depresses body mass more if the current conditions are severe, such as high population densities or adverse weather, than under benign environmental conditions. However, few studies have investigated the association between the fitness components and body mass costs of reproduction. Using 25years of individual-based capture-recapture data from Svalbard reindeer Rangifer tarandus platyrhynchus, we built a novel Bayesian state-space model that jointly estimated interannual change in mass, annual reproductive success and survival, while accounting for incomplete observations. The model allowed us to partition the differential effects of intrinsic and extrinsic factors on both non-reproductive mass change and the body mass cost of reproduction, and to quantify their consequences on demographic rates. Contrary to our expectation, the body mass cost of reproduction (mean=-5.8kg) varied little between years (CV=0.08), whereas the between-year variation in body mass changes, that were independent of the previous year's reproductive state, varied substantially (CV=0.4) in relation to autumn temperature and the amount of rain-on-snow in winter. This body mass loss led to a cost of reproduction on the next reproduction, which was amplified by the same environmental covariates, from a 10% reduction in reproductive success in benign years, to a 50% reduction in harsh years. The reproductive mass loss also resulted in a small reduction in survival. Our results show how demographic costs of reproduction, driven by interannual fluctuations in individual body condition, result from the balance between body mass costs of reproduction and body mass changes that are independent of previous reproductive state. We illustrate how a strong context-dependent fitness cost of reproduction can occur, despite a relatively fixed body mass cost of reproduction. This suggests that female reindeer display a very conservative energy allocation strategy, either aborting their reproductive attempt at an early stage or weaning at a relatively constant cost. Such a strategy might be common in species living in a highly stochastic and food limited environment.

Travel-Related Economic Burden of Chimeric Antigen Receptor TCell Therapy Administration by Site of Care.

IntroductionWe previously examined how expanding access to chimeric antigen receptor (CAR) T cell therapy administration sites impacted patient travel distances and time. In the current study, we estimated travel-related economic burden associated with site-of-care options among patients with relapsed/refractory diffuse large B cell lymphoma.MethodsWe used geographic information system methods to quantify travel-related economic burden across three site-of-care scenarios: academic hospitals; academic and community multispecialty hospitals; and academic and community multispecialty hospitals plus nonacademic specialty oncology network centers. Socioeconomic status, administration sites, and county of residence were derived from the US Census Bureau and publicly available sources. Travel costs were based on governmental guidelines, US census wage data, and Bureau of Transportation Statistics. Travel distance and time to the nearest CAR T cell therapy administration sites were estimated from previous research.ResultsTotal national estimated costs associated with traveling for CAR T cell therapy were $21.1 million if CAR T cell therapy was offered exclusively in academic hospitals, and $14.7 million if expanded to include community hospitals plus nonacademic specialty oncology network centers, representing a $6.5-million reduction associated with expanding access to eligible patients. The largest cost-saving component was lodging/meals. Regional and demographic cost differences were statistically significant between academic hospitals and nonacademic hospitals/specialty oncology centers. In all scenarios, patients living below the federal poverty level (FPL) had higher weighted mean total costs versus patients living above the FPL. White and Native American patients were estimated to have the highest weighted mean total costs across race/ethnicity groups. For all subgroups, costs were reduced by expanding access beyond academic hospitals.ConclusionCAR T cell therapy is currently restricted to academic hospitals; total travel costs could be substantially decreased if access is expanded to nonacademic hospitals and specialty oncology centers. Patients in rural areas and those living below the FPL are particularly disadvantaged by restricted access.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12325-021-01839-y.

The best defence is not being there: avoidance of larger carnivores is not driven by risk intensity

AbstractSpecies interactions are key factors determining the distribution and structure of species assemblages. Owing to their central positions, mid‐ranking mammalian carnivores are involved in interactions with numerous species, including competition for resources and instances of killing by higher ranking predators. Lethal interactions can directly influence species’ demography. However, the fear of lethal interactions, competition or both may also affect when and where individuals are active (i.e. non‐lethal interactions). Although differences in body–size and trophic overlap are known predictors of the frequency of lethal interactions, their influence on non‐lethal interactions is uncertain. Through camera trapping, we studied non‐lethal interactions between a small mesocarnivore (pine marten), a potential killer and intense competitor (red fox) and a moderate competitor and unlikely killer (Eurasian badger). We determined overlap and differences in their diel activity patterns and the degree of spatial overlap in two seasons with contrasting resource availability. Additionally, we estimated the effect of larger carnivore detection rates on pine marten detection rates. We also compared time intervals between pine marten visits to baited stations in the absence and presence of either or both larger carnivores. Our results are consistent with pine martens distributing their daily activity to maximize overlap with prey and to minimize competition and risk of aggression over the spatial scale. Pine martens also responded to the immediate threat of larger carnivores irrespective of the threat they pose by taking 4–7 days longer to re‐visit a station. Small‐scale non‐lethal interactions such as these may enable pine martens to coexist closely with two larger carnivores, yet it remains uncertain whether their population incurs a demographic cost through restricted access to resources. Carnivore's risk‐avoidance strategies could be harnessed to protect prey species of interest. However, our results suggest avoidance is short‐lived and recurrent stimuli would be necessary.

Cost, reach, and representativeness of recruitment efforts for an online skin cancer risk reduction intervention trial for young adults.

Despite its increasing use, few studies have reported on demographic representativeness and costs of research recruitment via social media. It was hypothesized that cost, reach, enrollment, and demographic representativeness would differ by social media recruitment approach. Participants were 18-25 year-olds at moderate to high risk of skin cancer based on phenotypic and behavioral characteristics. Paid Instagram, Facebook, and Twitter ads, unpaid social media posts by study staff, and unpaid referrals were used to recruit participants. Demographic and other characteristics of the sample were compared with the 2015 National Health Interview Survey (NHIS) sample. Analyses demonstrated significant differences among recruitment approaches regarding cost efficiency, study participation, and representativeness. Costs were compared across 4,274 individuals who completed eligibility screeners over a 7-month period from: Instagram, 44.6% (of the sample) = 1,907, $9 (per individual screened); Facebook, 31.5% = 1,345, $8; Twitter, 1% = 42, $178; unpaid posts by study staff, 10.6% and referred, 6.5%, $1. The lowest rates of study enrollment among individuals screened was for Twitter. Most demographic and skin cancer risk factors of study participants differed from those of the 2015 NHIS sample and across social media recruitment approaches. Considering recruitment costs and number of participants enrolled, Facebook and Instagram appeared to be the most useful approaches for recruiting 18-25 year-olds. Findings suggest that project budget, target population and representativeness, and participation goals should inform selection and/or combination of existing and emerging online recruitment approaches.

Outpatient Parotidectomy, a Safety and Financial Review.

The objective of this study is to investigate the safety, efficacy, and potential cost-savings of the outpatient parotidectomy procedure. This is a retrospective chart review of all patients who underwent a parotidectomy at a large academic center from 2015 through 2019 including demographic data, postoperative complications, drain placement, readmission, and financial cost. A comparison was performed between patients who underwent an outpatient vs inpatient parotidectomy. A total of 335 patients underwent parotidectomy (136 outpatient; 199 inpatient). Comparison of patient demographics, common comorbidities, tumor size, tumor type, postoperative complications, and readmission rate was similar between the inpatient and outpatient cohorts. The overall mean cost difference between inpatient parotidectomy and outpatient parotidectomy for all years was $1528.58 (95%CI: $1139-$1916). The outpatient parotidectomy procedure has a comparable safety profile to the inpatient procedure while providing a significant cost-savings benefit.

The ecological causes and consequences of hard and soft selection.

Interactions between natural selection and population dynamics are central to both evolutionary-ecology and biological responses to anthropogenic change. Natural selection is often thought to incur a demographic cost that, at least temporarily, reduces population growth. However, hard and soft selection clarify that the influence of natural selection on population dynamics depends on ecological context. Under hard selection, an individual's fitness is independent of the population's phenotypic composition, and substantial population declines can occur when phenotypes are mismatched with the environment. In contrast, under soft selection, an individual's fitness is influenced by its phenotype relative to other interacting conspecifics. Soft selection generally influences which, but not how many, individuals survive and reproduce, resulting in little effect on population growth. Despite these important differences, the distinction between hard and soft selection is rarely considered in ecology. Here, we review and synthesize literature on hard and soft selection, explore their ecological causes and implications and highlight their conservation relevance to climate change, inbreeding depression, outbreeding depression and harvest. Overall, these concepts emphasise that natural selection and evolution may often have negligible or counterintuitive effects on population growth-underappreciated outcomes that have major implications in a rapidly changing world.

Adaptive variation in the development of extraembryonic membranes of gekkotan embryos: A meta-analytical approach.

Highly mineralized rigid-shelled eggs characterize one lineage of gekkotans. In contrast, poorly mineralized flexible-shelled eggs characterize basal lineages of gekkotans and all other squamates. Low oxygen permeability of rigid-shelled eggs is associated with small eggs and hatchlings, and long incubation lengths compared to flexible-shelled gekkotan eggs. These features represent a demographic cost for species with rigid-shelled eggs. This cost is offset, at least in part, because mortality due to desiccation and predation is reduced for rigid-shelled eggs relative to flexible-shelled eggs. Developmental traits may also compensate for the low oxygen permeability of rigid-shelled eggs. Oviposition, for example, occurs at earlier developmental stages for gekkotans with rigid- versus flexible-shelled eggs. Such early oviposition facilitates development because eggs move from the relatively hypoxic oviduct to the much better oxygenated nest environment. In this study, I tested the hypothesis that the growth of the yolk sac (YS) and chorioallantoic membrane (CAM) of gekkotans with rigid-shelled eggs is initiated and completed earlier than those of gekkotans with flexible-shelled eggs. I measured the surface area of eggs covered by the YS and CAM from oviposition to hatching and determined which of four nonlinear models provide the best fit for growth curves. I also compiled a data set on embryonic metabolism of gekkotans and other lizards in order to place growth of the YS and CAM in the context of energy utilization of lizard embryos overall. Growth of the YS and CAM of gekkotans with rigid-shelled eggs is accelerated relative to that of gekkotans with flexible-shelled eggs and may serve to separate the cost of YS and CAM development from that of the embryo itself. Adaptive variation in YS and CAM development may extend to birds, crocodilians, and turtles as they also exhibit life history variation that affects oxygen availability to embryos during development.

Excess mortality in Europe and Serbia during the COVID-19 pandemic in 2020

The 2020 pandemic came at a huge demographic cost, particularly regarding the increase in mortality. In this paper we examine excess deaths in Serbia and 34 other European countries in 2020. Methodological inconsistencies and big differences in how COVID-19 deaths were recorded across different countries make it difficult to make any cross-country comparisons, even with the scope limited only to Europe. Since the number of total deaths is a methodologically solid indicator, we looked at the differences between the total number of deaths in 2020 and compared that to deaths in 2019. The lowest increase in mortality - below 5% - occurred in countries in the north of Europe (Norway, Denmark, Finland, Latvia), while the highest increase - over 18% - was recorded in the southern and central parts of the continent (Albania, Northern Macedonia, Spain, Belgium, Poland, Slovenia, Russia). There is no clear geographical regularity. In 2020, Serbia had 12.6% more deaths compared to 2019, which was close to the European average. Within Serbia, statistical differences between regions were not large. Measuring the contribution of COVID-19 deaths to excess mortality is much more problematic. The excess death ratio is more helpful for understanding methodological and data-gathering issues than finding evidence about composition and divergence in mortality. According to this indicator (based on preliminary data), only 25% of excess deaths in Serbia in 2020 were caused by COVID-19, while the European average was 54%. However, in many (primarily Eastern European) countries in 2020, the indirect consequences of COVID-19 on the health of the population were more significant than the direct ones. It is precisely the ratio of COVID-19 diagnoses that led to death in total mortality that shows this. The final results may confirm this statement or indicate potential data manipulation. While this paper focuses only on the year 2020, as of Q1 of 2021, the pandemic is not nearing its end. Based on preliminary data published daily, Serbia had more COVID-19 deaths in the first four months of 2021 than for the whole of 2020. This indicates that the consequences of the pandemic for Serbia will be dire in 2021, regardless of the course the pandemic takes.