Species loss leads to community closure

Global extinction of a species is sadly irreversible. At a local scale, however, extinctions may be followed by re-invasion. We here show that this is not necessarily the case and that an ecological community may close its doors for re-invasion of species lost from it. Previous studies of how communities are assembled have shown that there may be rules for that process and that limitations are set to the order by which species are introduced and put together. Instead of focusing on the assembly process we randomly generated simple competitive model communities that were stable and allowed for two to 10 coexisting species. When a randomly selected single species was removed from the community, the cascading species loss was recorded and frequently the resulting community was more than halved. Cascading extinctions have previously been recorded, but we here show that the relative magnitude of the cascade is dependent on community size (and not only trophic structure) and that the reintroduction of the original species lost often is impossible. Hence, species loss does not simply leave a void potentially refilled, but permanently alters the entire community structure and consequently the adaptive landscape for potential re-invaders.     

Invasion under a trade-off between density dependence and maximum growth rate

The invasion of alien species and genotypes is an increasing concern in contemporary ecology. A central question is, what life-history traits enable invasion amidst populations of wild species and conventional cultivars? In order to invade, the initially rare species must perform better than their resident competitors. We conducted a mathematical analysis and simulation of a two-species extension of the Maynard Smith and Slatkin model for population dynamics in discrete time to study the role of density dependence as different types of competition in the invasion of new species. The type of density dependence ranged from scramble to contest competition. This led to intrinsic dynamics of the species range from point equilibrium to cycles and chaos. The traits were treated either as free parameters or constrained by a trade-off resulting from a common fixed strength of density dependence or equilibrium density. Resident and intruder traits had up to ten-fold differences in all of the parameters investigated. Higher equilibrium density of the intruder allowed invasion. Under constrained equilibrium density, an intrinsically stable intruder could invade an unstable resident population. Scramble competition made a population more susceptible to invasion than contest competition (e.g., limitation by light or territory availability). This predicts that a population which is mainly limited by food (or nutrients in plants) is more likely to be invaded than a population limited by a hierarchical competition, such as light among plants. The intruder population may have an effect on the resident population's dynamics, which makes the traditional invasion analysis unable to predict invasion outcome.     

Assessment of Heart Rate Variability Thresholds from Incremental Treadmill Tests in Five Cross-Country Skiing Techniques

The assessment of heart rate variability (HRV) thresholds (HRVTs) as an alternative of Ventilatory thresholds (VTs) is a relatively new approach with increasing popularity which has not been conducted in cross-country (XC) skiing yet. The main purpose of the present study was to assess HRVTs in the five main XC skiing-related techniques, double poling (DP), diagonal striding (DS), Nordic walking (NW), V1 skating (V1), and V2 skating (V2).Ten competitive skiers completed these incremental treadmill tests until exhaustion with a minimum of one to two recovery days in between each test. Ventilatory gases, HRV and poling frequencies were measured. The first HRV threshold (HRVT₁) was assessed using two time-domain analysis methods, and the second HRV threshold (HRVT₂) was assessed using two non-time varying frequency-domain analysis methods. HRVT₁ was assessed by plotting the mean successive difference (MSD) and standard deviation (SD) of normalized R-R intervals to workload. HRVT₁ was assessed by plotting high frequency power (HFP) and the HFP relative to respiratory sinus arrhythmia (HFP_RSA) with workload. HRVTs were named after their methods (HRVT_1-SD; HRVT_1-MSD; HRVT_2-HFP; HRVT_2-HFP-RSA). The results showed that the only cases where the proposed HRVTs were good assessors of VTs were the HRVT_1-SD of the DS test, the HRVT_1-MSD of the DS and V2 tests, and the HRVT_2-HFP-RSA of the NW test. The lack of a wider success of the assessment of HRVTs was reasoned to be mostly due to the high entrainment between the breathing and poling frequencies. As secondary finding, a novel Cardiolocomotor coupling mode was observed in the NW test. This new Cardiolocoomtor coupling mode corresponded to the whole bilateral poling cycle instead of corresponding to each poling action as it was reported to the date by the existing literature.     

Synthesis and Biological Evaluation of Dideoxunucleosides Containing A Difluoromethylene Unit

Abstract

2′-difluoro and 3′-difluoro dideoxynucleosides containing thymine and cytosine as the base were synthesized. These compounds inhibited HeLa cell growth and Moloney leukemia virus to a modest degree.     

Early life of fathers affects offspring fitness in a wild rodent

Intergenerational fitness effects on offspring due to the early life of the parent are well studied from the standpoint of the maternal environment, but intergenerational effects owing to the paternal early life environment are often overlooked. Nonetheless, recent laboratory studies in mammals and ecologically relevant studies in invertebrates predict that paternal effects can have a major impact on the offspring's phenotype. These nongenetic, environment‐dependent paternal effects provide a mechanism for fathers to transmit environmental information to their offspring and could allow rapid adaptation. We used the bank vole Myodes glareolus, a wild rodent species with no paternal care, to test the hypothesis that a high population density environment in the early life of fathers can affect traits associated with offspring fitness. We show that the protein content in the diet and/or social environment experienced during the father's early life (prenatal and weaning) influence the phenotype and survival of his offspring and may indicate adaptation to density‐dependent costs. Furthermore, we show that experiencing multiple environmental factors during the paternal early life can lead to a different outcome on the offspring phenotype than stimulated by experience of a single environmental factor, highlighting the need to study developmental experiences in tandem rather than independent of each other.     

Ultraviolet screening by slug tissue and tight packing of plastids protect photosynthetic sea slugs from photoinhibition

Photosynthesis Research - One of the main mysteries regarding photosynthetic sea slugs is how the slug plastids handle photoinhibition, the constant light-induced damage to Photosystem II of...     

Acclimation of Chlamydomonas reinhardtii to extremely strong light

Photosynthesis Research - Most photosynthetic organisms are sensitive to very high light, although acclimation mechanisms enable them to deal with exposure to strong light up to a point. Here we...     

Community stability under different correlation structures of species’ environmental responses

The outcome of species interactions in a variable environment is expected to depend on how similarly different species react to variation in environmental conditions. We study community stability (evenness and species diversity) in competitive communities that are either closed or subjected to random migration, under different regimes of environmental forcing. Community members respond to environmental variation: (i) independently (IR), (ii) in a positively correlated way (CR), or (iii) hierarchically, according to niche differences (HR). Increasing the amplitude of environmental variation and environmental reddening both reduce species evenness in closed communities through a reduction in species richness and increased skew in species abundances, under all three environmental response scenarios, although autocorrelation only has a minor effect with HR. Open communities show important qualitative differences, according to changes in the correlation structure of species’ environmental responses. There is an intermediate minimum in evenness for HR communities with increasing environmental amplitude, explained by the interaction of changes in species richness and changes in the variance of within-species environmental responses across the community. Changes in autocorrelation also lead to qualitative differences between IR, CR and HR communities. Our results highlight the importance of considering mechanistically derived, hierarchical environmental correlations between species when addressing the influence of environmental variation on ecological communities, not only uniform environmental correlation across all species within a community.     

Natural hierarchy emerges from energy dispersal

Hierarchical organization of ‘systems within systems’ is an apparent characteristic of nature. For many biotic and abiotic systems it is known how the nested structural and functional order builds up, yet the general principle why matter evolves to hierarchies has remained unfamiliar to many. We clarify that increasingly larger integrated systems result from the quest to decrease free energy according to the 2nd law of thermodynamics. The argumentation is based on the recently derived equation of motion for natural processes. Hierarchically organized energy transduction machinery emerges naturally when it provides increased rates of energy dispersal. Likewise, a hierarchical system will dismantle into its constituents when they as independent systems will provide higher rates of entropy increase. Since energy flows via interactions, decreasing strengths of interactions over increasingly larges lengths scales mark natural boundaries for nested integrated systems.     

Maternal investment in relation to sex ratio and offspring number in a small mammal – a case for Trivers and Willard theory?

1.  Optimal parental sex allocation depends on the balance between the costs of investing into sons vs. daughters and the benefits calculated as fitness returns. The outcome of this equation varies with the life history of the species, as well as the state of the individual and the quality of the environment.
2.  We studied maternal allocation and subsequent fecundity costs of bank voles, Myodes glareolus , by manipulating both the postnatal sex ratio (all-male/all-female litters) and the quality of rearing environment (through manipulation of litter size by −2/+2 pups) of their offspring in a laboratory setting.
3.  We found that mothers clearly biased their allocation to female rather than male offspring regardless of their own body condition. Male pups had a significantly lower growth rate than female pups, so that at weaning, males from enlarged litters were the smallest. Mothers produced more milk for female litters and also defended them more intensively than male offspring.
4.  The results agree with the predictions based on the bank vole life history: there will be selection for greater investment in daughters rather than sons, as a larger size seems to be more influencial for female reproductive success in this species. Our finding could be a general rule in highly polygynous, but weakly dimorphic small mammals where females are territorial.
5.  The results disagree with the narrow sense Trivers & Willard hypothesis, which states that in polygynous mammals that show higher variation in male than in female reproductive success, high-quality mothers are expected to invest more in sons than in daughters.