The significance of partial migration for food web and ecosystem dynamics

Migration is ubiquitous and can strongly shape food webs and ecosystems. Less familiar, however, is that the majority of life cycle, seasonal and diel migrations in nature are partial migrations: only a fraction of the population migrates while the other individuals remain in their resident ecosystem. Here, we demonstrate different impacts of partial migration rendering it fundamental to our understanding of the significance of migration for food web and ecosystem dynamics. First, partial migration affects the spatiotemporal distribution of individuals and the food web and ecosystem-level processes they drive differently than expected under full migration. Second, whether an individual migrates or not is regularly correlated with morphological, physiological, and/or behavioural traits that shape its food-web and ecosystem-level impacts. Third, food web and ecosystem dynamics can drive the fraction of the population migrating, enabling the potential for feedbacks between the causes and consequences of migration within and across ecosystems. These impacts, individually and in combination, can yield unintuitive effects of migration and drive the dynamics, diversity and functions of ecosystems. By presenting the first full integration of partial migration and trophic (meta-)community and (meta-)ecosystem ecology, we provide a roadmap for studying how migration affects and is affected by ecosystem dynamics in a changing world.     

Biological traits and living conditions of Maya Indian and non Maya girls from Merida,Mexico

A total of 522 girls and their families from low and middle social strate were examined in the northern part of Merida (Yucatan) during 1988 and 1989. Marital radius in the parental generation was relatively long (146 km), and it was six times longer for non-Maya and mixed couples than Maya. Living and housing conditions were similar for both Maya and non-Maya (mixed couples typically had an intermediate condition), except for sewage system (sanitation). The Maya income was 64% lower. Maya men and women were short. The girls from Merida were short, hyper-brachycephalic (short headed), and europrosopic (broad face). Among them, Maya girls were even shorter, more round-headed, and more broad-faced than non-Maya girls. Menarche occurred on the average at an age of 12.6 years in mothers and 12.1 years in daughters. As the generation time was about 25 years, there was a slow acceleration of maturation (0.2 years per decade). Presumably, also stature has increased in recent years.     

Influence of plant domestication on plant-pollinator interactions: Floral attributes and floral visitor communities in wild and cultivated squash plants

Premise

Domestication of plant species results in phenotypic modifications and changes in biotic interactions. Most studies have compared antagonistic plant-herbivore interactions of domesticated plants and their wild relatives, but little attention has been given to how domestication influences plant-pollinator interactions. Floral attributes and interactions of floral visitors were compared between sister taxa of the genus Cucurbita (Cucurbitaceae), the domesticated C. moschata, C. argyrosperma ssp. argyrosperma and its wild progenitor C. argyrosperma ssp. sororia in the place of origin.

Methods

We conducted univariate and multivariate analyses to compare floral morphological traits and analyzed floral reward (nectar and pollen) quantity and quality between flowers of wild and domesticated Cucurbita taxa. Staminate and pistillate flowers of all three taxa were video recorded, and visitation and behavior of floral visitors were registered and analyzed.

Results

Most floral morphological characteristics of flowers of domesticated taxa were larger in both staminate and pistillate flowers. Staminate and pistillate flowers presented distinct correlations between floral traits and integration indices between domesticated and wild species. Additionally, pollen quantity and protein to lipid ratio were greater in domesticated species. Cucurbit pollen specialists, Eucera spp., had the highest probability of visit for all Cucurbita taxa.

Conclusions

We provide evidence that floral traits of domesticated and wild Cucurbita species experienced different selection pressures. Domesticated Cucurbita species may have more resources invested towards floral traits, thereby increasing attractiveness to pollinators and potentially plant reproductive success. Wild ancestor plant populations should be conserved in their centers of origin to preserve plant-pollinator interactions.     

Trade-offs and synergies between ecosystem productivity and stability in temperate grasslands

Aim

It is crucial to monitor how the productivity of grasslands varies with its temporal stability for management of these ecosystems. However, identifying the direction of the productivity–stability relationship remains challenging because ecological stability has multiple components that can display neutral, positive or negative covariations. Furthermore, evidence suggests that the direction of the productivity–stability relationship depends on the biotic interactions and abiotic conditions that underlie ecosystem productivity and stability. We decipher the relationships between grassland productivity and two components of its stability in four habitat types with contrasting environments and flora.

Location

France.

Time period

2000–2020.

Major taxa

Grassland plant species.

Methods

We used c. 20,000 vegetation plots spread across French permanent grasslands and remotely sensed vegetation indices to quantify grassland productivity and temporal stability. We decomposed stability into constancy (i.e., temporal invariability) and resistance (i.e., maximum deviation from average) and deciphered the direct and indirect effects of abiotic (namely growing season length and nitrogen input) and biotic (namely plant taxonomic diversity, trait diversity and community-weighted mean traits) factors on productivity–stability relationships using structural equation models.

Results

We found a positive relationship between productivity and constancy and a negative relationship between productivity and resistance in all habitats. Abiotic factors had stronger effects on productivity and stability compared with biotic factors. A longer growing season enhanced grassland productivity and constancy. Nitrogen input had positive and negative effects on grassland productivity and resistance, respectively. Trait values affected the constancy and resistance of grassland more than taxonomic and trait diversity, with effects varying from one habitat to another. Productivity was not related to any biotic factor.

Main conclusions

Our findings reveal how vital it is to consider both the multiple components of stability and the interaction between environment and biodiversity to gain an understanding of the relationships between productivity and stability in real-world ecosystems, which is a crucial step for sustainable grassland management.     

Vertically stratified frugivore community composition and interaction frequency in a liana fruiting across forest strata

Vertical stratification is a key feature of tropical forests and structures plant–frugivore interactions. However, it is unclear whether vertical differences in plant-frugivore interactions are due to differences among strata in plant community composition or inherent preferences of frugivores for specific strata. To test this, we observed fruit removal of a diverse frugivore community on the liana Marcgravia longifolia in a Peruvian rain forest. Unlike most other plants, Marcgravia longifolia produces fruits across forest strata. This enabled us to study effects of vertical stratification on fruit removal without confounding effects of plant species and stratum. We found a high number of visits of a few frugivore species in the understorey and a low number of visits of many different frugivores in the canopy and midstorey. Whereas partial and opportunistic frugivores foraged across strata with differing frequencies, obligate frugivores were only found eating fruits in the higher strata. Avian frugivores foraging in the canopy were mainly large species with pointed wings, whereas under- and midstorey avian foragers were smaller with rounded wings. Our findings suggest a continuous shift in the frugivore community composition along the vertical gradient, from a few generalized frugivores in the understorey to a diverse set of specialized frugivores in the canopy. This shift in the frugivore community leads to correlated, reciprocal changes from specialized to generalized plant-frugivore interactions. Thus, we conclude that vertical niche differentiation between species in tropical forests persists even when food resources are available across strata. This highlights its role for promoting biodiversity and ecosystem functioning.     

THE MEASUREMENT OF SELECTION ON QUANTITATIVE TRAITS: BIASES DUE TO ENVIRONMENTAL COVARIANCES BETWEEN TRAITS AND FITNESS

The use of regression techniques for estimating the direction and magnitude of selection from measurements on phenotypes has become widespread in field studies. A potential problem with these techniques is that environmental correlations between fitness and the traits examined may produce biased estimates of selection gradients. This report demonstrates that the phenotypic covariance between fitness and a trait, used as an estimate of the selection differential in estimating selection gradients, has two components: a component induced by selection itself and a component due to the effect of environmental factors on fitness. The second component is shown to be responsible for biases in estimates of selection gradients. The use of regressions involving genotypic and breeding values instead of phenotypic values can yield estimates of selection gradients that are not biased by environmental covariances. Statistical methods for estimating the coefficients of such regressions, and for testing for biases in regressions involving phenotypic values, are described.     

ON THE LOW HERITABILITY OF LIFE-HISTORY TRAITS

Life-history traits such as longevity and fecundity often show low heritability. This is usually interpreted in terms of Fisher's fundamental theorem to mean that populations are near evolutionary equilibrium and genetic variance in total fitness is low. We develop the causal relationship between metric traits and life-history traits to show that a life-history trait is expected to have a low heritability whether or not the population is at equilibrium. This is because it is subject to all the environmental variation in the metric traits that affect it plus additional environmental variation. There is no simple prediction regarding levels of additive genetic variance in life-history traits, which may be high at equilibrium. Several other patterns in the inheritance of life-history traits are readily predicted from the causal model. These include the strength of genetic correlations between life-history traits, levels of nonadditive genetic variance, and the inevitability of genotype-environment interaction.     

小麦根系特征对干旱胁迫的响应

干旱胁迫时, 小麦(Triticum aestivum)根系率先产生应激响应, 同时向地上部发出信号, 诱导地上部发生生理反应, 从而提高植株抗旱能力。根系构型包括平面几何性状和立体几何结构(即拓扑构型), 具有遗传稳定性和可塑性。干旱胁迫影响根系理化特性, 如根源化学信号、根系细胞酶类和根系渗透作用的响应。根系通过调整其解剖学结构和水分吸收动力等来适应干旱胁迫。该文从根系构型、理化特性和解剖学结构3个方面, 系统阐述了小麦根系特征对干旱胁迫的响应, 并探讨了其与干旱胁迫的关系和当前研究中存在的问题, 以期为相关研究提供参考。