The mechanistic basis for higher‐order interactions and non‐additivity in competitive communities

Motivated by both analytical tractability and empirical practicality, community ecologists have long treated the species pair as the fundamental unit of study. This notwithstanding, the challenge of understanding more complex systems has repeatedly generated interest in the role of so‐called higher‐order interactions (HOIs) imposed by species beyond the focal pair. Here we argue that HOIs – defined as non‐additive effects of density on per capita growth – are best interpreted as emergent properties of phenomenological models (e.g. Lotka–Volterra competition) rather than as distinct ‘ecological processes’ in their own right. Using simulations of consumer‐resource models, we explore the mechanisms and system properties that give rise to HOIs in observational data. We demonstrate that HOIs emerge under all but the most restrictive of assumptions, and that incorporating non‐additivity into phenomenological models improves the quantitative and qualitative accuracy of model predictions. Notably, we also observe that HOIs derive primarily from mechanisms and system properties that apply equally to single‐species or pairwise systems as they do to more diverse communities. Consequently, there exists a strong mandate for further recognition of non‐additive effects in both theoretical and empirical research.     

An optimal foraging and migration model for juvenile plaice

Summary A state-dependent model has been used to predict daily and tidal patterns of migration, feeding and inactivity in juvenile plaice (Pleuronectes platessa L.) in their intertidal and shallow subtidal nursery areas. Vertical position, quantity of energy reserves and fullness of the gut characterized the state of individual fishes. If feeding is visually mediated, the model predicts that, by night, plaice should move to areas of low predation risk and become inactive, whereas by day, plaice should migrate to feed in areas of high prey encounter rate. Vertical zones adopted by day and night and, hence, patterns of migration, should depend on the distributions of predators and prey. When prey are more abundant in the intertidal zone, plaice should move onshore to feed as the tide rises and when prey are more abundant offshore, plaice should move offshore to feed by day. If predators are equally abundant in all zones, the fish should behave as if no predators were present, having no effective refuge. An increase in the abundance of predators with depth results in the restriction of plaice activities to shallower vertical zones, depending on the magnitude of the predation threat. Zones adopted thus depend on the trade-off between energy intake and predation risk. Concordance between predicted behaviour and observed patterns is evident in contrasting habitats. Migration and feeding in the Wadden Sea, where prey are more abundant on intertidal flats, is dominated by the tidal component, whereas on impoverished exposed beaches of the west coast of Scotland, the diurnal component is dominant. Tidally related behaviour persists in the latter environment, not predicted by the model and may be a consequence of using endogenous rhythms to approach optimal behavioural patterns.     

Information-Theoretic Analysis of Neural Coding

We describe an approach to analyzing single- and multiunit (ensemble) discharge patterns based on information-theoretic distance measures and on empirical theories derived from work in universal signal processing. In this approach, we quantify the difference between response patterns, whether time-varying or not, using information-theoretic distance measures. We apply these techniques to single- and multiple-unit processing of sound amplitude and sound location. These examples illustrate that neurons can simultaneously represent at least two kinds of information with different levels of fidelity. The fidelity can persist through a transient and a subsequent steady-state response, indicating that it is possible for an evolving neural code to represent information with constant fidelity.     

The growth strategy of the Gram-positive rod

Abstract Bacteria grow by enlarging their envelope in such a way that osmotic pressure does not normally cause physical rupture. The strategy of Bacillus subtilis for both cylindrical elongation and pole formation is now substantially defined. Side-wall growth takes place by laying down new peptidoglycan, which is then displaced outwards, stretched and discarded; cross walls are laid down in the absence of stress, and then stretched and bulged outward as the septum is split and the pole is formed.     

整合电路理论的生态廊道及其重要性识别

景观连接度被认为是影响诸多生态过程的一个重要因素.基于最小累积阻力模型的最小成本路径识别方法可以有效识别异质性景观中的功能连接,已被广泛应用到景观的功能连接评价与生态廊道模拟的研究中.基于电路理论的连接度模型用电阻代替了图论中的边、用电阻距离代替成本距离,来衡量异质性景观的功能连接.本文以SIMMAP 2.0软件生成的模拟景观为对象,借助于Linkage Mapper工具和Circuitscape软件,探讨如何将最小累积阻力模型与基于电路理论的连接度模型相结合来识别生态廊道及其景观要素的相对重要性.结果表明: 两种模型在应用中各有优势,互为补充.最小成本路径方法可以有效识别栖息地之间的最小成本廊道,基于电路理论的连接度模型通过电流密度的计算可以有效识别对景观连接性有重要影响的景观要素和“夹点”地区,并且“夹点”的位置不受廊道宽度的影响,在廊道重要性识别研究中具有明显优势.该方法可为区域生态保护规划和生态廊道设计提供科学依据.     

Reproductive significance of feeding on saprobic and arbuscular mycorrhizal fungi by the collembolan, Folsomia candida

1. Collembolans have often been credited with negatively affecting arbuscular mycorrhizal (AM) symbioses, mainly by grazing and severing the associated external fungal network from host roots. However, most previous experiments were performed using relatively 'clean' systems where other, non-mycorrhizal, fungi were largely excluded. Yet, plant rhizospheres harbour a wide variety of highly palatable non-AM fungi, most of which have saprobic lifestyles.
2. In this study we isolated and cultured several rhizosphere fungi, and the collembolan , Folsomia candida , from the Long-Term Mycorrhiza Research Site, University of Guelph, Canada, to test the hypothesis that, given a choice, collembolans would prefer to feed on saprobic fungi and that such a choice is of adaptive significance to the animals.
3. A laboratory food preference experiment revealed that F. candida favours common saprobic fungi over a variety of AM fungi. Coincidentally, fecundity levels across two Folsomia generations were higher when animals fed exclusively on the preferred fungus, Alternaria alternata . When fed less palatable fungi, fecundity was greatly reduced; in fact animals from the F1 generation were unable to produce any eggs when placed on an exclusive diet of one of the following three AM fungi, Acaulospora spinosa, Scutellospora calospora and Gigaspora gigantea .
4. These results indicate that a strict diet of AM fungi by collembolans has reproductive consequences. Therefore, we propose that under natural conditions these animals spend more time feeding on common saprobic fungi rather than their AM counterparts. This suggests that previous 'clean' studies that investigated the interactions between collembolans and AM fungi may have reported exaggerated effects of animal grazing. The influence of collembolans on the functioning of AM symbioses, under more natural conditions, remains not well understood.     

Theories for ecological restoration in changing environment: Toward ‘futuristic’ restoration

Ecological restoration is one of the fastest growing fields in applied ecology providing new ideas and opportunities for biological conservation and natural resource management. Despite countless attempts in the past, large portions of restoration projects have been considered unsuccessful mainly due to: unrealistic goals; inadequate restoration plans based on an ad-hoc approach; lack of explicit and quantified evaluation criteria for restoration success; lack of ecological understanding; social, economic, and political constraints; or combinations of these factors. Existing ecological theories, particularly succession theories, may provide a conceptual framework for a restoration trajectory. However, projecting a desirable trajectory and outcome is often challenged by the unpredictability of ecological communities in the changing environment. Particularly, the sustainability of reconstructed historic ecosystems appears to be an unlikely goal in the ever-changing and unpredictable future environment. This paper calls for a shift in the restoration paradigm from historic to futuristic. A futuristic restoration is: (i) to set realistic and dynamic (instead of static) goals for future, instead of past, environment; (ii) to assume multiple trajectories acknowledging the unpredictable nature of ecological communities and ecosystems; (iii) to take an ecosystem or landscape approach, instead of ad-hoc gardening, for both function and structure; (iv) to evaluate the restoration progress with explicit criteria, based on quantitative inference; and (v) to maintain long-term monitoring of restoration outcomes. A theoretical framework for futuristic restoration, in terms of goals, trajectories, evaluation criteria, and monitoring, along with a historical perspective is presented in this paper.     

基于"经筋理论"针刀治疗对早中期膝骨关节炎患者骨代谢指标和血清TIMP-1、MMP-3、MMP-13的影响

摘要 目的：探讨基于"经筋理论"针刀治疗对早中期膝骨关节炎（KOA）患者骨代谢指标和血清金属蛋白酶抑制物-1（TIMP-1）、基质金属蛋白酶（MMP）-3、MMP-13的影响。方法：根据随机数字表法,将2021年1月至2023年1月期间就诊于新疆医科大学附属第一医院的120例早中期KOA患者分为对照组（n=60,常规治疗）和研究组（n=60,对照组的基础上接受"经筋理论"针刀治疗）。对比两组疗效、量表评分[疼痛视觉模拟评分（VAS）、西安大略和麦克马斯特大学骨关节炎调查表（WOMAC）]、骨代谢指标[抗酒石酸盐酸性磷酸酶异构体（TRACP-5b）、骨特异性碱性磷酸酶（BALP）、骨钙素（BGP）]和血清TIMP-1、MMP-3、MMP-13。结果：与对照组相比,研究组的临床总有效率更高（P<0.05）。与对照组相比,研究组治疗后WOMAC、VAS评分和血清MMP-3、MMP-13、TRACP-5b水平更低,TIMP-1、BALP、BGP水平更高（P<0.05）。结论：基于"经筋理论"针刀治疗早中期KOA患者,可有效减轻疼痛症状,提高临床治疗效果,可能与改善骨代谢指标和血清TIMP-1、MMP-3、MMP-13水平有关。