Patchy Environment Research Articles

Run-and-halt motility of droplets in response to light

SummaryMicroscopic motility is a property that emerges from systems of interacting molecules. Unraveling the mechanisms underlying such motion requires coupling the chemistry of molecules with physical processes that operate at larger length scales. Here, we show that photoactive micelles composed of molecular switches gate the autonomous motion of oil droplets in water. These micelles switch from large trans-micelles to smaller cis-micelles in response to light, and only the trans-micelles are effective fuel for the motion. Ultimately, it is this light that controls the movement of the droplets via the photochemistry of the molecules composing the micelles used as fuel. Notably, the droplets evolve positive photokinetic movement, and in patchy light environments, they preferentially move toward peripheral areas as a result of the difference in illumination conditions at the periphery. Our findings demonstrate that engineering the interplay between molecular photo-chemistry and microscopic motility allows designing motile systems rationally.

Dynamics of additional food provided predator–prey system with habitat fragmentation

Due to human-caused deforestation, global warming, and other environmental factors, habitat fragmentation became widespread. This fragmentation has a variety of detrimental repercussions for many species as well as humans, especially in the agricultural economy. It causes insect outbreaks, the expansion of alien species, and disrupts biological management by rendering the habitat unsuitable for natural enemies in agriculture. Providing natural enemies with additional food is one method to improve the ecosystem and support them. In this study, we assumed that the ecosystem is separated into two patches and that predators can easily migrate from one patch to the next, while prey stays inside its patch’s territory. We looked at the impact of offering more food to predators in a patchy environment using dynamical systems theory. The permanence, stability, and various bifurcations that occur in the system are studied using a rigorous mathematical analysis. The study looks at how predator’s access to other food sources affects pest management. By adjusting the provided food’s characteristic qualities, such as (nutritional) quality and quantity, one can limit and manage the pest in one or both patches, as well as eliminate predators from the ecosystem. This research reveals that providing predators with additional food (of specified quality and quantity) can help in controlling chaotic behavior in the system. The findings of the study are supported by numerical simulations.

Invasion analysis of a two‐species Lotka–Volterra competition model in an advective patchy environment

AbstractIn this paper, we study a two‐species Lotka–Volterra competition patch model over a stream, where the individuals are subject to both random and directed movements and the two species are assumed to be identical except for the movement rates. We treat one species as the resident species and the other one as a mutant/invading species and study whether the resident species can be invaded. We also obtain the global dynamics of the model for certain parameter ranges.

Concurrent assessment of functional types in extant vegetation and soil seed banks informs environmental constraints and mechanisms of plant community turnover in temperate forests of south-eastern Australia

Our understanding of how environmental heterogeneity shapes plant community dynamics is largely based on above-ground diversity despite the importance of seed banks as reservoirs of genetic and taxonomic diversity that buffer plant populations and influence vegetation following disturbance. Using a plant functional trait approach, this study examined the importance of fire-related germination cues and environmental determinants of plant community turnover in wet forests of south-eastern Australia – forests of both high conservation value and the focus of current timber harvesting. We surveyed extant vegetation, soil seed banks, forest structure and edaphic properties across 62 sites burnt in 1939 and not subsequently affected by wildfire or logging. A total of 46 families, and 99 species were identified in extant vegetation with 43 and 126 respectively in the soil seed bank, with only 32% of species co-occurring in both species’ pools. Despite historically long fire return intervals, the soil seed bank demonstrated a clear positive response to fire-related germination cues (heat in combination with smoke) that were concentrated in hard-seeded species dispersed by ants. Seeds from early successional species showed no response to fire cues, while species typical of the wetter margins of these forests were killed by high heat. The soil seed bank was dominated by species associated with early successional stages, consistent with the initial floristics model of succession. Woody species were largely restricted to extant vegetation and replacement is most likely to occur from future seed rain. Spatially structured environmental heterogeneity shaped plant turnover with the relative strength of environmental controls differing among functional types and pools of diversity. Differential response of the combined species pool relative to extant vegetation demonstrates that the soil seed bank provides a storage effect. Forest management practices that generate patchy and heterogenous environments, including the intensity of regeneration burns and density of overstorey species, will benefit biodiversity conservation through overstorey structural controls on resource availability and diversity of understorey vegetation, that is transferred to soil seed banks via tight abiotic controls and seed inputs.

A new approach for investigating spatial relationships of ichnofossils: a case study of Ediacaran–Cambrian animal traces

AbstractTrace fossils record foraging behaviors, the search for resources in patchy environments, of animals in the rock record. Quantification of the strength, density, and nature of foraging behaviors enables the investigation of how these may have changed through time. Here, we present a novel approach to explore such patterns using spatial point process analyses to quantify the scale and strength of ichnofossil spatial distributions on horizontal bedding planes. To demonstrate the utility of this approach, we use two samples from the terminal Ediacaran Shibantan Member in South China (between 551 and 543 Ma) and the early Cambrian Nagaur Sandstone in northwestern India (between 539 and 509 Ma). We find that ichnotaxa on both surfaces exhibited significant nonhomogeneous lateral patterns, with distinct levels of heterogeneity exhibited by different types of trace fossils. In the Shibantan, two ichnotaxa show evidence for mutual positive aggregation over a shared resource, suggesting the ability to focus on optimal resource areas. Trace fossils from the Nagaur Sandstone exhibit more sophisticated foraging behavior, with greater niche differentiation. Critically, mark correlation functions highlight significant spatial autocorrelation of trace fossil orientations, demonstrating the greater ability of these Cambrian tracemakers to focus on optimal patches. Despite potential limitations, these analyses hint at changes in the development and optimization of foraging at the Ediacaran/Cambrian transition and highlight the potential of spatial point process analysis to tease apart subtle differences in behavior in the trace fossil record.

P8. Anterior Cingulate Cortex Tracks the Distribution of Depleting Reward in Freely Moving Rhesus Macaques

Foraging is a canonical decision-making behavior that has likely shaped functional neuroanatomy. Foragers in patchy environments are able to efficiently maximize their food intake by balancing the exploitation of resource patches with exploration for new patches. Making patch-leaving decisions requires the maintenance and integration of multiple forms of information. We have hypothesized that such decisions involve the generation and maintenance of a discrete continuous and abstract decision variable.

Particle foraging strategies promote microbial diversity in marine environments.

Microbial foraging in patchy environments, where resources are fragmented into particles or pockets embedded in a large matrix, plays a key role in natural environments. In the oceans and freshwater systems, particle-associated bacteria can interact with particle surfaces in different ways: some colonize only during short transients, while others form long-lived, stable colonies. We do not yet understand the ecological mechanisms by which both short- and long-term colonizers can coexist. Here, we address this problem with a mathematical model that explains how marine populations with different detachment rates from particles can stably coexist. In our model, populations grow only while on particles, but also face the increased risk of mortality by predation and sinking. Key to coexistence is the idea that detachment from particles modulates both net growth and mortality, but in opposite directions, creating a trade-off between them. While slow-detaching populations show the highest growth return (i.e., produce more net offspring), they are more susceptible to suffer higher rates of mortality than fast-detaching populations. Surprisingly, fluctuating environments, manifesting as blooms of particles (favoring growth) and predators (favoring mortality) significantly expand the likelihood that populations with different detachment rates can coexist. Our study shows how the spatial ecology of microbes in the ocean can lead to a predictable diversification of foraging strategies and the coexistence of multiple taxa on a single growth-limiting resource.

Hunter-gatherer Mobility Analysed Through δ18O in the Patchy Environment of the Paraná Valley, South American Lowlands

ABSTRACT In this study we analyse the mobility of complex hunter-gatherers in the Lower Paraná wetland (South America) through δ18O values. To do this, we characterise the isotopic composition of water and bioapatite of stenoic and sedentary species from the region and the surrounding Pampa plain, and then we compare them with those obtained in human bones recovered at local archaeological sites. The results show that humans appear to have developed spatial stability strategies within certain areas, which is consistent with archaeological models of social circumscription among these pre-Columbian populations. Other finding of this study shows that any organism that moves along the middle and lower Paraná valley will not present differences in its δ18O values, but small transverse movements will produce significant variations, which relativises to some degree, the concept of ‘local’ and ‘non-local’ in the region. This study also addresses the methodological problems related to the characterisation of δ18O values in irregular environments, highlighting the importance of developing baselines based on local biocenoses.

Functional importance of bird-dispersed habitat for the early recruitment of Taxus chinensis in a fragmented forest

The relationship between bird habitat selection and seed deposition is well established; however, knowledge remains limited on the functional importance of bird habitat for the early recruitment of seed deposition and seedlings in remnant fragmented forests. Here, we evaluated the post-foraging habitat use by birds and quantified the effects of habitat factors on seed deposition and seedling distribution of the endangered Chinese yew Taxus chinensis in a fragmented forest. Birds preferentially frequented fruiting trees for perching (85%, T. Chinensis and Machilus thunbergii trees). Tree cover, height, crown size, and girth were the most important factors affecting habitat use by birds. Consequently, the number of deposited seeds was positively affected by three tree-associated perching traits (girth, cover, and crown size). Seedling distribution strongly overlapped with the distribution of deposited seeds, confirming that seedlings could survive in bird-dispersed habitats. Increasing tree girth, cover, and crown size may enhance seedling recruitment. Our results highlighted the functional importance of large trees in patchy environments for supplying suitable sites for bird habitat use, which also fitted the requirement for early recruitment of T. chinensis. Consequently, protecting remaining large trees in fragmented forests should be considered in forest conservation and management.

The role of food odor in invertebrate foraging.

Foraging for food is an integral part of animal survival. In small insects and invertebrates, multisensory information and optimized locomotion strategies are used to effectively forage in patchy and complex environments. Here, the importance of olfactory cues for effective invertebrate foraging is discussed in detail. We review how odors are used by foragers to move toward a likely food source and the recent models that describe this sensory-driven behavior. We argue that smell serves a second function by priming an organism for the efficient exploitation of food. By appraising food odors, invertebrates can establish preferences and better adapt to their ecological niches, thereby promoting survival. The smell of food pre-prepares the gastrointestinal system and primes feeding motor programs for more effective ingestion as well. Optimizing resource utilization affects longevity and reproduction as a result, leading to drastic changes in survival. We propose that models of foraging behavior should include odor priming, and illustrate this with a simple toy model based on the marginal value theorem. Lastly, we discuss the novel techniques and assays in invertebrate research that could investigate the interactions between odor sensing and food intake. Overall, the sense of smell is indispensable for efficient foraging and influences not only locomotion, but also organismal physiology, which should be reflected in behavioral modeling.

The Global dynamics of a SIR model considering competitions among multiple strains in patchy environments

<abstract><p>Pandemics, such as Covid-19 and AIDS, tend to be highly contagious and have the characteristics of global spread and existence of multiple virus strains. To analyze the competition among different strains, a high dimensional SIR model studying multiple strains' competition in patchy environments is introduced in this work. By introducing the basic reproductive number of different strains, we found global stability conditions of disease-free equilibrium and persistence conditions of the model. The competition exclusion conditions of that model are also given. This work gives some insights into the properties of the multiple strain patchy model and all of the analysis methods used in this work could be used in other related high dimension systems.</p></abstract>

Using chemical reaction network theory to show stability of distributional dynamics in game theory

<p style='text-indent:20px;'>This article shows how to apply results of chemical reaction network theory (CRNT) to prove uniqueness and stability of a positive equilibrium for pairs/groups distributional dynamics that arise in game theoretic models. Evolutionary game theory assumes that individuals accrue their fitness through interactions with other individuals. When there are two or more different strategies in the population, this theory assumes that pairs (groups) are formed instantaneously and randomly so that the corresponding pairs (groups) distribution is described by the Hardy–Weinberg (binomial) distribution. If interactions times are phenotype dependent the Hardy-Weinberg distribution does not apply. Even if it becomes impossible to calculate the pairs/groups distribution analytically we show that CRNT is a general tool that is very useful to prove not only existence of the equilibrium, but also its stability. In this article, we apply CRNT to pair formation model that arises in two player games (e.g., Hawk-Dove, Prisoner's Dilemma game), to group formation that arises, e.g., in Public Goods Game, and to distribution of a single population in patchy environments. We also show by generalizing the Battle of the Sexes game that the methodology does not always apply.</p>

Population persistence under two conservation measures: Paradox of habitat protection in a patchy environment.

Anthropogenic modification of natural habitats is a growing threat to biodiversity and ecosystem services. The protection of biospecies has become increasingly important. Here, we pay attention to a single species as a conservation target. The species has three processes: reproduction, death and movement. Two different measures of habitat protection are introduced. One is partial protection in a single habitat (patch); the mortality rate of the species is reduced inside a rectangular area. The other is patch protection in a two-patch system, where only the mortality rate in a particular patch is reduced. For the one-patch system, we carry out computer simulations of a stochastic cellular automaton for a "contact process". Individual movements follow random walking. For the two-patch system, we assume an individual migrates into the empty cell in the destination patch. The reaction-diffusion equation (RDE) is derived, whereby the recently developed "swapping migration" is used. It is found that both measures are mostly effective for population persistence. However, comparing the results of the two measures revealed different behaviors. ⅰ) In the case of the one-patch system, the steady-state densities in protected areas are always higher than those in wild areas. However, in the two-patch system, we have found a paradox: the densities in protected areas can be lower than those in wild areas. ⅱ) In the two-patch system, we have found another paradox: the total density in both patches can be lower, even though the proportion of the protected area is larger. Both paradoxes clearly occur for the RDE with swapping migration.

Patterns of thermal adaptation in a globally distributed plant pathogen: Local diversity and plasticity reveal two-tier dynamics.

Plant pathogen populations inhabit patchy environments with contrasting, variable thermal conditions. We investigated the diversity of thermal responses in populations sampled over contrasting spatiotemporal scales, to improve our understanding of their dynamics of adaptation to local conditions. Samples of natural populations of the wheat pathogen Zymoseptoria tritici were collected from sites within the Euro‐Mediterranean region subject to a broad range of climatic conditions. We tested for local adaptation, by accounting for the diversity of responses at the individual and population levels on the basis of key thermal performance curve parameters and “thermotype” (groups of individuals with similar thermal responses) composition. The characterization of phenotypic responses and genotypic structure revealed the following: (i) a high degree of individual plasticity and variation in sensitivity to temperature conditions across spatiotemporal scales and populations; and (ii) geographic variation in thermal response among populations, with major alterations due to seasonal patterns over the wheat‐growing season. The seasonal shifts in functional composition suggest that populations are locally structured by selection, contributing to adaptation patterns. Further studies combining selection experiments and modeling are required to determine how functional group selection drives population dynamics and adaptive potential in response to thermal heterogeneity.

Transition fronts of Fisher–KPP equations in locally spatially inhomogeneous patchy environments

This paper is devoted to the study of spatial propagation dynamics of species in locally spatially inhomogeneous patchy environments or media. For a lattice differential equation with monostable nonlinearity in a discrete homogeneous media, it is well-known that there exists a minimal wave speed such that a traveling front exists if and only if the wave speed is not slower than this minimal wave speed. We shall show that strongly localized spatial inhomogeneous patchy environments may prevent the existence of transition fronts (generalized traveling fronts). Transition fronts may exist in weakly localized spatial inhomogeneous patchy environments but only in a finite range of speeds, which implies that it is plausible to obtain a maximal wave speed of existence of transition fronts.

Global stability for a new predator\u2013prey model with cross-dispersal among patches based on graph theory

In this paper, cross-dispersal is considered in a predator–prey model with a patchy environment. A new predator–prey model with cross-dispersal among patches is constructed. A new cross-dispersal matrix is established by the coupling relationship between vertices. First, an existence theorem of the positive equilibrium for the new model is obtained. Secondly, based on the idea of constructing Lyapunov functions and a graph-theoretical approach for coupled systems, sufficient conditions that the positive equilibrium of the new model is globally asymptotically stable in R^{2n}_{+} are derived on a network with strongly connected graphs. Thirdly, based on the theory of asymptotically autonomous systems, Lyapunov functions method and graph theory, a stability theorem for the positive equilibrium of the new model is established on a complex network without strongly connected graphs. Finally, two examples are given to illustrate main results.

Asymptotic behavior of the principal eigenvalue and the basic reproduction ratio for periodic patch models

This paper is devoted to the study of the asymptotic behavior of the principal eigenvalue and the basic reproduction ratio associated with periodic population models in a patchy environment for small and large dispersal rates. We first deal with the eigenspace corresponding to the zero eigenvalue of the connectivity matrix. Then we investigate the limiting profile of the principal eigenvalue of an associated periodic eigenvalue problem as the dispersal rate goes to zero and infinity, respectively. We further establish the asymptotic behavior of the basic reproduction ratio in the case of small and large dispersal rates. Finally, we apply these results to a periodic Ross-Macdonald patch model.

Multi-layered model for rock-paper-scissors game: A swarm intelligence sustains biodiversity

Much literature exists for rock-paper-scissors (RPS) game. It is well known in a single habitat that spatial models are more stable than well-mixed population. However, the mechanism of spatial stabilization has been unclear. In the present article, we study multilayer model of RPS game in a patchy environment; respective patches are set as lattices. The predation probability of one of three species is assumed to be reduced as a parameter. Simulations on two-layer system reveal the opposite result to those on a single-habitat system. Namely, the well-mixed population becomes stable. In contrast, extinction occurs by random migration in spatially-explicit model, when the reduced predation probability is below a certain critical value. The extinction in spatial model is found to be caused by the collapse of a kind of swarm intelligence (SI). In RPS system, large swarms of each species are automatically protected from its predator. Such a self-organized protection is one of the simplest examples of SI. We also discuss some serious problems for random migration.

Determining the effects of wind-aided midge movement on the outbreak and coexistence of multiple bluetongue virus serotypes in patchy environments

Bluetongue virus (BTV) has 27 serotypes with some of them coexisting in different environments which make its control difficult. Wind-aided midge movement is a known mechanism in the spread of BTV. However, its effects on the dynamics of multiple BTV serotypes are not clear. Ordinary differential equation (ODE) and continuous-time Markov chain (CTMC) models for two BTV serotypes in an environment divided into two patches depending on the risk of infection are formulated and analysed. By approximating the CTMC model with a multitype branching process, an estimate for the probability of a major outbreak of two BTV serotypes is obtained. It is shown that without movement a major outbreak occurs in the high-risk patch, but with cattle or midge movement it occurs in both patches. When a major outbreak occurs, numerical simulations of the ODE model illustrate possible coexistence in both patches if the patches are connected by midge or cattle movement. Sensitivity analysis, based on the Latin hypercube sampling method, identified midge mortality and biting rates as being the most important in determining the magnitude of the probability of a major outbreak. These results indicate the significance of wind-aided midge movement on the outbreak and coexistence of multiple BTV serotypes in patchy environments.

The bigger the better? Predation and prey size choice in a patchy environment

Prey individuals vary in their body size even within groups and are often scattered heterogeneously in patchy environments. A foraging predator has to evaluate and select the patches where it can maximize its energetic gains. We studied the foraging behavior of a predator (little egret, Egretta garzetta) hunting prey groups (goldfish, Carassius auratus) that differed in body size and composition across three different patches (one large, one mixed, and one small). We quantified predator’s stay time, return time and size-specific kills of the prey. The egret spent a similar amount of total time foraging in the three patches; however, it spent more time per-visit in pools containing large-bodied fish and also returned to those pools soonest after leaving to forage elsewhere, suggesting that the predators employ a time management strategy to maximize energetic returns. Furthermore, the egret preferentially killed larger individuals. Such size-selective predation can shift the prey size structure in the landscape and influence the dynamics of species interactions and eventually the structure of the communities.