Risky movement increases the rate of range expansion

The movement rules used by an individual determine both its survival and dispersal success. Here, we develop a simple model that links inter-patch movement behaviour with population dynamics in order to explore how individual dispersal behaviour influences not only its dispersal and survival, but also the population's rate of range expansion. Whereas dispersers are most likely to survive when they follow nearly straight lines and rapidly orient movement towards a non-natal patch, the most rapid rates of range expansion are obtained for trajectories in which individuals delay biasing their movement towards a non-natal patch. This result is robust to the spatial structure of the landscape. Importantly, in a set of evolutionary simulations, we also demonstrate that the movement strategy that evolves at an expanding front is much closer to that maximizing the rate of range expansion than that which maximizes the survival of dispersers. Our results suggest that if one of our conservation goals is the facilitation of range-shifting, then current indices of connectivity need to be complemented by the development and utilization of new indices providing a measure of the ease with which a species spreads across a landscape.     

Are there general mechanisms of animal home range behaviour? A review and prospects for future research

Home range behaviour is a common pattern of space use, having fundamental consequences for ecological processes. However, a general mechanistic explanation is still lacking. Research is split into three separate areas of inquiry - movement models based on random walks, individual-based models based on optimal foraging theory, and a statistical modelling approach - which have developed without much productive contact. Here we review recent advances in modelling home range behaviour, focusing particularly on the problem of identifying mechanisms that lead to the emergence of stable home ranges from unbounded movement paths. We discuss the issue of spatiotemporal scale, which is rarely considered in modelling studies, as well as highlighting the need to consider more closely the dynamical nature of home ranges. Recent methodological and theoretical advances may soon lead to a unified approach, however, conceptually unifying our understanding of linkages among home range behaviour and ecological or evolutionary processes.     

森林-农业景观格局变化的社会-生态系统模拟模型方法进展

社会-生态系统(SES)模拟模型是景观格局分析和决策的有效工具,能表征景观格局变化的社会-生态效应及景观决策的复杂反馈机制。文献综述了森林-农业景观格局的SES模型方法进展发现:(1)多数模型对景观过程与社会经济决策的反馈关系分析不足;(2)应集成多种情景模拟和景观效应分析方法,完善现有SES模型的理论方法基础;(3)通过集成格局优化模型和自主体模型会有效改进SES模型功能,具体途径包括:集成情景-生态效应的景观格局模拟方法、完善景观决策的理论基础、加强集成模型的不确定性分析、降低模型复杂性和综合定性-定量数据等。研究结果有助于理解多尺度森林-农业景观格局在社会-生态系统中的重要作用,能更好地支持跨学科集成模型开发与应用。     

Socially informed random walks: incorporating group dynamics into models of population spread and growth

Simple correlated random walk (CRW) models are rarely sufficient to describe movement of animals over more than the shortest time scales. However, CRW approaches can be used to model more complex animal movement trajectories by assuming individuals move in one of several different behavioural or movement states, each characterized by a different CRW. The spatial and social context an individual experiences may influence the proportion of time spent in different movement states, with subsequent effects on its spatial distribution, survival and fecundity. While methods to study habitat influences on animal movement have been previously developed, social influences have been largely neglected. Here, we fit a 'socially informed' movement model to data from a population of over 100 elk (Cervus canadensis) reintroduced into a new environment, radio-collared and subsequently tracked over a 4-year period. The analysis shows how elk move further when they are solitary than when they are grouped and incur a higher rate of mortality the further they move away from the release area. We use the model to show how the spatial distribution and growth rate of the population depend on the balance of fission and fusion processes governing the group structure of the population. The results are briefly discussed with respect to the design of species reintroduction programmes.     

Quantitative analysis of bottlenose dolphin movement patterns and their relationship with foraging

1. Broad-scale telemetry studies have greatly improved our understanding of the ranging patterns and habitat-use of many large vertebrates. However, there often remains considerable uncertainty over the function of different areas or the factors influencing habitat selection. Further insights into these processes can be obtained through analyses of finer scale movement patterns. For example, search behaviour may be modified in response to prey distribution and abundance. 2. In this study, quantitative analysis techniques are applied to the movements of bottlenose dolphins, recorded from land using a theodolite, to increase our understanding of their foraging strategies. Movements were modelled as a correlated random walk (CRW) and a biased random walk (BRW) to identify movement types and using a first-passage time (FPT) approach, which quantifies the time allocated to different areas and identifies the location and spatial scale of intensive search effort. 3. Only a quarter of the tracks were classed as CRW movement. Turning angle and directionality appeared to be key factors in determining the type of movement adopted. A high degree of overlap in search effort between separate movement paths indicated that there were small key sites (0.3 km radius) within the study area (4 km(2)). Foraging behaviour occurred mainly within these intensive search areas, indicating that they were feeding sites. 4. This approach provides a quantitative method of identifying important foraging areas and their spatial scale. Such techniques could be applied to movement paths for a variety of species derived from telemetry studies and increase our understanding of their foraging strategies.     

动物移动网络研究对景观生态学的贡献

景观生态学在其发展之初的20世纪80年代, 提出了关于景观网络研究(包括景观网络概念、网络结构指数和景观连接度)的基本构想, 这些构想需要在景观过程的研究中逐渐被落实和发展。动物移动过程因动物在斑块或廊道上有着独特丰富的属性特征、与周围资源环境之间存在复杂反馈而区别于无机物运移的景观过程, 则动物移动网络研究在实现关于景观网络研究的基本构想、推动景观生态学发展中贡献独特。因此, 总结动物移动网络研究的来源脉络及其对景观生态学的理论贡献对于景观网络领域和景观生态学学科的发展都具有重要意义。本文抓住景观生态学发展之初提出的关于景观网络研究的基本构想, 寻找和剖析其中所蕴含的景观生态学思想, 追踪这些思想如何被落实、发展、并形成目前的三个热点方向: 动物移动网络模拟、重要值评价和景观连接度分析; 总结这三个方向的研究进展, 指出整合动物的空间行为特征是必然发展趋势; 揭示出动物移动网络研究始终都以发掘斑块或廊道的动物有机体的属性特征(如种群数量)、以及描述这种属性在不同斑块或廊道之间的差异和联系为方向, 正是这种属性的发掘有效地落实、发展和丰富了关于景观网络研究的最初构想, 对景观生态学的贡献比其他过程更为独特。文章还总结了我国动物移动网络研究与国际研究相比较为滞后的现状, 指出其暂时尚未显示出对我国景观生态学的独特贡献; 强调发展源于跟踪定位数据的动物空间行为生态学研究是减小差距的重要、必要前提。期望本文能引发关于景观网络乃至景观生态学理论发展的方向性思考, 为研究者提供参考。     

Distribution,movements and diet of nocturnal fishes on temperate reefs

We counted nocturnal fishes both day and night, and monitored the position of tagged individuals on temperate reefs in New South Wales, Australia. Pempheris affinis and P. multiradiata were the most abundant nocturnal planktivores on Sydneys rocky reefs and showed great differences in diel migration behaviour. Both species were observed in deep shelter sites during the day (5–10m), and most emerged into the water column at night. P. multiradiata was found to undergo extensive vertical and horizontal migrations. In contrast, P. affinis remained within daytime depth strata, with tagged individuals often moving less than 20m at night. Tagged adult P. affinis returned to tagging sites for up to 7weeks, indicating high site fidelity. Dietary analysis demonstrated that small and large pempherids differed in diet and the timing of foraging, suggesting a size-based transition from diurnal to nocturnal foraging. Stratified sampling of planktonic assemblages at different depths during the day and night showed spatial variation in the availability of prey items at different times of the day. Amphipods, the main prey of large fish, were only available during the night, and concentrated in shallow water, whereas decapod larvae, consumed mainly by small fish, were abundant day and night. Large P. affinis also fed on polychaetes, which were never found in the stomachs of P. multiradiata, suggesting that these species may have different prey requirements, or that these polychaetes are only found in deep water where foraging P. affinis were abundant. We found no general model for the Pempheridae. The movements and behaviour of nocturnal fishes varied greatly by species, and this may be due to differences in body size, and/or physiological (e.g. visual ability) and ecological constraints.     

Risk analysis and management decisions for weed biological control agents: Ecological theory and modeling results

Biologically based control methods offer many advantages for the control of invasive plant species; however, these methods are not without risks to native species. Thus, there is a need for more effective and efficient methods of risk analysis for biological control agents. We show how the process of ecological risk assessment established by the United States’ Environmental Protection Agency may be adapted to improve assessment of the risks of proposed biological control agents. We discuss the risks posed by weed biological control agents, and present a simple individual-based model of herbivorous insect movement and oviposition on two species of host plant, a target invasive plant species and a non-target native species, in simulated landscapes. The model shows that risks of non-target impacts may be influenced by the details of the movement behavior of biological control agents in heterogeneous landscapes. The specific details of insect movement that appear to be relevant are readily measured in field trials and the general modeling approach is readily adapted to real landscapes. Current biological control risk assessments typically emphasize effects analysis at the expense of exposure analysis; the modeling approach presented here provides a simple and feasible way to incorporate exposure analyses. We conclude that models such as ours should be given serious consideration as part of a comprehensive strategy of risk assessment for proposed weed biological control agents.