Determining spatial and temporal scales for management: lessons from whaling

Selection of the appropriate management unit is critical to the conservation of animal populations. Defining such units depends upon knowledge of population structure and upon the timescale being considered. Here, we examine the trajectory of eleven subpopulations of five species of baleen whales to investigate temporal and spatial scales in management. These subpopulations were all extirpated by commercial whaling, and no recovery or repopulation has occurred since. In these cases, time elapsed since commercial extinction ranges from four decades to almost four centuries. We propose that these subpopulations did not recover either because cultural memory of the habitat has been lost, because widespread whaling among adjacent stocks eliminated these as sources for repopulation, and/or because segregation following exploitation produced the abandonment of certain areas. Spatial scales associated with the extirpated subpopulations are frcequently smaller than those typically employed in management. Overall, the evidence indicates that: (1) the time frame for management should be at most decadal in scope (i.e., <100 yr) and based on both genetic and nongenetic evidence of population substructure, and (2) at least some stocks should be defined on a smaller spatial scale than they currently are.     

Choosing appropriate temporal and spatial scales for ecological restoration

Classic ecological restoration seems tacitly to have taken the Clementsian “balance of nature” paradigm for granted: plant succession terminates in a climax community which remains at equilibrium until exogenously disturbed after which the process of succession is restarted until the climax is reached. Human disturbance is regarded as unnatural and to have commenced in the Western Hemisphere at the time of European incursion. Classic ecological restoration thus has a clear and unambiguous target and may be conceived as aiming to foreshorten the natural processes that would eventually lead to the climax of a given site, which may be determined by its state at “settlement”. According to the new “flux of nature” paradigm in ecology a given site has notelos and is constantly changing. Human disturbance is ubiquitous and long-standing, and at certain spatial and temporal scales is “incorporated”. Any moment in the past 10,000 years that may be selected as a benchmark for restoration efforts thus appears to be arbitrary. Two prominent conservationists have therefore suggested that the ecological conditions in North America at the Pleistocene—Holocene boundary, prior to the anthropogenic extinction of the Pleistocene megafauna, be the target for ecological restoration. That suggestion explicitly assumes evolutionary temporal scales and continental spatial scales as the appropriate frame of reference for ecological restoration. However, ecological restoration should be framed in ecological spatio-temporal scales, which may be defined temporally in reference to ecological processes such as disturbance regimes and spatially in reference to ecological units such as landscapes, ecosystems, and biological provinces. Ecological spatio-temporal scales are also useful in achieving a scientifically defensible distinction between native and exotic species, which plays so central a role in the practice of ecological restoration and the conservation of biodiversity. Because post-settlement human disturbances have exceeded the limits of such scales, settlement conditions can be justified scientifically as appropriate targets of restoration efforts without recourse to obsolete teleological concepts of equilibria and without ignoring the presence and ecological influence of indigenous peoples.     

The effect of semi-natural habitats on aphids and their natural enemies across spatial and temporal scales

Semi-natural habitats in agricultural landscapes are generally assumed to enhance the biological control of insect pests based on native beneficial insects, by providing alternative prey and hosts, resources and refuges for overwintering. We hypothesized that natural enemies of winter wheat aphids should arrive sooner in fields near semi-natural habitats. We compared aphid, hoverfly (larvae and eggs) and parasitized aphid (mummies) abundances in 54 winter wheat fields located in southern France from 2003 to 2007. Six surveys were recorded each spring and were split into the early period (defined as the period before the peak of aphid growth) and the late period (after the peak). The wheat fields differed by their surrounding landscape composition measured as the proportion of semi-natural habitats (woods, hedges and grasslands), at three different spatial scales: 200 m, 500 m, and 1200 m. Despite great variability in abundance data between years, the abundance of hoverflies appeared more sensitive to landscape composition than aphid abundance was. Early abundance for both aphids and hoverflies was positively related to wood cover, but not late abundance in spring. The abundance of hoverflies was positively related to hedge and grassland cover at all spatial scales and both periods considered. Aphid parasitism was higher near hedges at the small spatial scale late in the spring. Our results confirmed that higher proportions of semi-natural habitats in agricultural landscapes enhance the biological control of pests, but this effect depends on the spatial scale, the time period in the spring and the natural enemies considered.     

Characteristic spatial and temporal scales unify models of animal movement

Animal movements have been modeled with diffusion at large scales and with more detailed movement models at smaller scales. We argue that the biologically relevant behavior of a wide class of movement models can be efficiently summarized with two parameters: the characteristic temporal and spatial scales of movement. We define these scales so that they describe movement behavior both at short scales (through the velocity autocorrelation function) and at long scales (through the diffusion coefficient). We derive these scales for two types of commonly used movement models: the discrete-step correlated random walk, with either constant or random step intervals, and the continuous-time correlated velocity model. For a given set of characteristic scales, the models produce very similar trajectories and encounter rates between moving searchers and stationary targets. Thus, we argue that characteristic scales provide a unifying currency that can be used to parameterize a wide range of ecological phenomena related to movement.     

Relationships between aboveground biomass and plant cover at two spatial scales and their determinants in northern Tibetan grasslands

The relationships between cover and AGB for the dominant and widely distributed alpine grasslands on the northern Tibetan Plateau is still not fully examined. The objectives of this study are to answer the following question: (1) How does aboveground biomass (AGB) of alpine grassland relate to plant cover at different spatial scales? (2) What are the major biotic and abiotic factors influencing on AGB–cover relationship? A community survey (species, cover, height, and abundance) was conducted within 1 m × 1 m plots in 70 sites along a precipitation gradient of 50–600 m. Ordinary linear regression was employed to examine AGB–cover relationships of both community and species levels at regional scale of entire grassland and landscape scale of alpine meadow, alpine steppe, and desert steppe. Hierarchical partitioning was employed to estimate independent contributions of biotic and abiotic factors to AGB and cover at both scales. Partial correlation analyses were used to discriminate the effects of biotic and abiotic factors on AGB–cover relationships at two spatial scales. AGB and community cover both exponentially increased along the precipitation gradient. At community level, AGB was positively and linearly correlated with cover for all grasslands except for alpine meadow. AGB was also linearly correlated with cover of species level at both regional and landscape scales. Contributions of biotic and abiotic factors to the relationship between AGB and cover significantly depended on spatial scales. Cover of cushions, forbs, legumes and sedges, species richness, MAP, and soil bulk density were important factors that influenced the AGB–cover relationship at either regional or landscape scale. This study indicated generally positive and linear relationships between AGB and cover are at both regional and landscape scales. Spatial scale may affect ranges of cover and modify the contribution of cover to AGB. AGB–cover relationships were influenced mainly by species composition of different functional groups. Therefore, in deriving AGB patterns at different spatial scales, community composition should be considered to obtain acceptable accuracy.     

Plant reproductive allocation predicts herbivore dynamics across spatial and temporal scales

Life-history theory suggests that iteroparous plants should be flexible in their allocation of resources toward growth and reproduction. Such plasticity could have consequences for herbivores that prefer or specialize on vegetative versus reproductive structures. To test this prediction, we studied the response of the cactus bug (Narnia pallidicornis) to meristem allocation by tree cholla cactus (Opuntia imbricata). We evaluated the explanatory power of demographic models that incorporated variation in cactus relative reproductive effort (RRE; the proportion of meristems allocated toward reproduction). Field data provided strong support for a single model that defined herbivore fecundity as a time-varying, increasing function of host RRE. High-RRE plants were predicted to support larger insect populations, and this effect was strongest late in the season. Independent field data provided strong support for these qualitative predictions and suggested that plant allocation effects extend across temporal and spatial scales. Specifically, late-season insect abundance was positively associated with interannual changes in cactus RRE over 3 years. Spatial variation in insect abundance was correlated with variation in RRE among five cactus populations across New Mexico. We conclude that plant allocation can be a critical component of resource quality for insect herbivores and, thus, an important mechanism underlying variation in herbivore abundance across time and space.     

森林多目标经营单元的时空尺度扩展

森林多目标经营是我国林业发展的重要趋势,而森林本身的特性以及国内外的众多研究证明,森林多目标经营需要考虑多个时空尺度,以满足其生态、经济和社会效益的综合发挥。在界定多功能林业和森林多目标经营的概念及基础上,系统地分析了传统森林经营时空尺度和现代森林多目标经营时空尺度的联系与区别,提出现代森林多目标经营单元空间尺度上应该满足区域、景观和林分多尺度的需要,而在时间尺度上则要综合考虑短期、中期和长期,并以露水河林业局为例给出具体的研究思路,以期为我国开展森林多目标经营提供借鉴。     

Interference at several temporal and spatial scales between two chestnut insects

Detection of interspecific competition between insects is often sensitive to scaling. We give an example of scale-dependent interference between the weevil Curculio elephas and the moth Cydia splendana, which both have larvae that develop in the fruits of chestnut Castanea sativa. Measures at three scales were considered: chestnut, husk (with one to three fertile fruits) and tree. Data come from observations in the field over 14 years, complemented by experiments done directly in trees. Data on individual chestnut fruits revealed a marked statistical interference between the two insects. Experiments demonstrated that presence of a moth larva in a fruit usually inhibits weevil egg-laying. Conversely, weevil presence does not strongly modify moth larval behavior. Cases of double infestation often correspond to fruits first attacked by the weevil. With measures on husks, interference between the two insects was observed only in some trees; its intensity was always weaker than in the chestnuts themselves. At the scale of entire trees, rates of infestation by each insect are not correlated. Interference in chestnut fruits is interpreted by assuming that the weevil female either is sensitive to a repellent molecule originating from a moth larva or its frass, or can detect moth larval sounds. Mechanisms governing infestation rates from data per tree are discussed in relation to those found at fruit scale and to plant-insect interactions. The need to estimate available resources both from quantitative and qualitative points of view is emphasized.     

Differences in epiphyte biomass and community composition along landscape and within-crown spatial scales

Vascular epiphytes contribute to the structural, compositional, and functional complexity of tropical montane cloud forests because of their high biomass, diversity, and ability to intercept and retain water and nutrients from atmospheric sources. However, human-caused climate change and forest-to-pasture conversion are rapidly altering tropical montane cloud forests. Epiphyte communities may be particularly vulnerable to these changes because of their dependence on direct atmospheric inputs and host trees for survival. In Monteverde, Costa Rica, we measured vascular epiphyte biomass, community composition, and richness at two spatial scales: (1) along an elevation gradient spanning premontane forests to montane cloud forests and (2) within trees along branches from inner to outer crown positions. We also compared epiphyte biomass and distribution at these scales between two different land-cover types, comparing trees in closed canopy forest to isolated trees in pastures. An ordination of epiphyte communities at the level of trees grouped forested sites above versus below the cloud base, and separated forest versus pasture trees. Species richness increased with increasing elevation and decreased from inner to outer branch positions. Although richness did not differ between land-cover types, there were significant differences in community composition. The variability in epiphyte community organization between the two spatial scales and between land-cover types underscores the potential complexity of epiphyte responses to climate and land-cover changes.     

A test of spatial memory and movement patterns of bumblebees at multiple spatial and temporal scales

Naive bumblebee foragers appear to use movement rules at smallspatial and temporal scales, but it is not clear whether theserules determine movement patterns as the scales increase. Onestrategy for efficient foraging used by bumblebees is near-farsearch, involving short flights when in good patches of flowersand longer flights when in poor patches. Bumblebees also demonstratethe use of a spatial memory strategy by returning repeatedlyto patches of flowers, and even following the same route betweenflowers, over periods of days. We attempted to determine atwhat spatial scales bumblebees use spatial memory while foragingwithin a patch and after how many flower visits spatial memoryoutweighs near-far search. Bumblebees in the laboratory foragedon a 4 x 4 array of artificial flowers with distances rangingfrom 10 to 80 cm between flowers in two simple spatial patterns.The proportion of visits to flowers containing a sucrose rewardwas monitored for either 100 or 400 flower visits in two separateexperiments, after which the locations of the rewarding andnonrewarding flowers were interchanged, producing a mirror image.A drop in accuracy after the mirror image switch would indicatethat the bees had memorized the location of rewarding flowers.Mirror image tests, and comparisons to a simulation model ofnear-far search based on actual flight distances, indicate thatnaive bumblebees used near-far search on flowers 10 cm apartbut increasingly used spatial memory as experience and spatialseparation increased. Bumblebees thus have multiple tacticsavailable to forage efficiently in different environments.     

A spatio-temporal LSTM model to forecast across multiple temporal and spatial scales

This paper presents a novel spatio-temporal LSTM (SPATIAL) architecture for time series forecasting applied to environmental datasets. The framework was applied for three different ocean datasets: current speed, temperature, and dissolved oxygen. Network implementation proceeded in two directions that are nominally separated but connected as part of a natural environmental system – across the spatial (between individual sensors) and temporal dimensions of the sensor data. Data from twenty ocean sensors were used to train the model. Results were compared against four baseline models: two machine learning algorithms generated by robust autoML frameworks, and two deep neural networks based on CNN and LSTM, respectively. Results demonstrated ability to accurately replicate complex signals and provide comparable performance to state-of-the-art benchmarks. Learning from multiple sensors simultaneously increased robustness to missing data. This paper addresses two fundamental challenges related to environmental applications of machine learning: 1) data sparsity, particularly in a challenging ocean environment, and 2) environmental datasets are inherently connected in the spatial and temporal directions while classical ML approaches only consider one of these at a time. Furthermore, sharing of parameters across all input steps makes SPATIAL a fast, scalable, and easily-parameterized forecasting framework.     

Interactions between spatial and temporal scales in the evolution of dispersal rate

The evolution of dispersal rate is studied with a model of several local populations linked by dispersal. Three dispersal strategies are considered where all, half or none of the offspring disperse. The spatial scale (number of patches) and the temporal scale (probability of local extinction) of the environment are critical in determining the selective advantage of the different dispersal strategies. The results from the simulations suggest that an interaction between group selection and individual selection results in a different outcome in relation to the spatial and temporal scales of the environment. Such an interaction is able to maintain a polymorphism in dispersal strategies. The maintenance of this polymorphism is also scale-dependent. This study suggests a mechanism for the short-term evolution of dispersal, and provides a testable prediction of this hypothesis, namely that loss of dispersal abilities should be more frequent in spatially more continuous environments, or in temporally more stable environments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Population dynamics and potential of fisheries stock enhancement: practical theory for assessment and policy analysis

The population dynamics of fisheries stock enhancement, and its potential for generating benefits over and above those obtainable from optimal exploitation of wild stocks alone are poorly understood and highly controversial. I review pertinent knowledge of fish population biology, and extend the dynamic pool theory of fishing to stock enhancement by unpacking recruitment, incorporating regulation in the recruited stock, and accounting for biological differences between wild and hatchery fish. I then analyse the dynamics of stock enhancement and its potential role in fisheries management, using the candidate stock of North Sea sole as an example and considering economic as well as biological criteria. Enhancement through release of recruits or advanced juveniles is predicted to increase total yield and stock abundance, but reduce abundance of the naturally recruited stock component through compensatory responses or overfishing. Economic feasibility of enhancement is subject to strong constraints, including trade-offs between the costs of fishing and hatchery releases. Costs of hatchery fish strongly influence optimal policy, which may range from no enhancement at high cost to high levels of stocking and fishing effort at low cost. Release of genetically maladapted fish reduces the effectiveness of enhancement, and is most detrimental overall if fitness of hatchery fish is only moderately compromised. As a temporary measure for the rebuilding of depleted stocks, enhancement cannot substitute for effort limitation, and is advantageous as an auxiliary measure only if the population has been reduced to a very low proportion of its unexploited biomass. Quantitative analysis of population dynamics is central to the responsible use of stock enhancement in fisheries management, and the necessary tools are available.     

Importance of temporal variability at different spatial scales for diversity of floodplain aquatic communities

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Plant traits respond to the competitive neighbourhood at different spatial and temporal scales

Background and Aims Clonal plants can plastically modify their traits in response to competition, but little is known regarding the spatio-temporal scale at which a competitive neighbourhood determines the variability in species traits. This study tests the hypothesis that the local neighbourhood can be expected to influence the processes that are involved in competition tolerance and avoidance, and that this effect depends on organ lifespan.Methods Fragments of the rhizomatous Elytrigia repens (Poaceae) were sampled in 2012 in experimental plant communities that varied in species identity and abundance. These communities had been cultivated since 2009 in mesocosms in a common garden. Fragment performance, shoot and clonal traits were measured, and the effects of past and present local neighbourhoods of five different radius sizes (5–25 cm) were examined. Past and present local neighbourhood compositions were assessed in 2011 and 2012, respectively.Key Results Most of the measured traits of E. repens responded to the local neighbourhood (5–10 cm radius), with an additional effect of the larger neighbourhood (20–25 cm radius) on ramet height, leaf dry matter content, maximal internode length and specific rhizome mass. Contrary to the expectation of the hypothesis, the temporal influence was not due to the organ lifespan. Indeed, five of the eight traits studied responded to both the past and present neighbourhoods. With the exception of specific rhizome mass, all trait responses were explained by the abundance of specific species.Conclusions This study demonstrates that the traits of a single clonal individual can respond to different competitive environments in space and time. The results thus contribute to the understanding of competition mechanisms.     

Modelling the spatial and temporal variability of diatoms in the River Murray

We have developed a simple mechanistic model, which simulates the temporal and spatial variability of concentrations of the diatom Aulacoseira granulata in the River Murray, NSW Australia, over large distances under different flow conditions. The model incorporates a simple growth function determined by the availabilities of silica and light, and by temperature. It also includes losses due to sinking and downstream advection. The model is tested against weekly measurements for the period 1981-1990, at three sites separated by 1100 km. The seasonal cycle of Aulacoseira concentrations along the river is well represented by the model. During times of high flow, the concentrations of Aulacoseira remain fairly uniform along the river as the diatoms have insufficient time to grow before being advected downstream.      

Interdependence of plankton spatial distribution and plancton biomass temporal oscillations: mathematical simulation

The dynamics of aquatic biological communities in a patchy environment is of great interest in respect to interrelations between phenomena at various spatial and time scales. To study the complex plankton dynamics in relation to variations of such a biologically essential parameter as the fish predation rate, we use a simple reaction-diffusion model of trophic interactions between phytoplankton, zooplankton, and fish. We suggest that plankton is distributed between two habitats one of which is fish-free due to hydrological inhomogeneity, while the other is fish-populated. We show that temporal variations in the fish predation rate do not violate the strong correspondence between the character of spatial distribution of plankton and changes of plankton biomass in time: regular temporal oscillations of plankton biomass correspond to large-scale plankton patches, while chaotic oscillations correspond to small-scale plankton patterns. As in the case of the constant fish predation rate, the chaotic plankton dynamics is characterized by coexistence of the chaotic attractor and limit cycle.     

How spatial and temporal scales influence understanding of Sperm Whale distribution: a review

For much of the past two centuries, sperm whaling has been economically very profitable, and therefore whalers and, more recently, scientists have tried to understand Sperm Whale ( Physeter macrocephalus ) distribution and the factors controlling it. However, due to their deep-living mode of life, their cosmopolitan distribution and our limited knowledge about their main prey species, the task has proved very difficult. This paper reviews studies of Sperm Whale distribution and the factors controlling it. The conclusions of these studies are very equivocal and often appear to contradict one another. It is suggested that this apparent confusion is mainly due to poorly defined spatial and temporal scales, the use of only one scale in most studies and the absence of consideration of the spatial and temporal scales at which relevant oceanographic processes occur. It is concluded that multiscale studies, covering the scales of oceanographic process, are needed to obtain a better understanding of Sperm Whale distribution.