Spatial Distribution Of Animals Research Articles

Disparate home range dynamics reflect nutritional inadequacies on summer range for a large herbivore

AbstractThe spatial distribution of animals has consequences for nutrition, predator–prey dynamics, spread of diseases, and population dynamics in general. Animals must establish a home range to secure adequate resources to fuel their energy needs. Home ranges, therefore, are temporally and spatially dynamic, given the changing requirements of an animal and the availability of resources on the landscape. We used data from two populations of bighorn sheep with contrasting population dynamics following pneumonia epizootics and different habitat quality on their summer range to test the hypothesis that the distribution and size of home ranges are influenced by environmental conditions and reproductive status. We used a combination of data from 768 vegetation transects and remotely sensed metrics to index forage quality of consecutive biweekly home ranges for 27 bighorn sheep, June–August 2019–2021. There were population differences in home range dynamics that were consistent with resource limitations in the population declining in abundance. Animals in both populations increased the size of their home range through the summer in association with declining forage quality indexed by plant phenology. Furthermore, animals in the Whiskey Mountain population without offspring had home ranges more than twice the size of animals with offspring, whereas there were no differences in the home range size between animals with and without offspring in Jackson. We demonstrated that limitations young offspring impose on space use of a mother may have consequences for animals living where larger home ranges are needed to secure adequate resources—sheep on Whiskey Mountain had to travel 1000 m from escape terrain to access the same amount of biomass that the Jackson sheep could access directly adjacent to escape terrain. Forage quality and availability influence movement and space use. In the presence of disease, movement and space use may influence pathogen transmission and persistence. Thus, forage availability may play an indirect role in population dynamics in the presence of disease, which is another line of evidence for how environmental and nutritional conditions may influence population dynamics when coping with disease.

Can GPS monitoring help farmers select the best nutritional management strategy for finishing sheep on pasture?

Global Positioning System (GPS) allows monitoring of grazing herds remotely through real-time data collection. We hypothesized that GPS monitoring will establish preferential routes and grazing sites to find the best feeding strategy (supplementation versus no-supplementation) for sheep finished in a Caatinga rangeland (seasonally dry tropical forest) throughout different seasons of the year (rainy period, transition period, and drought period). The experiment was conducted on a 37.9 ha-Caatinga rangeland and comprised 84 days, subdivided into three 28-day periods (rainy, transition, and drought period). Four rumen cannulated sheep were used for estimation of pasture composition during each collection period based on extrusa samples. Twenty-four intact ram lambs (Santa Ines × Dorper F1 crossbred) grazing on Caatinga rangeland were used to test the effects of supplementation on performance, nutrient intake, and nutrient digestibility during the different seasons. The animals were fitted with GPS collars before being released into the Caatinga to monitor their behavioral activity. Greater walking distance, longer grazing time, higher kernel density, and higher walking speed were detected (P < 0.05) for non-supplemented animals, irrespective of season. The supplemented sheep showed greater (P < 0.05) nutrient intake and nutrient digestibility across all experimental periods compared to the non-supplemented animals. Supplemented animals showed greater (P < 0.05) final body weight and average daily gain compared to non-supplemented animals. During the transition and drought periods, supplementation affected all performance variables. In conclusion, GPS is a useful tool to highlight grazing sites according to different seasons and monitor the behavior of F1 Santa Ines × Dorper sheep finished on Caatinga rangeland. Thus, GPS monitoring aids in establishing the best supplementation strategy and consequently reduces productive and environmental losses caused by the spatial distribution of animals and irregular forage use. In addition, supplementation can offset the negative impacts of low forage supply on sheep grazing Caatinga areas.

Precipitation, vegetation productivity, and human impacts control home range size of elephants in dryland systems in northern Namibia.

Climatic variability, resource availability, and anthropogenic impacts heavily influence an animal's home range. This makes home range size an effective metric for understanding how variation in environmental factors alter the behavior and spatial distribution of animals. In this study, we estimated home range size of African elephants (Loxodonta africana) across four sites in Namibia, along a gradient of precipitation and human impact, and investigated how these gradients influence the home range size on regional and site scales. Additionally, we estimated the time individuals spent within protected area boundaries. The mean 50% autocorrelated kernel density estimate for home range was 2200 km2 [95% CI:1500–3100 km2]. Regionally, precipitation and vegetation were the strongest predictors of home range size, accounting for a combined 53% of observed variation. However, different environmental covariates explained home range variation at each site. Precipitation predicted most variation (up to 74%) in home range sizes (n = 66) in the drier western sites, while human impacts explained 71% of the variation in home range sizes (n = 10) in Namibia's portion of the Kavango‐Zambezi Transfrontier Conservation Area. Elephants in all study areas maintained high fidelity to protected areas, spending an average of 85% of time tracked on protected lands. These results suggest that while most elephant space use in Namibia is driven by natural dynamics, some elephants are experiencing changes in space use due to human modification.

Estimating the abundance of a group‐living species using multi‐latent spatial models

AbstractStatistical models use observations of animals to make inferences about the abundance and distribution of species. However, the spatial distribution of animals is a complex function of many factors, including landscape and environmental features, and intra‐ and interspecific interactions. Modelling approaches often have to make significant simplifying assumptions about these factors, which can result in poor model performance and inaccurate predictions.Here, we explore the implications of complex spatial structure for modelling the abundance of the Serengeti wildebeest, a gregarious migratory species. The social behaviour of wildebeest leads to a highly aggregated distribution, and we examine the consequences of omitting this spatial complexity when modelling species abundance. To account for this distribution, we introduce a multi‐latent framework that uses two random fields to capture the clustered distribution of wildebeest.Our results show that simplifying assumptions that are often made in spatial models can dramatically impair performance. However, by allowing for mixtures of spatial models accurate predictions can be made. Furthermore, there can be a non‐monotonic relationship between model complexity and model performance; complex, flexible models that rely on unfounded assumptions can potentially make highly inaccurate predictions, whereas simpler more traditional approaches involve fewer assumptions and are less sensitive to these issues.We demonstrate how to develop flexible spatial models that can accommodate the complex processes driving animal distributions. Our findings highlight the importance of robust model checking protocols, and we illustrate how realistic assumptions can be incorporated into models using random fields.

Ecological engineering across a spatial gradient: Sociable weaver colonies facilitate animal associations with increasing environmental harshness.

The spatial distribution of animals in a landscape depends mainly on the distribution of resources. Resource availability is often facilitated by other species and can positively influence local species diversity and affect community structure. Species that significantly change resource availability are often termed ecosystem engineers. Identifying these species is important, but predicting where they have large or small impacts is a key challenge that will enhance the usefulness of the ecosystem engineering concept.In harsh and stressful environments, the stress gradient hypothesis predicts that community structure and function will be increasingly influenced by facilitative interactions.To test this hypothesis, we investigate how the ecosystem engineering role and importance of sociable weavers Philetairus socius varies across a spatial gradient of harshness, for which aridity served as a proxy. These birds build large colonies that are home to hundreds of weavers and host a wide range of avian and non‐avian heterospecifics. We investigated the use of weaver colonies on multiple taxa (invertebrates, reptiles, birds and mammals) at multiple sites across a >1,000 km aridity gradient.We show that sociable weaver colonies create localized biodiversity hotspots across their range. Furthermore, trees containing sociable weaver colonies maintained localized animal diversity at sites with lower rainfall, an effect not as pronounced at sites with higher rainfall.Our results were consistent with predictions of the stress gradient hypothesis, and we provide one of the first tests of this hypothesis in terrestrial animal communities. Facilitation and amelioration by ecosystem engineers may mitigate some of the extreme impacts of environmental harshness.

European Plethodontid Salamanders on the Forest Floor: Testing for Age-Class Segregation and Habitat Selection

Spatial distribution of animals is affected by environmental and social factors, acting both at inter- and intraspecific levels, and generating patterns of segregation or aggregation. Several studies investigated age-class segregation of the European Cave Salamander Speleomantes strinatii, in underground environments, showing a clear spatial segregation. We investigated the spatial distribution of S. strinatii on the forest floor, on 111 plots surveyed three times/season for two consecutive seasons, in northern Italy during autumn 2017 and spring 2018. We analyzed count data to model co-abundance of adults and juveniles, using a conditional two-species N-mixture model, incorporating environmental covariates. In contrast with what was observed in underground environments, we recorded no spatial segregation between juvenile and adult of S. strinatii on the forest floor. Instead, we found that adults and juveniles showed different responses to environmental features.

Досвід малоресурсного дослідження фауни за допомогою фотопасток

The tasks of managing animal populations (conservation, exploitation, and control) require reliable initial information for their implementation. This information includes a number of parameters: spatial distribution, annual and daily cycles of activity, abundance and its dynamics, ecosystem relationships, reproduction, nutrition, mortality, and others. Of this broad set, abundance and territorial distribution are of basic importance. They affect all other parameters. However, these indicators are the most sensitive to the influence of factors of qualification and motivation of the performer. The solution to this problem leads to searching for ways to unify methods in order to reduce errors in the assessment. One of the solutions to this problem is the introduction of technical means such as camera traps. Camera traps have become an increasingly popular tool in wildlife research. With its help, the following tasks are solved: assessment of the number and spatial distribution of animals, daily and seasonal activity, and much more. This tool avoids the factor of subjectivity. At the same time, in our conditions, the price of a camera trap is high for a researcher. However, the methodological requirements for the study require the use of more than ten cameras. Thus, it becomes necessary to comprehend low-resource research and the results that they can bring. During 2018, research was carried out in the territory of the Chornobyl Reserve using six camera traps. The placement of camera traps was not systematic, but corresponded to the diversity of habitats. The objects of research were such representatives of mammals as the elk, deer, wolf, roe deer, wild boar, fox, raccoon dog, and hare. They are the ones that make up the set of species that can be effectively captured by a camera trap. The following results were obtained: daily activity, spatial distribution, quantitative characteristics of groups. As the results have shown, even a small number of camera traps makes it possible to assess the presence of the largest animals and their daily activity. It should be noted that this group of species is of the greatest interest from the viewpoint of regulation and protection. Numerical parameters such as quantity and relative abundance cannot be used for estimation. This is due to the high sensitivity to local conditions.

Group behaviours and individual spatial sorting before departure predict the dynamics of collective movements in horses

Establishing how collective decisions emerge is central to our understanding of animal societies. A frequent approach in collective behaviour studies is to look for leaders that will trigger and direct group movements. Relatively few studies on collective movements, notably in mammals, have taken the events preceding group departures into account. Success in recruitment can depend on the arousal state, the behaviour and the spatial distribution of animals before departure. We tested the effect of these factors on recruitment in two groups of nine domestic mares, Equus ferus caballus, at pasture. Predeparture periods were compared to control periods to identify their unique characteristics and to understand how they can predict the following collective outcome. We found that predeparture periods were characterized by the simultaneous increase in the number of active and goal-oriented individuals as well as in group cohesion. However, while the temporal patterns of activity and dispersion were unique to predeparture periods, those of orientation were not different from control periods. We also found that before departure individuals started to move towards the future goal area and to position themselves along the front–back axis. Moreover, the front-to-back position of group members was linked to the order in which they joined a collective movement. Finally, the duration of the joining process was positively correlated with the group dispersion. Our findings demonstrate that decision making is a continuous process and emphasize the necessity, in the study of collective decisions, to look beyond the event of initiation itself and the identity of the initiator as recruitment depends on group state before and at departure.

Desiccation resistance in Central European carabid species: effects of body size and habitat preferences

Water is the limiting factor for all organisms. Due to global climate change, prolonged drought periods are predicted and the importance of drought-related research is increasing. Water, together with temperature, determines the abundance and spatial distribution of animals. In this study, we investigated the effects of body size and habitat preference on desiccation resistance of carabid beetles under controlled laboratory condition. Firstly, we measured the longevity of 641 carabid individuals belonging to 18 species. These beetles were exposed to extremely low relative humidity (ca. 15-20%) using silica gel bags within experimental Petri dishes. Secondly, the rate of water loss was measured for 236 individuals belonging to eight carabid species. Rate of water loss was measured using exposition to the same extremely dry conditions, but only for 12 hours. Body size was represented by elytron length and live weight was also measured to analyse effects of body condition (weight corrected for structural size). Experimental beetles were collected in different habitats ranging from extremely dry to very wet conditions. Carabids were provided with food and water ad libitum for at least 7 days prior to the experiments. All experiments were performed using a climatic chamber set to a long day (16L:8D) and the constant temperature of 20°C. The preliminary results show that species from wet habitats were more sensitive to desiccation and larger species were more resistant (survived for a longer time) compared to smaller species. Species from wet habitats had higher water loss rate compared to species originating from dry habitats. At the intraspecific level, individuals with larger body size (elytron length) survived longer than smaller individuals. Interestingly, the rate of water loss was affected by initial body condition and sex but not by structural body size at the intraspecific level. The most resistant species was Pseudoophonus rufipes. This species was not superior to other species with respect to water loss rate but it had the highest relative water content. It is also possible that P. rufipes has some other physiological or behavioural adaptation enabling a better survival under stressful, dry condition. This issue could be investigated in a future study.

Demography of the endangered butterfly Euphydryas aurinia (Lepidoptera: Nymphalidae): A case study of populations in sub-Mediterranean dry calcareous grasslands

We studied a population of the regionally endangered marsh fritillary butterfly Euphydryas aurinia inhabiting a system of loosely connected dry calcareous grasslands in sub-Mediterranean Slovenia. Our goal was to set the basis for a long-term monitoring of this butterfly in four meadows using mark-release-recapture (MRR). We determined its demographic parameters, dispersal, behaviour and utilization of nectar plants in different quality patches. Total population size was estimated to be approximately 347 males (95% confidence interval: 262-432) and 326 females (95% confidence interval: 250-402), with an unbiased sex ratio. The average lifespans were 6.3 and 8.6 days, respectively. Daily population sizes followed a parabola with marked protandry. Both sexes were relatively highly mobile with both occasionally moving over half a kilometre. The spatial distribution of animals seemed to be associated with patch size, host plant densities and nectar sources, resulting in much higher population densities in the largest patch. Adult behaviour differed between the sexes, with females resting more and flying less than males. Behaviour also changed during daytime and with the progression of the season. Adults were confirmed to be opportunistic feeders, since as many as ten nectar sources were detected. We conclude that demographic parameters differ greatly among regions and habitats, thus conservation aims should be planned accordingly. Although the population studied is apparently in good condition, there are threats that may hamper the long-term persistence of the species in this area: succession, intensification of mowing and overgrazing.

Unmanned Aircraft Systems complement biologging in spatial ecology studies

The knowledge about the spatial ecology and distribution of organisms is important for both basic and applied science. Biologging is one of the most popular methods for obtaining information about spatial distribution of animals, but requires capturing the animals and is often limited by costs and data retrieval. Unmanned Aircraft Systems (UAS) have proven their efficacy for wildlife surveillance and habitat monitoring, but their potential contribution to the prediction of animal distribution patterns and abundance has not been thoroughly evaluated. In this study, we assess the usefulness of UAS overflights to (1) get data to model the distribution of free-ranging cattle for a comparison with results obtained from biologged (GPS-GSM collared) cattle and (2) predict species densities for a comparison with actual density in a protected area. UAS and biologging derived data models provided similar distribution patterns. Predictions from the UAS model overestimated cattle densities, which may be associated with higher aggregated distributions of this species. Overall, while the particular researcher interests and species characteristics will influence the method of choice for each study, we demonstrate here that UAS constitute a noninvasive methodology able to provide accurate spatial data useful for ecological research, wildlife management and rangeland planning.

Establishing the link between habitat selection and animal population dynamics

Although classical ecological theory (e.g., on ideal free consumers) recognizes the potential effect of population density on the spatial distribution of animals, empirical species distribution models assume that species–habitat relationships remain unchanged across a range of population sizes. Conversely, even though ecological models and experiments have demonstrated the importance of spatial heterogeneity for the rate of population change, we still have no practical method for making the connection between the makeup of real environments, the expected distribution and fitness of their occupants, and the long‐term implications of fitness for population growth. Here, we synthesize several conceptual advances into a mathematical framework using a measure of fitness to link habitat availability/selection to (density‐dependent) population growth in mobile animal species. A key feature of this approach is that it distinguishes between apparent habitat suitability and the true, underlying contribution of a habitat to fitness, allowing the statistical coefficients of both to be estimated from multiple observation instances of the species in different environments and stages of numerical growth. Hence, it leverages data from both historical population time series and snapshots of species distribution to predict population performance under environmental change. We propose this framework as a foundation for building more realistic connections between a population's use of space and its subsequent dynamics (and hence a contribution to the ongoing efforts to estimate a species' critical habitat and fundamental niche). We therefore detail its associated definitions and simplifying assumptions, because they point to the framework's future extensions. We show how the model can be fit to data on species distributions and population dynamics, using standard statistical methods, and we illustrate its application with an individual‐based simulation. When contrasted with nonspatial population models, our approach is better at fitting and predicting population growth rates and carrying capacities. Our approach can be generalized to include a diverse range of biological considerations. We discuss these possible extensions and applications to real data.

Using simulations of past and present elephant (Loxodonta africana) population numbers in the Okavango Delta Panhandle, Botswana to improve future population estimates

An ability to reliably estimate population numbers, trends and densities of wildlife has a prominent role in conservation and management of wetlands. We use aerial surveys and simulation techniques to explore the results of past and present elephant population surveys in the Okavango Delta Panhandle, Botswana, and use these to propose a technique of simulation to improve counts in the future. Population numbers and density estimates from past survey results show large fluctuations, which are unlikely to come from reproduction. Reasons for such variations could be attributed to imprecision in survey techniques or may be because only part of the elephant range is being surveyed. Simulated surveys of hypothetical elephant populations were used to explore the effect of different survey techniques, spatial distributions of animals and spatial scale on the precision of aerial survey population estimates and trends. Our study reveals the usefulness of using simulations to test the reliability of survey data and plan more efficient surveys. We also find that while there may be some uncertainty in individual population estimates, there is more certainty in the recorded trends. These findings reinforce the need to address elephant management in the Okavango and surrounding wetland systems and call for the urgent consideration of management strategies such as fence realignments to affect the objectives of the Kavango Zambezi Transfrontier Conservation Area (KAZA TFCA) initiative, which will help relieve elephant population pressure.

Fish gut microecosystem: a model for detecting spatial pattern of microorganisms

The spatial distribution pattern of organisms is a basic issue in understanding the mechanisms of community assembly. Although the spatial distributions of animals and plants have been well studied, those of microorganisms are still being debated. In this study, we used a fish gut microecosystem to detect the spatial pattern of microbes, because it can provide a relatively unified and stable environment. Results suggest that the turnover of intestinal bacterial assemblages showed a weak but highly significant negative correlation between similarity and distances in the microbial community, in respect of both grass carp intestinal loci distances and the geographical distance between fish sampling sites. Our results also suggest that intestinal bacterial assemblages responded to differences within the external environment and within different parts of the fish themselves. These results show that some, or possibly all, microbes are restricted in their distribution and that environmental factors are also important influences on the structure of intestinal bacterial assemblages. The fish gut microecosystem is useful in promoting study of the spatial distribution patterns of microorganisms.

The influence of native versus exotic streetscape vegetation on the spatial distribution of birds in suburbs and reserves

AbstractAimManagement practices in the landscape matrix can have significant effects on the spatial distribution of animals within adjacent protected areas. This has been well established in agricultural and forested areas, but less is known about how management of the suburban matrix affects adjacent reserves. We argue that it is critically important to understand the impact of suburban management on reserves, as flawed planning decisions can have negative conservation outcomes and waste limited resources.LocationCanberra, Australian Capital Territory, Australia.MethodsWe examined bird distribution patterns in suburbs and adjacent reserves to the effects of two suburban management practices: (1) street tree planting and (2) boundary design. We focused on three groups of birds with known responses to urbanization: native urban‐intolerant species (native avoiders), native urban‐tolerant species (native adapters) and exotic urban‐tolerant species (exotic adapters).ResultsWe found that suburbs with ≥30% native (Eucalyptus) street trees and reserves adjacent to these suburbs had significantly higher bird species richness, native adapter species richness and probability of reporting exotic adapters than those with exotic trees. The type of street trees, however, did not affect the probability of reporting native avoiders. These species were more likely to be reported when habitat complexity was high. Only native adapters responded to boundary design, with higher species richness when the boundary type was a local or unsealed road as opposed to an arterial road.Main conclusionsNative street trees provide foraging resources for birds that would be reduced or absent in exotic streetscapes, enabling native streetscapes to support a rich community of birds. Furthermore, native streetscapes increase bird richness and diversity in adjacent reserves. This result has important conservation implications for suburb and reserve management practices. Our study provides evidence that the establishment and retention of native suburban streetscapes is an important management strategy for improved bird conservation.

The Importance of Temporal and Spatial Vegetation Structure Information in Biotope Mapping Schemes: A Case Study in Helsingborg, Sweden

Temporal and spatial vegetation structure has impact on biodiversity qualities. Yet, current schemes of biotope mapping do only to a limited extend incorporate these factors in the mapping. The purpose of this study is to evaluate the application of a modified biotope mapping scheme that includes temporal and spatial vegetation structure. A refined scheme was developed based on a biotope classification, and applied to a green structure system in Helsingborg city in southern Sweden. It includes four parameters of vegetation structure: continuity of forest cover, age of dominant trees, horizontal structure, and vertical structure. The major green structure sites were determined by interpretation of panchromatic aerial photographs assisted with a field survey. A set of biotope maps was constructed on the basis of each level of modified classification. An evaluation of the scheme included two aspects in particular: comparison of species richness between long-continuity and short-continuity forests based on identification of woodland continuity using ancient woodland indicators (AWI) species and related historical documents, and spatial distribution of animals in the green space in relation to vegetation structure. The results indicate that (1) the relationship between forest continuity: according to verification of historical documents, the richness of AWI species was higher in long-continuity forests; Simpson's diversity was significantly different between long- and short-continuity forests; the total species richness and Shannon's diversity were much higher in long-continuity forests shown a very significant difference. (2) The spatial vegetation structure and age of stands influence the richness and abundance of the avian fauna and rabbits, and distance to the nearest tree and shrub was a strong determinant of presence for these animal groups. It is concluded that continuity of forest cover, age of dominant trees, horizontal and vertical structures of vegetation should now be included in urban biotope classifications.

Bayesian Spatial Point Process Modeling of Line Transect Data

This paper develops a Bayesian approach for spatial inference on animal density from line transect survey data. We model the spatial distribution of animals within a geographical area of interest by an inhomogeneous Poisson process whose intensity function incorporates both covariate effects and spatial smoothing of residual variation. Independently thinning the animal locations according to their estimated detection probabilities results into another spatial Poisson process for the sightings (the observations). Prior distributions are elicited for all unknown model parameters. Due to the sparsity of data in the application we consider, eliciting sensible prior distributions is important in order to get meaningful estimation results. A reversible jump Markov Chain Monte Carlo (MCMC) algorithm for simulation of the posterior distribution is developed. We present results for simulated data and a real data set of minke whale pods from Antarctic waters. The main advantages of our method compared to design-based analyses are that it can use data arising from sources other than specifically designed surveys and its ability to link covariate effects to variation of animal density. The Bayesian paradigm provides a coherent framework for quantifying uncertainty in estimation results.

Impact of the spatial and temporal arrangement of pastoral use on land degradation around animal concentration points

AbstractIn mobile pastoral systems, the spatial movement of herders is tied to requirements such as water, markets and medical services, resulting in the concentration of livestock in particular areas and subsequent desertification in those areas. The spatial and temporal distributions of these requirements are subject to changes in external forces, such as political regimes and economic systems. To assess and counteract desertification requires an understanding of, and ability to predict, the spatial and temporal arrangements of such concentration points and how these arrangements cause or inhibit desertification. To this end we developed a model that explicitly simulates how animals and vegetation interact. The model has spatial settings for extensive pasture to represent the points at which animals concentrate. We found that the spatial dynamics of the interaction between animal behavior and vegetation were nonlinear and markedly affected the size of the area desertified, and that the distribution of grazing pressure was more important than total grazing pressure, which had only a limited influence on desertification. These findings indicate that application of the carrying capacity concept is not capable of preventing desertification in extensive pasture, even under equilibrium conditions. Therefore, explicit management of the spatial distribution of animals is essential to prevent desertification in extensively grazed rangelands. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Spatial properties of a forest buffalo herd and individual positioning as a response to environmental cues and social behaviour

Many animals aggregate into organized temporary or stable groups under the influence of biotic and abiotic factors, and some studies have shown the influence of habitat features on animal aggregation. This study, conducted from 2002 to 2004 in the Dzanga-Ndoki National Park, Central African Republic, studied a herd of forest buffaloes (Syncerus caffer nanus) to determine whether spatial aggregation patterns varied by season and habitat. Our results show that both habitat structure and season influenced spatial aggregation patterns. In particular, in open habitats such as clearings, the group covered a larger area when resting and was more rounded in shape compared to group properties noted in forest during the wet season. Moreover, forest buffaloes had a more aggregated spatial distribution when resting in clearings than when in the forest, and individual positions within the herd in the clearing habitat varied with age and sex. In the clearings, the adult male (n = 24) was generally, on most occasions, located in the centre of the herd (n = 20), and he was observed at the border only four times. In contrast, females (n = 80) occupied intermediate (n = 57), peripheral (n = 14) and central positions (n = 9) within the group. Juveniles (n = 77) also occurred in intermediate (n = 64) and peripheral positions (n = 13). Based on these results, we concluded that habitat characteristics and social behaviour can have relevant effects on the spatial distribution of animals within a group.

Understanding mechanism of spatial ecological phenomena: a preface to the special feature on “Spatial statistics”

Understanding of the mechanism underlying the spatial distribution of animal and plant populations is one of the central themes in ecology. Ecological patterns tend to have scale dependency, which is problematic for a comparative approach, but could itself indicate the underlying ecology governed by biological and physical phenomena operating on characteristic spatial scales (O’Neill 1989; Powell 1989; Levin 1992; Tuda 1993). Theoretical studies such as host–parasitoid models by Hassell et al. (1991) and Comins et al. (1992) have explored population behavior in spatially explicit lattice space. Similar phenomena can also be found in other fields of science (e.g., Kaneko 1984). There has been a gap between the advanced theory and understanding of crude spatial data in spatial ecology. Recent advances in spatial statistics, however, shed light on empirical spatial ecology (e.g., Dale et al. 2002; Perry et al. 2002). Direct observation of marked organisms (e.g., Tuda and Shima 2002) and bottle experiments (Huffaker 1958; recent reviews, Bonsall and Hassell 2005; Cadotte et al. 2005; Jessup et al. 2005; Holyoak and Lawler 2005; Sabelis et al. 2005; Tuda and Shimada 2005) may be the most basic and simple approach to capturing spatial mechanisms in ecology. Nevertheless, spatial statistics proposed or applied here can bring greater understanding of mechanisms when larger sets of data with a wider range of spatial scales are available. In practice, information we obtain may be limited to a single snapshot of multiple transitional states or quantitative attributes of a single state on a map. On the contrary, richer information may be available as timeserial data of spatial patterns more like an animation. Here, I have invited papers tackling ecological spatial dynamics: Schlicht and Iwasa (2007) aim to handle both snapshots and animations of forest disturbance patterns. The other two papers (Yamanaka et al. 2007; Kim et al. 2007) elucidate spatial correlations from animations of quantitative spatio-temporal data for multiple transitional states, making full use of established spatial statistical methods. Schlicht and Iwasa (2007) proposed two statistical methods and tested their relevancy by fitting them to three hypothetical spatial patterns, generated by simulating models that employed different numbers of states (two, three, and continuous states respectively). The first method that detects directionality of regeneration waves succeeded in distinguishing two-state and three-state hypothetical data, whereas the second method, which detects spatial-scale dependency in the variance of fractions of states, distinguished the three-state and continuous-state hypothetical data. The kind of data most suitable for the two methods is the temporal dynamics of spatial patterns for the first method and single snapshots of spatial patterns for the second method. The authors applied these methods to observed forest disturbance patterns and detected proper models. This study not only provides forest ecologists with the most parsimonious descriptive models that may narrow down possible ecological mechanisms underlying observed spatial patterns, but can also be extended to analyses of other spatial distributions of plants and animals. Yamanaka et al. (2007) tested two hypotheses, resource concentration and reaction diffusion, on the mechanism inducing spatial distribution of the ragweed beetle. The nonparametric autoand cross-correlation functions, developed by Bjornstad and his colleagues, were applied to the 3-year seasonal spatial dynamics of a resource (the ragweed) and its herbivorous predator (the ragweed beetle). The resource concentration hypothesis was only weakly supported. The nonparametric crosscorrelation with time lags between the weed and the beetle, on the other hand, supported trophic interaction between the two at a certain spatial lag, thereby leading Spatial statistics in ecology