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Living on the edge: Heterogeneity in vegetation type cover as key factor of the habitat occupied by Dolichotis patagonum at landscape scale
... The heterogeneous and large-scale geospatial data are generated regularly using Information and Communication Technology (ICT) for remote sensing, crowd sourcing, etc. It requires new insights, efficient algorithms, data storage and architecture to enable the geocomputation in a reasonable amount of time (Shi and Nellis 2014;Alonso et al. 2017a;Rold an et al. 2017). Due to the rising of large-scale geospatial data and complex computation requirements, various critical issues and challenges are faced by the users during the computations over the already developed geocomputation model such as biodiversity models, hydrological models, climate models, etc. . ...
The parallel processing and distributed GIServices provide an efficient approach to address the geocomputation challenges in biodiversity modeling. Using the widely applied Spatial Biodiversity Model (SBM) as an illustration, this study demonstrates parallelization of the spatial landscape algorithms based on message passing interface (MPI) in cluster computing. The geocomputation based on MPI is performed to characterize the spatial distribution of Biological Richness (BR) for Indian landscape using developed high-performance cluster computing-based model named as SBM-HPC. In performance analysis, the execution time is reduced by 56.42%–81.41% (or the speedups of 2.29–5.38) using the parallel and cluster computing environment. Also, the spatial landscape algorithms of the model are extended to integrate large-scale geodata from online map services archives using distributed GIServices. To validate BR map, the phytosociological data is collected using participatory GIS approach. Furthermore, regression analysis between derived BR map and Shannon-Wiener index (Hˈ) represents high correlation coefficient R² values.
• Highlights
• Development of spatial biodiversity model using parallel computing on the cluster.
• Geocomputation of spatial landscape indices using large-scale geospatial datasets.
• Distributed GIService integration in model to compute distributed data archives.
• Prediction of biological richness pattern and validation using participatory GIS.
• Characterize correlations between biological richness and bioclimatic patterns.
Across modified landscapes, anthropic factors can affect habitat selection by animals and consequently their abundance and distribution patterns. The study of the spatial structure of wild populations is crucial to gain knowledge on species' response to habitat quality, and a key for the design and implementation of conservation actions. This is particularly important for a low-density and widely distributed species such as the mara (Dolichotis patagonum), a large rodent endemic to Argentina across the Monte and Patagonian drylands where extensive sheep ranching predominates. We aimed to assess the spatial variation in the abundance of maras and to identify the natural and anthropic factors influencing the observed patterns in Península Valdés, a representative landscape of Patagonia. We conducted ground surveys during the austral autumn from 2015 to 2017. We built density surface models to account for the variation in mara abundance, and obtained a map of mara density at a resolution of four km 2. We estimated an overall density of 0.93 maras.km-2 for the prediction area of 3,476 km 2. The location of ranch buildings, indicators of human presence, had a strong positive effect on the abundance of maras, while the significant contribution of the geographic longitude suggested that mara density increases with higher rainfall. Although human presence favored mara abundance, presumably by providing protection against predators, it is likely that the association could bring negative consequences for maras and other species. The use of spatial models allowed us to provide the first estimate of mara abundance at a landscape scale and its spatial variation at a high resolution. Our approach can contribute to the assessment of mara population abundance and the factors shaping its spatial structure elsewhere across the species range, all crucial attributes to identify and prioritize conservation actions.
RESUMEN. La mara (Dolichotis patagonum) construye madrigueras que podrían constituir un recurso para
otras especies. Con el fin de estimar la abundancia de madrigueras y documentar su utilización por parte de
otros vertebrados, se realizaron relevamientos en seis áreas en Península Valdés y se observaron 42 madrigueras
con cámaras de video durante el día. En promedio se encontraron 0.62 madrigueras/km2
y se registraron cinco
especies adicionales utilizándolas. Concluimos que la mara provee un recurso utilizado por otras especies y es
un caso de estudio que debe ser profundizado en el marco de la ingeniería de ecosistemas.
ABSTRACT. Warrens of Dolichotis patagonum as resource for other vertebrates in Península Valdés. Maras
(Dolichotis patagonum) dig warrens which could be a resource for other species. In order to estimate the
abundance of warrens and to document their use by other vertebrates, surveys were conducted in six areas of
Península Valdés and 42 warrens were surveyed with video cameras during day-time. We found an average
of 0.62 warrens/km2
and recorded use by five additional species. We conclude that maras provide a resource
used by other species and is a case study that must be further researched within the framework of ecosystem
engineering theory.
We characterized the habitat use by maras (Dolichotis patagonum) on a microhabitat scale in the area surrounding the warren, assessing the conditioning effect of the warren over space use and exploitation of other resources. We evaluated the relationships between the probability and intensity of use, habitat configuration and distance to the warren, counting feces along transects departing from each warren. Our results showed that the location of breeding warrens was positively associated with the habitat use by maras on a microhabitat scale. The core area of the annual activity of maras was concentrated around the warren and there was no evidence of alternative areas of activity. According to the fitted models, maras used microhabitats with a high proportion of bare soil and close to infrastructure elements. The spatial autocorrelation components indicated that intensively used patches are small and disperse. The patterns of habitat use observed in this study suggest that maras use multipurpose areas including the breeding site and resources needed throughout the year. These patterns suggest that warrens are good all year-round indicators of mara habitat use and spatial ecology.
The diet of mara (Dolichotis patagonum, Zimmeraman 1780) within the limits of Sierra de las Quijadas National Park (San Luis, Argentina) is described. Other studies regarding mara's diet showed that mara, feeds on different species of grasses and shrubs. However, there is controversy regarding the proportions of these items in the diet or whether this proportion varies seasonally. Considering mara's body size, anatomical features and physiology, we suggest that mara feeds on grasses in a greater proportion than shrubs and forbs. Moreover, giving that in this region precipitation varies considerably between seasons; it is also expected to find a correlation between the diet of mara and seasons. Fecal pellets of mara were collected during four periods including two dry, and two wet seasons. Relative frequency of each item in scats was determined by microhistological analysis. Results support the hypothesis that mara shows preference for grasses, despite they are less available than shrubs and forbs and that this preference remains constant through seasons regardless of the precipitation regime. The characteristics of mara's diet and the ecological implications of these findings are discussed.
In species showing distributions attached to particular features of the landscape or conspicuous signs, counts are commonly made by making focal observations where animals concentrate. However, to obtain density estimates for a given area, independent searching for signs and occupancy rates of suitable sites is needed. In both cases, it is important to estimate detection probability and other possible sources of variation to avoid confounding effects on measurements of abundance variation. Our objective was to assess possible bias and sources of variation in a two-step protocol in which random designs were applied to search for signs while continuously recording video cameras were used to perform abundance counts where animals are concentrated, using mara (Dolichotis patagonum) as a case study. The protocol was successfully applied to maras within the Península Valdés protected area, given that the protocol was logistically suitable, allowed warrens to be found, the associated adults to be counted, and the detection probability to be estimated. Variability was documented in both components of the two-step protocol. These sources of variation should be taken into account when applying this protocol. Warren detectability was approximately 80% with little variation. Factors related to false positive detection were more important than imperfect detection. The detectability for individuals was approximately 90% using the entire day of observations. The shortest sampling period with a similar detection capacity than a day was approximately 10 hours, and during this period, the visiting dynamic did not show trends. For individual mara, the detection capacity of the camera was not significantly different from the observer during fieldwork. The presence of the camera did not affect the visiting behavior of adults to the warren. Application of this protocol will allow monitoring of the near-threatened mara providing a minimum local population size and a baseline for measuring long-term trends.
Terrestrial herbivory in the Chaco, Monte and Patagonia natural regions of Argentina shows similar pattems to equivalent regions of North America, as weil as distinctive features. Peculiarities include the near absence of native large her-bivores, itre ttlg1t diversity and abundance of leaf-cuting ants, and a considerable number of plants showing adaptations against predation and for dispersion by large herbivores. All these features might be linked to evolutionary interactions ."ith th" diverse fauna of laige herbivores which became extinct during the Pleistocene. Overgrazing fiom domestic ungulates in the Chaco has transformed the original parkland landscape provoking widespread encroachment of woody u.gltutiott, the near extinction of grasslands and some of their largest herbivores, and an increment of medium-sized rodents, which, in turn, can keep the system in a new "disclimaxic" equilibrium. In the Monte and Patagonia the results of overgtazing on the natural vegetation have also been dramatic, although les spectacular in terms of landscape alteration. These characteristics suggest lines along rvhich future tesearch efforts could be focused. RESUMEN La herbivoria terrestte en las regiones naturales del (haco, Monte y Patagonia de la Argentina muestra patrones simila-res con regiones equivalentes de Norte America, asi como caracteristicas peculiares. Estas iltimas incluyen una marcada pobnza di grandei herbivoros, la gran abundancia y diversidad de hormigas cortadoras de hojas, y un considerable nri-mero de plantas que muestran adaptaciones contra la depredaci6n y parc la dispersi6n por grandes herbivoros. Todas estas caracteristicas pueden ser vinculadas con la diversa fauna de grandes herbivoros que se extingui6 durante el Pleis-toceno. El sobrepastoreo por ungulados domdsticos ha transformado el paisaje de parque original del Gtaco, a trav6s de una invasi6n generalizada de la vegetaci6n lefrosa,1a casi extinci6n de 1os pastizales y de algunos de sus grandesherbi-voros, y un incremento de roedores de tamafro mediano, los cuales pueden mantener el sistema en un nuevo equilibrio "disclimdxico". En el Monte y Patagonia los efectos del sobrepastoreo han sido tarnbitjn intensos, aunque menos espec-taculares en t6rminos de alteraci6n del paisaje. Estas caracteristicas sugieren lineas a lo largo de las cuales pueden orien-tarse futuros esfuetzos de investigacion. Palabras clave: Regiones semiaridas neotropicales, Chaco, Monte, Patagonia, sabanas, herbivorfa, efectos del pastoreo, hormigas cortadoras de hojas.
Accurate and efficient monitoring of habitat structure on rangelands is important for understanding wildlife responses to land management practices. Unfortunately, studies of wildlife responses to changes in habitat structure often use monitoring techniques that fail to measure variation in multiple structural dimensions. Our objectives were to evaluate relationships between measures of habitat structure in a shrubland community and to discuss the usefulness of several techniques in integrating multiple structural dimensions into a single index of habitat structure. We evaluated relationships between shrub cover, herbaceous cover, shrub patch number, average shrub patch size, average vegetation height, visual obstruction across multiple strata of a profile board, cone of vulnerability, and angle of obstruction using a principle component analysis. Many of these variables were redundant with each other. Average visual obstruction estimates, using a profile board, were associated with variability in vertical structure as indicated by its association with height. Coefficients of variation for cone of vulnerability and visual obstruction were dependent upon their means and of limited use in describing horizontal patchiness. In contrast, shrub patch number was not linearly correlated with any other single measure in our analysis, and may be useful in describing horizontal patchiness. Cone of vulnerability and angle of obstruction are recently developed techniques that provided useful, single indices of multidimensional habitat structure. Efficient monitoring of wildlife habitat structure should employ multiple, independent techniques that measure distinct dimensions of habitat structure or a single measure that integrates multiple dimensions.
We analyzed the relation between early winter distribution and density of female moose (Alces alces L.) and habitat heterogeneity in interior Alaska. We tested for effects of vegetation type, topography, distance to rivers and towns, occurrence and timing of fire, and landscape metrics. A spatial linear model was used to analyze effects of independent variables organized at multiple scales. Because densities of moose vary widely as a result of differences in management and other factors, a spatial response surface of the log of moose density was fit to remove large-scale effects. The analysis revealed that the densest populations of moose occurred closer to towns, at moderate elevations, near rivers, and in areas where fire occurred between 11 and 30 years ago. Furthermore, moose tended to occur in areas with large compact patches of varied habitat and avoided variable terrain and nonvegetated areas. Relationships of most variables with moose density occurred at or below 34 km2, suggesting that moose respond to environmental variables within a few kilometres of their location. The spatial model of density of moose developed in this study represents an important application for effective monitoring and management of moose in the boreal forest.
Although maras (Dolichotis patagonum) are among the most representative mammals of South America, knowledge on the ecological processes affecting their conservation is scarce. In particular, the study of habitat requirements and its relationship with breeding success is necessary to identify possible threats and develop conservation action for this endemic mammal. I investigated habitat selection patterns by maras and their relationship with breeding success in Península Valdés, Argentine Patagonia. Maras bred from mid-August to late December, and they tended to build the breeding warrens in open, grass-dominated habitats more than expected while avoided closed habitats dominated by taller shrubs. Mean number of breeding adults per warren was 4.26, while mean number of pups born per warren was 4.46. Overall, 30 (45%) of 67 pups survived until the 6th week of life, but pups born in warrens located in open habitats survived significantly better than pups born in warrens located in closed habitats (50% vs. 30% of the pups born). As grass-dominated areas uphold the highest densities of domestic sheep and habitat modification due to overgrazing is a widespread process across arid Patagonia, effects on the availability of suitable breeding sites for maras are likely to occur and require further investigation.
a b s t r a c t In this review, we compiled published results on biological interactions at different spatial scales in the Monte desert of Argentina and identified gaps in current knowledge. We presented evidence of competitive and facilitative plant–plant conspecific and heterospecific interactions, and plant–soil– microbes interactions in relation to the abiotic environment at the fine patch-scale. We also showed evidence of animal–animal interactions and plant–animal interactions at the community scale through study cases involving both native and introduced herbivores. Moreover, we identified bottom-up and top-down forces governing the interactions between granivores (birds, ants, and small mammals) and seed availability/production at the community scale. At the landscape scale, we discussed feedbacks between domestic grazers and the spatial patterns of resources and their interrelationships with processes occurring at other scales. We concluded that research has steadily increased during the last 6 years but knowledge on biological interactions in the Monte desert is still scarce, particularly at a land-scape scale.
Resource selection functions (RSF) can be used to explore the role of scale in determining patterns of habitat use. We estimated RSFs for 93 radiocollared adult female elk (Cervus canadensis) with resource availability defined at four spatial scales and two seasons in Yellowstone National Park. Habitat selection differed markedly among scales and seasonal ranges. During winter elk moved to ranges at lower elevations where snow water equivalents were low and selected landscapes with a mix of forest and open vegetation at all spatial scales. Areas of high vegetation diversity were selected at large spatial scales during summer, whereas elk selected less diverse areas on winter range. During summer elk selected forests that burned 12-14 y earlier, but they used these burns less than expected by chance during winter. Habitat selection by elk occurred at multiple spatial scales; thus, we cannot prescribe a single scale as being best for modelling habitat use by elk. Instead, selection of an appropriate scale will vary depending on the research question or management issue at hand.
Assessing the associations between spatial patterns in population abundance and environmental heterogeneity is critical for
understanding various population processes and for managing species and communities. This study evaluates responses in the
abundance of the European rabbit (Oryctolagus cuniculus), an important prey for predators of conservation concern in Mediterranean ecosystems, to environmental heterogeneity at
different spatial scales. Multi-scale habitat models of rabbit abundance in three areas of Doñana, south-western Spain, were
developed using a spatially extensive dataset of faecal pellet counts as an abundance index. The best models included habitat
variables at the three spatial scales examined: distance from lagoons (broad scale), mean landscape shrub coverage and interspersion
of pastures (home-range scale), and shrub and pasture cover (microhabitat scale). These variables may well have been related
to the availability of food and refuge for the species at the different scales. However, the models’ fit to data and their
predictive accuracy for an independent sample varied among the study regions. Accurate predictions in some areas showed that
the combination of variables at various spatial scales can provide a reliable method for assessing the abundance of ecologically
complex species such as the European rabbit over large areas. On the other hand, the models failed to identify abundance patterns
in a population that suffered the strongest demographic collapse after viral epidemics, underlining the difficulty of generalizing
this approach. In the latter case, factors difficult to implement in static models such as disease history and prevalence,
predator regulation and others may underlie the lack of association. Habitat models can provide useful guidelines for the
management of landscape attributes relevant to rabbits and help improve the conservation of Mediterranean communities. However,
other influential factors not obviously related to environmental heterogeneity should also be analyzed in more detail.
We describe a general framework for understanding the ecological processes that operate at landscape scales. The composition of habitat types in a landscape and the physiognomic or spatial arrangement of those habitats are the two essential features that are required to describe any landscape. As such, these two features affect four basic ecological processes that can influence population dynamics or community structure. The first two of these processes, landscape complementation and landscape supplementation, occur when individuals move between patches in the landscape to make use of non-substitutable and substitutable resources, respectively. The third process, source-sink dynamics, describes the consequences of having different individuals in the same population occupy habitat patches of different qualities. The fourth process, the neighborhood effect, describes how landscape effects can be amplified when the critical resources are in the landscape immediately surrounding a given patch. Definition of these landscape features and general processes will allow a better synthesis of how landscape variation affects populations and communities.
Aim In a selected literature survey we reviewed studies on the habitat heterogeneity-animal species diversity relationship and evaluated whether there are uncertainties and biases in its empirical support. Location World-wide. Methods We reviewed 85 publications for the period 1960-2003. We screened each publication for terms that were used to define habitat heterogeneity, the animal species group and ecosystem studied, the definition of the structural variable, the measurement of vegetation structure and the temporal and spatial scale of the study. Main conclusions The majority of studies found a positive correlation between habitat heterogeneity/diversity and animal species diversity. However, empirical support for this relationship is drastically biased towards studies of vertebrates and habitats under anthropogenic influence. In this paper, we show that ecological effects of habitat heterogeneity may vary considerably between species groups depending on whether structural attributes are perceived as heterogeneity or fragmentation. Possible effects may also vary relative to the structural variable measured. Based upon this, we introduce a classification framework that may be used for across-studies comparisons. Moreover, the effect of habitat heterogeneity for one species group may differ in relation to the spatial scale. In several studies, however, different species groups are closely linked to 'keystone structures' that determine animal species diversity by their presence. Detecting crucial keystone structures of the vegetation has profound implications for nature conservation and biodiversity management.
The aim of this overview paper is to analyze the use of various landscape metrics and landscape indices for the characterization of landscape structure and various processes at both landscape and ecosystem level. We analyzed the appearance of the terms landscape metrics/indexes/indices in combination with seven main categories in the field of landscape ecology [1) use/selection and misuse of metrics, 2) biodiversity and habitat analysis; 3) water quality; 4) evaluation of the landscape pattern and its change; 5) urban landscape pattern, road network; 6) aesthetics of landscape; 7) management, planning and monitoring] in the titles, abstracts and/or key words of research papers published in international peer-reviewed scientific journals indexed by the Institute of Science Information (ISI) Web of Science (WoS) from 1994 to October 2008. Most of the landscape metrics and indices are used concerning biodiversity and habitat analysis, and also the evaluation of landscape pattern and its change (up to 25 articles per year). There are only a few articles on the relationships of landscape metrics/indices/indexes to social aspects and landscape perception.
Analysis of Phylogenetics and Evolution (APE) is a package written in the R language for use in molecular evolution and phylogenetics.
APE provides both utility functions for reading and writing data and manipulating phylogenetic trees, as well as several advanced
methods for phylogenetic and evolutionary analysis (e.g. comparative and population genetic methods). APE takes advantage
of the many R functions for statistics and graphics, and also provides a flexible framework for developing and implementing
further statistical methods for the analysis of evolutionary processes.
Availability: The program is free and available from the official R package archive at http://cran.r-project.org/src/contrib/PACKAGES.html#ape. APE is licensed under the GNU General Public License.
Measuring percent occurrence of objects from digital images can save time and expense relative to conventional field measurements. However, the accuracy of image analysis had, until now, not reached the level of the best conventional field measurements. Additionally, most image-analysis software programs require advanced user training to successfully analyze images. Here we present a new software program, 'SamplePoint,' that provides the user a single-pixel sample point and the ability to view and identify the pixel context. We found SamplePoint to allow accuracy comparable with the most accurate field-methods for ground-cover measurements. Expert use of the program requires minimal training and its ease of use allows rapid measurements from image data. We recommend SamplePoint for calibrating the threshold-detection level of image-analysis software or for making direct measurements of percent occurrence from digital images.
Maras (Dolichotis patagonum) dig warrens which could be a resource for other species. In order to estimate the abundance of warrens and to document their use by other vertebrates, surveys were conducted in six areas of Península Valdés and 42 warrens were surveyed with video cameras during day-time. We found an average of 0.62 warrens/km² and recorded use by five additional species. We conclude that maras provide a resource used by other species and is a case study that must be further researched within the framework of ecosystem engineering theory.
Changes in the vegetation and soil surface were assessed along a grazing intensity gradient on rangelands of the Punta Ninfas area in southern Argentina, Thirty-two transects were sampled in areas with different grazing intensity, Bray-Curtis polar ordination and simple correlation were used to display changes in community composition and measure association between different community attributes. The first axis expressed the changes in species composition along a gradient of grazing intensity, The extremes of the gradient were represented by shrub and grass steppes. Shrub steppes dominated in heavily grazed areas close to permanent water points, while grass steppes dominated in lightly grazed areas in the extremes of the paddocks, A significant negative relation (r = -0.81, p<0.05) between grass and shrub cover suggested that grasses decreased as shrub increased, Flechilla (Stipa tenuis Phil,) and flechilla negra [Piptochaetium napostaense (Speg,) Hackel ap Stuckert.] were the main decreaser grasses while quilembai (Chuquiraga avellanedne Cav.) was the main shrub invading the grass steppes, Uneroded soil surface conditions decreased, and the size and frequency of crusted and desert pavement areas and mounds increased with shrub cover, Three states or stages of range degradation were identified along the gradient of grazing intensity, Grass steppe represented the most desirable state in term of livestock production and soil stability, while shrub steppe represented the most degraded and least productive state.
The paper presents a selection of results of a study of habitat preferences of 10 ungulate species on a South African nature reserve. Habitat parameters influencing the distribution of the ungulates were evaluated by incorporating a series of multiple regression analyses and correspondence analysis. The two approaches showed some similarities among preferences of ungulates in relation to the habitat parameters examined. Use of the combination of the broad view provided by the components of the correspondence analysis and the power of discrimination of individual parameters given by the multiple regression is suggested. The combination of different analytical approaches aids in overcoming limitations within each analysis and may provide further insights into the composition of the investigated system.
The prey base for Patagonian carnivores has been altered greatly over the past 150 years due to widespread overgrazing by livestock, invasions by exotic wildlife, and hunting. On ranches in northern Patagonia carnivores consume mostly exotic species, and native herbivores are ecologically extinct in their role as prey. In this study we compare diets of the culpeo (Lycalopex culpaeus), chilla (L. griseus), puma (Puma concolor), Geoffroy's cat (Leopardus geoffroyi), colocolo (L. colocolo), and hog-nosed skunks (Conepatus chinga and C. humboldtii) in a reserve with a mostly native prey base to their diets on the ranches, and evaluate how differences in prey bases affect trophic interactions among carnivores. Carnivores in the reserve consumed mostly native prey. Dietary overlap among carnivores was not significant on the reserve, but was highly significant on the ranches. This homogenization of diets where densities of native species are reduced could lead to stronger negative interactions among carnivores, altering the composition of the carnivore assemblage to the detriment of the more specialized species. Study of carnivore diets may be a relatively quick way to evaluate the conservation status and ecological functionality of prey assemblages in Patagonia and other areas where these have been altered.
The mara Dolichotis patagonum is a cursorial rodent typical of savannas, steppes and grasslands. In the Monte of Argentina, where the typical vegetation is an open scrub with a ground layer of scarce herbs and unvegetated spaces of sandy soil, difference in mara abundance between protected and grazed areas suggest a preference for open areas. The main purpose of this paper is to assess how D. patagonum uses the habitat, especially with reference to the vegetation structure. The abundance of mara feces was considered as a measure of its spatial activity and was correlated with cover of three vegetational strata in two study sites: one in Ñacuñán Ecological Reserve and another in a contiguous grazed area. Significant correlationas were obtained with percent bare ground (positive) and percent shrub cover (negative). It is concluded that the mara preferencially selects habitats with large representation of bare ground. This results in its increased presence in grazed areas. In contrast, mara abundance is markedly lower in areas with large accumulations of shrubs and herbs. Adequate management of grazed as well as of protected areas is recommended to enhance the conservation status of this species.
Effective management of natural populations depends heavily on the capacity for understanding and predicting their habitat requirements. For endemic and threatened species like the mara (Dolichotis patagonum), this information is extremely necessary for populations survival. I investigated and constructed a mathematical habitat model for the mara, with the capacity to predict the probability of finding animals in a particular environment. In the Monte Desert, maras prefer habitats with low shrub density and high percentage of bare soil. The area used by each couple of maras was 7.73 ha and shows an aggregation pattern. Contrary to expectation, about 94% of these areas were in habitats created by human activities. Grazed, burned and crop areas seem to be prefered by maras when natural open habitat disappear. This information and the results of habitat requirements can be used to monitor the status of mara populations and predict potential population extinctions according to habitat variables.
The mara is a caviid rodent, endemic and resident in the arid region of central and south Argentina. Little is known about its ecology in the wild, but its diurnal and superterrestrial way of life rises interest concerning its temporal activity rhythms related to environmental variables, as well as behavioural strategies for the species’ adaptation to semi‐desert environments. Surveys over two or three consecutive days were made from March 1982 to March 1983 and from October 1986 to July 1988, recording the number of active animals and environmental variables. It was demonstrated that the annual activity of D. patagonum was positively influenced by light, precipitation and temperature and negatively by darkness and relative humidity. These variables probably influence the long‐term endogenous rhythms of the species. The daily activity was unimodal in winter and bimodal in the other seasons, and it was related especially with temperature. A favourable thermal environment was detected near 20° C. Daily activity of mara reduced during winter and summer with alternate periods of activity and rest, probably related to the species energetic balance. These strategies are important for the successful adaptation of the mara to Monte environment.
Maras, Dolichotis patagonum, were observed and radio-tracked in Argentina. They travelled as monogamous pairs that bred either alone at solitary burrows or communally at settlements where up to 29 pairs shared warrens.
Members of a mara settlement grazed within 2.5 km of the communal warrens, using intensively about 1 ha per day, within drifting daily ranges of 11 ha, seasonal ranges of 98 ha and annual ranges of 193 ha.
Their home ranges drifted continuously. Consequently, the long-term movements of neighbouring pairs overlapped substantially, but at any given moment they were territorially spaced.
Monogamous, drifting territoriality is explained by the patchy dispersion of food, the need to minimize interference competition, and a cycle of grazing and fallowing in the use of food plants.
Two hypotheses explaining the adaptive significance of settlements are evaluated: one relates to resource availability (through the indirect effect of ground water and sheep dung on vegetation); and the other relates to predation (through the protective influence of human dwellings). The size of sheep flocks grazing at outstations during January provide a measure of the resource richness of patches where maras graze, and the richness of these patches in the dry season appear to limit the number of maras breeding at each settlement during the following wet season.
Maras face extremes of resource dispersion between the wet and dry seasons: in the former, sparsely dispersed grazing and interference competition favour spacing out and territoriality; in the latter, clumping of resources facilitates pairs congregating in herds around outstations and dry lagoons. Superimposed upon the ecological factors favouring spacing out during the wet season are the sociological factors that cause the maras to den communally. The resulting compromise is a social system unique among mammals.
Question: Do coexisting plant life forms differ in overall phenology, leaf traits and patterns of leaf litterfall?
Location: Patagonian Monte, Chubut Province, Argentina.
Methods: We assessed phenology, traits of green and senesced leaves and the pattern of leaf litterfall in 12 species of coexisting life forms (perennial grasses, deciduous shrubs, evergreen shrubs).
Results: We did not identify differences in phenology, leaf traits and patterns of leaf litterfall among life forms but these attributes contrasted among species. Independent of the life form, the maintenance of green leaves or vegetative growth during the dry season was mostly associated with leaves with high leaf mass per area (LMA) and high concentration of secondary compounds. Low LMA species produced low litterfall mass with low concentration of secondary compounds, and high N concentration. High LMA species produced the largest mass of leaf litterfall. Accordingly, species were distributed along two main dimensions of ecological variation, the dimension secondary compounds in leaves ‐ length and timing of the vegetative growth period (SC ‐ VGP) and the dimension leaf mass per area ‐ leaf litterfall mass (LMA ‐ LLM).
Conclusions: Phenology, leaf traits and leaf litterfall varied among species and overlapped among life forms. The two dimensions of ecological variation among species (SC ‐ VGP, LMA ‐ LLM) represent distinct combinations of plant traits or strategies related to resource acquisition and drought tolerance which are reflected in the patterns of leaf litterfall.
Mara social organization involves a combination of monogamous territoriality and co-operative, communal breeding that has not otherwise been described among mammals.
Some pairs reared their young in communal warrens, and pup survival was greater in warrens with larger memberships.
Pairs visited their young once daily, and females resisted, sometimes unsuccessfully, the attempts of interloping youngsters to nurse. Stolen nursing facilitated the survival of orphans.
More adults were present at larger creches, and total vigilance was thus increased despite each pair spending less time sitting-alert and less time at the warren. The proportion of the day for which at least one pair was vigilant at the warren increased to 90% with larger creche sizes.
Pups were much more likely to emerge from the warren when adults were present, and in the absence of adults were more likely to be sitting-alert close to the entrance.
These observations are compatible with hypotheses explaining the mara's social system in terms of resource dispersion, anti-predator behaviour and thermoregulation.
The concept of the ecological trap, a low-quality habitat that animals prefer over other available habitats of higher quality, has appeared in the ecological literature irregularly for over 30 years, but the topic has received relatively little attention, and evidence for traps remains largely anecdotal. Recently, however, the ecological trap concept has been the subject of a flurry of theoretical activity that is likely to raise its profile substantially, particularly in conservation biology. Ecological trap theory suggests that, under most circumstances, the presence of a trap in a landscape will drive a local population to extinction. A number of empirical studies, almost all of birds, suggest the existence of traps and demonstrate the difficulties of recognizing them in the field. Evidence for ecological traps has primarily been found in habitats modified by human activities, either directly (e.g., through the mowing of grassland birds' nests) or indirectly (e.g., via human-mediated invasion of exotic species), but some studies suggest that traps may occur even in relatively pristine areas. Taken together, these theoretical and empirical results suggest that traps may be relatively common in rapidly changing landscapes. It is therefore important for conservation biologists to be able to identify traps and differentiate them from sinks. Commonly employed approaches for population modeling, which tend to assume a source-sink framework and do not consider habitat selection explicitly, may introduce faulty assumptions that mask the effects of ecological traps and lead to overly optimistic predictions about population persistence. Given the potentially dire consequences of ecological traps and the accumulating evidence for their existence, greater attention from the community of conservation biologists is warranted. In particular, it is important for conservation biologists and managers to incorporate into conservation planning an explicit understanding of the relationship between habitat selection and habitat quality.
Loss of species richness and reduced abundance have been the main responses to perturbations of small-and medium-sized mammals in arid and semi-arid areas. Nonetheless, some mammal species whose habitat requirements are met in disturbed patches may benefit from structural changes in the environment brought about by perturbations. In desert areas of Argentina different mammal responses are attributable to both a lower complexity of disturbed patches and a decrease in sheltered places. Therefore, species associated with high plant cover either decrease in number or become locally extinct at sites affected by fire or grazing, whereas species using open areas are favored by these events. The negative effects historically assigned to different disturbances may be mitigated by adopting a hierarchical approach that considers patch diversity in different successional stages as well as the multiple opportunities of patch occupation by mammal species.
The influence of the intensity of land use on small mammals in the ecoregion Nama Karoo, Namibia was investigated within the biodiversity programme BIOTA. Changes in species diversity and abundance were investigated across a fence separating heavily grazed communal and lightly grazed government owned rangeland. Assessing and monitoring of the small mammal populations were done seasonally from 2001-2003 on each of 2ha plots by using capture-mark-recapture methods. In total, 311 individuals representing nine species were caught within 5760 trap nights. Species richness, total abundance, species diversity and settlement was lower in the over-grazed area. The most abundant species were the Gerbillinae, Gerbillurus vallinus and Tatera leucogaster. T. leu-cogaster did not occur in the overgrazed area. Due to the loss of grass cover, smaller bush diversity, bush encroach-ment and smaller arthropod abundance in the overgrazed area, changes in the small mammal community were most likely caused by the loss of food resources, available dew, disruption of habitat structures, cover and shelter and by increased predation risk. Only the 'desert' species, G. vallinus, was favoured by the degraded land. It is also obvious that the uncontrolled grazing in the communal lands has affected the biodiversity and the regeneration potential, thus leading to land degradation.
Modes of locomotion and escape tactics are attributes that affect the structure of animal communities, promoting exploitation of different microhabitats and the coexistence of different species. Bipedal locomotion is considered to be more effective than a quadrupedal gait in escaping attacks by predators because it allows for higher speed, a faster response to attack, sudden changes of direction and better detection of aerial raptors. The aim of this study was to determine the type of locomotion used at the moment of escape by three rodent species of the Monte desert –Eligmodontia typus, Akodon molinae and Graomys griseoflavus. The study was carried out in three plant communities of the Ñacuñán Reserve (Mendoza). All three species showed differences in both mode of escape and locomotory pattern. Graomys griseoflavus exhibited the highest proportion of escapes using quadrupedal saltation. The mode of locomotion employed by E. typus varied according to the type of plant communities it inhabited. Those occurring at open sites (Medanal community) exhibited a greater propensity to jump during escapes than those from more sheltered habitats (Algarrobal community). Akodon molinae relied primarily on a quadrupedal gait when fleeing from predators, which would explain its greater dependence on plant cover. Therefore, the morphological and behavioural characteristics of these species are related to their mode of locomotion and the strategies they employ to diminish the risk of predation.
A number of studies demonstrate that plant cover provides prey animals with refuges to decrease vulnerability to predators. However, others suggest plant cover to visually obstruct detection of predators or conspecifics. We suggest these seemingly conflicting results can, to some extent, be resolved if overhead vs. lateral cover are distinguished. We recorded seasonal variation in vigilance activity of a natural population of degus (Octodon degus), a diurnal, semi-subterranean and social rodent from central Chile. We used these data to determine whether cover provided by herbaceous vegetation is mostly obstructive. The height of herbaceous vegetation in the habitat of degus varied seasonally, and the ability of degus (estimated from human observers) to detect potential predators decreased when herbaceous vegetation was high. This effect was more important for degus using quadruped postures and when dealing with terrestrial simulated predators. Accordingly, degus adjusted the quality rather than the quantity of their vigilance activity: male and female degus allocated similarly more time to bipedal vigilance when the height of herbs was high. Such increase in bipedal vigilance seemed to occur at the expense of quadruped vigilance instead of foraging time. Collectively, these results support the hypothesis that cover of herbaceous vegetation is mostly obstructive to degus when active above ground, a finding that contrasts with previous evidence supporting that shrub cover provides refuges against predators. The differential effects of shrubs and herbs on degu vigilance are likely linked to differences in the costs and benefits associated with each cover type. For degus, shrubs may provide more overhead (protective) than lateral (obstructive) cover.
In recent years, studies of bird-habitat relationships undertaken in the context of habitat fragmentation have led to the widespread use of species categorisation according to their response to edge alongside mature forest patches (edge species, interior species, interior-edge generalist species). In other research contexts, especially in less fragmented landscapes dominated by a forested land base in various age classes, bird-habitat relationships are often described in relation to their use of various successional stages (early-successional species, mature forest species, generalist species). A simple comparison of these two commonly-used classifications schemes in a close geographical range for 60 species in eastern North America as well as for 36 species in north-western Europe clearly reveals that in these two particular biomes the two classifications are not independent. We believe that this association is not only a semantic issue and has important ecological consequences. For example, almost all edge species are associated with early-successional habitats when a wide range of forest age-classes are found in a given area. Accordingly, we suggest that most species considered to prefer edge habitats in agricultural landscapes are in fact only early-successional species that could not find shrubland conditions apart from the exposed edges of mature forest fragments. To be considered a true edge species, a given species should require the simultaneous availability of more than one habitat type and consequently should be classified as a habitat generalist in its use of successional stages. However, 28 out of 30 recognised edge species were considered habitat specialists in terms of successional status. Based on these results, we conclude that “real edge species” are probably quite rare and that we should make a difference between true edge species and species which in some landscapes, happen to find their habitat requirements on edges.
Predicting the spatial distribution of wildlife populations is an important component of the development of management strategies
for their conservation. Landscape structure and composition are important determinants of where species occur and the viability
of their populations. In particular, the amount of suitable habitat and its level of fragmentation (i.e. how broken apart
it is) in a landscape can be important determinants of the distribution and abundance of biological populations(Hanski, 1998;
Fahrig, 2003). In addition to the role of habitat, anthropogenic impacts, such as wildlife mortality on roads or direct wildlife-human
conflict, can also have large impacts on the distribution and abundance of a species (Fahrig et al., 1995; Woodroffe and Ginsberg,
1998; Naves et al., 2003). Therefore, if we are to manage landscapes to successfully conserve wildlife, it is important that
we understand the role of these landscape processes in determining their distributions.
The spatial heterogeneity of populations and communities plays a central role in many ecological theories, for instance the theories of succession, adaptation, maintenance of species diversity, community stability, competition, predator-prey interactions, parasitism, epidemics and other natural catastrophes, ergoclines, and so on. This paper will review how the spatial structure of biological populations and communities can be studied. We first demonstrate that many of the basic statistical methods used in ecological studies are impaired by autocorrelated data. Most if not all environmental data fall in this category. We will look briefly at ways of performing valid statistical tests in the presence of spatial autocorrelation. Methods now available for analysing the spatial structure of biological populations are described, and illustrated by vegetation data. These include various methods to test for the presence of spatial autocorrelation in the data: univariate methods (all-directional and two-dimensional spatial correlograms, and two-dimensional spectral analysis), and the multivariate Mantel test and Mantel correlogram; other descriptive methods of spatial structure: the univariate variogram, and the multivariate methods of clustering with spatial contiguity constraint; the partial Mantel test, presented here as a way of studying causal models that include space as an explanatory variable; and finally, various methods for mapping ecological variables and producing either univariate maps (interpolation, trend surface analysis, kriging) or maps of truly multivariate data (produced by constrained clustering). A table shows the methods classified in terms of the ecological questions they allow to resolve. Reference is made to available computer programs.
Shrub encroachment due to overgrazing has led to dramatic changes of savanna landscapes and is considered to be one of the most threatening forms of rangeland degradation e.g. via habitat fragmentation. Mammalian carnivores are particularly vulnerable to local extinction in fragmented landscapes. However, our understanding of how shrub encroachment affects mammalian carnivores is poor. Here we investigated the relative sensitivities of ten native carnivores to different levels of shrub cover ranging from low (<5%) to high shrub cover (>25%) in 20 southern Kalahari rangeland sites. Relative abundance of carnivores was monitored along 40 sand transects (5 m × 250 m) for each site.Our results show that increasing shrub cover affects carnivore species differently. African wild cats, striped polecats, cape foxes and suricates were negatively affected, whereas we found hump-shaped responses for yellow mongooses, bat-eared foxes and small-spotted genets with maximum abundance at shrub covers between 10 and 18%. In contrast, black-backed jackals, slender mongooses and small spotted cats were not significantly affected by increasing shrub cover. However, a negative impact of high shrub cover above 18% was congruent for all species.We conclude that intermediate shrub cover (10–18%) in savanna landscapes sustain viable populations of small carnivores.
In this study the spatial patterns and dynamics of vegetation patches along a grazing gradient in the steppe ofLarrea divaricataandStipaspp. in NE Patagonia (Argentina) are described. A general effect of grazing is the reduction of total plant cover resulting from the decrease in cover of perennial grasses (Stipa speciosa, Poa ligularis, Stipa tenuis) and some tall shrubs (Chuquiraga hystrix, Bougainvillea spinosa, Lycium chilense). Dwarf shrubs (Nassauvia fueguianaandJunellia seriphioides) increase their cover under medium and/or high grazing pressures. Plant species are spatially grouped into patches which alternate with areas of bare soil. Eleven types of vegetation patch differing in the dominant plant functional type or species, floristic richness and size were identified with different relative frequency along the grazing gradient. Based on these results, it is postulated that grazing forces the replacement of large patches dominated by tall shrubs with high species richness, byLarrea divaricatapatches or small dwarf shrub patches with low species richness and the extinction of grass patches. This results from: (1) disruption of local balances of species deletions and additions; (2) fragmentation of large patches; and (3) formation of new vegetation patches. These changes lead to differing plant spatial organization and heterogeneity along the grazing gradient which may be described by characteristic arrays of vegetation patches.
Arid ecosystems present a two-phase mosaic structure of high- and low-cover patches. Vegetation patches differ among ecosystems in size and shape. However, recent studies indicate striking similarities in patch dynamics and in mechanisms explaining their origin and maintenance. Two major types of system, banded and spotted vegetation, which are characterized by patch shape, both originate from common mechanisms, although each is dominated by a different driver. Banded vegetation occurs when water is the dominant driver of the redistribution of materials and propagules, whereas spotted vegetation results when wind is the major redistribution driver. Model analysis indicates that patchy vegetation structure enhances primary production.
Ecologists can be overwhelmed by the number of metrics available to quantify landscape structure. Clarification of interrelationships and redundancy is needed to guide metric selection and interpretation for the purpose of landscape monitoring. In this study we identified independent components of class- and landscape-level structure in multiple landscapes in each of three large and geographically disjunct study areas. We used FRAGSTATS and principal components analysis (PCA) to identify independent components of landscape structure, and cluster analysis to group the components. We then calculated the universality, strength, and consistency of the identified landscape structure components. At the class-level we identified 24 independent configuration components. Seven of these components were nearly universal and consistent in interpreted meaning. At the landscape-level there were 17 independent structure components. Eight of these components were universal and consistent. These results indicate that there are consistent combinations of metrics that universally describe the major attributes of landscape structure at the class- and landscape-levels.
The Origin of Species. Penguin Books
- C Darwin
Darwin, C., 1859. The Origin of Species. Penguin Books, Oxford, United Kingdom.
lme4: Linear Mixed-effects Models Using S4 Classes. R package version 0
- D Bates
- M Maechler
- B Bolker
Bates, D., Maechler, M., Bolker, B., 2011. lme4: Linear Mixed-effects Models Using S4
Classes. R package version 0.999375-39. http://CRAN.R-project.org/package¼lme4.
Efectos del disturbio por pastoreo ovino sobre la comunidad de artr opodos epígeos en Península Vald es
- G H Cheli
Cheli, G.H., 2009. Efectos del disturbio por pastoreo ovino sobre la comunidad de
artr opodos epígeos en Península Vald es (Chubut, Argentina). Universidad
Nacional del Comahue, Bariloche, p. 283.
Sources of variation in a two-step monitoring protocol for species clustered in conspicuous points: Dolichotis patagonum as a case study
- Alonso Rold An
- V Bossio
- L Galv An
Alonso Rold an, V., Bossio, L., Galv an, D.E., 2015. Sources of variation in a two-step
monitoring protocol for species clustered in conspicuous points: Dolichotis
patagonum as a case study. PLoS One 10, e0128133. http://dx.doi.org/10.1371/
journal.pone.0128133.
Spatial pattern and ecological analysis. Vegetation 80, 107e138
- P Legendre
- M J Fortin
- R J C Le On
- D Bran
- M Collantes
- J M Paruelo
- A Soriano
Legendre, P., Fortin, M.J., 1989. Spatial pattern and ecological analysis. Vegetation
80, 107e138.
Le on, R.J.C., Bran, D., Collantes, M., Paruelo, J.M., Soriano, A., 1998. Grandes unidades
de vegetaci on de la Patagonia extra andina. Pp. 125-144. In: Oesterheld, M.,
Aguiar y, M.R., Paruelo, J.M. (Eds.), En: Ecosistemas Patag onicos, vol. 8. Ecologia
Austral, pp. 75e308.