Endemic to the central mountains of the Trans-Mexican Volcanic Belt, the volcano rabbit Romerolagus diazi , known locally as the zacatuche, is a threatened species at risk of extinction. In the Ajusco-Chichinautzin Mountain Range, the Pelado and Tlaloc volcanoes are core distribution areas for this species; however, suitable habitat within these areas is patchy. We analyzed the habitat of this species at the landscape level, taking into account biotic, abiotic, and anthropogenic factors. We used geographic information systems for the habitat analysis and a linear mixed-effects model to identify the habitat patches available, analyze them in the FRAGSTATS program, and calculate their landscape metrics. To identify the habitat of the volcano rabbit, we used its relative abundance index in the context of land use and vegetation, elevation, slope, road and highway density, and distance to human settlements. The analyses indicated that the relative abundance index of this species decreases with increasing proximity to human settlements and with increasing road and highway density.
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Endemic to the central mountains of the Trans-Mexican Volcanic Belt, the volcano rabbit Romerolagus diazi , known locally as the zacatuche, is a threatened species at risk of extinction. In the Ajusco-Chichinautzin Mountain Range, the Pelado and Tlaloc volcanoes are core distribution areas for this species; however, suitable habitat within these areas is patchy.
We analyzed the habitat of this species at the landscape level, taking into account biotic, abiotic, and anthropogenic factors. We used geographic information systems for the habitat analysis and a linear mixed-effects model to identify the habitat patches available, analyze them in the FRAGSTATS program, and calculate their landscape metrics. To identify the habitat of the volcano rabbit, we used its relative abundance index in the context of land use and vegetation, elevation, slope, road and highway density, and distance to human settlements.
The analyses indicated that the relative abundance index of this species decreases with increasing proximity to human settlements and with increasing road and highway density. At the landscape level, there are patches of habitat available to the species, covering Most of the patches are 2, m 2 in area and regular in shape square ; however, because they are small patches it is possible that they will disappear.
The largest patches are located on the Pelado and Tlaloc volcanoes, and coincide with the core distribution areas of the volcano rabbit described in the literature. The expansion of urban areas that accompanies the growth of the human population and the demand for space and resources is the main force driving the modification of natural landscapes Calvete et al.
Habitat transformation can destroy, degrade, and fragment landscapes, creating patches of habitat that differ in size, quality, and degree of isolation, depending on the intensity and frequency of transformation Hanski ; Hanski and Ovaskainen ; Garden et al.
The isolation of patches, which affects patch quality and the dispersal capacity of organisms, has negative effects on species richness and abundance. Patches are habitat fragments where conditions are suitable for species establishment.
They form part of the landscape and are immersed in a matrix, i. Corridors are linear habitat structures that cross the matrix and connect patches of habitat Forman ; Turner et al.
Depending on the state of the matrix, landscapes can be described from the perspective of an island biogeography model, or as a landscape mosaic. In the former, unique patches are surrounded by a homogeneous matrix, analogous to islands in an ocean MacArthur and Wilson The latter is spatially complex, with a matrix comprised of a heterogeneous assemblage of different types of patches Forman To understand the dynamics of a species in a landscape, in addition to taking vegetation cover into account, it is necessary to consider the abiotic components i.
The success with which these 3 elements are incorporated into an analysis of the landscape determines the quality of the information and tools available for the conservation of species and their habitat. Its populations are distributed in patches at elevations above 2, m a. The distribution area of the volcano rabbit is limited to approximately The Ajusco-Chichinautzin Mountain Range is located in the middle of the Trans-Mexican Volcanic Belt, and these mountains are an important part of the distribution area of R.
This area has patches of bunch grasses surrounded by pine, oak, and fir forests, and crassicaule scrub, with the latter considered the last natural barrier between the urban sprawl of Mexico City and that of the city of Cuernavaca, and therefore of great importance in the conservation of the volcano rabbit Rizo-Aguilar et al.
The presence of zacatonal appears to be a requirement for the survival of the volcano rabbit on the landscape, but there are suitable zacatonals in good condition where the volcano rabbit has not been recorded Hunter and Cresswell ; Rizo-Aguilar et al. The volcano rabbit also may respond to human activities such as habitat fragmentation and landscape modification in the mountainous landscape of the Ajusco-Chichinautzin Mountain Range.
We describe, analyze, and model the configuration of the landscape for the volcano rabbit in the Ajusco-Chichinautzin Mountain Range using the island biogeography model.
We identified the location of habitat suitable for the volcano rabbit based on its distribution and relative abundance index RAI , and taking into account biotic and abiotic factors, as well as human intervention. The study was done in the Ajusco-Chichinautzin Mountains over an area of km 2 with an upper elevation limit of 2, m a.
The landscape analysis was done in 2 stages. The first was fieldwork to estimate the distribution and RAI of the volcano rabbit, and to obtain data about the vegetation cover. To avoid errors in the results associated with the sampling method and to facilitate the classification of the satellite images, the data and analyses were grouped into 3 zones: the Tlaloc Volcano, the Pelado Volcano, and the Coajomulco forests, partially under legal protection by federal decree Fig.
Study area. The main physiographic features of the Ajusco-Chichinautzin Mountain Range are shown. Dotted lines are the limits of the federal Protected Natural Areas PNA and polygons with hatching are human settlements. In these surveys, an intensive search was carried out in the areas with bunch grasses on the Tlaloc Volcano, the Pelado Volcano, and in the Coajomulco forests, accessed via roads, trails, and paths.
To ensure independence, and following the procedure outlined by Rizo-Aguilar et al. The plots were georeferenced using a GPS device. For vegetation cover, geographic coordinates were noted when areas with continuous zacatonal were encountered. Pine, oak, and fir forests were georeferenced when continuous tree cover was encountered with no zacatonal and the understory was dominated by shrubs and herbaceous plants.
When it was possible to access crop fields, areas with livestock, and pastures, these also were georeferenced to document land use.
The crassicaule scrub was not georeferenced, as this type of cover was not encountered during the surveys.
All records for the RAI of the volcano rabbit obtained during fieldwork were used to construct a shape format layer to project the data in the ArcGIS The plots were grouped into 3 zones Tlaloc Volcano, Pelado Volcano, Coajomulco forests with the aim of grouping RAI by area and analyzing whether there were differences in the distribution and abundance patterns of this species among these zones. Landscape variables used for explaining the latrine numbers of volcano rabbit Romerolagus diazi in the Ajusco-Chichinautzin Mountain Range, Mexico, including a description of the categories of the land use and vegetation variable.
The classification method used was IsoData Classification , separating the pixels into 40 categories for the study area and then grouping them into 8 categories using points obtaining during field work as reference. To avoid assessment errors and confusing pixels for the shadow effect, the classification was carried out separately for each zone, thus avoiding classifying zacatonal pixels on the Tlaloc Volcano as the cultivated areas represented by the pixels on the Pelado Volcano.
The 3 zones were then joined to make up the Ajusco-Chichinautzin landscape. To evaluate the reliability of classification, the index Kappa was used, which indicates the level of concordance between the observed data and the classification. The index was estimated using points taken in the field, including the reference points; the errors of omission and commission were also calculated for each category Rosenfield and Fitzpatrick-Lins ; Stephens et al.
The vegetation cover layer was complemented with the polygons representing areas under cultivation, localities human populations , and roads, all areas adverse to the establishment of volcano rabbit populations. The polygons of human settlements present in the Ajusco-Chichinautzin Mountains were obtained, including those that surround the study area.
Using the human settlements, a layer was created for distance to the nearest town with a resolution of 30 m, in the Euclidean distance extension from the ArcGIS It was generated based on the roads and highways present in the Ajusco-Chichinautzin Mountains, given that this infrastructure facilitates and increases the access of people to areas with natural cover. Each roadway was assigned a value of 4 to 17 depending on its characteristics such as lane width, number of lanes, and the type of surface pavement, no pavement— INEGI , with the highest value of 17 representing the 5-lane Mexico-Cuernavaca highway, and lower values for the various types of roads and trails within the study area.
The slope of the land was estimated using the slope extension from the ArcGIS The raster was calculated using the digital elevation model, calculating the difference in elevation between pixels to estimate slope. On the Iztaccihuatl Volcano, the probability of occurrence for the volcano rabbit decreases with increasing slope Hunter and Cresswell The Extract Multi Values to Point extension was then used to extract the information from each of the layers for each plot with its relative volcano rabbit abundance.
This generates a table linked to the RAI shape file for the volcano rabbit in which each plot is associated with a zone, a type of land use and vegetation, distance to the nearest human settlement, an accessibility value, elevation, and slope. The relationship between volcano rabbit RAI and the information of the 6 layers was analyzed with a mixed-effects linear model run in RStudio v 0.
This model was chosen because it is more sensitive to the distribution of the data and also allows factors to be grouped into fixed and random effects Venables and Ripley ; Crawley ; Bolker To find the minimal best-fit model, a stepwise simplification of models was carried out, making comparisons between models that progressively included and excluded different factors Crawley The saturated model included the zones as a random factor, and the fixed factors were distance to the nearest town, accessibility index, slope, elevation, soil use, and vegetation.
The Akaike Information Coefficient was used to select the best-fit model. The results were projected in ArcGIS The values of the random factors were multiplied by their respective layers. The operations were run in the Map Algebra extension. To fine-tune the results and avoid error when defining the components of the spatial heterogeneity Li and Reynolds , the towns, roads, bare soil, cultivated areas, rosetophyllous scrub, forest, and forest with zacatonal were projected to create a homogeneous matrix of unsuitable habitat and delimit the patches of habitat suitable for the volcano rabbit.
The patches of habitat defined with the mixed linear model were used to estimate landscape composition and configuration. For composition, the total number of patches available for the species on the landscape was calculated. For configuration, patch size, distribution, and density were used, along with shape index, proximity, distance between patches, connectivity, and cohesion McGarigal The shape index of the patches makes it possible to analyze their regularity; as the value approaches 1, the patches are more square in shape, and as values approach 0, patches are more irregularly shaped McGarigal and Marks The proximity index indicates the degree of patch isolation; a value of 0 indicates the patch is isolated at a certain radius McGarigal and Marks , and the radius we used was 4, m, which is the mean dispersal distance for this species Uriostegui-Velarde Finally, the mean Euclidean distance to the nearest neighbor between patches and the landscape connectivity were calculated.
In 50 of the plots sampled there were no latrines, and only in 5 plots were there more than latrines. On average, the Tlaloc Volcano had more latrines and the plots with the greatest number of latrines On the Pelado Volcano, there were 2 plots with more than latrines, but there were 33 plots with no latrines.
In Coajomulco forest, only 1 plot had more than 50 latrines, and on average had more latrines than the Pelado Volcano and less than the Tlaloc Volcano.
Vegetation and land use classification had a Kappa index of 0. Of the entire area 55, ha , Of the plots where volcano rabbit RAI was estimated, 17 were located in zacatonal , 50 in forest with zacatonal , 40 in zacatonal with forest, 18 in forest, 17 in crops, and 2 in scrub. The plots with the most latrines were located in zacatonal and zacatonal with forest.
The layer with distance to human settlements has values ranging from 0 m to zones neighboring the towns to 8, m for the zones located furthest from human settlements. The plot with volcano rabbits present that was closest to human settlements was m from the nearest human settlement with 2 latrines recorded, and the furthest was 8, m away with 57 latrines.
The plot with the greatest number of latrines was located 7, m away from the nearest human settlements Fig. The accessibility index calculated for the Ajusco-Chichinautzin Mountains was 0 to Values close to 0 indicate the absence of roads and as the index increases, narrow unpaved roads appear, and higher values refer to the main roads with a greater number lanes, and that are generally paved.
The highest accessibility value for the plots was Forty-six plots had an accessibility value lower than 1 Fig. The highest elevation in the study area was 3, m a. All of the plots sampled for the presence of volcano rabbits were located above 2, m a.
The plot with the highest rabbit RAI was located at 3, m a. The highest plot was at 3, m a. The plot with the most latrines had a slope of 0. Relationship between the explanatory variables and RAI relative abundance index of the volcano rabbit Romerolagus diazi by zone.
The term zon is zone and LUV is land use and vegetation. The coefficient values for the random factor were 0. Results of the simplest linear mixed-effect model relating latrine numbers of volcano rabbits Romerolagus diazi and landscape variables in the Ajusco-Chichinautzin Mountain Range, Mexico, including values for the fixed and random factors and the P -values.
The range emerged during the Quaternary period , with intense volcanic activity that closed the lacustrine basin of Mexico , depriving it of its only natural drainage towards the Balsas river basin. Ajusco is part of the geological subprovince of the lakes and volcanoes of the Anahuac, located within the Trans-Mexican Volcanic Belt. The area has diverse habitats and species due to its unique geographic and climatic conditions. There are species of fungi, 10 species of amphibians, 43 species of reptiles, 1, species of insects and spiders, of birds 36 exclusive to this region , 5 species of fish, of plants, and 7 types of vegetation in addition to forests of pine, oyamel and oak. From Wikipedia, the free encyclopedia.
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