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Home Documents Animal Biodiversity and Conservation issue Post on Apr views. Montserrat FerrerFotomecnica i impressi: Anaximperator, libllula emperador, liblula emperador, Emperor dragonfly Jordi Domnech. Animal Biodiversity and Conservation, The Isthmus of Tehuantepec in Oaxaca, Mexico, is one of the countrys most important regions from a zoogeographical perspec-tive due to the large number of endemic Neotropical species found there.

Animal Biodiversity and Conservation issue 37.1 (2014)

The highest species richness and alpha diversity were recorded in the preserved area, whereas the disturbed area exhibited half the diversity found in the preserved area. A high interchange of species was also observed between zones. In both areas, the highest relative abundance occurred during the rainy season. Habitat degradation and human activities seem to affect the diversity of mammal species in the region.

ResumenLa diversidad de los mamferos de talla grande y mediana en Juchitn, istmo de Tehuantepec, Oaxaca, Mxico. El istmo de Tehuantepec en Oaxaca, Mxico, humsna una de las regiones ms importantes del pas desde el punto de vista zoogeogrfico, ya que alberga evolocacin gran cantidad de especies endmicas neotropicales. Entre septiembre de y agosto dese realiz un muestreo de mamferos de talla mediana y grande en el municipio de Juchitn, y comparamos su diversidad en dos zonas con distintos niveles de impacto ecoloccin definido de acuerdo con las estimaciones de las actividades eccolocacin, la densidad de ganado y la degradacin del hbitat.

La mayor riqueza de especies y de diversidad alfa se registraron en la zona conser-vada, mientras que la zona perturbada presenta la mitad de la diversidad encontrada en la zona conservada. Se observ un fuerte intercambio de especies entre ambas zonas. En ambas zonas, la mayor abundancia relativa se observ durante la poca de lluvias. La degradacin del hbitat y las actividades humanas al parecer afectan a la diversidad de especies de mamferos en la regin.

Politcnico Nacional, Oaxaca, Mxico. November, with an average annual rainfall of The annual average temperature is The first sampling area was located on the hill of Tolistoque, northeast of Juchitan 16 35′ 5. The vegetation is tropical deciduous forest. The second sampling area was south of the Protected Communal Area northeast of Juchitan 16 32′ This area is dedicated to farming activities, with gallery forest areas around irrigation canals, and tropical deci-duous forest remnants fig.

We applied an indirect sampling method. Such methods are sometimes the only option available to study the distribution and abundance of inaccessible vertebrates such as mediumsized and large mammals Sutherland, These methods also have some advantages over direct methods as they are easier to implement and independent of the time of day, which is important when target species are nocturnal, cryptic and difficult to capture or recapture because their traces remain for long periods of time Bilenca et al.

In order to measure the contribution of different agents, we re-corded 14 metrics at each site by means of two 50 m long transects at each site table 1. Disturbance was measured on a scale ofwhere zero is the least disturbance. The values were calculated as follows: To search for traces of medium and large mammals, monthly samples were taken from September to August During each period, four transects two in each zone of 4. We used a Mexican mammal field guide Aranda, to identify tracks and feces, and compared these with the reference material on traces of ma-mmals of Oaxaca, of the Collection of Mammalogy OAX.

Ten camera traps Cuddeback Expert were also used for the last six sampling periods to confirm the presence of the species five in each zone. These were placed at approximately 1. IntroductionOne of the issues of greatest interest in ecology is the relationship between habitat structure and the struc-ture of animal communities.


Habitat disturbance and habitat fragmentation influence both the original plant communities and the heterogeneity and complexity of the entire ecosystem. This, in turn, influences the availability of resources, and affects the birth and dea-th rates of several species, thus affecting vertebrate diversity August, ; Soule et al.

The functional significance of these species lies in their ecological roles, such as seed dispersal and predation on numerous plant species. These functional roles may change the structure and composition of the ecosystem.

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Moreover, these species influence the community structure and complexity on the trophic levels in which they are ecolocxcin, due to their regulatory role as preys and predators Roemer humanz al. The loss of these organisms could have devastating effects because they contribute in many ways to the functioning of the natural ecosystem Alon-so et al. Given the importance of these species, studies identifying and predicting the environmental changes that may affect their diversity are essential, and in such studies, relative abundance and species diversity are usually used as indicators Carrillo et al.

Fur-thermore, this ecoolocacin has a particular importance from a zoogeographical perspective because it lies in the zone where the Nearctic and Neotropical regions ecklocacin. This important corridor between the Atlantic and costal Pacific plains represents a significant barrier for highland mammal species, and also favors a high de-gree of endemicity Peterson et al.

However, this diversity may be declining dramatically, due to hunting and habitat modification derived from crops and lives-tock. Therefore, the aim of this study was to identify the differences in diversity, in terms of abundance and heterogeneity, of mediumsized and large mammals in two areas with differing degrees of anthropogenic disturbance.

If anthropogenic environmental changes affect mammal communities, we hypothesized that the area with greater human disturbance would exhibit a lower diversity of medium and large mammals. MethodsThe study area is located in the coastal plain of Te-huantepec, northeast of the city of Juchitan, Oaxaca, Mexico, at m a.

The climate is subhumid and warm. There is a marked dry season from December to May, and a rainy season from June to Animal Biodiversity and Conservation The camera circuit was pro-grammed to remain active for 24 hours, and the camera locations were georeferenced with a GPS Garmin Etrex. Cameras were checked monthly.

Photographic records were prepared according to Botello et al. Data analysisSpecies inventories were evaluated using Clenchs asymptotic models of species accumulation with the program Species Accumulation, for which the data were previously randomized times with the EstimateS program, version 8.

The relative species abundance index for each area and season dry and rainy was calculated as the total number of signs found per species, divided by the distance sampled Carrillo et al. A MannWhitney U test was applied to determine whether there were significant differences in relative abundance between areas and seasons Zar, Ecollocacin species diversity of each area and season was determined according to the ShannonWiener entropy index H.

Dominance D was estimated with the BergerParker index Whittaker,which is an humanna method to measure species diversity: The lower the dominance, the higher the species diversity, and vice versa. Pielous eveness index J was determined as the proportion of diversity observed in relation to the maximum diversity expected Magurran, To compare the Shannon index between areas, we applied the Students t test modified by Hutchenson Magurran, Geographic location and vegetation types around the study area in the Isthmus of Tehuantepec, Oaxaca, Mexico.

Ubicacin geogrfica y tipos de vegetacin en el entorno de la zona de estudio en el istmo de Tehuantepec, Oaxaca, Mxico. Humaan of the disturbance index of livestock density variables, human activities variables and land degradation variables. Valores del ndice de perturbacin de las variables relativas a la densidad de ganado, las actividades humanas y la degradacin del suelo.


Variable Acronym DescriptionLivestock density Goat droppings frequency Goat Computed from presence of goat dung in ten randomly chosen 1 m squares along the transect; frequency was defined as the fraction of squares with positive records. Cattle droppings frequency Catt Bovine and equine dung, computed as ecolocaci Goat. Browsing Brow All shrubs and trees that were rooted within the transect were thoroughly examined ecolcacin signs of browsing.

The ratio of browsed to total plants was calculated as an index of browsing intensity. Livestock trail density Ltra Livestock uses welldefined trails to move while browsing. The number of these per meter along the transect was recorded. Soil compaction Comp The constant trampling of livestock along tracks causes soil compaction, which affects water infiltration.

A cylinder of This procedure was repeated on a spot with no evidence of trampling. The degree humna soil compaction was calculated as the ratio of the time recorded on the trail and in the untrampled terrain. Human activities Fuelwood extraction Fuel Peasants cut branches for fuel. This metric was measured as Brow, but taking machete cuts into account. Human trails density Ecplocacin It was measured as Ltra, but recording trails used by people to travel.

Settlement proximity Prox Proximity was defined as the multiplicative inverse of the distance to the closest towns in km. Contiguity to activity cores Core A core was defined as a place where human activities normally take place, such hmuana houses, cornfields, mines and chapels.

Contiguity was recorded at each transect if a core was less than m away. The fraction of transects contiguous to a core was used as a metric. Land use Luse In several studies the percent of land cover devoted to agriculture, humqna or induced pastures, or urban areas is used as a measure of disturbance. Here, the fraction of the study area used for these purposes was visually estimated.

Evidence of fires Fire Most of these are initiated by people, either to clear an area, promote pasture growth for livestock, or accidentally. The presence or absence of evidence at a study site was recorded as one or zero. Animal Biodiversity and Conservation We used the exponential ShannonWiener index, in which all the species in the community are weighted in exact proportion to their abundance Jost, ; Moreno et al. ResultsThe least disturbed area was located on the Tolis-toque hill, hereafter called the ‘preserved area’.

The area located southeast of La Venta ecoolocacin named the ‘disturbed area’, and it showed greater disturbance due to its proximity to centers of activity, changes in land use, and islands table 2. Clenchs species accumulation model was the best choice for the data, although asymptote was not reached in the study area. Of all the records, 79 The records belonged to 18 species, 18 genera, 12 families and six orders of medium and large mammals table 4.

Through the use of camera traps, 82 photographs of mammals were obtained, confirming the presence humanna ten of the species recorded by indirect methods.

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In terms of relative abundance, Urocyon cinereoar-genteus was the species with the highest abundance in the preserved area 0. In both areas, the highest relative abundance of species was observed in the rainy season. The highest diversity was recorded during the rainy season in the preserved area Land degradation Erosion Eros Overgrazing and human activities increase erosion.

Ecooocacin only considered spots where the soil showed tracks of strong and frequent removal of material by water such as ravines as unequivocal evidence of erosion.

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