Valeria E. Campos

Endozoochory by native and exotic herbivores in dry areas: consequences for germination and survival of Prosopis seeds.

Mammalian herbivores can play a role in the endozoochorous dispersal of Prosopis seeds in the arid zones of Argentina, and the introduction of exotic mammals can change relevant parameters of the plants reproductive ecology. Our specific goals were to quantify the seeds of Prosopis flexuosa , P. chilensis and P. torquata contained in the faeces of native [mara ( Dolichotis patagonum ), guanaco ( Lama guanicoe )] and exotic [donkey ( Equus asinus ) and hare ( Lepus europaeus )] mammals, and to determine the mortality, germination percentage and germination speed of seeds borne in faeces, compared with those collected from trees. In 2006, seeds were collected directly from trees or removed from mammal faeces. Seeds were counted and classified as apparently healthy or damaged. P. torquata and P. flexuosa seeds were found in the dung of guanaco, hare and mara, whereas only P. flexuosa seeds appeared in donkey faeces. P. chilensis seeds were only found in guanaco faeces. There was a notable relative abundance of seeds contained in small herbivore faeces in comparison to the large herbivores. The passage through the digestive tract of animals modified seed germination capacity and speed, with great variability between animal species. Guanacos had greater effects than donkeys on mortality, germination percentage and germination speed. Differences between the effects of both smaller-sized herbivores on seeds were much smaller.

Octomys mimax (Rodentia: Octodontidae)

Abstract Octomys mimax O. Thomas, 1920, the viscacha rat, is a surface-dwelling rodent, endemic to the Monte biome of western Argentina. The genus Octomys is monotypic and represents a basal clade within the family Octodontidae. O. mimax is strictly herbivorous and is found in low-elevation arid environments characterized by galleries or rock formations. In these environments, O. mimax nests within rock crevices located inside ravines with relatively low vegetation cover. O. mimax is solitary and mostly nocturnal. Nocturnal activity coupled with a basal metabolic rate and thermal conductance lower than expected for body mass of O. mimax probably represent strategies for water conservation in this species.

Remote sensing variables as predictors of habitat suitability of the viscacha rat (Octomys mimax), a rock-dwelling mammal living in a desert environment

Identifying high-quality habitats across large areas is a central goal in biodiversity conservation. Remotely sensed data provide the opportunity to study different habitat characteristics (e.g., landscape topography, soil, vegetation cover, climatic factors) that are difficult to identify at high spatial and temporal resolution on the basis of field studies. Our goal was to evaluate the applicability of remotely sensed information as a potential tool for modeling habitat suitability of the viscacha rat (Octomys mimax), a rock-dwelling species that lives in a desert ecosystem. We fitted models considering raw indices (i.e., green indices, Brightness Index (BI) and temperature) and their derived texture measures on locations used by and available for the viscacha rat. The habitat preferences identified in our models are consistent with results of field studies of landscape use by the viscacha rat. Rocky habitats were well differentiated by the second-order contrast of BI, instead of BI only, making an important contribution to the global model by capturing the heterogeneity of the substratum. Furthermore, rocky habitats are able to maintain more vegetation than much of the surrounding desert; hence, their availability might be estimated using SATVI (Soil Adjusted Total Vegetation Index) and its derived texture measures: second-order contrast and entropy. This is the first study that evaluates the usefulness of remotely sensed data for predicting and mapping habitat suitability for a small-bodied rock dwelling species in a desert environment. Our results may contribute to conservation efforts focused on these habitat specialist species by using good predictors of habitat quality.

Microhabitat selection by Octomys mimax (Rodentia: Octodontidae) in the Monte Desert is affected by attributes and thermal properties of crevices

Fil: Campos, Valeria Evelin. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Fisicas y Naturales. Instituto y Museo de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Fisicas y Naturales. Departamento de Biologia; Argentina

Trophic interactions between the native guanaco (Lama guanicoe) and the exotic donkey (Equus asinus) in the hyper-arid Monte desert (Ischigualasto Park, Argentina)

Exotic herbivores have detrimental effects on the ecosystems where they are introduced, at the level of plant communities and ecosystem processes. The native guanaco Lama guanicoe and the exotic feral donkey Equus asinus coexist in Ischigualasto Provincial Park. We quantified food availability in a plant community in the park during the wet and dry seasons, analyzed diet composition of both herbivores (by microhistological analysis of feces), and assessed the relationship between diet and plant availability and the overlap between donkey and guanaco diets. In both seasons, shrub species represented the most abundant cover type in the area, whereas grasses were the lowest plant cover during the wet season and almost non-existent in the dry season. The diet of the exotic donkey showed a high intake of grasses, and the trophic niche breadth did not change along the year. The guanaco’s diet was based on the most abundant food resources (shrubs), which constituted at least 60% of the diet; it was less diverse during the dry season. The diets of donkey and guanaco showed high overlap during the dry season. We can assume, at least during the dry season, the existence of a potential competition between guanaco and donkey, which may be higher if the donkey density increases.

The effects of poaching and habitat structure on anti-predator behavioral strategies: A guanaco population in a high cold desert as case study

The effects of poaching on wildlife have been widely studied in conservation biology and can be heterogeneous, particularly on ungulates. These effects can be estimated through different methodologies whose use depends on several conditions such as Flight-initiation distance (FID). Our objectives were: 1- to evaluate whether poaching affects the FID and group structure of a guanaco (Lama guanicoe) population in a high cold desert in San Juan (Argentina); 2- to assess whether habitat structure (slope and vegetation cover) influences FID and group structure in this population. The study area included a site with poaching (unprotected area), and a site without poaching (protected area). We recorded 100 groups of guanacos: 70 in the protected and 30 in the unprotected area. FID and group size were greater in the unprotected than in the protected area, whereas proportions of group categories (with offspring, without offspring and solitary) were similar between areas. Besides, in relation to habitat structure, FID increased when vegetation cover decreased. On the other hand, FID and group size were not affected by slope. Our study shows that guanacos respond to poaching pressure as do other ungulate species, and that other factors such as vegetation cover also affect this behavior. Managers should be aware when interpreting FID due to its relation to habitat structure; the guanaco appears to assume greater risk (lower FID) in areas with high vegetation cover.

Habitat selection by the viscacha rat (Octomys mimax, Rodentia: Octodontidae) in a spatially heterogeneous landscape

Abstract The viscacha rat Octomys mimax is endemic to western Argentina; it inhabits lowland deserts and uses rocky crevices as resting sites. The aim of this study was to assess macrohabitat selection relative to the occurrence of rocky crevices and to evaluate seasonal variations in macrohabitats selected by this rodent in Ischigualasto Provincial Park, San Juan, Argentina. Random locations were classified as used or available based on signs recorded in rocky crevices. We confirmed the absence of the viscacha rat in macrohabitats with sandy or silty substrates. We provide new records of viscacha rat in creosote bush scrub, the most abundant macrohabitat of the Monte Desert. This result extends the known range of macrohabitat use for this species. The viscacha rat increased the number of rocky crevices used in the dry season, probably because the species increased its foraging area due to the low food resource abundance. Another possible reason is an increase in density due to new births and dispersal of young in this season. The present study highlights the importance of considering signs of presence for species with low capturability as well as of collecting data throughout multiple seasons for a better understanding of habitat selection and species distribution.

Richness of plants, birds and mammals under the canopy of Ramorinoa girolae, an endemic and vulnerable desert tree species

Dominant woody vegetation in arid ecosystems supports different species of plants and animals largely dependent on the existence of these habitats for their survival. The chica (Ramorinoa girolae) is a woody leguminous tree endemic to central-western Argentina and categorized as vulnerable. We evaluated 1) richness of plants, birds and mammals associated with the habitat under its canopy, 2) whether richness is related to the morphological attributes and to the features of the habitat under its canopy, and 3) behavior displayed by birds and mammals. We recorded presence/absence of plants under the canopy of 19 trees in Ischigualasto Provincial Park. Moreover, we recorded abundance of birds and mammals and signs of mammal activity using camera traps. Our camera traps captured more than 80, 90 and 50 % of plants, birds and mammals, respectively. The coverage estimate was 83 % for birds and 89 % for mammals. Bird species richness decreased by -43 %, for every unit increase in number of stems; although richness of plants and mammals was not explained by any variable considered. Birds and mammal species invested more time in foraging than they did in moving or resting under canopies. The abundance of South American gray fox (Lycalopex griseus) increased 9 % with abundance of birds, though not with abundance of mammals. This is the first study to assess the role of R. girolae in the provision of biodiversity-related ecosystem services; a relevant aspect because their conservation can enhance biodiversity in arid ecosystems.