Paula Taraborelli

Cooperative vigilance: The guanaco's (Lama guanicoe) key antipredator mechanism

The concept of sociality has been associated with the effectiveness of antipredator mechanisms, like cooperative vigilance and the dilution effect. Lama guanicoe (guanaco) is a social native herbivore in South America and a social species. The objectives of this study were to evaluate the antipredator responses of different-sized groups of guanacos in areas with varying predation risks and to determine antipredator mechanisms in guanacos. For this, we measured different antipredator responses to a potential predator (human subjects). Detection of predator and flight distances from predator both increased with a greater number of guanacos per group and with greater distances among guanacos within the social group. Both buffer distance and flight time decreased with a greater number of guanacos per group, but increased with greater distances among guanacos inside the social group. Solitary adult males moved shorter distance and mixed groups moved greater distances. Flight distances were greater in areas with tall and dense vegetation than in areas with low vegetation. Buffer distance and flight time were shorter in undulating land than on flat lands, and groups were usually observed on hill slopes. Our results suggest that the benefit of social grouping in guanacos is the increased probability of avoiding predator with cooperative vigilance and not with the dilution effect. This means that a predator could be detected earlier when approaching a guanaco group than when approaching a solitary individuals and could thus be avoided.

Different antipredator responses by Microcavia australis (Rodentia, Hystricognate, Caviidae) under prédation risk

[The antipredator response of rodents may depend on the species of predator and the structure of the vegetation. To investigate these effects, we compared the antipredator response of Microcavia australis to two predator models. We used two populations occurring at sites of the Monte desert that differ in plant structure and availability, and in predation risk. At Nacunan plant cover is 54.3%, the major risk of predation is from raptors. At El Leoncito plant cover is 21.9%, the predation risk is similar by raptors and carnivores. In addition we investigated whether olfactory cues for different predators may elicit different antipredator responses in absence of visual cues. This was done by presenting feces of two predators and controls in an experimental set-up. The exposed individuals reduced their activity in response to feces of both predators and not in response to the control, but they did not respond in the same way to each predator (their response to each predator was not the same). The results show that M. australis recognizes different predators through both sight and smell, and that the response may be influenced by vegetation structure., The antipredator response of rodents may depend on the species of predator and the structure of the vegetation. To investigate these effects, we compared the antipredator response of Microcavia australis to two predator models. We used two populations occurring at sites of the Monte desert that differ in plant structure and availability, and in predation risk. At Nacunan plant cover is 54.3%, the major risk of predation is from raptors. At El Leoncito plant cover is 21.9%, the predation risk is similar by raptors and carnivores. In addition we investigated whether olfactory cues for different predators may elicit different antipredator responses in absence of visual cues. This was done by presenting feces of two predators and controls in an experimental set-up. The exposed individuals reduced their activity in response to feces of both predators and not in response to the control, but they did not respond in the same way to each predator (their response to each predator was not the same). The results show that M. australis recognizes different predators through both sight and smell, and that the response may be influenced by vegetation structure.]

Spatial and seasonal dynamic of abundance and distribution of guanaco and livestock: insights from using density surface and null models.

Monitoring species abundance and distribution is a prerequisite when assessing species status and population viability, a difficult task to achieve for large herbivores at ecologically meaningful scales. Co-occurrence patterns can be used to infer mechanisms of community organization (such as biotic interactions), although it has been traditionally applied to binary presence/absence data. Here, we combine density surface and null models of abundance data as a novel approach to analyze the spatial and seasonal dynamics of abundance and distribution of guanacos (Lama guanicoe) and domestic herbivores in northern Patagonia, in order to visually and analytically compare the dispersion and co-occurrence pattern of ungulates. We found a marked seasonal pattern in abundance and spatial distribution of L. guanicoe. The guanaco population reached its maximum annual size and spatial dispersion in spring-summer, decreasing up to 6.5 times in size and occupying few sites of the study area in fall-winter. These results are evidence of the seasonal migration process of guanaco populations, an increasingly rare event for terrestrial mammals worldwide. The maximum number of guanacos estimated for spring (25951) is higher than the total population size (10000) 20 years ago, probably due to both counting methodology and population growth. Livestock were mostly distributed near human settlements, as expected by the sedentary management practiced by local people. Herbivore distribution was non-random; i.e., guanaco and livestock abundances co-varied negatively in all seasons, more than expected by chance. Segregation degree of guanaco and small-livestock (goats and sheep) was comparatively stronger than that of guanaco and large-livestock, suggesting a competition mechanism between ecologically similar herbivores, although various environmental factors could also contribute to habitat segregation. The new and compelling combination of methods used here is highly useful for researchers who conduct counts of animals to simultaneously estimate population sizes, distributions, assess temporal trends and characterize multi-species spatial interactions.

Vigilance and foraging behaviour in a social desert rodent, Microcavia australis (Rodentia Caviidae)

Microcavia australis is a social species, diurnal and native to South America. This rodent provides an opportunity for analyzing the relationship between group size and the vigilance and foraging behaviour of the lesser cavy in two populations inhabiting two risky sites (El Leoncito and Ñacuñán). The study should reveal the mechanisms used by M. australis to reduce predation risk (many-eyes effect, cooperative vigilance or/and simple dilution of per capita risk). Continuous focal sampling was conducted at times of food shortage, food abundance and reproduction, from 2003–2005. A negative correlation was found between number of individuals per group and frequency of individual vigilance, and a positive correlation between rate and proportion of total group vigilance and the number of individuals per group of both sites. There was no correlation between the number of individuals per group and group foraging at either site. A benefit of social grouping in cavies is an increased probability of survival with group vigilance, although this implies no favourable impact on foraging activity. This should reveal an effect of group in the antipredator response, i.e. groups of larger size show lower levels of individual vigilance and improved efficiency in their vigilance behaviour. That is to say that a predator would be detected earlier when approaching a group than when approaching a solitary individual and could thus be avoided (many-eyes effect and cooperative vigilance).

New eco-morphological-behavioural approach of the chinchilla rats in the pre-Andean foothills of the Monte Desert (Argentina)

This study characterizes the ecology, behaviour and morphology of populations of Abrocoma schistacea and A. uspallata in north-western Argentina. We carried out live-trapping, tagging and recapture during 2006–2008. Burrow structure and vegetation were described. Diet composition and the activity of chinchilla rats were defined. Both species inhabit rock crevices in the pre-Andean foothills of the Monte Desert. Some of their morphological specializations for saxicolous life, such as foot pads for better traction on rocky surfaces and reduced nails, are convergent with those of other saxicolous species. Both species appear to be diurnal, with activity peaking in the early morning. Dietary analyses suggest trophic specialization by both species. Density of A. schistacea was of 0.15 ± 0.06 individuals ha−1; with individuals living in groups of 3–4 animals. Given their low abundance, restricted distribution and high level of habitat and food specialization, we urge that populations of this species be protected through effective management.

Influence of predation risk and plant structure on vigilance and intermittent locomotion in Microcavia australis (Rodentia, Caviidae)

The aim of this study was to analyze and compare vigilance behavior and intermittent locomotion at two sites (El Leoncito and Ñacuñán, Argentina) that differ in predation risk, plant structure, and plant resource availability. Subjects were lesser cavies (Microcavia australis), a social species that is semi-fossorial, diurnal, and native to South America. Continuous focal sampling was conducted during the day, at times of food shortage, food abundance, and reproduction from 2003 to 2005. The proportion of time spent vigilance was significantly higher at Ñacuñán, where vigilance peaked at midday and reached a minimum in the evening. This midday peak of vigilance at Ñacuñán was associated with a midday peak of danger from raptors as indicated by a raptor activity peak at that time. In contrast, both vigilance and predator activity at El Leoncito were constant through the day. Records of intermittent locomotion and number and duration of pauses in locomotion were significantly higher at El Leoncito, a difference that may have been due to the need for greater vigilance while moving across areas of less protective cover at this site.

Effects of live-shearing on population parameters and movement in sedentary and migratory populations of guanacos Lama guanicoe

Live-shearing of wild guanacos Lama guanicoe may affect their reproductive success and population resilience, and therefore it is important to assess the biological sustainability of obtaining their wool. We evaluated effects of capture and shearing on survival and reproduction, population parameters, daily movements, ranging behaviour and spatial distribution in sedentary and migratory populations. We assessed population variables by radio-telemetry and line-transect surveys before and after capture. We estimated high post-shearing survival rates in both populations and similar yearling production in shorn and non-shorn females in the migratory population. We did not find significant variations in density and population structure before and after shearing in the sedentary population, whereas in the migratory population density decreased and the population structure changed significantly after assembly of the capture structure, returning to pre-assembly levels 1 month later. The mean daily distance moved by radio-collared guanacos during the first 2 days after shearing was three times longer than during the following 30 days. There was a 25% decrease in the mean home-range size of shorn guanacos between the first and second month after shearing but this decline appeared to be associated with a seasonal change in movement, because a similar reduction occurred during the same period the following year, when the guanacos were not shorn. Live-shearing modified the spatial distribution pattern in the sedentary population but did not have a significant effect on the migratory population. Management of guanacos may contribute towards developing a biologically sustainable economic activity that promotes conservation of wildlife and habitats.