Summary of the number of groups and total individuals for <i>L. guanicoe</i> and domestic ungulates in the 9 surveys.

a<p>After removing 5% of extreme distance values in raw data (see text for details).</p><p>References: lg: guanaco; h: horses; c: cattle; gt: goats; s: sheep.</p

Spatial and Seasonal Dynamic of Abundance and Distribution of Guanaco and Livestock: Insights from Using Density Surface and Null Models

<div><p>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 (<i>Lama guanicoe</i>) 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 <i>L. guanicoe</i>. 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.</p></div

Spatial density distribution maps for <i>L guanicoe</i> and large-livestock in summer surveys.

<p>Maps for the 1220² prediction area were constructed according to the corresponding best-fit DSMs.</p

Seasonal abundance for <i>Lama guanicoe</i> and large-livestock during the 9 surveys.

<p>The bars correspond to standard deviation.</p

Study area in the northern part of La Payunia Reserve and surrounding area.

<p>It is located in Mendoza province, central-west Argentina.</p

Spatial density distribution maps for <i>L guanicoe</i> and large-livestock in fall surveys.

<p>Maps for the 1220² prediction area were constructed according to the corresponding best-fit DSMs.</p

Density surface models (DSM) selected for herbivores in all surveys.

<p>Percentage of explained deviance are given.</p

Estimated abundances for <i>L. guanicoe</i> (g), large-livestock (la), and small-livestock (sm), according to the best-fit DSMs.

<p>Coefficient of variation (CV), a 95% confidence interval and average density in the prediction area are given. Annual average of abundance and density for <i>L. guanicoe</i> and large-livestock is indicated at the bottom of the table.</p

Observed covariance in abundance (<i>U</i>) of <i>Lama guanicoe</i> compared to large-livestock (g.la) and small-livestock (g.sm) for all surveys and seasons.

<p>Upper (CI.up) and lower (CI.low) 95% confidence limits using the IT null model algorithm (replicates  =  5000), mean expected <i>U</i> value (<i>Ū</i>) and the standardized effect size (SES  =  (U–Ū)/sd<i>_Ū</i> ) are given.</p

Spatial density distribution maps for <i>L guanicoe</i> and large-livestock in winter surveys.

<p>Maps for the 1220² prediction area were constructed according to the corresponding best-fit DSMs.</p