Habitat partitioning among sympatric tinamous in semiarid woodlands of central Argentina.

Sympatric, phylogenetically related and morphologically similar species that overlap in their distributions at a regional scale display different patterns of co-occurrence at local assemblages. Occurrence of each species at local scales might be the result of interspecific competition for limiting resources. However, these patterns could also arise from species-specific habitat preferences along the abiotic or land use gradients. To assess the role of these mechanisms, we investigated niche partitioning among sympatric tinamou species occurring in semiarid woodlands of central Argentina. We used occupancy models incorporating habitat characteristics and interspecific interactions, while accounting for detectability, to examine the spatial overlap among elegant crested tinamous (Eudromia elegans), brushland tinamous (Nothoprocta cinerascens), and nothura tinamous (Nothura darwinii and N. maculosa) across a wide regional scale. In addition, we investigated time partitioning among these species by estimating the degree of overlap in their daily activity patterns. The regional distribution of the three species was influenced by the gradient in plant productivity and vegetation structure, in agreement with their broad habitat requirements. We also found that the occurrence of each species was presumably affected by the presence of one or two predator species. Models including interactions among tinamou species found weak negative and positive interactions among species pairs, suggesting that co-occurrence patterns were mainly driven by species-specific habitat use rather than interspecific competition. The three species were diurnal, showing two main peaks of activity, and overlapped widely in their overall diel activity, although subordinate species tended to shift their activity patterns to reduce encounters with the dominant tinamou species, suggesting some segregation in this niche dimension. Projected changes in rainfall seasonality and warmer conditions in this region could benefit elegant crested tinamous over the other two species, although climate and land use changes will likely have a negative impact on all tinamou species

Guanaco abundance and monitoring in Southern Patagonia: distance sampling reveals substantially greater numbers than previously reported

Background: Guanacos (Lama guanicoe) are thought to have declined in Patagonia mainly as a result of hunting and sheep ranching. Currently accepted estimates of total population size are extrapolated from densities obtained through strip transects in local studies. We used road surveys (8,141 km) and distance sampling to estimate guanaco density and population size over major environmental gradients of Santa Cruz, a large region in southern Patagonia. We also calculated the survey effort required to detect population trends in Santa Cruz. Results: We found considerable spatial variation in density (1.1 to 7.4 ind/km2), with a mean value of 4.8 ind/km2, which is more than twice the mean value guessed for central and northern Patagonia. Consequently, guanaco numbers in Santa Cruz were estimated at 1.1 million individuals (95% CI 0.7 to 1.6), which almost doubles current estimates of guanaco population size in South America. High guanaco abundance was found in arid lands, overgrazed and unable to support profitable sheep stocks. Detecting a 50% change in guanaco population size over a 10-year period requires substantial monitoring effort: the annual survey of between 40 and 80 30-km transects, which becomes up to 120 transects if trends are to be detected over 5 years. Conclusions: Regional patterns in guanaco density can only be detected through large-scale surveys. Coupling these surveys with distance sampling techniques produce robust estimates of density and its variation. Figures so obtained improve currently available estimates of guanaco population size across its geographic range, which seem to be extrapolated from strip counts over small areas. In arid lands degraded by sheep overgrazing, sustainable use of guanaco populations would help harmonize guanaco conservation, socio-economic progress of rural areas, and eventually the restoration of shrub-steppesPeer reviewe

Kernel density estimation on circular data from camera-trapping records of activity patterns of three tinamou species in areas of high and low occupancy (site use) of the potentially dominant tinamou species in caldén woodlands of central Argentina.

Grey shading indicates the overlap in species activity and is reported as the coefficient of overlap (Δ1) with 95% confidence intervals between brackets. Sample sizes in parentheses indicate the number of detections for each species. Vertical black dashed lines represent average sunrise and sunset at the study area.</p

Top single-species occupancy models (ΔAIC ≤ 2) used to evaluate the effects of climate, habitat, anthropic and biotic variables on the probability of occupancy (<i>Ψ</i>) and detection (<i>p</i>) of three sympatric tinamous in the caldén woodland region in central Argentina.

Variables with greater effect (i.e., 95% confidence intervals do not include zero) are marked in bold. Positive (+) and negative (-) signs denote direction of explanatory variables. Variable names refer to temperature seasonality (Tseas), precipitation seasonality (ppseas), enhanced vegetation index (EVI), closed caldén woodlands (closed woodland), open caldén woodlands (open woodland), shrublands (shrubland), and encounter rates of cattle (cattle), Geoffroy’s cat (gcat) and pampas cat (pcat). Covariates influencing the probability of detection correspond to the best model fitted for each tinamou species (see S2 Table); p(general1): p(+autumn-winter, -closed woodland, -shrubland, -human activity, +trail, -trapping effort); p(general2): p(-autumn-winter, +closed woodland, +shrubland, +trail, +trapping effort); p(general3): p(-date, -date2, -open woodland, -human activity, +trapping effort).</p

Seasonal daily activity patterns of three tinamou species based on kernel density estimation on circular data from camera-trapping records in caldén woodlands of central Argentina.

Sample sizes indicate the number of detections for each species. Vertical black dashed lines represent average sunrise and sunset at the study area. Grey boxes show the repetition of activity from one day to the next. Rugs indicate occurrences of photos for each species. (PDF)</p

Map of the study area in the caldén woodland region represented by green in the upper inset, within the political boundaries of La Pampa province, Argentina, and the 45 (10 × 10 km) grid square locations selected in current caldén woodlands marked with black dots.

The central inset shows an example of the sixteen camera traps installed at regular intervals in a 4 × 4 array within the grid. Background map: political boundaries and rivers were downloaded from data provided by Instituto Geográfico Nacional de la República Argentina (https://www.ign.gob.ar/NuestrasActividades/InformacionGeoespacial/CapasSIG), and the caldén woodland region was obtained from Ministerio de Medioambiente y Desarrollo Sostenible de la República Argentina (https://www.argentina.gob.ar/ambiente/bosques/primer-inventario-nacional-bosques-nativos). Land cover data was downloaded from data provided by the University of Maryland (https://glad.earthengine.app/view/global-land-cover-land-use-v1) under CCBY 4.0 International License.</p

Mean, standard deviation, and range values for the climatic, habitat (proportions), anthropogenic (encounter rates), and biotic (encounter rates) continuous variables estimated at every camera trap station (<i>n</i> = 706) in the caldén woodland region of central Argentina.

Mean, standard deviation, and range values for the climatic, habitat (proportions), anthropogenic (encounter rates), and biotic (encounter rates) continuous variables estimated at every camera trap station (n = 706) in the caldén woodland region of central Argentina.</p

Capture histories and time recordings for the three tinamou species, and climatic, habitat, anthropogenic, and biotic variables estimated at every camera trap station (<i>n</i> = 706) in the caldén woodland region of central Argentina.

Capture histories and time recordings for the three tinamou species, and climatic, habitat, anthropogenic, and biotic variables estimated at every camera trap station (n = 706) in the caldén woodland region of central Argentina.</p

Kernel density estimation on circular data from camera-trapping records of activity patterns of three tinamou species in caldén woodlands of central Argentina.

Grey shading indicates the overlap in species activity and is reported as the coefficient of overlap (Δ4) with 95% confidence intervals between brackets. Sample sizes in parentheses indicate the number of detections for each species. Vertical black dashed lines represent average sunrise and sunset at the study area. (PDF)</p

Top single-species detection models (ΔAIC ≤ 2) used to evaluate the effects of temporal, habitat, anthropic and survey covariates on the probability of detection (<i>p</i>), while holding occupancy as constant (<i>Ψ</i>(.)), for elegant crested tinamous (<i>Eudromia elegans</i>), brushland tinamous (<i>Nothoprocta cinerascens</i>), and nothura tinamous (<i>Nothura</i> spp.) in caldén woodlands in central Argentina.

Variables with greater effect (i.e., 95% confidence intervals do not include zero) are marked in bold. Positive (+) and negative (-) signs denote direction of explanatory variables. Variable names refer to autumn-winter season (autumn-winter), Julian date (date), closed caldén woodlands (closed woodland), open caldén woodlands (open woodland), shrublands (shrubland), encounter rates of humans (human activity), camera stations installed in trails (trail), and camera trapping effort (trapping effort). (PDF)</p