In the face of expanding farming and silviculture within the Uruguayan Savannah, it is crucial to comprehend how different species respond to these landscape alterations. Our extensive camera trap survey, covering various environments in two South American countries, provides unprecedented insights.
Occupancy dynamics: contrasting responses of Molina’s hog-nosed skunk and South American coati
The Molina’s hog-nosed skunk was detected in nearly twice as many sites as the South American coati, suggesting that it is much more common in the Uruguayan Savannah (Queirolo 2016). Despite the coati's association with forests, the sampling areas are located at the limit of its distribution, potentially leading to lower density and population numbers in these areas. While our study did not reveal significant differences in the effects of silviculture on both species' occupancy, a notable observation from the maps indicates a correlation between lower occupancy areas for both species and regions undergoing silviculture, particularly in Uruguay.
Our findings highlight a positive influence of forest cover on coati occupancy, contradicting a prior study with a distinct analytical approach (Lima et al. 2021). However, our results align with earlier research linking the coati to forested environments (Gompper and Decker 1998; Mena and Yagui 2019). In the predominantly grassland Uruguayan Savannah, especially in the less forested eastern portion where our sampling was focused, forested areas seem to play a more restrictive role compared to a primarily forest-dominated environment like the Atlantic Forest. Coati occupancy demonstrated a negative correlation with the percentage of grassland, a novel result indicating the species' preference for forested habitats. Molina’s hog-nosed skunk occupancy exhibited a positive correlation with the percentage of grassland, aligning with traditional knowledge about the species (Macdonald et al. 2018). The negative impact of forests on their occupancy may be due to the species favoring grasslands, potentially for defensive reasons against predators that climb trees. Additionally, the Molina’s hog-nosed skunk showed a positive correlation with the percentage of farming, echoing previous studies in the Uruguayan Savannah, and highlighting its adaptability to human-altered environments, even suburban areas (de Oliveira et al. 2013). These results are curious, considering the general reduction of mammal abundance in grasslands with expanding croplands (Lima et al. 2018). Molina’s hog-nosed skunk's prevalence in roadkill incidents in the Brazilian Uruguayan Savannah adds another layer to its complex relationship with human activities (Peters et al. 2011; Corrêa et al. 2017), especially given the association of grassland maintenance with cattle grazing and controlled fires (Andrade et al., 2024). Although our study did not explore prey availability, Molina’s hog-nosed skunk is known to prefer locations with higher potential prey abundance, as was shown in the Argentinian pampas (Castillo et al. 2012), besides the prominent muzzle, this species has claws and well-developed forelimbs to excavate the soil in search of fossorial small invertebrates (Donadio et al. 2001). In Rio Grande do Sul state, the Molina’s hog-nosed is omnivorous with a predominance of insects, among the insects in its diet, the order Coleoptera is the most common and abundant throughout all year (Peters et al. 2011). Peters et al (2011) also mention that many of the Coleoptera are considered agricultural pests, and have their abundance related to drought and expansion of cultivated areas which may explain its use of crop farms in the Uruguayan Savannah. There is no data if in Uruguayan Savannah the Molina’s hog-nosed skunk selects its habit in function of prey availability or other soil characteristics but is something worth investigating.
These occupancy patterns align with changes in landscape cover, with coatis predominantly appearing in more pristine sites, and Molina’s hog-nosed skunk demonstrating adaptability to grassland environments and resilience to potential landscape degradation.
The activity pattern does not differ from other areas (Donadio et al. 2001; Bianchi et al. 2016) the coati is mostly diurnal, and Molina’s hog-nosed skunks are nocturnal. We did not have enough data to make a more in-depth analysis regarding the activity. In other regions, both species displayed the capacity to alter their activity because of the anthropogenic influence (Galvez et al. 2021; Castillo and Lucherini 2022; Dutra et al. 2023)
Predicting occupancy in unsurveyed areas
The predicted coati occupancy was higher in the northeast portion of our study area (Fig. 3), specifically in the Serra do Sudeste. This region, overlapping with a forested area of the Uruguayan Savannah, is also where most of the previous detections of coatis were known (Trigo et al. 2013). The Serra do Sudeste stands out as part of the Uruguayan Savannah harboring more natural forests due to high humidity and temperature, while the eastern portion predominantly features riparian forests surrounded by grasslands (Bergamin et al. 2024). Brazil has stringent legislation protecting riparian forests, designating these areas as protected zones, while Uruguay's regulations are more context-dependent (Sparovek et al. 2011; Zarza et al. 2022). Despite the Uruguayan Savannah having a smaller proportion of forest areas, coatis show increased occupancy probabilities within these specific forested regions. The coati's ability to use secondary forests and to potentially travel long distances, coupled with its diet, suggests it may play a role in seed dispersion and the preservation of these forests, warranting further dietary studies within the Uruguayan Savannah ecoregion (Alves-Costa and Eterovick 2007).
While Molina's hog-nosed skunk does not exhibit high occupancy values compared to the South American coati, it shows more uniform values, capable of occupying most analyzed areas of the Uruguayan Savannah. Indeed, a recent study lists the Uruguayan Savannah as highly suitable for this species (Castillo and Caruso 2024). Temperature, a factor not considered in our ecoregion-scale analysis, may play a crucial role in modeling the skunk's distribution, deeming its inclusion in future studies necessary, especially considering climate change effects (Castillo et al. 2015; Castillo and Caruso 2024). The coati's predicted occupancy is higher in the eastern portion, where more forests are present, while the skunk's predicted occupancy is higher in the western portion. The IUCN reports a decreasing population trend for the skunk, though our previous studies question this idea, especially in Brazil (Kasper et al. 2013). Molina's hog-nosed skunk is frequently encountered by the local populations in the Uruguayan Savannah, often finding a place in traditional songs, making it a potential focal point for educational initiatives. Despite being a common species, it receives insufficient attention from science and conservation, highlighting the need for more research due to its probable interactions with a wide range of plants and animals (Gaston and Fuller 2007, 2008).
Special attention is drawn to silviculture, where the correlation, though not significant, appears in most top occupancy models. Indeed, maps for both species show low occupancy in areas corresponding to tree monocultures. This warrants careful follow-up, especially given the potential expansion of these plantations. In Uruguay, the forest sector has grown above the national average in recent years; also, in Rio Grande do Sul, there was a notable 30% increase in the silviculture area in the 2000s (Bencke 2009; Olmos and Pienika 2022).
Mesocarnivore conservation within the Uruguayan Savannah’s changing landscape
When examining the historical land cover, a distinct pattern emerges: the coati exclusively appeared in locations consistently marked as natural within the data frame, whereas the Molina's hog-nosed skunk displayed a more diverse transition history (Table 4). The skunk was prevalent in grassland sites that retained their natural state, but intriguingly, it also occupied areas where grasslands had been converted to crop farming. Additionally, Molina's hog-nosed skunk was found in forest sites that remained as such, suggesting a greater ability compared to the coati to cross a potentially unsuitable matrix to reach these areas. These findings underscore the exceptional adaptability of Molina's hog-nosed skunks, particularly when juxtaposed with the coati, a species already acknowledged for its resilience in the face of anthropogenic changes. The Uruguayan Savannah is considered at least vulnerable, but some authors mention that it may be more threatened, as highlighted by Dinerstein et al. (1995) and Loyola et al.(2009), which emerges as a critical focus in our study. Our research underscores the significance of riparian forests and hillside forests, protected by law in Brazil, in supporting species like the South American coati. Despite being perceived as rare in the ecoregion, our findings reveal the coati's as still resisting in the Uruguayan Savannah, but only in preserved sites.
Overall, in alignment with prior research, Molina's hog-nosed skunks exhibit a preference for open grassland areas, yet our study showcases their adaptability to altered environments. In contrast, there are endemic carnivorans within this ecoregion face a heightened risk of extinction due to the diminishing natural grasslands, as indicated by Tirelli et al. (2021). In fact, a disclaimer must be made about a concern that arose from our data. Our initial intention was to focus on four species of the Musteloidea superfamily (Macdonald et al. 2018), the two species evaluated in this study, the South American coati and Molina’s Hog-nosed skunk, but also the lesser grison (Galicts cuja) and the crab-eating raccoon (Procyon cancrivorus). Our initial expectation was to retrieve reasonable numbers to at least analyze Molina’s hog-nosed skunk and the crab-eating raccoon. But contrary to our expectations we lacked the number of records to conduct spatial and temporal analyses on the crab-eating raccoon. This may potentially be attributed to random effects; however, such an explanation seems unlikely. One of our designated study areas aligns with the location examined by one of the authors in a previous study (Tirelli et al. 2019). Despite differences in sampling efforts, this raises concerns, particularly given that our study encompassed diverse locations. It is conceivable that, in recent years, the crab-eating raccoon population has become more responsive to anthropogenic changes within the Uruguayan Savannah. This inference is supported by the species' heightened sensitivity to such alterations in the Atlantic Forest, as compared to the South American coati (Dutra et al. 2023). Another possibility is the spread of diseases like rabies and others, the crab-eating raccoon is known to carry antibodies for those but is not well know the effect of these diseases on this species (Cheida 2012). Rabies and canine distemper are diseases that play a role in controlling the populations of the northern raccoon (Procyon lotor) (Zeveloff 2002). This highlights the urgency of conducting studies on similar diseases in the crab-eating raccoon. In the near future, we aim to focus specifically on the ecology of the crab-eating raccoon, and there is an urge for other researchers to explore this subject further, underscoring the need for continued investigations involving this species and other fauna in the Uruguayan Savannah.