COS 25-1 - Ecology of semi-aquatic jaguars in the Brazilian Pantanal and responses to uncharacteristic wildfires

Abstract: The exchange of energy between terrestrial and aquatic ecosystems can strongly influence food webs and population dynamics, yet long-term studies of these effects are rare, especially in the context of climate change. Our objective was to study the effects of aquatic resource subsidies on a terrestrial apex predator population and the surrounding vertebrate community in a seasonally flooded protected area of the Brazilian Pantanal. Since 2014 we have monitored a population of jaguars (Panthera onca) using a combination of methods including camera traps, GPS collars, and diet studies. Using frequency of occurrence we found the diet of these jaguars (n = 138 scats) was dominated by fish (46%) and aquatic reptiles (55%), representing the first population known to feed extensively on fish and to minimally consume mammals (11%). Further, these heavy aquatic subsidies allowed for the highest jaguar population density estimate to date (12.4 jaguars/100 km²) derived from camera traps (8,065 trap nights) and GPS collars (n = 13). Contrary to their mostly solitary behavior elsewhere, we documented rare social interactions including same-sex adults fishing, co-traveling, and playing together. We document the effects of catastrophic wildfires in 2020 that burned over 4.5 million hectares of the Pantanal wetland, approximately 33% of the entire biome and including half of our study area. We used a before–after-control–impact (BACI) design to evaluate how jaguars and their prey respond to wildfire both at a population and individual level using camera traps and targeted searches. Preliminary results suggest that jaguars maintained their predominantly aquatic diet but that space use was altered post-fire. Our long-term monitoring further revealed that terrestrial mammal diversity has increased over time possibly linked to regional climatic drying trends. Finally, we conclude by summarizing the effects of aquatic subsidies and speculating on future trends in Pantanal for jaguar populations given climate change. Our study contributes to jaguar conservation efforts by demonstrating the importance of Pantanal to jaguars, the resilience of jaguars to wildfire, and how uncharacteristic wildfire events may shape trophic interactions at the interface of aquatic and terrestrial ecosystems.