Investigating the Role of Frugivorous Ungulates in Forest Nutrient Cycling
Barnes, Kristy Marie
Ungulates regulate important processes within their ecosystems, however their impact on nitrogen cycling remains unclear, and likely ecosystem and soil-specific. Much of the work examining the relationship has been in grasslands with forests only marginally explored. Given the different soil, plant, and ungulate compositions of these ecosystems, the interaction within forests must be considered independently. Further, previous studies primarily consider ungulates that eat nitrogen-rich plant tissue and do not consider non-grazers that primarily eat fruits and seeds. White-lipped peccaries provide a unique opportunity to explore how non-grazing ungulates impact forest nitrogen cycling. The ungulate has a large presence in Neotropical forests where they travel in large herds and constitute up to 34% of non-flying biomass. Therefore, areas of white-lipped peccary presence and absence can be used to evaluate the effect of a large non-grazing herbivore on the nitrogen cycle in neotropical forest. GPS data, supplemented by local knowledge have tracked white-lipped peccaries movement patterns in the fragmented Cerrado revealing some forest patches are inhabited while others are not used. This project quantifies and compares available soil nitrogen, total soil nitrogen, total soil carbon, and soil δ15N nitrogen values of 2mx2m plots of white-lipped peccaries use (n=6) and low/no white-lipped peccaries use (n=6). Since white-lipped peccaries do not largely alter nitrogen cycling through consumption, it is expected they accelerate the nitrogen cycle by both directly depositing available nitrogen and stimulating decomposition. Thus, in areas of white-lipped peccaries presence, we expect higher total nitrogen and available nitrogen values. We also expect patches with white-lipped peccaries will have higher δ15N values since studies have shown a correlation between a faster nitrogen cycles and higher δ15N signals. Forest patches with white-lipped peccaries only had significantly higher nitrate (p=.03). No other variable was significantly different in patches of white-lipped peccaries use, including ammonium, total nitrogen, or δ15N values. A Linear discriminate analysis using nitrate and pH was, however, able to discriminate patches of white-lipped peccaries presence and absence (21.4% error). Therefore, while in Cerrado the presence of white-lipped peccaries may not largely impact the nitrogen cycle, they may be adding nitrate to the system. The results did show a significant variation in the nitrogen amount and cycling processes between the two different region examined. A faster nitrogen cycle is evident in Bodoquena compared to Corguinho (100 km apart) with significantly higher nitrate (p=.03), total soil nitrogen (p< <<.0001), total soil carbon (p<<.0001), and δ15N values (p<<.0001). Further, within the Bodoquena region, patches with white-lipped peccaries had significantly higher soil nitrate (Mann Whitney p = 0.006), available soil nitrogen (Mann Whitney p = 0.05) and total soil nitrogen (Mann Whitney p = 0.02) concentrations. While pH may account for some of this difference (Kendall’s rank p =0.0334, τ = 0.373) a linear discrimination analysis using pH and soil nitrate was able to predict white-lipped peccary presence with 100% accuracy. Therefore, while underlying geologic differences between the two regions may account for some of the variations seen in the nitrogen it is likely the large ungulate also plays a significant role.