Publications by authors named "Pamela Graff"
Human activities alter biomass, nutrient availability, and species dominance in grasslands, impacting their richness, composition, and biomass production. Stability (invariability in time or space) can inform the predictability of plant communities in response to human activities. However, this measure has been simplistically analyzed for temporal (interannual) changes in live biomass, disregarding their spatial stability and the temporal stability of other plant community attributes.
View Article and Find Full Text PDFEcological models predict that the effects of mammalian herbivore exclusion on plant diversity depend on resource availability and plant exposure to ungulate grazing over evolutionary time. Using an experiment replicated in 57 grasslands on six continents, with contrasting evolutionary history of grazing, we tested how resources (mean annual precipitation and soil nutrients) determine herbivore exclusion effects on plant diversity, richness and evenness. Here we show that at sites with a long history of ungulate grazing, herbivore exclusion reduced plant diversity by reducing both richness and evenness and the responses of richness and diversity to herbivore exclusion decreased with mean annual precipitation.
View Article and Find Full Text PDFThe genus Paracles Walker, 1855 is one of the most diverse genera present in Arctiinae and some species have larvae with aquatic habits. Several larvae were found swimming in flooded areas in different grasslands and were bred to adults to identify the species: Paracles vulpina (Hbner, [1825]). The current knowledge of immature stages of this species is not useful to identify and discriminate from other species of Paracles.
View Article and Find Full Text PDFArticle Synopsis
- Dioecious plants are particularly vulnerable to environmental stresses, especially female plants, which can impact their population viability; positive interactions with other plants may help mitigate these effects.
- A field experiment with the dioecious grass Poa ligularis revealed that the presence of certain shrubs can significantly benefit female plants more than males regarding survival and reproduction.
- The study showed that female plants tend to be located closer to beneficial deep-rooted shrubs, while negative competition from shallow-rooted shrubs adversely affects their growth, highlighting the importance of plant interactions in harsh environments.
Article Synopsis
- The stress-gradient hypothesis suggests that species interactions depend on the stress factors and species strategies, but this idea is under-explored in real-world scenarios.
- The study involved a field experiment in the Patagonian steppe to examine how two dominant plant groups (shrubs and grasses) interact under different stress conditions like drought and water availability.
- Results indicated that positive interactions occurred under non-resource stress and when species strategies differed, while water-driven stress negatively impacted growth, emphasizing the role of stress-tolerant species in maintaining competitive ones in high-stress environments.
Article Synopsis
- Isolating the effects of species interactions, such as competition and facilitation, is crucial for understanding community dynamics in harsh environments.
- The study hypothesized that grazing pressure affects the balance between positive and negative interactions among palatable and unpalatable plant species by enhancing the protective benefits of unpalatable neighbors.
- Results showed that, under grazing conditions, unpalatable plants (like Stipa speciosa) facilitated the growth of palatable grasses (Poa ligularis and Bromus pictus) by reducing herbivory, contradicting prior beliefs that competition would dominate in these environments.