Dynamics of the Leaf-Litter Arthropod Fauna Following Fire in a Neotropical Woodland Savanna

Fire is an important agent of disturbance in tropical savannas, but relatively few studies have analyzed how soil-and-litter dwelling arthropods respond to fire disturbance despite the critical role these organisms play in nutrient cycling and other biogeochemical processes. Following the incursion of a fire into a woodland savanna ecological reserve in Central Brazil, we monitored the dynamics of litter-arthropod populations for nearly two years in one burned and one unburned area of the reserve. We also performed a reciprocal transplant experiment to determine the effects of fire and litter type on the dynamics of litter colonization by arthropods. Overall arthropod abundance, the abundance of individual taxa, the richness of taxonomic groups, and the species richness of individual taxa (Formiciade) were lower in the burned site. However, both the ordinal-level composition of the litter arthropod fauna and the species-level composition of the litter ant fauna were not dramatically different in the burned and unburned sites. There is evidence that seasonality of rainfall interacts with fire, as differences in arthropod abundance and diversity were more pronounced in the dry than in the wet season. For many taxa the differences in abundance between burned and unburned sites were maintained even when controlling for litter availability and quality. In contrast, differences in abundance for Collembola, Formicidae, and Thysanoptera were only detected in the unmanipulated samples, which had a lower amount of litter in the burned than in the unburned site throughout most of our study period. Together these results suggest that arthropod density declines in fire-disturbed areas as a result of direct mortality, diminished resources (i.e., reduced litter cover) and less favorable microclimate (i.e., increased litter desiccation due to reduction in tree cover). Although these effects were transitory, there is evidence that the increasingly prevalent fire return interval of only 1–2 years may jeopardize the long-term conservation of litter arthropod communities

Predictability of plant resource allocation: New theory needed?

Predictability is examined in plant responsiveness to stress, along with extents of resource trade-offs in growth/defence allocation, value of conflicting findings for theory development, and eventually, need for new theoretical concepts on the book’s subject. “Opportunities” are summarized plants possess in regulating resource allocation beyond apparent trade-offs and their associated “opportunity costs”, mediating to empirical and theoretical means for enhancing predictability. Acknowledging high functional and structural plasticity, and hence complexity, in plant responsiveness as a key feature of evolutionary success, both empirical capacities of molecular research are summarized in strengthening predictability across spatio-temporal scales and modelling as interacting theoretical concepts. Novel numerical and statistical modelling approaches are comprehended in reconciling conflicting empirical evidence and assessing degrees of universality. Not being unifying renders the “growth–differentiation-balance theory” falsifiable towards mechanistic consolidation as the grounds of advanced theory building. Mechanistic comprehension of plasticity becomes the key to plant system understanding