Small-scale spatial pattern and dynamics of experimental plant communities

Plant-plant interference is inherently local and seed dispersal generally limited. Both processes generate spatial and genetic structure within plant populations and communities that need to be better understood in order to predict dynamic community changes due for example to biodiversity loss or global change. There is increasingly strong theoretical evidence that spatial pattern is an essential factor controlling the species dynamics of many communities. In particular, one conclusion from spatial models is that intraspecific aggregation promotes coexistence by slowing down competitive exclusion. Whereas local interactions contribute to interspecific segregation, limited seed dispersal leads to aggregation at two hierarchical levels: i) species within communities and ii) genetically related individuals (e.g. siblings) within populations. However, especially for plant communities there is a need for experimental tests of the predictions generated from spatial models. The principal goal of this thesis was to narrow the gap between theoretical and empirical investigations on the role of spatial pattern in plant communities and population dynamics. I focused on the effects of spatial pattern on the dynamics of experimental plant communities at the level of species as well as at the level of genotypes within species. In particular, I (i) manipulated the spatial pattern, i.e. the relative frequency of intra- vs. interspecific contacts and (ii) contrasted the performance of genetically related (half-sibs) vs. non-related individuals. The basic goal of the experiments was to investigate whether different spatial patterns (random vs. aggregated) and relatedness of neighbors had any effects on population dynamics within experimental plant communities. The experiments provided interesting results and showed essential aspects of the role of intraspecific aggregation and sibling interference in regulating the dynamics of populations within experimental plant communities. I showed that weak competitors increased their fitness (e.g. biomass and seed production) when grown in neighborhoods of conspecifics compared to neighborhoods of heterospecifics, at least in the short run. The data further suggested that the advantages of intraspecific aggregation for weaker competitors might be independent of the species identity and that all other species are best avoided. An additional aggregation at the level of genotypes (e.g. seed families) suggested speciesspecific effects linked with seed size. For instance, I found negative sibling competition effects for the small-seeded species (Capsella), while rather positive effects for the largeseeded species (Stachys). Negative effects of sibling competition were also observed among relatives of sunflower seed families. By contrast, genetically similar individuals of the dimorphic species Senecio jacobaea increased their fitness (e.g. biomass) compared to genetically dissimilar individuals. However, also this species suggested seed traits specific relatedness effects (e.g. dispersal ability). Positive relatedness effects were more evident by seeds expected to aggregate more locally (without pappus) than by seeds expected to disperse wider (with pappus). Generally, I observed lower size variation (measured as coefficients of variation) among related compared to non-related individuals. This might be a consequence of more genetic uniformity and / or kin selection among relatives compared to non-relatives. Although, I could not provide strong evidence for sibling competition or kin selection, I believe that relatedness among plants, especially for species with highly localized dispersal, should play a considerable role in the regulation of local population dynamics. Similar to the species level, there must be subtle trade-offs (e.g. between neighbour relatedness and density) that determine the complicated local dynamics of plant communities. However, the question under which circumstances and to which extent relatedness effects are species-specific remains open and deserves further investigation. At the level of species, effects of intraspecific aggregation on the dynamics of experimental plant communities were clear and consistent throughout my experiments. By contrast, at the level of genotypes, they were less clear and to some extent contrasting. This emphasized the importance for further investigations on population dynamics at levels below that of species. From an applied point of view, findings of this thesis might help to give better information for management practices (e.g. restoring species rich communities). For example, by varying spatial pattern (random vs. intraspecifically aggregated) of selected species in wildflowers strips or fallows, the dominance of undesired species (e.g. Dipsacus sp.) and the exclusion of weaker species can be delayed

US APR vs EU APR, and the Substitute Tax on Loan Effects on These Formulas

This paper explores the theory, goals, outcomes and difficulties of consumer finance disclosure process, focusing mainly in the Substitute Tax (especially the Italian one) effects on EU APR vs US APR formula and the compound mechanism intrinsic subsistent in a constant mortgage for additional research and study, and a general technical analysis about IRR and EU/US APR relations. In particular, this study demonstrates that the supposed equivalence of IRR formula with APR formula is definitively incorrect under many aspects and empiric chases, while the most used constant mortgage has a typical anatocism deriving from compound interest-quota in each installment

Spatial patterns and species performances in experimental plant communities

Amongst the various hypotheses that challenged to explain the coexistence of species with similar life histories, theoretical, and empirical studies suggest that spatial processes may slow down competitive exclusion and hence promote coexistence even in the absence of evident trade-offs and frequent disturbances. We investigated the effects of spatial pattern and density on the relative importance of intra- and interspecific competition in a field experiment. We hypothesized that weak competitors increased biomass and seed production within neighborhoods of conspecifics, while stronger competitors would show increased biomass and seed production within neighborhoods of heterospecifics. Seeds of four annual plant species (Capsella bursa-pastoris, Stachys annua, Stellaria media, Poa annua) were sown in two spatial patterns (aggregated vs. random) and at two densities (low vs. high) in three different species combinations (monocultures, three and four species mixtures). There was a hierarchy in biomass production among the four species and C. bursa-pastoris and S. media were among the weak competitors. Capsella and Stellaria showed increased biomass production and had more individuals in the aggregated compared to the random pattern, especially when both superior competitors (S. annua, P. annua) were present. For P. annua we observed considerable differences among species combinations and unexpected pattern effects. Our findings support the hypothesis that weak competitors increase their fitness when grown in the neighborhood of conspecifics, and suggested that for the weakest competitors the species identity is not important and all other species are best avoided through intraspecific aggregation. In addition, our data suggest that the importance of spatial pattern for the other competitors might not only depend on the position within the hierarchy but also on the identity of neighbor species, species characteristics, below ground interactions, and other nonspatial factor

Effects of spatial pattern and relatedness in an experimental plant community

Many plant species show limited dispersal resulting in spatial and genetic substructures within populations. Consequently, neighbours are often related between each other, resulting in sibling competition. Using seed families of the annuals Capsella bursa-pastoris and Stachys annua we investigated effects of spatial pattern (i.e. random versus aggregated) on total and individual performance at the level of species and seed families under field conditions. At the level of species, we expected that inferior competitors increase, while superior competitors decrease their performance within neighbourhoods of conspecifics. Thus, we expected a species by spatial pattern interaction. Sibling competition, however, might reduce the performance of competitors, when genetically related, rather than non-related individuals are competing. Therefore, aggregations at the level of seed families could decrease the performance of competitors. Alternatively, if the opposite outcome would be observed, kin selection might be hypothesized to have occurred in the past. Because heavy seeds are expected to disperse less than light seeds, we further hypothesized that kin selection might be more likely to occur in superior competitors with heavy, locally dispersed seeds (e.g. Stachys) compared to inferior competitors with light, more distantly dispersed seeds (e.g. Capsella). We found a significant species by spatial pattern interaction. Indeed, the inferior competitor, Capsella, showed increased reproductive biomass production in aggregated compared to random patterns. Whereas, the performance of the superior competitor, Stachys, was to some extent decreased by intraspecific aggregation. Although statistically not significant, effects of intrafamily aggregations tended to be rather negative in Capsella but positive in Stachys. Our results confirmed that spatial patterns affect growth and reproduction of plant species promoting coexistence in plant communities. Although, we could not provide strong evidence for sibling competition or kin selection, our results suggested that competition among relatives was more severe for Capsella (lighter seeds) compared to Stachys (heavier seeds