Evaluation of two interaction techniques for visualization of dynamic graphs

Several techniques for visualization of dynamic graphs are based on different spatial arrangements of a temporal sequence of node-link diagrams. Many studies in the literature have investigated the importance of maintaining the user's mental map across this temporal sequence, but usually each layout is considered as a static graph drawing and the effect of user interaction is disregarded. We conducted a task-based controlled experiment to assess the effectiveness of two basic interaction techniques: the adjustment of the layout stability and the highlighting of adjacent nodes and edges. We found that generally both interaction techniques increase accuracy, sometimes at the cost of longer completion times, and that the highlighting outclasses the stability adjustment for many tasks except the most complex ones.Comment: Appears in the Proceedings of the 24th International Symposium on Graph Drawing and Network Visualization (GD 2016

Plant hybrid zones affect biodiversity: tools for a genetic-based understanding of community structure

Plant hybrid zones are dynamic centers of ecological and evolutionary processes for plants and their associated communities. Studies in the wild and in gardens with synthetic crosses showed that hybrid eucalypts supported the greatest species richness and abundances of insect and fungal taxa. In an updated review of 152 case studies of taxa associated with diverse hybridizing systems, there were 43 (28%) cases of hybrids being more susceptible than their parent species, 7 (5%) resistant, 35 (23%) additive, 35 (23%) dominant, and 32 (21%) showed no response to hybridization. Thus, most taxa respond to hybrids in ways that result in equal or greater abundance, and hybrids tend to accumulate the taxa of their parent species. These studies suggest that genetic-based plant traits affect the distribution of many species and that the variation in hybrids can be used as tools to examine the genetic components of community structure and biodiversity. Several patterns have emerged thus far. (1) Genetic variation between classes of hybrids (e.g., F1's vs. backcrosses) may equal or even exceed that found between species. (2) As a reflection of this genetic variation, herbivores are more likely to differentiate between hybrid classes than they are to differentiate between pure plant species. (3) The communities associated with different hybrid classes can differ from one another as well as from their parental species. (4) Generalist and specialist herbivores predictably vary in their responses to hybrids. (5) Plant hybrid zones may represent essential habitat for some arthropod species. (6) Even nesting birds respond to hybridizing plants. (7) Including multiple trophic levels and taxa from microbes to vertebrates, susceptible hybrid genotypes support greater biodiversity than resistant genotypes. (8) The effects of hybridization on common or keystone species can either positively or negatively affect biodiversity. The indirect impacts of hybridization on biodiversity may exceed the direct impacts and may result in 'apparent' herbivore resistance or susceptibility at the community level. (9) Although hybrids are often maligned, exotic or problem hybrids generally result from human disturbances, whereas native hybrids are part of natural ecosystems and should be conserved. Three predictions are made: (1) Intermediate genetic differences between the parental species will result in the greatest genetic variation in the hybrid zone, which in turn will have a positive effect on biodiversity. (2) Bidirectional introgression enhances species richness on hybrids, whereas F1 sterility and unidirectional introgression limit the accumulation of species on hybrids. (3) Although susceptible hybrids are likely to support the greatest biodiversity, the impacts of hybridization on keystone species will be crucial in determining the overall effect

Plant hybrid zones affect biodiversity: tools for a genetic-based understanding of community structure

Plant hybrid zones are dynamic centers of ecological and evolutionary processes for plants and their associated communities. Studies in the wild and in gardens with synthetic crosses showed that hybrid eucalypts supported the greatest species richness and abundances of insect and fungal taxa. In an updated review of 152 case studies of taxa associated with diverse hybridizing systems, there were 43 (28%) cases of hybrids being more susceptible than their parent species, 7 (5%) resistant, 35 (23%) additive, 35 (23%) dominant, and 32 (21%) showed no response to hybridization. Thus, most taxa respond to hybrids in ways that result in equal or greater abundance, and hybrids tend to accumulate the taxa of their parent species. These studies suggest that genetic-based plant traits affect the distribution of many species and that the variation in hybrids can be used as tools to examine the genetic components of community structure and biodiversity. Several patterns have emerged thus far. (1) Genetic variation between classes of hybrids (e.g., F1's vs. backcrosses) may equal or even exceed that found between species. (2) As a reflection of this genetic variation, herbivores are more likely to differentiate between hybrid classes than they are to differentiate between pure plant species. (3) The communities associated with different hybrid classes can differ from one another as well as from their parental species. (4) Generalist and specialist herbivores predictably vary in their responses to hybrids. (5) Plant hybrid zones may represent essential habitat for some arthropod species. (6) Even nesting birds respond to hybridizing plants. (7) Including multiple trophic levels and taxa from microbes to vertebrates, susceptible hybrid genotypes support greater biodiversity than resistant genotypes. (8) The effects of hybridization on common or keystone species can either positively or negatively affect biodiversity. The indirect impacts of hybridization on biodiversity may exceed the direct impacts and may result in apparent‚ÄövÑvp herbivore resistance or susceptibility at the community level. (9) Although hybrids are often maligned, exotic or problem hybrids generally result from human disturbances, whereas native hybrids are part of natural ecosystems and should be conserved. Three predictions are made: (1) Intermediate genetic differences between the parental species will result in the greatest genetic variation in the hybrid zone, which in turn will have a positive effect on biodiversity. (2) Bidirectional introgression enhances species richness on hybrids, whereas F1 sterility and unidirectional introgression limit the accumulation of species on hybrids. (3) Although susceptible hybrids are likely to support the greatest biodiversity, the impacts of hybridization on keystone species will be crucial in determining the overall effect

A genetic similarity rule determines arthropod community structure

We define a genetic similarity rule that predicts how genetic variation in a dominant plant affects the structure of an arthropod community. This rule applies to hybridizing cottonwood species where plant genetic variation determines plant-animal interactions and structures a dependent community of leaf-modifying arthropods. Because the associated arthropod community is expected to respond to important plant traits, we also tested whether plant chemical composition is one potential intermediate link between plant genes and arthropod community composition. Two lines of evidence support our genetic similarity rule. First, in a common garden experiment we found that trees with similar genetic compositions had similar chemical compositions and similar arthropod compositions. Second, in a wild population, we found a similar relationship between genetic similarity in cottonwoods and the dependent arthropod community. Field data demonstrate that the relationship between genes and arthropods was also significant when the hybrids were analysed alone, i.e. the pattern is not dependent upon the inclusion of both parental species. Because plant-animal interactions and natural hybridization are common to diverse plant taxa, we suggest that a genetic similarity rule is potentially applicable, and may be extended, to other systems and ecological processes. For example, plants with similar genetic compositions may exhibit similar litter decomposition rates. A corollary to this genetic similarity rule predicts that in systems with low plant genetic variability, the environment will be a stronger factor structuring the dependent community. Our findings argue that the genetic composition of a dominant plant can structure higher order ecological processes, thus placing community and ecosystem ecology within a genetic and evolutionary framework. A genetic similarity rule also has important conservation implications because the loss of genetic diversity in one species, especially dominant or keystone species that define many communities, may cascade to negatively affect the rest of the dependent community. © 2006 Blackwell Publishing Ltd