An assessment of the potential for pollination facilitation of a rare plant by common plants: Symphyotrichum sericeum (Asteraceae) as a case study

Pollination facilitation can occur when plant species share pollinators. Whether facilitation occurs depends on the flowering period overlap (synchrony), number of shared insect visitors (similarity), quantity and quality of insect visits, and the subsequent impact on seed production. Western Silvery Aster (Symphyotrichum sericeum (Vent.) G.L. Nesom) is a rare, self-incompatible plant visited by a wide range of generalist insect species. There are 22 common plant species that may facilitate insect visitation to the rare plant by supporting shared pollinators. Plant species with low synchrony and high similarity with S. sericeum are potential facilitators. In contrast, plant species with high synchrony and similarity likely act as competitors as the aggregative response to increasing plant density was saturating, suggesting that synchronously flowering species do not increase insect visitations. Hymenoptera responded more strongly than Diptera to increases in flowering stem density. These data suggest that facilitation of insect visitation between plant species via a numerical response that extends the flower season is possible but not likely via an aggregative response. Restoration of S. sericeum may therefore be more successful if potentially facilitating plants are grown with it; further testing of the impact of potential facilitators on seed production in S. sericeum is required.

Separating spatial search and efficiency rates as components of predation risk

Predation risk is an important driver of ecosystems, and local spatial variation in risk can have population-level consequences by affecting multiple components of the predation process. I use resource selection and proportional hazard time-to-event modelling to assess the spatial drivers of two key components of risk—the search rate (i.e. aggregative response) and predation efficiency rate (i.e. functional response)—imposed by wolves ( Canis lupus ) in a multi-prey system. In my study area, both components of risk increased according to topographic variation, but anthropogenic features affected only the search rate. Predicted models of the cumulative hazard, or risk of a kill, underlying wolf search paths validated well with broad-scale variation in kill rates, suggesting that spatial hazard models provide a means of scaling up from local heterogeneity in predation risk to population-level dynamics in predator–prey systems. Additionally, I estimated an integrated model of relative spatial predation risk as the product of the search and efficiency rates, combining the distinct contributions of spatial heterogeneity to each component of risk.

An aggregative response of the tropical Australian magpie goose (Anseranas semipalmata) to seasonal floodplains

We describe the spatial aggregation of the magpie goose (Anseranas semipalmata) in relation to the dynamics of the ephemeral floodplains of northern Australia. Past broad-scale studies have linked geese to floodplains dominated by the sedge, Eleocharis dulcis, but the type of response has not been determined, nor the impact of predation on food plants. Moreover, departure thresholds are not known. We develop hypotheses on aggregation and departure and confront these with field data. Thus, from 2005–2007 we established two sites on the floodplains of Kakadu National Park (three 1-ha plots per site, six plots in total) and used for monthly, dry season bird counts. An airboat was used to collect data from each of the six plots, including sedge tubers and measures of water level and soil viscosity. Further, we built exclosures (three per site, six in total) to test the impact of herbivory on E. dulcis. Generalized linear models and information theory were used to test the strength of supporting evidence for alternate hypotheses. Geese showed a clear aggregative response to E. dulcis tubers, were forced to depart following floodplain drying and had a marked impact on E. dulcis tuber density. Despite this, there was no evidence of a negative-feedback mechanism between plant–herbivore populations, suggesting that the system is driven by extrinsic parameters (here rainfall).

Study on Improved Ant Colony Algorithm in Dynamic Multi-Paths Route Guidance System

The traditional Dynamic Route Guidance System (DRGS) provides only the optimal path to the travelers, which may easily lead to aggregative response of the travelers and overcrowding drift. This paper presents an approach based on Ant Colony Optimization (ACO) for solving the k-shortest paths problem in DRGS. In order to improve the convergence rate, the basic ACO is improved by introducing direction function the weight coefficient of which can be adjusted to vary state transition rule and standardized transformation to eliminate the influence of the size and dimension of pheromone and heuristic information. Compared with basic ACO, simulation experiments indicate that the improved ACO is more effective and efficient.