Recurrent bridgehead effects accelerate global alien ant spread.

Biological invasions are a major threat to biological diversity, agriculture, and human health. To predict and prevent new invasions, it is crucial to develop a better understanding of the drivers of the invasion process. The analysis of 4,533 border interception events revealed that at least 51 different alien ant species were intercepted at US ports over a period of 70 years (1914-1984), and 45 alien species were intercepted entering New Zealand over a period of 68 years (1955-2013). Most of the interceptions did not originate from species' native ranges but instead came from invaded areas. In the United States, 75.7% of the interceptions came from a country where the intercepted ant species had been previously introduced. In New Zealand, this value was even higher, at 87.8%. There was an overrepresentation of interceptions from nearby locations (Latin America for species intercepted in the United States and Oceania for species intercepted in New Zealand). The probability of a species' successful establishment in both the United States and New Zealand was positively related to the number of interceptions of the species in these countries. Moreover, species that have spread to more continents are also more likely to be intercepted and to make secondary introductions. This creates a positive feedback loop between the introduction and establishment stages of the invasion process, in which initial establishments promote secondary introductions. Overall, these results reveal that secondary introductions act as a critical driver of increasing global rates of invasions

Analysis of a spatial Lotka-Volterra model with a finite range predator-prey interaction

We perform an analysis of a recent spatial version of the classical Lotka-Volterra model, where a finite scale controls individuals' interaction. We study the behavior of the predator-prey dynamics in physical spaces higher than one, showing how spatial patterns can emerge for some values of the interaction range and of the diffusion parameter.Comment: 7 pages, 7 figure

Can forest management based on natural disturbances maintain ecological resilience?

Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance

Comparing methods for measuring the rate of spread of invading populations

Measuring rates of spread during biological invasions is important for predicting where and when invading organisms will spread in the future as well as for quantifying the influence of environmental conditions on invasion speed. While several methods have been proposed in the literature to measure spread rates, a comprehensive comparison of their accuracy when applied to empirical data would be problematic because true rates of spread are never known. This study compares the performances of several spread rate measurement methods using a set of simulated invasions with known theoretical spread rates over a hypothetical region where a set of sampling points are distributed. We vary the density and distribution (aggregative, random, and regular) of the sampling points as well as the shape of the invaded area and then compare how different spread rate measurement methods accommodate these varying conditions. We find that the method of regressing distance to the point of origin of the invasion as a function of time of first detection provides the most reliable method over adverse conditions (low sampling density, aggregated distribution of sampling points, irregular invaded area). The boundary displacement method appears to be a useful complementary method when sampling density is sufficiently high, as it provides an instantaneous measure of spread rate, and does not require long time series of data. © 2010 The Authors.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

Canopy herbivore community structure: Large-scale geographical variation and relation to forest composition

1. Geographical distributions of individual foliage-feeding forest herbivore species have been found to be aligned closely with the distribution of their host trees, however little is known about the extent to which broad herbivore communities are geographically associated with distinct host communities. 2. Large-scale geographic variation in canopy herbivore communities in a 80 000 km2 area (the state of Maine, U.S.A.) was characterised using historical insect survey data. Variation in insect communities was compared with corresponding variation in forest over-storey composition, which was quantified using data from a regional forest inventory survey. 3. Principal components analysis was used to characterise associations among herbivore and tree species. Analysis of the herbivore data identified three main insect groups: group A corresponded to a single species (Choristoneura fumiferana), group B corresponded to pine-feeding species including Semiothisa sp. and group C corresponded to the spruce-feeding species Gilpinia hercyniae and Pikonema alaskensis. Analysis of the forest inventory data characterised three important forest types: northern hardwoods, eastern white pine, and northern spruce-fir forest types. 4. Spatial analyses were carried out on the first two components of each of the principal components analyses. Factor 1 of the insect data showed a trend of decreasing values from south to north, while factor 2 of the forest inventory data showed an opposite trend. These inverse trends reflected the distribution of the main contributing species to the principal components analysis, C. fumiferana and Pinus strobus respectively. These distributions were highlighted further by the significant negative cross-correlations that were found between the two factors up to distances of 120 km. 5. Analyses indicated a parallel between the geographic variation in the insect guilds associated with conifers and the geographic pattern of their conifer hosts. Hardwood-feeding caterpillars, on the other hand, did not form well-defined guilds and showed varying geographical distributions. The survey data showed varying quality in defining large-scale associations in the structures of herbivore and host communities. 6. Implications for biodiversity management are discussed.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe