Individual dispersal,landscape connectivity and ecological networks

Connectivity is classically considered an emergent property of landscapes encapsulating individuals' flows across space. However, its operational use requires a precise understanding of why and how organisms disperse. Such movements, and hence landscape connectivity, will obviously vary according to both organism properties and landscape features. We review whether landscape connectivity estimates could gain in both precision and generality by incorporating three fundamental outcomes of dispersal theory. Firstly, dispersal is a multi‐causal process; its restriction to an ‘escape reaction’ to environmental unsuitability is an oversimplification, as dispersing individuals can leave excellent quality habitat patches or stay in poor‐quality habitats according to the relative costs and benefits of dispersal and philopatry. Secondly, species, populations and individuals do not always react similarly to those cues that trigger dispersal, which sometimes results in contrasting dispersal strategies. Finally, dispersal is a major component of fitness and is thus under strong selective pressures, which could generate rapid adaptations of dispersal strategies. Such evolutionary responses will entail spatiotemporal variation in landscape connectivity. We thus strongly recommend the use of genetic tools to: (i) assess gene flow intensity and direction among populations in a given landscape; and (ii) accurately estimate landscape features impacting gene flow, and hence landscape connectivity. Such approaches will provide the basic data for planning corridors or stepping stones aiming at (re)connecting local populations of a given species in a given landscape. This strategy is clearly species‐ and landscape‐specific. But we suggest that the ecological network in a given landscape could be designed by stacking up such linkages designed for several species living in different ecosystems. This procedure relies on the use of umbrella species that are representative of other species living in the same ecosystem.     

Investigating the origin of transoceanic distributions: Mtdna shows Mabuya lizards (Reptilia,Scincidae) crossed the Atlantic twice

Phylogenies with even a rough time scale can be used to investigate the history of non‐volant taxa with disjunct distributions in widely separated land areas that were once connected. Basic methods for doing this are discussed. A partial phylogeny of Mabuya based on mtDNA (305 bp cytochrome b, 379 bp 12S rRNA and 388 bp 16S rRNA) is used to show that this genus invaded tropical America from Africa twice in the last 9 Myr, once reaching the American mainland and once the oceanic island of Fernando de Noronha, two journeys each of at least 3000 km. In general, phylogenetic evidence for multiple invasions is less equivocal than that suggesting a single invasion, which is more prone to sampling artefacts. Two alternative hypotheses explaining the presence of Mabuya in both Africa and tropical America are refuted on the basis of molecular clock considerations, namely that the occurrence of Mabuya in these continents pre‐dated their separation over 100 My ago and that it was introduced from one continent to the other by human activities. Like several other lizard groups that have made successful long‐distance transmarine colonizations, Mabuya has done this on many occasions. Phylogenetic results are also compatible with a SE Asian or Australasian origin of Mabuya followed by westward expansion.     

Monitoring and modeling the invasion of the fast spreading alien Senecio inaequidens DC. in an alpine region

We modeled the distribution of the South African alien Senecio inaequidens DC. in the Aosta Valley, Western Italian Alps, using data extracted from the Regional floristic database and from an intensive field survey carried out in years 2009–2010. The aims of the work were (1) to evaluate whether the species is in the introduction, colonization, or establishment stage of invasion, (2) to detect the environmental factors that drive the invasion process, and (3) to highlight the potential range of distribution of the alien species. The modeling framework was a stepwise generalized linear model (GLM), using gridded presence/absence data and environmental predictors such as topography, climate, land use, and anthropogenic and natural disturbances. GLM were fit both with and without an additional independent variable to take into account current dispersal limitations. S. inaequidens displayed a very fast spread in the Aosta Valley in the years 1990–2010. The species was positively associated with roads and rivers, southern slopes, and negatively with elevation. However, it was found at an elevation of 1600 m, showing the ability to reach higher elevations than those observed for other invasive alien species, and confirming to be pre-adapted to mountain conditions. The difference between the species distribution models, with and without dispersal constraints, suggested that the availability of seed sources still limits the potential distribution of the species, rather than the environmental variables, and that the realized regional niche differs to a great extent from the equilibrium niche. When limitations to the seed source cease (i.e., in the establishment stage), the species will likely invade large areas that are currently characterized by pastures and grasslands with native species of high agricultural importance. The invasion of S. inaequidens should therefore be considered a serious threat, due to its potential to invade mountain regions, and in particular to colonize habitats used for grazing and forage, thus leading to a high risk for cattle and human health. We discuss the relevance of the results both concerning communication with the public and to support local eradication and control activities. The inclusion of S. inaequidens in the “black list” of the regional law for the conservation of alpine flora (L.R. 45/2009) will help to transfer the information and support invasion control, in particular at medium elevations.     

The past,present and future of thermophilous Cyperus polystachyos Rottb. (Cyperaceae) on the island of Ischia (southern Italy)

Cyperus polystachyos is a hygrophilous, thermophilous and heliophilous plant with a punctiform distribution in southern Italy, where it is almost exclusively found on Ischia, an island in the Bay of Naples characterized by widespread volcanic hydrothermal activity. This species is a native of tropical and subtropical areas and there is evidence for ancient isolation events in the creation of its current distribution pattern. We have studied the historical literature available for this plant since 1800 and collected temporal and spatial presence data of this species in order to develop a habitat suitability map based on a GIS approach and using a multiple linear regression model. Moreover, we have used univariate and multivariate statistical analysis. The results show the importance of the environmental mosaic around fumaroles to preserve the species; urbanization and geothermal energy use of fumaroles in the past and the combination of abandonment of the typical agricultural system and the natural occurrence of reforestation in the present are the main causes of the decline in the number of populations.     

Hosts and distribution of Viscum album L. ssp. album in Croatia and Slovenia

Abstract

Viscum album L. ssp. album is semi-parasitic on deciduous trees and shrubs. In order to identify hosts and map the distribution of V. album ssp. album in Croatia and Slovenia, field research was carried out, and herbaria were surveyed. In Croatia and Slovenia, V. album ssp. album occurred on 59 taxa. In Croatia, there were 52 hosts (33 autochthonous and 15 allochthonous species, two cultivars and two hybrids). In Slovenia, there were 25 hosts (21 autochthonous and four allochthonous species). There were 18 hosts common to both countries, 34 hosts were found only in Croatia, and seven hosts only in Slovenia. The hosts belonged to 13 families. The majority of these (19 species) belong to the Rosaceae, followed by Salicaceae, Aceraceae, Betulaceae, Fagaceae, Juglandaceae, Tiliaceae, Hippocastanaceae, Ulmaceae, Oleaceae, Fabaceae, Moraceae and Viscaceae. All hosts have been previously recorded in the literature, except Alnus japonica (Thunb.) Steud., Amelanchier lamarckii F.G. Schroed. and Crataegus nigra Waldst. et Kit. The distribution of this mistletoe was scattered, due to the scattered distribution of hosts, local conditions, movement of bird-vectors, etc. A continuous distribution was found only in part of the distribution area of narrow-leaved ash (Fraxinus angustifolia Vahl).