Showing papers by "Daniel Sol published in 2008"

Grasping at the routes of biological invasions: a framework for integrating pathways into policy

Abstract: Summary 1. Pathways describe the processes that result in the introduction of alien species from one location to another. A framework is proposed to facilitate the comparative analysis of invasion pathways by a wide range of taxa in both terrestrial and aquatic ecosystems. Comparisons with a range of data helped identify existing gaps in current knowledge of pathways and highlight the limitations of existing legislation to manage introductions of alien species. The scheme aims for universality but uses the European Union as a case study for the regulatory perspectives. 2. Alien species may arrive and enter a new region through three broad mechanisms: importation of a commodity, arrival of a transport vector, and/or natural spread from a neighbouring region where the species is itself alien. These three mechanisms result in six principal pathways: release, escape, contaminant, stowaway, corridor and unaided. 3. Alien species transported as commodities may be introduced as a deliberate release or as an escape from captivity. Many species are not intentionally transported but arrive as a contaminant of a commodity, for example pathogens and pests. Stowaways are directly associated with human transport but arrive independently of a specific commodity, for example organisms transported in ballast water, cargo and airfreight. The corridor pathway highlights the role transport infrastructures play in the introduction of alien species. The unaided pathway describes situations where natural spread results in alien species arriving into a new region from a donor region where it is also alien. 4. Vertebrate pathways tend to be characterized as deliberate releases, invertebrates as contaminants and plants as escapes. Pathogenic micro-organisms and fungi are generally introduced as contaminants of their hosts. The corridor and unaided pathways are often ignored in pathway assessments but warrant further detailed consideration. 5. Synthesis and applications. Intentional releases and escapes should be straightforward to monitor and regulate but, in practice, developing legislation has proved difficult. New introductions continue to occur through contaminant, stowaway, corridor and unaided pathways. These pathways represent special challenges for management and legislation. The present framework should enable these trends to be monitored more clearly and hopefully lead to the development of appropriate regulations or codes of practice to stem the number of future introductions.

Brain Size Predicts the Success of Mammal Species Introduced into Novel Environments

Abstract: Large brains, relative to body size, can confer advantages to individuals in the form of behavioral flexibility Such enhanced behavioral flexibility is predicted to carry fitness benefits to individuals facing novel or altered environmental conditions, a theory known as the brain size-environmental change hypothesis Here, we provide the first empirical link between brain size and survival in novel environments in mammals, the largest-brained animals on Earth Using a global database documenting the outcome of more than 400 introduction events, we show that mammal species with larger brains, relative to their body mass, tend to be more successful than species with smaller brains at establishing themselves when introduced to novel environments, when both taxonomic and regional autocorrelations are accounted for This finding is robust to the effect of other factors known to influence establishment success, including introduction effort and habitat generalism Our results replicate similar findings in birds, increasing the generality of evidence for the idea that enlarged brains can provide a survival advantage in novel environments

Brains, lifestyles and cognition: are there general trends?

Abstract: Comparative and experimental approaches to cognition in different animal taxa suggest some degree of convergent evolution. Similar cognitive trends associated with similar lifestyles (sociality, generalism, new habitats) are seen in taxa that are phylogenetically distant and possess remarkably different brains. Many cognitive measures show positive intercorrelations at the inter-individual and inter-taxon level, suggesting some degree of general intelligence. Ecological principles like the unpredictability of resources in space and time may drive different types of cognition (e.g., social and non-social) in the same direction. Taxa that rank high on comparative counts of cognition in the field are usually the ones that succeed well in experimental tests, with the exception of avian imitation. From apes to birds, fish and beetles, a few common principles appear to have influenced the evolution of brains and cognition in widely divergent taxa.

The comparative analysis of historical alien introductions

Abstract: The comparative analysis of past introductions has become a major approach in investigating the rules governing invasions, yet their utility to understand the invasion process is not exempt of problems. The relevance of some of these problems has not yet been fully appreciated, but it has now become clear that not taking them into account may lead to invalid conclusions. Taking examples of the plants’ and birds’ literature, this paper reviews these difficulties by discussing the comparative analysis of region invasibility. The difficulties include biased information toward successful introductions, confounded effects of many explanatory variables, statistical non-independence of introduction events and taxonomic levels, and inappropriate definition of the units of study. Provided that there is good information on introduction events at the appropriate spatial scale, reliable results may be obtained by using modelling techniques that control for the effects of introduction effort and species properties while dealing with spatial and phylogenetic non-independence of introduction events. In conclusion, although important progress can be made in understanding the factors behind invasibility of regions by the comparative analysis of the past introductions, this will only be possible by acknowledging the existence of biases and confounding effects in historical introductions and by using appropriate methods to deal with them.

Do Successful Invaders Exist? Pre-Adaptations to Novel Environments in Terrestrial Vertebrates

Abstract: Central in invasion biology is to understand why alien species, whose initial populations are generally small and genetically depleted, can succeed to establish themselves in environments to which they have had no opportunity to adapt (Sax and Brown 2000). This paradox is usually resolved by invoking pre-adaptations of non-indigenous species to novel environments. The idea is that some species are successful invaders because they have attributes that pre-adapt them to survive and reproduce in novel environments (Mayr 1965). However, do we really have evidence that there exist properties of successful invaders? The goal of this chapter is to evaluate to what extent establishment success of terrestrial vertebrates may be understood by the existence of pre-adaptations of species to novel environments. This implies answering two interrelated questions: (1) do species differ in their invasion potential? And if so, (2) what are the features of the species that identify some as successful invaders? Answering these questions is important not only to fully understand how animals respond to new environmental conditions, but also to help identify and prevent situations where the risk is high that a species becomes established and causes ecological impact when introduced in a novel region.

Habitat selection and breeding success in Yellow‐legged Gulls Larus cachinnans

Abstract: The habitat selection and breeding performance of Yellow-legged Gulls Larus cachinnans were studied in the Medes Islands colony, northeastern Spain, during 1995 and 1996. Of the three main habitats on the islands (shrubs, grass and bare areas), gulls first occupied those with the highest percentage of tall vegetation. Gulls tended to select nest sites with 20–75% cover despite great differences in the cover in the habitats and territories, suggesting that the presence of a suitable nest site may play a major role in the choice of breeding habitat. Nest-site tenacity did not influence the preferences of gulls at any level since the same pattern of choice was observed in an area subjected to annual culls (i.e. where most of the breeding pairs were culled annually and replaced by naive birds). In spite of great differences in the physical characteristics of the habitats, little difference was found in breeding performance of the gulls between habitats. Gulls nesting in the least preferred habitat (i.e. mainly bare) had smaller clutches than those nesting in the other two habitats, possibly as a result of their later seasonal laying. Despite the similar breeding success in different habitats, gulls did not seem to distribute according to the ideal free model reported for Herring Gulls Larus argentatus since the density in the preferred habitat (i.e. shrubs) was never higher than in the other two. We suggest that the habitat selection by Yellow-legged Gulls within the colony could follow an ideal despotic distribution.

Brain size and the diversification of body size in birds.

Abstract: Large brains are associated with increased cognitive skills, enabling animals to use new environments and resources more successfully. Such behavioral flexibility is theoretically expected to have macroevolutionary consequences. First, populations of big‐brained individuals should more easily become established in new locations, increasing opportunities for allopatric speciation and decreasing chances that the species as a whole becomes extinct. Second, the ability to use new resources should place new selection pressures on populations, promoting adaptive diversification, a process termed “behavioral drive.” In this article, we show that the average brain size of a bird family explains a significant fraction ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\c...

Random sampling, abundance-extinction dynamics and niche-filtering immigration constraints explain the generation of species richness gradients

Abstract: Aim The paradigm that species’ patterns of distribution, abundance and coexistence are the result of adaptations of the species to their niches has recently been challenged by evidence that similar patterns may be generated by simple random processes. We argue here that a better understanding of macroecological patterns requires an integration of both ecological and neutral stochastic approaches. We demonstrate the utility of such an integrative approach by testing the sampling hypothesis in a species‐energy relationship of forest bird species. Location A Mediterranean biome in Catalonia, Spain. Methods To t est the sampling hypothesis we designed a metacommunity model that reproduces the stochastic sampling from a regional pool to predict local species richness variation. Four conceptually different sampling procedures were evaluated. Results We showed that stochastic sampling processes predicted a substantial part (over 40%) of the observed variation in species richness, but left considerable variation unexplained. This remaining variation in species richness may be better understood as the result of alternative ecological processes. First, the sampling model explained more variation in species richness when the probability that a species colonises a new locality was assumed to increase with its niche width, suggesting that ecological differences between species matter when it comes to explaining macroecological patterns. Second, extinction risk was significantly lower for species inhabiting high-energy regions, suggesting that abundance‐extinction processes play a significant role in shaping species richness patterns.

Introduction: genetics of colonizing species.

Abstract: Successful colonization of a new location involves a fourstep process: departure from the source, dispersal across a barrier, establishment, and range expansion in the new region. The hurdles at each step mean that a restricted subset of potential source species become established in the new location (Whittaker and Fernandez-Palacios 2007). Further, among the species that do successfully colonize, these same four hurdles result in genetic differentiation from the source (Lee 2002; Gilchrist and Lee 2007). Taking advantage of the many human-aided invasions throughout the world, a massive research program now focuses on the third and fourth stages of the colonization process (i.e., establishment and range expansion in the new location). Several book-length reviews on these stages have recently appeared (Sax et al. 2005; Allen and Lee 2006; Gilchrist and Lee 2007; Lockwood et al. 2007; Nentwig 2007). New Zealand has been particularly affected by invasive species (Allen and Lee 2006), and in the classic volume Genetics of Colonizing Species, Wodzicki (1965, p. 456) noted that it “offers an excellent opportunity to study the results of a large scale introduction of exotic species and their adaptation to a new environment.” The 2007 American Society of Naturalists symposium in New Zealand therefore seemed an ideal setting to discuss advances in the genetic changes underlying invasion. We asked contributors to this symposium to focus on original research, covering the spectrum of all four stages of the colonization process.

Artificial selection, naturalization, and fitness: Darwin's pigeons revisited

Abstract: Central in biology is the view that the commonly observed association between the phenotype and the ecology of organisms is the result of the process of natural selection. There are numerous examples where the current and/or past ecological pressures in which a trait presumably arose have been demonstrated. Less well documented, however, are cases where a species that has artificially been moved from its adaptive peak is seen to return to its ancestral state when exposed to the ancient selective regime. One of the few suggested cases is that of the feral pigeon (Columba livia), the free-living descends from domesticated, artificially selected rock pigeons. Contemporary feral pigeons are significantly closer in morphology to wild rock pigeons than to their more direct domestic ancestors, suggesting that natural selection has been reconstituting their wild phenotype. Because they still preserve some characters engendered through artificial selection during their ancestral period of domesticity, notably a tarsus that is disproportionally long for a terrestrial pigeon of its size, feral pigeons provide a rare opportunity to test whether natural selection is the process behind the reconstitution of the wild phenotype. In the present study, it is shown that feral pigeons with tarsi that depart the most from the wild phenotype appear to have limitations in the use of some food resources and, as a result, experience lower survival fitness. These findings support the view that natural selection is reconstituting the wild phenotype in feral pigeons. The possibility nonetheless remains that this process will never be fully completed. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 657–665.

Tourism and urban transport: Holding demand pressure under supply constraints

Abstract: Scholars and local planners are increasingly interested in tourism contribution to economic and social development To this regard, several European cities lead the world rankings on tourist arrivals, and their governments have promoted tourism activity Mobility is an essential service for tourists visiting large cities, since it is a crucial factor for their comfort In addition, it facilitates the spread of benefits across the city The aim of this study is to determine whether city planners respond to this additional urban transport demand pressure by extending supply services We use an international database of European cities Our results confirm that tourism intensity is a demand enhancing factor on urban transport Contrarily, cities do not seem to address this pressure by increasing service supply This suggests that tourism exerts a positive externality on public transport since it provides additional funding for these services, but it imposes as well external costs on resident users because of congestion given supply constraints

Motorways, tolls and road safety. Evidence from European panel data

Abstract: The use of tolls is being widespread around the world. Its ability to fund infrastructure projects and to solve budget constraints have been the main rationale behind its renewed interest. However, less attention has been payed to the safety effects derived from this policy in a moment of increasing concern on road fatalities. Pricing best infrastructures shifts some drivers onto worse alternative roads usually not prepared to receive high traffic in comparable safety standards. In this paper we provide evidence of the existence of this perverse consequence by using an international European panel in a two way fixed effects estimation.