bluuebunny/crossref_metadata_2025 huggingface dataset:
A statistical method for idiographic analyses in biogeographical research
Authors: Fattorini Simone
Published: February 2009

Idiographic analyses (i.e. detailed analyses of single species ranges) can be criticized for subjective and speculative reasoning. Medoid partition is suggested here as a method to perform a statistically supported idiographic analysis. The medoid algorithms attempt to group objects into clusters by finding a set of representative objects called medoids. If areas are the objects that are clustered using species occurrences (0/1) as variables, each cluster will be characterized by a medoid area. The species that characterize each medoid are representative of the entire cluster to which the medoid belongs and can be regarded as (statistically supported) species ‘characteristic’ of the main distributional patterns observed in the study system and can be used to draw idiographic observations. To illustrate the issues involved, the Coleoptera Tenebrionidae of the Aegean Islands (Greece) were analysed. Two species appeared to be characteristic of the Balkan cluster, while eight species were characteristic of the Anatolian one, and two species were equally distributed in both areas. Idiographic considerations based on these species outlined the importance of a Balkano–Anatolian discontinuity in the Aegean that prevented species dispersal between the two landmasses. This study illustrates that medoid analysis may help the researcher to find some representative patterns from a puzzling distribution. Traditional idiographic analyses can be biased by the fact that species are selected ad hoc. Thus, one cannot establish if results are truly objective or if the author intentionally selected, from a wider array of species, those that supported some preferred patterns. Medoid clustering uses the full array of species to find clusters of areas. After clusters are objectively defined, their medoids are examined to find species that mostly contributed to cluster definition, and the distribution patterns of these species are interpreted.
Distribution of myrmecochorous species over the landscape and their potential long‐distance dispersal by emus and kangaroos
Authors: Calviño‐Cancela María , He Tianhua , Lamont Byron B.
Published: February 2009

Topographical heterogeneity can create a mosaic of substrate types leading to the formation of isolated plant populations. Seed dispersal then becomes crucial for the colonization of such suitable but remote substrate types. We surveyed the distribution of seven elaiosome‐bearing species (myrmecochores) over 5 km2of natural heathland in southwestern Australia. Ants are the standard means of dispersal of these species, which provide limited dispersal (usually of a few metres). Six species were associated with particular substrate types (dune or swale) and all occurred as discrete populations, on average 270–500 m apart, with closest dune edges 280 m apart. We evaluated the possible roles of emus and kangaroos as alternative agents of long‐distance seed dispersal between substrate types. Their droppings contained viable seeds of three of the target species, as well as other myrmecochores, and were evenly distributed over the substrate types. While migration of these plant species between preferred substrate types seems unlikely when considering only their standard dispersal agents (ants), it is highly likely in the presence of emus (in particular) and kangaroos that act as non‐standard dispersers. This may have important consequences for plant species conservation by increasing habitat connectivity and favouring regional persistence.
Elephants and water provision: what are the management links?
Authors: Smit I. P. J. , Grant C. C. , Whyte I. J.
Published: February 2009

In a recent paper we demonstrated that elephant bull groups and mixed herds exhibited spatial and resource segregation across the Kruger National Park. It was found, inter alia, that both bull groups and mixed herds occurred more frequently closer to rivers than expected if they were randomly distributed, but that only bull groups occurred more frequently closer to the artificial waterholes. Although Chamaillé‐Jammes et al. (2007) accepted these results, they disagreed with our interpretation regarding the potential effect that closure of artificial waterholes might have. Here we address some of the specific concerns expressed and provide a broader context regarding water provision and elephant management. Although water provision can influence elephant density and distribution, we argue that the effectiveness of surface‐water manipulation as a management tool will depend on (1) natural surface‐water availability, (2) forage quality, (3) elephant densities, (4) position of a population on its growth trajectory, and (5) management objectives. Even though elephants are water‐dependent, the effectiveness of water provision as a management tool will therefore be area‐ and population‐specific and will depend on management objectives.
Fagus sylvatica L. recruitment across a fragmented Mediterranean Landscape, importance of long distance effective dispersal, abiotic conditions and biotic interactions
Authors: Kunstler Georges , Thuiller Wilfried , Curt Thomas , Bouchaud Monique , Jouvie René , Deruette Florian , Lepart Jacques
Published: February 2009

Native tree populations have been fragmented by anthropogenic disturbance worldwide, leaving them at risk from extinction. The possibility of sizable recovery of fragmented populations is a function of their dispersal, the abiotic conditions, and the biotic interactions. The relative importance of these three drivers for the recruitment rate of a fragmented population of the late‐successional Fagus sylvatica L. was analysed at the landscape scale in Causse du Larzac, southern margins of the Massif Central, in the South of France. We used regression models on observational data to analyse the response of Fagus recruitment rate to the distance to the nearest mature population, to climatic and geological variables, and to variables describing biotic interactions (pine vs. grassland, light, shrub cover). Distance to the nearest F. sylvatica adult population was the most important explanatory variable. Recruitment rate was also influenced by facilitative biotic interactions with shrubs, and by the climatic conditions of the plot. Recruitment occurred at a greater distance from the nearest mature population of Fagus in pine forests than in grassland. Dispersal was the major limitation to recruitment of F. sylvatica in this landscape. The recruitment rate was then modulated by the climate and positive biotic interactions. The activity of the European jay could be of great importance for such fragmented populations, because it can lead to long‐distance dispersal events and may result in a preferential dispersal towards pine forests.
Combined effects of bottlenecks and selfing in populations of Corella eumyota, a recently introduced sea squirt in the English Channel
Authors: Dupont L. , Viard F. , David P. , Bishop J. D. D.
Published: February 2009

The success of an exotic species depends notably on its capacity to initiate a new population from a few individuals, to survive genetic bottlenecks and to adapt locally. Species with multiple reproductive strategies (e.g. mixed‐mating system with both self‐ and cross‐fertilization) can be efficient colonizers. Herein we focus on Corella eumyota, an exotic ascidian that has rapidly invaded English Channel coasts in recent years. Interestingly, this brooding hermaphroditic ascidian is capable of self‐fertilization in the laboratory. We developed 12 microsatellite markers from an enriched library of genomic DNA to investigate the level of inbreeding and selfing in two putatively native populations (South Africa, N = 34, and New Zealand, N = 28) and to examine if founder effects were possibly associated with its recent introduction in two French populations (Perros‐Guirec, N = 22 and Brest; N = 25). Genetic polymorphism was very low in both native populations (i.e. less than 60% of the loci were polymorphic) and even lower in the introduced populations, one of which was monomorphic at all loci, suggesting a recent bottleneck. Fis and a new method based on multi‐locus heterozygosity were used to provide estimates of inbreeding. A high selfing rate was inferred in the South Africa population with both methods (s = 0.90), whereas in the other native population (New Zealand) a lower but significant estimate of selfing rate (s = 0.29) was obtained with the multi‐locus method. This variability of population selfing rate might be explained by a mixed‐mating system, allowing C. eumyota to reproduce through inbreeding and outbreeding according to mating possibilities; this trait may have favoured the rapid establishment of new populations in Europe.
The role of landscape texture in conservation biogeography: a case study on birds in south‐eastern Australia
Authors: Fischer Joern , Lindenmayer David B. , Montague‐Drake Rebecca
Published: February 2009

The binary classification of landscapes into suitable vs. unsuitable areas underlies several prominent theories in conservation biogeography. However, a binary classification is not always appropriate. The textural discontinuity hypothesis provides an alternative theoretical framework to examine the geographical distribution of species, and does not rely on a binary classification scheme. The texture of a given landscape is the combination of its vertical structural complexity and horizontal spatial grain. The textural discontinuity hypothesis states that biophysical features in the environment are scaled in a discontinuous way, and that discontinuities in the body size distribution of animals mirror these biophysical discontinuities. As a result of this relationship, a complex landscape texture should be associated with small‐bodied animals, whereas a simple landscape texture should be associated with larger‐bodied animals. We examined this hypothesis for birds in five landscapes in south‐eastern Australia that represented a gradient from simple to complex landscape texture. In landscapes with a complex texture, the number of detections of small birds was higher than expected, and the number of detections of larger‐bodied birds was lower than expected. The opposite pattern was found in landscapes with a simple texture. The pattern remained significant when only bird species found in each of the five landscapes were considered, which demonstrated that the association of landscape texture with body size was not an artefact of landscapes differing in their species pools. Understanding the effects of landscape texture on species distribution patterns may be a promising research frontier for conservation biogeography. We hypothesize that the active management of landscape texture may be used to attract or deter animals of certain body sizes. Consistent with other theories, the textural discontinuity hypothesis therefore suggests that managing entire landscapes, rather than only predefined patches, is an important conservation strategy.
Species richness patterns of obligate subterranean beetles (Insecta: Coleoptera) in a global biodiversity hotspot – effect of scale and sampling intensity
Authors: Zagmajster Maja , Culver David C. , Sket Boris
Published: February 2009

We studied species richness patterns of obligate subterranean (troglobiotic) beetles in the Dinaric karst of the western Balkans, using five grid sizes with cells of 80 × 80, 40 × 40, 20 × 20, 10 × 10, and 5 × 5 km. The same two hotspots could be recognized at all scales, although details differed. Differences in sampling intensity were not sufficient to explain these patterns. Correlations between number of species and number of sampled localities increased with increasing cell size. Additional species are expected to be found in the region, as indicated by jackknife 1, jackknife 2, Chao2, bootstrap, and incidence‐based coverage (ICE) species richness estimators. All estimates increased with increasing cell size, except Chao2, with the lowest prediction at the intermediate 20 × 20 km cell size. Jackknife 2 and ICE gave highest estimates and jackknife 1 and bootstrap the lowest. Jackknife 1 and bootstrap estimates changed least with cell size, while the number of single cell species increased. In the highly endemic subterranean fauna with many rare species, bootstrap may be most appropriate to consider. Positive autocorrelation of species numbers was highest at 20 × 20 km scale, so we used this cell size for further analyses. At this scale we added 137 localities with less positional accuracy to 1572 previously considered, and increased 254 troglobiotic species considered to 276. Previously discovered hotspots and their positions did not change, except for a new species‐rich cell which appeared in the south‐eastern region. There are two centres of troglobiotic species richness in the Dinaric karst. The one in the north‐west exhibited high species richness of Trechinae (Carabidae), while in the south‐east, the Leptodirinae (Cholevidae) were much more diverse. These centres of species richness should serve as the starting point for establishing a conservation network of important subterranean areas in Dinaric karst.
Standard yet unusual mechanisms of long‐distance dispersal: seed dispersal of Corymbia torelliana by bees
Authors: Wallace Helen M. , Howell Martin G. , Lee David J.
Published: February 2009

Mellitochory, seed dispersal by bees, has been implicated in long‐distance dispersal of the tropical rain forest tree, Corymbia torelliana (Myrtaceae). We examined natural and introduced populations of C. torelliana for 4 years to determine the species of bees that disperse seeds, and the extent and distance of seed dispersal. The mechanism of seed dispersal by bees was also investigated, including fruit traits that promote dispersal, foraging behaviour of bees at fruits, and the fate of seeds. The fruit structure of C. torelliana, with seed presented in a resin reward, is a unique trait that promotes seed dispersal by bees and often results in long‐distance dispersal. We discovered that a guild of four species of stingless bees, Trigona carbonaria, T. clypearis, T. sapiens, and T. hockingsi, dispersed seeds of C. torelliana in its natural range. More than half of the nests found within 250 m of fruiting trees had evidence of seed transport. Seeds were transported minimum distances of 20–220 m by bees. Approximately 88% of seeds were dispersed by gravity but almost all fruits retained one or two seeds embedded in resin for bee dispersal. Bee foraging for resin peaked immediately after fruit opening and corresponded to a peak of seed dispersal at the hive. There were strong correlations between numbers of seeds brought in and taken out of each hive by bees (r = 0.753–0.992, P < 0.05), and germination rates were 95 ± 5%. These results showed that bee‐transported seeds were effectively dispersed outside of the hive soon after release from fruits. Seed dispersal by bees is a non‐standard dispersal mechanism for C. torelliana, as most seeds are dispersed by gravity before bees can enter fruits. However, many C. torelliana seeds are dispersed by bees, since seeds are retained in almost all fruits, and all of these are dispersed by bees.
The influence of sampling intensity on the perception of the spatial distribution of tropical diversity and endemism: a case study of ferns from Bolivia
Authors: Soria‐Auza Rodrigo W. , Kessler Michael
Published: February 2009

The distribution of tropical plant and animal diversity is still poorly documented, especially at spatial resolutions of practical use for conservation. In the present study, we evaluated the level to which geographical incomplete data availability of species occurrence affects the perception of biodiversity patterns (species richness and endemism) among pteridophytes in Bolivia. We used a data base of Bolivian pteridophytes (27,501 records), divided it into three time periods (1900–70, up to 1990 and up to 2006), and created grid‐files at 15′‐resolution for species richness and endemism. For each of these biodiversity properties we estimated the species richness (Chao 2) and the index of sampling completeness (C index) per grid, and then all these variables at both species richness and endemism were correlated. Patterns of richness were fairly consistent along all periods; the richest areas were placed along the humid‐montane forest, even though they were strongly influenced by collecting intensity. Endemism had a lower degree of correlation with collecting intensity, but varied much more strongly through time than species richness. According to the C index, which gives the ratio between estimated (by Chao 2) and recorded values of species richness and endemism, both biodiversity properties tended to be undersampled in the richest grid cells. Inter‐temporal correlations showed sharper differences of correlations for endemism than species richness. Consequently, already in 1970, botanists had a correct idea of the spatial distribution of pteridophyte richness in Bolivia (even though the magnitude was grossly underestimated). In contrast, patterns of endemism, which are of high conservation importance, may not even today be reliably known.
How well do the existing and proposed reserve networks represent vertebrate species in Chile?
Authors: Tognelli Marcelo F. , de Arellano Pablo I. Ramirez , Marquet Pablo A.
Published: February 2009

Increasingly, biogeographical knowledge and analysis are playing a fundamental role in assessing the representativeness of biodiversity in protected areas, and in identifying critical areas for conservation. With almost 20% of the country assigned to protected areas, Chile is well above the conservation target (i.e. 10–12%) proposed by many international conservation organizations. Moreover, the Chilean government has recently proposed new conservation priority sites to improve the current protected area network. Here, we used all 653 terrestrial vertebrate species present in continental Chile to assess the performance of the existing and proposed reserve networks. Using geographical information systems, we overlaid maps of species distribution, current protected areas, and proposed conservation priority sites to assess how well each species is represented within these networks. Additionally, we performed a systematic reserve selection procedure to identify alternative conservation areas for expanding the current reserve system. Our results show that over 13% of the species are not covered by any existing protected area, and that 73% of Chilean vertebrate species can be considered partial gaps, with only a small fraction of their geographical ranges currently under protection. The coverage is also deficient for endemic (species confined to Chile) and threatened species. While the proposed priority sites do increase coverage, we found that there are still several gaps and these are not the most efficient choices. Both the gap analysis and the reserve selection analysis identified important areas to be added to the existing reserve system, mostly in northern and central Chile. This study underscores the need for a systematic conservation planning approach to redefine the conservation priority sites in order to maximize the representation of species, particularly endemic and threatened species.
The range of the curl‐crested jay: lessons for evaluating bird endemism in the South American Cerrado
Authors: Lopes Leonardo Esteves
Published: February 2009

The South American Cerrado is the largest tropical savanna of the world, and one of the most threatened biomes on the Earth. Levels of bird endemism in this biome are controversial, but the most up‐to‐date study points to 30 endemic species. In this paper, I analysed the recent range shift by one of those species, the curl‐crested jayCyanocorax cristatellus, comparing it with three other alleged Cerrado endemics (lesser nothuraNothura minor, chestnut‐capped foliage‐gleanerHylocryptus rectirostris, and grey‐backed tachuriPolystictus superciliaris) and a ‘near‐endemic’ (white‐banded tanagerNeothraupis fasciata). The curl‐crested jay expanded its range considerably into south‐eastern Brazil during the last century, colonizing extensive areas formerly covered by the Atlantic forest, which has been almost completely cleared by human activity. I found no evidence of recent range shift for the four other species studied, but demonstrated that the grey‐backed tachuri is not a Cerrado endemic. I found that the vegetation map used by previous authors to classify birds as endemics is imprecise and out‐of‐date, not depicting well the biome limits, resulting in an arbitrary, sometimes erroneous, classification. I suggested the adoption of a more modern and detailed Cerrado map. The necessity of a comprehensive review in the list of Cerrado's endemic birds in light of modern vegetation maps is highlighted.
Linking political and scientifically derived targets for global biodiversity conservation: implications for the expansion of the global network of protected areas
Authors: Soutullo Alvaro , De Castro Monica , Urios Vicente
Published: February 2009

Despite the global network of protected areas covers 12% of the world's land surface, its performance is still unsatisfactory. Although political and scientifically sound conservation targets usually portray different pictures of the task ahead, we show that in terms of priority areas for expanding the global network of reserves, there is much agreement between the political targets of the Convention on Biological Diversity (CBD), and the scientifically derived goals endorsed by international conservation organizations. Here we analyse four global databases to identify priority areas for fulfilling the CBD target of representing 10% of every ecological region within protected areas, and compare the distribution of priority regions for fulfilling that political target, with the distribution of the priority areas for global biodiversity conservation identified by Conservation International, the WWF, and the Wildlife Conservation Society on scientific basis. For 63% (549) of the world's terrestrial ecoregions the CBD 10% target is still not met; fulfilling it requires protecting another 4.6% of the Earth's land surface (6,239,894 km2). Yet, at least 78% of the priority regions for fulfilling that target lay within priority regions for the main global conservation strategies. By pursuing the political target set by the CBD much ancillary gains in terms of other global conservation objectives can be obtained.
GIS‐based niche models identify environmental correlates sustaining a contact zone between three species of European vipers
Authors: Martínez‐Freiría F. , Sillero N. , Lizana M. , Brito J. C.
Published: February 2009

The current range of European vipers is mostly parapatric but local‐scale allopatric distribution is common and few cases of sympatry are known. In the High Course of Ebro River, northern Spain, there is a contact zone between Vipera aspis, V. latastei, and V. seoanei. Sympatry was detected between aspis and latastei and also specimens with intermediate morphological traits. Presence‐data at a local scale (1 × 1 km) and ecological niche‐based models manipulated in a GIS were used to (1) identify how environmental factors correlate with the distribution of the three vipers and with the location of the sympatry area, and (2) identify potential areas for viper occurrence and sympatry. Ensemble for casting with 10 Maximum Entropy models identified a mixture of topographical (altitude, slope), climatic (precipitation, evapotranspiration, and minimum and maximum temperature), and habitat factors (land cover) as predictors for viper occurrence. Similar predicted probabilities according to the variation of some environmental factors (indicating probable sympatry) were observed only for aspis‐latastei and aspis‐seoanei. In fact, areas of probable occurrence of vipers were generally allopatric but probable sympatry between vipers was identified for aspis‐latastei in 76 UTM 1 × 1 km squares, for aspis‐seoanei in 23 squares, and latastei‐seoanei in two squares. Environmental factors correlate with the location of this contact zone by shaping the species range: some enhance spatial exclusion and constrain distribution to spatially non‐overlapping ranges, while others allow contact between species. The distribution in the contact zone apparently results from the balance between the pressures exerted by the different environmental factors and in the sympatry area probably by interspecific competition. Further ecological and genetical data are needed to evaluate the dynamics of the probable hybrid zone. GIS and niche‐modelling tools proved to be powerful tools to identify environmental factors sustaining the location of contact zones.
Species prioritization for monitoring and management in regional multiple species conservation plans
Authors: Regan Helen M. , Hierl Lauren A. , Franklin Janet , Deutschman Douglas H. , Schmalbach Heather L. , Winchell Clark S. , Johnson Brenda S.
Published: February 2009

Successful conservation plans are not solely achieved by acquiring optimally designed reserves. Ongoing monitoring and management of the biodiversity in those reserves is an equally important, but often neglected or poorly executed, part of the conservation process. In this paper we address one of the first and most important steps in designing a monitoring program – deciding what to monitor. We present a strategy for prioritizing species for monitoring and management in multispecies conservation plans. We use existing assessments of threatened status, and the degree and spatial and temporal extent of known threats to link the prioritization of species to the overarching goals and objectives of the conservation plan. We consider both broad and localized spatial scales to capture the regional conservation context and the practicalities of local management and monitoring constraints. Spatial scales that are commensurate with available data are selected. We demonstrate the utility of this strategy through application to a set of 85 plants and animals in an established multispecies conservation plan in San Diego County, California, USA. We use the prioritization to identify the most prominent risk factors and the habitats associated with the most threats to species. The protocol highlighted priorities that had not previously been identified and were not necessarily intuitive without systematic application of the criteria; many high‐priority species have received no monitoring attention to date, and lower‐priority species have. We recommend that in the absence of clear focal species, monitoring threats in highly impacted habitats may be a way to circumvent the need to monitor all the targeted species.
Phylogenetic autocorrelation of extinction threat in globally imperilled amphibians
Authors: Corey Sarah J. , Waite Thomas A.
Published: February 2009

The global extinction crisis demands immediate action to conserve species at risk. However, if entire clades such as superfamilies are at risk due to shared evolutionary history, a shift towards conserving clades rather than individual species may be needed. Using phylogenetic autocorrelation analysis, we demonstrate that multiple kinds of extinction threat clump within the amphibian tree of life. Our study provides insight into how these threats may collectively influence the extinction risk of whole clades, consistent with the supposition that related species, with similar traits, share an intrinsic vulnerability to common kinds of threat. Most strikingly, we find a significant concentration of ‘enigmatic’ decline and critically endangered status within families of the hyloid frogs. This phylogenetic clumping of risk is also geographically concentrated, with most threats found in Central and South America, and Australia, coinciding with reported outbreaks of chytridiomycosis. We speculate that the phylogenetic clumping of threat represents, in part, shared extinction proneness due to shared evolutionary history. However, even if the phylogenetic clumping of threat were simply a by‐product of shared geography, this concordance between phylogenetic and geographical patterns represents a prime opportunity. Where practical, we should implement conservation plans that focus on biogeographical regions where threatened clades occur, thereby improving our ability to conserve species. This approach could outperform the usual triage approach of saving individual species after they have become critically endangered.
Biological attributes affect the data of description of tiger moths (Arctiidae) in the Brazilian Cerrado
Authors: Ferro Viviane Gianluppi , Diniz Ivone Rezende
Published: February 2009

Previous studies have shown that macroecological variables such as body size and geographical range size may influence the probability of a species being described. We evaluated the description pattern of tiger moth species from the Brazilian Cerrado, and tested whether the date of description was influenced by the species biological attributes (body size, colour pattern, geographical range size, altitudinal range, latitudinal range, longitudinal range, degree of specificity to the Cerrado, and number of species of the same genus). The relationship between date of description for several arctiid taxa and predictor variables was investigated using simple and multiple regressions. All predictor variables explained significant variance in the year of description in some arctiid taxonomic groups. However, the relative importance of each predictor varied among taxa. Our analyses suggested that the tiger moths yet to be discovered in the Cerrado region will probably be small, with a restricted distribution, and endemic to the biome. We also showed, for the first time, that colour pattern is a significant variable in determining the description date of an animal group, with aposematic species being described first. We noted a significant decrease in numbers of tiger moth taxonomists in recent decades. The training of new tiger moth taxonomists is urgent because there is a significant relationship between the number of taxonomists and the number of described species.
Persistence of pyrophilous insects in fire‐driven boreal forests: population dynamics in burned and unburned habitats
Authors: Saint‐Germain Michel , Drapeau Pierre , Buddle Christopher M.
Published: February 2009

Several boreal insect species respond to smoke and heat generated by forest fires and use recent burns to reproduce in high numbers. Some of these species are rare or uncommon in undisturbed forests, and the contribution of recently burned habitats to their population dynamics has been deemed crucial by some to their long‐term persistence. Consequently, the severe decline seen in some species in Fennoscandia has been frequently linked with fire suppression. In this paper, we explore some aspects of the spatial dynamics of pyrophilous insect populations in relation to the expected relative contribution of burned and unburned habitats to their global population dynamics. Forest fires are, throughout the boreal forest biome, generally highly aggregated in some years while rare in most other years. The low connectivity between fire events and the typical life cycle seen in these species make it improbable that recent burns act as significant population sources. This leads us to suggest that populations of pyrophilous species may be more limited by the adequacy of the unburned matrix than by the occurrence of fire events. Moreover, by combining an age‐class distribution model and a dead wood availability model, we show that the quality of the unburned matrix increases in landscapes with longer fire cycles, in which pyrophilous insects should persist at higher population levels. We conclude that the degradation of the unburned habitat better explains the decline of pyrophilous insects than fire suppression alone.
Chytridiomycosis‐mediated expansion of Bufo bufo in a montane area of Central Spain: an indirect effect of the disease
Authors: Bosch Jaime , Rincón Pedro A.
Published: February 2009

Emerging infectious diseases (EIDs) may indirectly influence community structure by altering biotic interactions in which affected species participate. This kind of indirect effects has received little attention to date, although recent research suggest they may not be infrequent. Chytridiomycosis is an EID that is affecting amphibian assemblages worldwide. Here we present the first (to our knowledge) field evidence of its indirect effect on assemblage structure through the disruption of a biotic interaction. We have documented an expansion of the common toad (Bufo bufo) after chytridiomycosis nearly extirpated the midwife toad (Alytes obstetricans) in Peñalara Natural Park (Central Spain). Bufo bufo has significantly increased its number of breeding sites. All newly occupied breeding ponds were colonized once the large numbers of large, overwintering A. obstetricans tadpoles they had previously held disappeared. An experiment demonstrated that breeding B. bufo adults strongly avoided laying eggs in water containing A. obstetricans tadpoles, accounting for observed patterns of pond use. A second experiment failed to show any predation by large A. obstetricans tadpoles on B. bufo eggs, but other researchers have documented reductions in condition, growth and survival of B. bufo larvae caused by the presence of A. obstetricans tadpoles. In Peñalara, chytridiomycosis attacks B. bufo too, but its effect on it has been quite less severe than on A. obstetricans. Our findings show how, besides any chytridiomycosis direct effects, interspecific differences in its impact may alter assemblage–influencing biotic interactions and, hence, assemblage structure in indirect ways.
Bat assemblages on Neotropical land‐bridge islands: nested subsets and null model analyses of species co‐occurrence patterns
Authors: Meyer Christoph F. J. , Kalko Elisabeth K. V.
Published: February 2009

A fundamental goal of ecology is to understand whether ecological communities are structured according to general assembly rules or are essentially dictated by random processes. In the context of fragmentation, understanding assembly patterns and their mechanistic basis also has important implications for conservation. Using distribution data of 20 bat species collected on 11 islands in Gatún Lake, Panama, we tested for non‐randomness in presence–absence matrices with respect to nestedness and negative species co‐occurrence. We examined the causal basis for the observed patterns and conducted separate analyses for the entire assemblage and for various species submatrices reflecting differences in species’ trophic position and mobility. Furthermore, we explored the influence of weighting factors (area, isolation, abundance) on co‐occurrence analyses. Unweighted analyses revealed a significant negative co‐occurrence pattern for the entire assemblage and for phytophagous bats alone. Weighting analyses by isolation retained a pattern of species segregation for the whole assemblage but nullified the non‐random structure for phytophagous bats and suggested negative associations for animalivores and species with low mobility. Area‐ and abundance‐weighted analyses always indicated random structuring. Bat distributions followed a nested subset structure across islands, regardless of whether all species or different submatrices were analysed. Nestedness was in all cases unrelated to island area but weakly correlated with island isolation for incidence matrices of all species, phytophagous bats, and mobile species. Overall, evidence for negative interspecific interactions indicative of competitive effects was weak, corroborating previous studies based on ecomorphological analyses. Our findings indicate that bat assemblages on our study islands are most strongly shaped by isolation effects and species’ differential movement and colonization ability. From a conservation viewpoint this suggests that even in systems with high fragment–matrix contrast, a purely area‐based approach may be inadequate, and structural and functional connectivity among patches are important to consider in reserve planning.
The potential for hull‐mediated species transfers by obsolete ships on their final voyages
Authors: Davidson Ian C. , McCann Linda D. , Fofonoff Paul W. , Sytsma Mark D. , Ruiz Gregory M.
Published: February 2009

Shipping has contributed strongly to biological invasions in coastal ecosystems, transferring species in ballast tanks and on exposed underwater surfaces (hulls). A long history exists that documents biota associated with ships’ hulls, including some recent analyses of modern ships, but relatively little is known about the associated risks of invasion. In general, the likelihood of invasion is expected to increase with increasing propagule supply, which suggests that high‐density transfers on hulls may pose a relatively high invasion risk. Obsolete vessels are expected to be at an extreme end of the spectrum for biofouling, since they sit at anchorage for long periods and are towed at relatively slow speeds when moved, but this remains largely unexplored. In this paper, we quantified the biofouling communities of two obsolete vessels, one stationary for one decade and the other for two decades, before and after their final transit from California to Texas. Pre‐departure biofouling surveys across both vessels detected 22 species of macroinvertebrates. The biomass was dominated by the introduced bryozoan Conopeum chesapeakensis, which occurred in 98% of samples and created a three‐dimensional structure (2–5 cm thick). Mobile species, inhabiting the vertical biofouling matrix, were more numerous than sessile ones. Interestingly, the non‐native Asian clam Corbula amurensis, not previously associated with hull fouling assemblages, was recorded in 9% of samples. During the 43‐day voyage, organisms encountered salinity variation that ranged between zero (Panama Canal) and at least 37 parts per thousand (Brownsville, Texas) and temperatures that varied between 9.9 °C and 31.6 °C. Upon arrival in Texas, we measured an expected decrease in biofouling extent across both vessels but also a surprising increase in species richness (57 species were recorded), with small compositional differences between ships that did not exist prior to departure. Several species were recorded alive upon arrival, including non‐natives that are not known to be established in Texas waters. The physiological tolerance and associated risk of colonization have not yet been evaluated for these organisms, or for the broader species pool associated with a standing fleet (n > 200 ships) that may undergo similar movements. Nonetheless, a compelling case exists for vector management based on organism flux alone, to reduce the risk of coastwise and inter‐oceanic invasions.
A latitudinal gradient of beta diversity for exotic vascular plant species in North America
Authors: Qian Hong
Published: February 2009

Determining relationships between the ranges of introduced species and geographical and environmental factors is an important step in understanding the mechanisms and processes of the spread of introduced species. In this study, I examined the beta diversity and latitude relationship for all naturalized exotic species of vascular plants in North America at a continental scale. Beta diversity was calculated as the absolute value of the slope of the relationship between the natural logarithm of the Simpson index of similarity (lnS) and spatial distance between pairs of state‐level exotic floras within four latitudinal zones examined. Relative contributions of spatial distance and environmental difference to species turnover between exotic floras were examined. I found that beta diversity decreased monotonically from low to high latitudes: beta diversity for the southernmost zone was shallower than that for the northernmost zone by a factor of 2.6. Regression models of lnS in relation to spatial distance and environmental (climatic and topographical) difference for each latitudinal zone demonstrated that the explanatory power of these variables diminishes monotonically with latitude: the explained variance in lnS is 70.4%, 62.1%, 53.9%, and 33.9%, respectively, for the four latitudinal zones from south to north. For the southernmost zone, 58.3% of the variance in lnS is explained by climate variables and topography, and spatial distance explains only 2.3% of the variance. In contrast, for the northernmost zone, more than half the amount (22.5%) of the explained variance in lnS is attributable to spatial distance, and the remaining (18.9%) of the explained variance is attributable to climate variables and topography.
Range‐edge effects promote clonal growth in peripheral populations of the one‐sided wintergreen Orthilia secunda
Authors: Beatty Gemma E. , McEvoy Peter M. , Sweeney Oisín , Provan Jim
Published: February 2009

Existing in suboptimal conditions is a frequent occurrence for species inhabiting the cusp of their ecological range. In range‐edge populations of plants, the scarcity of suitable habitat may be reflected in small population sizes which may result in increased self‐pollination and/or inbreeding and an increase in the incidence of clonal reproduction. These factors may result in a decrease in levels of genetic diversity and a loss of potential adaptive variation that may compromise species’ ability to cope with changes in their environment, an issue that is particularly relevant today with the current concern surrounding global climate change and its effect on species’ distributional ranges. In the present study, we have compared the levels of clonal reproduction in the one‐sided wintergreen Orthilia secunda (L.) House in (1) populations from its main continuous distribution range, (2) populations occurring on the limits of the continuous range, and (3) peripheral populations outwith the species’ continuous distribution range. Range‐edge populations in Scotland and Sweden displayed significantly lower genotypic richness and diversity than those from the main area of the species’ distribution in these countries. Populations from Ireland, which occur in the temperate zone rather than the boreal conditions that are the preferred habitat for the species, and which represent relict populations left over from cooler periods in the Earth's history, displayed no within‐population genetic diversity, suggesting a complete lack of sexual reproduction. Furthermore, the genetic distinctiveness of the Irish populations, which contained alleles not found in either the Scottish or the Swedish populations, highlights the value of ‘trailing edge’ populations and supports the concept of ‘parochial conservation’, namely the conservation of species that are locally rare but globally common.
Selection of preadapted populations allowed Senecio inaequidens to invade Central Europe
Authors: Bossdorf Oliver , Lipowsky Annett , Prati Daniel
Published: February 2009

Invasive species often evolve rapidly in response to the novel biotic and abiotic conditions in their introduced range. Such adaptive evolutionary changes might play an important role in the success of some invasive species. Here, we investigated whether introduced European populations of the South African ragwort Senecio inaequidens (Asteraceae) have genetically diverged from native populations. We carried out a greenhouse experiment where 12 South African and 11 European populations were for several months grown at two levels of nutrient availability, as well as in the presence or absence of a generalist insect herbivore. We found that, in contrast to a current hypothesis, plants from introduced populations had a significantly lower reproductive output, but higher allocation to root biomass, and they were more tolerant to insect herbivory. Moreover, introduced populations were less genetically variable, but displayed greater plasticity in response to fertilization. Finally, introduced populations were phenotypically most similar to a subset of native populations from mountainous regions in southern Africa. Taking into account the species’ likely history of introduction, our data support the idea that the invasion success of Senecio inaequidens in Central Europe is based on selective introduction of specific preadapted and plastic genotypes rather than on adaptive evolution in the introduced range.
Combined modelling of distribution and niche in invasion biology: a case study of two invasive Tetramorium ant species
Authors: Steiner Florian M. , Schlick‐Steiner Birgit C. , VanDerWal Jeremy , Reuther Keefe D. , Christian Erhard , Stauffer Christian , Suarez Andrew V. , Williams Stephen E. , Crozier Ross H.
Published: February 2009

Spatial modelling of species distributions has become an important tool in the study of biological invasions. Here, we examine the utility of combining distribution and ecological niche modelling for retrieving information on invasion processes, based on species occurrence data from native and introduced ranges. Specifically, we discuss questions, concerning (1) the global potential to spread to other ranges, (2) the potential to spread within established invasions, (3) the detectability of niche differences across ranges, and (4) the ability to infer invasion history through data from the introduced range. We apply this approach to two congeneric pavement ants, Tetramorium sp.E (formerly T. caespitum (Linnaeus 1758)) and T. tsushimae Emery 1925, both introduced to North America. We identify (1) the potential of both species to inhabit ranges worldwide, and (2) the potential of T. sp.E and T. tsushimae, to spread to 23 additional US states and to five provinces of Canada, and to 24 additional US states and to one province of Canada, respectively. We confirm that (3) niche modelling can be an effective tool to detect niche shifts, identifying an increased width of T. sp.E and a decreased width of T. tsushimae following introduction, with potential changes in niche position for both species. We make feasible that (4) combined modelling could become an auxiliary tool to reconstruct invasion history, hypothesizing admixture following multiple introductions in North America for T. sp.E, and a single introduction to North America from central Japan, for T. tsushimae. Combined modelling represents a rapid means to formulate testable explanatory hypotheses on invasion patterns and helps approach a standard in predictive invasion research.
Rapid evolution in introduced species, ‘invasive traits’ and recipient communities: challenges for predicting invasive potential
Authors: Whitney Kenneth D. , Gabler Christopher A.
Published: February 2009

The damaging effects of invasive organisms have triggered the development of Invasive Species Predictive Schemes (ISPS). These schemes evaluate biological and historical characteristics of species and prioritize those that should be the focus of exclusion, quarantine, and/or control. However, it is not clear how commonly these schemes take microevolutionary considerations into account. We review the recent literature and find that rapid evolutionary changes are common during invasions. These evolutionary changes include rapid adaptation of invaders to new environments, effects of hybridization, and evolution in recipient communities. Strikingly, we document 38 species in which the specific traits commonly associated with invasive potential (e.g. growth rate, dispersal ability, generation time) have themselves undergone evolutionary change following introduction, in some cases over very short (≤ 10 year) timescales. In contrast, our review of 29 ISPS spanning plant, animal, and microbial taxa shows that the majority (76%) envision invading species and recipient communities as static entities. Those that incorporate evolutionary considerations do so in a limited way. Evolutionary change not only affects the predictive power of these schemes, but also complicates their evaluation. We argue that including the evolutionary potential of species and communities in ISPS is overdue, present several metrics related to evolutionary potential that could be incorporated in ISPS, and provide suggestions for further research on these metrics and their performance. Finally, we argue that the fact of evolutionary change during invasions begs for added caution during risk assessment.