Spatial autocorrelation and the analysis of invasion processes from distribution data: a study with the crayfish <Emphasis Type="Italic">Procambarus clarkii</Emphasis>

Complex spatial dynamics are frequent in invasive species; analyzing distribution patterns can help to understand the mechanisms driving invasions. We used different spatial regression techniques to evaluate processes determining the invasion of the red swamp crayfish Procambarus clarkii. We evaluated four a priori hypotheses on processes that may determine crayfish invasion: landscape alteration, connectivity, wetland suitability for abiotic and biotic features. We assessed the distribution of P. clarkii in 119 waterbodies in a recently invaded area. We used spatially explicit statistical techniques (spatial eigenvector mapping, generalized additive models, Bayesian intrinsic conditional autoregressive models) within an information-theoretic framework to assess the support of hypotheses; we also analyzed the pattern of spatial autocorrelation of data, model residuals, and eigenvectors. We found strong agreement between the results of spatial eigenvector mapping and Bayesian autoregressive models. Procambarus clarkii was significantly associated with the largest, permanent wetlands. Additive models suggested also association with human-dominated landscapes, but tended to overfit data. The results indicate that abiotic wetlands features and landscape alteration are major drivers of the species’ distribution. Species distribution data, residuals of ordinary least squares regression, and spatial eigenvectors all showed positive and significant spatial autocorrelation at distances up to 2,500 m; this may be caused by the dispersal ability of the species. Our analyses help to understand the processes determining the invasion and to identify the areas most at risk where screening and early management efforts can be focused. The comparison of multiple spatial techniques allows a robust assessment of factors determining complex distribution patterns.     

Factors affecting the local occurrence of the near-threatened bitterling (<Emphasis Type="Italic">Tanakia lanceolata</Emphasis>) in agricultural canal networks: strong attachment to its potential host mussels

Ecologically specialized species may be more susceptible to anthropogenic impacts than generalist species. Japan’s native bitterlings (subfamily Acheilognathinae), which are specialized to spawn on the gills of certain freshwater mussels, have been declining dramatically during the last few decades. To identify factors affecting the local occurrence of the threatened bitterling species Tanakia lanceolata, we measured its presence and absence, along with several environmental factors, at 68 sites within agricultural canal networks in the Lake Mikata basin, Fukui Prefecture, Japan. Based on the theoretical information approach of Akaike’s information criterion, generalized linear mixed models were constructed. These revealed that the species’ occurrence is strongly affected by five major factors: the presence of freshwater mussels Anodonta sp., water depth, floating plants coverage, the presence of bullfrogs, and submerged plants coverage. The probability of the presence of T. lanceolata was higher at shallower sites with lower floating plants coverage, located within channels containing mussel beds. These results suggest that mussel-containing channel systems are high-priority conservation zones for T. lanceolata.     

Dynamics of isolated <Emphasis Type="Italic">Saponaria bellidifolia</Emphasis> Sm. populations at northern range periphery

Four populations of Saponaria bellidifolia situated at the species’ northern range periphery (Apuseni Mountains, southeastern Carpathians) were monitored over a period of 5 years. They were chosen to represent different habitat types (rocky, fixed screes, open screes and grassy), disturbance regime (fire), and population sizes (categorized as large and small). The reproductive effort was quantified, and matrix models were used to describe the population dynamics and to assess population viability. Saponaria bellidifolia had very stable population dynamics in the harsh and stable abiotic conditions of the outcrops where populations occur. Habitat conditions exerted a notable influence on the species’ population reproductive performance, growth rate, and vital rates, whereas population size and climate did not have a clear-cut effect on the dynamics of the species. Saponaria bellidifolia maintains viable populations in the southeastern Carpathians, at its northern range periphery.     

Stem xylem features in three Quercus (Fagaceae) species along a climatic gradient in NE Spain

 Stem xylem features in two evergreen Quercus species (Q. coccifera and Q. ilex) and a deciduous one (Q. faginea) were analysed along an Atlantic-Mediterranean climatic gradient in which rainfall and winter cold experience strong variation. Mean maximum vessel diameter, vessel density, vessel element length, xylem transverse sectional area, Huber value (xylem transverse sectional area per leaf area unit), theoretical leaf specific conductivity (estimated hydraulic conductance per leaf area unit) and total leaf area were determined in 3-year-old branches. Q. faginea presented the widest vessels and the highest theoretical leaf specific conductivity while Q. coccifera showed the lowest total leaf area and the highest Huber value. Studied features did not exhibit significant correlations with mean minimum January temperature in any species but did show significant relationships with rainfall. In Q. coccifera, mean maximum vessel diameter, vessel element length and theoretical leaf specific conductivity increased with higher rainfall while vessel density decreased. Mean maximum vessel diameter and total leaf area in Q. ilex increased with precipitation whereas variables of Q. faginea did not show any significant trend. Results suggest that aridity, rather than minimum winter temperature, controls stem xylem responses in the studied evergreen species. Q. faginea traits did not show any response to precipitation, probably because this species develops deep roots, which in turn makes edaphic and topographic factors more important in the control of soil water availability. In response to aridity Q. coccifera only exhibits adjustment at a xylem level by reducing its water transport capacity through a reduction of vessel diameter without changing the amount of xylem tissue or foliage, whereas Q. ilex adjusts its water transport capacity in parallel to the foliage area. Received: 13 January 1997 / Accepted: 8 April 1997     

Summer-drought constrains the phenology and growth of two coexisting Mediterranean oaks with contrasting leaf habit: implications for their persistence and reproduction

This study analyses how coexisting evergreen and deciduous oaks adjust their phenology to cope with the stressful Mediterranean summer conditions. We test the hypothesis that the vegetative and reproductive growth of the winter deciduous (Quercus faginea Lam.) is more affected by summer drought than that of the evergreen [Quercus ilex L. subsp. ballota (Desf.) Samp.]. First, we assessed the complete aboveground phenology of both species during two consecutive years. Shoot and litter production and bud, acorn and secondary growth were monitored monthly. Second, we identified several parameters affected by summer conditions: apical bud size, individual leaf area (LA), leaf mass per area (LMA) and acorn yield in both species, and leaf-fall in Q. faginea; and analysed their variation over 10 years. Q. ilex performed up to 25% of shoot growth and most leaf development during summer, whereas Q. faginea completed most of both phenophases during spring. Secondary growth was arrested in summer under drought conditions. Approximately, 30–40% of bud and 40–50% of acorn growth was undertaken during summer in both species. Summer drought related to differences in LA, LMA and leaf senescence, but not to acorn yield. Both species had similar year-to-year patterns of acorn production, though yields were always lower in Q. faginea. Bud size decreased severely in both species during extremely dry years. In Q. ilex, bud size tended to alternate between years of large and small buds, and these patterns were followed by opposite trends in stem length. In Q. faginea, bud size was more stable through time. Q. ilex was more phenologically active during summer than Q. faginea, indicating a higher tolerance to drought. Furthermore, bud and fruit growth (the only two phenophases that both species performed during summer) were more severely affected by summer drought in Q. faginea than in the evergreen. The differential effects of summer drought on key phenophases for the persistence (bud growth) and colonization ability (fruit production) of both species may have consequences for their coexistence.     

Patterns of spatial genetic structure and diversity at the onset of a rapid range expansion: colonisation of the UK by the small red-eyed damselfly <Emphasis Type="Italic">Erythromma viridulum</Emphasis>

Species’ geographic ranges may vary in size in response to a change in environmental conditions. The specific genetic consequences of range expansions are context dependent, largely depending upon the rate of colonisation as well as the origins and numbers of founders, and the time since colonisation. Like other “charismatic” taxa, such as birds and lepidopterans, the distributions of odonates (dragonflies and damselflies) are well-known through substantial monitoring programmes co-ordinated by various societies. The small red-eyed damselfly Erythromma viridulum (Odonata: Zygoptera) has undergone a substantial, northward range expansion in Europe in the last 30 years and has recently-colonised two distinct areas in the UK. We quantify the immediate genetic consequences of this rapid colonisation by genotyping more than 1,400 E. viridulum from 39 sites across the northwest margin of this species’ geographic range. Levels of genetic diversity and spatial structure are impacted by this species recent range expansion and non-equilibrium conditions that drive weak genetic divergence, even at regional spatial scales. Populations of E. viridulum become less diverse towards the edge of this species’ distribution, presumably as a consequence of colonisation through a series of founder events. Specifically, there is a significant reduction in genetic diversity in the smallest, most recent focus of colonisation in the UK; however, there are generally low levels of genetic diversity across this E. viridulum’s northern range margin. While most populations are generally poorly differentiated, E. viridulum nonetheless consists of two distinct lineages that broadly differentiate between eastern and western Europe. Genetic divergence between the two UK colonisation foci are indicative of distinct immigration events from separate sources; however a general lack of spatial structure prevents us from pinpointing the specific origins of these migrant damselflies.     

Conservation of <Emphasis Type="Italic">Hymenocallis coronaria</Emphasis> genetic diversity in the presence of disturbance and a disjunct distribution

Evidence shows that dam construction has affected faunal species distribution and diversity in the southeastern U.S. However, the effects of this perturbation on aquatic flora of the region are heretofore uninvestigated. The objective for this research is to examine the effects of hydroelectric power generation and habitat characteristics on the size and distribution of populations of Hymenocallis coronaria (J. LeConte) Kunth (Amaryllidaceae), an emergent aquatic plant found in the southeastern United States, and to characterize its genetic variability in an effort to target conservation priorities. Multiple linear and logistic regression analyses show that hydropeaking does not have a significant effect on H. coronaria populations located downstream of dams, while other habitat variables associated with the streams are significantly positively related to population size and distribution. Analysis of 24 populations using seven universal cpDNA markers and six nDNA microsatellite markers indicates that the genetic structure for both genomes correlates with the location of a major gap in the species’ range, showing deep divergences in haplotype and population dendrograms between eastern and western regions. An AMOVA confirms that a substantial amount of genetic variation is found among regions, and very little variation is found within regions. The eastern and western regions have diverged for a significant time period, potentially due to the presence of a gene flow barrier in the middle of the species’ range caused by sub-standard habitat. Individual drainage basins contain unique cpDNA haplotypes and should be managed appropriately.     

Long-term changes in spatial patterns of emergent vegetation in a Mediterranean floodplain: natural versus anthropogenic constraints

This study describes the long-term changes of spatial patterns of cut-sedge (Cladium mariscus) and common reed (Phragmites australis) in the Spanish floodplain wetland Las Tablas de Daimiel. Using seven sets of aerial photographs, we determined changes in their spatial patterns (size of patches) between 1945 and 2001 that resulted from combinations of natural change and anthropogenic stress (irrigated agriculture, waste water discharge, fire, ploughing). Our approach consisted in using 1 ha cells as units of spatial resolution in principal coordinates of neighbour matrices and spatial correlograms to assess the spatial scale of interest and spatial patterns at (1) the whole wetland and (2) two areas of the wetland with locally contrasting biophysical settings and anthropogenic stress history. Results showed that vegetation spatial patterns were influenced by natural variability until the 1970s. Thereafter, anthropogenic perturbation became the main driver of vegetation change, especially in the lower part of the wetland where local impacts were stronger. Natural variability did not fragment cut-sedge patches, and the effects of biological traits were less important for its spatial pattern. By contrast, man-made change resulted in a marked cut-sedge cover decrease and patch fragmentation, and the importance of its biological traits on spatial patterns increased. The trends of reed spatial patterns were generally opposite to, but not as clear as those for, cut-sedge. The trends of spatial patterns were especially evident at very broad (3,500–10,000 m) and broad (1,000–3,400 m) spatial scales. Competition for space and abiotic factors (water quality and water depth) were not strong predictors of cover variability at the 1-ha scale, particularly in the lower area of the wetland. This suggests that other environmental variables need to be considered in spatially explicit modelling of vegetation spatial patterns in wetlands. Consideration of spatial hierarchies and species-specific ecological traits is paramount to the conservation of degraded wetlands.     

Global population genetic structure of the starlet anemone <Emphasis Type="Italic">Nematostella vectensis</Emphasis>: multiple introductions and implications for conservation policy

Distinguishing natural versus anthropogenic dispersal of organisms is essential for determining the native range of a species and implementing an effective conservation strategy. For cryptogenic species with limited historical records, molecular data can help to identify introductions. Nematostella vectensis is a small, burrowing estuarine sea anemone found in tidally restricted salt marsh pools. This species’ current distribution extends over three coast lines: (i) the Atlantic coast of North America from Nova Scotia to Georgia, (ii) the Pacific coast of North America from Washington to central California, and (iii) the southeast coast of England. The 1996 IUCN Red List designates N. vectensis as “vulnerable” in England. Amplified fragment length polymorphism (AFLP) fingerprinting of 516 individuals from 24 N. vectensis populations throughout its range and mtDNA sequencing of a subsample of these individuals strongly suggest that anthropogenic dispersal has played a significant role in its current distribution. Certain western Atlantic populations of N. vectensis exhibit greater genetic similarity to Pacific populations or English populations than to other western Atlantic populations. At the same time, F-statistics showing high degrees of genetic differentiation between geographically proximate populations support a low likelihood for natural dispersal between salt marshes. Furthermore, the western Atlantic harbors greater genetic diversity than either England or the eastern Pacific. Collectively, these data clearly imply that N. vectensis is native to the Atlantic coast of North America and that populations along the Pacific coast and in England are cases of successful introduction.     

Fish–environment Associations in the Coastal Waters of Andros Island, The Bahamas

Synopsis We surveyed fish communities and corresponding environmental conditions at three broadly similar coastal sites of eastern Andros Island, The Bahamas over a summer–winter–summer sequence to assess the relationship between detailed environmental features and fish species patterns. Environmental variables included covers of various benthic flora components, benthic flora diversity, floral canopy height, micro-crustacean diversity and density, water temperature, extent of destructive land-use and extent of invasion by human-introduced exotic terrestrial plants. Correspondence analysis (CA) indicated that spatial (site) differences in environmental characteristics were greater than temporal (seasonal) differences. Detrended canonical correspondence analysis (DCCA) was used to assess the strength of relationships between the environmental characteristics and the distribution patterns of 25 fish species. Environmental features deemed to be most important in influencing fish species patterns included benthic flora canopy height, extent of invasion by exotic terrestrial plants, cover of Batophora oerstedii, cover of Thalassia testudinum, turf cover, water temperature, micro-crustacean diversity, and micro-crustacean density. Based upon similarities in distribution patterns, fish species formed four clusters which, ultimately, reflected similarities in species’ feeding habits and preferences for habitats that likely maximize foraging success. We conclude that fish distribution patterns are related to environmental characteristics, and that anthropogenic coastal activity, by influencing coastal benthic characteristics, may influence the distribution and abundances of fish species in coastal habitats.     

Spatial Segregation of Congeneric Invaders in Central Pennsylvania, USA

Carduus acanthoides and Carduus nutans (plumeless and musk thistles) are among the most noxious weeds in the United States of America, presenting a serious challenge in cropping and pasture systems. Unfortunately, a lack of detailed spatial distribution information hampers both our ability to understand the factors affecting their invasive success, and the effectiveness of monitoring and management efforts. To examine patterns of distribution and co-occurrence at a local level, we sampled a 5000 km² area of central Pennsylvania that cut a transect across known areas of C. acanthoides and C. nutans infestation. A number of potential environmental explanatory variables were recorded and analyzed to examine whether they correlated with observed species distribution patterns. Patterns of forest density and spatial aggregation of the thistles were the primary covariates that significantly impacted both species’ distributions. The survey established that the frequency of sightings for each species diminished as the ranges converged, with only brief overlap: the two species are strongly negatively correlated in space. Understanding environmental correlates of infestation and the pattern of spatial dissociation of these two invasive species is an important step towards an improved understanding of the mechanisms underlying their invasive potential, and hence towards effective weed control.     

Potential impacts of climate change on habitat suitability of Fagus sylvatica L. forests in spain

Abstract

Fagus sylvatica forests are considered to be of Community interest according to Directive 92/43/EEC. Climate change predictions for Spain point to a warming scenario, coupled with decreasing rainfall, which may have an impact on their future distribution particularly at the extremes of its distribution area. Species distribution models incorporating bioclimatic, topographic and phytogeographic variables were used as predictors to assess their habitat suitability under current conditions and a climate change projection. Ten single models were generated and an ensemble-forecasting model was subsequently built by computing a consensus of single-model projections. The results revealed that ombrothermic indices are the main factors controlling the distribution of Spanish beech forests. They are highly vulnerable to climate change and could suffer a decline in their habitat suitability if climate trends observed are maintained in the future. The least favoured areas for them will be located close to the limit between the Temperate and Mediterranean climates, where they could suffer a loss of habitat suitability. Conversely, suitable new areas could be found mainly in western areas of the Cantabrian Range and in the Central Pyrenees.     

Predicting probability of occurrence and factors affecting distribution and abundance of three Ozark endemic crayfish species at multiple spatial scales

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Potential distribution of semi-deciduous forests in Castile and Leon (Spain) in relation to climatic variations

About 45% of the total surface area of the Castile and Leon region today can potentially be occupied by semi-deciduous forests, chiefly dominated by Quercus faginea Willd. and Quercus pyrenaica Lam. On the basis of extrapolated trends in annual mean temperature and precipitation in Castile and Leon observed over the 37-year period from 1961 to 1997 [del Río et al. 2005], predicted changes in the areas covered by Q. faginea and Q. pyrenaica forests in 2025, 2050 and 2075 were made. A decrease in Q. faginea forests may occur if observed trends in temperature and precipitation continue. With respect to Q. pyrenaica forests, they may increase in present Mediterranean areas and decreases in Temperate Submediterranean areas. In some cases, both types of forests could be replaced by deciduous forests. The predicted results in the natural distribution of vegetation types by the bioclimatic models can be used to establish policies for improved future nature conservation and land management.     

Space use patterns of mountain hare (<Emphasis Type="Italic">Lepus timidus</Emphasis>) on the Alps

Populations on the limits of species’ distribution can show different behavioral adaptations to strong ecological pressure than in the central part of the range. We investigated space use patterns of alpine mountain hare (Lepus timidus) at two areas on the southern edge of the species’ range. We monitored 34 hares between 2005 and 2008, estimating home range size, overlap, and site fidelity, and compared our results with space use in Scottish and North-European populations. Home ranges of mountain hares did not differ between two study areas with different habitat types. Subadult animals used larger ranges than adults and both age groups reduced home range size in autumn, a period that might be critical for hares due to changes in diet and/or high energy expenditure during the previous breeding season. Home ranges in these alpine populations were smaller than in Scandinavian populations but within the range of populations in different habitat types in Scotland. Seasonal home ranges overlapped considerably, but differed among the sexes: male–female overlap was higher than same sex (male–male and female–female) spatial overlap. Seasonal shifts of home ranges were small, and site fidelity remained high over the seasons, suggesting that resource distribution remained constant throughout the year and that the knowledge of an intensively frequented area is an important element of habitat quality. We concluded that habitat structure and availability of mates interact in affecting mountain hare space use in alpine habitats.     

Environmental constraints on the invasion of <Emphasis Type="Italic">Triadica sebifera</Emphasis> in the eastern United States: an experimental field assessment

Identifying the environmental constraints that affect the distribution of an invasive species is fundamental to its effective control. Triadica sebifera (Chinese tallow tree) has invaded the southeastern United States, but its potential for further range and habitat extension has been unresolved. We explored experimentally environmental factors in macro- and microhabitats that affect its persistence at five widely separated sites along the Atlantic seaboard of the United States and at two sites inland; three sites occur well beyond the tree’s current range. At each site, seeds and young vegetative plants (0.5–0.65 m tall) of T. sebifera were placed in four microhabitats (closed-canopy upland, closed-canopy lowland, open-canopy upland, and open-canopy lowland). Plant growth, leaf CO₂ assimilation rates, leaf N concentrations and δ¹³C ratios, and stem water potential were measured for two growing seasons. Percent seed germination was consistently higher in open-canopy microhabitats and lowest at northern and inland sites. T. sebifera grew in all open-canopy microhabitats, even 300–500 km beyond its current distribution. Plant growth in closed-canopy habitats was lower, attributable to lower carbon gain per unit leaf area in shaded compared with open-canopy environments, especially at northern and inland sites. Neither competition, other than canopy shade, nor grazing was a key constraint on distribution at any scale. Our results demonstrate that T. sebifera is dispersal limited at landscape scales but limited locally by dispersal and overstory shade; it has yet to occupy the full extent of its new range in North America. Quantifying environmental factors both within and well beyond a species’ current range can effectively highlight the limits on its distribution.     

Drainage-independent genetic structure and high genetic diversity of endangered freshwater pearl mussels (<Emphasis Type="Italic">Margaritifera margaritifera</Emphasis>) in northern Europe

Freshwater pearl mussels (Margaritifera margaritifera) are among the most critically threatened bivalve molluscs worldwide. An understanding of spatial patterns of genetic diversity is crucial for the development of integrative conservation strategies. We used microsatellites to study the genetic diversity and differentiation of 14 populations of M. margaritifera in central Sweden, an area which was described as a major secondary contact zone in postglacial colonisation for other species. Genetic diversity of Swedish pearl mussel populations was much greater than in central and southern Europe but similar to the genetic diversity observed in the northeastern portion of their European range. Genetic differentiation among populations was pronounced but to a large extent independent from present-day drainage systems. The complex patterns of genetic diversity and differentiation in pearl mussel seem to be strongly influenced by the species’ high degree of specialisation and extraordinary life history strategy which involves facultative hermaphrodism and an obligatory encystment stage on a host fish. Genetic drift effects and anthropogenic disturbances resulting in reduction of population size and loss of connectivity are less pronounced in northern pearl mussel populations compared to those in central and southern Europe.     

Environmental factors prevail over dispersal constraints in determining the distribution and assembly of Trichoptera species in mountain lakes

Aiming to elucidate whether large‐scale dispersal factors or environmental species sorting prevail in determining patterns of Trichoptera species composition in mountain lakes, we analyzed the distribution and assembly of the most common Trichoptera (Plectrocnemia laetabilis, Polycentropus flavomaculatus, Drusus rectus, Annitella pyrenaea, and Mystacides azurea) in the mountain lakes of the Pyrenees (Spain, France, Andorra) based on a survey of 82 lakes covering the geographical and environmental extremes of the lake district. Spatial autocorrelation in species composition was determined using Moran's eigenvector maps (MEM). Redundancy analysis (RDA) was applied to explore the influence of MEM variables and in‐lake, and catchment environmental variables on Trichoptera assemblages. Variance partitioning analysis (partial RDA) revealed the fraction of species composition variation that could be attributed uniquely to either environmental variability or MEM variables. Finally, the distribution of individual species was analyzed in relation to specific environmental factors using binomial generalized linear models (GLM). Trichoptera assemblages showed spatial structure. However, the most relevant environmental variables in the RDA (i.e., temperature and woody vegetation in‐lake catchments) were also related with spatial variables (i.e., altitude and longitude). Partial RDA revealed that the fraction of variation in species composition that was uniquely explained by environmental variability was larger than that uniquely explained by MEM variables. GLM results showed that the distribution of species with longitudinal bias is related to specific environmental factors with geographical trend. The environmental dependence found agrees with the particular traits of each species. We conclude that Trichoptera species distribution and composition in the lakes of the Pyrenees are governed predominantly by local environmental factors, rather than by dispersal constraints. For boreal lakes, with similar environmental conditions, a strong role of dispersal capacity has been suggested. Further investigation should address the role of spatial scaling, namely absolute geographical distances constraining dispersal and steepness of environmental gradients at short distances.     

<Emphasis Type="Italic">Stemonurus corrugatus</Emphasis> (Stemonuraceae,Icacinaceae s.l.) a new species from Sarawak

Summary   Stemonurus corrugatus Utteridge & Schori is described and illustrated as a new species from Sarawak, Malaysia. The new species is similar to S. grandifolius, S. scorpioides, and S. umbellatus, and morphological differences among the taxa are discussed. A distribution map and notes on the new species’ conservation status are provided.