Alien spider introductions to Europe supported by global trade

Global trade is permanently ongoing and increases its volume every year. In this study, the occurrence of 87 unintentionally introduced spider species alien to Europe is analysed. The analysis includes (1) the introduction potential of six different origin areas of the world according to trade volume, area size, and geographical distance; (2) the body size of native and alien species; and (3) occurrence in or at buildings (synanthropic) or in natural habitats. We found the eastern Palearctic as the most influencing origin area with 44 introduced spider species to Europe. The eastern Palearctic and the Indomalayan provided a significantly higher number of introductions than expected, whereas the Nearctic, Neotropical, and Afrotropical provided a significantly lower number of introduced species than expected. This can be explained with their lower trade volume, smaller area, larger geographical distance to Europe, and stronger climate differences to Europe. Comparing the body size of introduced and native European spider species of the same family, we found for Theridiidae significantly larger alien spiders and for all other tested families a trend to a larger body size of alien species compared to the native spiders. The family affiliation of alien spiders is the most important factor for synanthropic occurrence in Europe. On the base of a very conservative estimation of spider species introductions to Europe combined with possible effects of climate change, we predict for the near future a permanent increase in the number of alien spider species in Europe.     

Ballooning propensity of canopy and understorey spiders in a mature temperate hardwood forest

1. Spiders frequently disperse and colonise habitats through ballooning, a passive aerial dispersal process. Ballooning is pre‐eminent in open habitat spider communities and its propensity can be modulated by habitat conditions and availability, and by life‐history traits such as body size, degree of specialisation, and feeding behaviour. 2. Using spiders from the canopy and understorey of a north‐temperate hardwood forest as a model system, our main objectives were to detect if foliage spiders of a mature forest disperse through ballooning, and identify life‐history traits that influence ballooning propensity. 3. Our results demonstrate that foliage spiders living in the canopy and understorey of a mature forest do balloon, and in some cases have very high ballooning propensities similarly to open field spiders. Species level models showed that small body size had a strong positive effect on ballooning for juveniles of species with large‐bodied adults, while individuals of small‐bodied species initiated ballooning regardless of size, habitat or development stage. A generalised linear mixed model indicated that small size web‐building spiders from the Retro Tibial Apophysis (RTA) and Orbicularia clades had the highest propensity for foliage spiders of this north‐temperate hardwood forest. 4. In conclusion, we provide the first demonstration that forest spiders can have high ballooning propensities and that ballooning propensity is negatively affected by body size and positively affected by the prominent use of silk to catch prey. However, spiders originating from the canopy and understorey of a north‐temperate hardwood forest did not differ in their ballooning propensities.     

Responses of foliage‐living spider assemblage composition and traits to a climatic gradient in Themeda grasslands

For speciose, but poorly known groups, such as terrestrial arthropods, functional traits present a potential avenue to assist in predicting responses to environmental change. Species turnover is common along environmental gradients, but it is unclear how this is reflected in species traits. Community‐level change in arthropod traits, other than body size, has rarely been explored across spatial scales comparable to those examined here. We hypothesized that the composition and morphological traits of spider assemblages would differ across a gradient of climate and habitat structure. We examined foliage‐living spider assemblages associated with Themeda triandra grasslands along a 900 km climatic gradient in south‐eastern Australia. We used sweep‐netting to collect T. triandra‐associated spiders and counted juveniles and identified adults. We also measured morphological traits of adult spiders and noted their hunting mode. Associations with measures of habitat structure were less consistent than relationships with climate. Both juvenile and adult spiders were more abundant in warmer sites, although species richness was not affected by temperature. We found distinct turnover in species composition along the climatic gradient, with hunting spiders, particularly crab spiders (Thomisidae), making up a greater proportion of assemblages in warmer climates. A range of traits of spiders correlated with the climatic gradient. For example, larger spider species and species that were active hunters were more common in warmer climates. Changes in morphological traits across species, rather than within species drove the morphology‐climate relationship. Strong climate‐trait correlations suggest that it may be possible to predict changes in functional traits of assemblages in response to anthropogenic disturbances such as climate change.     

Environmental and spatial drivers of spider diversity at contrasting microhabitats

The relative importance of environmental and spatial drivers of animal diversity varies across scales, but identifying these scales can be difficult if a sampling design does not match the scale of the target organisms' interaction with their habitat. In this study, we quantify and compare the effects of environmental variation and spatial proximity on ground‐dwelling spider assemblages sampled from three distinct microhabitat types (open grassland, logs, trees) that recur across structurally heterogeneous grassy woodlands. We used model selection and multivariate procedures to compare the effects of different environmental attributes and spatial proximity on spider assemblages at each microhabitat type. We found that species richness and assemblage composition differed among microhabitat types. Bare ground cover had a negative effect on spider richness under trees, but a positive effect on spider richness in open grassland. Turnover in spider assemblages from open grassland was correlated with environmental distance, but not geographic distance. By contrast, turnover in spiders at logs and trees was correlated with geographic distance, but not environmental distance. Our study suggests that spider assemblages from widespread and connected open grassland habitat were more affected by environmental than spatial gradients, whereas spiders at log and tree habitats were more affected by spatial distance among these discrete but recurring microhabitats. Deliberate selection and sampling of small‐scale habitat features can provide robust information about the drivers of arthropod diversity and turnover in landscapes.     

Impacts of thermal mismatches on chytrid fungus Batrachochytrium dendrobatidis prevalence are moderated by life stage,body size,elevation and latitude

Global climate change is increasing the frequency of unpredictable weather conditions; however, it remains unclear how species‐level and geographic factors, including body size and latitude, moderate impacts of unusually warm or cool temperatures on disease. Because larger and lower‐latitude hosts generally have slower acclimation times than smaller and higher‐latitude hosts, we hypothesised that their disease susceptibility increases under ‘thermal mismatches’ or differences between baseline climate and the temperature during surveying for disease. Here, we examined how thermal mismatches interact with body size, life stage, habitat, latitude, elevation, phylogeny and International Union for Conservation of Nature (IUCN) conservation status to predict infection prevalence of the chytrid fungus Batrachochytrium dendrobatidis (Bd) in a global analysis of 32 291 amphibian hosts. As hypothesised, we found that the susceptibility of larger hosts and hosts from lower latitudes to Bd was influenced by thermal mismatches. Furthermore, hosts of conservation concern were more susceptible than others following thermal mismatches, suggesting that thermal mismatches might have contributed to recent amphibian declines.     

Effects of the abandonment of alpine summer farms on spider assemblages (Araneae)

In parallel with the current effects and responses to climate change ongoing changes of land use strongly affect alpine areas. The aim of this study was to analyse spider assemblages occurring on farmlands with differing stages of land use intensity. We collected the ground-dwelling spider fauna of semi-natural grasslands in currently farmed and abandoned farmland in the alpine zone of Hardangervidda, Norway, using pitfall traps. Trapping during the whole vegetation period resulted in 1,548 individuals belonging to 39 species of spiders. Linyphiids and lycosids dominated. The total number of species differ little between sites, but there was a general trend of increasing proportions of lycosids, gnaphosids and thomisids individuals and species, and a decrease in the proportion of linyphiids with farmland abandonment. Two main groupings of spider assemblages were found using a principal component analysis: One grouping was characteristic of intensely disturbed sites, mainly dominated by typical pioneer species. The other was characteristic of abandoned and less disturbed sites, dominated by widespread species. The abandonment of summer farms led to a succession in spider assemblages, including a decline in spider species with a high ballooning activity and an increase of species with a larger body size. We suggest that the main reason lies in the absence of disturbance by grazing including differing vegetation architecture and the proportion of bare ground with abandonment. Spider assemblages react quickly to environmental changes that occur in alpine habitats after abandonment. Thus, it is necessary to include spiders and other invertebrate animal indicator groups in field studies and experiments dealing with grazing impacts on alpine habitats.     

Geographic variation in body form of prehistoric Jomon males in the Japanese archipelago: Its ecogeographic implications

Diversity of human body size and shape is often biogeographically interpreted in association with climatic conditions. According to Bergmann's and Allen's rules, populations in regions with a cold climate are expected to display an overall larger body and smaller/shorter extremities than those in warm/hot environments. In the present study, the skeletal limb size and proportions of prehistoric Jomon hunter‐gatherers, who extensively inhabited subarctic to subtropical areas in the ancient Japanese archipelago, were examined to evaluate whether or not the inter‐regional differences follow such ecogeographic patterns. Results showed that the Jomon intralimb proportions including relative distal limb lengths did not differ significantly among five regions from northern Hokkaido to the southern Okinawa Islands. This suggests a limited co‐variability of the intralimb proportions with climate, particularly within genealogically close populations. In contrast, femoral head breadth (associated with body mass) and skeletal limb lengths were found to be significantly and positively correlated with latitude, suggesting a north‐south geographical cline in the body size. This gradient therefore comprehensively conforms to Bergmann's rule, and may stem from multiple potential factors such as phylogenetic constraints, microevolutionary adaptation to climatic/geographic conditions during the Jomon period, and nutritional and physiological response during ontogeny. Specifically, the remarkably small‐bodied Jomon in the Okinawa Islands can also be explained as an adjustment to subtropical and insular environments. Thus, the findings obtained in this study indicate that Jomon people, while maintaining fundamental intralimb proportions, displayed body size variation in concert with ambient surroundings. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

The effects of development,vegetation‐type conversion,and fire on low‐elevation Southern California spider assemblages

California sage scrub (CSS), a native ecosystem type of low‐elevation areas of Southern California, is increasingly threatened by urban development, altered fire regimes, and vegetation‐type conversion to non‐native grasslands. Using pitfall traps, we examined how suburbanization, type conversion, and fire influence ground‐dwelling spider assemblages in eastern Los Angeles County, CA, by surveying spiders in three habitats (CSS, non‐native grasslands, and suburban areas) before and after a fire that occurred in a small portion of our study site. Spider assemblages in the suburban habitat differed from those in CSS and non‐native grassland habitats, but CSS and grassland assemblages did not significantly differ. This suggests that the urban development, but not vegetation‐type conversion to non‐native grasslands, has significant effects on ground‐dwelling spider assemblages. Fire had no observable effect on assemblages. Because ground‐dwelling spiders were not impacted by fire and type conversion, increased fire frequencies, which often result in the establishment of non‐native grasses, may not deleteriously influence this animal group, a differing pattern from other taxonomic groups. However, the rapid urban development occurring in low‐elevation areas of Southern California means that species requiring non‐suburban sites for their survival (15 species, 24.1%) may be threatened and require conservation assessment.     

Body size explains interspecific variation in size–latitude relationships in geographically widespread beetle species

1. In most birds and mammals, larger individuals of the same species tend to be found at higher latitudes, but in insects, body size–latitude relationships are highly variable. 2. Recent studies have shown that larger‐bodied insect species are more likely to decrease in size when reared at increased temperature, compared with smaller‐sized species. These findings have led to the prediction that a positive relationship between body size and latitude should be more prevalent in larger‐bodied insect species. 3. This study measured the body size of > 4000 beetle specimens (12 species) collected throughout North America. Some beetle species increased in size with latitude, while others decreased. Importantly, mean species body size explained c. 30% of the interspecific variation in the size–latitude response. 4. As predicted, larger‐bodied beetle species were more likely to show a positive relationship between body size and latitude (Bergmann's rule), and smaller‐bodied species were more likely to show a negative body size–latitude relationship (inverse Bergmann's rule). 5. These body size–latitude patterns suggest that size‐specific responses to temperature may underlie global latitudinal distributions of body size in Coleoptera, as well as other insects.     

The global relationship between climate,net primary production and the diet of spiders

Aim We compiled data on prey utilization of spiders at a global scale to better understand the relationship between current climate or net primary production (NPP) and diet breadth, evenness and composition in spiders. We test whether the productivity and the diversity–climatic‐stability (DCS) hypotheses focusing on diversity patterns may also explain global patterns in prey utilization by web‐building and cursorial spiders. Location A global dataset of 95 data points from semi‐natural and natural terrestrial habitats spanning 41.3° S to 56.1° N. Methods We collected data on spider prey (29 groups, mostly order‐level invertebrate taxa) through extensive literature research to identify the relationship between climatic conditions and NPP and spider diets based on 66 studies of prey composition in 82 spider species. Results The number of prey groups in spider diets was positively related to NPP, after accounting for differences in sampling effort in the original studies. In general, diet breadth was significantly higher for spider species in tropical environments. Prey individuals in spider diets were more evenly distributed among different prey groups in warmer environments with lower fluctuations in precipitation. Collembola and other spiders were more common prey for spiders with a cursorial hunting mode. Myriapoda and Collembola were more common prey in cooler climates with more stable precipitation, whereas Isoptera, Lepidoptera, Psocoptera and Coleoptera showed the opposite pattern. Main conclusions The positive relationship between diet breadth and NPP and the negative relationship between prey evenness and seasonality in precipitation support the productivity and the DCS hypotheses, respectively. This effect on global patterns of invertebrate predator–prey interactions suggests that trophic interactions between spiders and their prey are sensitive to climatic conditions. Climatic conditions may not only affect spider community composition, but also considerably alter the functional role of these abundant invertebrate predators in terrestrial ecosystems.     

Broad‐scale geographic patterns in body size and hind wing development of western Palaearctic carabid beetles(Coleoptera: Carabidae)

Research into large‐scale ecological rules has a long tradition but has received increasing attention over the last two decades. Whereas environmental, especially climatic, influences on the geographic distribution of species traits such as body size are well understood in mammals and birds, our knowledge of the determinants and mechanisms which shape spatial patterns in invertebrate traits is still limited. This study analyzes macroecological patterns in two traits of the highly diverse invertebrate taxon of carabid beetles: body size and hind wing development, the latter being directly linked to species’ dispersal abilities. We tested for potential impacts of environmental variables (spatial, areal, topographic and climate‐related) representing both contemporary conditions and historical processes on large‐scale patterns in the two traits. Regression models revealed hump‐shaped relationships with latitude for both traits in the categories 1) all species, 2) widespread and 3) endemic (restricted‐range) species: body size and the proportion of flightless species increased from northern towards southern Europe and then decreased towards North Africa. The shared and independent influence of environmental factors was analyzed by variation partitioning. While contemporary environmental productivity and stability (represented by measures of ambient energy and water energy balance) had strong positive relationships with carabid body size, patterns in hind wing development were most notably influenced by topography (elevation range). Regions with high elevation range and low historical climate variability (since the last ice age), which likely offer long‐term stable habitats (i.e. glacial refugia), coincide with regions with high proportions of flightless species. Thus geographic patterns in carabid traits tend to be formed not only by recent climate but also by dispersal and historical climate and processes (i.e. glaciations and postglacial colonization).     

Temperature‐driven color lightness and body size variation scale to local assemblages of European Odonata but are modified by propensity for dispersal

1. Previous macrophysiological studies suggested that temperature‐driven color lightness and body size variations strongly influence biogeographical patterns in ectotherms. However, these trait–environment relationships scale to local assemblages and the extent to which they can be modified by dispersal remains largely unexplored. We test whether the predictions of the thermal melanism hypothesis and the Bergmann's rule hold for local assemblages. We also assess whether these trait–environment relationships are more important for species adapted to less stable (lentic) habitats, due to their greater dispersal propensity compared to those adapted to stable (lotic) habitats.
2. We quantified the color lightness and body volume of 99 European dragon‐ and damselflies (Odonata) and combined these trait information with survey data for 518 local assemblages across Europe. Based on this continent‐wide yet spatially explicit dataset, we tested for effects temperature and precipitation on the color lightness and body volume of local assemblages and assessed differences in their relative importance and strength between lentic and lotic assemblages, while accounting for spatial and phylogenetic autocorrelation.
3. The color lightness of assemblages of odonates increased, and body size decreased with increasing temperature. Trait–environment relationships in the average and phylogenetic predicted component were equally important for assemblages of both habitat types but were stronger in lentic assemblages when accounting for phylogenetic autocorrelation.
4. Our results show that the mechanism underlying color lightness and body size variations scale to local assemblages, indicating their general importance. These mechanisms were of equal evolutionary significance for lentic and lotic species, but higher dispersal ability seems to enable lentic species to cope better with historical climatic changes. The documented differences between lentic and lotic assemblages also highlight the importance of integrating interactions of thermal adaptations with proxies of the dispersal ability of species into trait‐based models, for improving our understanding of climate‐driven biological responses.

     

Factors shaping latitudinal patterns in communities of arboreal spiders in northern Europe

Predator effects on herbivores are often referred to as examples of biotic interactions that weaken with latitude, but more studies are needed to test for the generality of this pattern. To further the understanding of large‐scale geographical patterns in abundance and diversity of predatory arthropods, from 2008–2011 we explored spider communities in the canopies of primary forest trees of the boreal zone (Pinus sylvestris, Picea abies, Betula pubescens and B. pendula) along five latitudinal gradients in northern Europe, from 59 to 70°N and from 10 to 60°E. The abundance of arboreal spiders in Norway and Finland was about a half of that in Russia, presumably due to more intensive forest management in Scandinavia. The abundance, taxonomic and functional diversity of arboreal spiders generally decreased with latitude; however, actual weather conditions during the study years had little effect on this pattern. Coniferous species supported higher abundance and diversity of arboreal spiders than birches, but the poleward decrease in either abundance or taxonomic diversity of arboreal spiders did not differ between coniferous and deciduous tree species. In contrast, functional diversity on birches decreased with latitude greater than on coniferous trees. Euryphagous spiders showed stronger decrease with latitude in terms of both abundance and taxonomic diversity than more specialized (steno‐ and oligophagous) spiders. We attribute the general decrease in density and diversity of spiders with latitude to an increased pressure from apex predators (birds) rather than to direct effects of climate or changes in prey abundance. The abundance of spiders declined with the latitude to the greater extent than the densities of their potential prey did, suggesting a decrease in the strength of predator–prey interactions towards the north.     

Macroecological patterns of sexual size dimorphism in turtles of the world

Sexual size dimorphism (SSD) is a well‐documented phenomenon in both plants and animals; however, the ecological and evolutionary mechanisms that drive and maintain SSD patterns across geographic space at regional and global scales are understudied, especially for reptiles. Our goal was to examine geographic variation of turtle SSD and to explore ecological and environmental correlates using phylogenetic comparative methods. We use published body size data on 135 species from nine turtle families to examine how geographic patterns and the evolution of SSD are influenced by habitat specialization, climate (annual mean temperature and annual precipitation) and climate variability, latitude, or a combination of these predictor variables. We found that geographic variation, magnitude and direction of turtle SSD are best explained by habitat association, annual temperature variance and annual precipitation. Use of semi‐aquatic and terrestrial habitats was associated with male‐biased SSD, whereas use of aquatic habitat was associated with female‐biased SSD. Our results also suggest that greater temperature variability is associated with female‐biased SSD. In contrast, wetter climates are associated with male‐biased SSD compared with arid climates that are associated with female‐biased SSD. We also show support for a global latitudinal trend in SSD, with females being larger than males towards the poles, especially in the families Emydidae and Geoemydidae. Estimates of phylogenetic signal for both SSD and habitat type indicate that closely related species occupy similar habitats and exhibit similar direction and magnitude of SSD. These global patterns of SSD may arise from sex‐specific reproductive behaviour, fecundity and sex‐specific responses to environmental factors that differ among habitats and vary systematically across latitude. Thus, this study adds to our current understanding that while SSD can vary dramatically across and within turtle species under phylogenetic constraints, it may be driven, maintained and exaggerated by habitat type, climate and geographic location.     

Latitudinal and altitudinal body size variation among north-west European land snail species

Aim To investigate latitudinal and altitudinal patterns in body size variation among north‐west European land snail species, as well as factors influencing such patterns. Location Latitudinal patterns were investigated in north‐west Europe from the British Isles and France in the west to Finland, Poland, Slovakia and Hungary in the east and from Norway in the north to France (with the exception of the Mediterranean part of the country), Switzerland, Austria and Hungary in the south. Altitudinal patterns were examined in the Alps in Austria and Switzerland. Methods Data on latitudinal ranges of 366 north‐west European land snail species, on altitudinal ranges of 175 species from Austria and 150 species from Switzerland, and on their body sizes were used to test for the presence of interspecific latitudinal or altitudinal body size patterns. Four methods, Stevens’ method, the midpoint method, the across‐species method, and a phylogenetically controlled analysis (CAIC) were applied. Results As a result of the predominance of some small bodied clades at higher latitudes and some large bodied clades at lower latitudes, body size of north‐west European land snails decreases significantly with increasing latitude. However, little of the body size variation across species is explained by latitude and the phylogenetically controlled analysis showed that the decrease of body size with increasing latitude is not a result of repeated and independent evolution of an association between body size and latitude in many clades. There is no significant correlation between body size of land snail species and altitude in the Alps although a negative correlation of body size and altitude is frequent within species. Main conclusion If phylogenetic effects are controlled for, neither latitudinal nor altitudinal patterns in body size could be found. Bergmann's rule, which predicts a positive correlation between body size of species and latitude, could not be confirmed for north‐west European land snails.     

Water limitation prevails over energy in European diversity gradients of sheetweb spiders (Araneae: Linyphiidae)

Across large spatial scales, species richness in many taxa is mainly determined by climatic variables. However, some of the mechanisms behind large-scale patterns of species richness and abundance are expected to act on the community level, and on a smaller scale than the resolution of the data commonly used for deriving these patterns. We studied the distribution of sheetweb spiders (Araneae: Linyphiidae) across Europe using both standardised samples from local habitats and large-scale inventories. In the first approach, we analysed species and individual numbers from standardised pitfall traps from 17 locations distributed from northern Sweden to Spain and Greece. We also calculated Simpson indices to correct for different activity densities. Additionally, we analysed whether diversity of sheetweb spiders is sensitive to habitat type. In the second approach, we investigated the known sheetweb spider species richness of European countries and large islands. In both datasets, species richness of sheetweb spiders reached a maximum at about 55°N and declined towards the Mediterranean and the Arctic. In addition, species richness decreased from western (maritime) to eastern (continental) regions. Also Simpson diversity showed a hump-shaped relation to latitude, and was the only variable influenced by habitat type. In contrast to species richness and diversity, activity density increased monotonously with latitude. Towards the north, sheetweb spiders are likely limited by energy availability, towards the south, water limitation as well as bottom-up and top-down community interactions may reduce sheetweb spiders. Accordingly, their diversity does not follow the pattern of vertebrates, large insects and aquatic organisms, which depend more strongly on energy availability.     

Coping with the cold: energy storage strategies for surviving winter in freshwater fish

For many ectothermic animals, the acquisition, storage and depletion of lipids is integral to successfully coping with reduced metabolic rates and activity levels associated with cold, winter periods. In fish, lipids are crucial for overwinter survival and successful reproduction. The timing and magnitude of seasonal lipid storage should therefore vary predictably among fish with different thermal preferences and spawn times. Small‐ and large‐bodied fish should also face different constraints associated with season that influence lipid cycling. However, much work to date has been species‐ and location‐specific and a general conceptual model for the seasonal energy budgets of freshwater fish is lacking. Here, we conducted a comprehensive literature review of seasonal lipid levels in freshwater fishes. We predicted that warm and cool water species would be more likely to demonstrate peak lipid levels during warm months than cold water species, and expected a larger magnitude of annual lipid cycling in warm and cool water compared to cold water fish. We also expected dampened lipid cycling in larger fish due to their lower mass‐specific metabolic rates. Observed patterns in the timing and magnitude of lipid storage contradicted our prediction because lipid cycling was widespread across species, despite thermal guild, with peak lipid levels commonly occurring during warmer months, even in cold water fish. For body size effects, larger bodied fish species had dampened seasonal lipid cycling, as predicted. We developed a conceptual framework describing how the ‘scope’ for variation in annual lipid cycling changes with body size both among and within species in order to guide future work. Together, our findings suggest that energy acquired during warm months is broadly important for overwinter survival and reproduction in fishes, and provide a new perspective on the differential constraints and physiological responses to seasonality among freshwater fish. Improving our understanding of these dynamics is especially pressing given that a changing global climate is anticipated to alter existing seasonal signals.     

Factors influencing the appearance of spider (Araneae) and beetle (Coleoptera) assemblages in nests of great reed warbler Acrocephalus arundinaceus

The appearance of spider (Araneae) and beetle (Coleoptera) assemblages found in nests of great reed warbler Acrocephalus arundinaceus was studied, firstly to investigate breeding success and the amount of precipitation as potential factors which might affect the abundance and species richness of both groups. In addition, we compared the diversity of spider and beetle assemblages between nests found in different reed habitats, and considered the position of nests (above water or dry ground). In this study we selected five different randomly chosen reed habitats: two mining ponds, two small canals and one large canal. Great Reed Warbler nests were collected either shortly after fledging, or after the clutch had failed. Altogether, 12 species of spider and 19 species of beetle were collected. In both groups there was no significant difference in abundance between successful, lost and cuckoo-parasitized nests; however, there was a significant difference in species richness between the three nest categories in spider assemblages, which was not the case in beetle assemblages. The amount of precipitation did not affect beetle or spider abundance; only the species richness of spiders showed significant growth. Furthermore, we found no significant relationship between vegetation cover and the species richness and abundance of spiders and beetles. The diversity of both groups differed significantly according to reed habitat: beetle assemblages were most diverse by the large canal and spiders at the mining ponds.     

Importance of habitat structure to the arthropod food-web in Douglas-fir canopies

This study tested the hypothesis that habitat structure dictates the distribution and community composition of arboreal arthropods. A diverse arthropod assemblage of Douglas-fir canopies, which included Araneae, Psocoptera, Collembola and Homoptera, was chosen as a model system. Habitat structural diversity, defined as needle density and branching complexity of Douglas-fir branches, was manipulated in a four-month experiment by needle removal, thinning and tying of branches. Abundance of canopy spiders declined significantly following needle density reduction and branch thinning, branch tying significantly increased spider abundance. Distinct habitat utilization patterns were found among individual spider guilds. Orb weavers (Araneidae) dominated spider assemblages in structurally simple habitats, whereas tied branches were colonized primarily by sheet-web weavers (Linyphiidae) and nocturnal hunting spiders (Anyphaenidae and Clubionidae). Spider species richness and average body size of several spider species increased in structurally more complex habitats. Arboreal spiders appeared to be limited by strong bottom-up effects in the form of habitat quality and, to a lesser degree, prey availability. Habitat manipulations did not affect densities or biomass of flying arthropod colonists in the branch vicinity. Needle removal and branch thinning led to a significant decline in the abundance of Psocoptera and Collembola. Tying of branches resulted in an eight-fold increase in Collembola numbers, organisms most sensitive to habitat alterations. Canopy habitat structure modified vertical dispersal of Collembola from forest litter, which may have significant implications for arboreal consumers. Our results lend strong support to the importance of habitat structural diversity in explaining general patterns of arthropod abundance and diversity on plants.     

Will changes in phenology track climate change? A study of growth initiation timing in coast Douglas‐fir

Under climate change, the reduction of frost risk, onset of warm temperatures and depletion of soil moisture are all likely to occur earlier in the year in many temperate regions. The resilience of tree species will depend on their ability to track these changes in climate with shifts in phenology that lead to earlier growth initiation in the spring. Exposure to warm temperatures (‘forcing’) typically triggers growth initiation, but many trees also require exposure to cool temperatures (‘chilling’) while dormant to readily initiate growth in the spring. If warming increases forcing and decreases chilling, climate change could maintain, advance or delay growth initiation phenology relative to the onset of favorable conditions. We modeled the timing of height‐ and diameter‐growth initiation in coast Douglas‐fir (an ecologically and economically vital tree in western North America) to determine whether changes in phenology are likely to track changes in climate using data from field‐based and controlled‐environment studies, which included conditions warmer than those currently experienced in the tree's range. For high latitude and elevation portions of the tree's range, our models predicted that warming will lead to earlier growth initiation and allow trees to track changes in the onset of the warm but still moist conditions that favor growth, generally without substantially greater exposure to frost. In contrast, toward lower latitude and elevation range limits, the models predicted that warming will lead to delayed growth initiation relative to changes in climate due to reduced chilling, with trees failing to capture favorable conditions in the earlier parts of the spring. This maladaptive response to climate change was more prevalent for diameter‐growth initiation than height‐growth initiation. The decoupling of growth initiation with the onset of favorable climatic conditions could reduce the resilience of coast Douglas‐fir to climate change at the warm edges of its distribution.