Do cloud forest tree species differ in their suitability as a substrate for epiphytic bromeliads?

There is evidence for the existence of varying degrees of host preference in vascular epiphytes; certain tree species can be positively, neutrally, or negatively associated with epiphytes. The objective of this study was to evaluate whether tree species of the cloud forest differ in their suitability as a substrate for epiphytic bromeliads. To evaluate the association between epiphytic bromeliad cover and host tree species, we sampled 62 plots (each of 200 m²) in four cloud forest fragments in Veracruz, Mexico. For all trees ≥10 cm in diameter at breast height (DBH), we recorded species name, DBH, and percentage cover of bromeliads in categories of tree coverage. In total, 587 trees belonging to 52 species were recorded. All of the 10 tree species used to assess differences in epiphyte cover (each with a minimum of nine individuals) supported bromeliads, but mean bromeliad cover differed significantly among the tree species. The tree species that concentrated the highest bromeliad cover were Quercus sartorii (29.86%) and Liquidambar styraciflua (21.72%). Our results indicate that, while none of the tree species analyzed was a limiting host for epiphytic bromeliads in general, varying levels of bromeliad cover occur depending on the host species in tropical montane cloud forest fragments suggesting that certain tree species are better hosts than others. The implications for conservation efforts of differential tree species suitability as epiphyte hosts are discussed.     

Do species of invaded communities differ in their vulnerability to being eliminated by the dominant alien plants?

Invasions are associated with loss of diversity and changes in species composition. This study aims to provide evidence if this loss happens at random or if the loss is related to functional traits of native species. Traits of species in communities dominated by 13 plants alien to Central Europe were compared to those found in the adjacent uninvaded vegetation. There is a weak but significant non-random pattern in the distribution of traits between the invaded and adjacent uninvaded vegetation. For example, species possessing a taproot, annuals but also juveniles of trees tend to be proportionally more abundant in the invaded vegetation, suggesting they are impacted less than species with high clonal index, perennial polycarpic species and species without a taproot, which are proportionally more represented in the uninvaded vegetation. Fast laterally spreading species, trees’ juveniles and woody species in general are proportionally more frequent in the invaded vegetation, while biennials, slow laterally spreading species but also shrubs are proportionally more frequent in the uninvaded vegetation. Juveniles of trees may compete successfully with the aliens due to being adapted to thrive in low light conditions. Annuals may thrive in the invaded communities by possessing a life strategy different from most of the selected aliens. Possessing a taproot appears to be another trait important for the successful coexistence with the dominant invasive aliens, possibly pointing to the importance of underground competition. Clonal perennial polycarpic herbs are species functionally most similar to most of the selected aliens, and these species were found to be most underrepresented in the invaded vegetation.     

Do alien plants on Mediterranean islands tend to invade different niches from native species?

In order to understand invasions, it is important to know how alien species exploit opportunities in unfamiliar ecosystems. For example, are aliens concentrated in niches under-exploited by native communities, or widely distributed across the ecological spectrum? To explore this question, we compared the niches occupied by 394 naturalized alien plants with a representative sample from the native flora of Mediterranean islands. When niche structure was described by a functional group categorization, the distribution of native and alien species was remarkably similar, although “succulent shrubs” and “trees with specialized animal pollination mechanisms” were under-represented in the native species pool. When niche structure was described by Grime’s CSR strategy, the positioning of aliens and natives differed more strongly. Stress-tolerance was much rarer amongst the aliens, and a competitive strategy was more prevalent at the habitat level. This pattern is similar to previous findings in temperate Europe, although in those regions it closely reflects patterns of native diversity. Stressed environments are much more dominant in the Mediterranean. We discuss a number of factors which may contribute to this difference, e.g., competitive and ruderal niches are often associated with anthropogenic habitats, and their high invasibility may be due partly to introduction patterns rather than to a greater efficiency of aliens at exploiting them. Thus far, the reasons for invasion success amongst introduced species have proved difficult to unravel. Despite some differences, our evidence suggests that alien species naturalize across a wide range of niches. Given that their ecologies therefore vary greatly, one may ask why such species should be expected to share predictable traits at all?     

How do water transport and water storage differ in coniferous earlywood and latewood?

The goal of this research project was to determine the water transport behaviour of earlywood versus latewood in the trunk of 21-year-old Douglas-fir [Pseudostuga menziesii (Mirb.) Franco] trees. Specific conductivity (k(s)) and the vulnerability of xylem to embolism were measured on a single growth ring and in a subset of earlywood and latewood samples within the same ring. Earlywood/latewood ratio, trunk water potential (Psi) and relative water content (RWC) were used to predict differences in conductivities and vulnerability to embolism. Earlywood has about 11 times the k(s) of latewood, and up to 90% of the total flow occurred through the earlywood. Earlywood's vulnerability to embolism followed the same trend as that of the whole wood, with 50% loss of conductivity at -2.2 MPa (P(50)). Latewood was more vulnerable to embolism than earlywood at high Psi, but as Psi decreased, the latewood showed very little further embolism, with a P(50) <-5.0 MPa. The lowest trunk Psi estimated in the field was about -1.4 MPa, indicating that latewood and earlywood in the field experienced about 42% and 16% loss of k(s), respectively. The higher vulnerability to embolism in latewood than in earlywood at field Psi was associated with higher water storage capacity (21.8% RWC MPa(-1) versus 4.1% RWC MPa(-1), latewood and earlywood, respectively). The shape of the vulnerability curve suggests that air seeding through latewood may occur directly through pores in the margo and seal off at lower pressure than earlywood pores.     

Do protected areas in urban and rural landscapes differ in species diversity?

Previous studies from Central Europe and North America showed that species richness is higher in urban than in rural landscapes. Do protected areas, which can be found in both city and countryside, reflect this species richness pattern? The impact of urban land-use might reduce conservation success and necessitate special management strategies. We compared species richness and species spatial turnover of selected animal and plant taxa (carabids, butterflies, snails, birds, lichens, mosses, vascular plants) in 30 protected areas in the city of Halle and 56 protected areas in the adjacent rural district of Saalkreis (Central Germany). Species were mapped by experienced biologists within a systematic species inventory. We corrected species numbers for the effects of landscape structure (e.g. size, shape and distance of habitats) which might influence species diversity beyond urbanisation effects. Butterflies, birds and lichens had significantly higher species numbers in the rural protected areas. Species spatial turnover was higher among urban areas than among rural areas or pairs of urban and rural areas for most taxa. Diversity in all taxa depended on the size of a protected area. We discussed these patterns in the context of the general urban-rural species diversity patterns. Our results indicate an increasing isolation of species assemblages with urbanisation and highlight that space for protected areas is even more limited in urban than rural areas. An effective conservation of urban species diversity should include both typical urban and semi-natural habitats to cover the full range of species living in cities.     

Does global warming induce segregation among alien and native beetle species in a mountain-top?

The last few centuries have seen an increase in the mean air temperature of the planet, a phenomenon that is called “global warming”. One of the most sensitive habitats to the effects of global warming is the high-elevation mountain environments, because these habitats are characterized by low temperature. Cushion plants are one of the best-adapted growth forms in this habitat, generating more suitable sites for other plants and insects. In the present study, we experimentally evaluated the effects of global warming by open-top chambers on the abundance and interaction of two ladybirds at 3,600 m, growing over cushions of the Azorella monantha species in the Andes of central Chile. Additionally, we measured variation in temperature, water content, and food availability by the presence of open-top chambers as possible mechanisms of spatial segregation between ladybirds. Without open-top chambers, the abundance of native and alien beetles was similar; but with open-top chambers, the native beetle species is spatially segregated by alien species, decreasing in abundance. The open-top chambers increase temperature and food availability, but not water content. We suggest that under the global warming scenario, the native insects will decrease in abundance or become extinct by the presence of alien insects, at least in the high-elevation mountain environments.     

Do invasive alien plants benefit more from global environmental change than native plants?

Invasive alien plant species threaten native biodiversity, disrupt ecosystem functions and can cause large economic damage. Plant invasions have been predicted to further increase under ongoing global environmental change. Numerous case studies have compared the performance of invasive and native plant species in response to global environmental change components (i.e. changes in mean levels of precipitation, temperature, atmospheric CO₂ concentration or nitrogen deposition). Individually, these studies usually involve low numbers of species and therefore the results cannot be generalized. Therefore, we performed a phylogenetically controlled meta‐analysis to assess whether there is a general pattern of differences in invasive and native plant performance under each component of global environmental change. We compiled a database of studies that reported performance measures for 74 invasive alien plant species and 117 native plant species in response to one of the above‐mentioned global environmental change components. We found that elevated temperature and CO₂ enrichment increased the performance of invasive alien plants more strongly than was the case for native plants. Invasive alien plants tended to also have a slightly stronger positive response to increased N deposition and increased precipitation than native plants, but these differences were not significant (N deposition: P = 0.051; increased precipitation: P = 0.679). Invasive alien plants tended to have a slightly stronger negative response to decreased precipitation than native plants, although this difference was also not significant (P = 0.060). So while drought could potentially reduce plant invasion, increases in the four other components of global environmental change considered, particularly global warming and atmospheric CO₂ enrichment, may further increase the spread of invasive plants in the future.     

Effects of changes in tree species composition on water flow dynamics – Model applications and their limitations

Water-plant relations play a key role in the water cycling in terrestrial ecosystems. Consequently, changes in tree species composition may have distinct effects on the water retention capacity as well as on the pattern of streamflow generation. Such changes may result from modified interception properties and transpiration related to differences in canopy properties and root distribution. In order to evaluate the potential hydrological effects of the current silvicultural conversion from monocultural conifer stands into mixed or pure deciduous stands the hydrological model BROOK90 was applied to two forested upland catchments in Germany. The Rotherdbach catchment (9.4 ha, 93 yr-old Norway spruce) is situated in the Eastern Ore Mountains. The Schluchsee catchment (11 ha, 55-yr-old Norway spruce) is located in the higher altitudes of the Black Forest. The calibrated model is capable to describe rather well the temporal variation of streamflow but also the portions of the individual flow components. Data for a beech scenario were adapted for each site using a standard parameter set for deciduous trees provided by BROOK90. The annual discharge in the fictional beech stand at Rotherdbach is 30 to 50% higher compared to spruce with an increase of soil moisture and especially the slow streamflow components. This mainly results from low interception rates during winter time. In contrast, the spruce stand has a permanently higher interception rate. Effects of tree species conversion are moderate at Schluchsee. The annual discharge of a fictional beech stand at Schluchsee is 7 to 14% higher compared to spruce. There in contrast to Rotherdbach, effects of tree species conversion on soil moisture dynamics are small since vertical percolation in the highly permeable soil dominates and precipitation is abundant. Practical forestry will favorably establish mixed beech–spruce rather than pure beech stands. However, it is critical to simulate mixed stands with BROOK90. Therefore, a simple summation of model results from spruce and beech according to their respective area in a fictional mixed stand can only be a first approximation. Advanced hydrological simulation of mixed stand conditions should regard interactions of tree species and spatial parameter distribution. However, this is not yet feasible due to a distinct lack of information. As a consequence, there is a strong need to collect relevant hydrological and ecophysiological data in mixed stands in the future.     

Do exaptations facilitate mutualistic associations between invasive and native species?

As invasive species are key threats to ecosystem structure and function, it is essential to understand the factors underlying their success. Enigmatically, mutualistic organisms are often successful in colonizing novel environments even though they commonly persist only through intricate relationships with other species. Mutualistic ants, for example, protect aphids from natural enemies while collecting carbohydrate–rich honeydew. To facilitate this interaction, ants have evolved aggressive responses to aphid alarm pheromone emissions. As invasive and native mutualists have not evolved together, however, it is unclear if this form of cross-species communication exists between these two parties thereby facilitating these novel interactions. We address this hypothesis by assessing whether the invasive Argentine ant, Linepithema humile, responds to native poplar aphid, Chaitophorus populicola, alarm signals. Here, we show that interspecific signalling does exist in this newly established mutualistic interaction. Argentine ant workers exhibit increased aggression and double the number of visits to an aphid colony after an aphid alarm signal is emitted. We suggest that pre-adaptations may facilitate the emergence of mutualistic associations between many invasive and native species.     

Hybrid swarm as a result of hybridization between two alien and two native water frog species (genus Pelophylax) in Central Croatia: Crna Mlaka fishpond acting as a species melting pot?

Biological Invasions - Spreading of alien water frog species (genus Pelophylax) has been reported across Europe, posing a severe risk for the replacement or genetic swamping of indigenous species....     

Biological invasion on an oceanic island mountain: Do alien plant species have wider ecological ranges than native species?

Abstract. Spatial distribution patterns of alien plant species were compared with those of native species on a windward slope of Mt. Haleakala (3055 m). Oceanic islands are considered susceptible to biological invasion, and this study numerically tested this circumstantial evidence with the following questions: Are all habitats equally susceptible; and, do successful invaders have wider realized niches than natives? The mountain slope consists of three distinct altitudinal bioclimatic zones (hot moist lowland, wet montane cloud, and cool arid high-altitude zones). Ordination indicated that alien species' ranges and population expansions were clustered in the lowland and high-altitude zones. The lowland zone had been subjected to natural canopy dieback, and the high-altitude zone to grazing by domestic and feral ungulates. By contrast, the montane cloud forest was relatively intact in terms of number and cover of native species. Thus, susceptibility to alien invasion clearly differed among zones, and the primary causes seemed to be the obvious disturbance factors. The mean ecological range along the altitude-rainfall gradient was significantly (P < 0.05) greater for native than for alien species in most life-form groups. The reasons for the greater number of climate generalists among the natives vs. the range-restricted aliens appear to be related to: (1) the pre-alien condition with a depauperate flora which allowed for ‘ecological release’ of successful native colonizers, and (2) the climatic pre-adaptation of alien invaders which restricts them from penetrating over a broader spectrum of climatic zones in a floristic matrix subjected to increasing interspecific competition.     

Do plants and animals differ in phenotypic plasticity?

This paper compares the flexibility in the nexus between phenotype and genotype in plants and animals. These taxa although considered to be fundamentally different are found to be surprisingly similar in the mechanisms used to achieve plasticity. Although non-cognitive behaviour occurs in plants, its range is limited, while morphological and developmental plasticity also occur to a considerable extent in animals. Yet both plants and animals are subject to unique constraints and thus need to find unique solutions to functional problems. A true comparison between the plant and animal phenotype would be a comparison between plants and sessile photosynthesizing colonial invertebrates. Such comparisons are lacking. However, they would provide important insights into the adaptive significance of plasticity in these groups. It is also suggested that a comparison of inflexible traits in these groups would provide an understanding of the constraints, as well as the costs and benefits, of a plastic versus non-plastic phenotype in plants and animals.     

Do annual and perennial populations of an insect-pollinated plant species differ in mating system?

Background and AimsTheory predicts that outcrossing should be more prevalent among perennials than annuals, a pattern confirmed by comparative evidence from diverse angiosperm families. However, intraspecific comparisons between annual and perennial populations are few because such variation is uncommon among flowering plants. Here, we test the hypothesis that perennial populations outcross more than annual populations by investigating Incarvillea sinensis, a wide-ranging insect-pollinated herb native to China. The occurrence of both allopatric and sympatric populations allows us to examine the stability of mating system differences between life histories under varying ecological conditions.MethodsWe estimated outcrossing rates and biparental inbreeding in 16 allopatric and five sympatric populations in which both life histories coexisted using 20 microsatellite loci. In each population we measured height, branch number, corolla size, tube length and herkogamy for ~30 individuals. In a sympatric population, we recorded daily flower number, pollinator visitation and the fruit and seed set of annual and perennial plants.Key ResultsAs predicted, outcrossing rates (t) were considerably higher in perennial (mean = 0.76) than annual (mean = 0.09) populations. This difference in mating system was also maintained at sympatric sites where plants grew intermixed. In both allopatric and sympatric populations the degree of herkogamy was consistently larger in outcrossing than selfing plants. Perennials were more branched, with more and larger flowers than in annuals. In a sympatric population, annuals had a significantly higher fruit and seed set than perennials.ConclusionsGenetically based differences in herkogamy between annuals and perennials appear to play a key role in governing outcrossing rates in populations, regardless of variation in local ecological conditions. The maintenance of mating system and life history trait differentiation between perennial and annual populations of I. sinensis probably results from correlated evolution in response to local environmental conditions.     

Do artificial substrates favor nonindigenous fouling species over native species?

Exotic species are prominent constituents of fouling communities. If exotic fouling organisms colonize or compete better on a wider range of substrate types than native species, this may partially account for their high abundance in estuaries and bays. We used four artificial and four naturally occurring substrate types to compare initial settlement and percent cover of native and exotic fouling species through six months of community development. Both the identity of common taxa and the total number of species colonizing artificial versus natural substrate types were similar. Despite the similarities in species richness, relative abundance patterns between natural and artificial substrate types varied, particularly as the communities developed. Native species were initially in equal abundance on natural and artificial substrate types. Initially, the two most common exotic species, the colonial tunicates, Botrylloides violaceus Ritter and Forsyth and Botryllus schlosseri (Pallas), were also in similar, but low, abundance on artificial and natural substrates. As the communities developed, there was little change in abundance of exotic or native species on natural substrates. However, on artificial substrates the exotic tunicates increased dramatically and native species declined in abundance. Artificial surfaces may provide a novel context for competitive interactions giving exotic species a more “level playing field” in an environment for which they otherwise might not be as well adapted compared to long-resident native species. Additions of artificial substrates to nearshore environments may disproportionately favor exotic species by increasing local sources of exotic propagules to colonize all types of substrates.     

Do X and Y spermatozoa differ in proteins?

This article reviews the current knowledge about X- and Y-chromosomal gene expression during spermatogenesis and possible differences between X- and Y-chromosome-bearing spermatozoa (X and Y sperm) in relation to whether an immunological method of separation of X and Y spermatozoa might some day be feasible. Recent studies demonstrated that X- and Y-chromosome-bearing spermatids do express X- and Y-chromosomal genes that might theoretically result in protein differences between X and Y sperm. Most, if not all, of these gene products, however, are expected to be shared among X and Y spermatids via intercellular bridges. Studies on aberrant mouse strains indicate that complete sharing might not occur for all gene products. This keeps open the possibility that X and Y sperm may differ in proteins, but until now, this has not been confirmed by comparative studies between flow-cytometrically sorted X and Y sperm for H-Y antigen or other membrane proteins.     

Do sodium and potassium forms of Na,K-ATPase differ in their secondary structure?

Infrared spectroscopy in the amide I region of purified membrane-bound Na,K-ATPase preparation shows that Na+- and K+-bound forms of the enzyme have almost the same secondary structure. No difference is detected in the beta-structure (pleated sheets) content. This is contrary to the statement of the recent paper (Gresalfi, T. J., and Wallace, B. A. (1984) J. Biol. Chem. 259, 2622-2628) where a similar preparation was examined by circular dichroism spectroscopy and it was claimed that net 7% of protein peptide groups undergo a beta-sheet to alpha-helix conformational change upon Na,K-ATPase conversion from the K+ to the Na+ form. The discrepancy of the results is most likely caused by the particulate nature of the enzyme preparations used that could lead to optical artifacts in CD but not in IR measurements. A thorough comparison of IR spectra of these enzyme forms has revealed a very minor spectral difference which could suggest conformational perturbations, if any, of a much lower scale and another type than that claimed by Gresalfi and Wallace. The K+ form tends to absorb slightly more in the region of the alpha-helix band. This could reflect some distortion or a transition to a random coil structure of a small fraction of alpha-helical segments (less than or equal to 2% protein peptide groups) upon the enzyme conversion from the K+ to the Na+ form.     

Specificity in host-fungus associations: Do mutualists differ from antagonists?

Summary Physically intimate interactions between organisms are assumed to be highly specific, yet intimate mutualisms exhibiting little specificity are common and important in many communities. We compare host records for ectomycorrhizal fungi (mutualists) to those for biotrophic shoot fungi and necrotrophic root fungi (both antagonists) in order to test two alternative predictions: (1) intimate physical associations (biotrophy) are more specific than less intimate ones (necrotrophy); (2) antagonisms are more specific than mutualisms. Specificity of fungi for hosts supports prediction (1): ectomycorrhizal fungi and shoot biotrophs are more host specific than root necrotrophs. Fungal symbiont ranges of hosts supports prediction (2): woody hosts are associated with a greater number of mutualistic fungi than antagonistic fungi. The numbers of fungi in the three groups infecting hosts are all significantly positively correlated. This result suggests that some hosts are resistant to fungal invasion and others are quite susceptible. Thus, plants may not be able to erect selective barriers to only antagonistic fungi. The marked asymmetry of specificity from the perspectives of hosts vs fungi suggests that evolutionary and ecological processes act differently on partners in symbioses.