Increased Phenotypic Plasticity to Climate May Have Boosted the Invasion Success of Polyploid Centaurea stoebe

Phenotypic plasticity may allow organisms to cope with altered environmental conditions as e.g. after the introduction into a new range. In particular polyploid organisms, containing more than two sets of chromosomes, may show high levels of plasticity, which could in turn increase their environmental tolerance and invasiveness. Here, we studied the role of phenotypic plasticity in the invasion of Centaurea stoebe (Asteraceae), which in the native range in Europe occurs as diploids and tetraploids, whereas in the introduced range in North America so far only tetraploids have been found. In a common garden experiment at two sites in the native range, we grew half-sibs of the three geo-cytotypes (native European diploids, European tetraploids and invasive North American tetraploids) from a representative sample of 27 populations. We measured the level and the adaptive significance of phenotypic plasticity in eco-physiological and life-history traits in response to the contrasting climatic conditions at the two study sites as well as three different soil conditions in pots, simulating the most crucial abiotic differences between the native and introduced range. European tetraploids showed increased levels of phenotypic plasticity as compared to diploids in response to the different climatic conditions in traits associated with rapid growth and fast phenological development. Moreover, we found evidence for adaptive plasticity in these traits, which suggests that increased plasticity may have contributed to the invasion success of tetraploid C. stoebe by providing an advantage under the novel climatic conditions. However, in invasive tetraploids phenotypic plasticity was similar to that of native tetraploids, indicating no evolution of increased plasticity during invasions. Our findings provide the first empirical support for increased phenotypic plasticity associated with polyploids, which may contribute to their success as invasive species in novel environments.     

Climate Change May Boost the Invasion of the Asian Needle Ant

Following its introduction from Asia to the USA, the Asian needle ant (Pachycondyla chinensis) is rapidly spreading into a wide range of habitats with great negative ecological affects. In addition, the species is a concern for human health because of its powerful, sometimes deadly, sting. Here, we assessed the potential of P. chinensis to spread further and to invade entirely new regions. We used species distribution models to assess suitable areas under current climatic conditions and in 2020, 2050 and 2080. With a consensus model, combining five different modelling techniques, three Global Circulation (climatic) Models and two CO₂ emission scenarios, we generated world maps with suitable climatic conditions. Our models suggest that the species currently has a far greater potential distribution than its current exotic range, including large parts of the world landmass, including Northeast America, Southeast Asia and Southeast America. Climate change is predicted to greatly exacerbate the risk of P. chinensis invasion by increasing the suitable landmass by 64.9% worldwide, with large increases in Europe (+210.1%), Oceania (+75.1%), North America (+74.9%) and Asia (+62.7%). The results of our study suggest P. chinensis deserves increased attention, especially in the light of on-going climate change.     

Climate Change Likely to Facilitate the Invasion of the Non-Native Hydroid,Cordylophora caspia,in the San Francisco Estuary

Climate change and invasive species can both have negative impacts on native species diversity. Additionally, climate change has the potential to favor invasive species over natives, dealing a double blow to native biodiversity. It is, therefore, vital to determine how changing climate conditions are directly linked to demographic rates and population growth of non-native species so we can quantitatively evaluate how invasive populations may be affected by changing conditions and, in turn, impact native species. Cordylophora caspia, a hydrozoan from the Ponto-Caspian region, has become established in the brackish water habitats of the San Francisco Estuary (SFE). We conducted laboratory experiments to study how temperature and salinity affect C. caspia population growth rates, in order to predict possible responses to climate change. C. Caspia population growth increased nonlinearly with temperature and leveled off at a maximum growth rate near the annual maximum temperature predicted under a conservative climate change scenario. Increasing salinity, however, did not influence growth rates. Our results indicate that C. caspia populations in the SFE will benefit from predicted regional warming trends and be little affected by changes in salinity. The population of C. caspia in the SFE has the potential to thrive under future climate conditions and may subsequently increase its negative impact on the food web.     

Movement Behavior of Native and Invasive Small Mammals Shows Logging May Facilitate Invasion in a Tropical Rain Forest

Invasive species pose one of the greatest threats to biodiversity. This study investigates the extent to which human disturbance to natural ecosystems facilitates the spread of non‐native species, focusing on a small mammal community in selectively logged rain forest, Sabah, Borneo. The microhabitat preferences of the invasive Rattus rattus and three native species of small mammal were examined in three‐dimensional space by combining the spool‐and‐line technique with a novel method for quantifying fine‐scale habitat selection. These methods allowed the detection of significant differences for each species between the microhabitats used compared with alternative, available microhabitats that were avoided. Rattus rattus showed the greatest preference for heavily disturbed habitats, and in contrast to two native small mammals of the genus Maxomys, R. rattus showed high levels of arboreal behavior, frequently leaving the forest floor and traveling through the understory and midstory forest strata. This behavior may enable R. rattus to effectively utilize the complex three‐dimensional space of the lower strata in degraded forests, which is characterized by dense vegetation. The behavioral flexibility of R. rattus to operate in both terrestrial and arboreal space may facilitate its invasion into degraded forests. Human activities that generate heavily disturbed habitats preferred by R. rattus may promote the establishment of this invasive species in tropical forests in Borneo, and possibly elsewhere. We present this as an example of a synergistic effect, whereby forest disturbance directly threatens biodiversity and indirectly increases the threat posed by invasive species, creating habitat conditions that facilitate the establishment of non‐native fauna.     

Initial Stages of Tundra Shrub Litter Decomposition May Be Accelerated by Deeper Winter Snow But Slowed Down by Spring Warming

The Arctic climate is projected to change during the coming century, with expected higher air temperatures and increased winter snowfall. These climatic changes might alter litter decomposition rates, which in turn could affect carbon (C) and nitrogen (N) cycling rates in tundra ecosystems. However, little is known of seasonal climate change effects on plant litter decomposition rates and N dynamics, hampering predictions of future arctic vegetation composition and the tundra C balance. We tested the effects of snow addition (snow fences), warming (open top chambers), and shrub removal (clipping), using a full-factorial experiment, on mass loss and N dynamics of two shrub tissue types with contrasting quality: deciduous shrub leaf litter (Salix glauca) and evergreen shrub shoots (Cassiope tetragona). We performed a 10.5-month decomposition experiment in a low-arctic shrub tundra heath in West-Greenland. Field incubations started in late fall, with harvests made after 249, 273, and 319 days of field incubation during early spring, summer and fall of the next year, respectively. We observed a positive effect of deeper snow on winter mass loss which is considered a result of observed higher soil winter temperatures and corresponding increased winter microbial litter decomposition in deep-snow plots. In contrast, warming reduced litter mass loss during spring, possibly because the dry spring conditions might have dried out the litter layer and thereby limited microbial litter decomposition. Shrub removal had a small positive effect on litter mass loss for C. tetragona during summer, but not for S. glauca. Nitrogen dynamics in decomposing leaves and shoots were not affected by the treatments but did show differences in temporal patterns between tissue types: there was a net immobilization of N by C. tetragona shoots after the winter incubation, while S. glauca leaf N-pools were unaltered over time. Our results support the widely hypothesized positive linkage between winter snow depth and litter decomposition rates in tundra ecosystems, but our results do not reveal changes in N dynamics during initial decomposition stages. Our study also shows contrasting impacts of spring warming and snow addition on shrub decomposition rates that might have important consequences for plant community composition and vegetation-climate feedbacks in rapidly changing tundra ecosystems.     

Regional and Landscape-scale Patterns of Shrub Invasion in Tropical Savannas

The shrubby vine Cryptostegia grandiflora and the shrub Ziziphus mauritiana were both introduced to northern Australia over 100 years ago and have become invasive in savanna woodland environments. Data from a land resource survey were used to examine regional- and landscape-scale distribution patterns of these species in the Dalrymple Shire, an area of over 6 1/2 million hectares in northeast Queensland. Each species was present at 10% of the 2362 sites examined and most frequent and abundant close to Charters Towers, the major settlement of the regions. C. grandiflora was recorded at 50 % of sites within 20 km of the town and in 14 out of 21 of the region's major sub-catchments. Z. mauritiana was recorded at 32 % of sites within 20km of Charters Towers, but in only three sub-catchments. Little of the variation in frequency and abundance of C. grandiflora and Z. mauritiana was accounted for by landscape factors, including geology, soils, or vegetation. While survey results do not absolutely distinguish between history, habitat and disturbance in explaining the weed's current distributions within the region, a strong influence of historical factors is suggested. Both exotic species were much less abundant than Carissa spp., a native taxon that has purportedly increased in the region in recent decades. In spite of their current prominence as weeds, there is potential for further increase by both C. grandiflora and Z. mauritiana. This increase could include expansion from the zone of high abundance and proliferation within that zone. While the results of such surveys must be interpreted with caution, they can yield useful information about regional patterns of plant invasion.     

Ecosystem Consequences of Exotic Earthworm Invasion of North Temperate Forests

The invasion of north temperate forests by exotic species of earthworms is an important issue that has been overlooked in the study and management of these forests. We initiated research to address the hypothesis that earthworm invasion will have large consequences for nutrient retention and uptake in these ecosystems. In this special feature of Ecosystems, we present five papers describing results from our experiment. In this paper, we (a) introduce our experimental approach and conceptual model of how earthworms influence forest ecosystem processes, (b) describe the characteristics of the study areas and earthworm communities at our two study locations, and (c) provide a brief overview and synthesis of the main findings. The most dramatic effect of earthworm invasion was the loss of the forest floor at an undisturbed forest site, which altered the location and nature of nutrient cycling activity in the soil profile. Invasion changed soil total carbon (C) and phosphorus (P) pools, carbon–nitrogen (C:N) ratios, the loss and distribution of different soil P fractions, and the distribution and function of roots and microbes. Response to invasion varied with site characteristics and earthworm species. Our results suggest that exotic earthworm invasion is a significant factor that will influence the structure and function of northern temperate forest ecosystems over the next few decades. Regional evaluations of these forests will need to consider the presence or absence of earthworms along with other important ecosystem drivers, such as pollution, climate, and underlying soil characteristics.     

Negative Effects of an Exotic Grass Invasion on Small-Mammal Communities

Exotic invasive species can directly and indirectly influence natural ecological communities. Cheatgrass (Bromus tectorum) is non-native to the western United States and has invaded large areas of the Great Basin. Changes to the structure and composition of plant communities invaded by cheatgrass likely have effects at higher trophic levels. As a keystone guild in North American deserts, granivorous small mammals drive and maintain plant diversity. Our objective was to assess potential effects of invasion by cheatgrass on small-mammal communities. We sampled small-mammal and plant communities at 70 sites (Great Basin, Utah). We assessed abundance and diversity of the small-mammal community, diversity of the plant community, and the percentage of cheatgrass cover and shrub species. Abundance and diversity of the small-mammal community decreased with increasing abundance of cheatgrass. Similarly, cover of cheatgrass remained a significant predictor of small-mammal abundance even after accounting for the loss of the shrub layer and plant diversity, suggesting that there are direct and indirect effects of cheatgrass. The change in the small-mammal communities associated with invasion of cheatgrass likely has effects through higher and lower trophic levels and has the potential to cause major changes in ecosystem structure and function.     

Observations on the Invasion and Endoparasitic Behavior of the Root Lesion Nematode Pratylenchus penetrans

The endoparasitic behavior of Pratylenchus penetrans was examined using video-enhanced contrast microscopy to observe living nematodes inside root tissue. Feeding behavior could be separated into phases of probing, cell penetration by the stytet, salivation, and food ingestion for brief and extended periods. After cell penetration, a small "salivation zone" was formed around the stylet tip. No feeding tubes were observed. Feeding and migration were interrupted by rest phases when a nematode became characteristically coiled inside a cell. Tissue damage was caused primarily by migration and extended feeding periods. Aspects of egg laying and molting are also described.     

Estimating the Potential for Adaptation of Corals to Climate Warming

The persistence of tropical coral reefs is threatened by rapidly increasing climate warming, causing a functional breakdown of the obligate symbiosis between corals and their algal photosymbionts (Symbiodinium) through a process known as coral bleaching. Yet the potential of the coral-algal symbiosis to genetically adapt in an evolutionary sense to warming oceans is unknown. Using a quantitative genetics approach, we estimated the proportion of the variance in thermal tolerance traits that has a genetic basis (i.e. heritability) as a proxy for their adaptive potential in the widespread Indo-Pacific reef-building coral Acropora millepora. We chose two physiologically different populations that associate respectively with one thermo-tolerant (Symbiodinium clade D) and one less tolerant symbiont type (Symbiodinium C2). In both symbiont types, pulse amplitude modulated (PAM) fluorometry and high performance liquid chromatography (HPLC) analysis revealed significant heritabilities for traits related to both photosynthesis and photoprotective pigment profile. However, quantitative real-time polymerase chain reaction (qRT-PCR) assays showed a lack of heritability in both coral host populations for their own expression of fundamental stress genes. Coral colony growth, contributed to by both symbiotic partners, displayed heritability. High heritabilities for functional key traits of algal symbionts, along with their short clonal generation time and high population sizes allow for their rapid thermal adaptation. However, the low overall heritability of coral host traits, along with the corals'' long generation time, raise concern about the timely adaptation of the coral-algal symbiosis in the face of continued rapid climate warming.     

Septin 11 Restricts InlB-mediated Invasion by Listeria

Septins are filament-forming GTPases implicated in several cellular functions, including cytokinesis. We previously showed that SEPT2, SEPT9, and SEPT11 colocalize with several bacteria entering into mammalian non-phagocytic cells, and SEPT2 was identified as essential for this process. Here, we investigated the function of SEPT11, an interacting partner of SEPT9 whose function is still poorly understood. In uninfected HeLa cells, SEPT11 depletion by siRNA increased cell size but surprisingly did not affect actin filament formation or the colocalization of SEPT9 with actin filaments. SEPT11 depletion increased Listeria invasion, and incubating SEPT11-depleted cells with beads coated with the Listeria surface protein InlB also led to increased entry as compared with control cells. Strikingly, as shown by fluorescence resonance energy transfer, the InlB-mediated stimulation of Met signaling remained intact in SEPT11-depleted cells. Taken together, our results show that SEPT11 is not required for the bacterial entry process and rather restricts its efficacy. Because SEPT2 is essential for the InlB-mediated entry of Listeria, but SEPT11 is not, our findings distinguish the roles of different mammalian septins.Septins were discovered in the budding yeast Saccharomyces cerevisiae (1) where they organize into a ring at the mother-bud neck during cell division (2). Septins are GTPases of 30-65 kDa found in most eukaryotes, except plants, sharing an essential role in cytokinesis (3, 4). Fourteen septins have been identified in humans and classified on the basis of sequence identity into four distinct groups (3, 5). Septins from different groups polymerize into hetero-oligomeric protein complexes and filaments and may associate with cellular membranes, actin filaments, and microtubules (6, 7). Septins are increasingly regarded as novel cytoskeletal elements (8), but their role in post-mitotic events remains poorly understood.The crystal structure of the SEPT2-SEPT6-SEPT7 complex recently highlighted that septins, as opposed to actin and microtubules, form non-polar filaments (9). In the SEPT7-SEPT6-SEPT2-SEPT2-SEPT6-SEPT7 complex, SEPT2 has a central role in filament formation (9), whereas SEPT6 is thought to be replaceable with other SEPT6 group members, including SEPT11 (3). Widely expressed in mammalian tissues (10), SEPT11 may also be a substitute for SEPT6 in other mammalian septin complexes such as SEPT7-SEPT9-SEPT11 (10) or SEPT5-SEPT7-SEPT11 (11). Because other septins homologous to SEPT11 might compensate for its deficiency (12), the degree to which SEPT11 is required for septin filament structure and function is not yet known. Listeria monocytogenes is an invasive bacterium that enters into most mammalian cells in vitro through the interaction of the bacterial surface protein InlB with its host cellular receptor Met, the hepatocyte growth factor receptor (13). We originally identified SEPT9 associated with phagosomes containing latex beads coated with InlB (14). Given the association of septins with the cytoskeleton, and the importance of the cytoskeleton in bacterial invasion, we have started investigating septin function during infection of invasive bacteria in non-phagocytic cells. We have discovered that SEPT9, and its interacting partners SEPT2 and SEPT11, are recruited as 0.6-μm collars next to actin at the site of entry of invasive bacteria (15). Although functional studies using siRNA³ have revealed an essential role for SEPT2 in regulating bacterial entry, the role of SEPT11 has not yet been investigated. We thus addressed SEPT11 function in the context of Listeria infection.     

Climate change and the potential distribution of an invasive shrub, Lantana camara L

The threat posed by invasive species, in particular weeds, to biodiversity may be exacerbated by climate change. Lantana camara L. (lantana) is a woody shrub that is highly invasive in many countries of the world. It has a profound economic and environmental impact worldwide, including Australia. Knowledge of the likely potential distribution of this invasive species under current and future climate will be useful in planning better strategies to manage the invasion. A process-oriented niche model of L. camara was developed using CLIMEX to estimate its potential distribution under current and future climate scenarios. The model was calibrated using data from several knowledge domains, including phenological observations and geographic distribution records. The potential distribution of lantana under historical climate exceeded the current distribution in some areas of the world, notably Africa and Asia. Under future scenarios, the climatically suitable areas for L. camara globally were projected to contract. However, some areas were identified in North Africa, Europe and Australia that may become climatically suitable under future climates. In South Africa and China, its potential distribution could expand further inland. These results can inform strategic planning by biosecurity agencies, identifying areas to target for eradication or containment. Distribution maps of risk of potential invasion can be useful tools in public awareness campaigns, especially in countries that have been identified as becoming climatically suitable for L. camara under the future climate scenarios.     

Invasion dynamics of Lantana camara L. (sensu lato) in South Africa

Lantana camara L. (sensu lato) has a wide range of impacts throughout its global invasive range. Here we review the mechanisms driving its invasion dynamics in South Africa at national (biome, habitat) and regional (within a protected area) scales. Although only three introduction events into South Africa have been recorded (the earliest in 1858), as of 1998 L. camara was found in over 2 million ha (total area), with a condensed area of about 70,000 ha. Moreover, L. camara is present in most of the country's major biomes and a diversity of habitats, confirming its broad ecological tolerance. Using correlative bioclimatic models, we show that under future climate conditions, L. camara's range in South Africa could expand considerably over the coming decades. While human-mediated dispersal and climatic suitability have been crucial in shaping L. camara's current broad-scale distribution in South Africa, dispersal by birds and along rivers are important drivers of invasion at landscape scales. For example, current evidence suggests that in the Kruger National Park, L. camara has spread primarily along rivers. We conclude with a discussion on the implications of the different invasion dynamics for biological control and management, and provide recommendations for future research.     

Soil Fertility and the Impact of Exotic Invasion on Microbial Communities in Hawaiian Forests

Exotic plant invasions into Hawaiian montane forests have altered many important nutrient cycling processes and pools. Across different ecosystems, researchers are uncovering the mechanisms involved in how invasive plants impact the soil microbial community-the primary mediator of soil nutrient cycling. We examined whether the invasive plant, Hedychium gardnerianum, altered microbial community composition in forests dominated by a native tree, Metrosideros polymorpha, under varying soil nutrient limitations and soil fertility properties within forest plots of the Hawaii long-term substrate age gradient (LSAG). Microbial community lipid analysis revealed that when nutrient limitation (as determined by aboveground net primary production [ANPP]) and soil fertility were taken into account, plant species differentially altered soil microbial community composition. Microbial community characteristics differed under invasive and native plants primarily when N or P was added to the older, highly weathered, P-limited soils. Long-term fertilization with N or P at the P-limited site led to a significant increase in the relative abundance of the saprophytic fungal indicator (18:2 omega 6c,9c) under the invasive plant. In the younger, N-limited soils, plant species played a minor role in influencing soil microbial community composition. We found that the general rhizosphere microbial community structure was determined more by soil fertility than by plant species. This study indicates that although the aggressive invasion of a nutrient-demanding, rapidly decomposable, and invasive plant into Hawaiian forests had large impacts on soil microbial decomposers, relatively little impact occurred on the overall soil microbial community structure. Instead, soil nutrient conditions were more important determinants of the overall microbial community structure within Hawaii's montane forests.     

气候变暖对我国鸟类分布的影响

研究了１０年来国内有关鸟类分布及越冬地变化的资料,结合我国近年来气候变暖的事实,初步探讨了气候变暖对我国鸟类可能产生的影响,并针对这些影响提出了一些保护对策。     

Influence of Temperature on Exotic Daphnia lumholtzi and Implications for Invasion Success

We investigated the effects of water temperature on the exoticcladoceran Daphnia lumholtzi in a eutrophic Kansas reservoir(USA) and under laboratory conditions. Daphnia lumholtzi demonstrateda distinct late summer appearance in the reservoir at temperaturesbetween 26 and 31°C, which corresponded with steep declinesin the densities of native Daphnia spp. Laboratory life-tableexperiments confirmed that D. lumholtzi performs well at elevatedwater temperatures. The intrinsic rate of increase (r), netreproductive rate (R_o), age at first reproduction, survivorship(l_x) and molting rates all demonstrate that D. lumholtzi hasa high temperature optimum between 20 and 30°C. A comparisonof literature-reported r-values indicates that the reproductiverate of D. lumholtzi is comparable with other Daphnia spp. between20 and 25°C, but also implies that D. lumholtzi may out-performsome Daphnia spp. at temperatures >25°C. Collectively,these results suggest that D. lumholtzi may be taking advantageof a late summer thermal niche, and that this invader may continueto colonize lakes and reservoirs in the southern US. However,life table data also indicate that D. lumholtzi performs poorlyat temperatures < 10°C, which may inhibit the range expansionof this invader into northern waters.     

Range Expansion of Moose in Arctic Alaska Linked to Warming and Increased Shrub Habitat

Twentieth century warming has increased vegetation productivity and shrub cover across northern tundra and treeline regions, but effects on terrestrial wildlife have not been demonstrated on a comparable scale. During this period, Alaskan moose (Alces alces gigas) extended their range from the boreal forest into tundra riparian shrub habitat; similar extensions have been observed in Canada (A. a. andersoni) and Eurasia (A. a. alces). Northern moose distribution is thought to be limited by forage availability above the snow in late winter, so the observed increase in shrub habitat could be causing the northward moose establishment, but a previous hypothesis suggested that hunting cessation triggered moose establishment. Here, we use recent changes in shrub cover and empirical relationships between shrub height and growing season temperature to estimate available moose habitat in Arctic Alaska c. 1860. We estimate that riparian shrubs were approximately 1.1 m tall c. 1860, greatly reducing the available forage above the snowpack, compared to 2 m tall in 2009. We believe that increases in riparian shrub habitat after 1860 allowed moose to colonize tundra regions of Alaska hundreds of kilometers north and west of previous distribution limits. The northern shift in the distribution of moose, like that of snowshoe hares, has been in response to the spread of their shrub habitat in the Arctic, but at the same time, herbivores have likely had pronounced impacts on the structure and function of these shrub communities. These northward range shifts are a bellwether for other boreal species and their associated predators.     

Insects Overshoot the Expected Upslope Shift Caused by Climate Warming

Along elevational gradients, climate warming may lead to an upslope shift of the lower and upper range margin of organisms. A recent meta-analysis concluded that these shifts are species specific and considerably differ among taxonomic lineages. We used the opportunity to compare upper range margins of five lineages (plants, beetles, flies, hymenoptera, and birds) between 1902–1904 and 2006–2007 within one region (Bavarian Forest, Central Europe). Based on the increase in the regional mean annual temperature during this period and the regional lapse rate, the upslope shift is expected to be between 51 and 201 m. Averaged across species within lineages, the range margin of all animal lineages shifted upslope, but that of plants did not. For animals, the observed shifts were probably due to shifts in temperature and not to changes in habitat conditions. The range margin of plants is therefore apparently not constrained by temperature, a result contrasting recent findings. The mean shift of birds (165 m) was within the predicted range and consistent with a recent global meta-analysis. However, the upslope shift of the three insect lineages (>260 m) exceeded the expected shift even after considering several sources of uncertainty, which indicated a non-linear response to temperature. Our analysis demonstrated broad differences among lineages in their response to climate change even within one region. Furthermore, on the considered scale, the response of ectothermic animals was not consistent with expectations based on shifts in the mean annual temperature. Irrespective of the reasons for the overshooting of the response of the insects, these shifts lead to reorganizations in the composition of assemblages with consequences for ecosystem processes.