Uncolonized Areas Research Articles

Invasibility framework to predict the early colonization of alien Sonneratia in mangrove: Implications for coastal area management

Invasibility, or an ecosystem's susceptibility to invasion, plays a critical role in managing biological invasions but is challenging to quantify due to its dependence on specific ecosystem variables. This limitation restricts the practical application of this concept in the control of alien species. This study aims to simplify invasibility into measurable components and develop an applicable framework to predict early colonization of alien plants within the coastal mangrove ecosystem. We used the unchanneled path length (UPL), a widely applied hydrological connectivity-related indicator, to assess the accessibility of the mangrove. The enhanced vegetation index (EVI), positively correlated with above-ground biomass, was used to evaluate the potential competitive intensity. Firstly, building on existing studies, we developed a four-quadrant concept model integrating the effects of EVI and UPL on the early colonization of the alien species Sonneratia apetala. Our results revealed significant differences in EVI and UPL values between colonized and uncolonized areas, with colonized regions displaying markedly lower values (P < 0.001). Additionally, logistic regression showed a significant negative association between the probability of successful colonization by S. apetala and both indicators (P < 0.001). These results validate the effectiveness of our conceptual model. Furtherly, we identified four key niche opportunities for exotic species in mangrove: mudflats outside the mangrove forest, tidal creeks, canopy gaps, and unmanaged abandoned aquaculture ponds. Overall, this study provides important insight into the ecological processes of alien S. apetala colonization and practical information for management of coastal areas susceptible to invasion. Additionally, it presents a case study on the practical application of the concept of invasibility in the management of alien species.

Potential effect of managing connectivity to contain disease spread among free‐ranging wild boar (Sus scrofa) in disparate landscapes

Abstract Landscape connectivity is a major factor shaping the spread of pathogens in wildlife populations. By managing connectivity, transmission pathways can be broken and disease spread be contained, particularly in the early phases of an outbreak. Having witnessed recent outbreaks of African Swine Fever in free‐ranging wild boar (Sus scrofa) in Belgium, Germany and Italy, offices for disease control are on the alert also in other western European countries. This study investigates the potential effect of managing landscape connectivity to contain disease spread among free‐ranging wild boar in disparate landscapes. It involves research into (1) the ease with which wildlife corridors can be blocked for wild boar, (2) the connectivity of wild boar habitat and (3) the impact of landscape fragmentation on connectivity management. This is addressed by carrying out GIS analyses and performing graph operations on the wild boar networks in different biogeographical regions of Switzerland. The results of doing research into the three above‐mentioned objects show that, regarding the first, most wildlife corridors are hard to block for wild boar, because their features or location make fencing difficult. Regarding the second, the wild boar habitat is connected. Opening wildlife passages that are currently under construction may allow wild boar to disperse to hitherto uncolonized areas. Regarding the third, all wild boar networks could be partially decomposed by blocking the easy to block corridors and closing the passages. Network decomposition would be easiest to achieve in the region where the built infrastructure is most abundant. All over Switzerland, the potential epidemic size could be reduced by 25% when blocking the minimal set of corridors and passages that cut the networks to non‐decomposable components. This study suggests that (a) combining connectivity analysis with fragmentation analysis is key to explaining why a specific measure of disease containment is more effective in one landscape than in the other, (b) complementing the permeability model with a species distribution model is essential to identify connected habitat patches for the species of concern and (c) connectivity metrics should consider also the surface area of occupied habitat patches and relative abundance of the species of concern.

Modelled dispersal of snow crab (Chionoecetes opilio) larvae and potential settlement areas in the western Barents Sea

Abstract Since the mid-1990s, a snow crab (Chionoecetes opilio) population has established in the eastern Barents Sea. Spawning females and newly hatched larvae are now also found in the central Barents Sea, warranting speculations on a further westward colonization by pelagic larvae. Here, we model the potential for larval dispersal and settlement into uncolonized areas in the western Barents Sea. We used a biophysical model of ocean currents and hydrography, coupled with a Lagrangian dispersal algorithm and larval survival functions as response to temperature. The model predicts limited dispersal from the central Barents Sea to western areas, primarily due to a mismatch between prevailing temperature regimes and temperature tolerances for the different larval stages. In addition, there was limited westward transport of water masses with temperatures that would allow completion of the pelagic larval development. We speculate that for larvae to successfully supply benthic recruits to the remaining uncolonized areas in the western Barents Sea, adult crabs would first need to establish new spawning aggregations, for example along the western slopes of the Barents Sea shelf. Immediate implications are limited potential for expanding the fishery to the western areas of the Barents Sea.

Damaging and protective interactions of lichens and biofilms on ceramic dolia and sculptures of the International Museum of Ceramics, Faenza, Italy

Although ceramic objects are an important part of the worldwide cultural heritage, few investigations on the effects of lithobiontic growth on their outdoor conservation are available in the literature. Many aspects of the interaction between lithobionts and stones are still unknown or strongly debated, as in the case of equilibria between biodeterioration and bioprotection. This paper describes research on the colonization by lithobionts on outdoor ceramic Roman dolia and contemporary sculptures of the International Museum of Ceramics, Faenza (Italy). Accordingly, the study i) characterized the mineralogical composition and petrographic structure of the artworks, ii) performed porosimetric measurements, iii) identified lichen and microbial diversity, iv) elucidated the interaction of the lithobionts with the substrates. Moreover, v) the measurements of variability in stone surface hardness and in water absorption of colonized and uncolonized areas were collected to assess damaging and/or protective effects by the lithobionts. The investigation showed how the biological colonization depends on physical properties of the substrates as well on climatic conditions of environments in which the ceramic artworks are located. The results indicated that lichens Protoparmeliopsis muralis and Lecanora campestris may have a bioprotective effect on ceramics with high total porosity and pores with very small diameters, as they poorly penetrate the substrate, do not negatively affect surface hardness and are able to reduce the amount of absorbed water limiting the water ingress. By contrast, Verrucaria nigrescens, here widely found in association with rock-dwelling fungi, deeply penetrate terracotta causing substrate disaggregation, with negative consequences on surface hardness and water absorption. Accordingly, a careful evaluation of the negative and positive effects of lichens must be carried out before deciding their removal. Regarding biofilms, their barrier efficacy is related to their thickness and composition. Even if thin, they can impact negatively on substrates enhancing the water absorption in comparison to uncolonized parts.

Characterization of a biofilm and the pattern outlined by its growth on a granite-built cloister in the Monastery of San Martiño Pinario (Santiago de Compostela, NW Spain)

The upper zone of the background walls of the processional cloister of the Monastery of San Martiño Pinario (Santiago de Compostela, Galicia, Spain) is affected by a deep green, highly hydrophobic subaerial biofilm. The pattern that the biofilm follows the walls suggests that particular microclimatic conditions induce changes in the biofilm properties. To test this hypothesis, taxonomic and structural identification of the biofilm was carried out by respectively light microscopy and confocal laser scanning microscopy. In addition, the chemical composition was determined by quantification of extracellular polymeric substances in the extracellular matrix of the biofilm, and hydrophobicity was determined by contact angle and water drop penetration time of biofilm and cells. Furthermore, the bioprotective or biodeteriorative role of the biofilm on the cloister is discussed on the basis of the results of stereoscopic microscope observations, X-ray diffraction and attenuated total reflectance-Fourier transform infrared spectroscopy analysis of granite samples from uncolonized areas and from underneath the biofilm. The findings showed that Apatococcus lobatus is the predominant algae in the biofilm. The presence of this alga is favoured by water condensation and it neither damages nor protects the substrate, only causing an aesthetic impact.

Wing polymorphisms of Pterostichus melanarius (Coleoptera: Carabidae) (Illiger, 1978) in Alberta pulse crops

In a 6 week research project, a wing-dimorphic carabid species was studied to identify the proportions of macropterous (large functional wings) individuals and brachypterous (short, rudimentary wings) individuals from different pulse growing regions of Alberta. Pterostichus melanarius I. (Coleoptera: Carabidae) can be short-winged (SW) due to brachyptery being a dominant gene or long-winged (LW) individuals causing macroptery. Although macroptery is a recessive trait, the LW morph persists through the recolonization of populations due to human disturbance. Their ability to fly facilitates their dispersal across Alberta to uncolonized areas. Samples of P. melanarius were captured as bycatch from pea leaf weevil, Sitona lineatus L. (Coleoptera: Curculionidae) pitfall traps from the East, Capital, and Central regions of Alberta. Traps were positioned on a 175 meter transect pea and faba field margins in spring and again in the fall. Captured P. melanarius were identified and separated by collection site and date and stored in 95% ethanol until measurements. The beetles from the bycatch samples were sexed using tarsal characteristics. Anterior tarsal segments of the front pair of tarsi are dilated in males and normal in females. After being identified and recorded as “M” or “F”, they were mounted on a foam board with insect pins for measurement. The elytra (forewings) length and width was measured followed by measurement of their hindwings. They were classified as “SW” or “LW” depending on the functionality of their wings. Out of 440 individuals from the Capital region, 17.1% of captured P. melanarius were LW and 83.0% were SW. From the Central region 21.6% of 495 beetles were LW and 83.4% of them were SW. In the East region less P. melanarius were captured and from 94 individuals, 46.8% were LW and 53.2% were SW. Macropterous individuals are more common in the East region due to recolonization of populations whereas in the Central and Capital region the proportions of SW are much larger. In regions that have established populations of P. melanarius the proportions of SW are greater than LW.

INTEGER PROGRAMMING APPROACH TO CONTROL INVASIVE SPECIES SPREAD BASED ON CELLULAR AUTOMATON MODEL

AbstractWe propose a new optimization model that captures the spatial dynamics of invaders by a cellular automaton model and finds the optimal solution to control its spread within a 0–1 integer programming framework. The model seeks a solution by minimizing the total costs to implement treatments for preventing the spread and damage caused by invaders’ colonization. By incorporating a cellular automaton model governed by state‐ and distance‐dependent probability rule of colonization, the model is transformed into a linear model, so that a 0–1 integer programming formulation is used to evaluate and compare an optimal allocation of treatments on colonized and uncolonized areas. The study uses a hypothetical map to show that treatments on colonized cells are more effective when implemented at the front line of the invaders, while treatments on uncolonized areas are effective when conducted with some distance or buffer zone away from the front line. These buffer zones are likely to be colonized regardless of treatment. Under annual budget limits, treatments on colonized cells are implemented first. With heterogeneity in the invaders’ dynamics, the proposed optimization model provides an optimal allocation of treatments much different from the solution with homogeneous environment. However, treatment at the front line of the invading species is always recommended.

Reconstructing the reproductive mode of an Ediacaran macro-organism.

Enigmatic macrofossils of late Ediacaran age (580-541 million years ago) provide the oldest known record of diverse complex organisms on Earth, lying between the microbially dominated ecosystems of the Proterozoic and the Cambrian emergence of the modern biosphere. Among the oldest and most enigmatic of these macrofossils are the Rangeomorpha, a group characterized by modular, self-similar branching and a sessile benthic habit. Localized occurrences of large in situ fossilized rangeomorph populations allow fundamental aspects of their biology to be resolved using spatial point process techniques. Here we use such techniques to identify recurrent clustering patterns in the rangeomorph Fractofusus, revealing a complex life history of multigenerational, stolon-like asexual reproduction, interspersed with dispersal by waterborne propagules. Ecologically, such a habit would have allowed both for the rapid colonization of a localized area and for transport to new, previously uncolonized areas. The capacity of Fractofusus to derive adult morphology by two distinct reproductive modes documents the sophistication of its underlying developmental biology.

Loss of Hypermethylated in Cancer 1 (HIC1) in Breast Cancer Cells Contributes to Stress-induced Migration and Invasion through β-2 Adrenergic Receptor (ADRB2) Misregulation

The transcriptional repressor HIC1 (Hypermethylated in Cancer 1) is a tumor suppressor gene inactivated in many human cancers including breast carcinomas. In this study, we show that HIC1 is a direct transcriptional repressor of β-2 adrenergic receptor (ADRB2). Through promoter luciferase activity, chromatin immunoprecipitation (ChIP) and sequential ChIP experiments, we demonstrate that ADRB2 is a direct target gene of HIC1, endogenously in WI-38 cells and following HIC1 re-expression in breast cancer cells. Agonist-mediated stimulation of ADRB2 increases the migration and invasion of highly malignant MDA-MB-231 breast cancer cells but these effects are abolished following HIC1 re-expression or specific down-regulation of ADRB2 by siRNA treatment. Our results suggest that early inactivation of HIC1 in breast carcinomas could predispose to stress-induced metastasis through up-regulation of the β-2 adrenergic receptor.

Range-expanding populations of a globally introduced weed experience negative plant-soil feedbacks.

BackgroundBiological invasions are fundamentally biogeographic processes that occur over large spatial scales. Interactions with soil microbes can have strong impacts on plant invasions, but how these interactions vary among areas where introduced species are highly invasive vs. naturalized is still unknown. In this study, we examined biogeographic variation in plant-soil microbe interactions of a globally invasive weed, Centaurea solstitialis (yellow starthistle). We addressed the following questions (1) Is Centaurea released from natural enemy pressure from soil microbes in introduced regions? and (2) Is variation in plant-soil feedbacks associated with variation in Centaurea's invasive success?Methodology/Principal FindingsWe conducted greenhouse experiments using soils and seeds collected from native Eurasian populations and introduced populations spanning North and South America where Centaurea is highly invasive and noninvasive. Soil microbes had pervasive negative effects in all regions, although the magnitude of their effect varied among regions. These patterns were not unequivocally congruent with the enemy release hypothesis. Surprisingly, we also found that Centaurea generated strong negative feedbacks in regions where it is the most invasive, while it generated neutral plant-soil feedbacks where it is noninvasive.Conclusions/SignificanceRecent studies have found reduced below-ground enemy attack and more positive plant-soil feedbacks in range-expanding plant populations, but we found increased negative effects of soil microbes in range-expanding Centaurea populations. While such negative feedbacks may limit the long-term persistence of invasive plants, such feedbacks may also contribute to the success of invasions, either by having disproportionately negative impacts on competing species, or by yielding relatively better growth in uncolonized areas that would encourage lateral spread. Enemy release from soil-borne pathogens is not sufficient to explain the success of this weed in such different regions. The biogeographic variation in soil-microbe effects indicates that different mechanisms may operate on this species in different regions, thus establishing geographic mosaics of species interactions that contribute to variation in invasion success.

Moonmilk Deposits Originate from Specific Bacterial Communities in Altamira Cave (Spain)

The influence of bacterial communities on the formation of carbonate deposits such as moonmilk was investigated in Altamira Cave (Spain). The study focuses on the relationship between the bacterial communities at moonmilk deposits and those forming white colonizations, which develop sporadically throughout the cave. Using molecular fingerprinting of the metabolically active bacterial communities detected through RNA analyses, the development of white colonizations and moonmilk deposits showed similar bacterial profiles. White colonizations were able to raise the pH as a result of their metabolism (reaching in situ pH values above 8.5), which was proportional to the nutrient supply. Bacterial activity was analyzed by nanorespirometry showing higher metabolic activity from bacterial colonizations than uncolonized areas. Once carbonate deposits were formed, bacterial activity decreased drastically (down to 5.7% of the white colonization activity). This study reports on a specific type of bacterial community leading to moonmilk deposit formation in a cave environment as a result of bacterial metabolism. The consequence of this process is a macroscopic phenomenon of visible carbonate depositions and accumulation in cave environments.

Dalmatian toadflax (Linaria dalmatica) response to wildfire in a southwestern USA forest

Severe wildfires often facilitate the spread of exotic invasive species, such as Dalmatian toadflax (Linaria dalmatica). We hypothesized that toadflax growth and reproduction would increase with increasing burn severity in a ponderosa pine (Pinus ponderosa)-dominated forest. We measured toadflax density, cover, flowering stalks, and native species richness and cover on 327 plots for 3 y after a 2001 wildfire. Toadflax stem density, cover, and flowering stalks increased in 2003, then decreased in 2004 in all burn severity classes, but remained higher than initial 2002 values. Toadflax spread to previously uncolonized areas, though stem density decreased in unburned plots. Transition matrices showed that more plots on moderately (73%) and severely (74%) burned areas classified as high toadflax density in 2002 remained high density in 2004. Deterministic matrix modeling using 2002 to 2004 transition probabilities projected that the percentage of high-density plots would stabilize on moderately and severely burned sites at 41 and 61%, respectively. In contrast, 20-y rates of change (X) for unburned and low-severity burn sites were < 1.0, and stabilizing at 2% for unburned plots and 19% for low-severity burn plots. Post-wildfire conditions in high-severity burned areas favour increased density, cover, reproduction, and spread of Dalmatian toadflax, while native species richness was reduced, suggesting that the invasive species would persist, at least in the short term, at the expense of natives.

Investigating intra-bone isotopic variations in bioapatite using IR-laser ablation and micromilling: Implications for identifying diagenesis?

The potential of in situ microsampling (micromilling and IR-laser ablation) to detect intra-sample isotopic variation resulting from diagenesis and/or natural remodeling of bone was examined in this study. Modern sheep bones were exposed to microbial populations to induce diagenesis and the δ 13C and δ 18O values of bioapatite structural carbonate and phosphate were determined for these samples and for diagenetically modified archaeological samples from three different environments. No significant differences were found between the δ 13C laser or δ 18O laser values of microbially colonized and uncolonized areas on the modern bone surfaces, or between well-preserved and poorly preserved regions of the archaeological material. However, high degree of intra-sample variation was observed in δ-values obtained using IR-laser ablation, some of which arose from methodological challenges associated with this method. Further, δ 13C values obtained using IR-laser ablation were lower than those acquired by conventional analysis, likely because of contamination from organic matter in the samples. Isotopic compositions of structural carbonate samples obtained by micromilling were less variable. For both methods, however, significant differences in δ 13C and δ 18O values were observed for different bone surfaces. These variations may indicate differences in the isotopic compositions of food and water incorporated into osteons over a lifetime, and illustrate the relationship between bone remodelling and isotopic heterogeneity in bone. Overall, our results highlight the difficulties of using the IR-laser ablation method for measuring isotopic compositions of bone.

Seed rain and environmental controls on invasion of Picea abies into grassland

Although changes in land-use, climate, and the spread of introduced tree species have increased the global importance of tree invasions into grasslands, our ability to predict any particular invasion is limited. To elucidate mechanisms driving tree invasions of grasslands, we studied in detail how seed dispersal and fine-scale environment control the expansion of an introduced Picea abies Karst. (Norway spruce) population into Western Carpathian grassland. We mapped invading trees and measured tree size, fecundity, seed rain, seedling density, plant community composition, and light and soil environment within a 200 × 60 m belt across the invasion front. Maximum likelihood estimates of dispersal kernels suggested peak seed deposition directly underneath tree crowns where germination was poor, but mean dispersal distances were sufficiently large to generate overlapping seed shadows from multiple trees that saturated the invasion front with seeds further away from seed-dispersing trees. Partial Mantel tests indicated that germinant density was affected considerably less by seed rain than by moss cover (r = 0.54), overstory tree influence (r = −0.32), soil moisture (r = 0.21), grass cover (r = −0.15), and diffuse radiation (r = 0.13). However, these variables were not independent but formed complex multivariate gradients within the invasion front. Moss cover and soil moisture were negatively correlated with overstory tree influence and the resulting gradient clearly affected germinant density (partial Mantel r = 0.45). In contrast, positively correlated light and grass cover defined a gradient related weakly to germinant density (partial Mantel r = 0.05) as it integrated opposing effects of these variables on germinants. Seedlings had similar environmental associations, but except for the lasting positive effects of moss these tended to weaken with seedling size. Although a few seedlings may establish and survive in the more adverse environment of the outer edges of the invasion front, a significant population expansion may require a gradual build-up of the critical density of invading trees to reduce grass cover and facilitate germination on moist mossy seedbeds within uncolonized areas. Thus, Picea abies appears more likely to spread within temperate grasslands by gradual expansion of its population frontier rather than by advanced groups.

Aggregates of Resident Bacteria Facilitate Survival of Immigrant Bacteria on Leaf Surfaces

The fate of immigrant bacterial cells on leaves under stressful conditions was determined as a function of the anatomical features and the local spatial density of resident cells at their landing site. Pantoea agglomerans 299R was established on bean leaves and the survival of immigrant cells of Pseudomonas fluorescens A506 and Pseudomonas syringae B728a, as well as P. agglomerans itself, was determined by epifluorescence microscopy following subsequent exposure of plants to desiccation stress. Resident and immigrant bacterial strains constitutively expressed the cyan and the green fluorescent protein, respectively, and the viability of individual cells was assessed directly on leaf surfaces following propidium iodide staining. Although only a small fraction of the immigrant cells landed on established bacterial aggregates, their fate was usually strongly influenced by the presence of indigenous bacteria at the site at which they landed. Immigrants of P. agglomerans 299R or P. fluorescens A506 that arrived as solitary cells had about double the probability of survival when landing on aggregates formed by P. agglomerans 299R than when landing on uncolonized areas of the leaf surface. In contrast, the survival of P. syringae B728a was similar irrespective of whether it landed on colonized or uncolonized parts of a leaf. The nature of plant anatomical features at which immigrant bacteria landed also strongly influenced the fate of immigrant bacteria. The fraction of immigrant cells of each species tested that landed on veins, glandular trichomes, or epidermal cells altered by P. agglomerans that died was always less than when they landed on normal epidermal cells or at the base of hooked trichomes. Depending on the process by which immigrants arrive at a leaf, only a small fraction of cells may be deposited on existing bacterial aggregates. Although uncolonized sites differed greatly in their ability to influence the survival of immigrant cells, the fate of an immigrant bacterium will depend on the nature of the leaf structure on which it is deposited, and apparently indirectly on the amount of nutrients and water available at that site to support the development of bacterial aggregates.

Black-Tailed Prairie Dog Effects on Montana's Mixed-Grass Prairie

Forty paired sites were examined on the mixed-grass prairie of northeastern Montana to compare the effects of black-tailed prairie dog (Cynomys ludovicianus) colonies on native range vegetation. Thirty 0.25-m2 quadrats were placed on colonized and uncolonized locations and matched by environmental conditions. Cover and standing crop biomass of each plant species was estimated using a double sampling procedure where every third plot was clipped and estimated. A total of 2 400 quadrats were estimated, whereas 720 quadrats were clipped during the months of May–August of 2000 and 2001. Crude protein, digestibility, neutral detergent fiber, and acid detergent fiber were determined on the basis of vegetative classes (cool-season grasses, warm-season grasses, standing dead grass, forbs, and dwarf shrubs). Pairwise comparisons were made using paired t tests and differences were declared significant at the 0.05 level. Plant biomass of colonized sites was dominated by fringed sagewort (Artemisia frigida Willd.) (42%), blue grama (Bouteloua gracilis [HBK] Lag. ex Steud) (16%), and western wheatgrass (Agropyron smithii Rydb.) (16%). Uncolonized sites were dominated by Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young) (36%), western wheatgrass (13%), and blue grama (12%). Standing crop biomass, plant species richness, litter, standing crop crude protein, sagebrush canopy cover, and density were greater (P < 0.05) on uncolonized areas compared to colonized areas. Bare ground and crude protein concentration were greater (P < 0.05) on areas colonized by prairie dogs compared to uncolonized areas. Digestibility and fiber content of both areas were not different (P > 0.05). Activities associated with prairie dog colonies reduced plant productivity and plant species richness of the mixed-grass prairie by reducing cool-season perennial grasses and litter, increasing bare ground, and eliminating big sagebrush.

Black-Tailed Prairie Dog Effects on Montana's Mixed-Grass Prairie

Forty paired sites were examined on the mixed-grass prairie of northeastern Montana to compare the effects of black-tailed prairie dog (Cynomys ludovicianus) colonies on native range vegetation. Thirty 0.25-m2 quadrats were placed on colonized and uncolonized locations and matched by environmental conditions. Cover and standing crop biomass of each plant species was estimated using a double sampling procedure where every third plot was clipped and estimated. A total of 2 400 quadrats were estimated, whereas 720 quadrats were clipped during the months of May-August of 2000 and 2001. Crude protein, digestibility, neutral detergent fiber, and acid detergent fiber were determined on the basis of vegetative classes (cool-season grasses, warm-season grasses, standing dead grass, forbs, and dwarf shrubs). Pairwise comparisons were made using paired t tests and differences were declared significant at the 0.05 level. Plant biomass of colonized sites was dominated by fringed sagewort (Artemisia frigida Willd.) (42%), blue grama (Bouteloua gracilis [HBK] Lag. ex Steud) (16%), and western wheatgrass (Agropyron smithii Rydb.) (16%). Uncolonized sites were dominated by Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young) (36%), western wheatgrass (13%), and blue grama (12%). Standing crop biomass, plant species richness, litter, standing crop crude protein, sagebrush canopy cover, and density were greater (P &lt; 0.05) on uncolonized areas compared to colonized areas. Bare ground and crude protein concentration were greater (P &lt; 0.05) on areas colonized by prairie dogs compared to uncolonized areas. Digestibility and fiber content of both areas were not different (P &gt; 0.05). Activities associated with prairie dog colonies reduced plant productivity and plant species richness of the mixed-grass prairie by reducing cool-season perennial grasses and litter, increasing bare ground, and eliminating big sagebrush.

Spatial pattern of invading Dendroctonus micans (Coleoptera: Scolytidae) populations in the United Kingdom

The spatial pattern of Dendroctonus micans (Kug.) attacks on individual spruce stands was analysed at the regional scale in Britain using data collected between 1982 and 1984 by the British Forestry Commission. These survey data reflect at least 10 years of D. micans spread, in the absence of natural enemies and of pest management control measures. A large-scale spatial gradient in the attack density at the stand level was identified and modelled. The large-scale spatial trend model explained 31.3% of the variability, and divided the study area in three separate areas: a zone where the insect was well established and where attack density presented low variations, a transition zone where attack density sharply decreased, and a zone not yet colonized. Attack density was related to site and stand factors, and to landscape neighbourhood in a linear spatial regression model. The factors correlated to attack density and the spatial autocorrelation structure of remaining variability were found to vary according to the zones, reflecting the predominance of different ecological processes occurring in colonized and uncolonized areas. The shape and orientation of the large-scale spatial model was shown to be mostly influenced by the spatial distribution of early attacks.

A Critical Review of Assumptions About the Prairie Dog as a Keystone Species.

/ Prairie dogs (Cynomys spp.) have been labeled as keystone species because of their influence on biological diversity and ecosystem function. However, the validity of several assumptions used to support keystone status is questionable. We review the strength of the evidence and the magnitude of the prairie dog's effects on ecosystem structure and function. We use this review to reevaluate the keystone role for prairie dogs. Our goal is to encourage sound management of the prairie dog ecosystem by improving the ecological foundation of their keystone status. Our review confirms that prairie dogs affect a number of ecosystem-level functions but that their influence on prairie vertebrates may be less than previously suggested. Species richness and abundance patterns were variable among plants, mammals, and birds and were not consistently higher on prairie dog colonies compared to uncolonized areas. In addition, only nine of the 208 species listed in the literature as observed on or near prairie dogs colonies had quantitative evidence of dependence on prairie dogs. Abundance data indicated opportunistic use of colonies for an additional 20 species. A total of 117 species may have some relationship with prairie dogs, but we lacked sufficient data to evaluate the strength of this relationship. The remaining 62 species may be accidental or alien to the system. Despite our conclusion that some prairie dog functions may be smaller than previously assumed, collectively these functions are quite large compared to other herbivores in the system. We suggest that prairie dogs also provide some unique functions not duplicated by any other species and that continued decline of prairie dogs may lead to a substantial erosion of biological diversity and landscape heterogeneity across prairie and shrub-steppe landscapes. Thus, we concur that keystone status for prairie dogs is appropriate and may aid conservation efforts that help protect species dependent on prairie dogs and support other important ecosystem functions.KEY WORDS: Prairie dogs; Cynomys spp.; Keystone species; Ecosystem functions; Biological diversityhttp://link.springer-ny.com/link/service/journals/00267/bibs/24n2p177.html

Establishment and Phenology of the Parasitoid Microctonus hyperodae (Hymenoptera: Braconidae) in New Zealand

Environ Entomol. 27(6): 1386-1392 (1998) The South American weevil Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae) is one of New Zealand's worst pasture pests causing between NZ$78-251 million damage per year. Accordingly, the South American parasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae, Euphorinae) was released at Lincoln, Canterbury, in 1991 as a biological control agent for L. bonariensis. M h yperodae was first recovered from the field in January 1992 although noticeable population growth did not occur until a year later after which rates of parasitism increased very rapidly, although these rates declined over time. Under field conditions, M. hyperodae completed 3 generations per year after postdiapause development in September. Peak numbers of eggs occurred in late December, early March, and mid-May, respectively; the 3rd generation was much smaller than the first 2. A notable decline in percent parasitism between the 1st and 2nd generations (mid-December and mid-February each year) was related to a large influx of 1 st summer generation adult weevils during an intergenerational absence of adult parasitoids. Second parasitoid generation infection rates of the weevils were very high (>90%) by early March but soon declined as protracted autumnal (April-May) emergence of weevils, combined with immigration from surrounding uncolonized areas, increased the proportion of unparasitized weevils. The small 3rd generation of M. hyperodae may be important for parasitizing these late emerging weevils. Host and parasitoid phenology conformed approximately to an existing phenological model. Analysis of field data indicated that the day-degree requirements of M hyperodae egg and 1st, 2nd, 3rd,, and 4th larval stages above a threshold of 10.2°C were 14, 154, 28, 19, and 11, respectively.