Analysis of spatial and temporal variation in the community structure of yeasts associated with decayingOpuntia cactus

The microbial structure within, between, and over time in decaying cladodes of the common prickly pearOpuntia stricta was studied at each of two separate localities. In general, the effective number of yeast species and yeast species diversity increased as the rot aged to the observed maximum time of 4 weeks. Yeast heterogeneity at the two localities differed in the mode of environmental influence, with spatial variability (among rots) most important at one and temporal variability (within rots over time) most important at the other. Differences in cactus density and quality (age) are most likely determinants of the differences in yeast community structure.     

Analysis of the community structure of yeasts associated with the decaying stems of cactus. II.Opuntia species

A survey was made of yeast species associated with the decaying pads of 3 prickly pear cacti (Opuntia phaeacantha, O. ficus-indica, andO. lindheimeri) in Arizona and Texas. Yeast communities from 12 localities were compared among localities, amongOpuntia species, and with previous data on yeast communities associated with columnar cacti. The results indicate thatOpuntia necroses contain relatively more yeast species with broader physiological abilities in their communities than columnar necroses. It is argued that differences in chemistry of the opuntias and columnar forms in concert with the insect vectors specific for these cacti account for the differences in yeast community structure. It is further hypothesized that the differences in yeast community structure have been important in the evolution and maintenance of species diversity forDrosophila species which live in the decaying stems or cladodes of various cacti. Most of the yeast community evolution in the cacti is postulated to have proceeded by evolution in situ and not by additions and replacements from outside of the system.     

Analysis of the community structure of yeasts associated with the decaying stems of cactus. III.Stenocereus thurberi

Yeast communities in necroses of organpipe cactus (Stenocereus thurberi) were surveyed at 3 localities in Arizona. Quantitative analysis of random samples allows comparisons of the types and numbers of yeasts at 3 levels: within plants, between plants within a locality, and between localities. The analysis shows that the major source of variability is between plants. This pattern is identical with the pattern shown by agria cactus (Stenocereus gummosus) and is thought to be due to sampling different successional stages. No significant differences in estimates of the effective number of yeast species (ENS) in agria and organpipe samples were found. Comparisons of agria, organpipe, and prickly pear (Opuntia) cacti support the hypothesis that cactus chemistry is an important determinant of the yeast community structure which, in turn, is an important determinant of the diversity ofDrosophila species which utilize necrotic cacti as feeding and breeding substrates.     

The ecology of the yeast flora in necroticOpuntia cacti and of associatedDrosophila in Australia

A survey was made of the yeast communities isolated from necrotic tissue of 4 species of prickly-pear cacti (Opuntia stricta, O. tomentosa, O. monacantha, andO. streptacantha) which have colonized in Australia. Yeast communities were sampled from a number of localities and at different times. Cactus specific yeasts accounted for 80% of the total isolates, and the 3 most common species contributed 63% of the total. Comparisons of the species compositions of the yeast communities indicated that the differences among communities were greater betweenOpuntia species than between different localities within a single cactus species, and also that differences between years were greater than average differences between localities within years. Multivariate statistical tests of association between yeast community and physical features of rots indicated that temperature, pH, and age of rot all exerted some influence on the structure of the yeast community. Similar analyses involvingDrosophila species inhabiting these cactus rots suggested the existence of complex associations betweenDrosophila community, yeast community, and physical and chemical attributes of the cactus necroses.     

Identification of Fungal Species Associated with Cladode Spot of Prickly Pear and Their Sensitivity to Chitosan

México is the most important producer of prickly pear (Opuntia ficus‐indica) in the world. There are several fungal diseases that can have a negative impact on their yields. In this study, there was a widespread fungal richness on cladodes spot of prickly pears from México. A total of 41 fungi isolates were obtained from cladodes spot; 11 of them were morphologically different. According to the pathogenicity test, seven isolates caused lesions on cladodes. The morphological and molecular identification evidenced the isolation of Colletotrichum gloeosporioides, Alternaria alternata, Fusarium lunatum, Curvularia lunata. All these species caused similar symptoms of circular cladodes spot. However, it is noticeable that some lesions showed perforation and detachment of affected tissues by Fusarium lunatum. To our knowledge, this is the first report of the Fusarium lunatum as phytopathogenic fungus of cladodes of prickly pear. The chitosan inhibited the mycelium growth in the seven isolates of phytopathogenic fungi. Chitosan applications diminished the disease incidence caused by C. gloeosporioies and F. lunatum in 40 and 100%, respectively. Likewise, the lesion severity index in cladodes decreased. There are no previous reports about the application of chitosan on cladodes of prickly pears for the control of phytopathogenic fungi. Therefore, this research could contribute to improve the strategies for the management of diseases in prickly pear.     

Opposing forces of seed dispersal and seed predation by mammals for an invasive cactus in central Kenya

The invasive erect prickly pear cactus (Opuntia stricta) has reduced rangeland quality and altered plant communities throughout much of the globe. In central Kenya's Laikipia County, olive baboons (Papio anubis) frequently consume O. stricta fruits and subsequently disperse the seeds via defecation. Animal‐mediated seed dispersal can increase germination and subsequent survival of plants. However, consumption of seeds (seed predation) by rodents may offset the potential benefits of seed dispersal for cactus establishment by reducing the number of viable seeds. We investigated foraging preferences of a common and widely distributed small mammal—the fringe‐tailed gerbil (Gerbilliscus robustus), between O. stricta seeds deposited in baboon faeces versus control O. stricta seeds. In addition to providing evidence of seed predation on O. stricta by G. robustus, our data show that seed removal was higher (shorter time to use) for seeds within faeces than for control seeds. G. robustus clearly prefers seeds within faeces compared to control seeds. These results suggest that high abundances of rodents may limit successful establishment of O. stricta seeds, possibly disrupting seed dispersal via endozoochory by baboons.     

Morphological and phytochemical aspects of three alien Opuntia species on Euganean Hills in North-Eastern Italy

In this study, Opuntia stricta, O. engelmannii, and O. humifusa, naturalized alien units in the Euganean Hills (North-Eastern Italy), are investigated. Different morphological and physiological features both in cladodes collected in summer and winter and in fruits arisen from two blooms are reported. The morphological observations showed a different organization in epidermis/hypodermis of cladodes collected in winter and in summer, probably correlated to the individual plant reaction to a stressful factor as low temperature. Scanning electron microscopy observations revealed no differences in the deposition of waxes and stomata distribution in the epidermis of cladodes. The betacyanin analysis showed that cladodes produce these pigments only in the winter season. In all the species, the higher content of betacyanins was reached in the fruits from the second bloom, with O. stricta being the most rich. The amount of betacyanins is comparable to some commercial red beets used as a common source of betacyanins as natural food color.     

Association between Opuntia species invasion and changes in land-cover in the Mediterranean region

In Mediterranean regions, biological invasions pose a major threat to the conservation of native species and the integrity of ecosystems. In addition, changes in land‐cover are a widespread phenomenon in Mediterranean regions, where an increase in urban areas and major changes from agricultural abandonment to shrub encroachment and afforestation are occurring. However, the link between biological invasions and changes in land‐cover has scarcely been analyzed. We conducted a regional survey of the distribution of the two alien prickly‐pear cacti Opuntia maxima and O. stricta in Cap de Creus (Catalonia, Spain) and related patterns of invasion to spatially explicit data on land‐cover/change from 1973 to 1993 to test the hypotheses that the two Opuntia species invade areas that have experienced large land‐cover transformations. We found that Opuntia invasion is particularly high in shrublands and woodlands located near urban areas. O. maxima are over‐represented in the shrublands and O. stricta in the woodlands that were former crops. Crop coverage has dropped by 71% in this 20‐year period. This study highlights the role of past land‐cover in understanding the present distribution of plant invasions.     

Role of topography and soils in grassland structuring at the landscape and community scales

The relative importance of abiotic factors in community assembly is debated and thought to be dependent on the scale. I investigated the relative role of topography and soils as structuring agents at the landscape and the community scales in 126 subalpine calcareous grasslands in the Pyrenees, in terms of species composition and abundance. I wished to know: (1) the role of abiotic factors in the organization of plant communities across the landscape; (2) how much of the variation in community distribution was accounted for by abiotic factors; and (3) how well their role applied to the distribution of dominant species at the landscape and the community scales. The hypothesis was: abiotic factors play an important role in community distribution in the landscape, but species interactions are more important within communities. Multivariate methods generated four communities, organized in two contrasting groups along the main vegetation axis, which explained 13% of the variation: mesic grasslands (Nardus stricta and Festuca nigrescens communities) and xeric grasslands (Carex humilis and Festuca gautieri communities). Mesic communities were more acidic and fertile than xeric communities. Changes in the abiotic environment, accounting for up to 80% of the variation in the vegetation, were smooth, while the transition between xeric and mesic grasslands was sharp in terms of species composition. The distribution in the landscape of the first main species from each community was closely related to abiotic factors, which modeled poorly the abundance of the main species at smaller scales. At the within-community scale, the explanatory power of biotic relationships was community dependent, producing the most significant models for plants highly dominant within their communities, such as N. stricta and F. gautieri. Contrary to current hypothesis, there was a shift from mainly positive relationships among dominant species in fertile mesic communities to mainly negative in infertile xeric ones.     

Genetic differentiation of island populations: geographical barrier or a host switch?

In the Sonoran desert, there exists a diverse community of cactophilic drosophilids that exploit toxic, rotting cactus tissue as a food resource. The chemistry of the necrotic cactus tissue varies among species, and several drosphilid species have evolved specialized detoxification mechanisms and a preference for certain cactus types. In the present study, we compared the genetic structure of two columnar cactus species, Drosophila mettleri and Drosophila mojavensis, and two prickly pear species, Drosophila mainlandi and Drosophila hamatofila, which have all recently colonized Catalina Island off the coast of southern California. Because there are no columnar cactus species on Catalina Island, the two columnar specialists underwent a host switch to prickly pear cactus, the only cactus present on the island. Previous genetic studies of D. mettleri and D. mojavensis showed significant genetic differentiation between mainland and island populations, which could result from restricted gene flow as a result of the San Pedro Channel, or because of a host switch to prickly pear. To distinguish between these possibilities, we analyzed the genetic structure of the prickly pear species aiming to isolate the effects of geography versus host switching. The results obtained show little to no genetic differentiation for the prickly pear species, supporting the hypothesis that the genetic differentiation of the two columnar species is a result of a host switch from columnar cacti to prickly pear. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Overdispersion of body size in Australian desert lizard communities at local scales only: no evidence for the Narcissus effect

Both local and regional processes may contribute to community diversity and structure at local scales. Although many studies have investigated patterns of local or regional community structure, few have addressed the extent to which local community structure influences patterns within regional species pools. Here we investigate the role of body size in community assembly at local and regional scales in Ctenotus lizards from arid Australia. Ctenotus has long been noted for its exceptional species diversity in the Australian arid-zone, and previous studies have attempted to elucidate the processes underlying species coexistence within communities of these lizards. However, no consensus has emerged on the role of interspecific competition in the assembly and maintenance of Ctenotus communities. We studied Ctenotus communities at several hundred sites in the arid interior of Australia to test the hypothesis that body sizes within local and regional Ctenotus assemblages should be overdispersed relative to null models of community assembly, and we explored the relationship between body size dispersion at local and regional scales. Results indicate a striking pattern of community-wide overdispersion of body size at local scales, as measured by the variance in size ratios among co-occurring species. However, we find no evidence for body size overdispersion within regional species pools, suggesting a lack of correspondence between processes influencing the distribution of species phenotypes at local and regional scales. We suggest that size ratio constancy in Ctenotus communities may have resulted from contemporary ecological interactions among species or ecological character displacement, and we discuss alternative explanations for the observed patterns. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Inversion and allozyme polymorphism show contrasting patterns of microgeographical population structure in a natural population of Drosophila buzzatii from Argentina

Second chromosome inversions and genotypic frequencies at seven allozyme loci were determined in a natural population of the cactophilic species Drosophila buzzatii that uses as breeding sites the necrotic cladodes of the prickly pear Opuntia quimilo and the rotting stems of cardón, Trichocereus terschekii. Different processes govern the evolutionary fate of inversion and allozyme polymorphisms. A pattern of heterotic balance for inversions seems to be acting uniformly in each breeding site and could depend on different regimes of density‐dependent selection within cactus hosts. Patterns of variation of allozymes revealed significant heterogeneity in allele frequencies for Esterase‐1 (Est‐1) among O. quimilo rots and Aldehyde oxidase (Aldox) and Xanthine dehydrogenase (Xdh) among T. terschekii substrates and showed gene‐cactus effects only for Esterase‐2 (Est‐2). Consistent and significant excesses of homozygotes were detected at both the within‐rot and in the total population levels that could be accounted for by diversifying selection among individual breeding sites.     

An attempt to restore a central European species‐rich mountain grassland through grazing

Abstract. This paper describes the effects of re‐establishing seasonal cattle grazing by 0.7 animal.ha^‐1 on vegetation in a long‐term abandoned, and partly degraded, semi‐natural mountain pasture in the ?umava National Park, Czech Republic. There was very uneven grazing intensity inside the locality, and grazing preference changed during the season: cattle grazed most of the time in productive but species‐poor Deschampsia cespitosa swards, but changed to a species‐rich Violion caninae stand in the middle of the summer. A species‐rich Carex rostrata community was only grazed at the end of the season. Species‐poor swards dominated by Nardus stricta and Carex brizoides were mainly used as resting areas. Both grazing and excluding from grazing had a negative effect on species diversity of the Deschampsia cespitosa swards. The soil seed bank contained only few species that are characteristic of mountain grassland communities, and seed dispersal of the target species by cattle dung was also found to be very limited. Thus both grazing and exclusion from grazing are probably of limited value for the restoration of species‐rich grasslands from species‐poor Deschampsia cespitosa swards in this case.     

Phytogeography, range size and richness of Australian endemic Sauropus (Euphorbiaceae)

Aim To investigate the distribution of Australian species of Sauropus. The information obtained is used to (1) identify areas of highest richness and centres of endemism, (2) investigate latitudinal gradients of richness and range size, (3) determine the types of rarity shown, and (4) provide hypotheses on historical biogeography of the genus within Australia. Location Australia. Methods Specimens from 17 herbaria and field searches were examined and label and field information collated on distribution, habit and habitat. Distribution information was used to map all species within 784 grid cells of 1° × 1° and within the 97 Australian ‘ecological regions’. Morphometric cluster analysis of species was conducted using Kulczynski association and flexible UPGMA on 23 character states. Simple regression was used to correlate species richness, density and range size to changes in latitude. CLIMEX is used to match the climate of the region of highest richness in Australia with other areas of the world. Results Species richness was highest within the tropical north of Australia, and most species were associated with tropical savanna woodlands. Two areas were identified as centres of endemism and these corresponded closely to areas of high species richness. Four morphological groups were identified. One species (Sauropus trachyspermus) was found to be widespread, however all other species had small geographical ranges. Species richness and range size were significantly correlated with changes in latitude. Ten species were found to be of the rarest type, warranting conservation initiatives. Main conclusions Two regions of high richness and endemism of Sauropus occur, Thailand and Australia. Within Australia, the Kakadu‐Alligator River and the Cairns‐Townsville areas were identified as centres of endemism and high species richness for Sauropus. Australian Sauropus in general occur in similar communities and climates as other members of the genus elsewhere. Ten of the 27 species of Australian endemic Sauropus are extremely rare and warrant conservation initiatives. Correlations of latitude to species richness are potentially due to Sauropus radiating from the climatically stable top end of Australia. Increasing range size in more southern latitudes may also be due to stability of climates in the top end or because there is more available land area at these latitudes. Sauropus micranthus, the only non‐endemic species, is probably a more recent invader from the Tertiary period when tropical rain forests where more extensive and congruent with those of New Guinea.     

Experimental heatwaves facilitate invasion and alter species interactions and composition in a tropical host-parasitoid community

As mean temperatures increase and heatwaves become more frequent, species are expanding their distributions to colonise new habitats. The resulting novel species interactions will simultaneously shape the temperature-driven reorganization of resident communities. The interactive effects of climate change and climate change-facilitated invasion have rarely been studied in multi-trophic communities, and are likely to differ depending on the nature of the climatic driver (i.e., climate extremes or constant warming). We re-created under laboratory conditions a host-parasitoid community typical of high-elevation rainforest sites in Queensland, Australia, comprising four Drosophila species and two associated parasitoid species. We subjected these communities to an equivalent increase in average temperature in the form of periodic heatwaves or constant warming, in combination with an invasion treatment involving a novel host species from lower-elevation habitats. The two parasitoid species were sensitive to both warming and heatwaves, while the demographic responses of Drosophila species were highly idiosyncratic, reflecting the combined effects of thermal tolerance, parasitism, competition, and facilitation. After multiple generations, our heatwave treatment promoted the establishment of low-elevation species in upland communities. Invasion of the low-elevation species correlated negatively with the abundance of one of the parasitoid species, leading to cascading effects on its hosts and their competitors. Our study, therefore, reveals differing, sometimes contrasting, impacts of extreme temperatures and constant warming on community composition. It also highlights how the scale and direction of climate impacts could be further modified by invading species within a bi-trophic community network.     

Yeast communities in a natural tequila fermentation

Fresh and cooked agave,Drosophila spp., processing equipment, agave molasses, agave extract, and fermenting must at a traditional tequila distillery (Herradura, Amatitan, Jalisco, México) were studied to gain insight on the origin of yeasts involved in a natural tequila fermentations. Five yeast communities were identified. (1) Fresh agave contained a diverse mycobiota dominated byClavispora lusitaniae and an endemic species,Metschnikowia agaveae. (2)Drosophila spp. from around or inside the distillery yielded typical fruit yeasts, in particularHanseniaspora spp.,Pichia kluyveri, andCandida krusei. (3)Schizosaccharomyces pombe prevailed in molasses. (4) Cooked agave and extract had a considerable diversity of species, but includedSaccharomyces cerevisiae. (5) Fermenting juice underwent a gradual reduction in yeast heterogeneity.Torulaspora delbrueckii, Kluyveromyces marxianus, andHanseniaspora spp. progressively ceded the way toS. cerevisiae, Zygosaccharomyces bailii, Candida milleri, andBrettanomyces spp. With the exception ofPichia membranaefaciens, which was shared by all communities, little overlap existed. That separation was even more manifest when species were divided into distinguishable biotypes based on morphology or physiology. It is concluded that crushing equipment and must holding tanks are the main source of significant inoculum for the fermentation process.Drosophila species appear to serve as internal vectors. Proximity to fruit trees probably contributes to maintaining a substantialDrosophila community, but the yeasts found in the distillery exhibit very little similarity to those found in adjacent vegetation. Interactions involving killer toxins had no apparent direct effects on the yeast community structure.     

Life cycle and host range of Phycita sp. rejected for biological control of prickly acacia in Australia

Prickly acacia (Vachellia nilotica subsp. indica), a native of the Indian subcontinent, is a serious weed of the grazing areas of northern Australia and is a target for classical biological control. Native range surveys in India identified a leaf webber, Phycita sp. (Lepidoptera: Pyralidae) as a prospective biological control agent for prickly acacia. In this study, we report the life cycle and host‐specificity test results Phycita sp. and highlight the contradictory results between the no‐choice tests in India and Australia and the field host range in India. In no‐choice tests in India and Australia, Phycita sp. completed development on two of 11 and 16 of 27 non‐target test plant species, respectively. Although Phycita sp. fed and completed development on two non‐target test plant species (Vachellia planifrons and V. leucophloea) in no‐choice tests in India, there was no evidence of the insect on the two non‐target test plant species in the field. Our contention is that oviposition behaviour could be the key mechanism in host selection of Phycita sp., resulting in its incidence only on prickly acacia in India. This is supported by paired oviposition choice tests involving three test plant species (Acacia baileyana, A. mearnsii and A. deanei) in quarantine in Australia, where eggs were laid only on prickly acacia. However, in paired oviposition choice trials, only few eggs were laid, making the results unreliable. Although oviposition choice tests suggest that prickly acacia is the most preferred and natural host, difficulties in conducting choice oviposition tests with fully grown trees under quarantine conditions in Australia and the logistic difficulties of conducting open‐field tests with fully grown native Australian plants in India have led to rejection of Phycita sp. as a potential biological control agent for prickly acacia in Australia.     

Yeast Communities of Diverse Drosophila Species: Comparison of Two Symbiont Groups in the Same Hosts

The combination of ecological diversity with genetic and experimental tractability makes Drosophila a powerful model for the study of animal-associated microbial communities. Despite the known importance of yeasts in Drosophila physiology, behavior, and fitness, most recent work has focused on Drosophila-bacterial interactions. In order to get a more complete understanding of the Drosophila microbiome, we characterized the yeast communities associated with different Drosophila species collected around the world. We focused on the phylum Ascomycota because it constitutes the vast majority of the Drosophila-associated yeasts. Our sampling strategy allowed us to compare the distribution and structure of the yeast and bacterial communities in the same host populations. We show that yeast communities are dominated by a small number of abundant taxa, that the same yeast lineages are associated with different host species and populations, and that host diet has a greater effect than host species on yeast community composition. These patterns closely parallel those observed in Drosophila bacterial communities. However, we do not detect a significant correlation between the yeast and bacterial communities of the same host populations. Comparative analysis of different symbiont groups provides a more comprehensive picture of host-microbe interactions. Future work on the role of symbiont communities in animal physiology, ecological adaptation, and evolution would benefit from a similarly holistic approach.     

The influence of herbivory and weather on the vital rates of two closely related cactus species

Herbivory has long been recognized as a significant driver of plant population dynamics, yet its effects along environmental gradients are unclear. Understanding how weather modulates plant–insect interactions can be particularly important for predicting the consequences of exotic insect invasions, and an explicit consideration of weather may help explain why the impact can vary greatly across space and time. We surveyed two native prickly pear cactus species (genus Opuntia) in the Florida panhandle, USA, and their specialist insect herbivores (the invasive South American cactus moth, Cactoblastis cactorum, and three native insect species) for five years across six sites. We used generalized linear mixed models to assess the impact of herbivory and weather on plant relative growth rate (RGR) and sexual reproduction, and we used Fisher's exact test to estimate the impact of herbivory on survival. Weather variables (precipitation and temperature) were consistently significant predictors of vital rate variation for both cactus species, in contrast to the limited and varied impacts of insect herbivory. Weather only significantly influenced the impact of herbivory on Opuntia humifusa fruit production. The relationships of RGR and fruit production with precipitation suggest that precipitation serves as a cue in determining the trade‐off in the allocation of resources to growth or fruit production. The presence of the native bug explained vital rate variation for both cactus species, whereas the invasive moth explained variation only for O. stricta. Despite the inconsistent effect of herbivory across vital rates and cactus species, almost half of O. stricta plants declined in size, and the invasive insect negatively affected RGR and fruit production. Given that fruit production was strongly size‐dependent, this suggests that O. stricta populations at the locations surveyed are transitioning to a size distribution of predominantly smaller sizes and with reduced sexual reproduction potential.     

Endangered Cactus Restoration: Mitigating the Non-Target Effects of a Biological Control Agent (Cactoblastis cactorum) in Florida

The moth Cactoblastis cactorum (Berg), the poster child of weed biological control in Australia, has recently invaded the United States and threatens native cacti. Concern is greatest for the endangered semaphore cactus, Opuntia corallicola, of which only two known populations exist in the wild. We made three separate outplantings of O. corallicola, designed to bolster the number of extant cacti and to test the effectiveness of three different treatments to protect the cacti from Cactoblastis. In one outplanting, we tested the associational susceptibility hypothesis and found that cacti planted more than 20 m away from the common prickly pear cactus, Opuntia stricta, which act as a reservoir of Cactoblastis, were just as frequently attacked and killed by Cactoblastis as cacti planted within 5 m. In addition, Cactoblastis attack was greater in the shade than in the sun. In the second outplanting, we minimized the attack from Cactoblastis by using protective cages planted at least 500 m from O. stricta in areas not inhabited by cacti. Cages attracted the attention of local animals, which destroyed the cages and trampled the cacti inside to death. Crown rot caused high mortality in this outplanting. In the third outplanting, again conducted at least 500 m away from O. stricta, fertilization did not reduce crown rot mortality. We suggest that increasing populations of O. corallicola in Florida, by means of outplantings, will remain a challenge because of death from Cactoblastis when planted in areas where cacti normally grow and because of death from crown rot in areas where they do not. Because Cactoblastis is moving rapidly northward and westward and has already reached Charleston, South Carolina, rare cacti in the rest of the U.S. Southeast may be in danger. Eventually, many cactus species in the U.S. South, Southwest, and Mexico will likely be threatened by this moth.