Between-season Variation Research Articles

Floral Complexity Traits as Predictors of Plant-Bee Interactions in a Mediterranean Pollination Web.

Despite intensive research, predicting pairwise species associations in pollination networks remains a challenge. The morphological fit between flowers and pollinators acts as a filter that allows only some species within the network to interact. Previous studies emphasized the depth of floral tubes as a key shape trait that explains the composition of their animal visitors. Yet, additional shape-related parameters, related to the handling difficulty of flowers, may be important as well. We analyzed a dataset of 2288 visits by six bee genera to 53 flowering species in a Mediterranean plant community. We characterized the plant species by five discrete shape parameters, which potentially affect their accessibility to insects: floral shape class, tube depth, symmetry, corolla segmentation and type of reproductive unit. We then trained a random forest machine-learning model to predict visitor identities, based on the shape traits. The model’s predictor variables also included the Julian date on which each bee visit was observed and the year of observation, as proxies for within- and between-season variation in flower and bee abundance. The model attained a classification accuracy of 0.86 (AUC = 0.96). Using only shape parameters as predictors reduced its classification accuracy to 0.76 (AUC = 0.86), while using only the date and year variables resulted in a prediction accuracy of 0.69 (AUC = 0.80). Among the shape-related variables considered, flower shape class was the most important predictor of visitor identity in a logistic regression model. Our study demonstrates the power of machine-learning algorithms for understanding pollination interactions in a species-rich plant community, based on multiple features of flower morphology.

Wild bison as ecological indicators of the effectiveness of management practices to increase forage quality on open rangeland

Habitat manipulations through the use of fire or mechanical treatments are often used to combat woody plant encroachment and increase foraging opportunities for wildlife and livestock. This creates spatial heterogeneity in habitat quality that large herbivores should respond to in ways predicted by ideal free distribution theory. We monitored free-ranging bison to test whether, (1) manipulated habitats offer higher quality forage than habitats in undisturbed rangeland, (2) bison respond through changes in herd composition or activity to differences in habitat quality, and (3) burned and mechanically treated habitats offer similar forage qualities. We found that habitat types burned ∼10 years ago continue to produce higher quality forage as evidenced by bison fecal N concentration (14.4gkg−1 dry mass) than open (10.5gkg−1), closed (10.6gkg−1), or mechanically manipulated habitats (11.7gkg−1). Bison herd composition and activity did not vary across habitat types within seasons, despite some between-season variation in overall group composition with sexual segregation being most evident before mid-summer. For semi-arid rangelands encroached with woody vegetation (e.g. piñon–juniper in the western USA) our evidence from free-ranging bison indicates that burning results in higher quality forage than occurs in both mechanically manipulated and undisturbed habitats. Bison roam widely from water, sample available vegetation continuously, and are long-lived gregarious animals that learn to exploit the spatiotemporal heterogeneity in their large home ranges. Bison also have very similar diets to cattle and so, where bison and cattle are allowed to comingle, we suggest the foraging parameters of free-ranging bison are effective ecological indicators of rangeland quality for both bison and cattle.

Problems with the taxonomy of Phytoptus tetratrichus Nalepa 1890 (Acari: Eriophyoidea) inhabiting Tilia spp.: Analysis based on morphological variation among individuals

The purpose of this research was to investigate both the qualitative and quantitative morphological traits of Phytoptus tetratrichus Nalepa 1890 populations inhabiting three different lime tree species: Tilia cordata Mill., Tilia tomentosa Moench and Tilia americana L.. Morphological characters of two populations collected from T. cordata and T. tomentosa over three successive growing seasons were compared with the aid of canonical variate analysis. Additionally, individuals occurring on T. americana in a consecutive year were also studied. Protogyne and deutogyne females were differentiated using both qualitative and quantitative traits. For deutogyne females, individuals from all combinations of Tilia species × year (which constituted populations for comparison) clearly differed from each other. However, the differences between populations from T. cordata and T. tomentosa were less distinct. For protogyne females, observed differences were clearly visible. The between-season variation in morphological characters such as body size appeared to be quite large, indicating that morphological analysis based on observations from only a single season can be inaccurate. Deutogyne females of P. tetratrichus were observed to cause various types of damage symptoms: leaf-roll galls along the leaf edges of T. cordata; small round erinea on the lower leaf surface and small wart-like galls on the upper leaf surface of T. tomentosa; fingerlike galls on both leaf surfaces of T. americana.

Abiotic factors modulate phenotypic plasticity in an apomictic shrub [Miconia albicans (SW.) Triana] along a soil fertility gradient in a Neotropical savanna

Phenotypic plasticity is an important means by which plants cope with environmental heterogeneity; therefore, understanding variation in plant traits in heterogeneous habitats is important to predict responses to changing environments. In this study, we examined the patterns of intraspecific variation in leaf traits of Miconia albicans (Melastomataceae), a widespread, obligatory apomictic shrub, across a soil fertility gradient in the Cerrado (Brazilian savanna). We predicted high plasticity because selection favours high phenotypic plasticity in asexual populations with low genetic variability. Leaves were sampled in campo sujo (grassland), cerrado (savanna) and cerradão (woodland) in south-eastern Brazil during both dry and rainy seasons to calculate leaf area, specific leaf area, leaf tissue thickness, trichome and stomata density. We found significant between-season variation in leaf traits, indicating that the production of season-specific leaves is a strategy to cope with the strong seasonality. Both multivariate analysis and the relative distance plasticity index indicate lower plasticity during the dry season, especially under shade. Our results show that the phenotypic plasticity can be modulated by changes in abiotic factors and the combination of shade and drought can limit the expression of phenotypic plasticity.

The Need for Validation of Statistical Methods for Estimating Respiratory Virus-Attributable Hospitalization

Public policy regarding influenza has been based largely on the burden of hospitalization estimated through ecologic studies applying increasingly sophisticated statistical methods to administrative databases. None are known to have been validated by observational studies. The authors illustrated how 6 commonly applied statistical methods estimate virus-attributable hospitalization of children 6-23 months of age and compared the estimates with results obtained from a prospective study using virologic assessment. The proportions of pneumonia and influenza and of bronchiolitis hospitalizations attributable to respiratory syncytial virus and/or influenza were derived by using Serfling regression, periseason differences, Poisson regression with log link, negative binomial regression with identity link, and a Box-Jenkins transfer function. No method provided accurate or consistent estimates for both viruses and outcomes. Virus-attributable hospitalization estimates varied widely between statistical methods and between seasons, with greater between-season variation for admissions attributed to influenza compared with respiratory syncytial virus. Sophistication of statistical methods may have been interpreted as assurance that results are more accurate. Without validation against epidemiologic data, with viral etiology confirmed in individual patients, the accuracy of statistical methods in ecologic studies is simply not known. Until these methods are validated, their methodological limitations should be made explicit and proxy estimates used cautiously in guiding public policy.

Egg retention and ovoviviparity in clausiliids of the genus Vestia P. Hesse (Gastropoda: Clausiliidae)

The reproductive biology of three Carpathian clausiliids of the genus Vestia (V. gulo (E.A. Bielz, 1859), V. elata (Rossmassler, 1836) and V. turgida (Rossmassler, 1836)) was studied using two methods: (1) the presence of eggs was examined in uteri of snails collected in the wild; and (2) the reproduction of snails was observed for 2-4 years under laboratory conditions. All three species retained eggs (ovoviviparity sensu lato), but there was a variation in the stage of the development of embryos among the species: V. gulo retained embryos to a size of c. 1.3 embryonic whorls, then laid eggs that hatched after 7-10 days; V. elata retained embryos to a size of 1.8 whorls, then laid eggs that hatched after 2-4 days; and V. turgida retained the largest embryos with up to 2.9 embryonic whorls. Oviposition was observed rarely in the latter species so that most embryos probably hatched inside the parent (ovoviviparity sensu stricto). The number of retained eggs in a uterus differed signifi- cantly between V. gulo and V. turgida. The reproductive period of V. turgida was longer than that of V. gulo, with two distinct reproductive peaks in June and August. Eggs were spherical or slightly oval, partly calcified and resilient, but eggs of V. turgida were elongated and less resilient. Mean numbers of eggs in a single batch were: V. gulo, 9.44+ 3.73; V. elata, 4.50+ 2.07; and V. turgida, 3.83+ 2.12. Egg cannibalism was most intense in V. gulo, but was not observed in V. turgida. Under laboratory conditions V. gulo produced 1- 4 batches, V. elata 1-7 batches and V. turgida 1-6 batches of eggs. The three species each produce up to 30-34 juveniles per reproductive season, but the interspecific variation and between-season variation were very high. A possible relation of the reproduction mode with habitat preferences of the species is proposed.

Variation in egg-size in the Wedge-tailed Shearwater (Puffinus pacficus)

We assessed variation in the size of eggs of Wedge-tailed Shearwaters (Puffinus pacificus) within and between two colonies in eastern Australia. Eggs at Heron Island were significantly larger than at Lord Howe Island. We also found significant between-season variation in size of eggs at Heron Island, with larger eggs being laid in 2005 than 2006. Mean female size (as indicated by tarsal length) did not differ between the two colonies, or between seasons at Heron Island. However, as with other seabird species, larger females produced larger eggs. Overall, our results imply that facultative changes in female reproductive effort associated with changes in availability of resources are not the main cause of variation in egg-size in this species. The consistently smaller size of eggs for birds at Lord Howe Island compared with those from Heron Island suggests that obligate processes (e.g. natural selection) are more likely to be responsible.

Plant communities of a Central Namib inselberg landscape

Abstract. Three granite inselbergs and six dolerite dykes and their surroundings were investigated in the Central Namib, at the interface between the Namib Desert and Nama Karoo biomes. The main objectives of this study included a phytoso‐ciological interpretation of the described plant communities, explanation of the correlation of the communities with environmental variables and quantification of the relative contribution of different types of variables to structuring plant communities. Nine grassland and shrubland plant communities were recognized, largely organized according to general habitat, elevation, size of inselberg and geology. Soil properties, often thought to play an important role in arid environments, showed no clear patterns in the level of analyses used in this study. Other environmental parameters of importance in arid mountain habitats, such as slope aspect and angle, also played a minor role. The main implications of the study are: 1. Central Namib inselbergs, particularly granite domes, harbour diverse plant communities, often with species from neighbouring higher rainfall areas, and are thus of high conservation value. 2. The poor contribution of environmental variables in this study, which are conventionally used in field studies of plant community – environment relationships, may demand a critical review of additional parameters to be included when analysing plant community – environment relations in arid environments. In particular between‐season variation, phytogeographic aspects and the heterogeneity of microhabitats, often contained within a plant community, need to be taken into account.

Plant communities of a Central Namib inselberg landscape

Three granite inselbergs and six dolerite dykes and their surroundings were investigated in the Central Namib, at the interface between the Namib Desert and Nama Karoo biomes. The main objectives of this study included a phytoso- ciological interpretation of the described plant communities, explanation of the correlation of the communities with envi- ronmental variables and quantification of the relative contri- bution of different types of variables to structuring plant communities. Nine grassland and shrubland plant communi- ties were recognized, largely organized according to general habitat, elevation, size of inselberg and geology. Soil proper- ties, often thought to play an important role in arid environ- ments, showed no clear patterns in the level of analyses used in this study. Other environmental parameters of importance in arid mountain habitats, such as slope aspect and angle, also played a minor role. The main implications of the study are: 1. Central Namib inselbergs, particularly granite domes, harbour diverse plant communities, often with species from neigh- bouring higher rainfall areas, and are thus of high conservation value. 2. The poor contribution of environmental variables in this study, which are conventionally used in field studies of plant community - environment relationships, may demand a critical review of additional parameters to be included when analysing plant community - environment relations in arid environments. In particular between-season variation, phyto- geographic aspects and the heterogeneity of microhabitats, often contained within a plant community, need to be taken into account.

An analysis of climatic environments for plant-breeding purposes

Variations in the regional means of a number of growing-season climatic variables, and combinations of them, are not highly correlated with the long-term regional distribution of mean wheat yields in Western Australia or with their variation between years. The data suggest that the growing season is characterized by a cyclical alternation of favourable and unfavourable conditions for crop growth. This oscillating pattern varies in amplitude and wavelength as a result of unpredictable 'between'- and 'within'-season variation in the regional distribution of rainfall. In the central zone of the study area, wheat production is subject mainly to between-season variation whilst in more marginal areas yield variation is confounded by opposing and reciprocating within-season effects. The consequences for plant breeding are that specific regional environments expected on the basis of climate do not occur predictably in the short term. It is argued that breeding objectives, selection strategies and regional testing should initially avoid complications associated with specific marginal environments by concentrating on general adaptability within the central zone, which monitors between-season variation only. Subsequent evaluation for additional adaptive features specific to marginal areas should be undertaken.

Variation between apple fruits and its relation to keeping quality. III. Between-season variation in relation to seasonal climate.

Studies were made of seasonal effects on ripening changes and disorder incidence in different varieties of apples in Tasmania for the 10-year period, 1933-1943. Most of the changes associated with ripening, namely, ground colour change, acid loss, starch conversion, soluble solids accumulation, softening, and respiration rise did not necessarily keep pace with each other and responded differently to seasonal variation, but there appeared to be a constant relation between firmness and acid level. In the final analysis, seasonal variation in the level of disorders was mainly related to differences in mean fruit size and when the size factor was held constant between seasons the differences remaining were relatively small. In the case of pit, some of these remaining differences could be accounted for by differences in relative maturity but in the case of breakdown, relative incidence between seasons was not related to relative maturity. There was an association of early blossoming with low incidence of pit and breakdown independent of later differences in seasonal climate. The results support the theory that low temperatures in the months prior to harvest increased susceptibility to breakdown.