Water Relations of Red Clover Trifolium pratense L. as Affected by VA Mycorrhizal Infection and Phosphorus Supply Before and During Drought

Red clover Trifolium pratense L. plants were grown in a factorialdesign with four levels of added P and with and without a mycorrhizalinoculum, to test the separate effects of P nutrition and infectionon plant water relations. Under well-watered conditions, onlyuninfected plants on very low P soil showed reduced stomatalconductance and these had the lowest leaf P concentrations.During droughting, only plants with very high leaf P concentrationsmaintained high conductance. There was no evidence of increasedwater uptake by mycorrhizal plants. This and other evidencesuggests that mycorrhizal effects on water relations are secondaryconsequences of changes in P nutrition which are, in any case,inconsistent. Key words: Trifolium pratense, VAM, water relations, concentration, drought     

Behavioral Regulatory Mechanisms in the Social Homeostasis of Termites (Isoptera)

Recent progress in the elucidation of the behavioral mechanismsresponsible for maintaining the steady state in a termite colonyis discussed. It is pointed out that various homeostatic mechanismshave common behavioral mechanisms. The mechanisms involved innest repair and construction, foraging, defense, and generalmass movements within nests are explained. An experiment isdescribed in which differential responses to a discrete simplestimulus (heat) are made by two different castes of Nasulitermescorniger and the homeostatic significance emphasized. The factorsin volved in foraging behavior in Reticulitermes are described.An hypothesis for the significance of the behavioral phenomenonof head-banging in termites is put forward: it is consideredto be connected with the maintenance of accelerated activityin a colony after "General Alarm".     

A comparative study of the distribution and density of stomata in the British flora

The distribution of stomata over both leaf surfaces may affect both the photosynthetic rate and water use efficiency of species, implying that species with different photosynthetic and water requirements may also have different stomatal distributions. A database containing data on the distribution of stomata on the leaves of 469 British plant species was used to look for relationships between stomatal distribution (including both location on the leaf and density) and both habitat and morphological variables. Statistical models were applied to the data that minimized any effects that phylogenetic constraints may have had on the data.
Hypostomaty is common in woody species, species which typically occur in shaded habitats and species with large or glabrous leaves. Amphistomaty, however, predominates in species which occur in non-shaded habitats, species with small, dissected or hairy leaves, and in annual species. Amphistomaty, therefore, tends to occur in species where CO₂ may be limiting photosynthesis (unshaded environments), or where there are structures to prevent water loss from the leaf (e.g. hairs). Hypostomaty, however, occurs in slow-growing species (e.g. trees), species with leaves which have large boundary layers (large or entire leaves) and in species where CO₂ is unlikely to limit photosynthesis (shaded habitats).     

The relationship between floral display size, pollen carryover and geitonogamy in Myosotis colensoi (Kirk) Macbride (Boraginaceae)

The relative amounts of self- and cross-pollen deposited on stigmas depends on both the number of pollinator visits that occur within plants and the amount of pollen carryover. Data collected for Myosotis colensoi (Kirk) Macbride and compiled from a survey of the literature, reveal that pollen carryover is frequently very high (upwards of 80%) and this at least partially relieves some of the effects of geitonogamous pollinator movements. It is suggested that in some cases, selection for traits that confer a high rate of pollen carryover may occur. Aspects of the plant–pollinator interaction that are likely to influence pollen carryover are discussed.     

The influence of periphyton, detritus and shelter on invertebrate colonization of aquatic bryophytes

1. Artificial bryophytes were placed in a shaded and an unshaded New Zealand alpine stream to investigate why invertebrates colonized these structures and, by inference, real plants. Three experiments were conducted to investigate the influence of (i) periphyton and detritus (ii) shelter, and (iii) time, on invertebrate colonization. 2. In the first experiment, seven taxa at the unshaded site displayed a preference for substrata with high detrital and periphyton biomass, presumably reflecting a food relationship. At the shaded, less stable site, only two taxa displayed such a relationship. 3. Reducing substratum ‘stem’ density (i.e. ‘shelter’) in the second experiment had little effect on the biomass of periphyton at each site, and only at the shaded site was detrital biomass reduced on low-density substrata. Abundances of most of the twenty-two invertebrate taxa analysed were unaffected by stem density reduction: densities of only four taxa at the unshaded site, and two at the shaded site were reduced. 4. Stepwise multiple regression showed that invertebrate abundance was little affected by stem density at either site. Indeed, shelter was the primary factor influencing abundance of only two of twenty-two taxa at the unshaded site, and none at the shaded site. Abundances of most taxa were related to periphyton or detrital biomass at each site. 5. The third experiment investigated temporal relationships between invertebrate density, periphyton and detrital biomass, and exposure time of artificial bryophytes. Regression analyses indicated that of twenty-two taxa at the stable, unshaded site, eight were influenced by periphyton biomass, three by detrital biomass, and two by exposure time. At the unstable shaded site, abundances of only eight of twenty-two taxa were significantly related to the measured variables, of which exposure time was most important (four taxa).     

Climate as a driver of population variability in breeding Gentoo Penguins Pygoscelis papua at the Falkland Islands

Detecting and predicting how populations respond to environmental variability are eminent challenges in conservation research and management. This is particularly true for wildlife populations at high latitudes, many of which demonstrate changes in population dynamics associated with global warming. The Falkland Islands (Southwest Atlantic) hold one of the largest Gentoo Penguin Pygoscelis papua populations in the world, representing c. 34% of the global population. The numbers of breeding Gentoo Penguins at the Falkland Islands have shown a high degree of inter‐annual variability since monitoring commenced in 1990. However, proximate causes of annual variability in breeding numbers have not been explored. Here we examine 21 years of Gentoo Penguin breeding surveys from the Falkland Islands and assess whether inter‐annual variability in the number of breeding pairs were correlated with proxies of environmental variability. There was a positive correlation between the number of breeding pairs and a broad‐scale climatic variation index, the Southern Oscillation Index (SOI). In turn, the SOI was significantly correlated with spring sea surface temperature anomalies, indicating a more immediate atmospherically forced response to El Niño Southern Oscillation variability in the Southwest Atlantic than previously reported. However, we also describe a non‐linear response to environmental variability that may highlight foraging plasticity and/or the complexity of regional ecosystem interactions that operate across a range of different scales.     

Vegetation and flow regime in lowland streams

1. The hydrological regime is important to the distribution of benthic organisms in streams. The objective of this study was to identify relationships between hydrological variables, describing the flow regime, and macrophyte cover, species richness, diversity and community composition in Danish lowland streams.
2. We quantified macrophyte vegetation in 44 Danish streams during summer by cover, species richness and diversity. Flow regime was characterized by 18 non-intercorrelated variables describing magnitude, frequency and duration of low and high flow events, timing or predictability of flow and general flow variability.
3. We found support in the stepwise multiple regressions analysis for our expectation that macrophyte cover is lowest in streams with high flow variability and highest in streams with long duration of low flow and low flow variability. We found support for the intermediate disturbance hypothesis as there were significant quadratic relationships between species richness and diversity as functions of disturbance frequency. There was poor discrimination in a detrended correspondence analysis (DCA) analysis of macrophyte community composition between four twinspan groups separating streams with different hydrological properties. Moreover, we did not find any relationship between the presence of disturbance-tolerant species and hydrological disturbance, suggesting that plant community composition developed independently of stream hydrology.