Behaviour of specialist and generalist caterpillars on plantain (Plantago lanceolata)

Abstract.

• 1 Foraging patterns of specialist (Junonia coenia Hubner: Nymphalidae) and generalist (Spilosoma congrua Wlk.: Arctiidae) caterpillars on five genotypes of plantain (Plantago lanceolata L.: Plantaginaceae) were examined in an experimental garden.
• 2 Movement by the specialists reflected declining availability of new leaves. When direct sunlight was available, these caterpillars were usually exposed to it.
• 3 Although the generalists also preferred new leaves, they spent less than 50% of their time on the plantain and changed location more frequently than the specialists. They often hid at the base of plants or under leaves.
• 4 Plant genotype influenced the apparency of the specialists and damage by the herbivores.

     

The ploidy of plants obtained from anther culture of cauliflowers (Brassica oleracea var. botrytis)

Anther culture of four cultivars of autumn cauliflower gave embryo yields of 100 embryos (per 100 anthers cultured) for one cultivar, eight embryos for a second cultivar, and almost zero for the two other cultivars. From 986 embryos which were grown on, 418 plants were regenerated. The ploidy of the regenerants was assessed by measuring guard cell lengths, pollen size, and by chromosome counts at meiosis. Only 1% of the regenerants were haploid, 41% diploid, 5% triploid and 53% tetraploid. One octoploid plant was also found. The results are discussed in relation to equivalent results for Brussels sprouts, and the use of anther culture in the breediing of cauliflowers.     

Bryophytes and ecological niche theory

Classical niche theory, particularly in terms of competitive exclusion, does not appear to apply as well to bryophytes as to other organisms. Bryophyte communities, as well as those of other plants and of animals, can be thought of in terms of individual species each utilizing particular portions of various resource or habitat continua. Quantitative studies carried out since 1981, particularly those involving niche breadth and overlap, are reviewed. Special attention is given to niche diversification in Sphagnum , Splachnaceae, bryophyte communities in streams, and to ephemeral bryophyte communities. Some bryophyte communities appear to have equilibrium characteristics and to contain species with relatively narrow niche breadths and with no or only partial niche overlap. In many habitats, however, bryophyte communites have non-equilibrium characteristics and diversification of species in microhabitats is opportunistic. Do any bryophyte communities persist long enough for complete saturation by species which have realized niches determined by competitive interactions? Recent studies indicate that this is the case for at least some Sphagnum communities, but that it is the exception not the rule for bryophytes.     

Experimental investigations of diel vertical movements by lotic mayflies over substrate surfaces

SUMMARY. 1. The vertical distribution within the substrate of three lotic mayflies (Rhithrogena sp., Paraleptophlebia sp. and Baetis tricaudalus Dodds) was examined in laboratory streams to determine if diel patterns of vertical movement across substrate surfaces existed and whether light intensity, temperature, substrate composition or food availability influenced the observed movement patterns.
2. Rhithrogena sp. and B. tricaudatus exhibited significant diel movement from lower substrate surfaces during the day to upper surfaces at night, although >64% of B. tricaudalus occupied the upper surfaces throughout the 24 h period. In contrast, Parakplophlebia sp. larvae did not change their vertical distribution over the 24 h period.
3. The proportion of mayflies occupying substrate surfaces was influenced by the amount of upper and lower surface area available in the substrate and, possibly, crevice sizes associated with lower surfaces.
4. The movement of Rhiihrogena sp. from lower surfaces during the day to the upper surfaces during the night was influenced by changes in light intensity, but not by changes in food availability or water temperature.
5. The diel patterns of vertical movement exhibited by lotic mayflies in this investigation raise the possibility that at least some biotic interactions may vary over a diel cycle. These could include competitive interactions or temporal cycling of prey availability to predators.     

Seasonal shifts in host usage in Uroleucon gravicorne (Homoptera: Aphididae) and implications for the evolution of host alternation in aphids

ABSTRACT.

• 1 Uroleucon gravicome (Patch) feeds on annual Erigeron species and on perennial Solidago species.
• 2 To test whether Solidago and Erigeron are analogous to winter and summer hosts of typical host-alternating aphids, reproductive performance, host preferences, and host associations were measured for E.strigosus, S.juncea and S.nemoralis during spring, summer and autumn.
• 3 Caged individuals can reproduce on both genera throughout the season, though colonies are rare on Solidago during summer.
• 4 Developmental rate, adult weight, and fecundity decline between May and August on all hosts; however, the drop is least on E.strigosus, intermediate on S.nemoralis, and greatest on S.juncea.
• 5 Throughout the season, reproductive performance is at least as great on Erigeron as on Solidago, the difference being least in spring.
• 6 Soluble nitrogen content shows the same seasonal trends as reproductive performance, declining in all hosts, but declining least in E.strigosus.
• 7 Preference tests and field records show that U.gravicorne moves from Solidago to Erigeron when the first alatae mature in late spring, feeds on Erigeron during the summer, and, in late summer, returns to Solidago where overwintering eggs are laid.
• 8 Solidago is not nutritionally superior during spring or autumn; its use during those seasons may result from the need for good oviposition sites.

     

The Effect of Specific Sterols on Cell Size and Fatty Acid Composition of Tetrahymena pyriformis W

The size and fatty acid composition of Tetrahymena pyriformis W cells were influenced by the provision of a nutritional supplement of ergosterol, cholesterol, or tetrahymanol, but not of 20-isocholesterol. Ergosterol and cholesterol addition led to a reduction in cellular volume, an increase in glycerophospholipid saturated fatty acid content, and an increase in palmitoleic acid and its metabolic products when compared to unsupplemented controls. Tetrahymanol supplementation resulted in an increase in cellular volume, a decrease in saturated fatty acid content, and a reduction in palmitoleic acid and derivatives. 20-Isocholesterol was accumulated by the cells; however, this compound had no effect on any of the parameters followed in this investigation and had only a small depressant effect on tetrahymanol biosynthesis. Ergosterol and cholesterol had the same impact on the ciliates, even though the ergosterol-supplemented cells contained approximately three times as much free sterol as did cholesterol-grown cells. The amount of the free cholesterol and metabolic products in supplemented cultures was similar to the amount of tetrahymanol present in control cultures. This observation suggests that the cells recognize qualitative differences among the various polycyclic alcohols rather than responding to the amount of sterol present. Increased cellular levels of tetrahymanol led to a response unlike that of the true sterols, which again suggests that the high degree of specificity depends on the structure of the added polycyclic alcohol. The changes in fatty acid composition may be required to maintain proper interaction of the polar lipids and the polycyclic alcohols to give an appropriate degree of membrane fluidity.     

Effects of Visible and Ultraviolet Light on Carotene-deficient Mutants of Crypthecodinium cohnii

Synopsis.
The ability of carotenoids to protect a heterotrophic dinoflagellate, Crypthecodinium cohnii , from photodynamic damage by sunlight in the presence of an exogenous dye was demonstrated. Wild-type C. cohnii and 2 carotcnoid-deficient mutants were plated on agar-solidified media and exposed to natural sunlight. The wild-type strain, which synthesizes γ–carotene and β–carotene, had the lowest mortality. Mutant car 17 which accumulates mainly §–carotene had an intermediate mortality rate while the albino mutant, car 3, which contains only phytoene, lost viability most rapidly. Wild-type cells treated with diphenylaminc, a carotenogenic inhibitor, were killed at the same rate as mutant car 3. The survival rate of mutants on exposure to sunlight was dependent upon the chromophore length of the accumulated carotenoids. The 3 strains showed no difference in rate of mortality when exposed to ultraviolet light. Protection from sunlight by accumulation of carotenes may be an important ecological factor for this species whose natural habitat is tidepools.     

FLUXNET and modelling the global carbon cycle

Measurements of the net CO₂ flux between terrestrial ecosystems and the atmosphere using the eddy covariance technique have the potential to underpin our interpretation of regional CO₂ source–sink patterns, CO₂ flux responses to forcings, and predictions of the future terrestrial C balance. Information contained in FLUXNET eddy covariance data has multiple uses for the development and application of global carbon models, including evaluation/validation, calibration, process parameterization, and data assimilation. This paper reviews examples of these uses, compares global estimates of the dynamics of the global carbon cycle, and suggests ways of improving the utility of such data for global carbon modelling. Net ecosystem exchange of CO₂ (NEE) predicted by different terrestrial biosphere models compares favourably with FLUXNET observations at diurnal and seasonal timescales. However, complete model validation, particularly over the full annual cycle, requires information on the balance between assimilation and decomposition processes, information not readily available for most FLUXNET sites. Site history, when known, can greatly help constrain the model‐data comparison. Flux measurements made over four vegetation types were used to calibrate the land‐surface scheme of the Goddard Institute for Space Studies global climate model, significantly improving simulated climate and demonstrating the utility of diurnal FLUXNET data for climate modelling. Land‐surface temperatures in many regions cool due to higher canopy conductances and latent heat fluxes, and the spatial distribution of CO₂ uptake provides a significant additional constraint on the realism of simulated surface fluxes. FLUXNET data are used to calibrate a global production efficiency model (PEM). This model is forced by satellite‐measured absorbed radiation and suggests that global net primary production (NPP) increased 6.2% over 1982–1999. Good agreement is found between global trends in NPP estimated by the PEM and a dynamic global vegetation model (DGVM), and between the DGVM and estimates of global NEE derived from a global inversion of atmospheric CO₂ measurements. Combining the PEM, DGVM, and inversion results suggests that CO₂ fertilization is playing a major role in current increases in NPP, with lesser impacts from increasing N deposition and growing season length. Both the PEM and the inversion identify the Amazon basin as a key region for the current net terrestrial CO₂ uptake (i.e. 33% of global NEE), as well as its interannual variability. The inversion's global NEE estimate of −1.2 Pg [C] yr⁻¹ for 1982–1995 is compatible with the PEM‐ and DGVM‐predicted trends in NPP. There is, thus, a convergence in understanding derived from process‐based models, remote‐sensing‐based observations, and inversion of atmospheric data. Future advances in field measurement techniques, including eddy covariance (particularly concerning the problem of night‐time fluxes in dense canopies and of advection or flow distortion over complex terrain), will result in improved constraints on land‐atmosphere CO₂ fluxes and the rigorous attribution of mechanisms to the current terrestrial net CO₂ uptake and its spatial and temporal heterogeneity. Global ecosystem models play a fundamental role in linking information derived from FLUXNET measurements to atmospheric CO₂ variability. A number of recommendations concerning FLUXNET data are made, including a request for more comprehensive site data (particularly historical information), more measurements in undisturbed ecosystems, and the systematic provision of error estimates. The greatest value of current FLUXNET data for global carbon cycle modelling is in evaluating process representations, rather than in providing an unbiased estimate of net CO₂ exchange.     

Changes in species richness and composition in European acidic grasslands over the past 70 years: the contribution of cumulative atmospheric nitrogen deposition

Our study investigates the negative impact of nitrogen (N) deposition on species richness in acidic grasslands, based on a temporal comparison of vegetation data spanning a period of almost 70 years. We compiled a large data base of plots assigned to the Violion caninae grassland type, composed of managed, but unfertilized semi-natural grasslands on nutrient-poor, acidic soils. In total 1114 plots, mainly from Great Britain, the Netherlands and Germany, were compiled, dating back to 1939. Environmental site information included geographical and soil (mean Ellenberg values) variables as well as estimates of cumulative N and sulphur (S) deposition since 1939. Statistical analyses were carried out separately for the data subsets from the three regions. In all regions, the vegetation differentiation was mainly related to soil acidity and nutrient availability, as well as to the year of sampling and the cumulative amounts of N and S deposition. Plot-species richness of vascular plants and bryophytes (analysed for Great Britain only) decreased with time and analyses suggest these are affected by various factors, notably soil pH, but also latitude and cumulative N deposition. The latter explained more of the variation in species number than the year of sampling and cumulative S deposition, which supports the interpretation that the decline in species richness is mainly caused by increasing N availability and less by altered management and soil acidification. For Great Britain and Germany, cumulative N deposition showed a strong negative relationship with several biodiversity measures, especially the proportion of dicots, whereas it was positively related to the proportion of grass species. In general, our results give temporal evidence for the negative effect of N deposition on species richness in semi-natural vegetation.     

IDENTIFICATION OF BRITISH BAT SPECIES BY MULTIVARIATE ANALYSIS OF ECHOLOCATION CALL PARAMETERS

ABSTRACT

Previous studies have found variability and individual distinctiveness in the echolocation calls of bats. We consider two implications of individually distinct echolocation calls: 1) whether bats may be able to use such variation to recognise familiar conspecifics, and 2) whether investigators could use such variation to identify known individuals or to census populations. We compared the discriminability of the echolocation calls of big brown bats (Eptesicus fuscus) recorded in three situations: (a) while held in the hand, (b) while perched on a platform, and (c) while flying in an anechoic chamber. Using variables describing each sonar call, we employed discriminant function analysis (DFA) to assign calls to recording situation or to bat. Discrimination of calls by recording situation was largely unsuccessful, although flying calls could be distinguished from platform calls. Assignment of calls to individual bat across recording situations yielded 72% success, and, within a given recording situation, yielded 87% success. Stepwise DFA reduced the number of variables needed to discriminate between individuals with only a slight decrease in correct classification. These results suggest that bats (or researchers) may be able to use the information contained in the echolocation calls for individual recognition. Individual distinctiveness raises the possibility of censusing bats by sound. We used cluster analysis in an attempt to determine whether, given a sample of calls from an unknown number of bats, a reasonable estimate of the number of bats could be obtained. Results were unsatisfactory, suggesting that cluster analysis probably will not permit acoustic censusing of bats in the field.