FAECAL PRODUCTION AND AN ESTIMATE OF FOOD INTAKE IN THE WILD OF THE ANTARCTIC LIMPET NACELLA CONCINNA (STREBEL)

The Antarctic limpet Nacella concinna is common in shallow watersaround the Antarctic Peninsula, and has a mean density of 125individuals/m² at Signy Island (Picken, 1980). In the australsummer 1986/87 ammonia excretion and faecal egestion were measuredas part of a programme to develop a detailed individual energybudget for this species. Ammonia production was measured in 102 individuals ranging from3 to 720 mg dry weight. For a standard limpet of 200 mg dryweight, ammonia excretion was 0.13 µg-at/hr. Comparedwith previous measures of oxygen uptake these data suggest anO:N atomic ratio of between 15 and 25. The relationship betweenammonia excretion and dry weight could be expressed by a powercurve with a weight exponent of 0.82 (SE 0.042). Faecal production was measured in limpets freshly sampled fromthe field, and placed in dean seawater for 4 days. During thistime faecal production decreased (since the limpets were notfeeding), although only data from the first 24 hours were used.Again the relationship between faecal egestion and dry weightcould be expressed by a power curve, although this time theweight exponent was 0.94 (SE 0.101). The ash content of thefaecal strings increased significantly with the size of thelimpet, possibly because larger limpets were ingesting a greaterproportion of substrate during feeding. If this is so, thenthis would also explain the weight exponent dose to 1.0, ratherthan the value of about 0.8 to be expected from metabolic measures(since larger limpets would be passing relatively more faecalmaterial). If assimilation efficiency is known, then food intake in thewild may be estimated from a measurement of faecal egestionand faecal organic content (Clarke et at., 1988). Applying typicalvalues of assimilation efficiency for limpets (40 to 60%) suggestsa daily food intake in Nacella of 2 to 3% body weight per day.This is a quite typical figure for a grazing limpet, and suggeststhere is no resource limitation for Nacella at Signy in summer.     

Deposition and longevity of oviposition-deterring pheromone in the cabbage seed weevil

Abstract The cabbage seed weevil ( Ceutorhynchus assimilis Payk.) lays eggs singly into pods of oilseed rape ( Brassica napus L.) through punctures bored with the mouthparts, preferring pods not recently used for oviposition. A simple new choice test has been used to test individual components of egg-laying behaviour for their effect on oviposition site selection. It is confirmed that an oviposition-deterring pheromone (ODP) is deposited during abdomen brushing of the pod which follows egg-laying. Neither pin punctures, weevil feeding punctures, oviposition punctures nor eggs had any deterrent effect. Pods walked on by female weevils were not avoided by those laying eggs. Observations suggest that the ODP is sensed by contact chemoreceptors on the antennae. The deterrent effect lasted only 1–2 h. The implications of these findings on the adaptive significance of the pheromone and its possible use in pest control are discussed.     

Simulated climate change: are passive greenhouses a valid microcosm for testing the biological effects of environmental perturbations?

This paper considers the use of passive greenhouse apparatus in field experiments investigating the biological consequences of climate change. The literature contains many accounts of such experiments claiming relevance of greenhouse treatment effects to global change scenarios. However, inadequacies in microclimate monitoring, together with incomplete understanding of greenhouse modes of action, cast doubt upon such claims. Here, treatment effects upon temperature (magnitude, range, variation, rates of change), moisture (humidity, precipitation, soil water content), light (intensity, spectral distribution), gas composition, snow cover, and wind speed are reviewed in the context of Intergovernmental Panel on Climate Change (IPCC) predictions. It is revealed that greenhouses modify each of these potentially limiting factors in a complex and interactive manner, but that the relationship between this modification and forecast conditions of climate change is poor. Interpretation of biological responses, and their extrapolation to predictive models, is thus unreliable. In order that future greenhouse experiments may overcome criticisms of artefact and lack of rigour, two amendments to methodology are proposed: (1) objective-orientated design of greenhouse apparatus (2) multiple controls addressing individual environmental factors. The importance of a priori testing of microclimate treatment effects is stressed.     

Effects of Repetitive Acid Immersion, Red Light, and Gibberellin A3 Treatments on Phytochrome-mediated Germination Control in Skotodormant Lettuce Seeds

Dry lettuce seeds (Lactuca sativa L. cv. Grand Rapids), whichreceived 5 min far-red light (FR) 0.5 h after the onset of waterimbibition, showed 17% and 50% germination without and withacid immersion treatment (pH 0.1) for 1 h and rinsing with water,respectively. The acid treatment caused only 6% germinationor less in FR-treated seeds held for 10 to 30 d in dark storage.The 10 to 30 d skotodormant seeds did not respond to red light(R) or gibberellin A₃ (GA₃) singly, but showed 84% or higherpercentage germination if 1 h acid immersion was given beforeR or GA₃. The 20 d skotodormant seeds, which received R treatmentat day 10 but remained dormant showed 89% germination with onlyacid treatment. Similar values were obtained with 30 d skotodormantseeds which received one or two R treatments at day 10 or 20,i.e. the only requirement for these R-treated dormant seedswas an acid immersion. This releases the skotodormancy and rendersthe seeds more sensitive to R or GA₃, but the skotodormancywas initiated again if no light or hormone treatments were givenimmediately. The repetitive R or GA₃ treatments, which did notcause skotodormant seeds to germinate, lessened the degree ofskotodormancy. The germination of these skotodormant seeds canonly be induced by the synergistic action of R and GA₃. In thisstudy, GA₃ caused higher germination percentages in R-treatedskotodormant seeds than R stimulated in GA3-treated seeds. Itis suggested that (i) repetitive R or Ga₃ treatments maintaina high endogenous level of the far-red-absorbing form of phytochrome(P_fr) and GA activity, respectively, (ii) the accumulated stableintermediates of phytochrome persist in fully-imbibed skotodormantseeds for up to 20 d, without phytochrome expressing its functionuntil the seeds are acidified and (iii) a model is formulatedto interpret the results of acidification, growth promotersand R effects on germination of light-sensitive lettuce seeds. Key words: Phytochrome, Latuca saliva, seed germination, dark reversion of phytochrome, gibberellin A₃, acidification, skotodormancy     

Bumble bee workers drift to conspecific nests at field scales

1. Workers in several bee species travel to conspecific nests (‘drifting’), enter them, and produce male offspring inside them, so acting as intra‐specific social parasites. This adds a new dimension to bees' reproductive behaviour and spatial ecology, but the extent to which drifting occurs over field scales, i.e. at natural nest densities in field conditions, has been unclear. 2. Using the bumble bee Bombus terrestris (Linnaeus) as a model system, we sought to determine rates of worker drifting at field scales and the frequency of potential drifter workers in wild nests. 3. A field experiment with 27 colonies showed that workers travelled to, and became accepted in, conspecific nests that were up to 60 m away, although the number of accepted drifter workers within nests fell significantly with distance. The rate at which nests were entered by drifters was relatively high and significantly exceeded the rate at which drifters became accepted. 4. Microsatellite genotyping of eight field‐collected nests from Greater London, U.K., showed that a low frequency (3%) of workers were not full sisters of nestmate workers and hence were likely to have been drifter workers. 5. It is therefore concluded that workers can drift to conspecific nests over field scales and confirmed that successful drifting occurs in natural populations. Drifting appears to be a natural but low‐frequency behaviour permitting B. terrestris workers to gain direct fitness.     

Use of Lethal Control to Reduce Habituation to Blank Rounds by Scavenging Birds

Abstract Scavenging bird deterrence frequently fails due to habituation. We demonstrated such habituation by gulls and corvids to blank rounds used in a dawn-to-dusk regime at a landfill site in southern England. We then combined blank rounds with live rounds and shot birds whenever they attempted to land. Gull numbers declined significantly despite only 1.9% of the population being shot. Corvid numbers returned to precontrol levels despite 52.7% of the population being shot. We suggest that shooting reduces gull habituation to blank rounds but is ineffective at reducing habituation by corvids.     

Climate change and cattle nutritional stress

Owing to the complex interactions among climate, plants, cattle grazing, and land management practices, the impacts of climate change on cattle have been hard to predict. Predicting future grassland ecosystem functioning relies on understanding how changes in climate alter the quantity of forage produced, but also forage quality. Plant protein, which is a function of plant nitrogen concentrations, and digestible energy limit the performance of herbivores when in short supply; moreover, deficiencies can be expensive to mitigate. To better understand how changes in temperature and precipitation would affect forage protein and energy availability, we analyzed over 21 000 measurements of cattle fecal chemistry acquired over 14 years in the continental US. Our analysis of patterns in forage quality among ecologically defined regions revealed that increasing temperature and declining precipitation decreased dietary crude protein and digestible organic matter for regions with continental climates. Within regions, quality also declined with increased temperature; however, the effects of precipitation were mixed. Any future increases in precipitation would be unlikely to compensate for the declines in forage quality that accompany projected temperature increases. As a result, cattle are likely to experience greater nutritional stress in the future. If these geographic patterns hold as a proxy for future climates, agriculture will require increased supplemental feeds or the consequence will be a decrease in livestock growth.     

The use of digital video recorders in pollination biology

1. Digital video recording (DVR) devices, such as the GoPro Hero, have the potential to greatly benefit pollination ecology, but the advantages of digitally recording pollinator activity over direct human observation have not been formally assessed. 2. Two plant taxa, Lavandula angustifolia and Canna ‘sp.’, with differing floral morphology, were used to compare the value of DVR and direct observations in estimating honeybee (Apis mellifera) visitation, flower density and number of flowers visited per foraging bout. 3. The two methods yielded identical results when observing the structurally simple L. angustifolia at both high (10.54 ± 0.52 per plant) and low honeybee density (2.24 ± 0.20 per plant). However, DVR underestimated the number of flowers scored in the field of view (28.7 ± 1.8 direct vs. 22.7 ± 0.9 DVR), the number of honeybees observed (5.3 ± 0.8 direct vs. 3.7 ± 0.7 DVR) and the number of flowers visited during foraging bouts (8.3 ± 1.2 direct vs. 5.5 ± 1.0 DVR) on the more complex Canna ‘sp.’ 4. It is concluded that portable weatherproof DVR devices such as the GoPro Hero are valuable tools for pollination biologists, allowing a single researcher to make simultaneous observations of multiple plants in one or more sites, whilst also allowing the footage to be reviewed. However, DVR devices are limited by their depth and field of view when target plants are large or structurally complex.