Consequences of competition on the time budgets,growth and distributions of three species of terrestrial slugs

Summary The behavioural time budgets of two non-aggressive slugs and one aggreessive species were evaluated in monocultures or in 2-way combinations in field cages. The seasonal time budgets ofL. maximus, A. ater andA. columbianus in monoculture were remarkably similar despite their strong differences in physiological resource allocation. Similarity in physical design and resource utilization appeared to be more important determinants of behaviour. The time budgets showed distinct seasonal patterns associated with underlying physiological demands for reserve accumulation, sperm acquisition and oviposition.A. ater andL. maximus displayed a definite dispersal phase associated with femalephase maturation. In combination,A. ater andA. columbianus had no detectable effect on one another’s time budgets.L. maximus disrupted nearly every category of behaviour in these non-aggressive species, but its own time budget was not significantly different in the monoculture or in the two combinations, except for minor effects on resting and sexual behaviour.L. maximus appeared to be adapted to maximize behavioural disturbance of interspecific competitors while minimizing intraspecific effects.     

Resource allocation and time budgeting in adults of the cockroach,Periplaneta americana: The interaction of behaviour and metabolic reserves

Activity (to food, water and shelter) and resource allocation (mass budget, and size of various body components) were examined in populations of adult Periplaneta americana subjected to periods of starvation or sugar feeding. Following 13 days of starvation, roaches ate 5 times their normal daily ration and feeding required about 20 days to return to pre-starvation levels. When sucrose was substituted for the usual dog-food diet for 13 days, there was also a large increase in feeding initially. When the dog food was re-established, however, there was very little feeding for about one week. Although reproduction was markedly curtailed by starvation, females fed sucrose continued reproducing for at least 59 days. The results suggested that the roaches were mainly energy limited. Although the consumption of roaches was strongly affected by reserve depletion, eating was a small component of the time budget, and overall activity was relatively unchanged by starvation or sugar-feeding. There was a slight decrease in activity during starvation, but the circadian pattern remained unchanged. Females carrying oöthecae were highly active and were apparently attracted to food (even though they ate little). Thus the activity of the population was dominated by circadian rhythmicity and the reproductive cycle.     

Plant communities of extreme acidic waters: The Rio Tinto case

As one of the largest extreme acidic environments in the world the Río Tinto (Spain) constitutes a useful case to study the vegetation resistant to waters, sediments and soils with pH < 3 and high concentrations of S, Fe, Cu and other metals. In this territory two types of water courses coexist: the extreme acidic waters, with a low pH and high amounts of S and Fe, usually of a red color, and those that are not extremely acid, which include colorless acid, neutral and basic waters with much less S and Fe. An exhaustive study of the riparian vegetation present along the two first sections of the Río Tinto and in less extreme, neighboring water courses was carried out (61 inventories). Some water quality variables (pH, redox, Fe, Cu and O₂) were measured in sampled points. Correspondence between plant community composition and water quality was analyzed through hierarchical classification, detrended correspondence analysis and canonical correspondence analysis.Results indicate clear differences in vegetation between extremely acidic and less extreme water courses. A total of 50 emergent plant species have been found in extremely acidic waters. Among them the most frequent were Erica andevalensis Cabezudo and J. Rivera, Scirpoides holoschoenus (L.) Soják and Nerium oleander L. Additionally, pH, redox, Fe and O₂ concentrations were significantly related to the floristic data.     

Measuring weight outcomes for obesity intervention strategies: The case of a sugar-sweetened beverage tax

Taxing unhealthy foods has been proposed as a means to improve diet and health by reducing calorie intake and raising funds to combat obesity, particularly sugar-sweetened beverages (SSBs). A growing number of studies have examined the effects of such food taxes, but few have estimated the weight-loss effects. Typically, a static model of 3500 calories for one pound of body weight is used, and the main objective of the study is to demonstrate its bias. To accomplish the objective, we estimate income-segmented beverage demand systems to examine the potential effects of a SSB tax. Elasticity estimates and a hypothetical 20 percent effective tax rate (or about 0.5 cent per ounce) are applied to beverage intake data from a nationally representative survey, and we find an average daily reduction of 34–47 calories among adults and 40–51 calories among children. The tax-induced energy reductions are translated into weight loss using both static and dynamic calorie-to-weight models. Results demonstrate that the static model significantly overestimates the weight loss from reduced energy intake by 63 percent in year one, 346 percent in year five, and 764 percent in year 10, which leads to unrealistic expectations for obesity intervention strategies. The tax is estimated to generate $5.8 billion a year in revenue and is found to be regressive, although it represents about 1 percent of household food and beverage spending.     

The curse of taxonomic uncertainty in biogeographical studies of free-living terrestrial protists: a case study of testate amoebae from Amsterdam Island

Aim A current debate in microbial biogeography contrasts two views concerning the distribution of free‐living microorganisms. The first view assumes a ubiquitous distribution, while the second assumes that at least some species have limited geographical distributions. We tested for limited geographical distributions by identifying testate amoebae morphospecies from an extremely remote oceanic island where the potential for endemism is high. Location Amsterdam Island, Indian Ocean. Methods Sixty moss and water samples collected from the top of the volcano to the lowland were investigated for their testate amoeba content. Due to taxonomic uncertainties among the Argynnia (Nebela) dentistoma species complex (including A. antarctica), we also performed light and scanning electron microscopy investigations on the shell ultrastructure and biometric analyses on several specimens of this taxon. Results We identified a total of 43 testate amoeba taxa belonging to 15 genera. Only four testate amoeba taxa had previously been recorded on this island. Testate amoeba communities of Amsterdam Island are dominated by cosmopolitan ubiquitous euglyphid taxa such as Trinema lineare, Assulina muscorum and Corythion dubium. The length and width ranges for Argynnia dentistoma on Amsterdam Island overlap with other records of this species and of A. antarctica, suggesting that A. antarctica is not a distinct taxon. Main conclusions Although Amsterdam Island is among the most remote islands in the world, an extensive inventory of testate amoeba morphospecies provided no clear evidence for endemism. On the one hand, our detailed morphometric analysis of the A. dentistoma complex revealed that A. antarctica, a morphospecies previously suggested to display endemism, cannot be confidently distinguished from the cosmopolitan morphospecies A. dentistoma. On the other hand, five morphotaxa could not be identified with certainty and might represent new species, potentially with limited distribution. These examples illustrate how taxonomic uncertainties undermine biogeographical studies of testate amoebae. In order to allow better interpretation of morphology‐based testate amoeba distribution data, an assessment of genetic diversity among and within morphotaxa in relation to geographical distance for some common testate amoebae should be given high priority.     

What limits the distributions of coastally restricted terrestrial invertebrates? The case of coastal landhoppers (Crustacea: Amphipoda: Talitridae) in southern Tasmania

Aim A number of terrestrial invertebrates are known to have distributions limited to the immediate coastal zone, but the factors controlling their distributions are not well understood. This study was planned to correlate the distribution of a coastal terrestrial amphipod, Austrotroides maritimus Friend 1987, which is only found within 100 m of the high tide mark, with soil characteristics and salt deposition. Location South Cape Rivulet Bay on the south coast of Tasmania (146°47′ E, 43°36′ S). Methods Abundance of the amphipods was examined at four sites c. 200 m apart that varied in their exposure to onshore westerly winds. At each site four replicate transect lines were established 3 m apart, with pitfall traps set at 2‐m intervals. The lines were at right angles to the high water mark and extended beyond the inland limit of A. maritimus. Amphipods were trapped at three times of the year, in winter, spring and summer (1993–94), and the sodium content, organic content and moisture content of the soil at each trap site were measured. The sodium content of rain falling on the transects, was also measured, and lysimeters were used to assess the concentration of sodium in water penetrating the soil profile. Results The inland penetration of A. maritimus varied between 18 and 44 m from the seaward edge of woody terrestrial vegetation (itself <10 m horizontally from the high tide mark). Inland penetration increased from west to east around the bay, following an apparent gradient of increased exposure to onshore winds. At the most easterly and apparently most exposed site, however, the species penetrated only 18 m, but this site differed markedly from the others in its topography, caused by erosion of the dunes, with an 8‐m cliff at its seaward end. The soils at this site were also unusually clayey and waterlogged. Amphipod abundance did not correlate strongly with any of the soil parameters. The salt content of rainfall generally declined inland, as did the concentration of lysimeter leachate, but the inland declines were not all smooth, and both rainfall and lysimeter leachate concentration showed some tendency to increase inland at the most sheltered site. Main conclusions Austrotroides maritimus is strongly restricted to the immediate coastal zone. The extent of its inland penetration correlates with exposure to onshore winds, and circumstantial evidence supports the hypothesis that this may be due to differences in the amount of salts deposited.     

Improving conservation strategies of raptors through landscape ecology analysis: The case of the endemic Cuban Black Hawk

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