Contrasting structure and composition of the understory in species-rich tropical rain forests

In large samples of trees > or = 1 cm dbh (more than 1 million trees and 3000 species), in six lowland tropical forests on three continents, we assigned species with >30 individuals to one of six classes of stature at maturity (SAM). We then compared the proportional representation of understory trees (1-2 cm dbh) among these classes. The understory of the three Asian sites was predominantly composed of the saplings of large-canopy trees whereas the African and American sites were more richly stocked with trees of the smaller SAM classes. Differences in class representation were related to taxonomic families that were present exclusively in one continent or another. Families found in the Asian plots but not in the American plot (e.g., Dipterocarpaceae, Fagaceae) were predominantly species of the largest SAM classes, whereas families exclusive to the American plots (e.g., Melastomataceae sensu stricto, Piperaceae, and Malvaceae [Bombacacoidea]) were predominantly species of small classes. The African plot was similar to Asia in the absence of those American families rich in understory species, while similar to America in lacking the Asian families rich in canopy species. The numerous understory species of Africa were chiefly derived from families shared with Asia and/or America. The ratio of saplings (1-2 cm dbh) to conspecific canopy trees (>40 cm dbh) was lower in American plots than in the Asian plots. Possible explanations for these differences include phenology, moisture and soil fertility regimes, phyletic constraints, and the role of early successional plants in forest development. These results demonstrate that tropical forests that appear similar in tree number, basal area, and the family taxonomy of canopy trees nonetheless differ in ecological structure in ways that may impact the ecology of pollinators, dispersers, and herbivores and might reflect fundamental differences in canopy tree regeneration.     

Levels and trends of brominated flame retardants in the European environment

In this paper, we review those data which have recently become available for brominated flame retardants (particularly the brominated diphenyl ethers (BDEs) and hexabromocyclododecane (HBCD)) in samples from the European environment. Environmental compartments studied comprise the atmosphere, sediments and soils, sewage sludges, and a variety of biological samples and food chains. This is currently a very active research area, and we cite over 70 studies reported in the literature during 2003-04. Findings include that the input of BDEs (especially BDE209) to the Baltic Sea by atmospheric deposition now exceeds that of PCBs by a factor of almost 40 times. Sewage sludge samples from both industrial and background locations show concentrations of BDEs, HBCD and tetrabromobisphenol-A (TBBP-A) that are of a similar order, indicating that the major source is from diffuse leaching from products into wastewater streams from users, households and industries generally. Point-sources from industries using BFRs (e.g. the textile industry) also generate local hot-spots. Sediment core studies identified the presence of two of the three PBDE formulations. The penta-mix formulation was clearly present from the beginning of the 1970s, but the deca-mix only appeared in the late 1970s. BDE183, BDE209 and HBCD were detected in peregrine falcons from Sweden and other birds feeding on terrestrial food chains. BDEs are found widely distributed in fish, including those from high mountain lakes in Europe, as a consequence of long-range atmospheric transport and deposition. A temporal trend study in archived freeze-dried mussels from the Seine estuary, France, indicated an exponential increase in BDE concentrations during the period 1982-1993, which levelled off in 1999 and 2001 and then began to decline after 2002. HBCD was detected in liver and blubber samples from harbour seals and harbour porpoises from the Wadden and North Seas, though very few animals yielded positive values for TBBP-A. There are difficulties in comparing data on summation operatorBDE from studies in which different suites of BDE congeners have been determined, and we suggest a common suite which will allow the study of all three commercial PBDE formulations.     

Effects of Land-Use and Tsetse Fly Control on Bird Species Richness in Southwestern Ethiopia

Successful control of tsetse (Glossina spp.)-transmitted trypanosomiasis in the Ghibe Valley, Ethiopia, appears to have accelerated conversion of wooded grassland into cropland. Land conversion, in turn, may have fragmented wildlife habitat. Our objective was to assess the influence of the expansion of agricultural land-use, brought about by tsetse control, on ecological properties by using bird species richness and composition as indicators of environmental impacts. We sampled bird species richness and composition (using Timed-Species counts) and habitat structure (using field sampling and remote sensing) in four land cover/land-use types in areas subjected to tsetse fly control and adjacent areas without control. At the height of the growing season bird species numbers and vegetative complexity were greater in the small-holder, oxen-plowed fields and riparian woodlands than in wooded grasslands or in large-holder, tractor-plowed fields. Species composition was highly dissimilar (40–70% dissimilarity) comparing among land-use types, with many species found only in a single type. This implies that trypanosomiasis control that results in land conversion from wooded grasslands to small-holder farming in this region may have no adverse impacts on bird species numbers but will alter composition. These results also suggest that moderate land-use by humans (e.g., small-holder field mosaics) increases habitat heterogeneity and bird species richness relative to high levels of use (e.g., tractor-plowed fields). Tsetse control may be indirectly maintaining species richness in the valley by encouraging the differential spread of these small-scale, heterogeneous farms in place of large-scale, homogeneous farms. Nevertheless, if the extent of small-holder farms significantly exceeds that of present levels, negative impacts on bird species richness and large shifts in species composition may occur.     

Transient nestmate recognition cues contribute to a multicolonial population structure in the ant,Leptothorax curvispinosus

Summary Individual nests of the facultatively polygynous and polydomous ant, Leptothorax curvispinosus, were mapped at two sites, collected, and maintained under uniform laboratory conditions. Tests of worker acceptability between nests were conducted 2–4 weeks and 13–17 weeks after collection. Nests collected near to one another (0.09–1.87 m) were sometimes nonaggressive, and were significantly less aggressive than those from different sites (7 km apart); and there was no significant difference in aggressiveness between tests for these distance categories. However, aggression between nests collected farther away from one another at the same site (1.52–4.65 m) decreased significantly between tests: initially, the level of aggressiveness was equivalent to that between nests from different sites but later it was reduced to that between near nests. These results indicate that polydomous colonies of this species occur within multicolonial populations; and that colony segregation within local populations is largely maintained by transient environmentally-based nestmate recognition cues. More stable cues of genetic or environmental origin (or both) are also present and contribute to discrimination even after extended periods of culture under uniform conditions. These results suggest that the maintenance of colony autonomy within genetically highly interrelated populations may be the prime function of environmentally-based nestmate recognition cues. Colony autonomy under such circumstances may be important to maintain a relatively small but optimal colony size, or because the mechanisms which regulate colony growth, development, etc., require a limited colony size.     

Phenotype interactions in group behavior of honey bee workers (Apis mellifera L.)

Summary The alarm reaction of groups of honey bee workers was quantified using a metabolic bioassay. The genetic structure of these groups was varied in order to estimate the effects of worker interactions. Though the group phenotype was mainly determined by additive interactions, nonlinear effects were also found. Mixed worker groups, combined from colonies with similar reactivity in the bioassay, showed a stronger response than pure groups. This phenomenon, analogous to the overdominance model for individuals in classical genetics, has implications for mechanisms of natural and artificial selection in social populations and for the evolution of polyandry in social Hymenoptera.     

Self-organization of circadian rhythms in groups of honeybees (Apis mellifera L.)

Workers in social groups of honeybees (Apis mellifera L.) synchronize their individual free-running circadian rhythms to an overall group rhythm. By monitoring the activity of bees by recording the oxygen consumption and intragroup temperature, it is shown that the rhythm coordination is in part achieved by temperature fluctuations as an intragroup Zeitgeber. Trophallaxis was shown to have only a minor (if any) effect on circadian rhythm synchronization. A model incorporating a feed back loop between temperature and activity can plausibly explain the observed synchronization of individual rhythms in social groups as a self-organization phenomenon. Correspondence to: R.F.A. Moritz     

Effect of carbon dioxide concentration on calcification in the red coralline alga Bossiella orbigniana

The relationship between various experimental concentrations of CO₂ and calcification in Bossiella orbigniana (Decaisne) was studied by measuring Ca-45 incorporation into the crystalline matrix. Air containing CO₂ at partial pressures (P_{CO 2}) of 0.04 to 5.5% was bubbled through synthetic seawater in incubation vessels. The resultant pH values in the presence of plants ranged from 6.5 to 8.7. The maximum calcification rate appears to lie between 0.11 and 1.05% P_{CO 2}. The data suggest that calcification is controlled by a biological process that may be sensitive to pH and/or to the relative bicarbonate concentration. The data also suggest that a severalfold increase in CO₂ over the present atmospheric level might lead to increased calcification in this marine alga.