THE ORIGINS OF ADAPTIVE INTERSPECIFIC TERRITORIALISM

1. In order to understand fully the evolution of a behavioural trait one must not only consider whether it is adaptive in its present environment but also whether it originated as an adaptation to existing selective forces or as a fortuitous consequence of selection for a different role in other environments (i.e., as a pre-adaptation) or of selection for different traits (e.g., as a pleiotropic effect). In this paper interspecific territorialism is examined in species of humming-birds, sun-birds, tropical reef fishes, stingless bees, stomatopods, crayfish, and limpets as a means of determining its adaptiveness and its origins. 2. Humming-birds form complex assemblages with species sorted out among the available resources. Dominant species establish feeding territories where flowers provide sufficient nectar. A few large, dominant species, usually uncommon, are marauders on others' territories. Subordinate species establish territories where flowers are more dispersed or produce less nectar, or they fly a circuit from nectar source to nectar source when flowers are even more dispersed, a foraging pattern called ‘traplining’, or they steal nectar from the territorial species by being inconspicuous while foraging. Two species, Amazilia saucerottei and Selasphorus sasin, subordinate in one-to-one encounters, are able to take over rich resources by establishing several small territories within a territory of a dominant and forcing it to forage elsewhere. 3. Among humming-birds, territorial individuals attacked not only subordinate competitors but marauding humming-birds and some insects, which stayed in the territory and foraged at will, and seemingly inappropriate targets, such as non-competitors. This suggests that the stimulus for aggression is ‘any flying organism near the food resources’, regardless of its appearance. The behaviour rather than the identity of the intruder is the stimulus. 4. Sun-birds resemble humming-birds to the extent that dominants establish territories on rich nectar sources and subordinates establish territories on less rich nectar sources or steal from the territories of dominants. The diversity of foraging patterns is not so great as in humming-birds, perhaps because so few species of sun-birds have been studied. However, the advantage of territorialism has been measured in the sun-bird Nectarinia reichenowi. Individuals with territories lose much less nectar to competitors than do those without territories. 5. Field work on three species of tropical reef fishes involved a single aggressive species whose individuals attacked a wide range of species intruding on their territories. The stimulus for aggression in Pomacentrus jenkinsi seemed to be an “object moving through [its] territory”. As suggested for humming-birds, the stimulus is the behaviour rather than the identity of the intruder. 6. The relationships found in stingless bees, stomatopods, crayfish, and limpets are simpler. The dominant and subordinate species divide the resources in their habitat, the dominants' aggression preventing the subordinates from using resources that were otherwise available to them. 7. A general pattern emerges. Mutual interspecific territorialism occurs between species that (i) have different geographic ranges, (ii) occupy different habitats, or (iii) use different resources within the same habitat. Examples of two species holding separate territories on the same resources within the same habitat are rare and occur when the dominant species is rare relative to the available resources. These observations are contrary to the usual view that interspecific territorialism is an adaptation that permits co-existence of potential competitors within the same habitat. 8. Interspecific territorialism is sometimes adaptive and sometimes maladaptive, depending upon the species and the situation. 9. The general pattern of occurrence of the behaviour and the general nature of the stimulus for aggression, i.e., the behaviour rather than the identity of the intruder, suggest that interspecific territoriality is a fortuitous consequence of selection for intraspecific territorialism, the latter being not only an adaptation to the presence of conspecific competitors but a pre-adaptation to the presence of competitors of other species, should they occur.     

Inter‐regional comparison of land‐use effects on stream metabolism

1. Rates of whole‐system metabolism (production and respiration) are fundamental indicators of ecosystem structure and function. Although first‐order, proximal controls are well understood, assessments of the interactions between proximal controls and distal controls, such as land use and geographic region, are lacking. Thus, the influence of land use on stream metabolism across geographic regions is unknown. Further, there is limited understanding of how land use may alter variability in ecosystem metabolism across regions. 2. Stream metabolism was measured in nine streams in each of eight regions (n = 72) across the United States and Puerto Rico. In each region, three streams were selected from a range of three land uses: agriculturally influenced, urban‐influenced, and reference streams. Stream metabolism was estimated from diel changes in dissolved oxygen concentrations in each stream reach with correction for reaeration and groundwater input. 3. Gross primary production (GPP) was highest in regions with little riparian vegetation (sagebrush steppe in Wyoming, desert shrub in Arizona/New Mexico) and lowest in forested regions (North Carolina, Oregon). In contrast, ecosystem respiration (ER) varied both within and among regions. Reference streams had significantly lower rates of GPP than urban or agriculturally influenced streams. 4. GPP was positively correlated with photosynthetically active radiation and autotrophic biomass. Multiple regression models compared using Akaike’s information criterion (AIC) indicated GPP increased with water column ammonium and the fraction of the catchment in urban and reference land‐use categories. Multiple regression models also identified velocity, temperature, nitrate, ammonium, dissolved organic carbon, GPP, coarse benthic organic matter, fine benthic organic matter and the fraction of all land‐use categories in the catchment as regulators of ER. 5. Structural equation modelling indicated significant distal as well as proximal control pathways including a direct effect of land‐use on GPP as well as SRP, DIN, and PAR effects on GPP; GPP effects on autotrophic biomass, organic matter, and ER; and organic matter effects on ER. 6. Overall, consideration of the data separated by land‐use categories showed reduced inter‐regional variability in rates of metabolism, indicating that the influence of agricultural and urban land use can obscure regional differences in stream metabolism.     

Comparative adaptations of Aphanizomenon and Anabaena for nitrogen fixation under weak irradiance

1. In situ measurements of nitrogen fixation rates for Aphanizomenon in fertile Colorado lakes with low inorganic nitrogen concentrations demonstrated high efficiency of nitrogen fixation at low irradiance. 2. For study populations, rates of N₂ fixation in darkness and with alternating exposure to light and darkness were a higher percentage of light‐saturated rates for Aphanizomenon than for Anabaena, suggesting storage of reduced metabolites at high irradiance that are used subsequently by Aphanizomenon when cells are forced by mixing into zones of low irradiance. Also, saturation of N₂ fixation occurred over a lower range of irradiance for Aphanizomenon than for Anabaena. 3. High efficiency of N₂ fixation in Aphanizomenon at low or fluctuating irradiance is complementary to its previously demonstrated high efficiency of photosynthesis at low irradiance. Nitrogen fixation rate was also strongly related to DIN concentration; fixation was highest at low DIN (maximum < 5 μg L^?1) but was also most vulnerable to photoinhibition under such conditions. 4. The fixation capabilities of Aphanizomenon under weak or varying irradiance could explain its commonly observed domination over Anabaena when transparency is low and available nitrogen is scarce.     

Leaf breakdown in an Atlantic Rain Forest stream

The hypothesis of this study was that colonizers in decaying leaf litter prefer native species (Erythrina verna) to exotic ones (Eucalyptus camaldulensis and Protium heptaphyllum). Therefore, native species are expected to show higher breakdown rates, increased biomass, richness and density of invertebrate species, and increased biomass of decomposer fungi. Breakdown of leaf litter from these three species was assessed in an Atlantic Rain Forest stream. Four samples were collected during a period of 90 days and washed on a sieve to separate the invertebrates. Then, a series of leaf disks were cut to determine ash‐free dry mass and fungal biomass, and the remaining material was oven‐dried to determine the dry weight. Eucalyptus camaldulensis and E. verna showed higher breakdown rates than P. heptaphyllum, due to differences in leaf physical and chemical characteristics. The harder detritus (P. heptaphyllum) broke down more slowly than detritus with high concentrations of labile compounds (E. camaldulensis). The density of the invertebrates associated with detritus increased with time. There were no differences in density, taxonomic richness or biomass of invertebrates among the leaf types, which indicated that the invertebrates did not distinguish between exotic and native detritus. Fungal colonization varied among samples; E. camaldulensis showed the lowest ergosterol concentrations, mainly due to a high concentration of total phenolics. The detritus with the highest hardness value was colonized most slowly by fungi. These results showed that leaf breakdown in Atlantic Rain Forest streams could be affected either by changes in riparian vegetation, or by becoming more savanna‐like process due to climate change.     

Modeling and Analysis of the Effect of Training on \dot{V}O_{2} Kinetics and Anaerobic Capacity

In this paper, we present an application of a number of tools and concepts for modeling and analyzing raw, unaveraged, and unedited breath-by-breath oxygen uptake data. A method for calculating anaerobic capacity is used together with a model, in the form of a set of coupled nonlinear ordinary differential equations to make predictions of the kinetics, the time to achieve a percentage of a certain constant oxygen demand, and the time limit to exhaustion at intensities other than those in which we have data. Speeded oxygen kinetics and increased time limit to exhaustion are also investigated using the eigenvalues of the fixed points of our model. We also use a way of analyzing the oxygen uptake kinetics using a plot of vs which allows one to observe both the fixed point solutions and also the presence of speeded oxygen kinetics following training. A method of plotting the eigenvalue versus oxygen demand is also used which allows one to observe where the maximum amplitude of the so-called slow component will be and also how training has changed the oxygen uptake kinetics by changing the strength of the attracting fixed point for a particular demand.     

Characteristics affecting fibrinolytic activity and plasma fibrinogen concentrations.

As part of a study to determine the extent to which the haemostatic system is implicated in the onset of clinically manifest ischaemic heart disease, characteristics influencing fibrinolytic activity (FA) and plasma fibrinogen concentrations were examined in 1601 men aged 18-64 and 707 women aged 18-59 in several occupational groups in North-west London. In men FA noticeably decreased till the age of about 58, when there was a small rise. In women a small increase in FA between 18 and about 40 was followed by a slightly larger fall between 40 and 59. There was a pronounced negative association of FA with obesity. FA was significantly less in smokers than non-smokers, though the effect was not large. FA increased with alcohol consumption. FA in men appeared to be greatest in the lower social classes, and men on night shift had poorer FA than those on day work. FA was greater in women using oral contraceptives than in those not using these preparations. In both sexes FA increased with exercise, but there were no associations between any of the characteristics studied and the increase. Plasma fibrinogen concentrations increase with age and obesity, are higher in smokers than non-smokers, and fall with alcohol consumption. In women the concentrations are higher in those using oral contraceptives. The general epidemiology of FA and plasma fibrinogen concentrations suggests that they may well be implicated in the pathogenesis of ischaemic heart disease.     

Historical and Life History Factors in the Biogeography of Mayflies

SYNOPSIS. Cladistic analysis of mayflies suggests that dispersalwas very asymmetrical after the new land connection betweenNorth and South America. Twenty-one genera apparently movedfrom South to North and Central America, but there is good evidencefor only one North American genus moving into the south. Testablepredictions are possible once the boreal (Laurasian) or austral(Gondwanian) designations are made. For example, Paracloeodes,a genus of austral origin, was predicted to be found in SouthAmerica, and in North America in warm rivers north and eastof its known distribution. These predictions have been confirmed.Other characteristics of tropical mayflies, such as length oflarval period and emergence and mating patterns, may be usedto predict habitats and characteristics of present North Americangenera. Merger events and consequent dispersal of organismshave profound influences on distributional patterns, and fromsuch information, biologically useful generalities can be made.     

Flexibility in crosstalk between H2B ubiquitination and H3 methylation in vivo

Histone H2B ubiquitination is a dynamic modification that promotes methylation of histone H3K79 and H3K4. This crosstalk is important for the DNA damage response and has been implicated in cancer. Here, we show that in engineered yeast strains, ubiquitins tethered to every nucleosome promote H3K79 and H3K4 methylation from a proximal as well as a more distal site, but only if in a correct orientation. This plasticity indicates that the exact location of the attachment site, the native ubiquitin-lysine linkage and ubiquitination cycles are not critical for trans-histone crosstalk in vivo. The flexibility in crosstalk also indicates that other ubiquitination events may promote H3 methylation.