Opposed latitudinal patterns of network‐derived and dietary specialization in avian plant–frugivore interaction systems

Latitudinal patterns of biodiversity have been studied for centuries, but it is only during the last decades that species interaction networks have been used to examine the proposed latitudinal gradient of biotic specialization. These studies have given idiosyncratic results, which may either be because of genuine biological differences between systems, different concepts and scales used to quantify biotic specialization or because the methodological approaches used to compare interaction networks were inappropriate. Here we carefully examine the latitudinal specialization gradient using a global dataset of avian plant–frugivore assemblages and interaction networks. In particular, we test whether network‐derived specialization patterns differ from patterns based on assemblage‐level information on avian dietary preferences on specific food types. We found that network‐derived measures of specialization (complementary specialization H₂′ and < d’>, modularity Q) increased with latitude, i.e. frugivorous birds divide the niche of fruiting plants most finely at high latitudes where they also formed more modular interaction networks than at tropical latitudes. However, the strength and significance of the relationship between specialization metrics and latitude was influenced by the methodological approach. On the other hand, assemblage‐level information on avian specialization on fruit diet (i.e. the proportion of obligate frugivorous bird species feeding primarily on fruit) revealed an opposed latitudinal pattern as more bird species were specialized on fruit diet in tropical than in temperate assemblages. This difference in the latitudinal specialization gradient reflects that obligate frugivores require a high diversity of fruit plants, as observed in tropical systems, and fulfil more generalized roles in plant–frugivore networks than bird species feeding on different food types. Future research should focus on revealing the underlying ecological, historical and evolutionary mechanisms shaping these patterns. Our results highlight the necessity of comparing different scales of biotic specialization for a better understanding of geographical patterns of specialization in resource–consumer interactions.     

FLOCKING AND FEEDING IN THE GREAT TIT PARUS MAJOR–AN EXPERIMENTAL STUDY

Some aviary experiments designed to investigate the survival value of flocking in the Great Tit Parus major are described.
An individual searching for a source of food is less likely to find it if he is on his own or in a pair than when in a flock of four. This is a result of local enhancement: with more pairs of eyes searching, some member of the flock is likely to come across the food sooner than would a lone bird, and once one finds the food, others in the flock more or less immediately assemble at the food source. Once the birds have found a source of food, dominance interactions play a role in determining which individuals obtain the most food.
If one bird finds a single item of food, both it and the other members of the flock rapidly alter their searching behaviour, concentrating their attention in the general area and /or type of place where the food item was found.
Even if a bird searches in a place and does not find food, the others in the group show some increase in searching effort in the same area or type of place. The extent to which they do this depends on whether they are used to finding food in clumps or dispersed.
The relevance of these findings to birds in the wild is discussed. It seems likely that local enhancement does occur in natural flocks, and the flocking in Great Tits is of benefit to the participants because they increase their effectiveness in finding food. However, the question of the survival value of mixed-species flocks of titmice remains unresolved.     

Linking optimal foraging behavior to bird community structure in an urban-desert landscape: field experiments with artificial food patches

Urban bird communities exhibit high population densities and low species diversity, yet mechanisms behind these patterns remain largely untested. We present results from experimental studies of behavioral mechanisms underlying these patterns and provide a test of foraging theory applied to urban bird communities. We measured foraging decisions at artificial food patches to assess how urban habitats differ from wildlands in predation risk, missed-opportunity cost, competition, and metabolic cost. By manipulating seed trays, we compared leftover seed (giving-up density) in urban and desert habitats in Arizona. Deserts exhibited higher predation risk than urban habitats. Only desert birds quit patches earlier when increasing the missed-opportunity cost. House finches and house sparrows coexist by trading off travel cost against foraging efficiency. In exclusion experiments, urban doves were more efficient foragers than passerines. Providing water decreased digestive costs only in the desert. At the population level, reduced predation and higher resource abundance drive the increased densities in cities. At the community level, the decline in diversity may involve exclusion of native species by highly efficient urban specialists. Competitive interactions play significant roles in structuring urban bird communities. Our results indicate the importance and potential of mechanistic approaches for future urban bird community studies.     

The effects of competitor density on aggressive behaviour and resource defence in a Poeciliid fish

To test the hypothesis that competitor density and time spent at a food resource influences aggressive behaviour in male swordtail, Xiphophorus sp., fish were kept at two densities (low: 18 fish m^?3; high: 54 fish m^?3) and aggressive behaviour was recorded with the time at the food resource used as a covariate. Competitor density is likely to affect the cost:benefit ratio of food defence. When density is low, there should be sufficient food for all individuals and intra‐specific interactions are expected to be rare, while at high densities, increased intra‐specific encounter rates mean that individuals may spend more time defending a resource than utilising it. Food resource defence should occur at intermediate densities. The frequency of aggression, i.e. bites, chases, and display behaviour was significantly positively influenced by time spent at the food resource (Bites: F_1,31 = 8.186, P = 0.007; Chases: F_1,31 = 6.439, P = 0.016; Displays: F_1,31 = 4.435, P = 0.043) suggesting that food resource defence occurred. Competitor density had no effect on food resource defence and minimal effect on the frequency of aggression with only one type of aggressive behaviour, male–male displays, showing a difference between densities (F_1,31 = 6.975, P = 0.013). This finding is suggested to be a result of the formation of dominance hierarchies in this species. Aggression from the dominant individual may be directed at only subordinates of the next dominance rank and subordinate behaviour may be restricted by status rather than immediate threat. In such a situation, aggression may be independent of competitor density.     

SEXUAL SELECTION THROUGH FEMALE CHOICE IN LAWES' PAROTIA,A LEK-MATING BIRD OF PARADISE

We studied sexual selection in Lawes' Parotia, a lek-mating bird of paradise, during 1981–1983 in Papua New Guinea. There was a high variance in mating success among males, with fewer than half of the individuals mating in any one year. This variance was independent of male-male interactions and disruptions. A role of female choice in sexual selection was suggested by the patterns of female visitation to courts and statistical correlations across males between phenotypic traits and mating success. Females repeatedly visited most males in their home ranges and began visiting males up to six weeks before mating. In one or more years, six aspects of male behavior and one morphological variable were positively correlated with mating success, but the probability values were not significant using a simultaneous inference test. Calculation of combined probability values across all three years revealed that one aspect of male display behavior, the probability of display, positively and significantly influenced mating status. The probability of display was also significantly correlated with relative mating success among males. Females showed strong fidelity to mates, both within and between seasons. Display sites of male Lawes' Parotia are variably dispersed, but mating success did not differ for grouped and solitary males. These data confirm an important role of female choice in sexual selection in birds of paradise but also suggest that female choice may be unrelated to the process of lek-initiation in this species.     

Diet and feeding behaviour of samango monkeys (Cercopithecus mitis labiatus) in Ngoye Forest, South Africa

The samango monkey occurs at the southern limit of the range of Cercopithecus mitis. Greater climatic seasonality at this latitude results in more predictable fruiting patterns. In addition, there are no diurnal sympatric primate frugivores. Under these conditions, the diet and feeding strategies of samango monkeys would be expected to differ notably from those of central or east African C. mitis subspecies. Contrary to these expectations, the preliminary observations reported here indicate that diets of samango and blue monkeys differ only superficially in the proportions of items eaten. Similarities in feeding behaviour are especially marked during the dry season period when fruit is not abundant. Both samango and blue monkeys tend to be less selective in their choice of food species and to eat available food species regardless of their energy content; a shift toward less nutritious items such as leaves is also noted. Feeding behaviour during the summer wet season is characterized by the selection of fruits with high-energy values. A high proportion of visits by the monkeys to areas of greater food availability suggests a concentration of feeding effort in food patches and the selection of higher energy food species within patches.     

The effect of habitat complexity on the functional response of a seed-eating passerine

Recent population declines of seed-eating farmland birds have been associated with reduced overwinter survival due to reductions in food supply. An important component of predicting how food shortages will affect animal populations is to measure the functional response, i.e. the relationship between food density and feeding rate, over the range of environmental conditions experienced by foraging animals. Crop stubble fields are an important foraging habitat for many species of seed-eating farmland bird. However, some important questions remain regarding farmland bird foraging behaviour in this habitat, and in particular the effect of stubble on farmland bird functional responses is unknown. We measured the functional responses of a seed-eating passerine, the Chaffinch Fringilla coelebs , consuming seeds placed on the substrate surface in three different treatments: bare soil, low density stubble and high density stubble. Stubble presence significantly reduced feeding rates, but there was no significant difference between the two stubble treatments. Stubble reduced feeding rates by reducing the maximum attack distance, i.e. the distance over which an individual food item is targeted and consumed. The searching speed, handling time per seed, proportion of time spent vigilant, duration of vigilance bouts and duration of head-down search periods were unaffected by the presence of stubble. The frequency of vigilance bouts was higher in the bare soil treatment, but this is likely to be a consequence of the increased feeding rate. We show the influence of a key habitat type on the functional response of a seed-eating passerine, and discuss the consequences of this for farmland bird conservation.     

Migratory and resident Blackcaps Sylvia atricapilla wintering in southern Spain show no resource partitioning

When different populations of the same bird species share non‐breeding habitats, competition for food may promote resource partitioning. We studied food choice by resident and migratory Blackcaps Sylvia atricapilla in sympatric wintering grounds in southern Spain. Resident Blackcaps have a larger bill, which may allow them to feed on a broader range of fruit sizes, and they may know the distribution of food better than do migrants. Based on fruit and bird counts, we transformed both fruit crop and bird abundance to a common energy currency. During two winters with low and high fruit production, available energy from fruit in mid‐January was estimated to be 80 and 1300 times, respectively, the daily requirements of Blackcaps. Furthermore, Blackcap numbers did not track between‐winter changes in fruit abundance during 10 consecutive years of monitoring, further suggesting that fruit food is not limiting. Analysis of food items from 760 samples of 717 individuals showed that migrants and residents fed primarily on fruits of Wild Olive Olea europaea sylvestris, the most energetic fruit resource. There was no evidence that the larger bills of resident Blackcaps provided any foraging benefit. Migratory Blackcaps fed on Wild Olives and invertebrates, two resources with high energetic and structural value, more frequently than did residents. This food choice could be more important for migratory Blackcaps because they have lower body mass to reduce wing load. Our results suggest that the wintering grounds of Blackcaps in Iberia provide abundant food that is used by sympatric migrants and residents without resource partitioning. Slight differences in food choice suggest that migrants might benefit from feeding on more nutritive food than residents to counteract the energetic constraints associated with a smaller body size.     

Food resource matching by foraging tits Parus spp. during spring-summer in a Mediterranean mixed forest; evidence for an ideal free distribution

We analysed whether patterns of microhabitat use by Blue Tits Parus caeruleus , Great Tits Parus major and Crested Tits Parus cristatus inhabiting a mixed forest consistently matched the patterns of food availability experienced by foraging birds during spring-summer. The use of five microhabitats by each bird species (the foliage of three tree species, shrubs and ground) and the availability of food in trees during the prebreeding, breeding and post-breeding periods of the birds' annual cycle were measured. All three tit species foraged mainly in the outer part of tree canopies (small branches and leaves or needles). Tit distributions between tree species matched food resource distributions irrespective of overall food resource levels, which varied four-fold between the study periods, and tit species. Tits also exploited secondary microhabitats (shrubs and ground) in periods of low food availability; Blue Tits tended to use shrubs, whereas Great and Crested Tits foraged on the ground. Between-trees distributions fitted that expected from an ideal free distribution, suggesting that food availability and intraspecific exploitative competition were the main factors governing tree use by tits. In contrast, patterns of use of secondary microhabitats (shrubs and ground) seemed to indicate a role for the species-specific morphological configurations of each tit species since Blue Tits are better adapted to hang and tended to forage in shubs, whereas Great and Crested Tits are better adapted to feed on horizontal surfaces and tended to forage on the ground. No evidence of interspecific interactions was observed. Overall, the results pointed to an independent exploitation of Mediterranean mixed forest by each bird species, food availability and food accessibility being the main factors affecting microhabitat use by foraging tits.     

Responses of a specialist and a generalist seed predator to variation in their common resource

Fluctuations of resources in time and space will influence not only species abundance but also interactions among species. For plant–consumer interactions, the effects of resource variation have mostly been studied in systems with high resource variability. Systems with moderate variations are less studied, although ecological and evolutionary dynamics of plants and consumers are likely to be affected also by less extreme variability. The effects of variation in a particular resource should depend on consumer diet width.
We examined how spatial and temporal variation in seed production in the perennial herb Lathyrus vernus influenced population dynamics and resource utilization in two beetle pre-dispersal seed predators with different host ranges over six years. The monophagous Apion opeticum occupied fewer patches and had lower densities than the oligophagous Bruchus atomarius . The proportion of seeds attacked increased with increases in seed production between years for both seed predators. A possible explanation for these patterns is that population dynamics of beetles are driven largely by local factors and that the same factors influence both beetle performance and seed production. In B. atomarius , patterns may also be influenced by a more pronounced preference for L. vernus in years with a high seed production in L. vernus . We conclude that relatively modest variation in seed production may result in responses that differ in both direction and extent from those usually observed in systems with high variation in seed production.     

Switching behavior, coexistence and diversification: comparing empirical community-wide evidence with theoretical predictions

Theory shows that the presence of behavioural switching between alternative resources can contribute to coexistence when competitors differ in trophic-related traits. In addition, switching can generate disruptive selection on such traits in a low-diversity community, increasing the number of species. Both of these processes should produce communities in which species differ in their values of the trophic trait, and display corresponding differences in the time-course of their switching from one resource to another. Here we present evidence for widespread switching behaviour for a diverse Mediterranean scrubland bird community. We show that species differ in a beak character related to their relative use of insect and fruit resource channels, and that the timing of switching is correlated with the relative use of resources. These patterns are consistent with theoretical predictions, suggesting a possible role of switching behaviour in promoting avian coexistence and diversification.     

Ontogenetic changes in the association between antipredator responses and growth variables

Abstract.  1. An organism's growth parameters are expected to depend on environmental constraints, such as predation risk and food supply. However, antipredator responses, food intake, and thus growth of an animal may be mediated by behavioural traits, which are likely to differ among developmental stages. In this study, it was investigated how the relationship between growth and behavioural antipredator responses changes during ontogeny in the time-constrained dragonfly species Libellula depressa , and which factors influenced specific behavioural decisions at different points in ontogeny.
2. The results revealed that behavioural strategies differed between larval developmental sages, depending on associations between larval growth, food supply, and predation risk. Early in ontogeny, faster development was correlated with high larval activity and high food supply. This resulted in high activity levels under high food conditions irrespectively of predator presence, and under low food supply in predator absence only. In the intermediate stage of development, all larvae displayed a high activity level, which was correlated in general with fast development. However, growth later in ontogeny was not only influenced by the activity level, but also by predator presence and food supply, with larvae reared under high food supply and/or in presence of predators attaining a higher final mass. Thus, not only the way in which larval growth parameters and behaviour are related changed during development, but also whether the factors influenced larval growth and behaviour. Once the larvae reached the ultimate stage of development, in which they overwinter, behavioural patterns observed were consistent with model predictions.
3. It is advocated that behavioural plasticity of prey organisms in different developmental stages should be analysed in the context of associated growth variables.     

Modelling irruptions and population dynamics of the great spotted woodpecker – joint effects of density and cone crops

Irruptive migrants are partially migrating species showing pronounced temporal variation in the number of migrants. Occasional irruptions are often explained by increased population density (per area) or lack of food. Similarly to population dynamics, these explanations are not mutually exclusive, but probably act in concert. Here we do a parallel analysis on the migration intensity and population dynamics of an irruptive migratory bird species, the great spotted woodpecker Dendrocopos major, in southern Finland. Both analyses include simultaneous effects of breeding density and cone crops of Scots pine Pinus sylvestris and Norway spruce Picea abies. A novel model for statistical analyses of irruptive migration intensity is developed. Population dynamics are investigated using log‐linear state‐space models. Woodpecker migration intensity is well explained by lack of spruce cones and increases proportionally to population density. Population dynamics is most successfully described with a density dependent model, where the natural logarithm of spruce cone availability previous autumn has a strong positive effect on population growth. This is likely to be due to lowered winter mortality and lowered emigration rates resulting from plentiful food availability. Although the species uses pine cones as a food resource in winter, the estimated impacts of pine cone crops on migration intensity and population dynamics are low, probably due to low annual variation in crop comparing to spruce cones. Large irruptions also tend to occur earlier in season, often before cones are a crucial food resource for the woodpeckers, suggesting that the woodpeckers use the amount of maturing cones as a cue for upcoming conditions. Our results show that the ecological role of different resources can differ considerably from the expected pattern based on the proportion of the resources in a species’ diet. Advantages of examining patterns of bird migration, population density and dynamics in unison are apparent.     

Intruder Pressure Affects Territory Size and Foraging Success in Asymmetric Contests in the Water Strider Gerris lacustris

The theory of evolutionarily stable strategies (ESS) in asymmetric contests predicts that the propensity of an individual to expose itself to risk during contests depends on the individual's resource-holding-potential (RHP) and on the value of the disputed resource (V) for the individual compared with that for an opponent. If encounters of a territory owner with individuals of high RHP and high food demands (V) increase in frequency, one should expect a decrease in total aggressiveness of the territory owner, and in consequence a decrease of its territory size. Such a decrease should result in a lower amount of food consumed by the territory owner. Using natural variability in RHP and V in Gerris lacustris, I experimentally tested these predictions. The average prey item has higher value (V) for reproductive female water striders (which probably transform most of their food into eggs), than for nonreproductive females and for males. Because males are smaller, they have lower RHP than females, as RHP depends on size. Thus the reproductive females are the class of individuals of high RHP and high food demands (high V). Most nonreproductive females defend food-based territories. I observed two groups of water striders in a seminatural laboratory setting. As predicted, there was a negative correlation between the rate of encounter with reproductive females and size of the territory, and a positive correlation between territory size and number of Drosophila flies consumed by the owner. Territories were smaller in the group with high rates of encounter between territory owners and reproductive females. Territory owners caught the same number of Drosophila flies as non-territorial individuals in this group. In contrast, in the group with fewer encounters between territory owners and reproductive females, territories were larger, and territory owners gained more food than non territorial water striders.     

Matching consumer feeding behaviours and resource traits: a fourth‐corner problem in food‐web theory

For decades, food web theory has proposed phenomenological models for the underlying structure of ecological networks. Generally, these models rely on latent niche variables that match the feeding behaviour of consumers with their resource traits. In this paper, we used a comprehensive database to evaluate different hypotheses on the best dependency structure of trait‐matching patterns between consumers and resource traits. We found that consumer feeding behaviours had complex interactions with resource traits; however, few dimensions (i.e. latent variables) could reproduce the trait‐matching patterns. We discuss our findings in the light of three food web models designed to reproduce the multidimensionality of food web data; additionally, we discuss how using species traits clarify food webs beyond species pairwise interactions and enable studies to infer ecological generality at larger scales, despite potential taxonomic differences, variations in ecological conditions and differences in species abundance between communities.     

Constraints affecting partial prey consumption by a crab spider,Diaea sp. indet. (Araneae: Thomisidae)

Summary The influence of feeding constraints on the feeding behaviour of Diaea sp. indet., was investigated. Diaea is a crab spider which ambushes its prey and practises extraintestinal digestion. A laboratory study was carried out using fruit flies, Drosophila immigrans, as prey. Diaea feeds from two sites on the prey — initially the head, followed by the posterior abdomen, with most of the prey's contents being extracted from the head. If additional prey are available, Diaea will, instead of switching to the posterior abdomen, catch a new prey item. The efficiency with which Diaea can extract food is influenced by changes which occur in the prey as a consequence of it being killed and fed on. Evaporative fluid loss from prey is an important constraint on food uptake because in influences the viscosity of the prey's contents. Regardless of whether a new prey item arrives, Diaea discards the prey item on which it is feeding before all of the available food has been extracted from it. The fluid content of the prey is not only part of the food the spider extracts, it is also a resource enabling efficient transfer of food from prey to predator. The value of the prey's fluid content as a resource decreases as a function of feeding time and as a consequence of the spider feeding on the prey.     

Native Birds and Alien Insects: Spatial Density Dependence in Songbird Predation of Invading Oak Gallwasps

Revealing the interactions between alien species and native communities is central to understanding the ecological consequences of range expansion. Much has been learned through study of the communities developing around invading herbivorous insects. Much less, however, is known about the significance of such aliens for native vertebrate predators for which invaders may represent a novel food source. We quantified spatial patterns in native bird predation of invading gall-inducing Andricus wasps associated with introduced Turkey oak (Quercus cerris) at eight sites across the UK. These gallwasps are available at high density before the emergence of caterpillars that are the principle spring food of native insectivorous birds. Native birds showed positive spatial density dependence in gall attack rates at two sites in southern England, foraging most extensively on trees with highest gall densities. In a subsequent study at one of these sites, positive spatial density dependence persisted through four of five sequential week-long periods of data collection. Both patterns imply that invading galls are a significant resource for at least some native bird populations. Density dependence was strongest in southern UK bird populations that have had longest exposure to the invading gallwasps. We hypothesise that this pattern results from the time taken for native bird populations to learn how to exploit this novel resource.     

A conflicting-tendency model of spider agonistic behaviour: Hybrid-pure population line comparisons

Contests over web-sites in the spider, Agelenopsis aperta, have been simulated by a model in which the next act of a spider is determined by the value of two ‘drives’ or ‘tendencies’, to attack and to flee. Such a model can explain the fact that F₁ hybrids between two geographical races of A. aperta are not intermediate between their parents, but are more aggressive than either. The model also accounts for the following features of the observed contests: (1) contests consist of a series of bouts, during which the spiders perform increasingly aggressive acts; (2) contests are usually won by the larger spider; (3) if sizes are equal, contests are usually won by the owner; (4) contests over excellent-quality sites are more costly than over poor-quality sites; and (5) transition probabilities for de-escalation, matching and escalation with respect to prior acts show site quality and weight bias trends. It is argued that a two-tendency model is the simplest that would account for these observations. The model also accurately simulates spider behaviour in agonistic contexts not used in its development (i.e. round-robin contests involving opponents from different populations, and a group of contests involving unequally-matched hybrid opponents).The main discrepancy between the model and observed encounters is that the model predicts that, if the owner is larger, the cost of a contest will not vary with the value of the disputed site. This is because the smaller intruder, having no knowledge of site quality (Riechert 1984) is expected to withdraw early in the contest, regardless of site quality. In the actual contests over excellent sites, estimated costs are higher even when the owner is larger and the intruder loses. The change in intruder behaviour associated with site value occurs following the first series of actions, but within the first bout of the interactions: our analyses indicate that any information conveyed by the owner concerning site value is not through overt behaviour (i.e. through the frequencies with which specific acts are performed).     

Diets of fruit-eating birds: what are the causes of interspecific differences?

Differences in fruit choice among the bird species of a Spanish shrubland were related to the size of fruits and to the lipid content of pulp. Lipid-rich fruits were selected by the bird species with slower food passage rates through the digestive tract. These bird species also fed frequently on insects and seeds. Bird species with faster food passage rates fed less on insects and seeds, and ate mainly fruits with pulp poor in lipids (rich in sugars and water). Studies of digestion in birds indicate that lipids require slower food passage rates for efficient digestion and intestinal transport than simple sugars. The available evidence indicates that the European bird species that show stronger preferences for lipid-rich fruits are no better as seed dispersers, from the point of view of the plants, than species choosing lipidpoor fruits. Thus, the degree of frugivory of birds, their fruit choice patterns and their effects on seed dispersal do not seem to be related to each other in the ways expected by the early models of the evolution of fleshy fruits.     

Foraging ecology of bison at the landscape and plant community levels: the applicability of energy maximization principles

Predictions of animal distribution and resource use require multi-scale consideration because animals can use different sets of selection criteria at different scales. We investigated whether patterns of distribution and resource use by free-ranging bison (Bison bison) in Prince Albert National Park, Saskatchewan, follow rules of energy maximization that hold across multiple scales. Optimality theory predicts specialization on Carex atherodes and frequency-independent selection among plant species; that is, local variation in C. atherodes biomass should not influence diet choice but only the time spent in individual patches. The summer use of resources within meadows was closely related to energy maximization principles. C. atherodes dominated the diet of bison, was selected in all meadows, and diet choice was frequency-independent among meadows in the bison range. In winter, diet was still dominated by C. atherodes, but frequency-dependent selection of Scolochloa festucacea and the relative use of Cirsium arvense were inconsistent with theoretical predictions. At a larger spatial scale, however, the probability of meadow use was not positively related to the abundance of Carex atherodes. During summer and winter, general landscape features within the daily radius of bison (2 km in summer and 1.3 km in winter), together with abiotic characteristics of meadows, had the major influence on the probability of meadow utilization. Our study suggests that bison distribution and resource use are influenced by abiotic and biotic factors which vary in importance at different spatio-temporal scales.