Bayesian characterization of uncertainty in species interaction strengths

Considerable effort has been devoted to the estimation of species interaction strengths. This effort has focused primarily on statistical significance testing and obtaining point estimates of parameters that contribute to interaction strength magnitudes, leaving the characterization of uncertainty associated with those estimates unconsidered. We consider a means of characterizing the uncertainty of a generalist predator’s interaction strengths by formulating an observational method for estimating a predator’s prey-specific per capita attack rates as a Bayesian statistical model. This formulation permits the explicit incorporation of multiple sources of uncertainty. A key insight is the informative nature of several so-called non-informative priors that have been used in modeling the sparse data typical of predator feeding surveys. We introduce to ecology a new neutral prior and provide evidence for its superior performance. We use a case study to consider the attack rates in a New Zealand intertidal whelk predator, and we illustrate not only that Bayesian point estimates can be made to correspond with those obtained by frequentist approaches, but also that estimation uncertainty as described by 95% intervals is more useful and biologically realistic using the Bayesian method. In particular, unlike in bootstrap confidence intervals, the lower bounds of the Bayesian posterior intervals for attack rates do not include zero when a predator–prey interaction is in fact observed. We conclude that the Bayesian framework provides a straightforward, probabilistic characterization of interaction strength uncertainty, enabling future considerations of both the deterministic and stochastic drivers of interaction strength and their impact on food webs.     

The ecology of the streptococci

All species of streptococci are divided into several groups according to the ecological niches they occupy. Members of the lactic acid group are found only in the plant environment and the dairy. Members of the pyogenic group and the buccal and intestinal residents of the subthermophilic group are found in intimate association only with homeothermic hosts. Members of the virulent pyogenic group, such asStreptococcus pyogenes, S. equi, andS. infrequens, are restricted to single hosts—the human, the horse, and the pig—whereas others, such asS. agalactiae can be found in several hosts. The intestinal dwellers of the subthermophilic group,S. bovis andS. equinus, occur in several animal species and are not isolated from other sources. The superficially homogeneousS. faecalis of the enteric group may actually consist of a group specifically restricted to the human host, and of a second group distributed among wild animals, insects, and plants. The latter group differs from the human type by the ability to hydrolyze starch and to produce a rennin-proteolytic type of curd in milk.Streptococcus faecium is widely distributed in both the homeothermic and poikilothermic environments, but no properties which differentiate the sources are known.Streptococcus faecium biot.casseliflavus has been isolated only from insects and plants.Streptococcus uberis occurs on the bovine lips and skin. Unidentified streptococci from all environments vary widely in properties. Many resembleS. lactis, S. faecalis, andS. faecium.     

Social structure emerges via the interaction between local ecology and individual behaviour

1. The formation of groups is a fundamental aspect of social organization, but there are still many questions regarding how social structure emerges from individuals making non-random associations. 2. Although food distribution and individual phenotypic traits are known to separately influence social organization, this is the first study, to our knowledge, experimentally linking them to demonstrate the importance of their interaction in the emergence of social structure. 3. Using an experimental design in which food distribution was either clumped or dispersed, in combination with individuals that varied in exploratory behaviour, our results show that social structure can be induced in the otherwise non-social European shore crab (Carcinus maenas). 4. Regardless of food distribution, individuals with relatively high exploratory behaviour played an important role in connecting otherwise poorly connected individuals. In comparison, low exploratory individuals aggregated into cohesive, stable subgroups (moving together even when not foraging), but only in tanks where resources were clumped. No such non-foraging subgroups formed in environments where food was evenly dispersed. 5. Body size did not accurately explain an individual's role within the network for either type of food distribution. 6. Because of their synchronized movements and potential to gain social information, groups of low exploratory crabs were more effective than singletons at finding food. 7. Because social structure affects selection, and social structure is shown to be sensitive to the interaction between ecological and behavioural differences among individuals, local selective pressures are likely to reflect this interaction.     

The feeding ecology of the dingo

Summary Changes in the diet of dingoes (Canis familiaris dingo) in response to measured fluctuations of prey populations were followed over 7 years. The study began after great rains had broken a long drought. Eruptions of rodents and rabbits followed, but some prey were always either relatively abundant (live cattle) or scarce (red kangaroo, lizards, birds). Cattle carcasses were increasingly available during a subsequent drought. Small and medium-sized prey, rodents (26%), lizards (12%) and rabbits (56%) were preferred, probably because they were easily caught. Only rabbits were caten consistently regardless of density. By contrast, large prey were eaten in relatively large amounts only during drought, with initial emphasis on red kangaroos (15% overall) and then cattle (17%) mostly as carcasses. The diet was functionally related to the respective abundances of all major prey species, but the relationship shifted during drought when predation on low populations was most severe. There was evidence that growth of resurging prey populations were suppressed by predation. Diets of dingoes did not differ significantly with age or sex. An hypothesis of alternation of predation is presented: dingoes feed sequentially on prey of increasing size (rodents, rabbits, red kangaroos, cattle) in response to rainy periods and subsequent droughts, meanwhile always concentrating on the staple prey (rabbits). The fluctuating abundances of small and medium-sized prey determined not only their own relative availabilities but also that of large prey, and hence determined the diet of the dingo at any time. Prey availability (catchability, accessability) appeared to be more important than prey abundance (numbers, biomass), and the dingo's flexible social organisation allowed versatility in hunting strategies and defence of resources. We conclude that dingoes do not always forage most efficiently as optimal foraging models predict because of the constraints imposed by the capricious environment in arid Australis, where prey availability fluctuates greatly and becomes limited and clumped in drought, so that dingoes may be faced with outright starvation. Instead we conclude that dingoes utilise a conservative feeding strategy and adopt any behaviour which provides at least a threshold quantity of energy or nutrient as part of a trade-off with other competing ecological requirements.     

The uncertainty principal in vision

During research into the relationship between the bandpass width of the spatial frequency characteristic (F) and the size (D) of the receptive field of the cat striate cortex it was found that F·D=1.2. Inaccuracy in spatial signal representation is thus related by an uncertainty principle to inaccuracy of frequency representation within the system of elements involved in information processing in the cat association cortex. The magnitude of the constant shows that the distribution functions of elements are sinusoids or cosinusoids modulated by square-wave impulses rather than Gabor elements. The magnitude of the constant and the fact that an uncertainty principle operates would support the hypothesis that the receptive fields of the visual cortex constitute a quasilinear basis.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 307–312, May–June, 1986.     

The teaching of ecology in Spain

The design of an interactive computer program in microbial genetics is described. The program is divided into three stages: background information, questions, and the simulation. The results of simulated conjugation experiments with Escherichia coli allow eight chromosomal genes to be sequenced. These genes can be mapped relative to eight different sites of F plasmid insertion and transfer orientation. The simulation requires the student to choose appropriate donor and recipient strains of the bacterium, and to specify the constituents of selective media on which the progeny of each cross are grown. The simulation mimics the experimental errors which can affect the results and hence their interpretation. The value of this simulation is that it permits the student to work at his own pace and to develop an understanding of techniques for studying microbial genetics.     

The ecology of Millepora

Attention is drawn to the lack of quantitative ecological information on the calcareous hydrozoan Millepora. In spite of their abundance and geological importance on reefs, little attention has been paid to the millepores compared to the dominant corals. The literature on distribution and abundance on reefs is reviewed and attention is drawn to sources of bias in reported estimates of Millepora abundance. Millepora is shown to have many of the same parasites and predators as scleractinians. The sparse data on growth and production are reviewed and compared with that of corals. The physiological and ecological responses of Millepora to storms and other disturbances appear to be similar to those of the scleractinans but the millepores have escaped attack by the starfish Acanthaster and appear to be immune to the common diseases of corals. The morphological similarities and ecological differences between millepores and scleractinians are discussed in terms of life-history strategies.     

The ecology of the scorpion Euscorpius flavicaudis in England

A large colony of Euscorpius flavicaudis was studied at Sheerness Docks, Isle of Sheppey, Kent. It was probably established in the late nineteenth century. The scorpions inhabit cracks in the dockyard perimeter wall where the mortar pointing has crumbled away. They are nocturnal, sit-and-wait, generalist predators. They are extremely sedentary: females leave their cracks fewer than 10 times per year; males are more active as they become vagrant prior to the mating season, which occurs in summer. Marked adults were resighted at intervals of over a year and the distance scorpions moved between resightings was not proportional to the interval. The number of scorpions seen per night was influenced by temperature, amount of rainfall and phase of the moon. In winter, the scorpions retreated far into the wall and, by doing so, reduced the risk of suffering mortality due to cold. During this time, they were seldom active. In general, this species does not behave in any way that can be correlated with living in a temperate rather than a desert area. This illustrates the extreme adaptability of scorpions.     

The structural aspect in the ecology of sea-grass communities

Summary 1. Sea-grasses are aquatic angiosperms which are completely adapted to life in the marine environment. They belong to 2 families, the Potamogetonaceae with 9 marine genera and the Hydrocharitaceae with 3 marine genera.2. All sea-grasses satisfy the following indispensable conditions for a successful existence in the sea: (a) high salt tolerance, (b) ability to grow when fully submerged, (c) well-developed rhizomes, (d) hydrophilous pollination, and (e) sufficient competitive power in the marine environment.3. Plant taxa which fulfill the first 4 conditions excellently, but have a reduced competition capacity, are unable to establish themselves successfully in the marine environment and are restricted to poikilohaline environments, such as brackish waters and continental salt waters. Moreover, some of these taxa occur in instable fresh-water environments.4. Within the group of the sea-grasses 6 different growth-forms can be distinguished: parvozosterids, magnozosterids, syringodiids, enhalids, halophilids and amphibolids.5. The growth-forms are linked with the environmental conditions: they show a distinct horizontal zonation and in the succession series they follow each other in a fixed sequence.6. The structure of the communities is also dependent on the dominating growthforms. The communities of parvozosterids and halophilids are very simple in structure. The magnozosterid vegetations show some differentiation. In the enhalid and amphibolid communities a marked stratification occurs, as an upper layer, characterized by photophilous epiphytes on the leaves, and a lower layer with sciophilous epiphytes on the rhizomes can be distinguished.7. Sea-grass communities alter the physical environment by stabilizing the bottom, slackening the water movements and increasing the sedimentation.8. Sea-grass vegetations form a food resource for many marine organisms and water fowl, and are also of some importance as shelter and nurseries for a number of animal species.

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Der strukturelle Aspekt in der Ökologie von Seegras-Gemeinschaften

Kurzfassung Seegräser sind aquatische Angiospermen, welche vollkommen an das Leben im Meer angepaßt sind. Sie gehören zu zwei Familien, den Potamogetonaceen mit 9 und den Hydrocharitaceen mit 3 marinen Gattungen. Für das Leben im Meer sind sie gut ausgerüstet mit Eigenschaften, die unbedingt für eine erfolgreiche Existenz erforderlich sind: hohe Salztoleranz, Fähigkeit, ganz untergetaucht zu gedeihen, Vorhandensein gut entwickelter Rhizome, hydrophile Bestäubung und ein ausreichendes Konkurrenzvermögen. Eine erfolgreiche Ansiedlung im Meer ist bereits ausgeschlossen, wenn die zuletzt erwähnte Eigenschaft nicht vorhanden ist. Es gibt nämlich eine Reihe von Gattungen, die in ihrer Beziehung zur Umwelt, insbesondere zum Salzgehalt, eine viel größere Toleranz besitzen als die Seegräser, aber ungenügend konkurrenzfähig sind gegenüber stenobionten Wasserpflanzen. Diese Gattungen sind beschränkt auf poikilohaline Gewässer und unstabile Süßwasserbiotope. Die Gesellschaften dieser Pflanzen werden zur Klasse der Ruppietea gestellt. Die echten Seegrasgesellschaften werden zusammengefaßt in der Klasse Zosteretea. Diese Gesellschaften sind noch ungenügend studiert worden; daher wird ihre Struktur von vielen Pflanzensoziologen nicht korrekt beurteilt. Der Verfasser bereitet eine Monographie über die Seegräser vor; er hatte Gelegenheit, alle bis jetzt bekannten Arten gründlich zu untersuchen und die Wichtigkeit ihrer morphologischen Merkmale für die Ökologie zu prüfen. Es stellte sich heraus, daß unter den Seegräsern 6 Wuchsformen unterschieden werden können, welche charakterisiert sind durch das Verästelungssystem, die Blattform und die Natur der Blattscheiden. Jede Wuchsform hat ihren eigenen Platz in der Zonierung und in der Sukzessionsreihe, und jede bedingt im großen und ganzen die Struktur der von ihr konstituierten Pflanzengesellschaft.