Interception and dispersal of artificial food falls by scavenging fishes in the abyssal Northeast Atlantic: early-season observations prior to annual deposition of phytodetritus

The hypothesis that the behaviour of deep-sea scavenging fishes is influenced by seasonal input of organic matter from the ocean surface was investigated by observing responses to baits placed on the sea floor at 4800 m depth in the NE Atlantic (48°50′N; 16°30′W) during spring (April 1994). Data from the present study are compared with those from previous studies of the same location made in summer 1989. The first fishes to arrive at baits were the grenadier Coryphaenoides (Nematonurus) armatus and the eel Histiobranchus bathybius, after delays of 28 and 29 min, respectively; these results are not significantly different from those of summer 1989. Similarly, other indices of activity (staying time and swimming speed) showed no evidence of differences between years/seasons. However, the rate of radial dispersal of bait (0.009 m s⁻¹) by C. (N.) armatus was much slower than in all previous studies. A change in the size distribution of C. (N.) armatus to smaller individuals in spring 1994 was also evident. It is suggested that the fish on the abyssal plain may not comprise a steady-state population and that major episodic or seasonal migrations may occur. Received: 18 October 1996 / Accepted: 20 December 1996     

A simulation model of rhizome networks for Fallopia japonica (Japanese knotweed) in the United Kingdom

Fallopia japonica (Japanese knotweed) is an aggressively invasive herbaceous perennial that causes substantial economic and environmental damage in the United Kingdom (UK). As such, it is of considerable concern to councils, environmental groups, private landowners and property developers. We construct a 3D correlated random walk model of the development of the subterranean rhizome network for a single stand of F. japonica. The formulation of this model uses detailed knowledge of the morphology and physiology of the plant, both of which differ in the UK to that of its native habitat due to factors including a lack of predation and competition, longer growth seasons and favourable environmental conditions in the UK. Field data obtained as a part of this study are discussed and used in the model for parameterisation and validation. The simulation captures the field data well and predicts, for example, quadratic growth in time for the stand area. Furthermore, the role of a selection of parameters on long-term stand development are discussed, highlighting some key factors affecting vegetative spread rates.     

Ecological costs and benefits of communal behavior in a presocial spider

Summary Philoponella oweni (Uloboridae) is a facultatively communal spider found in the southwestern United States. Solitary females and communal groups of females coexist in the same habitats. Communal females are known to produce more eggs than solitary females. Communal females might acquire the energy for the production of additional eggs by one of three means: they might have a longer life span, and thus more time in which to acquire energy; web maintenance might be more efficient in a communal group; or communal females might spend more time feeding. Field data from a marked population in Arizona showed the third alternative was true.Two possible causes for the greater time spent feeding by communal females were investigated; either the communal web or group is a more efficient trap for insects, or the communal groups are located at sites where insects are more abundant. Analysis of feeding rates and sticky trap data confirmed the second alternative.Potential web attachment sites are limited in some habitats, and mortality during dispersal is very high. When potential web attachment sites are scarce more of the population is found in communal groups; when they are abundant more of the population is solitary. The pattern of dispersal and overwintering is this species suggests that females renewing a colony in the spring could be related.     

Call structure may affect male mating success in the quacking frog<Emphasis Type="Italic"> Crinia georgiana</Emphasis> (Anura: Myobatrachidae)

We investigated the relationship between mating success, male size and variation in the advertisement call in the frog Crinia georgiana under field conditions. Mating success in 91 males was determined by following 32 females as they moved through the chorus. Our analyses indicated that successful males had a higher number of pulses in the first note and/or called at a higher rate. However, we did not detect a significant relationship between mating success and dominant frequency, the property that varied most strongly with body size, suggesting that size is not an important influence on mate choice in this species. Even so, smaller males were more successful if they called at a higher rate whereas larger males were more successful if they had more pulses in their first note. Accordingly, males of different size may use different calling tactics to attract females. These results provide a framework for further experimental studies aimed at investigating the independent impacts of both inter- and intra-sexual selection on the advertisement call and body size of C. georgiana.     

Localized defecation by pike: a response to labelling by cyprinid alarm pheromone?

Fathead minnows (Pimephales promelas) that have never encountered a predatory pike (Esox lucius), are able to detect conspecific alarm pheromone in a pike's diet if the pike has recently consumed minnows. It remains unclear how this minnow alarm pheromone is secreted by pike and if a pike is able to avoid being labelled as a potential predator by localizing these cues away from its foraging range. The first experiment determined that minnow alarm pheromone is present in pike feces when pike are fed minnows. Individual fathead minnows exhibited a fright response to a stimulus of pike feces if the pike had been fed minnows, but not if the pike had been fed swordtails, which lack alarm pheromone. Individual minnows also exhibited a fright reaction to alarm pheromone in the water (which contained no feces) housing pike which had been fed minnows, suggesting that alarm pheromone is also released in urine, mucous secretions and/or via respiration. The second experiment determined that test pike spent a significantly greater proportion of time in the home area of the test tanks (i.e. where they were fed) but the majority of feces were deposited in the opposite end of the test tank. By localizing their defecation away from the home or foraging area, pike may be able to counter the effects of being labelled as a predator by the alarm pheromone of the prey species.     

Exhaustible Resource Allocation in an Overlapping Generations Economy

This paper analyzes competitive allocations of an exhaustible resource in an overlapping generations economy. Conditions are given for the existence of equilibrium extraction rules such that both extraction and investment in future stocks are increasing and continuous in the current stock. The paper then considers the time paths of equilibrium allocations and shows that there are economies where equilibrium resource extractions and prices exhibit nonclassical behavior. This is illustrated through a finite horizon example in which extractions increase and prices decrease over the entire time horizon and an infinite horizon example where there are persistent cycles in extractions and prices and multiple equilibria. The paper concludes by examining welfare issues.     

Minimum effective release rate of antifoulants. 2. Effects of TBTCI, 2-furyl-n-pentyl ketone and coumaric acid at Snug harbor,Hawaii

Minimum effective release rate (MERR) of three antifoulants was examined at Snug harbor, Hawaii using a dynamic diffusion system. Among the three antifoulants tested TBTCI was found to be effective in preventing the settlement of Hydroides elegans and Crisea sp at 0.5 microg cm(-2) d(-1) flux rate. At a maximum flux rate of 10 microg cm(-2) d(-1) of 2-furyl-n-pentyl ketone larval settlement of both the test species were 32-36% reduced. More or less similar effect was seen at 10 microg cm(-2) d(-1) of coumaric acid. Non-toxic antifoulants, 2-furyl-n-pentyl ketone and coumaric acid exhibit specific activity against target species. MERR obtainedfor the three antifoulants is discussed.     

Fatty acid composition of organs and tissues of the tiger prawn Penaeus esculentus during the moulting cycle and during starvation

The fatty acids (FA) in neutral lipid (NL) and polar lipid (PL) of digestive gland, muscle and integument of Penaeus esculentus Haswell were analysed and compared during the moulting cycle and during starvation. The prawns were collected from Moreton Bay, Queensland, Australia, by trawling during 1985–1987, and were fed with a standard semi-purified diet. Compared with a natural diet, the artificial diet had much higher levels of 18:1n-9 and 18:2n-6, but only trace amounts of 20:4n-6, but there was no evidence of dietary imbalance. The fatty acid composition (percentage of total lipid) of the digestive gland changed markedly during the moulting cycle and during starvation, but the small changes observed in both muscle and integument suggested that these tissues maintained their composition under both conditions. When the fatty acids were calculated as absolute amounts, muscle composition, as well as that of the digestive gland, changed significantly. In the digestive gland, saturated FA (SFA), monounsaturated FA (MUFA), diunsaturated FA (DUFA) and polyunsaturated FA (PUFA) all increased up to the middle of the moulting cycle and then declined; with starvation all groups decreased. In muscle, SFA, MUFA and DUFA all increased during the moulting cycle; starvation caused SFA, MUFA and PUFA to decrease, whereas DUFA did not vary. Starvation caused both 18:2n-6 (linoleic) and 18:3n-3 (linolenic) in the digestive gland to reach or almost reach zero. The other essential PUFA, 20:4n-6 (arachidonic), 20:5n-3 (eicosapentaenoic) and 22:6n-3 (docosahexaenoic), decreased during the moulting cycle, but during starvation 20:4n-6 did not decrease as much. In muscle, the levels of 18:2n-6 and 18:3n-3 increased, while 20:4n-6, 20:5n-3 and 22:6n-3 remained approximately constant during the moulting cycle. Starvation reduced 20:5n-3 and 22:6n-3 to about 60%. The data suggest that levels of 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3 are regulated, and that 20:4n-6 can be synthesised from 18:2n-6. There is no clear evidence that 20:5n-3 and 22:6n-3 are essential in P. esculentus, but tissue catabolism of cell membranes during starvation may have provided sufficient amounts for maintenance.