Statistical modeling of seasonal and environmental influences on the population dynamics of an estuarine fish community

A statistical modeling study was performed on the population fluctuations of the 15 commonest fish species frequenting the tidal Scheldt estuary in Belgium. These included marine juvenile and seasonal visitors, estuarine residents and diadromous fish species that were recorded on the filter screens of a power plant cooling-water intake between September 1991 and April 2001. The species population abundance was regressed against a candidate set of 6 environmental variables and 13 instrumental variables, accounting for seasonality and long-term trends present in the data. Population abundances of the different species were, in general, best described by seasonal variables. Seasonal components contributed, on average, up to 63.8% of the variance explained by the models. Ten species were found to show a slightly negative, though significant, trend over the period of the survey. Most models also included at least one environmental variable, and 25.4% of the explained variance could be attributed to environmental fluctuations. Of all physico-chemical variables, dissolved oxygen was the most important predictor of fish abundance, suggesting that the estuary suffered from poor water quality during the survey. Temperature, salinity, freshwater flow, suspended solids and chlorophyll a concentrations were minor determinants of fish abundance.Communicated by O. Kinne, Oldendorf/Luhe     

Precision and accuracy of stable isotope signals in otoliths of pen-reared cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) when sampled with a high-resolution micromill

A high-resolution sampling technique for stable-isotope measurements in otoliths is now available, but little is known about the precision and accuracy of the results when using this technique. Otolith samples of pen-reared cod (Gadus morhua L.) with well-defined temperature history were obtained using this high-resolution sampling technique. Samples from different-aged cod otoliths were collected in two yearly increments corresponding to the calendar years 1994 and 1995, and the stable-oxygen (¹⁸O) and -carbon (¹³C) isotope compositions of the samples were measured. Otolith ¹⁸O values had a clear seasonal pattern in response to the seasonal water temperature. Otolith material deposited in the same calendar years of different-aged fish showed similar ¹⁸O values. High precision of the temperature estimate using otolith ¹⁸O values was obtained when comparing results from different otoliths. The accuracy of the temperature estimates, relative to measured mean monthly water temperature, was also high, but reduced sampling resolution in the otoliths significantly reduced the accuracy due to attenuation of the ¹⁸O signals. We found that the otolith ¹³C values had a cyclic pattern, roughly in phase with the ¹⁸O values. This was most likely caused by temperature-increased metabolism. Indications of age-specific otolith ¹³C values are also presented.Communicated by M. Kühl, Helsingør     

High-energy milling to decontaminate soils polluted by polychlorobiphenyls and atrazine

Mechanical energy has been used so far for running chemical reactions and for preparing new materials in absence of solvents. Very recently, the technology has been applied to solve environmental problems. In this paper, we describe the application of high-energy milling (HEM) for the remediation of soils contaminated by chlorinated organic compounds such as polychlorobiphenyls (PCBs) and agrochemicals like atrazine. NaBH₄ and LiAlH₄ have been successfully used for the total dehydrohalogenation of both classes of compounds, leaving a residue lower than 2 ppmw of the starting compound in the treated soil. LiAlH₄ was found to be more active than NaBH₄.     

Lévy walk patterns in the foraging movements of spider monkeys (<Emphasis Type="Italic">Ateles geoffroyi</Emphasis>)

Scale invariant patterns have been found in different biological systems, in many cases resembling what physicists have found in other, nonbiological systems. Here we describe the foraging patterns of free-ranging spider monkeys (Ateles geoffroyi) in the forest of the Yucatan Peninsula, Mexico and find that these patterns closely resemble what physicists know as Lévy walks. First, the length of a trajectorys constituent steps, or continuous moves in the same direction, is best described by a power-law distribution in which the frequency of ever larger steps decreases as a negative power function of their length. The rate of this decrease is very close to that predicted by a previous analytical Lévy walk model to be an optimal strategy to search for scarce resources distributed at random. Second, the frequency distribution of the duration of stops or waiting times also approximates to a power-law function. Finally, the mean square displacement during the monkeys first foraging trip increases more rapidly than would be expected from a random walk with constant step length, but within the range predicted for Lévy walks. In view of these results, we analyze the different exponents characterizing the trajectories described by females and males, and by monkeys on their own and when part of a subgroup. We discuss the origin of these patterns and their implications for the foraging ecology of spider monkeys.Communicated by D. Watts     

Distribution of deep-water gorgonian corals in relation to benthic habitat features in the Northeast Channel (Atlantic Canada)

The distribution and abundance of deep-water gorgonian corals were investigated along 52 transects at 183–498 m depth in the Northeast Channel, between Georges Bank and Browns Bank in the northwest Atlantic, using a remotely operated vehicle and a towed video-camera system. Three species (Paragorgia arborea, Primnoa resedaeformis, and Acanthogorgia armata) were observed. Primnoa occurred on 35 transects below 196 m depth, with highest local abundance in stands of 104 colonies per 100 m². Paragorgia was present on 21 transects deeper than 235 m, with highest local abundance of 49 colonies per 100 m². Acanthogorgia was observed at only four transects between 231 m and 364 m, with a local maximum abundance of 199 colonies per 100 m². The maximum abundance averaged for whole transects was 19.2 and 6.2 colonies per 100 m² for Primnoa and Paragorgia, respectively. The corals were more common in the outer part of the channel along the shelf break and slope than on the shelf in the inner part. All three species showed a patchy distribution with no signs of competitive exclusion at any spatial scale. Transects with high abundance of corals were characterised by depths greater than 400 m, maximum temperatures less than 9.2°C, and a relatively high percentage coverage of cobble and boulder (more than 19% and 6%, respectively). High temperatures probably control the upper depth limit of the corals, and Primnoa seems to tolerate slightly higher temperatures than Paragorgia. Abundance of both species was negatively correlated with average temperature and positively with cobbles. Together, temperature, percentage cobble and salinity accounted for 38% of the variance of Primnoa. The comparable figure for Paragorgia was 15%. The observed distribution indicated that the abundance of coral is controlled by additional factors such as larger-scaled topographic features governing the current regimes and thus also the supply of food and larvae.Communicated by R. J. Thompson, St. Johns     

Distribution of salmon-habitat potential relative to landscape characteristics and implications for conservation.

The geographic distribution of stream reaches with potential to support high-quality habitat for salmonids has bearing on the actual status of habitats and populations over broad spatial extents. As part of the Coastal Landscape Analysis and Modeling Study (CLAMS), we examined how salmon-habitat potential was distributed relative to current and future (+100 years) landscape characteristics in the Coastal Province of Oregon, USA. The intrinsic potential to provide high-quality rearing habitat was modeled for juvenile coho salmon (Oncorhynchus kisutch) and juvenile steelhead (O. mykiss) based on stream flow, valley constraint, and stream gradient. Land ownership, use, and cover were summarized for 100-m analysis buffers on either side of stream reaches with high intrinsic potential and in the overall area encompassing the buffers. Past management seems to have concentrated nonindustrial private ownership, agriculture, and developed uses adjacent to reaches with high intrinsic potential for coho salmon. Thus, of the area in coho salmon buffers, 45% is either nonforested or recently logged, but only 10% is in larger-diameter forests. For the area in steelhead buffers, 21% is either non-forested or recently logged while 20% is in larger-diameter forests. Older forests are most extensive on federal lands but are rare on private lands, highlighting the critical role for public lands in near-term salmon conservation. Agriculture and development are projected to remain focused near high-intrinsic-potential reaches for coho salmon, increasing the importance of effectively addressing nonpoint source pollution from these uses. Percentages of larger-diameter forests are expected to increase throughout the province, but the increase will be only half as much in coho salmon buffers as in steelhead buffers. Most of the increase is projected for public lands, where policies emphasize biodiversity protection. Results suggest that widespread recovery of coho salmon is unlikely unless habitat can be improved in high-intrinsic-potential reaches on private lands. Knowing where high-intrinsic-potential stream reaches occur relative to landscape characteristics can help in evaluating the current and future condition of freshwater habitat, explaining differences between species in population status and risk, and assessing the need for and feasibility of restoration.     

Scale-invariant movements of fishermen: the same foraging strategy as natural predators.

We analyzed the movement of fishing vessels during fishing trips in order to understand how fishermen behave in space while searching for fish. For that purpose we used hourly geo-referenced positions of vessels, provided by a satellite vessel monitoring system, for the entire industrial fleet (809 vessels) of the world's largest single species fishery (Peruvian anchovy, Engraulis ringens) from December 1999 to March 2003. Observed trajectories of fishing vessels are well modeled by Lévy random walks, suggesting that fishermen use a stochastic search strategy which conforms to the same search statistics as non-human predators. We show that human skills (technology, communication, or others) do not result in the fishermen's spatial behavior being fundamentally different from that of animal predators. With respect to probability of prey encounter, our results suggest that fishermen, on average, evolved an optimal movement pattern (mu = 2.00) among the family of Lévy random walks. This Lagrangian approach opens several perspectives in terms of operational management of the pelagic fish stock.     

Defining patch mosaic functional types to predict invasion patterns in a forest landscape.

Alien plant invasions contribute significantly to global changes by often affecting biodiversity and ecosystem processes. Operational methods for identifying landscape attributes that promote or constrain plant invasions are urgently needed to predict their future spread and manage them efficiently. We combined landscape and functional ecology concepts to define patch mosaic functional types (PMFTs) as groups of cells showing the same response to a plant invasion in a heterogeneous forest landscape. The invasion of a European temperate forest by the American black cherry (Prunus serotina) has been chosen as a case study. A set of variables was collected, mapped using a Geographic Information System, and analyzed with multivariate analyses to correlate landscape traits with Prunus serotina abundance in each cell of a grid overlaid on the forest. A risk index was derived and mapped for three invasion levels: seedling colonization, tree establishment, and ecosystem invasion. Five PMFTs were identified and characterized by a set of traits related to soil properties, land use, disturbance, and invasion history. Scots pine plantations on podzols were the most invasible, while cells dominated by hydromorphic or calcareous soils were the most resistant. Most colonized patch mosaics provided suitable conditions for future establishment and invasion. Being strongly spatially connected, suitable patches provide corridors for Prunus serotina to colonize new parts of the forest. Conversely, the most resistant PMFTs were spatially agglomerated in the south of the forest and could act as a barrier. Colonization, establishment, and invasion risk maps were finally obtained by combining partial risks associated with each landscape trait at the cell scale. Within a heterogeneous landscape, we defined and organized PMFTs into a hierarchy, according to their associated risk for colonization, establishment, or invasion by a given invasive species. Each hierarchical level should be associated with a management strategy aiming at reducing one or more partial risk. Monitoring safe areas, extending cutting rotations, harvesting recently colonized stands tree by tree, promoting a multilayered understory vegetation, cutting down reproducing alien trees, favoring shade-tolerant, fast-growing, native tree species, removing alien trees at the leading edge, and proposing soil enrichment or irrigation in heavily invaded areas are recommended.     

Male choice,fighting ability,assortative mating and the intensity of sexual selection in the milkweed longhorn beetle,Tetraopes tetraophthalmus (Coleoptera,Cerambycidae)

Summary Over five hundred adult longhorn milkweed beetles, Tetraopes tetraophthalmus, were individually marked and their copulatory success followed for one month in a pasture of Asclepias syriaca in northern Indiana, USA. Migration of beetles from the field site was greatest from areas of low population density. Dispersal was significantly greater for males experiencing low copulatory success; a similar but nonsignificant trend was observed for females. Large males, which displayed greater site tenacity than small males, copulated more frequently than small males because of their ability to displace small males from females. Both large and small males demonstrated a preference for large females in laboratory tests. Male preference in combination with aggressive displacement of small males results in size-assortative mating which was much stronger under conditions of high population density. It contributes to variance in male reproductive success since female size is known to be correlated with fecundity and offspring viability. Variance in copulatory success is similar for males and females, suggesting that both sexes experience similar intensities of sexual selection with respect to this component of reproductive success. Futhermore, comparison of this with other studies suggests that the intensity of sexual selection among males is positively correlated with the variance in body size which appears to be under both stabilizing and directional sexual selection in males but not in females.     

Group size and ectoparasitism affect daily survival probability in a colonial bird

Little is known in general about how group size or ectoparasitism affect survival in colonial animals. We estimated daily within-season survival probabilities for nesting adult and recently fledged juvenile cliff swallows (Petrochelidon pyrrhonota) at 239 colonies from 1983 to 2003 in southwestern Nebraska, USA. Some colonies had been fumigated to remove ectoparasites. We conducted mark-recapture at each colony site to estimate daily survival. There were no systematic differences between males and females in daily survival. Adults and juveniles occupying parasite-free colonies had, on average, 4.4% and 62.2% greater daily survival, respectively, than their counterparts in naturally infested colonies. Daily survival of all birds increased with colony size for both parasite-free colonies and those under natural conditions, although the effect was stronger for adults at fumigated sites and for juveniles. Average daily survival probability for adults tended to increase during warmer and drier summers. Although daily survival varied at some sites over the course of the nesting cycle, there were no strongly consistent within-year temporal effects on survival. Even small differences in daily survival probability can translate into large effects on mean lifespan. The deleterious effects of ectoparasites on daily survival within the season represent a previously unknown cost of ectoparasitism. The increase in within-season survival with colony size reflects the net effects of many costs and benefits associated with colony size. Ectoparasitism is probably the most important cost that tends to partly balance the positive effects of large colonies. The greater survival of cliff swallows in the larger colonies is a previously unknown advantage of colonial nesting.Communicated by P. Heeb