Ant gardens: interspecific recognition in parabiotic ant species

 In French Guiana, parabiotic societies (natural mixed colonies) are frequently found in ant gardens. Crematogaster limata parabiotica (Myrmicinae), often associated with Camponotus femoratus (Formicinae), was found for the first time in parabiosis with ponerine ants: Pachycondyla goeldii and Odontomachus mayi. A detailed study of the relationships between Cr. l. parabiotica and O. mayi showed that each species is aggressive towards allospecific or conspecific individuals belonging to another colony, but tolerates allospecific individuals from the multi-species society. Studies of cuticular substances of the four ant species were made using gas chromatography. The results showed that each species, living alone or in parabiosis, possesses a specific chemical profile. Thus, the ants are able to recognise nestmate and non-nestmate individuals of the associated species, even though their cuticular profiles are different. The hypothesis that the nestmate allospecific profile is learned is suggested to explain this pattern of recognition. Received: 5 June 1996 / Accepted after revision: 17 October 1996     

Reproductive effort of colonial and solitary breeding tree sparrows Passer montanus L.

A total of 250 nestboxes were arranged in five plots in a suburban area of Budapest, Hungary (19°04E, 47°41N). In each plot, 25 were placed at 50 m intervals to simulate solitary breeding and 25 3–5 m apart to simulate colonial breeding. Length of nest building period, feeding frequency, nestling mortality, nestlings' diet, productivity and parental condition were compared for colonial and solitary breeding tree sparrows Passer montanus. Parents with long nest-building periods, including the majority of first-year females, produced fewer young than parents which built over short periods. Parents fed nestlings morefrequently and nestlings had lower mortality in second than first broods; whether or not a third brood was reared was determined by the costs invested in first and second broods. Females that laid a third clutch had reared fewer young in first and second broods and were heavier than females that reared many young in two broods. Colonial birds had higher feeding frequencies, more similar diets and suffered lower nestling mortality than solitary parents for first broods, but they fed less frequently, diets were less similar, and nestling mortality was higher in second and third broods. It is suggested that colonial breeders benefited from the social stimulation of simultaneous feeding in first broods, but the advantage of synchronicity in feeding declined in second broods and the sparser breeding spacing of solitary parents was more advantageous for feeding in second and third broods. Birds that changed nest spacing between broods had fed nestlings less frequently and had higher nestling mortality before changing than birds which retained their spacing. Parents which changed from colonies to solitary nests fed more frequently with lower nestling mortality in the next brood than parents which retained colonial nests for their second (and third) brood. Solitary parents did not show such a relationship. The rearing of three broods caused higher weight loss in colonial than solitary parents.Correspondence to: L. Sasvári     

Accumulation of mesozooplankton in a wake area as a causative mechanism of the “island-mass effect”

Mesozooplankton biomass (as displacement volume and protein content) and electron-transport system (ETS) activity have been studied in the coastal waters around the Canary Islands. Increases in biomass and ETS activity, on a unit volume basis, were observed in the wakes of the islands. The biomass values obtained in the leeward area for Gran Canaria Island were up to ten times higher than those observed for typical oceanic waters around this archipelago. Sampling was performed in May 1986 at the end of the characteristic vertical mixing period in these waters. Relatively strong winds were recorded prior to sampling. Specific ETS activity was higher at the windward stations on the island shelf. This correlates with the observation in a recent study of increased primary production on the shelf area, where turbulence produced by the northerly trade winds has a marked effect. The persistence of this turbulence during a prolonged wind-pulse results in an accumulation of organisms in the wake of the islands due to current dynamics. This process is proposed as being an important causative mechanism of the island-mass effect. Different biomass values were recorded between circular and oblong islands. The latter are oriented towards the current and the northerly trade winds, and display significantly lower biomass values than the former.     

Critical thermal maxima and upper lethal temperatures for the calanoid copepods Acartia tonsa and A. clausi

Determination of the critical thermal maxima and upper lethal temperatures for Acartia tonsa Dana and A. clausi Giesbrecht revealed the relative temperature tolerance of the two species. A. tonsa exhibited a wider range of acclimation temperatures compared to A. clausi. The response of A. tonsa is related to its ubiquity in Atlantic Ocean estuaries (temperate and tropical), and its capacity to live in temperate waters throughout most of the year. Differences between upper lethal temperatures and critical thermal maxima were very narrow for A. tonsa from tropical and subtropical areas. This suggests that, in warm climates, this copepod lives close to its upper lethal temperature limits.Based in part on a dissertation submitted in partial fulfillment for the Ph.D. degree at the University of Rhode Island.     

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     

Chemical ornaments of male lizards <Emphasis Type="Italic">Psammodromus algirus</Emphasis> may reveal their parasite load and health state to females

Evidence for parasite-mediated sexual selection has been found in many species that use visual ornaments to attract females. However, in many animals, variation in female responses to scents of parasitized males suggests that parasitic infections might also affect information conveyed by pheromones (i.e., chemical ornaments). Thus, pheromones might also function in parasite-mediated sexual selection. We show here that female lizards Psammodromus algirus responded differently to femoral gland secretions of males according to the parasite load and health of these males. Scents of healthier males elicited more tongue flicks (a chemosensory behavior) by females, suggesting that these scents were more attractive. Chemical analyses showed that parasite load and the T-cell-mediated immune response were related to the variability in the proportions of some lipids in secretions of males. Further trials testing the chemosensory responses of females to chemical standards indicated that females actually discriminated the chemicals related to males’ health from other chemicals found in secretions. We suggest that these chemical ornaments may provide reliable information on the health and degree of parasitic infection of a male.     

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.     

Risk-averse foraging by bananaquits on negative energy budgets

Summary Adult bananaquits on negative energy budgets were presented with a patch containing two flower types with identical mean rewards, but different variances. The flower patch contained a random array of 85 yellow and 85 red artificial flowers. Flowers of one color were filled with the same quantity of nectar (constant flowers); flowers of the other color were filled with variable quantities of nectar (variable flowers). In the first series of experiments the birds were given three presentations, followed by three more presentations with the flower colors reversed, to control for color preferences. Some individuals were occasionally indifferent during a presentation, but overall the birds significantly preferred the constant flowers. In the second series of experiments two birds were give five presentations of the floral patch during a day at a rate less than minimally required to meet all 24-h energy costs. In all experiments, bananaquits on negative energy budgets were either indifferent or risk-averse, but never risk-prone. The absence of risk-prone foraging might be attributed to resource dispersion pattern, reward skew, or a species characteristic.     

Reef coral reproduction in the eastern Pacific: Costa Rica,Panamá, and Galápagos Islands (Ecuador). II. Poritidae

A comparative study of the reproductive ecology of the zooxanthellate, scleractinian corals Porites lobata Dana and P. panamensis Verrill was conducted from 1985 to 1991 in eastern Pacific reef environments that were severly impacted by the 1982–1983 El Niño warming events. P. lobata, a presumed broadcast spawner of large colony size, is widely distributed in the equatorial eastern Pacific, whereas P. panamensis, a brooder of small colony size, is abundant only on some reefs in Panamá. Both species were gonochoric with nearly 1:1 sex ratios in large study populations except for P. lobata at Caño Island that had 14% hermaphroditic colonies. Mature, unfertilized oocytes contained numerous zooxanthellae in both Porites species, and all planula developmental stages contained zooxanthellae in P. panamensis. Year-round sampling revealed high proportions of colonies with gonads, ranging from 30 to 68% in P. lobata and from 60 to 68% in P. panamensis. No clear relationship between numbers of reproductive colonies and the thermal stability of the habitat was evident in P. lobata: percent colonies with gonads at non-upwelling sites was 48 to 68% at Caño Island (Costa Rica) and Uva Island (Panamá), and at upwelling sites 30 to 50% at Saboga Island and Taboga Island (Panamá), and the Galápagos Islands (Ecuador). Similarly, 90% of all P. panamensis colonies were reproductive at Uva Island (a non-upwelling site), and 86% were reproductive at Taboga Island (an upwelling site). Upwelling at Taboga Island is seasonal, nevertheless P. panamensis produced mature gonads or planulae over most of the year (11 mo), whereas P. lobata exhibited reproductive activity during only 2 mo (May and June). No clear lunar periodicity was observed in P. panamensis (Taboga Island), but a high proportion of P. lobata showed increased gonadal development around full and new moon, especially at Caño and Uva Islands. Estimated fecundities were relatively high for P. lobata at Caño (4000 eggs cm^-2 yr^-1) and Uva (5200 eggs cm^-2 yr^-1) Islands, and notably low (70 to 110 eggs cm^-2 yr^-1) in the Galápagos Islands. P. panamensis mean fecundity at Taboga Island was 720 planulae cm^-2 yr^-1 or 4.0 mm³ cm^-2 yr^-1, which was lower than the egg volume production of P. lobata at Caño and Uva Islands (7.0 to 10.0 mm³ cm^-2 yr^-1). The capacity of P. lobata and P. panamensis to reproduce sexually supports the notion that eastern Pacific coral reef recovery may not be dependent on long-distance dispersal from central Pacific areas. However, sexual recruits of P. lobata are absent or uncommon at all eastern Pacific study sites while recruits of P. panamensis were common to abundant only at the Uva Island study site. Asexual fragmentation in P. lobata augments recruitment locally, but plays no role in P. panamensis recruitment.     

Fly ash content and distribution in lake sediments around a large power station: inferences from magnetic susceptibility analysis

The bulk magnetic susceptibility of sediments from artificial and natural lakes around a large coal-fired power station in NE Spain has been measured. Higher magnetic susceptibility values are found in lake sediments located SE of the power station. This distribution of susceptibility values is compatible with environmental and meterological studies of emissions from the power station, which indicate a dominant SE plume direction. Mineralogical studies, by means of X-ray diffraction and scanning electron microscopy, show that the highest susceptibility values found in the sediments are caused by magnetic iron spinels in the fly ash that is transferred to the environment by the power station particulate emissions. After the quantitative mineralogical studies of fly ash, two different methods of fly ash content determination in the sediments have been devised, showing very similar results. The low background magnetic susceptibility of the sediments in the study area and the high susceptibility resulting from the input of magnetic fly ash particles allows both delimitation of the polluted area around the power station, and quantification of the fly ash input into the natural sediments.