Multi-species Aggregations Research Articles

Unionid mussels influence macroinvertebrate assemblage structure in streams

Unionid mussels often occur as multispecies aggregates called mussel beds and in dense patches within the mussel beds themselves. Thus, their distributions are patchy at 2 spatial scales. We examined the association between mussel assemblage structure and macroinvertebrate assemblage structure at these 2 spatial scales in rivers of the Ouachita Highlands, Arkansas and Oklahoma, USA. We used multivariate variation partitioning techniques to relate variation in benthic macroinvertebrate distribution and abundance to variation in mussel assemblages, environmental variables, spatial variables, and overlapping or shared variation between these components. At the patch scale, total densities of macroinvertebrates and dominant groups (Oligochaeta, Chironomidae, Ephemeroptera, and Trichoptera) were significantly higher in patches containing mussels than where mussels were absent, and densities of macroinvertebrates were positively correlated with unionid density. In variation partitioning analyses, mussel assemblages explained almost ½ of the variation in macroinvertebrate assemblages at both spatial scales, even after removing effects of similar habitat (environmental variables) and biogeographic history (spatial variables).

Competition between aggregation and migration processes of a multi-species system

We propose a solvable multi-species aggregation–migration model, in which irreversible aggregations occur between any two aggregates of the same species and reversible migrations occur between any two different species. The kinetic behaviour of an aggregation–migration system is then studied by means of the mean-field rate equation. The results show that the kinetics of the system depends crucially on the details of reaction events such as initial concentration distributions and ratios of aggregation rates to migration rate. In general, the aggregate mass distribution of each species always obeys a conventional or a generalized scaling law and for most cases at least one species is scaled according to a conventional form with universal constants. Moreover, there is at least one species that can survive finally.

Behavior of bigeye (Thunnus obesus) and skipjack (Katsuwonus pelamis) tunas within aggregations associated with floating objects in the equatorial eastern Pacific

The horizontal and vertical movements of bigeye (Thunnus obesus Lowe, 1839) and skipjack (Katsuwonus pelamis Linnaeus, 1758) tunas within large multi-species aggregations associated with moored buoys or a drifting vessel were investigated, using ultrasonic telemetry and archival tags, along with sonar imaging, in the equatorial eastern Pacific Ocean (at 2°S–95°W and 2°N–95°W). Four sets of observations, each consisting of the concurrent monitoring of pairs of skipjack and/or bigeye with implanted acoustic or archival tags, were conducted in May 2002 and 2003. Ultrasonic telemetry data were not collected until 24 h or more after the fish were tagged and released, to avoid any abnormal behavior as a consequence of tagging. The pairs of acoustically tagged bigeye and skipjack, and also the entire aggregations, were primarily upcurrent of the moored buoy and downcurrent of the drifting vessel during the day. At night the aggregations were observed to be more diffuse, and the fish were feeding on organisms of the deep scattering layer. The aggregations returned to positions upcurrent of the buoy or downcurrent of the drifting vessel at dawn, commonly breezing at the surface within cohesive monospecific schools. The bigeye and skipjack had concurrent changes in depth records, occupying significantly greater mean depths at night than during the day, in most cases. When associated with a moored buoy, bigeye depth distributions were deeper during the day and night than those of skipjack, but bigeye depth distributions were shallower during the day and night than those of skipjack when associated with the drifting vessel. Simultaneous depth records of a large and a small bigeye with archival tags associated with a moored buoy also indicated diel changes in depth. The mean depth at night was significantly less than during the day for the larger bigeye, but the mean depth during the day was significantly less than during the night for the smaller bigeye. The mean depths during the day and night were significantly greater for the larger bigeye than the smaller.

The ecological and evolutionary consequences of sperm chemoattraction.

Chemical communication between sperm and egg is a critical factor mediating sexual reproduction. Sperm attractants may be significant evolutionarily for maintaining species barriers, and important ecologically for increasing gamete encounters. Still unresolved, however, are the functional consequences of these dissolved signal molecules. Here, we provide experimental evidence that sperm chemoattraction directly affects the magnitude of fertilization success. The recent discovery of L-tryptophan as a potent attractant to red abalone (Haliotis rufescens) sperm affords the opportunity to quantify how navigation affects gamete interactions. Sperm behavioral responses to manipulations of the natural tryptophan gradient around individual eggs reveals that both chemotaxis and chemokinesis significantly promote contacts. Our results show further that attractant release by means of diffusion effectively doubles the target size of red abalone eggs, which in turn significantly increases fertilization success. Although long theorized as potential barriers to hybridization, species-specific sperm attractants in red and green (Haliotis fulgens) abalone are only minor contributors to maintaining reproductive isolation. Because abalone typically live in dense, multispecies aggregations, chemically mediated navigation would prevent sperm from pointlessly tracking heterospecific eggs. Thus, even though reproductive isolation fundamentally resides at the level of membrane recognition proteins, species-specific sperm attractants may evolve to locate the right target within mixed gamete suspensions of closely related species.

Interspecific reciprocity explains mobbing behaviour of the breeding chaffinches, Fringilla coelebs.

When prey animals discover a predator close by, they mob it while uttering characteristic sounds that attract other prey individuals to the vicinity. Mobbing causes a predator to vacate its immediate foraging area, which gives an opportunity for prey individuals to continue their interrupted daily activity. Besides the increased benefits, mobbing behaviour also has its costs owing to injuries or death. The initiator of mobbing may be at increased risk of predation by attracting the predator's attention, especially if not joined by other neighbouring prey individuals. Communities of breeding birds have always been considered as temporal aggregations. Since an altruist could not prevent cheaters from exploiting its altruism in an anonymous community, this excluded any possibility of explaining mobbing behaviour in terms of reciprocal altruism. However, sedentary birds may have become acquainted since the previous non-breeding season. Migrant birds, forming anonymous communities at the beginning of the breeding season, may also develop closer social ties during the course of the breeding season. We tested whether a male chaffinch, a migrant bird, would initiate active harassment of a predator both at the beginning of the breeding season and a week later when it has become a member of a non-anonymous multi-species aggregation of sedentary birds. We expected that male chaffinches would be less likely to initiate a mob at the beginning of the breeding season when part of an anonymous multi-species aggregation of migratory birds. However, their mobbing activity should increase as the breeding season advances. Our results support these predictions. Cooperation among individuals belonging to different species in driving the predator away may be explained as interspecific reciprocity based on interspecific recognition and temporal stability of the breeding communities.

Enhancement of coral recruitment by in situ mass culture of coral larvae

New technologies for culturing and settling scleractinian coral larvae in the field are required to elucidate the role of recruitment in population dynamics and to provide options for reef rehabilitation. Natural multi-species aggregations of coral embryos, which frequently form slicks on the sea surface after large-scale annual spawnings, were identified as a potential resource for mass coral culture. Slicks containing billions of embryos were found at sea and several million embryos were sub-sampled and successfully cultured in simple floating ponds, moored over the reef. Coral larvae were maintained in the floating ponds until competent to settle, and then seeded onto the reef environment via hoses from the ponds to mesh enclosures temporarily fixed to the reef substratum. Reefal areas exposed to the cultured larvae exhibited a dramatic enhancement of coral larval recruit- ment compared to natural rates. The results demonstrate the ability to seed defined areas of reef with controlled densities of recruits. We conclude that natural spawning slicks, which have been noted on numerous reefs throughout the world, provide opportunities for very large-scale culture of corals, which may have application in reef rehabilitation and management strategies where natural recruit- ment is limited.

The natural history of the neotropical sand waspRubrica nasuta(Christ 1791) (Hymenoptera Sphecidae) in Brazil

The natural history of the sand wasp Rubrica nasuta (Christ 1791) was studied at the campus of the Universidade Federal de Minas Gerais, Belo Horizonte, state of Minas Gerais, Brazil. This is the first comprehensive study of this neotropical species. The biology of R. nasuta is compared with what is known about the three other species of Rubrica (J. Parker 1929). Females of R. nasuta excavate one-celled nests around 10 cm deep in sandy soils in multispecies aggregations of solitary digger wasps and bees in open areas, like dirt roads. Nesting activities occur in the rainy season from September to April. Females typically dig their nests in the morning. One female in 1992 required 2 hr and 28 min to excavate and complete her nest. During nest closure, she smoothed out the loose soil around the tunnel entrance, effectively disguising it. Provisioning is progressive and takes no longer than 10 days for a single larva (typically around 8 days) with some variation based on weather and prey availability. We estimated about 50 fly prey, especially Syrphidae and Stratiomydae, were required for one larva. From the 3rd day on, it is common in the morning to see a female open her nest, re-enter and exit the nest with uneaten pieces or even an entire prey item held in her mandibles, the so-called discharging behavior. During the dry season, with temperature around 9 °C, individual wasps will spend the night in mixed sleeping aggregations on grass inflorescences. Adults were seen taking nectar on plants with tiny flowers. Males patrol nesting sites and exhibit territorial behavior. When digging and provisioning, the females are always very alert against invaders, especially ants. Despite this vigilance, parasitism by a bombyliid fly is very common. Inquilinous miltogrammine flies emerged from R. nasuta nests. This is an interesting finding because members of Miltogramminae are commonly reported as nest parasites of solitary wasps.

The Possible Role of Volatile Secretions as Intra- and Interspecific Alarm Signals in Gyrinus Species

Gyrinid beetles have paired pygidial glands producing a secretion consisting of both a high molecular weight fraction, rendering them toxic for predatory fish, and usually also volatile fractions (8 of 10 north European Gyrinus species), which act as alarm signals. The presence of multi-species aggregations on the water surface raises the question whether the pygidial secretion of one species can elicit an escape response in other species. There were no differences in escape reaction to signals between two strongly scented species (G. aeratus and G. substriatus) and one species without obvious scent (G. opacus ). Furthermore, signals were received across the species borders, although only the two species emitting volatile components were able to alarm other individuals. The two scented species (G. aeratus and G, substriatus) often aggregate in large groups on open water, whereas the unscented species (G. opacus and G. minutus) rarely do so, but preferably occur singly or in loose groups among the emergent marginal vegetation of various standing waters. This suggests that the presence of alarm signals is correlated with behaviour and habitat choice. Furthermore, the putatively weak competitor G. opacus spends significantly more time below the water surface than G. substriatus, perhaps as a result of it lacking an alarm function. The occasional presence of individuals of the two unscented species in large aggregates of G. aeratus on open surface, may indicate that they may take advantage of the alarm signals produced by individuals of another species and as result escape approaching danger. It is not known whether G. opacus and G. minutus have lost the ability to produce volatile alarm substances or whether they never have had it. Comparisons with the ca 11000-year-old subfossil localities of G. opacus, however, indicate that at least from that date this species has inhabited localities similar to the present with respect to predation risks and other properties, i.e. mainly small, predatory fish-free waters.

Migration, habitat use, and competition among mobile corals (Scleractinia: Fungiidae) in the Gulf of Eilat, Red Sea

We examined the impact of seven species of mobile mushroom corals (Fungiidae) on the community structure of sheltered reef slopes in terms of their patterns of migration, habitat use and competition with other benthic organisms. On fringing reefs at Eilat, Red Sea, polyps detached at 1 to 6 cm length, and grew to 11–55 cm length. Attached mushroom corals were oriented vertically in reef cavities. Detached corals migrated downward on the reef slope and onto rubble or soft substratum at the reef base, at 29 to 71 cmyr−1. Mobility decreased with corallum size and extent of undersurface ornamentation. In aquaria, small corals righted themselves and migrated up to 6 cm d−1 by nocturnally inflating and pushing their tissues against the substratum. Autonomous coral behavior and storm-generated water motion appeared to account for most fungiid mobility at Eilat. Mushroom corals did not damage each other upon contact, even in multi-species aggregations, but unilaterally damaged non-fungiid scleractinian corals. Their dominance during contact interactions retards overgrowth by larger attached scleractinians, and mobility allows them to colonize soft substrata not accessible to most other reef corals.

Summer feeding ecology of harp seals (Phoca groenlandica) in relation to arctic cod (Boreogadus saida) in the Canadian high arctic

The diet and feeding behaviour of harp seals, Phoca groenlandica, was examined in two high arctic locations. Fish otoliths were used to evaluate dietary composition and aspects of the population dynamics of the major prey species, arctic cod, Boreogadus saida. Harp seals, primarily adults, arrive in the high arctic in mid to late June and depart by early October. Their migration is undertaken specifically for feeding. Harp seals feed intensively on arctic cod, often occurring in dense multispecies aggregations in late summer. The average weight of harp seal stomach contents was high; glutted individuals contained as much as 6% of their body weight in food. Although arctic cod declined in abundance between years, size of cod ingested was similar between areas and years, and overlapped completely with cod taken by other marine mammals. Age/size segregation of arctic cod may account for poor representation of fish <3 years old in the seal diet. Widespread reproductive failure of arctic cod could have a profound influence on the energy balance of adult harp seals since there does not appear to be an alternate food source of equivalent energy value and abundance in arctic waters. Increasing harp seal populations will likely result in increased competition with a host of arctic cod predators, particularly ringed seals.

ECONOMIC REGULATION OF TARGETING BEHAVIOR IN MULTISPECIES FISHERY

Fishing vessels, harvesting geographically dispersed and heterogeneous multispecies aggregates, are presumed to target on the most profitable pools. But, this behavior may lead to depletion of biologically valuable species, and consequent early closure by the management agency of the entire fishery.In this article, a simple model is analyzed in order to understand the dynamics of such targeting behavior. Further analysis explores the theoretical extent to which targeting might be altered through economic rationalization measures, landings taxes or quota markets, to achieve a more nearly optimal pattern of exploitation.

The spatial pattern of Enchytraeidae (Oligochaeta)

Spatial pattern of enchytraeids (Oligochaeta: Enchytraeidae) was studied in an experimental plot in an apple orchard near Bavorov, South Bohemia, Czechoslovakia. A total of 450 soil cores were taken in 1982, all individuals were determined (juveniles to genus, mature individuals to species) and counted. In total, 17 species of 4 genera were found. Both juveniles and mature individuals exhibited a distinctly aggregated spatial pattern. The distribution of the number of individuals in a sampling unit may be effectively fitted by the negative binomial distribution. The fit of Neyman type A distribution was considerably poorer. Comparing juveniles and mature individuals of the same genus using Lloyd's index of patchiness we found mature individuals to be slightly more aggregated than juveniles. Comparing the observed distribution of species number with that expected under the assumption of independence we may conclude that individuals appear in multispecies aggregation centres. These two conclusions support the hypothesis that aggregations are environmentally conditioned (abiotic factors and/or food availability) rather than caused by the type of reproduction.

Fine-scale multi-species aggregations of oceanic zooplankton

Sixteen Longhurst-Hardy Plankton Recorder tows were taken at different depths in the northwest Atlantic for analysis of fine-scale horizontal patchiness. Abundant species were non-randomly distributed in patches with scales of tens to hundreds of meters. Positive correlations between species abundances dominated, indicating that the patches were multi-species associations. Most horizontal pattern appeared to be of biological origin.

Comparative Ecology of Notropis albeolus, N. ardens and N. cerasinus (Cyprinidae) in the Upper Roanoke River Drainage, Virginia

Foods, feeding periodicity and microhabitat use are reported for coexisting Notropis albeolus, N. ardens and N. cerasinus in the upper Roanoke River drainage, Virginia. All three species primarily occupied pool habitats, ate aquatic insect larvae or terrestrial adult insects, and were diurnal feeders. Notropis ardens (subgenus Lythrurus) was ecologically segregated from N. albeolus and N. cerasinus (both subgenus Luxilus) in vertical spacing in the water column and in taxa of foods used. The two Luxilus species were ecologically more similar, segregated only by vertical differences in microhabitat. Overlaps in resource use among the three species pairs suggested congruence of phylogenetic and ecological similarities. INTRODUCTION The phenomenon of resource partitioning is well-documented in reptile, bird and mammal communities (cf., Pianka, 1973; Schoener, 1974), and in numerous freshwater fish communities closely related, coexisting species differ ecologically, e.g., in microhabitat, food or feeding chronology (Hartley, 1948; Keast, 1965, 1966, 1978; Zaret and Rand, 1971; Werner and Hall, 1976, 1979; Werner et al., 1977). It has often been assumed that some segregation in resource use is a requisite for coexistence of species, and that observed ecological differences among coexisting taxa result from past or present competitive interactions. However, uncritical acceptance of a competition model to account for ecological differences among coexisting fish species may be unwarranted (Sale, 1979), and the plausibility of alternative hypotheses should be considered. Mendelson (1975), for example, suggested that coexisting minnows used resources in patterns set by morphological preadaptation. In eastern North America, minnows of the genus Notropis (Cyprinidae) often occur in multispecies aggregations, using habitats and foods that superficially appear similar. However, Starrett (1950), Whitaker (1977), Gillen and Hart (1980) and Hoover (1981) showed trophic segregation among coexisting Notropis species, and Moyle (1973) and Baker and Ross (1981) demonstrated that coexisting Notropis species segregated vertically into different microhabits. Mendelson (1975) showed that four coexisting Notropis were ecologically segregated more by use of space than by diet. While these studies suggest the importance of dietary and microhabitat segregation among coexisting Notropis, there has been too little comparative research within this diverse genus (at least 119 species) to permit generalization about mechanisms that facilitate species coexistence. In this study we evaluate ecological segregation among three syntopic Notropis species, with emphasis on microhabitat, food and feeding chronology in a complex upland stream system. We also provide information on cold vs. warm weather ecology of the species. Our study focuses on Notropis albeolus (white shiner, subgenus Luxilus), N. ardens (rosefin shiner, subgenus Lythrurus) and N. cerasinus (crescent shiner, subgenus Luxilus), which are the three most common Notropis in the upper Roanoke River drainage above Salem, Virginia (Jordan, 1889; Cairns et al. 1971; Jenkins, 1979). All three coexist in the river mainstream and in larger tributaries, but N. cerasinus occurs somewhat further 'Address reprint requests to Matthews.

Spatial and temporal multi-species nesting aggregations in birds as anti-parasite and anti-predator defenses

1. The purpose of this study was to determine whether the yellow warbler (Dendroica petechia) derives any benefits from nesting in close proximity to its own and other species in reducing predator pressure or the incidence of brood parasitism by the brown-headed cowbird (Molothrus ater). 2. Yellow warblers nesting synchronously with their own and with neighbouring species resulted in a proportionate reduction in the number of nests preyed upon, suggesting a ‘swamping effect’ of the local predators. A significantly lower incidence of predation occurred at yellow warbler nests which were inside a gray catbird (Dumetella carolinensis) response range. This was thought to be the result of yellow warblers taking advantage of the catbird's nest-guarding behaviour and aggressive responses to predators. 3. Yellow warblers nesting synchronously with other yellow warblers were subject to a proportionately lower incidence of brood parasitism than asynchronous nests, suggesting a ‘swamping effect’ on the cowbird. A significantly lower incidence of brood parasitism occurred at yellow warbler nests which were in a red-winged blackbird (Agelaius phoeniceus) response range. The yellow warbler was thought to be taking advantage of the aggressive response of red-winged blackbirds to cowbirds. 4. Overall, yellow warblers which nested within the response range of red-winged blackbirds or gray catbirds had significantly higher nest success than other yellow warblers. This suggests that selection for defence against predators and cowbirds may lead to multi-species aggregations.

Commensalism in the Little Blue Heron

Abstract Little Blue Herons feed in association with White Ibis by using the ibis's movements to increase foraging effectiveness. When feeding near a White Ibis, a heron increased the number of prey caught without increasing its energetic costs of foraging. The strike rate of a bird was higher when feeding commensally than when feeding alone, but its success per strike did not increase because of the commensal association. This increased energy return when feeding commensally resulted from greater opportunity for commensal herons to observe and attempt to catch prey rather than from an increased probability of their catching a prey item after it had been observed. The results of this study of a non-obvious commensal relationship suggest that many previously reported associations among water birds are also commensal. It also supports the hypothesis that multispecies aggregations of ciconiiforms may be characterized by cryptic forms of commensalism.

Behavior and Ecology of Some North American Cyprinid Fishes

Form of the nest, nest-building and reproductive be- havior, and social interactions are described in five species of cyprinids associated with Notropis cornutus, N. rubellus, and hybrid N. cornutus X N. rubellus during the breeding season. Environmental and social factors which maintain species isolation are discussed. Reproductive and social behavior of the three shiners is described and compared. The parent species differ in ten behavioral characteris- tics. In six characters the hybrid resembles N. cornutus and in three it resembles N. rubellus. The hybrid and N. cornutus often feed on the bottom and occur in backwaters. They usually form large, multispecies aggregates while N. rubellus often are in separate schools. Spawning temperature is 70 F or higher for N. rubellus and 60 F or more for the other two forms. Nest digging and defense of a definite bottom territory is present only in N. cornutus. A tilt display by the male preceding spawnings and a spawning clasp are present in N. cornutus, rare in the hybrid, and absent in N. rubellus. The number of head butts during a parallel-swimming behavior is low in N. cornutus, high in N. rubellus, and intermediate in the hybrid. Over-all aggression is higher in N. cornutus than in either N. rubellus or the hybrid. In the spring of 1959, 1960, and 1961 I studied the reproductive behavior and ecology of the cyprinid fishes Notropis cornutus (Mitchill), Notropis rubellus (Agassiz), and the hybrid between them. Much of the basic reproductive behavior of these forms was described by Raney (1940a; 1940b) and Pfeiffer (1955). The present study concerns the behavior of the three forms in a single population known consistently to contain many hybrids, attempts to determine how be- havioral characteristics of the parent species are represented in the hybrid, and considers the factors maintaining the high incidence of hybrids. I found that these fishes carry out most territorial and repro- ductive activities over the pebble nests of other cyprinids such as Hybopsis micropogon (Cope), Semotilus corporalis (Mitchill), Semo- tilus atromaculatus (Mitchill), and Exoglossum maxillingua (Le Sueur), a situation previously described by Hankinson (1932), Raney (1940a), and others. I also found that most shiners spawn over the nests during their construction or shortly after their completion and only rarely after the nests were deserted by the resident species. This circumstance facilitated observations on the nest-building, territorial, and reproductive behaviors of several species and on various kinds of interspecific encounters. This report presents additional information on the behavior of several cyprinids, with emphasis on nest-building, reproduction, and cohabitation of nest sites. This information may shed some light on the complex factors controlling interspecific encounters and their signi- ficance in species isolation and hybridization. 313