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Interspecific Interactions (interspecific + interaction)
Selected AbstractsPATTERNS OF INTERSPECIFIC INTERACTIONS IN THE ULVA -DOMINATED INTERTIDAL COMMUNITY IN A SOUTHERN COAST OF KOREAJOURNAL OF PHYCOLOGY, Issue 2000Y.J. Bhang In the southern coast of Korea, rocky intertidal zones where green tide commonly occurs are dominated by Ulva pertusa, red algal turf (a mixed stand of Gigartina intermedia and Gigartina teedii) and species of Enteromorpha with highly opportunistic occurrence. To investigate their interspecific interactions, a field experiment was carried out using press effect of one species removal from permanent plots (20 x 20cm) set up on two different tidal heights. Mechanisms of interaction were also attempted using artificial plants to test the possible effects of shading, scouring, allelopathy of U. pertusa on the turf algae. The turf-forming red algae lowered the abundance of U. pertusa presumably by inhibiting the recruitment of U. pertusa; this effect was consistent along the tidal height. However, the greater abundance of Enteromorpha was observed in the presence of turf in the upper zone, indicating a positive effect of turf on Enteromorpha. Once U. pertusa was successfully recruited and grown to the adult plant, it inhibited the growth of turf by shading, which was effective both in winter and summer regardless of desiccation stress. No scouring and allelopathic effects of U. pertusa on the turf were detected. When an open substrate was provided, Enteromorpha colonized the space faster than any other species in the upper zone, but the turf was the fastest one followed by U. pertusa and Enteromorpha in the lower zone. Results indicated that patterns of interaction represented a complex network with no ultimate winner and the outcomes of interaction varied over time and space. [source] Effects of Interspecific Interactions between Microcystis aeruginosa and Chlorella pyrenoidosa on Their Growth and PhysiologyINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2007Min Zhang Abstract Interactions between Microcystis aeruginosa and Chlorella pyrenoidosa were analyzed by flow cytometry and by phytoplankton pulse-amplitude-modulated fluorimetry (Phyto-PAM) in joint cultures as well as in cultures separated by dialysis membranes. Results showed that the growth of C. pyrenoidosa was greater than that of M. aeruginosa, and that the growth of M.aeruginosa but not the growth of C. pyrenoidosa was significantly inhibited by the interactions between M. aeruginosa and C. pyrenoidosa. Culture filtrates of these two algae showed no apparent effects on the growth of the competing species. For M. aeruginosa, decreases in esterase activity, chlorophyll a fluorescence, and maximum quantum yield were observed in joint cultures, indicating that the metabolic activity and photosynthetic capacity of M.aeruginosa were suppressed. Light limitation from the shading effect of C. pyrenoidosa may be the main reason for such inhibition. For C. pyrenoidosa, esterase activity was suppressed in membrane-separated and joint cultures, suggesting that C.pyrenoidosa was probably affected by allelopathic substances secreted by M.aeruginosa. However, no significant difference was observed in the chlorophyll a fluorescence and maximum quantum yield of C. pyrenoidosa in the two cultures. In addition, interspecific interactions induced a reduction in size in both M. aeruginosa and C.pyrenoidosa, which may contribute to the development of C. pyrenoidosa dominance in the present study. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photobiont Selectivity and Interspecific Interactions in Lichen Communities.PLANT BIOLOGY, Issue 4 2003Abstract: Lichen communities are characterised by interspecific interactions that not only include interactions between different lichen species but also between the symbionts within a single lichen species. The community "Bunte Erdflechtengesellschaft", growing on weathered calciferous rocks known as Gravel Alvar on Gotland (Baltic Sea, Sweden), shows a high complexity of inter- and intraspecific interactions, including Fulgensia bracteata, F. fulgens, Toninia sedifolia, Squamarina cartilaginea, Psora decipiens and Lecidea lurida. F. bracteata and F. fulgens are the dominant species of this community, showing a tendency to overgrow the other species involved and even parasitic behaviour. Culture experiments have been performed to investigate the selectivity of the mycobiont of F. bracteata towards a variety of potential photobionts. The results provide evidence for the selectivity of the mycobiont and varying compatibility of the respective symbionts that can be interpreted as a cascade of interdependent processes of specific and non-specific reactions of the symbionts involved. [source] Spatio-temporal variation of avian foraging in the rocky intertidal food webJOURNAL OF ANIMAL ECOLOGY, Issue 1 2001Masakazu Hori Abstract 1While birds are top predators in most rocky intertidal communities, the relationship between foraging pattern and variability in food web structure has not been studied. This study examined the spatio-temporal variation of both avian foraging and food web structure at an intertidal rocky shore in northern Japan over a 1-year period. 2Seventeen bird species foraged on the intertidal rocky shore. Crows and gulls were dominant, and their major prey was sea urchins that migrated from the sub-tidal to intertidal habitat. Interspecific interactions (i.e. stealing of food, utilization of food waste by other species) occurred between crows and gulls especially when feeding on sea urchins. The prey of the birds showed spatial and temporal partitioning. 3The number of prey items consumed per day by the dominant birds varied with various factors. Factors strongly affecting the foraging pattern of crows were waves, tides, humans and gulls, and those strongly affecting the foraging pattern of gulls were tides, humans, sea urchins and crows. 4In the rocky intertidal food web, most of the top predators were birds, and most of the birds were omnivores. The birds consumed many more species than did other consumers. Food-resource partitioning caused spatio-temporal compartmentation among subwebs in which the top predators were dominant birds. 5Analysis of food web statistics (i.e. web size, numbers of links, linkage density, chain lengths) revealed that the presence/absence of birds did not change the relationships between web size and the other statistics. The food web statistics depended on web size, and the web size was positively related with time spent emersed and temperature when birds were both present and not present. 6Birds often foraged across habitat boundaries, and the main food resource of top predators was the prey species from the subtidal habitat. Therefore, the spatial scale of the Hiura rocky intertidal food web temporally varied with birds foraging across habitat boundaries. [source] Living together: behavior and welfare in single and mixed species groups of capuchin (Cebus apella) and squirrel monkeys (Saimiri sciureus)AMERICAN JOURNAL OF PRIMATOLOGY, Issue 1 2010Rebecca Leonardi Abstract There are potential advantages of housing primates in mixed species exhibits for both the visiting public and the primates themselves. If the primates naturally associate in the wild, it may be more educational and enjoyable for the public to view. Increases in social complexity and stimulation may be enriching for the primates. However, mixed species exhibits might also create welfare problems such as stress from interspecific aggression. We present data on the behavior of single and mixed species groups of capuchin monkeys (Cebus apella) and squirrel monkeys (Saimiri sciureus) housed at the Living Links to Human Evolution Research Centre in the Royal Zoological Society of Scotland's Edinburgh Zoo. These species associate in the wild, gaining foraging benefits and decreased predation. But Cebus are also predators themselves with potential risks for the smaller Saimiri. To study their living together we took scan samples at ,15,min intervals on single (n=109) and mixed species groups (n=152), and all occurrences of intraspecific aggression and interspecific interactions were recorded. We found no evidence of chronic stress and Saimiri actively chose to associate with Cebus. On 79% of scans, the two species simultaneously occupied the same part of their enclosure. No vertical displacement was observed. Interspecific interactions were common (>2.5/hr), and equally divided among mildly aggressive, neutral, and affiliative interactions such as play. Only one aggressive interaction involved physical contact and was non-injurious. Aggressive interactions were mostly (65%) displacements and vocal exchanges, initiated almost equally by Cebus and Saimiri. Modifications to the enclosure were successful in reducing these mildly aggressive interactions with affiliative interactions increasing in frequency and diversity. Our data suggest that in carefully designed, large enclosures, naturally associating monkeys are able to live harmoniously and are enriched by each other. Am. J. Primatol. 72:33,47, 2010. © 2009 Wiley-Liss, Inc. [source] Park's Tribolium competition experiments: a non-equilibrium species coexistence hypothesisJOURNAL OF ANIMAL ECOLOGY, Issue 5 2003Jeffrey Edmunds Summary 1In this journal 35 years ago, P. H. Leslie, T. Park and D. B. Mertz reported competitive exclusion data for two Tribolium species. It is less well-known that they also reported ,difficult to interpret' coexistence data. We suggest that the species exclusion and the species coexistence are consequences of a stable coexistence two-cycle in the presence of two stable competitive exclusion equilibria. 2A stage-structured insect population model for two interacting species forecasts that as interspecific interaction is increased there occurs a sequence of dynamic changes (bifurcations) in which the classic Lotka,Volterra-type scenario with two stable competitive exclusion equilibria is altered abruptly to a novel scenario with three locally stable entities; namely, two competitive exclusion equilibria and a stable coexistence cycle. This scenario is novel in that it predicts the competitive coexistence of two nearly identical species on a single limiting resource and does so under circumstances of increased interspecific competition. This prediction is in contradiction to classical tenets of competition theory. [source] Small and large anemonefishes can coexist using the same patchy resources on a coral reef, before habitat destructionJOURNAL OF ANIMAL ECOLOGY, Issue 5 2002Akihisa Hattori Summary 1According to meta-population models, a superior competitor and a superior disperser can coexist in a patchy environment. The two anemonefishes, a large aggressive Amphiprion clarkii Bennett and a small less-aggressive A. perideraion Bleeker, use the same host anemone Heteractis crispa Ehrenberg on a coral reef, Okinawa, Japan, where most of the hosts disappeared after the coral bleaching in 1998. Their microhabitat (host) use and coexistence, and the quality and quantity of microhabitats were investigated in 1988, 1989, 1999 and 2000 on the coral reef. Their interspecific interaction was also examined. 2Before the habitat destruction, the two species coexisted. Although A. clarkii was behaviourally dominant over A. perideraion in a cohabiting group, A. perideraion was a superior competitor in terms of site displacement, because A. perideraion could displace a microhabitat. Adult A. clarkii emigrated from a cohabiting group probably due to the high cost of interactions with adult A. perideraion . Although it is easier to defend a small area for a larger species, sharing a host with adult A. perideraion may not pay for A. clarkii because A. clarkii needs a larger area. 3A. clarkii was not only a superior disperser, which was able to find a vacated host, but also a pioneer species that was able to use newly settled small hosts. Larval A. clarkii settled on such a small host because they were able to move to larger hosts for future reproduction, while A. perideraion did not settle on a small host because of low mobility after settlement. Microhabitat (host) with various sizes might have promoted their coexistence. 4After the habitat destruction, the superior competitor A. perideraion went extinct locally due probably to lack of small host utilization ability. The present study implies that the difference in body size between the two competitors plays an important role in their coexistence, because species with different body sizes can have different mobility and require different amounts of resources. [source] Can vertebrate predation alter aggregation of risk in an insect host,parasitoid system?JOURNAL OF ANIMAL ECOLOGY, Issue 3 2002William F. Fagan Summary 1,Insect host,parasite systems allow investigations of the trophodynamics of ecological communities within a well-formed theoretical context. A little explored feature of such systems involves the interplay between generalized consumers and host,parasitoid dynamics. I report a study investigating how the impacts of generalized consumers, viewed here as interaction modifications, may influence the stability of a particular interspecific interaction. 2,In a study involving overwintering oothecae of the praying mantis Stagmomantis limbata (Hahn), birds damaged 36% of oothecae, 85% of which had also been parasitized by winter-active, multivoltine torymid wasps of the genus Podagrion. Birds preferentially preyed upon oothecae oviposited high on trees, but such predation was often incomplete, leaving both viable and parasitized mantid eggs inside damaged oothecae. 3,Two factors allowed bird damage to influence the distribution of risk of parasitism among oothecae and among hosts. These were (1) that some parasites , but no mantids , emerged successfully prior to bird predation and (2) that extensive post-damage foraging by parasitoids occurred, but that the nature of this foraging was altered little by oothecal damage. 4,In all, bird damage engendered a fourfold increase (from 1·5 to 6·5) in the CV2 of parasitism risk among hosts (a stability criterion that has been proposed for host,parasitoid interactions) and increased the relative importance of host-density-dependent parasitism. The role of timing of the two natural enemy impacts for stability of the host,parasitoid interaction is discussed. [source] Atlantic hagfish exploit prey captured by other taxaJOURNAL OF FISH BIOLOGY, Issue 2 2006P. J. Auster Observations of Atlantic hagfish Myxine glutinosa exploiting prey captured, but not fully consumed, by the horse star Hippasteria phrygiana and Jonah crab Cancer borealis are described. Such interactions are defined as encounter competition. These represent the first reported observations of this type of interspecific interaction for Atlantic hagfish. [source] Phylogeography and the geographic cline in the armament of a seed-predatory weevil: effects of historical events vs. natural selection from the host plantMOLECULAR ECOLOGY, Issue 13 2006HIROKAZU TOJU Abstract Japanese camellia (Camellia japonica) and its seed predator, the camellia weevil (Curculio camelliae), provide a notable example of a geographic mosaic of coevolution. In the species interaction, the offensive trait of the weevil (rostrum length) and the defensive trait of the plant (pericarp thickness) are involved in a geographically-structured arms race, and these traits and selective pressures acting on the plant defence vary greatly across a geographical landscape. To further explore the geographical structure of this interspecific interaction, we tested whether the geographical variation in the weevil rostrum over an 800-km range along latitude is attributed to local natural selection or constrained by historical (phylogeographical) events of local populations. Phylogeographical analyses of the mitochondrial DNA sequences of the camellia weevil revealed that this species has experienced differentiation into two regions, with a population bottleneck and subsequent range and/or population expansion within each region. Although these phylogeographical factors have affected the variation in rostrum length, analyses of competing factors for the geographical variation revealed that this pattern is primarily determined by the defensive trait of the host plant rather than by the effects of historical events of populations and a climatic factor (annual mean temperature). Thus, our study suggests the overwhelming strength of coevolutionary selection against the effect of historical events, which may have limited local adaptation. [source] Aggregation and species coexistence in fleas parasitic on small mammalsECOGRAPHY, Issue 2 2006Boris R. Krasnov The aggregation model of coexistence states that species coexistence is facilitated if interspecific aggregation is reduced relative to intraspecific aggregation. We investigated the relationship between intraspecific and interspecific aggregation in 17 component communities (the flea assemblage of a host population) of fleas parasitic on small mammals and hypothesized that interspecific interactions should be reduced relative to intraspecific interactions, facilitating species coexistence. We predicted that the reduction of the level of interspecific aggregation in relation to the level of intraspecific aggregation would be positively correlated with total flea abundance and species richness of flea assemblages. We also expected that the higher degree of facilitation of flea coexistence would be affected by host parameters such as body mass, basal metabolic rate (BMR) and depth and complexity of burrows. Results of this study supported the aggregation model of coexistence and demonstrated that, in general, a) conspecific fleas were aggregated across their hosts; b) flea assemblages were not dominated by negative interspecific interactions; and c) the level of interspecific aggregation in flea assemblages was reduced in relation to the level of intraspecific aggregation. Intraspecific aggregation tended to be correlated positively to body mass, burrow complexity and mass-independent BMR of a host. Positive interspecific associations of fleas tended to occur more frequently in species-rich flea assemblages and/or in larger hosts possessing deep complex burrows. Intraspecific aggregation increased relative to interspecific aggregation when species richness of flea infracommunities (the flea assemblage of a host individual) and component communities increased. We conclude that the pattern of flea coexistence is related both to the structure of flea communities and affinities of host species. [source] The importance of interspecific interactions for breeding-site selection: peregrine falcons seek proximity to raven nestsECOGRAPHY, Issue 6 2004Fabrizio Sergio The advent of GIS is initiating a rapid increase in the utilization of wildlife-habitat models as tools for species and habitat management. However, such models rarely include estimates of interspecific interactions among explanatory variables. We tested the importance of such variables by using the peregrine falcon Falco peregrinus, a medium-sized raptor frequently reported to be affected by heterospecifics, as a model species. In an Alpine population, compared to random locations, peregrines selected breeding sites farther from conspecifics, on taller cliffs, with higher availability of farmland and closer to raven Corvus corax nests. Within suitable habitat, peregrines selected sites near ravens and far from elevations associated with golden eagle Aquila chrysaetos nests. Productivity increased with cliff size, farmland availability (rich in the local main prey) and with proximity to ravens, suggesting that the observed choices were adaptive. Finally, at the regional level, peregrine density peaked at low elevation and was positively associated with raven density. The results suggested an active breeding association of peregrines with ravens, which may provide early-warning cues against predators and safe alternative nest-sites. They also confirmed the importance of including estimates of interspecific interactions among explanatory variables, which may: 1) make models more realistic; 2) increase their predictive power by lowering unexplained variance due to unmeasured factors; 3) provide unexpected results such as the cryptic, large-scale breeding association of our study; and 4) stimulate further hypothesis formulation and testing, ultimately leading to deeper ecological knowledge of the study system. [source] Escape from natural enemies during climate-driven range expansion: a case studyECOLOGICAL ENTOMOLOGY, Issue 3 2008ROSA MENÉNDEZ Abstract 1.,A major, and largely unexplored, uncertainty in projecting the impact of climate change on biodiversity is the consequence of altered interspecific interactions, for example between parasitoids and their hosts. The present study investigated parasitism in the Brown Argus butterfly, Aricia agestis; a species that has expanded northward in Britain during the last 30 years in association with climate warming. 2.,Aricia agestis larvae suffered lower mortality from parasitoids in newly colonised areas compared with long-established populations. This result was consistent over four consecutive generations (2 years) when comparing one population of each type, and also when several populations within the historical and recently colonised range of the species were compared within a single year. Thus, A. agestis appears to be partially escaping from parasitism as it expands northwards. 3.,Reduced parasitism occurred despite the fact that several of the parasitoid species associated with A. agestis were already present in the newly colonised areas, supported predominantly by an alternative host species, the Common Blue butterfly, Polyommatus icarus. 4.,As the species expand their distributions into areas of increased climatic suitability, invasion fronts may escape from natural enemies, enhancing rates of range expansion. The results suggest that the decoupling of interspecific interactions may allow some species to exploit a wider range of environments and to do so more rapidly than previously thought possible. [source] Morphological variation in relation to flower use in bumblebeesENTOMOLOGICAL SCIENCE, Issue 2 2006Maki N. INOUE Abstract To understand resource partitioning in a bumblebee community, we analyzed various morphological characters. A total of 1269 individuals of six bumblebee species, Bombus ardens, B. hypocrita, B. diversus, B. ignitus, B. honshuensis and B. beaticola, were examined and principal component analysis showed that the bumblebee species were clearly differentiated. Glossa, prementa and head lengths were positively correlated with the second component, and a longer proboscis was associated with a narrower body, which may help bees to intrude into and access deep-lying nectar sources. Bombus diversus, with a long proboscis and narrow body, preferred flowers with a long corolla tube, whereas B. hypocrita and B. ignitus, which have short proboscises and wide bodies, visited flowers with short corollas or dish-shaped flowers. Two pairs of consubgeneric species that have similar morphological characteristics, B. ardens and B. beaticola, and B. hypocrita and B. ignitus, divided flower resources by habitat selection and seasonal partitioning. For resource partitioning among bumblebee species, not only morphology but also other factors, such as habitat and seasonal preference, flower use, foraging behavior, and interspecific interactions, are responsible. [source] PHYTOPHAGOUS INSECT,MICROBE MUTUALISMS AND ADAPTIVE EVOLUTIONARY DIVERSIFICATIONEVOLUTION, Issue 5 2008Eric M. Janson Adaptive diversification is a process intrinsically tied to species interactions. Yet, the influence of most types of interspecific interactions on adaptive evolutionary diversification remains poorly understood. In particular, the role of mutualistic interactions in shaping adaptive radiations has been largely unexplored, despite the ubiquity of mutualisms and increasing evidence of their ecological and evolutionary importance. Our aim here is to encourage empirical inquiry into the relationship between mutualism and evolutionary diversification, using herbivorous insects and their microbial mutualists as exemplars. Phytophagous insects have long been used to test theories of evolutionary diversification; moreover, the diversification of a number of phytophagous insect lineages has been linked to mutualisms with microbes. In this perspective, we examine microbial mutualist mediation of ecological opportunity and ecologically based divergent natural selection for their insect hosts. We also explore the conditions and mechanisms by which microbial mutualists may either facilitate or impede adaptive evolutionary diversification. These include effects on the availability of novel host plants or adaptive zones, modifying host-associated fitness trade-offs during host shifts, creating or reducing enemy-free space, and, overall, shaping the evolution of ecological (host plant) specialization. Although the conceptual framework presented here is built on phytophagous insect,microbe mutualisms, many of the processes and predictions are broadly applicable to other mutualisms in which host ecology is altered by mutualistic interactions. [source] SEQUENTIAL RAPID ADAPTATION OF INDIGENOUS PARASITOID WASPS TO THE INVASIVE BUTTERFLY PIERIS BRASSICAEEVOLUTION, Issue 8 2007Shingo Tanaka The introduction of a new species can change the characteristics of other species within a community. These changes may affect discontiguous trophic levels via adjacent trophic levels. The invasion of an exotic host species may provide the opportunity to observe the dynamics of changing interspecific interactions among parasitoids belonging to different trophic levels. The exotic large white butterfly Pieris brassicae invaded Hokkaido Island, Japan, and quickly spread throughout the island. Prior to the invasion, the small white butterfly P. rapae was the host of the primary parasitoid Cotesia glomerata, on which both the larval hyperparasitoid Baryscapus galactopus and the pupal hyperparasitoid Trichomalopsis apanteroctena depended. At the time of the invasion, C. glomerata generally laid eggs exclusively in P. rapae. During the five years following the invasion, however, the clutch size of C. glomerata in P. rapae gradually decreased, whereas the clutch size in P. brassicae increased. The field results corresponded well with laboratory experiments showing an increase in the rate of parasitism in P. brassicae. The host expansion of C. glomerata provided the two hyperparasitoids with an opportunity to choose between alternative hosts, that is, C. glomerata within P. brassicae and C. glomerata within P. rapae. Indeed, the pupal hyperparasitoid T. apanteroctena shifted its preference gradually to C. glomerata in P. brassicae, whereas the larval hyperparasitoid B. galactopus maintained a preference for C. glomerata in P. rapae. These changes in host preference may result from differential suitability of the two host types. The larval hyperparasitoid preferred C. glomerata within P. rapae to C. glomerata within P. brassicae, presumably because P. brassicae larvae attacked aggressively, thereby hindering the parasitization, whereas the pupal hyperparasitoid could take advantage of the competition-free resource by shifting its host preference. Consequently, the invasion of P. brassicae has changed the host use of the primary parasitoid C. glomerata and the pupal hyperparasitoid T. apanteroctena within a very short time. [source] Temporal changes in replicated experimental stream fish assemblages: predictable or not?FRESHWATER BIOLOGY, Issue 9 2006WILLIAMJ. Summary 1.,Natural aquatic communities or habitats cannot be fully replicated in the wild, so little is known about how initially identical communities might change over time, or the extent to which observed changes in community structure are caused by internal factors (such as interspecific interactions or traits of individual species) versus factors external to the local community (such as abiotic disturbances or invasions of new species). 2.,We quantified changes in seven initially identical fish assemblages, in habitats that were as similar as possible, in seminatural artificial streams in a 388-day trial (May 1998 to May 1999), and compared the change to that in fish assemblages in small pools of a natural stream during a year. The experimental design excluded floods, droughts, immigration or emigration. The experimental fish communities diverged significantly in composition and exhibited dissimilar trajectories in multivariate species space. Divergence among the assemblages increased from May through August, but not thereafter. 3.,Differences among the experimental assemblages were influenced by differences that developed during the year in algae cover and in potential predation (due to differential survival of sunfish among units). 4.,In the natural stream, fish assemblages in small pools changed more than those in the experimental units, suggesting that in natural assemblages external factors exacerbated temporal variation. 5.,Our finding that initially identical assemblages, isolated from most external factors, would diverge in the structure of fish assemblages over time suggests a lack of strong internal, deterministic controls in the assemblages, and that idiosyncratic or stochastic components (chance encounters among species; vagaries in changes in the local habitat) even within habitat patches can play an important role in assemblage structure in natural systems. [source] Ecological effects of perturbation by drought in flowing watersFRESHWATER BIOLOGY, Issue 7 2003P. S. Lake SUMMARY 1Knowledge of the ecology of droughts in flowing waters is scattered and fragmentary, with much of the available information being gathered opportunistically. Studies on intermittent and arid-zone streams have provided most of the information. 2Drought in streams may be viewed as a disturbance in which water inflow, river flow and water availability fall to extremely low levels for extended periods of time. As an ecological perturbation, there is the disturbance of drought and the responses of the biota to the drought. 3Droughts can either be periodic, seasonal or supra-seasonal events. The types of disturbance for seasonal droughts are presses and for supra-seasonal droughts, ramps. 4In droughts, hydrological connectivity is disrupted. Such disruption range from flow reduction to complete loss of surface water and connectivity. The longitudinal patterns along streams as to where flow ceases and drying up occurs differs between streams. Three patterns are outlined: ,downstream drying', ,headwater drying' and ,mid-reach drying'. 5There are both direct and indirect effects of drought on stream ecosystems. Marked direct effects include loss of water, loss of habitat for aquatic organisms and loss of stream connectivity. Indirect effects include the deterioration of water quality, alteration of food resources, and changes in the strength and structure of interspecific interactions. 6Droughts have marked effects on the densities and size- or age-structure of populations, on community composition and diversity, and on ecosystem processes. 7Organisms can resist the effects of drought by the use of refugia. Survival in refugia may strongly influence the capacity of the biota to recover from droughts once they break. 8Recovery by biota varies markedly between seasonal and supra-seasonal droughts. Faunal recovery from seasonal droughts follows predictable sequences, whilst recovery from supra-seasonal droughts varies from one case to another and may be marked by dense populations of transient species and the depletion of biota that normally occur in the streams. 9The restoration of streams must include the provision of drought refugia and the inclusion of drought in the long-term flow regime. [source] Effects of Interspecific Interactions between Microcystis aeruginosa and Chlorella pyrenoidosa on Their Growth and PhysiologyINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2007Min Zhang Abstract Interactions between Microcystis aeruginosa and Chlorella pyrenoidosa were analyzed by flow cytometry and by phytoplankton pulse-amplitude-modulated fluorimetry (Phyto-PAM) in joint cultures as well as in cultures separated by dialysis membranes. Results showed that the growth of C. pyrenoidosa was greater than that of M. aeruginosa, and that the growth of M.aeruginosa but not the growth of C. pyrenoidosa was significantly inhibited by the interactions between M. aeruginosa and C. pyrenoidosa. Culture filtrates of these two algae showed no apparent effects on the growth of the competing species. For M. aeruginosa, decreases in esterase activity, chlorophyll a fluorescence, and maximum quantum yield were observed in joint cultures, indicating that the metabolic activity and photosynthetic capacity of M.aeruginosa were suppressed. Light limitation from the shading effect of C. pyrenoidosa may be the main reason for such inhibition. For C. pyrenoidosa, esterase activity was suppressed in membrane-separated and joint cultures, suggesting that C.pyrenoidosa was probably affected by allelopathic substances secreted by M.aeruginosa. However, no significant difference was observed in the chlorophyll a fluorescence and maximum quantum yield of C. pyrenoidosa in the two cultures. In addition, interspecific interactions induced a reduction in size in both M. aeruginosa and C.pyrenoidosa, which may contribute to the development of C. pyrenoidosa dominance in the present study. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Two-species asymmetric competition: effects of age structure on intra- and interspecific interactionsJOURNAL OF ANIMAL ECOLOGY, Issue 1 2007TOM C. CAMERON Summary 1The patterns of density-dependent resource competition and the mechanisms leading to competitive exclusion in an experimental two-species insect age-structured interaction were investigated. 2The modes of competition (scramble or contest) and strength of competition (under- to overcompensatory) operating within and between the stages of the two species was found to be influenced by total competitor density, the age structure of the competitor community and whether competition is between stages of single or two species. 3The effect of imposed resource limitation on survival was found to be asymmetric between stages and species. Environments supporting both dominant and subordinate competitors were found to increase survival of subordinate competitors at lower total competitor densities. Competitive environments during development within individual stage cohorts (i.e. small or large larvae), differed from the competitive environment in lumped age classes (i.e. development from egg,pupae). 4Competition within mixed-age, stage or species cohorts, when compared with uniform-aged or species cohorts, altered the position of a competitive environment on the scramble-contest spectrum. In some cases the competitive environment switched from undercompensatory contest to overcompensatory scramble competition. 5Such switching modes of competition suggest that the relative importance of the mechanisms regulating single-species population dynamics (i.e. resource competition) may change when organisms are embedded within a wider community. [source] Owls and rabbits: predation against substandard individuals of an easy preyJOURNAL OF AVIAN BIOLOGY, Issue 2 2008Vincenzo Penteriani The interactions among the multiple factors regulating predator-prey relationships make predation a more complex process than previously thought. The degree to which substandard individuals are captured disproportionately seems to be better a function of the difficulty of prey capture than of the hunting techniques (coursing vs. ambushing predators). That is, when the capture and killing of a prey species is easy, substandard individuals will be predated in proportion to their occurrence in the prey population. In the present study, we made use of eagle owls Bubo bubo and their main prey, the rabbit Oryctolagus cuniculus: (a) the brightness of the white tails of rabbits seems to be correlated with the physical condition of individuals, (b) by using the tails of predated rabbits as an index of individual condition, we found that eagle owls seem to prefer substandard individuals (characterized by duller tails), and (c) by using information from continuous radiotracking of 14 individuals, we suggest that the difficulty of rabbit capture could be low. Although the relative benefits of preying on substandard individuals should considerably decrease when a predator is attacking an easy prey, we hypothesise that the eagle owl preference for substandard individuals could be due to the easy detection of poor individuals by a visual cue, the brightness of the rabbit tail. Several elements allow us to believe that this form of visual communication between a prey and one of its main predators could be more widespread than previously thought. In fact: (a) visual signalling plays a relevant role in intraspecific communication in eagle owls and, consequently, visual signals could also play a role in interspecific interactions, and (b) empirical studies showed that signals may inform the predator that it has been perceived, or that the prey is in a sufficiently healthy state to elude the predator. [source] Influence of environmental factors on the growth and interactions between salt marsh plants: effects of salinity, sediment and waterloggingJOURNAL OF ECOLOGY, Issue 3 2000Jonathan M. Huckle Summary 1,Artificial environmental gradients were established in a series of pot experiments to investigate the effect of salinity, sediment type and waterlogging on the growth, and interactions between Spartina anglica and Puccinellia maritima. In each experiment, one environmental variable was manipulated and plants grown in pairwise combinations to examine the effect of the environmental factor on the intensity of intra- and interspecific interactions, quantified using the Relative Neighbour Effect (RNE) index. 2,Puccinellia was found to exert an asymmetric, one-way competitive dominance above ground over Spartina in experiments where gradients of sediment type and waterlogging were established. The intensity of the competition was highest in conditions with the least abiotic stress and lower or non-existent where stress was increased. 3,The intensity of the above-ground competition was greatest in loam and least in sand sediments. Reduction in competitive intensity in sand was accompanied by an increase in below-ground Spartina biomass and it is suggested that the production of rhizomes is a potential mechanism by which this species can expand vegetatively into areas without competition. 4,Interspecific competition on Spartina from Puccinellia also varied in intensity in the waterlogging experiment, being more intense in non-immersed treatments, where abiotic stress was reduced. 5,The competitive dominance of Puccinellia and the competition avoidance mechanism shown by Spartina in these experiments help to explain the successional interactions between the species along environmental gradients in natural salt marsh communities. [source] PATTERNS OF INTERSPECIFIC INTERACTIONS IN THE ULVA -DOMINATED INTERTIDAL COMMUNITY IN A SOUTHERN COAST OF KOREAJOURNAL OF PHYCOLOGY, Issue 2000Y.J. Bhang In the southern coast of Korea, rocky intertidal zones where green tide commonly occurs are dominated by Ulva pertusa, red algal turf (a mixed stand of Gigartina intermedia and Gigartina teedii) and species of Enteromorpha with highly opportunistic occurrence. To investigate their interspecific interactions, a field experiment was carried out using press effect of one species removal from permanent plots (20 x 20cm) set up on two different tidal heights. Mechanisms of interaction were also attempted using artificial plants to test the possible effects of shading, scouring, allelopathy of U. pertusa on the turf algae. The turf-forming red algae lowered the abundance of U. pertusa presumably by inhibiting the recruitment of U. pertusa; this effect was consistent along the tidal height. However, the greater abundance of Enteromorpha was observed in the presence of turf in the upper zone, indicating a positive effect of turf on Enteromorpha. Once U. pertusa was successfully recruited and grown to the adult plant, it inhibited the growth of turf by shading, which was effective both in winter and summer regardless of desiccation stress. No scouring and allelopathic effects of U. pertusa on the turf were detected. When an open substrate was provided, Enteromorpha colonized the space faster than any other species in the upper zone, but the turf was the fastest one followed by U. pertusa and Enteromorpha in the lower zone. Results indicated that patterns of interaction represented a complex network with no ultimate winner and the outcomes of interaction varied over time and space. [source] Preferences of the Ponto-Caspian amphipod Dikerogammarus haemobaphes for living zebra musselsJOURNAL OF ZOOLOGY, Issue 3 2009J. Kobak Abstract A Ponto-Caspian amphipod Dikerogammarus haemobaphes has recently invaded European waters. In the recipient area, it encountered Dreissena polymorpha, a habitat-forming bivalve, co-occurring with the gammarids in their native range. We assumed that interspecific interactions between these two species, which could develop during their long-term co-evolution, may affect the gammarid behaviour in novel areas. We examined the gammarid ability to select a habitat containing living mussels and searched for cues used in that selection. We hypothesized that they may respond to such traits of a living mussel as byssal threads, activity (e.g. valve movements, filtration) and/or shell surface properties. We conducted the pairwise habitat-choice experiments in which we offered various objects to single gammarids in the following combinations: (1) living mussels versus empty shells (the general effect of living Dreissena); (2) living mussels versus shells with added byssal threads and shells with byssus versus shells without it (the effect of byssus); (3) living mussels versus shells, both coated with nail varnish to neutralize the shell surface (the effect of mussel activity); (4) varnished versus clean living mussels (the effect of shell surface); (5) varnished versus clean stones (the effect of varnish). We checked the gammarid positions in the experimental tanks after 24 h. The gammarids preferred clean living mussels over clean shells, regardless of the presence of byssal threads under the latter. They responded to the shell surface, exhibiting preferences for clean mussels over varnished individuals. They were neither affected by the presence of byssus nor by mussel activity. The ability to detect and actively select zebra mussel habitats may be beneficial for D. haemobaphes and help it establish stable populations in newly invaded areas. [source] Mandibular fractures in short-finned pilot whales, Globicephala macrorhynchusMARINE MAMMAL SCIENCE, Issue 1 2010Mollie Sue Oremland Abstract This study's objective was to investigate mandibular fractures in 50 short-finned pilot whales, Globicephala macrorhynchus, from two mass strandings. Based on current theories that this species is sexually dimorphic and polygynous, hypotheses were: (1) males should suffer more frequent or more substantial mandibular fractures than should females, and (2) fracture occurrence should increase with male reproductive maturity and potential correlates of maturity, such as age and length. Fractures were described and correlated with physical characteristics to infer possible explanations for injuries. Mandibular fractures were surprisingly common in males and females, being found in more than half of the animals examined (27/50, or 54% overall; 17/36 or 47% of females and 10/14 or 71% of males). Length was the only correlate of fracture presence; the proportion of animals showing evidence of fracture increased with length. These results offer some support to initial hypotheses, but there must be another set of consequences that contribute to mandibular fractures in females. A combination of intra- and interspecific interactions and life history characteristics may be responsible for fractures. Further research from a larger sample of this and other cetacean species are suggested to help elucidate both the causes and implications of mandibular fractures. [source] Speciation in fig pollinators and parasitesMOLECULAR ECOLOGY, Issue 8 2002George D. Weiblen Abstract Here we draw on phylogenies of figs and fig wasps to suggest how modes of speciation may be affected by interspecific interactions. Mutualists appear to have cospeciated with their hosts to a greater extent than parasites, which showed evidence of host shifting. However, we also repeatedly encountered a pattern not explained by either cospeciation or host switching. Sister species of fig parasites often attack the same host in sympatry, and differences in ovipositor length suggest that parasite speciation could result from divergence in the timing of oviposition with respect to fig development. These observations on fig parasites are consistent with a neglected model of sympatric speciation. [source] A comprehensive framework for the evaluation of metacommunity structureOIKOS, Issue 6 2010Steven J. Presley The metacommunity framework is a powerful platform for evaluating patterns of species distribution in geographic or environmental space. Idealized patterns (checkerboard, Clementsian, evenly spaced, Gleasonian and nested distributions) give the framework shape. Each pattern represents an area in a multidimensional continuum of metacommunity structures; however, the current approach to analysis of spatial structure of metacommunities is incomplete. To address this, we describe additional non-random structures and illustrate how they may be discerned via objective criteria. First, we distinguish three distinct forms of species loss in nested structures, which should improve identification of structuring mechanisms for nested patterns. Second, we define six quasi-structures that are consistent with the conceptual underpinnings of Clementsian, Gleasonian, evenly spaced and nested distributions. Finally, we demonstrate how combinations of structures at smaller spatial extents may aggregate to form Clementsian structure at larger extents. These refinements should facilitate the identification of best-fit patterns, associated structuring mechanisms, and informative scales of analysis and interpretation. This conceptual and analytical framework may be applied to network properties within communities (i.e. structure of interspecific interactions) and has broad application in ecology and biogeography. [source] Competition and intraguild egg predation among freshwater snails: re-examining the mechanism of interspecific interactionsOIKOS, Issue 11 2007Andrew M. Turner Experimental and field studies suggest that freshwater snail species have negative effects on each other's population growth rates. Because snails share similar diets, these interactions have been interpreted as the result of exploitative competition, but they could also result from intraguild predation. Here we present three experiments aimed at testing the hypothesis that interspecific interactions among three species of freshwater gastropod (Helisoma trivolvis, Physa acuta and Stagnicola elodes) are mediated by intraguild egg predation. Foraging trials, conducted in a laboratory, showed that some snails readily prey on eggs, but the extent of egg predation depended on both the identity of the snail predator and the identity of the egg mass. Of the three species considered, Stagnicola had the largest effect on egg mortality and Physa had no effect on egg mortality. Foraging trials also showed that the eggs of Physa were the most vulnerable to predators and that the eggs of Stagnicola were largely invulnerable. A study conducted in large outdoor mesocosms assessed the occurrence of egg mortality in an environment of more extensive spatial scale and complexity. The results largely mirrored those of the laboratory study, with Stagnicola being the most voracious predator and the eggs of Physa being most vulnerable to predation. The reproductive success of Physa and Stagnicola raised in sympatry and allopatry was assessed in a mesocosm study conducted over three months. Recruitment of both species was depressed in sympatry, but patterns of growth in the survivors suggest contrasting mechanisms of suppression: Physa suppressed Stagnicola via exploitative competition, but Stagnicola suppressed Physa via egg predation. These experiments support the hypothesis that freshwater snail assemblages are structured by strong interspecific interactions and that a rich interplay of egg predation and interspecific competition underlie interactions among the members of this guild. [source] Architectural and growth traits differ in effects on performance of clonal plants: an analysis using a field-parameterized simulation modelOIKOS, Issue 5 2007Radka Wildová Individual traits are often assumed to be linked in a straightforward manner to plant performance and processes such as population growth, competition and community dynamics. However, because no trait functions in isolation in an organism, the effect of any one trait is likely to be at least somewhat contingent on other trait values. Thus, to the extent that the suite of trait values differs among species, the magnitude and even direction of correlation between values of any particular trait and performance is likely to differ among species. Working with a group of clonal plant species, we assessed the degree of this contingency and therefore the extent to which the assumption of simple and general linkages between traits and performance is valid. To do this, we parameterized a highly calibrated, spatially explicit, individual-based model of clonal plant population dynamics and then manipulated one trait at a time in the context of realistic values of other traits for each species. The model includes traits describing growth, resource allocation, response to competition, as well as architectural traits that determine spatial spread. The model was parameterized from a short-term (3 month) experiment and then validated with a separate, longer term (two year) experiment for six clonal wetland sedges, Carex lasiocarpa, Carex sterilis, Carex stricta, Cladium mariscoides, Scirpus acutus and Scirpus americanus. These plants all co-occur in fens in southeastern Michigan and represent a spectrum of clonal growth forms from strong clumpers to runners with long rhizomes. Varying growth, allocation and competition traits produced the largest and most uniform responses in population growth among species, while variation in architectural traits produced responses that were smaller and more variable among species. This is likely due to the fact that growth and competition traits directly affect mean ramet size and number of ramets, which are direct components of population biomass. In contrast, architectural and allocation traits determine spatial distribution of biomass; in the long run, this also affects population size, but its net effect is more likely to be mediated by other traits. Such differences in how traits affect plant performance are likely to have implications for interspecific interactions and community structure, as well as on the interpretation and usefulness of single trait optimality models. [source] Interspecific and intraspecific interactions between salt marsh plants: integrating the effects of environmental factors and density on plant performanceOIKOS, Issue 2 2002Jonathan M. Huckle There has been much debate about the role of plant interactions in the structure and function of vegetation communities. Here the results of a pot experiment with controlled environments are described where three environmental variables (nutrients, sediment type and waterlogging) were manipulated factorially to identify their effects on the growth and intensity of interactions occurring between Spartina anglica and Puccinellia maritima. The two species were grown in split-plot planting treatments, representing intraspecific and interspecific addition series experiments, to determine individual and interactive effects of environmental factors and plant interactions on plant biomass. Above-ground growth of both species involved interactions between the environmental and planting treatments, while below-ground, environmental factors affected the biomass irrespective of planting treatments. It was suggested that this difference in growth response is evidence that in our experiment plant interactions between the two species occur primarily at the above-ground level. The intensity of plant interactions varied in a number of ways. First, interactions between Spartina and Puccinellia were distinctly asymmetrical, Puccinellia exerting a competitive effect on Spartina, with no reciprocal effect, and with a facilitative effect of Spartina on Puccinellia in low nutrient conditions. Second, the interactions varied in intensity in different environmental conditions. Interspecific competitive effects of Puccinellia on Spartina were more intense in conditions favourable to growth of Puccinellia and reduced or non-existent in environments with more abiotic stress. Third, intraspecific competition was found to be less intense for both species than interspecific interactions. Finally, the intensity of plant interactions involving both species was more intense above ground than below ground, with a disproportionate reduction in the intensity of interspecific competition below relative to above ground in treatments with less productive sediments and greater immersion. This is interpreted as reflecting a potential mechanism by which Spartina may be able to evade competitive neighbours. [source] | |||||||||||||||||||||||||