Predator-prey interactions in size-structured fish communities: implications of prey growth

Predator-prey interactions among size-structured populations may be strongly influenced by factors which affect growth rates of prey. I examined the importance of prey growth in the interaction between large-mouth bass (Micropterus salmoides) and their prey, bluegill (Lepomis macrochirus), by analyzing diets and growth rates of bass in a set of seven lakes in south-central Wisconsin. Sizes of bluegill consumed by bass changed dramatically across a gradient of bluegill growth, which resulted in differing patterns of bass growth. In lakes with slow bluegill growth, small bass fed on the youngest bluegill cohort, but large bass were capable of feeding on several age classes. Consequently, bass growth rates were strongly size-dependent; small bass ate small prey and had low growth, but growth rates increased substantially with size as bass ate progressively larger prey. When bluegill had high growth rates, they quickly reached a size refuge from predation and bass of all sizes were restricted to feeding on the youngest/smallest prey. In these lakes, bass growth rates were more uniform across bass sizes. Because growth rates influence population size-distributions, variation in bluegill growth can have strong effects on the structure of bass populations. These effects could potentially feed back to further influence the interaction between predator and prey.     

Predator-prey interactions between ectoparasites

Vertebrates represent a resource frequently exploited by ectoparasites. But the ectoporosites themselves also represent a resource that can be exploited by specialized predators. Some o f these predators have been classified as ectoparasites, but in some cases the vertebrate blood in their crops comes from their blood-sucking prey. In fact, as Lance Durden explains, the assemblage o f arthropods that inhabit the vertebrate skin surface, or pelage, seems to show a complete spectrum of adaptations from predators to facultative and obligate blood-suckers, together with those feeding on other materials in this special habitat. The dynamics of their interactions are further complicated by responses of the host to the arthropods, and much further study is needed before the role o f predators in controlling ectoparasites can be clarified.     

Positive interactions in communities

Current concepts of the role of interspecific interactions in communities have been shaped by a profusion of experimental studies of interspecific competition over the past few decades. Evidence for the importance of positive interactions - facilitations - in community organization and dynamics has accrued to the point where it warrants formal inclusion into community ecology theory, as it has been in evolutionary biology.     

Interspecies interactions within oral microbial communities.

While reductionism has greatly advanced microbiology in the past 400 years, assembly of smaller pieces just could not explain the whole! Modern microbiologists are learning "system thinking" and "holism." Such an approach is changing our understanding of microbial physiology and our ability to diagnose/treat microbial infections. This review uses oral microbial communities as a focal point to describe this new trend. With the common name "dental plaque," oral microbial communities are some of the most complex microbial floras in the human body, consisting of more than 700 different bacterial species. For a very long time, oral microbiologists endeavored to use reductionism to identify the key genes or key pathogens responsible for oral microbial pathogenesis. The limitations of reductionism forced scientists to begin adopting new strategies using emerging concepts such as interspecies interaction, microbial community, biofilms, polymicrobial disease, etc. These new research directions indicate that the whole is much more than the simple sum of its parts, since the interactions between different parts resulted in many new physiological functions which cannot be observed with individual components. This review describes some of these interesting interspecies-interaction scenarios.     

植物邻体间的正相互作用

植物间的正负相互作用是构建植被群落的重要因素,也是群落生态学研究的中心内容之一。近20a来,植物间正相互作用的研究得到快速发展。综述了正相互作用的定义,不同植物群落中的直接、间接正相互作用及其发生机制,正相互作用研究的实验和模型方法,正负相互作用随胁迫梯度的变化及正相互作用对群落构建的影响。探讨了正相互作用研究前景:(1)进一步理解正负相互作用的平衡及其对群落构建的影响;(2)加深对全球变暖背景下的正相互作用的认识;(3)需把正相互作用研究同进化联系起来;(4)充分发挥正相互作用在生态系统中的推动力作用,把正相互作用应用到生态恢复中,为恢复退化生态系统服务。     

The qualitative approach in investigating the role of species interactions on stability of natural communities

Community models with competition and mutualism are qualitatively analyzed using the methodology of loop analysis combined with computer stochastic simulation. The concept of "moving equilibrium" in the growth rate of the species is discussed in 14 "tables of predictions", presented as analytical tools that can help to shed light on controversial ecological issues such as direct versus indirect interaction and positive feedback effects on stability. While the stochastic simulation shows that only little or no difference exists in probability of stability between models with competition and models with mutualism, the related tables of predictions show that the networks among links are able to activate indirect interactions, with both negative and positive effects, between any pair of species. This phenomenon makes it difficult to determine how much stability is related to the direct interactions.     

Predator-prey interactions in Lake Michigan: model predictions and recent dynamics

Synopsis Several years ago, we used a bioenergetics model to evaluate the impact of increasing salmonid stocking on the highly variable alewife forage base in Lake Michigan. At that time, we forecast an alewife population decline and the following system-wide effects: increased abundances of large zooplankton, decreased salmonid growth rates, increased diet breadth of salmonids, niche shifts among competitors of the alewife, increased alewife growth rates and increased densities of fishes suppressed by alewife. Alewives have continued to decline steadily since 1981 and are now reduced to a density similar to early outbreak levels in the early 1960s. Recent reports on fish growth rates, zooplankton size and fish community structure support our projections regarding system-wide responses to the alewife decline.     

Population genomics in natural microbial communities

Little is known about the evolutionary processes that structure and maintain microbial diversity because, until recently, it was difficult to explore individual-level patterns of variation at the microbial scale. Now, community-genomic sequence data enable such variation to be assessed across large segments of microbial genomes. Here, we discuss how population-genomic analysis of these data can be used to determine how selection and genetic exchange shape the evolution of new microbial lineages. We show that once independent lineages have been identified, such analyses enable the identification of genome changes that drive niche differentiation and promote the coexistence of closely related lineages within the same environment. We suggest that understanding the evolutionary ecology of natural microbial populations through population-genomic analyses will enhance our understanding of genome evolution across all domains of life.     

Predator-prey ratios in communities of freshwater invertebrates: the role of enemy free space

SUMMARY.

• 1 The ratio: number of predator species/number of prey species is reviewed using comprehensive faunal lists for a range of freshwater habitats in Britain and North America. Prey species are defined as detritivores, herbivores and fungivores; predators eat metazoan animals as the main component of their diet. Our data refer only to invertebrates.
• 2 The numbers of predators and prey species are apparently very closely correlated in freshwater communities (r=0.84, In transformed data), with an average ratio of predators to prey of 0.36. The average ratio of predators to prey changes from 0.48 in small (species-poor) collections to 0.29 in large (species-rich) collections.
• 3 We suggest that an approximately constant ratio of predators to prey may be generated by: (a) the number of predator species being a function of the number of broad classes or kinds of prey; and (b) the number of prey species being constrained by competition between prey for ‘enemy free space’, i.e. species that are too similar are unable to coexist with shared predators.

     

Predator-prey system structure in patchy and ephemeral phytotelmata: Aquatic communities in small aroid axils

Mechanisms allowing the persistence of an aquatic predator-prey system in tiny pools (the mean ca. 0.5 ml) held by taro axils were analyzed from the viewpoint of temporal and spatial patterns of habitat use. Predatory larvae of a mosquitoTopomyia tipuliformis concentrated in young axils, while 9 other taxa utilized both young and old axils or concentrated more in older axils. The total prey density was lower in axils with the predator but the density of each prey taxon (except for a few cases) and the number of prey taxa did not differ between axils with and without predators. This indicates thatT. tipuliformis is a general predator and does not influence prey community organization through selective removal of particular prey taxa. Inter-axil distribution ofT. tipuliformis was aggregated in the first instar but uniform in the third and fourth instars due to intraspecific cannibalism, which assures the survival of a single individual under short food supply. Distributions of prey taxa were mostly aggregated, fitting the negative binomial distribution. Thirty seven out of 45 associations of 10 taxa were independent with 3 negative (between the predator and some late-colonizing prey) and 5 positive (between some prey taxa) associations. Probabilistic refuges (produced by independent aggregated distributions) reduced interspecific encounters which may result in competition and predation, and thus probably facilitated prey coexistence. There was no evidence for the importance of predation in structuring the prey community. This system may be prey-dominated in that predator persistence depends on prey community existence but prey community structure depends less on predation.     

Predator-prey interactions between two amphibian species: effects of insecticide exposure

The presence of environmental contaminants may alter predator-prey interactions among aquatic species by altering activity levels of predators or prey, or by altering predator avoidance behavior. The outcome of a predatory encounter may be dependent upon whether both species are exposed to a contaminant simultaneously, or whether exposure occurs only in one of the species. In a laboratory experiment, I used the insecticide carbaryl to examine predation of southern leopard frog tadpoles (Rana sphenocephala) by adult red-spotted newts (Notophthalmus viridescens) under four conditions: both tadpoles and newts exposed, neither tadpoles nor newts exposed, and either newts or tadpoles only exposed. After one hour, exposed newts consumed half as many tadpoles as non-exposed newts. Carbaryl potentially affected newt activity enough to reduce time spent searching for prey, or may have altered the speed and coordination necessary to capture tadpoles. After six hours, non-exposed and exposed newts consumed similar numbers of tadpoles, most likely indicating recovery from exposure. After 24 h, predation rates were lowest when both newts and tadpoles were simultaneously either exposed or not exposed, and were greatest when newts and tadpoles were not exposed simultaneously. This study suggests that when tadpoles and newts are exposed to a sublethal level of a contaminant simultaneously, that predation rates do not differ from those observed under natural conditions, but exposure of either predator or prey at different times can disrupt predator-prey dynamics. This revised version was published online in August 2006 with corrections to the Cover Date.     

Predator-prey interactions between Isochrysis galbana and Oxyrrhis marina. III. Mathematical modelling of predation and nutrient regeneration

A mathematical model was derived to simulate ingestion, growthand nitrogen (N) regeneration for the phagotrophic dinoflagellateOxyrrhis marina. Two types of experimental study were undertaken:prey-deplete O.marina were supplied with lsochrysis galbanain continuous darkness (thus preventing growth of the prey),and predator-prey interactions were also followed in culturesmaintained in a light-dark cycle (allowing growth of the prey).During light-dark cycles, Oxyrrhis volume increased more inthe light phase than in the dark. Digestion of isochrysis lasted{small tilde}0.3 days. with an average maximum ingestion rateof 55 prey predator–1 day–1 During active predation,30% of Oxyrrhis-carbon (C) was lost from the particulate phase:per day, with this loss falling to 10%: per day at the cessationof herbivory when cannibalism became noticeable. Ingestion wasmodelled as a function of prey density, C-loss and divisionas functions of cellular predator C. with cannibalism by Oxyrrhisalso included. Two N-regeneration expressions were investigated:one proposed by D.A.Caron and J.C.Goldman (Journal of Protozoology.35, 247–249, 1988) and an alternative function which relatedN regeneration to intracellular carbon and N based on the conceptof an optimal Oxyrrhis C:N ratio. The latter was more successfulin simulating batch culture data and did not require a priorcalculation of Oxyrrhis gross growth efficiency. The model ofOxyrrhis numbers, C and N contained only nine parameters whosevalues were fully obtainable from batch culture experiments.By using this model, we were able to use a single parameterset to simulate the transient dynamics of Oxyrrhis ingestingN-replete and N-stressed prey. Further experiments in whichOxyrrhis grew on Isochrysis in light-dark cycles were simulatedby combining the Oxyrrhis model with the nutrient-processingmodel for Isochrysis of K.Davidson et al. (Journal of PlanktonResearch, 15, 351–359, 1993). The dynamics of the fullpredator-prey model were found to be sensitive to the levelof sophistication of the prey model; the Quota model was foundto be less successful than the nutrient-processing prey model.Theoretical model runs indicated the importance of being ableto simulate changes in both prey numbers and biomass, and alsoin including realistic equations for nutrient regeneration frompredators in microbial predator-prey models.     

Yeast communities in a natural tequila fermentation

Fresh and cooked agave,Drosophila spp., processing equipment, agave molasses, agave extract, and fermenting must at a traditional tequila distillery (Herradura, Amatitan, Jalisco, México) were studied to gain insight on the origin of yeasts involved in a natural tequila fermentations. Five yeast communities were identified. (1) Fresh agave contained a diverse mycobiota dominated byClavispora lusitaniae and an endemic species,Metschnikowia agaveae. (2)Drosophila spp. from around or inside the distillery yielded typical fruit yeasts, in particularHanseniaspora spp.,Pichia kluyveri, andCandida krusei. (3)Schizosaccharomyces pombe prevailed in molasses. (4) Cooked agave and extract had a considerable diversity of species, but includedSaccharomyces cerevisiae. (5) Fermenting juice underwent a gradual reduction in yeast heterogeneity.Torulaspora delbrueckii, Kluyveromyces marxianus, andHanseniaspora spp. progressively ceded the way toS. cerevisiae, Zygosaccharomyces bailii, Candida milleri, andBrettanomyces spp. With the exception ofPichia membranaefaciens, which was shared by all communities, little overlap existed. That separation was even more manifest when species were divided into distinguishable biotypes based on morphology or physiology. It is concluded that crushing equipment and must holding tanks are the main source of significant inoculum for the fermentation process.Drosophila species appear to serve as internal vectors. Proximity to fruit trees probably contributes to maintaining a substantialDrosophila community, but the yeasts found in the distillery exhibit very little similarity to those found in adjacent vegetation. Interactions involving killer toxins had no apparent direct effects on the yeast community structure.