Individual versus community level processes and pattern formation in a model of sand dune plant succession

A cellular automata model of a sand dune plant community on Galveston Island, Texas, USA was utilized to test hypotheses regarding individual plant interactions and their impact upon community organization. Simulations demonstrated that both an environmental gradient and facilitative succession resulted in the formation of characteristic sand dune patterns. The results showed that the plant patterns were due to individual plant responses to their environment within their local neighborhood, yet these responses were constrained by the global history of the community. The local neighborhood was related to the “zone of influence” concept, “field of neighborhood” models, and “ecological field” theory. It is proposed that plants responded individualistically to environmental conditions within the local neighborhood and that plants were constrained by the community-unit beyond the local neighborhood. The ratio of the scale of environmental variability versus the scale of a plant's local neighborhood determined the relative importance of the individual and the community in forming pattern. This work makes important contributions to the Gleasonian–Clementsian debate, sand dune successional theory, and in pattern-based, deductive hypothesis testing with cellular automata models.     

Long-term variation of organochlorine residues and assemblages of epibenthic organisms in a shallow North Florida (USA) estuary

A 4-year study (1972–1976) determined long-term trends of organochlorine residues (DDT, DDE, DDD, PCB's, mirex) and trawl-susceptible organisms in a shallow, river-dominated estuary in North Florida (Apalachicola Bay, USA). Moderate levels of such compounds were found in various species prior to the restricted use of DDT in 1972. A subsequent precipitous decline in organochlorine besidues was attributed to decreased upland usage, major flushing of the river basin in early 1973, and various factors associated with estuarine function. No mirex was found in sediments or aquatic organisms. Apparently, the half-life of organochlorines is relatively short in this bay system. Various statistical methods were used to test the relationships of different physico-chemical and biological parameters. During the 4-year study period, seasonal river flow fluctuations dominated water color, turbidity, salinity, nutrients (NO₃), chlorophyll a, and the temporal succession of fishes in the bay. Certain long-term trends of fish associations were noted; relative dominance of key fish species declined and stabilized while bay-wide species richness and diversity increased with time. Qualitative changes in species representation determined the long-term pattern of community variability. This was consonant with a distinctive fish fauna during the first year of sampling. The bay anchovy Anchoa mitchilli was dominant during 9 of the first 12 monts of the project; this influenced the time-related changes in community indices. Temporally clustered fish associations reflected the importance of river flow in the estuarine environment. Direct correlation of fish distribution with the rapid disappearance of organochlorine compounds was complicated by aperiodic natural phenomena such as storms and river fluctuations. Population and community trends appeared consistent with other studies showing similar patterns of dominance of stress-resistant fish populations and related changes in community parameters. In this case, the relatively predictable annual succession of fish associations allowed an appraisal of key forcing functions. Due to the high level of seasonal and annual biological variability in this estuary, there were some problems in the application of linear statistical models to the data base. Although the long-term trend of relative species representation is useful as an index of stress, new techniques are needed to analyze extensive field data so that functions such as trophic interactions are included in the estimation of causal relationships. There are indications that such effects could be related to the impact of organochlorine compounds on estuarine systems.     

Deviations from predictions of the metabolic theory of ecology can be explained by violations of assumptions

The metabolic theory of ecology (MTE) is based on models derived from the first principles of thermodynamics and biochemical kinetics. The MTE predicts that the relationship between temperature and species richness of ectotherms should show a specific slope. Testing the validity of this model, however, depends on whether empirical data do not violate assumptions and are obtained within contour conditions. When dealing with richness gradients, the MTE must be empirically tested only for ectothermic organisms at high organization levels and when their body size as well as abundance does not vary with temperature gradients. Here we evaluate whether the magnitude of the deviations in slope expected from the MTE to empirical data for New World amphibians is due to the violations of model assumptions and to lack of generality due to restricting contour conditions. We found that the MTE correctly predicted biodiversity patterns only at higher levels of organization and when assumptions of the basic model were not violated. Approximately 60% of the deviations from the MTE-predicted slope across amphibian families were due to violations of the model assumptions. The hypothesis that richness patterns are a function of environmental temperature is too restrictive and does not take complex environmental and ecological processes into account. However, our results suggest that it may be possible to obtain multiple derivations of the MTE equation if idiosyncrasies in spatial and biological/ecological issues that are essential to understanding biodiversity patterns are considered.     

紫茎泽兰入侵过程中生物群落的交互作用

生物入侵在全球范围内影响了生物群落的结构与功能,打破了群落内物种共存的生态格局,继而反馈性影响全球环境。该文就外来杂草紫茎泽兰入侵对生物群落之间交互作用的影响进行了分析。1）紫茎泽兰通过竞争排斥降低了土著植物群落的多样性,造成依赖于土著植物的节肢动物群落减少或丧失适宜的栖息环境。2）打破了土著植物与节肢动物之间相互依存的状态,并通过单优群落优势和强烈化感作用制约天敌昆虫的自然控制作用。3）通过改变地表生境和枯落物种类影响土壤动物群落。4）引起土壤微生物群落组成和功能的变化,改变土壤中可利用资源的形式和数量,影响并重塑了生物种间互作模式,并动态反馈于地面植物群落新格局的形成。分析指出：1）入侵过程中群落之间的交互作用通过多层次生态过程对群落结构与功能的生态改变发挥影响。2）入侵对生物群落的改变所产生的生态驱动反馈性作用于群落互作模式的重塑、群落和生态系统新格局的重建。同时,指出了生物入侵对群落影响的复杂性以及后续研究的方向。     

Competitive organization of the soft-bottom macrobenthic communities of southern California lagoons

The sandy-bottom macrobenthic community of Mugu Lagoon, a relatively pristine southern California (USA) marine lagoon, demonstrated (1) nearly constant community composition over 37 months of observation, (2) relatively little temporal variability in the population densities of the most abundant species over 37 months, and (3) a pattern of depth stratification in which very little vertical overlap existed among the six most abundant species. The only two species whose vertical distributions overlapped broadly showed horizontal spatial segregation, each abundant in different areas within the sand habitat. These community characteristics imply the importance of biological factors in structuring the sand benthos. The relatively large volume required for living space by these macrofauna suggests that competition for space may be the biological factor most important in determining the observed temporal and spatial abundance patterns. The muddy-sand community and the mud community of Mugu Lagoon also revealed similar patterns of stratification: new abundant species replaced species at the same sedimentary level while not greatly affecting species populations at other non-overlapping levels. In the sand community of Tijuana Slough, two of the abundant species of Mugu Lagoon's sand community were nearly absent as an apparent result of human over-exploitation. Probably in response, densities of species living at the sedimentary levels normally occupied by the missing species were much higher than would be predicted if competition for space were unimportant. In field experiments, removal of the deposit feeder Callianassa californiensis resulted in high recruitment of Sanguinolaria nuttallii, whereas control areas showed no S. nuttallii recruitment. Experiments also suggest that negative intraspecific interactions between Cryptomya californica individuals may explain the observed rapid emigration from areas of artificially high density. Perhaps the relatively great environmental predictability of southern California lagoons has permitted competitive interactions to play a singnificant role in determining the temporal and spatial abundance patterns of the soft-bottom macrobenthos.     

The influence of experience on risk taking: results from a common-garden experiment on populations of Eurasian perch

Predation is often thought of as an unforgiving and strong selective force, quickly selecting against maladaptive behaviour in the prey. It is argued that experience is likely to have low influence on the phenotypic response to predation, as failing to react correctly to a predator may mean death to the prey and no second chance to learn and correct the behaviour. Individuals from different populations of Eurasian perch are known to differ in risk-taking behaviour. Variation in predation pressure has been suggested as a key factor causing these differences, but little is known about the underlying mechanism by which predation generates risk-taking phenotypes in perch. We compared the degree of boldness between two natural populations of Eurasian perch, living under different predation regimes, and the same populations hatched and reared under identical conditions, free from predation. By this common-garden approach, we sought to investigate patterns in the influence of inheritance and experience on boldness phenotype. The wild fish differed in risk taking, with fish from the low predation-risk population acting bolder than fish from the high-risk environment. In the reared fish, both populations behaved equally bold. Only the fish originating from the high predation population showed different behaviour when comparing wild and reared ecotypes. Our results suggest that experience has an important impact on the response to predators and that geographic variation in risk taking between populations of Eurasian perch to a high degree is shaped by adjustments to the current environment. Habituation had an effect of risk-taking behaviour over the experimental period, but consistent differences between individuals were also found. Furthermore, we also show, by the estimation of variance components, that the behaviour we observe is affected by a range of random effects, such as aquaria and group membership, that in concert shapes the behaviour of an individual perch.     

A new hypothesis concerning the nature of small pelagic fish clusters: An individual-based modelling study of Sardinella aurita dynamics off West Africa

Coastal populations of small pelagic fish display nested aggregation levels. Above the level of the school structure, clusters are observed the nature of which has not been definitively determined. We hypothesized that these clusters corresponded to a materialisation of the microcohorts originating from successive spawnings of fish populations in their vital domain.A candidate individual-based model was developed to investigate this hypothesis. This model is based on pattern-oriented modelling of a concrete documented case: the dynamics of the round sardinella (Sardinella aurita) population living off the West African coasts and subject to environmental fluctuations caused by seasonal upwelling. The simulated agents were round sardinella microcohorts situated and moving in a discretised physical environment. The combined effects of environmental forcing (temperature, wind, retention) and inner biological dynamics (reproduction, growth and mortality, competition) condition the dynamics of this population.The modelled behaviour generated realistic dynamic patterns (population distribution, spawning zones, periods and plasticity, biomass fluctuations), which were obtained simultaneously and successfully compared with observations. The steady-state number of microcohorts obtained after simulation convergence was similar to the number of clusters observed in situ in this area for this population.The realism and diversity of the patterns simultaneously simulated suggested the cluster-microcohort equivalence hypothesis as a candidate framework accounting for the origin of the clusters observed in situ. Within this preliminary exploration, we discuss the consistency of the hypothesis and the accuracy of the model. If the correspondence between clusters and microcohorts proves to be real, it may be transient and progressively modified by other environmental factors. If stable over time, as simulated in the model, the number of observed clusters should be related to the number of spawning events in the species’ lifetime.     

Acquisition of fission–fusion social organization in a chimpanzee (Pan troglodytes troglodytes) community released into the wild

The social aspects of primate reintroduction are of primary importance to the success of release programs and need to be assessed through the study of changes in social behavior over time. This study reports on the development of social structure and organization in a community of 37 chimpanzees (Pan troglodytes troglodytes) released into the wild in the Conkouati Douli National Park, Republic of Congo. Analyses of post-release monitoring data collected over 10 years on association patterns between individuals show that during the years following individual releases, chimpanzees exhibited changing social structure and organization until they stabilized in one community living in a fission–fusion system. Social organization development was directly affected by several factors including community size and experience in the wild, while social structure was affected by individual characteristics: gender, pre-release history, and release history. Similarities between social structure and organization observed in the released community and wild chimpanzee communities demonstrate that the release program is a success from a social point of view.     

Organization of Plethodon salamander communities: guild-based community assembly

A long-standing goal in evolutionary ecology is to determine whether the organization of communities is reflective of underlying deterministic processes. In this study, I examined patterns of species co-occurrence among eastern Plethodon salamanders and determined whether they were consistent with predictions from a guild model of competition-based community assembly. Using a database of 45 species and 4540 geographic sites, I found that patterns of co-occurrence were significantly nonrandom at both a regional and continental scale, and species of different size guilds were distributed more evenly in sites than was expected by chance. Sites with the highest species richness had consistent patterns of community composition, and with few exceptions, the same five species were present at all sites. Taken together, these results imply that larger Plethodon communities are assembled from simpler communities in a manner consistent with what is predicted through competitive mechanisms and suggest that stable species combinations are possible to achieve at various levels of species richness. These results also provide strong evidence consistent with the hypothesis that competitive-based community assembly is a general phenomenon in Plethodon and that interspecific competition is prevalent among the eastern species of this group.     

Vulnerability associated with “symptoms similar to those of mercury poisoning” in communities from Xingu River,Amazon basin

The Brazilian Amazon is known to be a region with high levels of mercury (Hg) in the environment and studies point to an association between high levels of natural mercury in the mother rock and the vast number of clandestine gold mines. Other studies already report the contamination of fish in this region, as well as high levels of Hg in biological material from environmentally exposed populations. On the other hand, this is one of the least developed regions of the planet and it is necessary to understand the vulnerability factors in these populations that may be intoxicated by this element. The purpose of the present study was to investigate the vulnerability factors in communities from Xingu River—Amazon basin probably exposed to Hg. A cross-selection study in two cities localized in Xingu River was conducted, and the sample contained was 268 individuals. sociodemographic questions, lifestyle, diet habits and health conditions were collated. The majority of the sample was female, between 30 and 59 years old, had less than 3 years of educational level and lived in the local of study more than 240 months. There was regular fish consumption (95.9%), principally carnivorous species (80.5%). The visual problem has a highest prevalence (43.3%) between the health problems and about the symptoms of Hg intoxication, memory loss (42.9%), weakness (35.1%), fatigue (34.3%), mood changes (28.7%) and difficulties in concentration (27.2%) was most reported. The female sex, age over 60, educational level below 3 years of study, did not had flush toilet, smoke and least one chronic non-communicable disease represent higher probability to had symptoms of Hg intoxication. Lack of access to health services, low education level and income evidence the susceptibility of this community to diseases and injuries. The vulnerable groups identified in this study should be a priority in public health and environmental health policies.     

Lake of flies, or lake of fish? A trophic model of Lake Malawi

Ecosystem-focused models have, for the first time, become available for the combined demersal and pelagic components of a large tropical lake ecosystem, Lake Malawi. These provide the opportunity to explore continuing controversies over the production efficiencies and ecological functioning of large tropical lakes. In Lake Malawi these models can provide important insight to the effect of fishing on fish composition, and the potential competition that the lakefly Chaoborus edulis may have with fisheries production. A mass-balanced trophic model developed for the demersal fish community of the southern and western areas of Lake Malawi was integrated with an existing trophic model developed for the open-water pelagic. Input parameters for the demersal model were obtained from a survey of fish distributions, fish food consumption studies, and from additional published quantitative and qualitative information on the various biotic components of the community. The model was constructed using the Ecopath approach and software. The graphically presented demersal food web spanned four trophic levels and was based primarily on consumption of detritus, zooplankton and sedimented diatoms. Zooplankton was imported into the system at trophic levels three and four through fish predation on carnivorous and herbivorous copepods and Chaoborus larvae. It is proposed that the primary consumption of copepods was by fish migrating into the pelagic zone. Chaoborus larvae in the demersal were probably consumed near the lakebed as they conducted a daily migration from the pelagic to seek refuge in the sediments. This evidence for strong benthic-pelagic coupling provided the opportunity for linking the demersal model to the existing model for the pelagic community so producing the first model for the complete ecosystem. Energy fluxes through the resulting combined model demonstrated that the primary import of biomass to the demersal system was detritus of pelagic origin (72.1%) and pelagic zooplankton (10.6%). Only 15.8% of the biomass consumed within the demersal system was of demersal origin. Lakefly production is efficiently utilised by the lake fish community, and any attempt to improve fishery production through introduction of a non-native plantivorous fish species would have a negative impact on the stability and productivity of the lake ecosystem.     

依据(代)生物体对化学品的反应预测对生态系统服务功能的影响

保护生态系统服务功能越来越多地被作为风险评估的目标,但是目前生态风险评估的终点和评估生态系统服务功能受到的潜在影响之间有很大的差距。作者提出了一个框架,将常用的生态毒理学终点与对种群和群落的影响以及生态系统的服务功能联系起来。这个框架建立在机制效应模型的长足进步上,这些模型旨在跨越多种生物组织,并解释各种生物相互作用和反馈。为了说明这一点,作者引入了2个研究案例,它们采用了已完善和已验证的机制效应模型：鱼种群的inSTREAM个体模型和AQUATOX生态系统模型。他们还展示了动态能量平衡理论可以为解释组织级毒性提供一种通用货币。他们认为,一个基于机制模型的框架,可以预测化学品暴露对生态系统服务的影响,再结合经济估值,可以为环境管理提供一种有用的方法。作者强调了使用这个框架的潜在好处以及未来工作中需要解决的挑战。
精选自Forbes, V. E., Salice, C. J., Birnir, B., Bruins, R. J.F., Calow, P., Ducrot, V., Galic, N., Garber, K., Harvey, B. C., Jager, H., Kanarek, A., Pastorok, R., Railsback, S. F., Rebarber, R. and Thorbek, P. (2017), A framework for predicting impacts on ecosystem services from (sub)organismal responses to chemicals. Environmental Toxicology and Chemistry, 36: 845–859. doi: 10.1002/etc.3720
详情请见http://onlinelibrary.wiley.com/doi/10.1002/etc.3720/full
     

Response of balanced network models to large-scale perturbation: Implications for evaluating the role of small pelagics in the Gulf of Maine

Exploring the response of an ecosystem, and subsequent tradeoffs among its biological community, to human perturbations remains a key challenge for the implementation of an ecosystem approaches to fisheries (EAF). To address this and related issues, we developed two network (or energy budget) models, Ecopath and Econetwrk, for the Gulf of Maine ecosystem. These models included 31 network “nodes” or biomass state variables across a broad range of trophic levels, with the present emphasis to particularly elucidate the role of small pelagics. After initial network balancing, various perturbation scenarios were evaluated to explore how potential changes to different fish, fisheries and lower trophic levels can affect model outputs. Categorically across all scenarios and interpretations thereof, there was minimal change at the second trophic levels and most of the “rebalancing” after a perturbation occurred via alteration of the diet matrix. Yet the model results from perturbations to a balanced energy budget fall into one of three categories. First, some model results were intuitive and in obvious agreement with established ecological and fishing theory. Second, some model results were counter-intuitive upon initial observation, seemingly contradictory to known ecological and fishing theory; but upon further examination the results were explainable given the constraints of an equilibrium energy budget. Finally, some results were counter-intuitive and difficult to reconcile with theory or further examination of equilibrium constraints. A detailed accounting of biomass flows for example scenarios explores some of the non-intuitive results more rigorously. Collectively these results imply a need to carefully track biomass flows and results of any given perturbation and to critically evaluate the conditions under which a new equilibrium is obtained for these types of models, which has implications for dynamic simulations based off of them. Given these caveats, the role of small pelagics as a prominent component of this ecosystem remains a robust conclusion. We discuss how one might use this approach in the context of further developing an EAF, recognizing that a more holistic, integrated perspective will be required as we continue to evaluate tradeoffs among marine biological communities.     

Variation in plasma levels of insulin-like growth factor-I (IGF-I) in lingcod: relationships among season,size, and gonadal steroids

The physiological response of a fish to its environment is mediated through the endocrine axis controlling growth. Therefore, growth-regulating hormone levels can serve as ecologically relevant indicators of fish growth rate. We quantified variation in plasma insulin-like growth factor-I (IGF-I) to evaluate its potential as an indicator of growth in lingcod, an economically and ecologically important bottomfish species in the northeast Pacific. An information-theoretic model selection approach was used to test the hypothesis that variation in lingcod IGF-I is related to season, body size, and gonadal steroid concentration. Season and a length × season interaction were the most important predictors of plasma IGF-I among the variables we evaluated, suggesting that season and body size should be explicitly accounted for when interpreting endocrine patterns in wild fish populations. This is among the few studies that have measured and interpreted patterns of IGF-I in wild fish and the first to describe seasonal endocrine profiles in lingcod.     

Quantifying and comparing size selectivity among Alaskan sockeye salmon fisheries

Quantifying long-term size-selective harvest patterns is necessary for understanding the potential evolutionary effects on exploited species. The comparison of fishery selection patterns on the same species subject to different gear types, in different areas, and over multi-decadal periods can reveal the factors influencing selection. In this study we quantified and compared size-selective harvest by nine Alaskan sockeye salmon (Oncorhynchus nerka) fisheries to understand overall patterns. We calculated length-specific linear selection differentials (the difference in average length of fish before vs. after fishing), which are produced by different combinations of exploitation rates and length-selectivity values, and nonlinear standardized differentials, describing disruptive selection, across all years for each fishery. Selection differentials varied among years, but larger fish were caught in 73% of years for males and 84% of years for females, leaving smaller fish to spawn. Disruptive selection was observed on female and male fish in 84% and 92% of years, respectively. Linear selection was stronger on females than males in 77% of years examined, and disruptive selection was stronger on males in 71% of years. Selection pressure was influenced by a combination of factors under and beyond management control; analyses using mixed-effects models indicated that fisheries were less size selective in years when fish were larger than average and had lower exploitation rates. The observed harvest of larger than average sockeye salmon is consistent with the hypothesis that size-selective fishing contributes to decreasing age and length at maturation trends over time, but temporal variability in selection and strong disruptive selection suggests that the overall directional pressure is weaker than is often assumed in evolutionary models.     

Bottlenose dolphins and aquaculture: interaction and site fidelity on the north-eastern coast of Sardinia (Italy)

Owing to the worldwide growth of aquaculture over the last years, new habitats have been created through the supplement of nutrients. This addition of nutrients affects the whole marine food web, resulting in predator species such as bottlenose dolphins becoming attracted to these areas. During this 5-year-long study that was carried out along the north-eastern coast of Sardinia (Italy), bottlenose dolphin’s history of exposure to aquaculture perturbations and their effects was documented. The interaction with a fish farm was assessed by studying the site fidelity, group dynamics, and seasonal and yearly occurrence. In all, 1,838 hours were spent in the field. Behavioural observations showed that the predominant activity (89 % of the time) in the fish farm was foraging (predation and depredation). The occurrence of bottlenose dolphins appeared to be related with the seasons and with the fish farm harvesting operations. Thus, the peak dolphin occurrence in the fish farm area throughout Fall coincides with the period in which they spend most of their time foraging. A relatively small community remained resident interacting with the fish farm over a long period of time. Hence, these individuals gained intimate knowledge on how to capitalize on the fish farm industry. This heterogeneity in site fidelity and residence patterns is highly relevant when coastal management initiatives are considered.     

Observations on the diurnal vertical migrations of an oceanic animal community

Diurnal changes in abundance caused by vertical migrations have been examined in populations of copepods, ostracods, euphausiids, amphipods, decapods, chaetognaths, siphonophores and fish. The animals were taken in a series of hauls made over a 24 h period with an opening-closing midwater trawl system (RMT 1+8), consisting of a net of 1 m² mouth area combined in the same frame as one of 8 m² mouth area. The samples were taken at 250 m depth in a position 30°N; 23°W on 7/8 April 1972. The specific composition of the community and the numbers of individuals changed continuously with time. The numbers of fish, decapods and chaetognaths increased at night, but those of copepods, ostracods and euphausiids decreased. More species of fish, decapods and copepods were present by night than by day, whereas the numbers of species per haul for other groups remained fairly constant. The relative abundances of groups caught by the RMT 1 have been analysed, but similar treatment of the RMT 8 samples was impossible as only 3 groups were taken from this net. Non-migrants were a minority in every group except chaetognaths. Migrant species have been put into one of 6 transitory categories according to their patterns of abundance and hence migrations. Within each category, migratory behaviour varied both inter- and intraspecifically. The patterns of abundance of many species were smooth and continuous, suggesting slow migratory cycles of small amplitude. Conversely, extensive migrants had discontinuous patterns and presumably more rapid movements. Few migrants had a steady numerical plateau between their upward and downward migrations, and most apparently moved up or down continuously. The presence of migratory species in the sampled layer depended upon the time of day or night. It is concluded that, in a vertical series of hauls, the depths of occurrence of migrants will vary with the sampling time. Further-more, a vertical series will show a species minimum migration range but not necessarily its maximum. Individuals of some species were out of phase with the migrations of their main populations. There is evidence that the distributions and migrations of some species of decapods, euphausiids, copepods and fish could be related to the distribution of underwater light. Three pairs of congeneric copepod species were both spatially and temporally segregated for at least part of their diurnal cycles. Such an orderly arrangement could provide a means of reducing competition between species. Some species, however, overtook others on their migrations and the pattern of underwater light cannot, therefore, regulate the distribution of all species in the same way.     

Habitat biodiversity as a determinant of fish community structure on coral reefs

Increased habitat diversity is often predicted to promote the diversity of animal communities because a greater variety of habitats increases the opportunities for species to specialize on different resources and coexist. Although positive correlations between the diversities of habitat and associated animals are often observed, the underlying mechanisms are only now starting to emerge, and none have been tested specifically in the marine environment. Scleractinian corals constitute the primary habitat-forming organisms on coral reefs and, as such, play an important role in structuring associated reef fish communities. Using the same field experimental design in two geographic localities differing in regional fish species composition, we tested the effects of coral species richness and composition on the diversity, abundance, and structure of the local fish community. Richness of coral species overall had a positive effect on fish species richness but had no effect on total fish abundance or evenness. At both localities, certain individual coral species supported similar levels of fish diversity and abundance as the high coral richness treatments, suggesting that particular coral species are disproportionately important in promoting high local fish diversity. Furthermore, in both localities, different microhabitats (coral species) supported very different fish communities, indicating that most reef fish species distinguish habitat at the level of coral species. Fish communities colonizing treatments of higher coral species richness represented a combination of those inhabiting the constituent coral species. These findings suggest that mechanisms underlying habitat-animal interaction in the terrestrial environment also apply to marine systems and highlight the importance of coral diversity to local fish diversity. The loss of particular key coral species is likely to have a disproportionate impact on the biodiversity of associated fish communities.     

Larval fishes in the zooplankton community of the North Pacific Central Gyre

Patterns of species structure are described for the larval fish assemblage in the North Pacific Central Gyre. About 30,000 larvae, primarily of mesopelagic fish species, were identified for 7 cruises. Samples were collected using Isaacs-Kidd plankton trawls on 6 cruises over a 4 1/2 year period; stratified samples were taken with an opening/closing bongo net on one late-summer cruise. Data on absolute and relative abundances, size ranges and summertime depth distributions of over 150 species of larvae are presented. The depth distribution and abundance of the ichthyoplankton are compared to those of the total zooplankton community. The larval assemblage is also examined with respect to the known adult mesopelagic fish assemblage. Seasonal changes in ichthyoplankton species structure occur but, within seasons, species structure is remarkably constant from year to year. Despite seasonal changes in species abundance and rank order of abundance, a constant cumulative frequency structure was found to exist in the ichthyoplankton, both between seasons and between years. The implications of this result are discussed in light of similar findings in a terrestrial community and with respect to possible mechanisms of regulation.     

Horizontal distribution patterns of presettlement reef fish: are they influenced by the proximity of reefs?

The distribution patterns of presettlement reef fish and how they were influenced by the proximity of reefs were investigated off the coast of Northland, New Zealand, from 1981–1986. We used ichthyoplankton tows and visual counts of fish. Distributions of presettlement fish of some species were influenced by the proximity of reefs, regardless of whether reefs were on the coast of the mainland or islands across the shelf. Presettlement fish of families that lay demersal eggs were most abundant near reefs: Gobiescocidae, Acanthoclinidae, Tripterygiidae, Eleotridae, and Gobiidae. The distribution of presettlement sparids, mullids (pelagic eggs), and blenniids and monacanthids (demersal eggs) was not determined in a predictable way by the proximity of reefs. High-frequency sampling over three days suggested that patches of presettlement sparids of 1 to 2 km in dimension may move quickly through a study area. High abundance of presettlement gobiescocids and tripterygiids were found in 0 to 2 m of water over rocky reefs at high and low tides. Presettlement eleotrids were associated with reefs in deeper water (3 to 20 m) and in some habitats with aggregations of mysids. The lack of general patterns of distribution for presettlement reef fish suggests that modelling patterns of drift of these fish as a single group is inappropriate; this concurs with evidence from tropical waters.