The predictability of helminth community structure in space: a comparison of fish populations from adjacent lakes

Patterns in helminth community structure can suggest that various processes are acting to shape parasite communities into organised, non-random assemblages of species. It is not clear, however, whether a pattern observed in one host population at one time would be observed again at another time, or at the same time in a different but comparable host population. Here, we test the repeatability of parasite community structure in space, and to a lesser extent time, with data on helminth parasites of two fish species, perch Perca fluviatilis and roach Rutilus rutilus, collected in different seasons from four adjacent lakes in Central Finland. Since populations of the same fish species harbour the same parasite species and were sampled in the same way, we would expect similar patterns in the structure of their helminth parasites if the same structuring processes are acting in all lakes. We found that no pairwise association between the most common helminth species were observed consistently between seasons within lakes, or among lakes during the same season. Similarly, nested subset patterns of species assembly were observed in some samples, but not consistently between seasons or among lakes. The lack of repeatability in space and between seasons shown by these analyses indicates that although helminth community structure often departs from randomness, it does not do so in a consistent and predictable manner. There may be some general, large-scale processes acting to structure helminth communities, but local or seasonal influences can often either mask their action, or play more important roles themselves.     

Nested assemblages resulting from host size variation: the case of endoparasite communities in fish hosts

Nested species subsets are a common pattern in many types of communities found in insular or fragmented habitats. Nestedness occurs in some communities of ectoparasites of fish, as does the exact opposite departure from random assembly, anti-nestedness. Here, we looked for nested and anti-nested patterns in the species composition of communities of internal parasites of 23 fish populations from two localities in Finland. We also compared various community parameters of nested and anti-nested assemblages of parasites, and determined whether nestedness may result simply from a size-related accumulation of parasite species by feeding fish hosts. Nested parasite communities were characterised by higher prevalence (proportion of infected fish) and intensities of infection (number of parasites per fish) than anti-nested communities; the two types of non-random communities did not differ with respect to parasite species richness, however. In addition, the correlation between fish size and the number of parasite species harboured by individual fish was much stronger in nested assemblages than in anti-nested ones, where it was often nil. These results were shown not to be artefacts of sampling effort or host phylogeny. They apply to both assemblages of adult and larval parasites, which were treated separately. Since species of larval parasites are extremely unlikely to interact with one another in fish hosts, the establishment of nestedness appears independent of the potential action of interspecific interactions. The species composition of these parasite communities is not determined from within the community, but rather by the extrinsic influence of host feeding rates and how they amplify differences among parasite species in probabilities of colonisation or extinction. Nested patterns occur in parasite communities whose fish hosts accumulate parasites in a predictable fashion proportional to their size, whereas anti-nested communities occur in parasite communities whose fish hosts do not, possibly because of dietary specialisation preventing them from sampling the entire pool of parasite species available locally. Thus, nestedness in parasite communities may result from processes somewhat different from those generating nested patterns in free-living communities.     

The role of environmental and spatial processes in structuring native and non‐native fish communities across thousands of lakes

Quantifying the role of spatial patterns is an important goal in ecology to further understand patterns of community composition. We quantified the relative role of environmental conditions and regional spatial patterns that could be produced by environmental filtering and dispersal limitation on fish community composition for thousands of lakes. A database was assembled on fish community composition, lake morphology, water quality, climatic conditions, and hydrological connectivity for 9885 lakes in Ontario, Canada. We utilized a variation partitioning approach in conjunction with Moran's Eigenvector Maps (MEM) and Asymmetric Eigenvector Maps (AEM) to model spatial patterns that could be produced by human‐mediated and natural modes of dispersal. Across 9885 lakes and 100 fish species, environmental factors and spatial structure explained approximately 19% of the variation in fish community composition. Examining the proportional role of spatial structure and environmental conditions revealed that as much as 90% of the explained variation in native species assemblage composition is governed by environmental conditions. Conversely on average, 67% of the explained variation in non‐native assemblage composition can be related to human‐mediated dispersal. This study highlights the importance of including spatial structure and environmental conditions when explaining patterns of community composition to better discriminate between the ecological processes that underlie biogeographical patterns of communities composed of native and non‐native fish species.     

Surface water connectivity drives richness and composition of Arctic lake fish assemblages

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The effects of predation by juvenile fish on the meiobenthic community structure in a natural pond

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Helminth communities of four commercially important fish species from Chetumal Bay, Mexico

The relative importance of ecology and evolution as factors determining species richness and composition of the helminth communities of fish is a matter of current debate. Theoretical studies use host-parasite lists, but these do not include studies on a temporal or spatial scale. Local environmental conditions and host biological characteristics are shown to influence helminth species richness and composition in four fish species (Eugerres plumieri, Hexanematichthys assimilis, Oligoplites saurus, and Scomberomorus maculatus) in Chetumal Bay, Mexico. With the exception of H. assimilis, the helminth communities had not been previously studied and possible associations between environmental and host biological characteristics as factors determining helminth species richness and composition using redundancy analysis (RDA) are described. Thirty-four helminth species are identified, with the highest number of species (19 total (mean = 6.3 +/- 2.1)) and the lowest (9 (4.0 +/- 1.0)) occurring in H. assimilis and S. maculatus, respectively. The larval nematodes Contracaecum sp. and Pseudoterranova sp. were not only the helminth species shared by all four host species but also were the most prevalent and abundant. Statistical associations between helminth community parameters and local ecological variables such as host habitat use, feeding habits, mobility, and time of residence in coastal lagoons are identified. Phylogeny is important because it clearly separates all four host species by their specialist parasites, although specific habitat and feeding habits also significantly influence the differentiation between the four fish species.     

Trade-off between number and length of remote videos for rapid assessments of reef fish assemblages

Remote underwater videos are widely employed to assess the structure and composition of reef fish assemblages but the sampling effort employed on each survey differs considerably, indicating that both the number of assessments and video length could be optimized. We searched for this optimal sampling effort in remote video samples to conduct rapid assessments of community composition and discussed the relation between number of replicates and video length, and how it impacts the method's efficiency to characterize species assemblages. Remote video recordings from tropical reefs in northeastern Brazil were used to investigate how fish species richness and composition builds across time and number of assays. Videos as short as 5 min successfully recorded species richness, requiring about five repetitions to record most species that compose 80% of the total biomass. Recording species composition required even less time in these reefs, setting a minimum of 3 min with the same five videos. By comparing the detected richness per analysed time unit, we found several shorter videos recorded for more species than a few longer videos, indicating that increasing the sampling coverage in the reef area might be better than just extending the video length for rapid assessments.     

A general test of the interactive-isolationist continuum in gastrointestinal parasite communities of fish

Parasite communities are generally believed to lie somewhere along the interactive-to-isolationist continuum, i.e. from rich assemblages of species with high colonisation rates in which interspecific interactions play an important structuring role, to species-poor assemblages where interactions are unlikely. This framework has become one of the paradigms of parasite community ecology. There is, however, no objective way of ranking a set of parasite communities in terms of the extent of interactivity among their constituent species. Here, we propose a simple index of interactivity based on the general likelihood of species co-occurrence, and thus on the potential for interactions, and we apply it to component communities of gastrointestinal helminth parasites from 37 species of marine fish hosts. The index essentially collapses several features of parasite communities thought to influence the degree of interactivity into a single number independent of the number of hosts examined or the total number of species in a component community. The range of values obtained here suggests that the potential interactivity in helminth communities of fish covers almost the full spectrum of possibilities, i.e. from isolationist to highly interactive communities. Although derived from presence/absence data only, the index correlates relatively strongly with the total parasite abundance per host, as well as the total prevalence of infection and the mean infracommunity richness. In other words, it captures properties of the community that influence interactivity. The use of the index in comparative studies may help in determining whether interactive helminth communities are, as widely believed, more common in endothermic vertebrate hosts than in fish hosts.     

Mass coral bleaching causes biotic homogenization of reef fish assemblages

Global climate change is altering community composition across many ecosystems due to nonrandom species turnover, typically characterized by the loss of specialist species and increasing similarity of biological communities across spatial scales. As anthropogenic disturbances continue to alter species composition globally, there is a growing need to identify how species responses influence the establishment of distinct assemblages, such that management actions may be appropriately assigned. Here, we use trait‐based analyses to compare temporal changes in five complementary indices of reef fish assemblage structure among six taxonomically distinct coral reef habitats exposed to a system‐wide thermal stress event. Our results revealed increased taxonomic and functional similarity of previously distinct reef fish assemblages following mass coral bleaching, with changes characterized by subtle, but significant, shifts toward predominance of small‐bodied, algal‐farming habitat generalists. Furthermore, while the taxonomic or functional richness of fish assemblages did not change across all habitats, an increase in functional originality indicated an overall loss of functional redundancy. We also found that prebleaching coral composition better predicted changes in fish assemblage structure than the magnitude of coral loss. These results emphasize how measures of alpha diversity can mask important changes in the structure and functioning of ecosystems as assemblages reorganize. Our findings also highlight the role of coral species composition in structuring communities and influencing the diversity of responses of reef fishes to disturbance. As new coral species configurations emerge, their desirability will hinge upon the composition of associated species and their capacity to maintain key ecological processes in spite of ongoing disturbances.     

Homogeneity of parasite assemblages of Dules auriga (Serranidae) in hydrographically heterogeneous sites

Parasite assemblages of Dules auriga are described for the first time from samples caught during research cruises in two localities of the Argentine–Uruguayan Common Fishing Zone (AUCFZ) and are compared with four additional samples collected by commercial catches from the same region. A total of 178 fish were examined and 13 parasite species were found. This showed low species richness, a condition observed in some other small benthic species at a low trophic level. The composition of the parasite fauna was similar to those found on other host species in the region, sharing the same set of dominant species with other sympatric fishes, which have been identified as both typical and as indicators of this ecoregion: Grillotia carvajalregorum, Corynosoma australe and Hysterothylacium sp. Multivariate similarity analyses at the infracommunity and the component community levels indicated that the two samples caught at different latitudes in the AUCFZ display almost identical parasite assemblages. This repeatability in assemblage structure was also observed across samples from commercial catches. The homogeneity of the parasite assemblages is considered to be an intrinsic property of fish inhabiting the AUCFZ, independent of their ecology and trophic level.     

Artificial waterway design affects fish assemblages in urban estuaries

Fishes were collected from residential canal estates leading directly off natural estuaries and artificial lakes with control tidal exchange in south-east Queensland, Australia, to test the model that the difference in artificial waterway design affects fish assemblages. A total of 17 779 fish representing 52 species was caught, including 23 species of economic importance (45% of the catch). Total fish abundance and species richness differed little among sites within or between the two artificial habitats (canals and lakes) in either of the seasons sampled (winter and spring). Multivariate analysis showed, however, that assemblages differed among sites within the same artificial habitat. The differences were best explained by the distance sites were from open water, while salinity, water temperature and dissolved oxygen explained little of the variability. Most species were found in canals and lakes, but there were enough differences in composition between the habitats to detect a difference in both seasons (significant ANOSIM tests). Salinity was lower in lakes because of the tidal restrictions, and while this was only weakly correlated with differences in fish assemblages, it had the most explanatory power of any environmental variable. New recruits arrived later in lakes than canals, perhaps because of the barriers to tidal flow. A survey the following year showed that differences among individual lakes were consistent through time, offering insights into the influence of different tidal barriers on fish assemblages. The design change from canals to lakes has a minor influence on fish assemblages and alters the timing of recruitment.     

Ecological impact of introduced fish in high altitude lakes: a case of study from the European Alps

Fish introduction is a major threat to alpine lake biota leading to the loss of native species and to the degeneration of natural food-webs. This study provides an extensive investigation on the impact of the introduced fish Salvelinus fontinalis on the native communities of alpine lakes in the Gran Paradiso National Park. We compared the macroinvertebrate and zooplankton communities of six stocked and nine fishless lakes with a repeated sampling approach during the summers 2006–2009. The impact of fish presence on alpine lake fauna is often mediated by the strong seasonality governing these ecosystems, and it dramatically affects the faunal assemblage of littoral macroinvertebrates and the size, structure, and composition of the pelagic zooplankton community with a strong selective predation of the more visible taxa. Direct ecological impacts include a decrease or extinction of non-burrower macroinvertebrates and of large zooplankton species, while small zooplankton species and burrower macroinvertebrates were indirectly advantaged by fish presence. Due to the existence of a compensation between rotifers and crustaceans, fish presence does not affect total zooplankton biomass and diversity even if fish are a factor of ecological exclusion for large crustaceans. These compensatory mechanisms are a key process surrounding the impact of introduced fish in alpine lakes.     

Spatial predictors of fish species composition in European lowland lakes

Composition of animal communities can be shaped by both local and regional processes. Among others, dispersal of organisms links local and regional patterns and determines the similarity of communities at increasing spatial distances. Unique and shared spatial and environmental contributions to fish community composition were calculated for watercourse distances between 49 hydrologically connected lakes in the German lowland area. Variation partitioning indicated a dominant unique effect of spatial predictors on fish community composition, whereas the effects of lake morphometry and productivity were weaker. The spatial effect was attributable to an uneven occurrence of small, littoral fish species found even at the small spatial extension covered here (maximum spatial distance ?550 km). Distance decay of community similarity was moderate, but significant, if all 31 fish species were considered, but the slope of the decay function became steeper if only 11 small‐sized, primarily littoral species were included. These results suggest that fish in European lowland lakes can be considered a metacommunity with limited dispersal along watercourse connections in particular for small‐sized species. The analysis supports that for an appropriate evaluation of spatial effects on fish community similarity, reliable estimates of local richness are required which include in particular also rare, small‐sized species occurring primarily in littoral areas. Furthermore, watercourse distance is a more reliable approximation than Euclidean distance to the real spatial dimension of fish dispersal.     

Non-native fishes and native species diversity in freshwater fish assemblages across the United States

The proliferation of non-native species in North American freshwater ecosystems is considered a primary threat to the integrity of native community structure. However, a general understanding of consistent and predictable impacts of non-native species on native freshwater diversity is limited, in part, because of a lack of broad-scale studies including data from numerous localities across multiple drainages. This study uses data from 751 localities collected during the United States Geological Survey (USGS) National Water Quality Assessment (NAWQA) program to examine the influence of non-native fish species on native freshwater fish assemblages across the United States. In general, no significant differences in native fish richness and diversity measures were detected between sites with only native species and sites containing non-native species. However, at sites with non-native species, the number of non-native species present was negatively correlated with native species richness and Shannon diversity and positively correlated with native evenness. Non-native piscivores were negatively correlated with native species richness and Shannon diversity and positively correlated with native evenness. Native piscivores were positively correlated with native richness and diversity and negatively correlated with native evenness at sites with only native species. Our results suggest that from a superficial perspective, native species richness and diversity are not different among sites with and without non-native species. However, when patterns of native species richness and diversity are examined at sites containing non-native species, correlations between non-native and native species richness and diversity imply the expected negative effect of invasive taxa. Additionally, non-native piscivores appear to have a significant negative effect on native taxa and possibly represent a novel selective force on naive native prey.     

Parasite community structure within and across host populations of a marine pelagic fish: how repeatable is it?

The geographical variation in parasite community structure among populations of the same host species remains one of the least understood aspects of parasite community ecology. Why are parasite communities clearly structured in some host populations, and randomly assembled in others? Here, we address this fundamental question using data on the metazoan parasite communities of different host size-classes of four distinct populations of a small pelagic fish, the Argentine anchovy, Engraulis anchoita, from the South West Atlantic. Within each fish sample, fish length was correlated with both the total intensity of parasites and species richness among infracommunities. More importantly, average fish length correlated with mean infracommunity richness and mean total intensity across the fish samples, indicating that the characteristics of parasite assemblages in a fish population are strongly influenced by the size of its fish in relation to those in other populations. Nested subset patterns were observed in about half of the fish samples. This means that the presence or absence of parasite species among fish individuals is often not random; however, no repeatability of nestedness among component communities was observed. Average fish length did not influence directly the likelihood that a parasite assemblage was significantly nested. However, variables influenced by average fish length, namely mean infracommunity richness and mean total intensity, determine the probability that a nested hierarchy will be observed; host size may thus indirectly affect parasite community structure either itself or via its influence on host movement and feeding patterns. To some extent, this apparent link may be due to the sensitivity of nestedness analyses to the proportion of presence in a presence/absence matrix; this in itself is a biological feature of the parasite community, however, which is associated with mean host length.     

Community concordance between the fish and aquatic birds of lakes in northern Alberta, Canada: the relative importance of environmental and biotic factors

1. Community concordance measures the degree to which patterns in community structure in a set of sites are similar between two different taxonomic groups. Although seldom incorporated into studies of lake ecosystems, aquatic birds can be influenced by the same environmental features of lakes which affect fish and invertebrates, and can interact with these organisms directly as predators, competitors or prey. We surveyed lakes in north-central Alberta, Canada, to determine if co-occurring fish and aquatic bird assemblages displayed concordance, and assessed the relative importance of environmental and biotic factors in contributing to observed concordance.
2. In 41 lakes (3–305 ha), we encountered seven species of fish and thirty-one avian taxa which subsequently were used in multivariate analyses. Fish assemblages dominated by large piscivores were in large deep lakes, whereas fishless lakes and lakes with only small-bodied fish were small and shallow, and thus, prone to winter hypoxia. Bird assemblages displayed three general patterns: (a) small shallow lakes supported a 'core' of widespread species (between three and eight species per lake); (b) large, deep lakes supported more species (between 11 and 16), including large, aerially foraging piscivores; and (c) large, shallow lakes supported the most species (between 15 and 23), including many ducks.
3. Randomization tests of matrix concordance and Mantel tests both showed that fish and bird assemblages were significantly concordant. Concordance reflected the fact that both groups were strongly affected by the same key environmental factors, principally lake size and maximum depth, and to a lesser extent, productivity and geographic isolation. Direct interactions between birds and fish, such as predation and competition, appeared to play much smaller roles in shaping the two assemblages.     

Spatial variation in relative abundance of a widespread, numerically dominant fish species and its effect on fish assemblage structure

Collections of fish assemblages from streams in the midwestern United States were used to examine assemblage-level effects of spatial variation in relative abundance of the red shiner, Cyprinella lutrensis, a widespread and highly abundant minnow species. This species has been widely introduced outside its native range and is suspected to have impacted local assemblages where it has become established. Given its overall dominance of midwest fish assemblages, and its suspected impact on assemblage structure, we asked if structure of the residual fish assemblages (red shiners excluded) was a function of the relative abundance of red shiners throughout the native range of C. lutrensis in the USA. Although red shiner ranked first in abundance in half of the assemblages and numerically dominated 28% of the assemblages, red shiner relative abundance in an assemblage had no detectable effect on richness, diversity, evenness, or complexity of other (residual) species in the assemblage. Relative abundance of red shiners did have a positive effect on the abundance of benthic minnows in the residual assemblage, but not on water column minnows that are ecologically most like red shiners. Environmental factors did not explain a significant amount of the variation in relative abundance of red shiners, but did explain some variation in residual assemblage structure. Although widespread and numerically dominant at many localities, red shiners do not appear to have a strong impact on local fish assemblage structure within their native range. This is in sharp contrast to the reported negative effects of red shiners on fish assemblages where they have been introduced outside their native range.     

Ecological determinants of parasite acquisition by exotic fish species

Disease‐mediated threats posed by exotic species to native counterparts are not limited to introduced parasites alone, since exotic hosts frequently acquire native parasites with possible consequences for infection patterns in native hosts. Several biological and geographical factors are thought to explain both the richness of parasites in native hosts, and the invasion success of free‐living exotic species. However, the determinants of native parasite acquisition by exotic hosts remain unknown. Here, we investigated native parasite communities of exotic freshwater fish to determine which traits influence acquisition of native parasites by exotic hosts. Model selection suggested that five factors (total body length, time since introduction, phylogenetic relatedness to the native fish fauna, trophic level and native fish species richness) may be linked to native parasite acquisition by exotic fish, but 95% confidence intervals of coefficient estimates indicated these explained little of the variance in parasite richness. Based on R²‐values, weak positive relationships may exist only between the number of parasites acquired and either host size or time since introduction. Whilst our results suggest that factors influencing parasite richness in native host communities may be less important for exotic species, it seems that analyses of general ecological factors currently fail to adequately incorporate the physiological and immunological complexity of whether a given animal species will become a host for a new parasite.     

Effects of macrophyte complexity and hydrometric level on fish assemblages in a Neotropical floodplain

Habitat heterogeneity provided by aquatic macrophytes and water level variations (flood pulse) are essential factors in structuring fish assemblages. This study aimed to describe the fish species that prefers macrophytes covered areas and to evaluate how macrophytes complexities and a flood pulse influence the structure of fish assemblages and selected attributes (viz. fish species density, species richness and evenness). Sampling was performed with seining nets in five floodplain lakes associated with the Baía River, before (November to December 2011) and after (February to July 2012) a flood, considering different degrees of macrophyte complexity (Absent, intermediate, and high). A total of 48 fish species was recorded, with Characiformes the most dominant. Eight species were indicators of high complexities (seven before the flood and only one after). Significant differences among the different degrees of macrophyte complexity and before and after the flood were found for assemblage structure, species density and richness. Fish assemblage attributes were high in higher habitat heterogeneity provided by macrophytes, but all before the flood. Nevertheless, macrophyte stands with high and intermediate complexity were less affected by the flood, suggesting that the structure propitiated by macrophytes favors the persistence of the fish assemblage in floodplain lakes. Therefore, any action towards conservation of fish assemblages in macrophytes should consider dam operation upstream, to ensure seasonality of flood pulses.     

Valley‐scale hydrogeomorphology drives river fish assemblage variation in Mongolia

River hydrogeomorphology is a major driver shaping biodiversity and community composition. Here, we examine how hydrogeomorphic heterogeneity expressed by Functional Process Zones (FPZs) in river networks is associated with fish assemblage variation. We examined this association in two distinct ecoregions in Mongolia expected to display different gradients of river network hydrogeomorphic heterogeneity. We delineated FPZs by extracting valley‐scale hydrogeomorphic variables at 10 km sample intervals in forest steppe (FS) and in grassland (G) river networks. We sampled fish assemblages and examined variation associated with changes in gradients of hydrogeomorphology as expressed by the FPZs. Thus, we examined assemblage variation as patterns of occurrence‐ and abundance‐based beta diversities for the taxonomic composition of assemblages and as functional beta diversity. Overall, we delineated 5 and 6 FPZs in river networks of the FS and G, respectively. Eight fish species were found in the FS river network and seventeen in the G, four of them common to both ecoregions. Functional richness was correspondingly higher in the G river network. Variation in the taxonomic composition of assemblages was driven by species turnover and was only significant in the G river network. Abundance‐based taxonomic variation was significant in river networks of both ecoregions, while the functional beta diversity results were inconclusive. We show that valley‐scale hydrogeomorphology is a significant driver of variation in fish assemblages at a macrosystem scale. Both changes in the composition of fish assemblages and the carrying capacity of the river network were driven by valley‐scale hydrogeomorphic variables. River network hydrogeomorphology as accounted for in the study has, therefore, the potential to inform macrosystem scale community ecology research and conservation efforts.