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1.
An aquatic biological survey was conducted in 1979–1980 to determine the effects of drainage from an active coal strip-mine on Trout Creek, in northwest Colorado, U.S.A. Sampling was conducted over four seasons at four stations for periphyton, benthic invertebrates and fish. Periphyton in Trout Creek changed in the relative abundance of algae divisions in no apparent relation to mining. Diatoms were the predominant division at all sites. Golden-brown algae were abundant in spring at the stations upstream and adjacent to the mine. Blue-green algae were relatively important at stations upstream and downstream of the mine in winter. Benthic invertebrates exhibited a progressive increase in density, biomass and number of taxa from the upstream station to the downstream station. Shannon-Wiener diversity index for bethic invertebrates decreased slightly downstream of mine drainage but remained indicative of a clean water community. Aquatic insects (especially Trichoptera) were the predominant invertebrates at all stations. Analysis of functional groups of benthic invertebrates revealed increased importance of collector species at the lower sites while shredders were most important upstream of the mine. Unlike the invertebrates, fish exhibited slightly lower biomass at the station adjacent to the mine. The decrease was due to fewer salmonids. However, salmonid density and biomass increased substantially at the station just downstream of the mine. Non-game species (suckers and minnows) increased in numbers downstream and were most abundant at the lowest station. This coal strip-mine had little discernable adverse effects on the periphyton and invertebrates of Trout Creek. Fish populations did not appear to be significantly affected by the mine. Apparently, the presence of settling ponds and a buffer zone of unmined land between the mine and the stream helped to minimize adverse effects. 相似文献
2.
We examined the metazoan parasite fauna of the bigeye flounder, Hippoglossina macrops, in a latitudinal gradient of the southeastern Pacific (ca. 25 degrees S-33 degrees S) to assess whether their parasites show latitudinal and/or biogeographical patterns, and to determine if these patterns agree well with those observed for free-living organisms. In total, 331 fish from 6 localities were analyzed. Eighteen parasite species, including 5 ecto- and 13 endoparasites, were found in the bigeye flounder. Neoheterobothrium chilensis, Floridosentis sp., and Corynosoma australe were the most prevalent parasite species. Ecto- and endoparasites of H. macrops showed different latitudinal patterns. Only endoparasite species show a distributional pattern concordant with biogeographic areas recognized for free-living organisms; this finding was supported by cluster analyses showing 2 major divisions. The first joined the most northern localities (25 degrees S-26 degrees S), and the second consisted of 2 subgroups: (1) 28 degrees S-30 degrees S, and (2) 31 degrees S-32 degrees S. A multivariate analysis of infracommunities showed significant differences in the parasitic load of H. macrops from different latitudes. The latitudinal differences in the prevalence and abundance of the parasites might be explained by differing oceanographic conditions in water masses. These physical conditions could affect the dispersal ability of the infective stages of ecto-parasites, and produce zoogeographical breaks that could affect the distribution of intermediate hosts (invertebrate and vertebrate prey), subsequently affecting the transmission of endoparasites. 相似文献
3.
Effects of cooling water discharge on the structure and dynamics of epilithic algal communities in the northern Baltic 总被引:1,自引:0,他引:1
The Forsmark Biotest Basin is a shallow coastal ecosystem that receives brackish cooling-water discharge from a nuclear power
plant. The effects of the discharge on epilithic algal communities were investigated by analysing samples taken every third
week throughout one year at 11 sites differentially affected by temperature and/or flow rate enhancement. Community variation
was summarized in a canonical correspondence analysis (CCA) of species abundances as a function of site and date. The temperature
increase favoured blue-green algae at the expense of red and brown algae. Blue-green algae were however abundant in summer
in stagnant water, whether heated or not, and some red and brown algae became abundant in winter in heated sites with flowing
water. Green algae and diatoms increased in biomass in the heated sites, but not in relative cover-abundance. The absence
of ice and snow cover at sites with heated and/or flowing water caused autumn species to persist into winter, because of the
higher light intensity (compared with natural conditions) and the absence of the mechanical abrasion by ice. The thermal discharge
lowered species diversity (Shannon-Weaver index) both in summer and winter at sites with flowing water, but not at sites with
quiescent or stagnant water. CCA showed alternate periods of stability and rapid change within the seasonal cycle. Individual
species were placed according to their optimum; red and brown algae in winter/spring, green algae in spring/summer, blue-green
algae in summer, and diatoms at various times. Exceptions to this pattern were species endo- or epiphytic on species of a
different group. Analysis of the effects of temperature, flow rate and ice cover on the seasonal pattern of particular species
showed that different species respond in individualistic ways to different combinations of these environmental variables. 相似文献
4.
The distribution of parasites among hosts is often characterised by a high degree of heterogeneity with a small number of hosts harbouring the majority of parasites. Such patterns of aggregation have been linked to variation in host exposure and susceptibility as well as parasite traits and environmental factors. Host exposure and susceptibility may differ with sexes, reproductive effort and group size. Furthermore, environmental factors may affect both the host and parasite directly and contribute to temporal heterogeneities in parasite loads. We investigated the contributions of host and parasite traits as well as season on parasite loads in highveld mole-rats (Cryptomys hottentotus pretoriae). This cooperative breeder exhibits a reproductive division of labour and animals live in colonies of varying sizes that procreate seasonally. Mole-rats were parasitised by lice, mites, cestodes and nematodes with mites (Androlaelaps sp.) and cestodes (Mathevotaenia sp.) being the dominant ecto- and endoparasites, respectively. Sex and reproductive status contributed little to the observed parasite prevalence and abundances possibly as a result of the shared burrow system. Clear seasonal patterns of parasite prevalence and abundance emerged with peaks in summer for mites and in winter for cestodes. Group size correlated negatively with mite abundance while it had no effect on cestode burdens and group membership affected infestation with both parasites. We propose that the mode of transmission as well as social factors constrain parasite propagation generating parasite patterns deviating from those commonly predicted. 相似文献
5.
The role of ecological and phylogenetic processes is fundamental to understanding how parasite communities are structured. However, for coral reef fishes, such information is almost nonexistent. In this study, we analyzed the structure of the parasite communities based on composition, richness, abundance, and biovolume of ecto- and endoparasites of 14 wrasse species (Labridae) from Lizard Island, Great Barrier Reef, Australia. We determine whether the structure of the parasite communities from these fishes was related to ecological characteristics (body size, abundance, swimming ability, and diet) and/or the phylogenetic relatedness of the hosts. We examined 264 fishes from which almost 37,000 individual parasites and 98 parasite categories (types and species) were recorded. Gnathiid and cestode larvae were the most prevalent and abundant parasites in most fishes. Mean richness, abundance, and biovolume of ectoparasites per fish species were positively correlated with host body size only after controlling for the host phylogeny, whereas no such correlation was found for endoparasites with any host variable. Because most ectoparasites have direct transmission, one possible explanation for this pattern is that increased space (host body size) may increase the colonization and recruitment of ectoparasites. However, endoparasites generally have indirect transmission that can be affected by many other variables, such as number of prey infected and rate of parasite transmission. 相似文献
6.
Robert Poulin 《Ecography》1999,22(3):246-250
Across species, abundance usually correlates negatively with body size. This intuitive pattern may result from size-dependent resource requirements in habitats where only finite amounts of resources are available. Among parasite species, it is possible that some resource limitations arc less severe than for free-living animals although this may depend on the type of parasites. The interspecific relationship between body size and abundance (measured as prevalence and intensity of infection) among parasites was tested in two groups of parasites. Among helminth endoparasites of fish, parasite body size correlated positively with prevalence and negatively with intensity of infection. Among copepod ectoparasites of fish, body size correlated positively with both prevalence and intensity. These trends were observed after controlling for the confounding influences of phylogeny and sampling effort. These contrasting patterns may result from the more intense link between body size and intensity-dependent regulation in endoparasites than in ectoparasites. The results of this comparative analysis suggest that parasite body size could be an important factor determining aspects of parasite abundance and distribution, including aggregation. 相似文献
7.
Cludio Estêvo Farias da Cruz Sandra Mrcia Tietz Marques Inês Andretta 《Zoo biology》2019,38(4):384-388
To monitor and evaluate potential risks to birds’ health, invertebrate species that have been used as live food items had their body contents searched for endoparasites. The contents of approximately 10,000 invertebrates were analyzed. A principal component analysis was performed to study the relationship between the presence/absence of endoparasites and the characteristics of the invertebrates. In most of them, including the species preferred by birds such as caterpillars, waxworms, mealworms, most grasshoppers, and spiders, no organism was identified. Such findings suggest a low potential for parasite transmission associated with its consumption by birds. Although they had unknown or even unlikely implications for the birds’ health, gregarines, oxyurides Leidynema sp., and digenetic trematodes Monolecithotrema sp. were found in samples from woodlice, cockroaches, and centipedes, respectively. The only avian parasites observed in this study were Heterakis gallinarum in samples from earthworms and Acuaria spiralis from woodlice. Suggestively, soil invertebrates showed a higher prevalence of endoparasites and may represent a higher potential risk in comparison to the other categories of invertebrates sampled herein. Detritivory and collected origin were also explanatory variables related to the presence of endoparasites in the current study. 相似文献
8.
Martina Dávidová Radim Blažek Teodora Trichkova Emmanuil Koutrakis Özcan Gaygusuz Ertan Ercan Markéta Ondračková 《Aquatic Ecology》2011,45(3):377-387
In aquatic ecosystems, fish play a key role in parasite accumulation and transmission to predacious animals. In the present
study, realized on seven populations of a small cyprinid fish species, the European bitterling Rhodeus amarus, we investigated (1) the role of the European bitterling as a potential intermediate or paratenic host, (2) the ability of
the fish to accumulate parasites with similar final host group, and (3) its significance as a potential source of parasite
infection in the ecosystem in respect to habitat characteristics. A total of 36 parasite species were recorded; 31 species
(90% of all parasite specimens) were classified as endoparasites. Most of the endoparasites were found in the larval life
stage, using bitterling as an intermediate or paratenic host. In particular, parasite community structure showed significantly
higher proportions of allogenic parasites in comparison with autogenic. The supposed co-occurrence of parasite species with
identical final host groups showed only a weak association. The adjacent reservoir areas were a significant determinant of
both the total and infracommunity parasite species richness and for the mean parasite abundance. No relationship between the
distance of sampling site from the adjacent reservoir and parasite community characteristics was found. As a small-sized fish
with a wide distribution range and high local abundances, the European bitterling can represent a natural prey for a wide
range of piscivorous predators. Due to its susceptibility to the number of larval endoparasites, this fish species may therefore
fulfill the role as important transmitter of parasites to their final hosts. 相似文献
9.
Eelgrass,Zostera marina,as essential fish habitat for young‐of‐the‐year winter flounder,Pseudopleuronectes americanus (Walbaum, 1792) in Maine estuaries
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M. A. Lazzari 《Zeitschrift fur angewandte Ichthyologie》2015,31(3):459-465
Distribution and density by habitat for age‐0, young‐of‐the‐year (YOY) winter flounder, Pseudopleuronectes americanus (Walbaum, 1792), were compared for two Maine estuaries to help define essential fish habitat for this life history stage. Two estuaries (Weskeag River and Penobscot Bay) along Mid‐coast Maine were sampled monthly with daytime 1.0 m2 fixed‐frame throw traps around neap low tide, May–December over two consecutive years (2003–2004). Both eelgrass and adjacent sand/mud (20–60 cm deep) were randomly sampled with equal effort (4–12 samples per month) at two sites in both the Weskeag River and Penobscot Bay. Significantly higher densities of YOY winter flounder (2–9 cm TL) occurred in eelgrass relative to sand/mud. Density increased significantly in both habitats in 2004, and was higher in Penobscot Bay relative to the Weskeag River. YOY densities compared by eelgrass coverage within throw traps were found to be significantly higher in eelgrass that exceeded 30% coverage when compared with adjacent sand/mud areas and eelgrass coverage of 10–20%. YOY occurred in all months sampled (May–December); no density differences existed by month. These results indicate that very shallow (<0.6 m) eelgrass habitat is of key importance to YOY winter flounder in Maine estuaries and should be viewed as essential fish habitat (EFH) for this species and life stage. 相似文献
10.
Despite the fact that most host populations are infected by a community of different parasite species, the majority of empirical studies have focused on the interaction between the host and a single parasite species. Here, we explore the hypothesis that host population dynamics are affected both by single parasite species and by the whole parasite community. We monitored population density and breeding productivity of two populations of willow ptarmigan ( Lagopus lagopus ) in northern Norway for 8 and 11 years, respectively, and sampled eukaryotic endoparasites. We found that increasing abundances of the cestode Hymenolepis microps was associated with increased breeding mortality and reduced annual growth rate of the host population in both areas, and reduced host body mass and body condition in the area where such data were available. In one of the areas, the abundance of the nematode Trichostrongylus tenuis was associated with reductions in host body mass, body condition and breeding mortality and the filaroid nematode Splendidofilaria papillocerca was negatively related to host population growth rates. The parasite community was also negatively related to host fitness parameters, suggesting an additional community effect on host body mass and breeding mortality, although none of the parasites had a significant impact on their own. The prevalence of parasites with very different taxonomical origins tended to covary within years, suggesting that variability in the parasite community was not random, but governed by changes in host susceptibility or environmental conditions that affected exposure to parasites in general. Other variables including climate, plant production and rodent densities were not associated with the recorded demographic changes in the host population. 相似文献
11.
A. J. Lymbery M. Hassan D. L. Morgan S. J. Beatty R. G. Doupé 《Journal of fish biology》2010,76(7):1770-1785
In this study, 1429 fishes of 18 different species (12 native and six exotic) were sampled from 29 localities to compare the levels of parasitism between native and exotic fish species and to examine the relationship between environmental degradation and parasite diversity. Forty‐four putative species of parasites were found and most of these appear to be native parasites, which have not previously been described. Two parasite species, Lernaea cyprinacea and Ligula intestinalis, are probably introduced. Both were found on or in a range of native fish species, where they may cause severe disease. Levels of parasitism and parasite diversity were significantly greater in native fishes than in exotic species, and this may contribute to an enhanced demographic performance and competitive ability in invading exotics. Levels of parasitism and parasite diversity in native fishes were negatively related to habitat disturbance, in particular to a suite of factors that indicate increased human use of the river and surrounding environment. This was due principally to the absence in more disturbed habitats of a number of species of endoparasites with complex life cycles, involving transmission between different host species. 相似文献
12.
Surfaces immersed in the marine environment are under intense fouling pressure by a number of invertebrates and algae. The regulation of this fouling can often be attributed to the bacterial biofilm that quickly develops on the surface of any available substratum in the ocean. The bacterial community composition on the surface of the green alga Dictyosphaeria ocellata was investigated and compared to those found on two other green algae, Batophora oerstedii and Cladophoropsis macromeres, and on a reference surface from three sites along the Florida Keys. Although the bacterial community composition of D. ocellata was not consistent across the sites, it was significantly different from the other algae and the reference surface at two of the three sites tested. Methanol extracts of D. ocellata significantly affected the abundance of bacteria and composition of the bacterial community on Phytagel? plates when compared to solvent controls, suggesting that the alga regulates the bacterial community by producing active metabolites. 相似文献
13.
Aquatic predators and habitat permanence can jointly affect benthic invertebrate biomass and community composition. In 2006
I sampled fish and invertebrates in ten ponds embedded in a seasonal wetland before and after a natural drought. Drought reduced
fish biomass and density leaving some ponds in a fishless condition when rains returned in July. In July, large aquatic insects
and crayfish colonized and reproduced in the ponds, but did not colonize all of the ponds equally. Using measurements of fish
abundance and other environmental parameters of the ponds, I conducted linear regression analyses to explore potential drivers
of variable invertebrate biomass in July. Fish biomass had a negative effect on invertebrate biomass and it explained more
of the variation in total invertebrate biomass and total non-shrimp biomass than fish abundance (number of fish caught). Dissolved
oxygen and pond depth were both correlated with fish biomass, but were poorer predictors of invertebrate biomass. Ponds with
few or no fish had 20× greater total biomass and 200× more non-shrimp biomass than ponds with high fish biomass. Shrimp dominated
the invertebrate composition, and were only found in the two deepest ponds with the highest fish biomass; predatory insects
and crayfish dominated the other eight ponds. When taxa were analyzed separately, fish biomass explained a large portion of
the variation for predatory insects (Coleoptera, Hemiptera, and Odonata) and crayfish (Procambarus alleni), but dissolved oxygen was the best predictor of larval stratiomyid (order Diptera) biomass. These results are generally
consistent with studies demonstrating negative effects of fish on large predatory invertebrates, but also suggest that more
severe local droughts can seasonally enhance insect and crayfish populations by generating fishless or nearly fishless conditions.
Handling editor: J. Trexler 相似文献
14.
Francisco Gerson Araújo Benjamin Carvalho Teixeira Pinto Tatiana Pires Teixeira 《Hydrobiologia》2009,618(1):89-107
This study aimed to evaluate environmental influences on fish distribution and to assess the extent to which concepts in river
ecology accommodate levels of spatio-temporal heterogeneity of fish assemblages in a 1,080-km long tropical river. A total
of 25 sites were sampled between November 2002 and March 2003 in two seasons (summer/wet versus winter/dry). A thermal gradient
separating the upper reaches from the lower reaches was detected. The middle-upper reaches showed higher conductivity and
lower dissolved oxygen and pH levels compared with the other reaches. Although some significant associations were found between
some fish abundance and environmental variables, the most abundant species (Tilapia rendalli, Geophagus brasiliensis, and Oligosarcus hepsetus) occurred in most sites and under most environmental conditions. Fish community structure varied more in space (longitudinal)
than through time (seasonal). The community in the lower reach species was more diverse in comparison with the other reaches.
Differences in the fish assemblage structure among the longitudinal river sections appear to have been influenced by the effects
of damming, and seem to be partially consistent with the Serial Discontinuity Concept, which views dams as discontinuities
within the river continuum. Only the lower river reach showed seasonal differences in the fish community structure, attributable
to the influence of flooding. Management plans and biodiversity conservation will benefit by considering the effects of dam
disruption and flood increased connectivity to the lotic systems.
Handling editor: J. Trexler 相似文献
15.
Effects of livestock grazing on aboveground insect communities in semi-arid grasslands of southeastern Arizona 总被引:1,自引:0,他引:1
Sandra J. Debano 《Biodiversity and Conservation》2006,15(8):2547-2564
Despite the importance of invertebrates in grassland ecosystems, few studies have examined how grassland invertebrates have
been impacted by disturbances in the southwestern United States. These grasslands may be particularly sensitive to one common
disturbance, livestock grazing, because they have not recently evolved in the presence of large herds of bison, an important
mammalian herbivore. This study examined how livestock grazing influenced vegetation-associated insect communities in southeastern
Arizona. Insect abundance, richness, diversity, community composition, and key environmental variables were compared between
sites on active cattle ranches and sites on a 3160 ha sanctuary that has not been grazed by cattle for over 25 years. Vegetation-associated
insect communities were found to be sensitive to livestock grazing. Overall abundance of these insects was lower on grazed
grasslands, and certain insect orders appeared to be negatively affected by livestock grazing; beetles were less rich, flies
were less diverse, and Hymenoptera were less rich and diverse on grazed sites. Conversely, Hemiptera were more diverse on
grazed sites. Species composition of vegetation-associated insect communities also differed and was significantly correlated
with percent vegetation cover and number of shrubs. Insect species responsible for these differences were taxonomically diverse,
and included herbivores and predators/parasites. When compared to other studies conducted in areas of the United States that
fall within the historic range of bison, this study suggests that invertebrates in areas outside this range may be more sensitive
to grazing pressure. 相似文献
16.
M. J. Kennard B. J. Pusey A. H. Arthington B. D. Harch S. J. Mackay 《Hydrobiologia》2006,572(1):33-57
Multivariate predictive models are widely used tools for assessment of aquatic ecosystem health and models have been successfully
developed for the prediction and assessment of aquatic macroinvertebrates, diatoms, local stream habitat features and fish.
We evaluated the ability of a modelling method based on the River InVertebrate Prediction and Classification System (RIVPACS)
to accurately predict freshwater fish assemblage composition and assess aquatic ecosystem health in rivers and streams of
south-eastern Queensland, Australia. The predictive model was developed, validated and tested in a region of comparatively
high environmental variability due to the unpredictable nature of rainfall and river discharge. The model was concluded to
provide sufficiently accurate and precise predictions of species composition and was sensitive enough to distinguish test
sites impacted by several common types of human disturbance (particularly impacts associated with catchment land use and associated
local riparian, in-stream habitat and water quality degradation). The total number of fish species available for prediction
was low in comparison to similar applications of multivariate predictive models based on other indicator groups, yet the accuracy
and precision of our model was comparable to outcomes from such studies. In addition, our model developed for sites sampled
on one occasion and in one season only (winter), was able to accurately predict fish assemblage composition at sites sampled
during other seasons and years, provided that they were not subject to unusually extreme environmental conditions (e.g. extended
periods of low flow that restricted fish movement or resulted in habitat desiccation and local fish extinctions). 相似文献
17.
Parasites and environmental conditions can have direct and indirect effects on individuals. We explore the relationship between
salinity and parasites in an endemic New Mexico State threatened fish, the White Sands pupfish (Cyprinodon tularosa). Spatial variation in salinity limits the distribution of the endemic springsnail (Juturnia tularosae) within Salt Creek, a small desert stream. The springsnail is the presumed intermediate host for trematodes that infect the
White Sands pupfish, and trematode prevalence and intensity in pupfish are positively associated with the springsnail. Salinity
and parasites both have negative impacts on pupfish, but in areas of high salinity, pupfish can effectively escape parasites.
Pupfish trematodes were absent from sites lacking snails. At the upstream site, the absence of parasites and lower variance
in salinity were correlated with larger pupfish that were in better condition than pupfish at either the middle or lower sites.
Springsnails were present in the middle section, an area with moderate salinity, and all pupfish had trematodes (median abundance
847 trematodes/fish). Lipid levels and condition were lowest in fish from the middle site. Additionally, fewer older fish
indicated an increased mortality rate. At the lower site, springsnails were absent due to high salinity; pupfish trematode
abundance was much lower (six trematodes/fish), and fish condition was intermediate. An additional experiment revealed that
snail activity and survival were significantly reduced at high salinities commonly present at the lower site. Although both
high salinity and parasites significantly affect pupfish, parasites might be more detrimental. 相似文献
18.
Adult worms of the blood-feeding monogenean parasite Neoheterobothrium hirame, which cause anemia in the Japanese flounder Paralichthys olivaceus, attach to the host fish by embedding their posterior part deeply into the host tissue. To investigate the possibility that cellular responses of the host fish can eliminate N. hirame, flounder were experimentally infected with N. hirame larvae and reared in either fed or starved conditions. Mature parasites were identified on the buccal cavity wall of the fish 33 d post-infection (Day 33). Monocytes/macrophages and granulocytes increased rapidly in the blood and infected sites after the appearance of mature parasites. These cells adhered to the tegument of the parasites. In addition, a few cells with large electron-dense granules (DGCs) were observed in the inflammatory foci. On Day 47, the tegument of some parasites collapsed partially and were phagocytosed by the infiltrated host cells. Some infiltrated cells adhered directly to the inner tissues of the parasites. On Day 54, in the fed fish group, the loss of the tegument led to damage of the parasites' inner tissue by a large number of infiltrated cells. In this group, the elimination of the parasites was noted from Day 47 to 54. These observations probably suggest that the cellular response of the host fish destructed the parasite's posterior part embedded in the tissue, thereby eliminating the parasites. On the other hand, a high mortality was observed in the starved group. The starved fish developed much more severe anemia than the fed fish, and the elimination of the parasites was not observed in this group. The results of the present study suggest that flounder can eliminate N. hirame if they are fed sufficiently. 相似文献
19.
SUMMARY. 1. Field experiments in a fishless stream were carried out on an abundant caddisfly with a predatory, net-spinning larva, Plectrocnemia conspersa (Curtis), to assess whether net site availability affects their microdistribution.
2. Net sites were supplemented by adding nought, one or four artificial structures to replicated patches on the stream bed. In each of three experiments at different seasons (summer, autumn and late winter), caddis densities increased significantly in patches with extra net sites.
3. The response of caddis to supplemented net sites could be affected by the subsidiary effects of food and offish. These potential interactions were assessed in each experiment by varying net site density in two additional treatment stretches in which (1) prey abundance was increased by releasing Daphnia , and (2) brown trout ( Salmo trutta L.) were enclosed. The responses of caddis in these two treatments were compared to that in the reference stretch, where only net site density varied.
4. Increased food abundance enhanced the response of caddis to net site supplementation in winter, when natural prey was least abundant, but not in summer or autumn. We suggest that extra food affects the mechanism determining net building only when prey availability is below some threshold.
5. The presence of fish precluded any effect of extra net sites in summer, but had no effect in autumn (the winter fish treatment was lost). We suggest fish predation reduced the densities of caddis in summer, so that net sites no longer limited local densities. In autumn, fallen leaves provided refugia from fish, which consequently were less effective predators of P. conspersa. 相似文献
2. Net sites were supplemented by adding nought, one or four artificial structures to replicated patches on the stream bed. In each of three experiments at different seasons (summer, autumn and late winter), caddis densities increased significantly in patches with extra net sites.
3. The response of caddis to supplemented net sites could be affected by the subsidiary effects of food and offish. These potential interactions were assessed in each experiment by varying net site density in two additional treatment stretches in which (1) prey abundance was increased by releasing Daphnia , and (2) brown trout ( Salmo trutta L.) were enclosed. The responses of caddis in these two treatments were compared to that in the reference stretch, where only net site density varied.
4. Increased food abundance enhanced the response of caddis to net site supplementation in winter, when natural prey was least abundant, but not in summer or autumn. We suggest that extra food affects the mechanism determining net building only when prey availability is below some threshold.
5. The presence of fish precluded any effect of extra net sites in summer, but had no effect in autumn (the winter fish treatment was lost). We suggest fish predation reduced the densities of caddis in summer, so that net sites no longer limited local densities. In autumn, fallen leaves provided refugia from fish, which consequently were less effective predators of P. conspersa. 相似文献
20.
SUMMARY 1. A challenge has been issued to ecologists to find quantitative ecological relationships that have predictive power. A predictive approach has been successful when applied to biomonitoring using stream invertebrates with the River Invertebrate Prediction and Classification System (RIVPACS). This approach, to our knowledge, has not been applied to freshwater fish assemblages.
2. This paper describes the initial results of the application of a regional predictive model of freshwater fish occurrence using 200 reference sites sampled in the Manawatu–Wanganui region of New Zealand over late summer/autumn 2000. In brief (i) sites were classified into biotic groups (ii) the physical and chemical characteristics that best describe variation among these groups were determined and (iii) the relationship between these environmental variables and fish communities was used to predict the fauna expected at a site.
3. Reference sites clustered into six groups based on fish density and community composition. Using 14 physical variables least influenced by human activities, a discriminant model allocated 70% of sites to the correct biological classification group. The variables that best separated the site groups were mainly large-scale variables including altitude, distance from the coast, lotic ecoregion and map co-ordinates.
4. The model was further validated by randomly removing 20% of the sites, rebuilding the model and then determining the number of removed sites correctly allocated to their original biotic groups using environmental variables. Using this process 67% of the removed sites were correctly reassigned to the six predetermined groups.
5. A further 30 sites were used to determine the ability of the model to detect anthropogenic impact. The observed over expected taxa ( O / E ) ratios were significantly lower than the reference site O / E ratios, indicating a response of the fish assemblages to the known stressors. 相似文献
2. This paper describes the initial results of the application of a regional predictive model of freshwater fish occurrence using 200 reference sites sampled in the Manawatu–Wanganui region of New Zealand over late summer/autumn 2000. In brief (i) sites were classified into biotic groups (ii) the physical and chemical characteristics that best describe variation among these groups were determined and (iii) the relationship between these environmental variables and fish communities was used to predict the fauna expected at a site.
3. Reference sites clustered into six groups based on fish density and community composition. Using 14 physical variables least influenced by human activities, a discriminant model allocated 70% of sites to the correct biological classification group. The variables that best separated the site groups were mainly large-scale variables including altitude, distance from the coast, lotic ecoregion and map co-ordinates.
4. The model was further validated by randomly removing 20% of the sites, rebuilding the model and then determining the number of removed sites correctly allocated to their original biotic groups using environmental variables. Using this process 67% of the removed sites were correctly reassigned to the six predetermined groups.
5. A further 30 sites were used to determine the ability of the model to detect anthropogenic impact. The observed over expected taxa ( O / E ) ratios were significantly lower than the reference site O / E ratios, indicating a response of the fish assemblages to the known stressors. 相似文献