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1.
Although the common carp (Cyprinus carpio), an invasive benthic fish from Eurasia, has long been strongly implicated in the disappearance of vegetative cover and reduced
waterfowl abundance in North American shallow lakes, the details of this relationship are obscure. This study documented ecological
changes in a recently restored shallow lake (Hennepin and Hopper Lakes, IL, USA) at a time that it was experiencing a large
increase in its carp population. We estimated the abundance and biomass of carp 7 years after this lake had been restored
and then back-calculated carp population size across time while examining changes in the lake’s plant and waterfowl communities.
We found that the biomass of carp remained below ~30 kg/ha for 5 years following restoration, but then increased to ~100 kg/ha
in the sixth year following a strong recruitment event. Although a carp biomass of <30 kg/ha had no discernible effects on
vegetative cover (which exceeded 90%) or waterfowl (which exceeded 150,000 individuals during fall censuses), the increase
to 100 kg/ha was associated with a ~50% decrease in both vegetative cover and waterfowl. A further increase in carp biomass
to over 250 kg/ha during the seventh year coincided with a decrease in the vegetative cover to 17% of the lake’s surface and
a decline in waterfowl use to ~10% of its original value. These data suggest that the common carp is extremely damaging to
the ecological integrity of shallow lakes when its density exceeds ~100 kg/ha. Since the biomass of carp in Midwestern shallow
lakes commonly exceeds this value by 3–4 times, it seems likely that carp are responsible for the large-scale habitat deterioration
described in many of these ecosystems.
Handling editor: J. Cambray 相似文献
2.
Comparative analysis of nutrients,chlorophyll and transparency in two large shallow lakes (Lake Taihu,P.R. China and Lake Okeechobee,USA) 总被引:5,自引:0,他引:5
This article compares limnological attributes of two of the world’s largest shallow lakes—Lake Okeechobee in Florida, USA
and Lake Taihu in P.R. China. Both the systems support an array of ecological and societal values including fish and wildlife
habitat, public water supply, flood protection, and recreation. Both have extensive research programs, largely because of
concern regarding the lakes’ frequent cyanobacterial blooms. By evaluating these systems together, we compare and contrast
properties that can generally advance the understanding and management of large shallow lowland lakes. Because of shallow
depth, long fetch, and unconsolidated mud sediments, water chemistry, and transparency in both the lakes are strongly influenced
by resuspended sediments that affect light and nutrient conditions. In the central region of both the lakes, where depth is
the greatest, evaluation of limiting factors by a trophic state index approach indicates that light most often limits phytoplankton
biomass. In contrast, the more sheltered shoreline areas of both the lakes display evidence of nitrogen (N) limitation, which
also has been confirmed in nutrient assays conducted in earlier studies. This N limitation most likely is a result of excessive
levels of phosphorus (P) that have developed in the lakes due to high external loads over recent decades and the currently
high internal P recycling. Comparisons of these lakes show that Lake Taihu has higher N than, similar total phosphorus (TP)
and similar light conditions to that of Lake Okeechobee, but less chlorophyll a (CHL). The latter may be as a result of lower winter temperatures in Lake Taihu (around 5°C) compared to Lake Okeechobee
(around 15°C), which could reduce phytoplankton growth and abundance through the other seasons of the year. In these systems,
the important role of light, temperature, and nutrients in algal bloom dynamics must be considered, especially due to possible
adverse and unintended effects that might occur with projects such as sediment removal, and in the long term, in regard to
buffering lake responses to external load reduction.
Handling editor: D. Hamilton 相似文献
3.
Northern pike (Esox lucius) were introduced to the northern Susitna Basin of south-central Alaska in the 1950’s, and have since spread throughout the
upper Cook Inlet Basin. Extirpations of several native fish populations have been documented in this area. It is hypothesized
here that invasive pike remodel the ecology of lakes by removing vulnerable prey types and that these changes are reflected
in the diet of invasive pike. Trends in pike diet suggest that pike switch to less desirable but more abundant macroinvertebrate
prey as preferred fish prey are eliminated. The impacts of pike introduction were studied in detail for one species of resident
fish, the threespine stickleback (Gasterosteus aculeatus). Stickleback abundance decreases as pike invasion progresses. Conductivity is a significant environmental predictor of stickleback
abundance, with higher conductivity apparently mitigating population reduction. Higher conductivity water may lessen the physiological
costs of developing more robust armor, which reduces vulnerability to predation. Maximum lake depth also appears to predict
stickleback abundance, though this trend was only marginally significant. Deeper lakes may provide an open-water refuge from
pike predation by allowing stickleback to exist outside of the pike inhabited littoral zone. These findings indicate the importance
of diverse habitat types and certain chemical and physical characteristics to the outcome of invasion by fish predators. 相似文献
4.
Despite a recent surge of interest in temporary lentic systems, a strong theory linking the biota to its environment has not
emerged. Using data from 10 temporary ponds at Mammoth Cave National Park, Kentucky, USA, we investigated how invertebrate
communities were structured along environmental gradients, both between and within ponds. Samples were collected with a benthic
corer in winter and spring, and a sweep net in spring. Six between-pond and two within-pond datasets were created. Between-pond
analyses yielded significant CCA’s with only one of the six data sets. The ranges of environmental variables (EV’s) within
ponds were often similar to the ranges of EV’s when averaged and compared between ponds. Some taxa were aggregated in a single
pond, and richness increased with pond area. The theory that richness increases with hydroperiod did not apply to these systems.
Within-pond analyses yielded more consistent relationships, with both CCA’s being significant. Sample depth was the best predictor
of invertebrate richness and abundance, with most taxa preferring shallow habitats. Richness and abundance were higher in
both shallow ponds and shallow areas of deep ponds than in deep areas of deep ponds. Standardizing sample depth may be an
effective way to remove this gradient as a confounding variable in future research. The presence of within-pond gradients,
possibly coupled with the limited dispersal and random colonization of tolerant taxa, makes between-pond comparisons difficult.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorised users.
Handling editor: S. Declerck 相似文献
5.
Gravel pits support waterbird diversity in an urban landscape 总被引:1,自引:1,他引:0
Few studies exist documenting changes in rotifer communities over long time intervals. Here, we explore seasonal and long-term
variation in rotifer communities in four Polish lakes sampled in 1976 and again in 1997. Rarefied, asymptotic species richness
did not differ significantly across study years, although values in 1997 tended to be higher. Simpson’s and Shannon–Wiener
diversity measures provided inconsistent temporal results, with only the former indicating significantly higher richness in
1997. Sorensen’s coefficient of community similarity was as high among lakes in 1976 (0.81) and in 1997 (0.76) as within lakes
across the 21-year span (0.77). Nonlinear redundancy analysis of species’ abundances revealed large, consistent seasonal changes
across lakes, smaller consistent shifts between sampling periods, and small differences between lakes. Collectively, these
metrics indicate that species composition was relatively stable among lakes within years and within lakes between years, while
species’ abundance patterns were far more variable and most affected by season.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Handling editor: S. I. Dodson 相似文献
6.
Eleanor B. Mackay Ian D. Jones Andrew M. Folkard Stephen J. Thackeray 《Hydrobiologia》2011,666(1):85-97
Community structure and diversity patterns of pelagic copepods were investigated for the coastal areas and in the marine lakes
of the Palau islands in the West Pacific. We conducted field surveys during 2004–2007 and collected zooplankton samples from
eight coastal areas and 16 marine lakes. The marine lakes in the islands of Palau are limnologically classified into two types,
meromictic and holomictic lakes. Species diversity indices (Margalef’s species richness d′, Shannon–Wiener index H′, and Simpson’s dominance) were measured at each sampling site. The copepod community structure was analyzed using multivariate
analyses, hierarchical cluster analysis, and non-metric multidimensional scaling (MDS) from the PRIMER package. A total of
36 copepod taxa were identified to the genus or species level from Calanoida, Cyclopoida, Harpacticoida, and Poecilostomatoida.
Multivariate analysis based on the Bray–Curtis similarity index revealed that copepod assemblages could be classified into
three different groups according to their habitat: (I) meromictic lakes, (II) holomictic lakes with an exceptionally shallow
and flat basin (type A holomictic lakes), (III) holomictic lakes with a deep basin (type B holomictic lakes), and all coastal
areas. The meromictic lakes were characterized by markedly decreased species diversity (d′ = 0.15, H′ = 0.41) in which only two brackish-water species, Bestiolina similis and Oithona dissimilis, were dominant. Type A holomictic lakes were characterized by relatively low levels of species diversity (d′ = 1.25, H′ = 1.35). In contrast, type B holomictic lakes were characterized by relatively high levels of species diversity, which was
comparable to that of coastal areas. This result indicated that zooplankton assemblages in the type B holomictic lakes were
closely related to a coastal community. The present study showed that the species diversity of pelagic copepods varies according
to the level of isolation and the local environmental conditions for each marine lake. 相似文献
7.
Drought-induced changes in nutrient concentrations and retention in two shallow Mediterranean lakes subjected to different degrees of management 总被引:3,自引:0,他引:3
Arda Özen Burcu Karapınar İsmail Kucuk Erik Jeppesen Meryem Beklioglu 《Hydrobiologia》2010,646(1):61-72
While extensive knowledge exists on the relationship between nutrient loading and nutrient concentrations in lakes in the
cold temperate region, few studies have been conducted in warm lakes, not least in warm arid lakes. This is unfortunate as
a larger proportion of the world’s lakes will be situated in arid climates in the future due to climate change and a larger
proportion will suffer from a higher frequency of intensive drought. We conducted a comprehensive 11–13 year mass balance
study in two interconnected shallow Mediterranean lakes in Turkey, covering a period with substantial changes in climate conditions.
The upstream lake was only affected by natural changes in nutrient loading, while the downstream lake was additionally influenced
by sewage diversion and restoration by fish removal. Contrasting to experience from north temperate lakes we found an increase
in in-lake concentrations of total phosphorus and inorganic nitrogen (ammonia as well as nitrate) in dry years despite lower
external nutrient loading, and submerged macrophytes did not increase the nitrogen retention capacity of the lakes. In contrast,
fish removal modulated the nitrogen concentration as in north temperate lakes, but the effect was not long-lasting. Our results
suggest that climate warming reduces the nutrient retention capacity of shallow lakes in the Mediterranean and exacerbates
eutrophication. Lower thresholds of nutrient loading for shifting turbid shallow lakes to a clear water state are therefore
to be expected in arid zones in a future warmer climate, with important management implications. 相似文献
8.
Ciliate and bacterial densities and their link with eutrophication were studied in fourteen shallow lakes in northwest Spain.
Total phosphorus (TP) in these lakes varied between 30 μg l−1 and 925 μg l−1 and chlorophyll a concentration (chla) between 0.5 μg l−1 and 107 μg l−1. Bacterial abundance ranged from 1 × 106 to 14 × 106 cells ml−1, while ciliate abundance ranged from 0.6 cells ml−1 to 229 cells ml−1. Lakes were classified into three trophic types from their TP and chla concentrations. Bacterial abundance was significantly
correlated with trophic type, as well as with TP and with chla separately, whereas ciliate abundance was only correlated with
chla. No significant relationship could be established between bacterial and ciliate abundance across the trophic gradient.
A general pattern was observed in the ratios of bacterial abundance to TP and chla concentrations, of decreasing ratios with
increases in the nutrient loading. This pattern was not found for ciliates. The dominant zooplankton group in 13 of the 14
lakes studied was Rotifera, which accounted for a mean of 71% of total zooplankton abundance (41% of zooplankton biomass).
The positive correlation between bacteria and ciliates with this group, and the absence of any relationship with Cladocera
suggest that top down control by cladocerans was weaker in our lakes than previously shown in northern European shallow lakes.
Rotifers could be important predators of bacteria in the high-nutrient lakes of our study. Higher slopes of regressions on
bacterial abundance towards the hypertrophic range indicate that top-down control was weaker in our lakes than in northern
European shallow lakes. 相似文献
9.
Maximum growing depth of macrophytes in Loch Leven,Scotland, United Kingdom,in relation to historical changes in estimated phosphorus loading 总被引:2,自引:0,他引:2
Eutrophication is common in shallow lakes in lowland areas. In their natural state, most shallow lakes would have clear water
and a thriving aquatic plant community. However, eutrophication often causes turbid water, high algal productivity, and low
species diversity and abundance of submerged macrophytes. A key indicator of the ecological state of lake ecosystems is the
maximum growing depth (MGD) of aquatic plants. However, few studies have yet quantified the relationship between changes in
external phosphorus (P) input to a lake and associated variation in MGD. This study examines the relationship between these
variables in Loch Leven, a shallow, eutrophic loch in Scotland, UK. A baseline MGD value from 1905 and a series of more recent
MGD values collected between 1972 and 2006 are compared with estimated P loads over a period of eutrophication and recovery.
The results suggest a close relationship between changes in MGD of macrophytes and changes in the external P load to the loch.
Variation in MGD reflected the ‘light history’ that submerged macrophytes had been exposed to over the 5-year period prior
to sampling, rather than responding to short term, within year, variations in water clarity. This suggests that changes in
macrophyte MGD may be a good indicator of overall, long term, changes in water quality that occur during the eutrophication
and restoration of shallow lakes. 相似文献
10.
We have modeled habitat shift for reproduction to examine the relationship between the timing of migration and population
stability, by modifying Takimoto’s (Am Nat 162:93–109, 2003) consumer–resource model with a consumer’s ontogenetic niche shift.
We found that equilibrium was always locally unstable if migration occurs at a fixed time or level of energy storage, whereas
it could be stable if the timing of migration was adaptively flexible to maximize reproductive output. The general conditions
for stability were safer breeding rather than feeding habitat and abundant resources at the feeding habitat. These results
imply that both adopting an adaptive plastic strategy in the timing of migration and choosing to migrate from a rich feeding
habitat to a safe breeding habitat can contribute to population stability. We also found that reduced reproductive success
with delays in migration, and the survival rate after reproduction, had complicated effects on stability, depending on resource
availability at the feeding habitat. The equilibrium was more likely to be stable when reproduction success was only slightly
(or greatly) reduced or survival rate was high (or low) if the feeding habitat was rich (or poor). These are significant predictions
for ecological study of migrating animals. 相似文献
11.
Common carp (Cyprinus carpio) is one of world’s most invasive fish and managers have long searched for practical control strategies for this species. In temperate systems, common carp forms large winter aggregations that can be located with telemetry and removed with seine nets. This has been viewed as an excellent management possibility, but its success has been mixed. Using a modeling approach, we demonstrate that the usefulness of winter seining in controlling common carp in temperate North American lakes depends on whether carp populations are driven by one of two distinct recruitment dynamics. In lakes where carp can easily recruit within systems from which they are being removed, such as within productive lakes with poor communities of micropredators, winter seining is unlikely to be effective. Even very high removal rates (90 % adults annually) were not sufficient to reach management goal (biomass <100 kg/ha) in such systems. However, in regions with strong predatory communities where carp can recruit only in outlying, seasonally unstable marshes, removal rates as low as 30 % annually or 50 % every other year were able to reduce carp biomass below the management threshold. Such removal rates are achievable as they fall within the range of empirically measured values. Because many carp populations are driven by external recruitment dynamics, strategically conducted winter removal could be used to control this species in a large number of systems across temperate North America and elsewhere. 相似文献
12.
Biological Traits Successfully Predict the Effects of Restoration Management on Macroinvertebrates in Shallow Softwater Lakes 总被引:2,自引:2,他引:0
H. H. van Kleef W. C. E. P. Verberk R. S. E. W. Leuven H. Esselink G. van der Velde G. A. van Duinen 《Hydrobiologia》2006,565(1):210-216
Many shallow softwater lakes are being affected by eutrophication and acidification. In these small lakes decaying organic
material usually accumulates and characteristic plant and animal species disappear. In many degraded lakes organic matter
and macrophytes are being removed in order to restore the lakes to their original state. To assess the effects of restoration
management in softwater lakes on aquatic macroinvertebrates, changes in the species assemblages were studied in four degraded
lakes in the Netherlands undergoing restoration measures. The degraded lakes still harboured species characteristic of pristine
softwaters. However, most of these species were not recorded after restoration measures were taken. Species’ densities declined
dramatically during the execution of restoration measures. Swimming and abundant species were more likely to survive the restoration
measures than other species. The first years after restoration, the lakes did not meet the habitat requirements for a number
of species. Species requiring vegetation for ovipositioning, animal food sources and swards of vegetation as habitat declined.
Because recolonization is expected to be restricted, it is recommended to ensure the survival of relict populations when taking
measures to restore degraded softwater lakes. This may be achieved by phasing restoration measures in space and time, hereby
minimizing mortality during the execution of restoration measures and by preserving habitat conditions required by characteristic
species. 相似文献
13.
Crustacean zooplankton data were compiled from long-term observational studies at seven large shallow Florida lakes, to determine
whether there are general characteristics in regard to species composition, body size, and biomass. In particular, we examined
whether patterns in body size and species richness fit empirical models developed by Stanley Dodson. The lakes included range
in size from 125 to 1730 km2 and encompass mesotrophic to hyper-eutrophic conditions. We found that zooplankton biomass was strongly dominated by one
species of calanoid copepod—Arctodiaptomus dorsalis. Large daphnids were absent, and Cladocera assemblages were dominated by small taxa such as Ceriodaphnia, Chydorus, and Eubosmina. The total number of species of pelagic cladocerans (8–12) was consistent with Dodson’s predictions based on lake area. The
average size of crustacean zooplankton in Florida lakes is small in comparison with temperate communities. A. dorsalis is the smallest calanoid copepod in North America, and the mean length of Cladocera (0.6 mm) is consistent with Dodson’s
results that size decreases from temperate to tropical zones. Total biomass of crustacean zooplankton was very low, ratios
of zooplankton to phytoplankton biomass (0.01–0.1) are among the lowest reported in the literature, and the zooplankton displayed
short-lasting early spring peaks in biomass. Cladocera were almost entirely absent in spring and summer. Factors known to
occur in Florida lakes, which appear to explain these characteristics of biomass, include intense fish predation and high
summer water temperature. 相似文献
14.
Factors linked with intraspecific variation in trophic diversity are still poorly understood in generalist species like the
Montagu’s harrier (Circus pygargus) but may have important implications for conservation management at a wide scale. We described geographic patterns of Montagu’s
harrier diet across Eurasia, gathering diet data from 30 studies in 41 areas from 11 countries. We grouped prey as invertebrates,
reptiles, small mammals, large mammals, eggs, small birds and large birds, and calculated the contribution of each prey type
to the diet (as % biomass) and Shannon’s Diversity Index for each study site. We analysed qualitative estimates of prey abundance
in relation to latitude and longitude, then diet composition in relation to habitat of the study area and prey abundance estimates.
Diet diversity of Montagu’s harriers increased from north to south, while abundance of all prey groups other than small mammals
showed the opposite trends. Agricultural areas in northern latitudes seemed to hold high densities of small mammals, but low
densities of alternative prey. Overall, birds were the main prey in most of Montagu’s harrier’s distribution range, although
the relative importance of each prey type in the diet was significantly explained by its local abundance and habitat, confirming
the opportunistic foraging strategy of this raptor species. Consumption of mammals was an exception to this trend, being negatively
associated with the abundance of alternative prey, suggesting that this prey is not preferred. Trophic diversity in this species
could be influenced by land-use changes through variations in the abundance and availability of prey, which could impact its
population dynamics. This may be particularly important for northern populations of Montagu’s harriers breeding in agricultural
habitats, where trophic diversity is already low. 相似文献
15.
Life-history studies provide a global framework for comparison of fish species responses and trade-offs facing ecological
and environmental constrains. A broad comparison among fishes’ early growth and condition traits is performed in order to
determine ecological patterns of early development regarding latitudinal distribution, habitat use and life-history strategies.
Based on Winemiller and Rose (1992) classification of life-history strategies, data on early growth and condition indices of 46 fish species worldwide was analysed.
Available information on fishes’ early features, namely first year length percentage (relative to species maximum theoretical
length), age at maturation and Fulton’s condition index (K), provided a good segregation of species by latitudinal distribution and habitat use, and evidenced the categories of the
three-endpoint model. Higher larvae and juvenile growth rates and condition indices (K, mean RNA–DNA ratios and protein contents) were associated with tropical and temperate fish species that occur in complex
or variable habitats (respectively coral reefs and estuaries). These species selected for the opportunistic and periodic strategies,
investing highly in rapid growth in order to increase survival probability to counter high mortality rates during early stages
or unstable habitat conditions. Later age at maturation, slower larvae and juvenile growth as well as lower mean condition
indices were consistent with fish species from more stable or predictable environments, as polar regions and freshwater habitats,
which selected for the equilibrium strategy. Nonetheless, differences in energy allocation strategies during early stages
were not observed, evidencing the scarcity of available data regarding condition indices and/or the importance of integrating
life-history intermediate strategies. Future research into condition indices and other physiological processes, for a broader
set of species and for a wider latitudinal and habitat range including seasonal variability (particularly for species from
tropical and polar regions), is essential to better understand or test current theories of species ecological patterns. The
use of direct quantitative measures of young fishes’ metabolic investment and fitness constitutes a new approach for life-history
studies, and should be fundamental for predicting species’ responses to acute environmental or human constrains, especially
in a global climate change scenario that is expected to affect distribution and abundance of fish species worldwide. 相似文献
16.
W. J. Liss G. L. Larson E. A. Deimling L. M. Ganio R. L. Hoffman G. A. Lomnicky 《Hydrobiologia》1998,379(1-3):63-75
We investigated the impact of abiotic factors and trout density on distribution and abundance of diaptomid copepods in high-elevation
lakes in North Cascades National Park Service Complex (NOCA), Washington, USA. The most common large diaptomid, D. kenai (mean
length = 1.88 mm), was able to persist over a wide range of abiotic factors, but the small herbivorous diaptomid, D. tyrrelli
(mean length = 1.18 mm), was restricted to shallow lakes (maximum depth < ≈ 10 m) with relatively high concentrations of total
Kjeldahl nitrogen and total phosphorous. There was a significant negative relationship between the density of D. tyrrelli
and the density of large diaptomids ( D. kenai and D. arcticus), which could imply interaction between large and small diaptomids.
The abundance of large diaptomids was significantly lower in shallow lakes with high densities of reproducing trout (> 250
fish ha-1) than in fishless lakes, in deep lakes with reproducing trout, or in lakes where trout do not reproduce and are
0periodically stocked with fry at low densities (average 179 fry a-1). In lakes where chemical conditions were suitable for
D. tyrrelli, the small diaptomid was often abundant when trout density was high and large diaptomids were either absent or
in low abundance. Our research suggests that trout density, nutrient concentration, and lake depth influence the abundance
of diaptomid copepods in high lakes in NOCA.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
18.
Habitat selection analysis provides useful information on how animals become distributed in response to spatial heterogeneity. Here, we analyze the habitat use and selection of different water bodies (marsh, swamps and round shallow lakes) by capybaras (Hydrochoerus hydrochaeris) and their relation to environmental variables during contrasting climate-hydrological seasons in the Esteros del Iberá (Corrientes, Argentina). We evaluated the intensity of use by capybaras through the total number of individuals (abundance) in each water body, the number and mean size of social groups, and the physical and vegetation characteristics of the environment. The capybaras used marsh and swamps according to availability in both seasons, while they used rounded shallow lakes less than their available would suggest in summer. The use intensity of different rounded shallow lakes estimated based on group size did not show significant differences. In contrast, significant differences were observed when evaluated by the number of individuals in each rounded shallow lake. Different intensity of use was closely associated with environmental and vegetation characteristics. The results show that habitat suitability for capybaras is associated with vegetation cover and “embalsados” in the low-lying area rather than with the morphometry of the rounded shallow lakes. The pattern of habitat selection may depend on forage quality, water availability for thermoregulation and mating, and presence of shelter and resting sites. On the other hand, the present study shows how the size, shape and the abundance of different types of water bodies affect population abundance and density. 相似文献
19.
Roman Lyach 《Ecology and evolution》2022,12(7)
The crucian carp (Carassius carassius, L.) and the brown trout (Salmo trutta, L.) are vanishing from freshwater ecosystems of central Europe. To conserve both species, tailor‐made conservation management of habitats and populations of both species was implemented and tested in the Czech Republic (central Europe). This management was adjusted to reflect the ecological needs of both species. This study aimed to describe the results of a tested in situ management and to analyze the population growth of brown trout and crucian carp under ideal conditions. An experiment was performed at 14 small gravel pit lakes. Seven of them were adjusted to fit the crucian carp habitat requirements while the other seven were treated as a control group. The same experiment was done on 14 smaller streams and with brown trout. The occurrence and growth of crucian carp and brown trout were surveyed over 2 years. A significantly faster growth of both crucian carp and brown trout was observed on the adjusted lakes and streams in comparison to the control group ones. Trout and carp prospered on small streams and gravel pit lakes (respectively) that were free of angling, fish stocking, pollution, piscivorous predators, and competition with hybridizing species like Prussian carp (Carassius auratus, L.) or hatchery‐reared brown trout. 相似文献
20.
Understanding the Relationships between Landscape Connectivity and Abundance of Ixodes ricinus Ticks
Estrada-Peña A 《Experimental & applied acarology》2002,28(1-4):239-248
The density of Ixodes ricinus ticks in a heterogeneous landscape of northern Spain was determined and associated with some aspects of habitat topology.
The habitat mosaic was used to quantify connectivity between patches of different tick density. The analysis revealed that
patches with high tick abundance are ‘stepping-stone’ territories that, when removed from the landscape, cause large changes
in connectivity. Sites with medium tick abundance do not cause such a critical transition in connectivity. Patches with low
tick abundance, but optimal abiotic conditions for survival are located within the minimum cost corridors network joining
the patches, while those sites where the tick has been intermittently collected are located at variable distances from this
network. These results suggest that tick distribution in a zone is highly affected not only by abiotic variables (vegetation
and weather) but also by host movements. Whether these high-density ‘stepping-stone’ patches occur in other tick species needs
to be evaluated because of the potential implications of these foci for human health.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献