Tangled webs: reciprocal flows of invertebrate prey link streams and riparian zones

1. Streams and their adjacent riparian zones are closely linked by reciprocal flows of invertebrate prey. We review characteristics of these prey subsidies and their strong direct and indirect effects on consumers and recipient food webs. 2. Fluxes of terrestrial invertebrates to streams can provide up to half the annual energy budget for drift‐feeding fishes such as salmonids, despite the fact that input occurs principally in summer. Inputs appear highest from closed‐canopy riparian zones with deciduous vegetation and vary markedly with invertebrate phenology and weather. Two field experiments that manipulated this prey subsidy showed that it affected both foraging and local abundance of stream fishes. 3. Emergence of adult insects from streams can constitute a substantial export of benthic production to riparian consumers such as birds, bats, lizards, and spiders, and contributes 25–100% of the energy or carbon to such species. Emergence typically peaks in early summer in the temperate zone, but also provides a low‐level flux from autumn to spring in ice‐free streams. This flux varies with in‐stream productivity, and declines exponentially with distance from the stream edge. Some predators aggregate near streams and forage on these prey during periods of peak emergence, whereas others rely on the lower subsidy from autumn through spring when terrestrial prey are scarce. Several field experiments that manipulated this subsidy showed that it affected the short‐term behaviour, growth, and abundance of terrestrial consumers. 4. Reciprocal prey subsidies also have important indirect effects on both stream and riparian food webs. Theory predicts that allochthonous prey should increase density of subsidised predators, thereby increasing predation on in situ prey and causing a negative indirect effect via apparent competition. However, short‐term experiments have produced either positive or negative indirect effects. These contrasting results may be due to characteristics of the subsidies and individual consumers, but could also result from differences in experimental designs. 5. New study approaches are needed to better determine the direct and indirect effects of reciprocal prey subsidies. Experiments coupled with comparative research will be required to measure their effects on individual consumer fitness and population demographics. Future work should investigate whether reciprocal prey fluxes stabilise linked stream–riparian ecosystems, explore how landscape context affects the magnitude and importance of subsidies, and determine how impacts of human disturbance can propagate between streams and riparian zones via these trophic linkages. Study of these reciprocal connections is helping to define a more holistic perspective of catchments, and has the potential to shape new directions for ecology in general.     

Importance of terrestrial subsidies for native brook trout in Appalachian intermittent streams

相似文献   

Contribution of terrestrial invertebrates to the annual resource budget for salmonids in forest and grassland reaches of a headwater stream

1. The annual input, contribution to the diet of salmonids, and quantitative input of terrestrial invertebrates to four reaches with contrasting forest (n=2) and grassland riparian vegetation (n=2) were compared in a Japanese headwater stream.
2. The annual input of terrestrial invertebrates falling into the forest reaches (mean±1 SE=8.7×10³±0.3×10³ mg m^?2 year^?1) was 1.7 times greater than that in the grassland reaches (5.1×10³±0.8×10³ mg m^?2 year^?1), with clear seasonality in the daily input of invertebrates in both vegetation types. The daily input, however, differed between the vegetation types only in summer, when it rose to a maximum in both vegetation types.
3. Fish biomass also differed among the seasons in both vegetation types, being less in the grassland reaches. The contribution of terrestrial invertebrates to the salmonid diet in the forest and grassland reaches was 11 and 7% in spring, 68 and 77% in summer, 48 and 33% in autumn, and 1 and 1% in winter, respectively. The prey consumption rate of fish, which was similar between the vegetation types, increased with stream temperature and was highest in summer. Terrestrial invertebrates supported 49% (mean±1 SE=5.3×10³±0.4×10³ mg m^?2 year^?1) of the annual, total prey consumption (10.9×10³±1.7×10³ mg m^?2 year^?1) by salmonids in the forest and 53% (2.0×10³±0.3×10³ mg m^?2 year^?1) (3.8×10³±0.6×10³ mg m^?2 year^?1) in the grassland reaches.
4. Salmonids were estimated to consume 51 and 35% of the annual total (falling plus drift) input of terrestrial invertebrates in the forest and grassland reaches, respectively. The input of terrestrial invertebrates by drift, however, was almost equal to the output in both vegetation types, suggesting that the reach‐based, in‐stream retention of terrestrial invertebrates almost balanced these falling in.
5. Difference in the riparian vegetation, which caused spatial heterogeneity in the input of terrestrial invertebrates, could play an important role in determining the local distribution of salmonids.     

Larval Chironomidae (Diptera) of the Big Thicket streams

Eighty-seven species of chironomid larvae were collected from streams in the Big Thicket area of southeast Texas. Samples of leaf debris, wood debris, and sand were taken from the streams and the larvae occupying the substrates were analyzed. Four subfamilies were represented including Tanypodinae (12 species), Diamesinae (2 species), Orthocladiinae (30 species), and Chironominae (43 species). Dominant species included Lopescladius sp., Polypedilum ? convictum, Polypedilum ? halterale, Cladotanytarsus sp. group A, Rheotanytarsus sp., and Tanytarsus sp. 2. A brief account of the habitat and the distribution of each species encountered during this study is given.     

APPLIED ISSUES: Effects of habitat rehabilitation on brown trout (Salmo trutta) in boreal forest streams

1. Degradation of stream habitat because of anthropogenic activities (e.g. channelisation) has had a dramatic impact on fluvial environments and their biota, and as a consequence, increasing effort has been directed towards the restoration of degraded rivers. However, a major problem is that the success (or failure) of restoration has been rarely tested using a well‐designed monitoring programme to allow reliable detection of an impact, if any exists. We used a spatially and temporally replicated, balanced Before‐After‐Control‐Impact design to assess the impact of stream habitat rehabilitation on the densities and growth of brown trout of three age‐classes in North Finnish forest streams. 2. Three separate sections in each of six streams were selected for the study. After 3 years of pre‐rehabilitation monitoring, two randomly selected sections in each stream were restored; one using large woody debris and boulders and the other using only boulders. A third section remained as an unmodified control. Monitoring of fish densities continued for 3 years after rehabilitation. 3. Rehabilitation clearly increased streambed complexity, but did not have detectable effects on brown trout stocks in either of the rehabilitation schemes (LWD or stones), except for age‐2+ and older fish which decreased in abundance compared to control reaches. A severe drought after rehabilitation in late summer 2002 reduced densities of trout to a low level in all streams, overriding any local effects of rehabilitation. Rehabilitation structures seemed to provide some safeguard against drought for age‐2 and older, but not for the younger age‐classes. 4. Our results add to the growing body of literature suggesting that large‐scale regional factors may overwhelm local management efforts. To be successful in the future, stream rehabilitation schemes must include drought refuge areas for fish and other stream biota.     

Effects of woody debris and the supply of terrestrial invertebrates on the diet and growth of brown trout (Salmo trutta) in a boreal stream

相似文献   

High levels of mercury contamination in a necrophage dung beetle of the Amazon rainforest (Scarabaeidae: Scarabaeinae)

This study represents the first evidence of mercury contamination in the family Scarabaeidae, with a close focus on Coprophanaeus lancifer, the largest copro-necrophagous beetle in South America. This work shows the repartition of total mercury (THg) in the insect body and lays the groundwork for additional future studies. Abstract in Spanish is available with online material.     

甘肃马鹿夏冬季在祁连山高山草地的放牧行为

为了揭示甘肃马鹿放牧行为的季节差异及其与草地状况和气候等因素的关系,夏季和冬季在祁连山高山草地进行了观察研究。夏季,甘肃马鹿在灌丛中的采食速度从出牧到午间逐渐加快,午后至归牧变化趋势不明显;觅食速度日动态呈增加趋势;每步采食口数上午逐渐增大,午间最高,下午逐渐减少;在不同草地中,甘肃马鹿活动时间的长短依次为灌丛草地>莎草地>禾草地,采食速度依次为禾草地>莎草地>灌丛草地,觅食速度依次为莎草地>禾草地>灌丛草地,每步采食口数依次为禾草地>灌丛草地>莎草地;采食/反刍时间比2.4,1d反刍4次,反刍前后均采食,归牧前有1次采食高峰。冬季,马鹿的采食速度和每步采食口数日变化呈凸抛物线型,午间最高,采食速度与气温显著正相关;觅食速度的日变化呈凹抛物线,午间最低,与气温显著负相关;采食/反刍时间比为4.0,1d反刍2次,归牧前反刍时间较长,其后不再采食。冬季,马鹿的采食时间、反刍时间、采食速度、觅食速度、反刍咀嚼速度、每食团咀嚼次数和反刍总食团数比夏季低,采食行为的日动态较夏季稳定,但反刍行为的个体间差异高于夏季。     

Stoneflies (Plecoptera) in the diet of brook trout (Salvelinus fontinalis Mitchell) in Libby Creek,Wyoming, USA

The stonefly component of a naturally reproducing population of brook trout ( Salvelinus fontinalis) was studied by analyzing 216 stomach pump samples collected between May 15 and August 10, 1991 and 1992, from Libby Creek, an alpine stream in the Medicine Bow National Forest in Wyoming. Stoneflies constituted 10.3% of the total items recovered and were the second most abundant order in the samples. Nineteen species of Plecoptera representing five families were identified. Approximately 43% of all stoneflies were Sweltsa lamba; the next most prevalent species was Zapada haysi (12%). The other prevalent insect orders in the samples were Diptera (57.2%), Ephemeroptera (8.4%) and Trichoptera (6.1%). Terrestrial Coleoptera, Hymenoptera, and Hemiptera were most common in July and August. This revised version was published online in July 2006 with corrections to the Cover Date.     

DNA barcoding at riverscape scales: assessing biodiversity among fishes of the genus Cottus (Teleostei) in northern Rocky Mountain streams

There is growing interest in broad‐scale biodiversity assessments that can serve as benchmarks for identifying ecological change. Genetic tools have been used for such assessments for decades, but spatial sampling considerations have largely been ignored. Here, we demonstrate how intensive sampling efforts across a large geographical scale can influence identification of taxonomic units. We used sequences of mtDNA cytochrome c oxidase subunit 1 and cytochrome b, analysed with maximum parsimony networks, maximum‐likelihood trees and genetic distance thresholds, as indicators of biodiversity and species identity among the taxonomically challenging fishes of the genus Cottus in the northern Rocky Mountains, USA. Analyses of concatenated sequences from fish collected in all major watersheds of this area revealed eight groups with species‐level differences that were also geographically circumscribed. Only two of these groups, however, were assigned to recognized species, and these two assignments resulted in intraspecific genetic variation (>2.0%) regarded as atypical for individual species. An incomplete inventory of individuals from throughout the geographical ranges of many species represented in public databases, as well as sample misidentification and a poorly developed taxonomy, may have hampered species assignment and discovery. We suspect that genetic assessments based on spatially robust sampling designs will reveal previously unrecognized biodiversity in many other taxa.     

Long-term Annual and Seasonal Changes of Meta- and Protozooplankton in Lake Müggelsee (Berlin): Effects of Eutrophication,Grazing Activities,and the Impact of Predation

Annual changes of rotifers, copepods, cladocerans, the ciliate Epistylis rotans, and larvae of Dreissena polymorpha were analysed for the period 1908–1990. Though food resources increased 6–10 fold in the course of eutrophication, only rotifers and Epistylis increased accordingly. Probably as a result of increased predation pressure crustaceans increased only twice. The seasonal pattern of metazoans and protozoans (flagellates, sarcodines, ciliates) were analysed for 12 and 3 years, resp. During winter and spring, large heterotrophic flagellates and ciliates dominated the zooplankton and were responsible for a pronounced - formerly underestimated - grazing pressure on phytoplankton. In early summer, metazoan filter-feeders were often able to cause a significant reduction of phyto- and protozooplankton. However, during some years, phytoplankton declined in the absence of a pronounced grazing pressure. Field data and experiments revealed that predators were able to regulate the density of cladocerans in early summer (mainly cyclopoids) and summer (mainly Leptodora, smelt and fish juveniles).     

The distribution of the Rocky Mountain tailed frog (Ascaphus montanus) in relation to the fluvial system: implications for management and conservation

The mating, egg-laying, and larval development of tailed frogs occur in dynamic mountain streams. During the lengthy (up to 5 years) aquatic residency these species are vulnerable to channel disturbances that can be exacerbated by land uses. Researchers have highlighted specific tailed frog habitat associations but never in the context of fluvial system processes. Based on an extensive regional study with a watershed-wide sampling strategy, we demonstrate that the Rocky Mountain tailed frog (Ascaphus montanus) is limited to contributing basins of roughly 0.3–100 km² in size, with peak numbers in basins up to 35 km². We conclude that the primary determinant of tailed frog distribution patterns in a watershed is basin area, a proximate variable for channel process domain and regional stream discharge: tailed frogs are adapted to cascade and step-pool channel morphologies that characterize these small basins, presumably because they afford more bedform stability and pore-space refugia than do smaller, colluvial headwaters, or larger, floodplain-forming plane bed and pool-riffle bedforms of mainstem rivers. Secondarily, climate and physiography interact to influence occurrence and abundance at the watershed level by controlling such variables as runoff, water temperature, and sedimentation regime. This point has important management implications because it forces us to recognize that in complex ecosystems, wildlife habitat associations are contingent on site-specific interactions amongst fluvial system control variables: significance levels of any one variable to tailed frog distribution will not necessarily be consistent among basins. The study clearly shows that case studies can produce conflicting results when they lack a process-based understanding of ecological response.     

Use of guilds for modelling avian responses to vegetation in the Intermountain West (USA)

Aim Individually focused conservation management of many species is expensive and logistically impractical. Mesofilter conservation methods may facilitate the simultaneous management of multiple species. We used data on distributions of two sets of avian guilds, based on dependence on riparian vegetation and on nest location, to relate occurrence rates to environmental variables. Variables were selected by expert opinion and are likely to be affected by changes in climate and land use. Location Data were collected from 2001–06 in four adjacent mountain ranges in the central Great Basin (Lander, Nye and Eureka counties, Nevada, USA): the Shoshone Mountains and the Toiyabe, Toquima and Monitor ranges. Methods Data on occurrence of birds, vegetation composition and vegetation structure were obtained in the field. Geographical coordinates and the normalized difference vegetation index were derived from a digital elevation model and a satellite image. To construct a general model for guilds as a whole, while allowing flexibility for variation in the functional responses of individual species, we applied multivariate adaptive regression splines. Results The predictive capacity of expert knowledge of relationships between birds and vegetation was inconsistent. Latitude, longitude and elevation may constrain the response of some guilds to changes in vegetation structure and composition. Guild‐based models were useful for modelling species with sparse distributions, which are difficult to model individually. In essence, this method supplements models for the individual species with patterns for the guild to which they belong. Main conclusions Guilds of birds appeared to have predictable associations with selected attributes of vegetation structure and composition. The criteria by which species are grouped into guilds may affect the success of predictions and management interventions. Our derived models offer the potential to predict effects on the avifauna of management or climate‐driven change in vegetation.     

Differences between Lactococcus garvieae isolated from the genus Seriola in Japan and those isolated from other animals (trout, terrestrial animals from Europe) with regard to pathogenicity, phage susceptibility and genetic characterization

AIMS: To clarify the epidemiological relationship between Lactococcus garvieae isolates from the Seriola in Japan and isolates from other animals. METHODS AND RESULTS: A total of 32 isolates obtained from aquatic (the genus Seriola and trout) and terrestrial animals (cow, pig, cat, dog and horse) was used to evaluate its pathogenicity to yellowtail and mouse, phenotype (KG+ and KG-), its susceptibility to three bacteriophages and the pattern of pulsed field gel electrophoresis (PFGE). Lactococcus garvieae isolated from Seriola showed strong pathogenicity to yellowtail, while isolates from trout showed weak pathogenicity and those obtained from terrestrial animals showed no distinct pathogenicity. Only, the isolates from the genus Seriola in Japan showed susceptibility to the bacteriophages. The results of PFGE pattern indicate that the isolates obtained from the Seriola predict homogeneity, while there is no similarity among the isolates obtained from different animals. CONCLUSION: This experiment indicates that L. garvieae isolated from Seriola in Japan appears to be very different from the isolates obtained from other animals, and the isolates prevalent among the genus Seriola in Japan might be homogeneous. SIGNIFICANCE AND IMPACT OF THE STUDY: This study suggests that a particular genetic group that has specially adapted and acquired virulence toward yellowtail were prevalent among the genus Seriola in Japan.     

Peritrich ciliates epizoic on larvae of Brachycentrus subnubilus (Trichoptera): importance in relation to the total protozoan population in streams

The numerical abundance of peritrich ciliates epizoic on larvae of Brachycentrus subnubilus in an English chalk stream is described for an 18-month period. Peaks in the epizoic population occurred during winter at a time when protozoan populations in other stream habitats were low. Ciliates were absent from the first three instars of their host, but were abundant on fourth and fifth instar larvae. Estimates of generation times in the field were made for the ciliate populations (January – February 186 h; July – August 471 h). The relative importance of the epizoic ciliate population as a whole is considered in relation to other protozoan populations in the streams.     

A comparison of the effect of long-term starvation on responses to low-temperature stress by juvenile rainbow (Oncorhynchus mykiss) and brown (Salmo trutta) trout reveal different responses in the two species

Biometric parameters and oxidative stress indicators were measured in liver and muscle samples from rainbow trout and brown trout juveniles exposed to a 45-day starvation period at low water temperature. As a general tendency, hepatic antioxidant enzyme activities in both species increased with fasting to eliminate the harmful effects of reactive oxygen species (ROS). However, the metabolic response to food deprivation in the muscle of each species was different. Lipid peroxidation levels in both species increased with starvation. We concluded that (1) low water temperature enhances ROS production in salmonids because of increased polyunsaturated fatty acid content in the cell membrane; (2) starvation significantly impaired the growth parameters of brown trout, yet the reverse was found for rainbow trout; and (3) despite this negative interaction, brown trout juveniles can physiologically tolerate oxidative stress caused by starvation and can therefore be cultivated under stressful conditions even in their early life stages.     

Differential adaptation to water deprivation in first-instar nymphs of the German cockroach (Blattella germanica) and the brown-banded cockroach (Supella longipalpa)

This study compares the relative abilities of rist-instar nymphs of the german cockroach (Blattella germanica L.) and the brown-banded cockroach (Supella longipalpa F.) to survive prolonged periods of food and/or water deprivation.S. longipalpa nymphs survived significantly longer thanB. germanica nymphs when drinking water was absent, but the advantage ofS. longipalpa overB. germanica disappeared if food was also absent. These results are consistent with the hypothesis thatS. longipalpa is adapted to drier habitats than isB. germanica, and suggest thatS. longipalpa nymphs may be more capable of producing and utilizing extra metabolic water from food thanB. germanica nymphs. Evidence from the literature suggests that this species difference applies mainly to juveniles, since adults ofB. germanica andS. longipalpa do not differ in ability to withstand water deprivation, regardless of food availability.