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1.
Johan Watz Olle Calles Niclas Carlsson Teemu Collin Ari Huusko Jrgen Johnsson Per Anders Nilsson Johnny Norrgrd Daniel Nyqvist 《Freshwater Biology》2019,64(1):71-80
- Habitat structural complexity affects the behaviour and physiology of individuals, and responses to the environment can be immediate or influence performance later in life through delayed effects.
- Here, we investigated how structural enrichment, both pre‐release in the hatchery rearing environment and post‐release in the wild, influenced winter growth and site fidelity of brown trout stocked into side channels of a regulated river.
- Experiencing structural enrichment in the rearing environment during 3 months in autumn had no pre‐release effect on growth, but a delayed positive effect after release during the subsequent winter. Moreover, trout recaptured in wood‐treated sections of the side channels had grown more than trout recaptured in control sections. Wood enrichment in the side channels also increased overwinter site fidelity.
- These results show that adding structure during a relatively short period may alter growth trajectories, and adding wood to side channels is a cost‐effective method to enhance winter habitat carrying capacity for juvenile salmonids in regulated rivers.
2.
- Bitterling fishes (Subfamily: Acheilognathinae) spawn in the gills of living freshwater mussels and obligately depend on the mussels for reproduction. On the Matsuyama Plain, Japan, populations of unionid mussels—Pronodularia japanensis, Nodularia douglasiae, and Sinanodonta lauta—have decreased rapidly over the past 30 years. Simultaneously, the population of a native bitterling fish, Tanakia lanceolata, which depends on the three unionids as a breeding substrate, has decreased. Furthermore, a congeneric bitterling, Tanakia limbata, has been artificially introduced, and hybridisation and genetic introgression occur between them. Here, we hypothesised that decline of the unionids has enhanced this invasive hybridisation through competition for the breeding substrate.
- Three study sites were set in three streams on the Matsuyama Plain. We collected adult bitterling fishes (native T. lanceolata, introduced T. limbata, and foreign Rhodeus ocellatus ocellatus) once a week from April to October 2013 to measure their densities in streams and to examine seasonal differences in female ovipositor length, which elongates in the breeding season. Simultaneously, we set quadrats and captured unionids and measured environmental conditions. Each unionid individual was kept separately in its own aquarium to collect ejected bitterling eggs/larvae. Tanakia eggs and larvae were genotyped using six microsatellite markers and the mitochondrial cytochrome b gene.
- Introduced T. limbata was more abundant, had a longer breeding period, and produced more juveniles than native T. lanceolata. Hybrids between the two species occurred at all sites, and in total 101 of the 837 juveniles genotyped were hybrids. The density of P. japanensis was low, at most 0.42 individuals/m2. Nodularia douglasiae and S. lauta have nearly or totally disappeared from these sites. Hybrid clutches of Tanakia species occurred more frequently where the local density of P. japanensis was low. Mussels were apparently overused and used simultaneously by three species of bitterlings.
- Decline of freshwater unionid populations has enhanced hybridisation of native and invasive bitterling fishes through increasing competition for breeding substrate. We showed that rapid decline of host mussel species and introduction of an invasive congener have interacted to cause a rapid decline of native bitterling fish.
- Degradation of habitat and the introduction of invasive species interact to cause a cascade of extinctions in native species. In our study, obligate parasite species are threatened because the host species are disappearing, which means there is a serious threat of coextinction.
3.
Hierarchy theory provides a conceptual framework for understanding the influence of differently scaled processes on the structure of stream communities. Channel form, instream habitat, and stream communities appear to be hierarchically related, but the strength of the relationships among all components of this hypothesized hierarchy have not been examined. We sampled channel form, instream habitat, fishes, and macroinvertebrates in a channelized stream in Mississippi and Alabama to examine the hypothesis that a hierarchical relationship exists among channel form, instream habitat, and stream communities. Instream habitat, fishes, and macroinvertebrates were sampled in May, July, and September 2000. Measurements of channel form were obtained in July 2000. Mantel tests, multiple regressions, and correlation analyses were used to assess strength of the relationships among channel form, instream habitat, and stream communities. Positive correlations were observed between channel form and instream habitat, and correlations observed between these factors were the greatest observed in our study. Overall, fish and macroinvertebrate communities exhibited stronger relationships with instream habitat than with channel form. Species richness, evenness, and abundance tended to exhibit greater correlations with instream habitat, while species composition had greater correlations with channel form. We concluded that channel form, instream habitat, and stream communities were hierarchically related. 相似文献
4.
Recognition that beavers are integral components of stream ecosystems has resulted in an increase in beaver‐mediated habitat restoration projects. Beaver restoration projects are frequently implemented in degraded stream systems with little or no beaver activity. However, selection of restoration sites is often based on habitat suitability research comparing well‐established beaver colonies to unoccupied stream sections or abandoned colonies. Because beavers dramatically alter areas they occupy, assessing habitat conditions at active colonies may over‐emphasize habitat characteristics that are modified by beaver activity. During 2015–2017, we conducted beaver activity surveys on streams in the upper Missouri River watershed in southwest Montana, United States, to investigate habitat selection by beavers starting new colonies in novel areas. We compared new colony locations in unmodified stream segments to unsettled segments to evaluate conditions that promoted colonization. Newly settled stream segments had relatively low gradients (β ± SE = ?0.72 ± 0.27), narrow channels (β = ?1.31 ± 0.46), high channel complexity (β = 0.76 ± 0.42), high canopy cover of woody riparian vegetation (β = 0.56 ± 0.21), and low‐lying areas directly adjacent to the stream (β = 0.36 ± 0.24), where β denotes covariate effect sizes. Habitat selection patterns differed between our new settlement site analysis and an analysis of occupied versus unoccupied stream segments, suggesting that assessing habitat suitability based on active colonies may result in misidentification of suitable site conditions for beaver restoration. Our research provides recommendations for beaver restoration practitioners to select restoration sites that will have the highest probability of successful colony establishment. 相似文献
5.
Aurélio F. Tonetto Ricardo Cardoso‐Leite Cleto K. Peres Pitagoras da C. Bispo Ciro Cesar Z. Branco 《Freshwater Biology》2014,59(8):1687-1694
- Habitat complexity is thought to play an important role in various ecological communities, but its role under variable natural conditions is not well understood, particularly in lotic habitats where the complexity of the substratum influences the diversity and abundance of the benthic community.
- We investigated the effects of the habitat complexity of the substratum, as represented by fractal structure, on the establishment of stream macroalgae. We also analysed the influence of hydraulic conditions associated with variations in the fractal dimension of the substratum. We hypothesised that habitats with higher surface complexity would have higher macroalgal abundance and that hydraulic conditions would affect macroalgal establishment differently on surfaces of differing complexity.
- We designed a field experiment to elucidate the role of habitat complexity (represented by the fractal dimension and density of roughness elements) and consequent hydraulic conditions (assessed by the Reynolds number and drag forces) on algal growth. Sterile artificial substrata with five levels of complexity were placed in four unshaded streams. After 60 days of complete submergence, the substrata were removed from the streams, and the per cent cover of macroalgae was measured.
- We used a principal components analysis (PCA) to reduce the dimensionality and collinearity among our variables (fractal dimension, density of roughness elements, Reynolds number and drag force) and summarise them adequately. Axis 1 (PC1) values were used in a linear model to assess the relationship between the variables and macroalgal cover.
- PC1 explained 82.2% of the variability in substratum complexity and hydraulic condition. The fractal dimension and density of the roughness elements were negatively related with PC1, whereas the Reynolds number and drag force were related positively. Hydraulic conditions differed among each level of complexity, with the Reynolds number and drag force decreasing with increasing complexity. Macroalgal cover increased on surfaces with lower turbulence and drag force, indicating that less aggressive conditions are suitable for macroalgal colonisation. Additionally, the establishment of macroalgae was greatest on the leading edge of flat‐top ridges, where the water velocity slows and the current changes direction.
- Habitat complexity and hydraulic conditions play an important role in the establishment of macroalgae in streams and could explain their naturally patchy distribution.
6.
We examined the aquatic macroinvertebrate community response to habitat rehabilitation activities in an incised, sand‐bed stream. Seventy‐two large wood (LW) structures were placed along 2 km of Little Topashaw Creek (37 km2 watershed) in north‐central Mississippi, USA. Macroinvertebrate collections were made from bed sediments, LW, leaf packs and qualitative multi‐habitat sampling during 2 years prior to and 2 years following LW addition. Addition of LW tripled the availability of wood substrate but had no measurable effect on macroinvertebrate abundance or family richness. Ordination analyses revealed subtle differences in community composition between treated and untreated conditions, but these were related to antecedent discharge (occurrence of high flows during the preceding 6 months) and bed sediment composition rather than the availability of LW. Restoration of incising, sand‐bed streams must include measures that address perturbed hydrology and degraded water quality as well as instream treatments. Published in 2010. This article is a US Government work and is in the public domain in the USA. 相似文献
7.
Charles van Riper III Kristina L. Paxton Chris O'Brien Patrick B. Shafroth Laura J. McGrath 《Restoration Ecology》2008,16(1):155-167
Many of the world’s large river systems have been greatly altered in the past century due to river regulation, agriculture, and invasion of introduced Tamarix spp. (saltcedar, tamarisk). These riverine ecosystems are known to provide important habitat for avian communities, but information on responses of birds to differing levels of Tamarix is not known. Past research on birds along the Colorado River has shown that avian abundance in general is greater in native than in non‐native habitat. In this article, we address habitat restoration on the lower Colorado River by comparing abundance and diversity of avian communities at a matrix of different amounts of native and non‐native habitats at National Wildlife Refuges in Arizona. Two major patterns emerged from this study: (1) Not all bird species responded to Tamarix in a similar fashion, and for many bird species, abundance was highest at intermediate Tamarix levels (40–60%), suggesting a response threshold. (2) In Tamarix‐dominated habitats, the greatest increase in bird abundance occurred when small amounts of native vegetation were present as a component of that habitat. In fact, Tamarix was the best vegetation predictor of avian abundance when compared to vegetation density and canopy cover. Our results suggest that to positively benefit avian abundance and diversity, one cost‐effective way to rehabilitate larger monoculture Tamarix stands would be to add relatively low levels of native vegetation (～20–40%) within homogenous Tamarix habitat. In addition, this could be much more cost effective and feasible than attempting to replace all Tamarix with native vegetation. 相似文献
8.
Invasive alien plants affect the functioning of ecosystems by altering plant–animal interactions, such as pollination, which may impede natural regeneration of native plant species. In Mauritius, we studied the reproductive traits and pollination ecology of the rare endemic cauliflorous tree Syzygium mamillatum in a restored forest (all alien plant species removed) and an adjacent unrestored area (degraded by alien plants). Flowers of S. mamillatum were only visited by generalist bird species. Although the initial number of flower buds per tree in the restored forest tended to be higher than that of trees in the unrestored area, final fruit set and the number of seeds per fruit were lower in the restored forest. This corresponded with lower bird visitation rates in the restored area. Additionally, during budding stage, most trees were severely attacked by lepidopteran larvae, and bud loss through herbivory was higher in the restored forest. Thus, the difference in reproductive performance of S. mamillatum between the two localities was caused by contrasting herbivore attack and bird visitation behavior in restored and unrestored areas. Our findings illustrate the importance of restoration efforts in mimicking the original physical structure of habitats and interaction structure of interspecific relationships, and the difficulty of doing so given the imperfect knowledge and the reality that many native species have become locally extinct and replaced by exotic species. 相似文献
9.
Stream channel reaches consist of a series of geomorphic units (e.g. pools, runs and riffles) that mitigate flow velocity and provide a variety of aquatic habitat. The hydraulic signature of each geomorphic unit is unique and should remain so during variable flow conditions in order to satisfy habitat requirements. We use the hydraulic signatures measured at different geomorphic units in a recent channel realignment project to evaluate suitability of reaches and geomorphological units for target fish species. In 2009, 650 m of creek and valley were realigned in Brampton, Ontario, to facilitate development. In 2013, water velocity, depth, temperature and channel substrate were measured at cross‐sections between 1 May and 15 October. The assessment illustrated that while geomorphic units have unique signatures during moderate to low‐flow conditions, at high‐flow conditions the boundaries between geomorphic units blurred. Furthermore, our findings suggest that suitable water depth, velocity and temperature conditions existed at least 68% of the time over the entire study period but was reduced during the estimated spawning period for the target species. Specifically, water depth was only ideal for approximately 38% of the spawning period. Finally, in cases where both geomorphic and ecologic systems interface (e.g. channel restoration), it is important to view the whole picture. This study contributes to the on‐going discussion on restoration and success and is particularly useful in light of recent stream restoration trends in rapidly expanding urban regions around the globe. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
10.
Many successful invasions have taken place in systems where harmful disturbance has changed habitat conditions. However, less attention has been paid to the role of habitat restoration, which modifies habitats and thus also has the potential to facilitate invasions. We examined whether in‐stream habitat restorations have the potential to either facilitate or resist invasion by two widely introduced non‐native stream salmonids, Salvelinus fontinalis Mitchill and Oncorhynchus mykiss Walbaum, in Finland. A physical habitat simulation system was used to calculate whether the habitat area for the target species increased or decreased following the restorations. For comparison, we also reported results for four native stream fish species. The simulations showed that the restored streams provided the highest amount of usable habitat area for the native species, particularly for Salmo salar L. and Gottus gobio L. However, it was interesting to note that the restorations significantly increased habitat quality for the two non‐native species, especially at low flows. Nevertheless, the non‐native species had the lowest amount of usable habitat area overall. The modeling results indicated that not only habitat destruction but also habitat restoration could contribute to the spread of non‐native species. Fisheries and wildlife managers should be aware of the possibility, when restoring habitats in order to preserve native ecosystems, that non‐native species could manage to gain a foothold in restored habitats and use them as population sources for further spread. Knowing the widespread negative effect of non‐native species, this risk should not be underestimated. 相似文献
11.
- Groundwater‐fed rivers, such as the chalk streams of southern England, exhibit high levels of stability (e.g. flow and temperature) and physical homogeneity (e.g. depth and substrate grain size). However, growth of instream macrophytes is highly variable depending on season, providing an important but ever‐changing source of cover for stream‐dwelling salmonids, such as brown trout (Salmo trutta).
- In this study, the behavioural ecology of brown trout inhabiting a chalk stream was assessed during periods that included summer and winter. In a reach of the River Lambourn (Berkshire, UK), a combination of physical habitat mapping, electric‐fishing, passive integrated transponder and radio telemetry was used to quantify trout: (1) density relative to physical and thermal characteristics; (2) movement patterns; and (3) performance, in terms of growth.
- Trout density was positively related to depth during winter (February) and spring (May), but not at the end of summer (September). Despite no statistical relation between trout density and macrophytes, periods of strong and no association between density and depth coincided with sparse and extensive macrophyte cover throughout the study reach, respectively.
- Despite being greater for some fish in winter compared to summer, the daily distance moved was generally low (<3.5 m/day). While growth was mostly positive, less mass was gained, and performance deviated farther from optimal levels predicted by a growth model, during periods that included winter.
- A number of factors probably contributed to lower growth in winter, including costs of reproduction, temperatures—which deviated farther from those optimal for growth—and/or an inability to maximise energy intake, e.g. due to time spent holding position in deeper areas as cover provided by macrophytes declined.
- Despite the lack of extremes in chalk stream environments, the behavioural ecology of brown trout appears to be influenced by seasonal variation in instream cover provided by macrophytes. This emphasises the importance of balancing the management (e.g. cutting and removal) of macrophytes with the ecological benefits they provide.
12.
Nicola T. Munro David B. Lindenmayer Joern Fischer 《Ecological Management & Restoration》2007,8(3):199-207
Summary We reviewed the literature on fauna in revegetation in Australian agricultural areas. Of 27 studies, 22 examined birds, with few studies focusing on other faunal groups (four to six studies for each remaining group) and nine examined multiple groups. Existing evidence suggests that revegetation provides habitat for many species of bird and some arboreal marsupials. Species richness of birds was greater in revegetated areas that were large, wide, structurally complex, old and near remnant vegetation. Bats, small terrestrial mammals, reptiles and amphibians did not appear to benefit significantly from revegetation in the short term. Evidence to date suggests that revegetation is not a good replacement of remnant vegetation for many species. Key information gaps exist in the faunal response to (i) revegetation as it ages; (ii) different structural complexities of revegetation; (iii) revegetation that is composed of indigenous vs. non-indigenous plant species; and (iv) revegetation that is in riparian vs. non-riparian locations. In addition, little is known on the value of revegetation for declining or threatened fauna, or of the composition of fauna in revegetation. There is a need to better understand the balance between quantity of revegetation in the landscape, and the quality or complexity of revegetation at the patch scale. Based on current evidence, we recommend revegetation be conducted in patches that are large, wide and structurally complex to maximize the benefits to fauna. 相似文献
13.
Influences of habitat complexity on the diversity and abundance of epiphytic invertebrates on plants 总被引：10，自引：0，他引：10
SUMMARY 1. The compound influence of habitat complexity and patch size on stream invertebrate assemblages associated with submerged macrophytes was investigated through field sampling of two natural macrophyte species with contrasting leaf morphologies (complex, Ranunculus yezoensis; simple, Sparganium emersum) and an experiment with two artificial plants with different levels of morphological complexity. 2. The artificial plant experiment was designed to separate the effects of habitat area (patch size) and habitat complexity, thus enabling a more rigorous assessment of complexity per se than in previous studies where only a single patch size was used. Simple and complex artificial plants were established with five different patch sizes corresponding to the range found in natural plants. 3. Invertebrates occurred on both complex and simple forms of natural and artificial plants at similar abundances with dipterans and ephemeropterans being predominant. Taxon richness was higher on structurally complex Ranunculus than on simple Sparganium and was similarly higher on the complex artificial plant than on the simple one, over the entire range of habitat patch sizes. Thus, architectural complexity affected the taxon richness of epiphytic invertebrates, independently of habitat scale. 4. On the natural plants there was no difference in the abundance (both number of individuals and biomass) of invertebrates between simple and complex forms, while on artificial plants more invertebrates occurred on complex than on simple forms. The amount of particulate organic matter, >225 μm (POM) and chlorophyll a showed mixed patterns on natural and artificial plants, suggesting that the availability of these resources is not an overriding proximate factor controlling invertebrate abundance on plants. The difficulty of extrapolating from experimental results involving use of artificial plants is discussed, especially when considering the relationship between habitat structure and the occurrence of epiphytic invertebrates on natural plants. 相似文献
14.
Mônica Ceneviva‐Bastos Carmen G. Montaña Christopher M. Schalk Plínio B. Camargo Lilian Casatti 《Austral ecology》2017,42(8):908-919
The loss of riparian forests can disrupt the structure and function of lotic ecosystems through increased habitat homogenization and decreased resource diversity. We conducted a field experiment and manipulated structural complexity and basal resource diversity to determine their effect on multiple aspects of community and food‐web structure of degraded tropical streams. In‐stream manipulations included the addition of woody debris (WD) and the addition of wood and leaf packs (WLP). The addition of structural complexity to degraded streams promoted detritus retention and had a positive effect on stream taxonomic richness, abundance and biomass. At the conclusion of the experiment, abundance and richness in the WD‐treated reaches increased by over 110% and 80%, respectively, while abundance and richness in the WLP‐treated reaches increased by over 280% and 170% respectively. Wood debris and leaves were consumed only by few taxa. Detritivorous taxa were the most abundant trophic guild at the beginning and at the end of the experiment. Food webs in treated reaches were relatively more complex in terms of links and species at the conclusion of the experiment, with highest maximum food chain length in the WD treatments and highest number of trophic species, links, link density, predators and prey at the WLP treatment. Despite differences observed in diet‐based food webs, there was little variation in isotopic niche space, likely due to the high degree of omnivory and trophic redundancy, which was attributed to the importance of fine detritus that supported a broad range of consumers. Even in these degraded streams, aquatic taxa responded to the addition of increased complexity suggesting that these efforts may be an effective first step to restoring the structure and function of these food webs. 相似文献
15.
Many efforts have been undertaken to reduce the impairment of stream ecosystems by wastewaters and other pollution, leading to a remarkable improvement of the water quality in most parts of Central Europe. Actually, the most severe disturbance to stream systems in Central Europe is the structural degradation of stream morphology. Restoration practices increasing the structural heterogeneity of formerly degraded stream sections are necessary to create new habitats at different scales that could provide habitat for a diverse invertebrate community. Increasing biodiversity of aquatic invertebrates strengthens the ecological integrity of streams and is therefore a desirable goal in stream restoration. Nevertheless, recent studies focusing on the effect of structural restoration of stream sections often displayed results that did not really met the preset goal of increasing invertebrate diversity. This might be due to sometimes severe disturbance caused by the restoration practice itself, impairing the established invertebrate community in the restored stream section. Additionally, the potential for immigration of new species into the restored stream section is often limited. Therefore, several important prerequisites must be accounted for in the planning of restoration practices to improve structurally degraded stream sections, when the goal of restoration is increasing invertebrate diversity. 相似文献
16.
Jeffrey D. Fore Amy B. Alford David C. Blackwood Tom A. Blanchard 《Restoration Ecology》2019,27(6):1483-1494
Valley‐plug formation is a challenging consequence of stream channelization especially in physiographic regions with highly erodible soils. Upstream channel degradation and incision results in accelerated sediment delivery processes wherein downstream aggradation decreases stream power and creates sand‐clogged channels. Channel reconstruction is now meeting hydrogeomorphic goals related to valley‐plug remediation, yet there exists a need to understand how this practice also facilitates ecological restoration. We evaluated fish trait response to in‐stream habitat conditions in channelized, recently restored, and “least‐disturbed” reference reaches of Coastal Plain streams in West Tennessee. Restored reaches were ecologically similar to channelized reaches, having higher proportions of nest‐guarding omnivores that were correlated with higher percentages of pool habitats and lower wetted width:depth ratios compared to reference reaches. Reference reaches had higher proportions of fast‐water dwelling and specialized insectivores that were correlated with high abundance of large woody debris, high‐wetted width:depth ratios, and low percentages of pool habitats. We conclude that in‐stream habitats in reconstructed channels have yet to promote reach‐scale ecological restoration relative to fish assemblage organization because trait‐habitat associations were not similar to reference conditions. However, our results lend to the development of ecological restoration targets that can be incorporated in future channel reconstruction projects in valley‐plugged, channelized streams of the Coastal Plain. 相似文献
17.
Flow diversion and invasive species are two major threats to freshwater ecosystems, threats that restoration efforts attempt to redress. Yet, few restoration projects monitor whether removal of these threats improve target characteristics of the ecosystem. Fewer still have an appropriate experimental design from which causal inferences can be drawn as to the relative merits of removing exotic fish, restoring flow, or both. We used a dam decommissioning in Fossil Creek, Arizona, to compare responses of native fish to exotic fish removal and flow restoration, using a before‐after‐control‐impact design with three impact treatments: flow restoration alone where exotics had not been present, flow restoration and exotic fish removal, and flow restoration where exotics remain and a control reach that was unaffected by restoration actions. We show that removal of exotic fish dramatically increased native fish abundance. Flow restoration also increased native fish abundance, but the effect was smaller than that from removing exotics. Flow restoration had no effect where exotic fish remained, although it may have had other benefits to the ecosystem. The cost to restore flow ($12 million) was considerably higher than that to eradicate exotics ($1.1 million). The long‐term influence of flow restoration could increase, as travertine dams grow and re‐shape the creek increasing habitat for native fish. But in the 2‐year period considered here, the return on investment for extirpating exotics far exceeded that from flow restoration. Projects aimed to restore native fish by restoring flow should also consider the additional investment required to eradicate exotic fish. 相似文献
18.
BRIAN G. LAUB Daniel W. BAKER Brian P. BLEDSOE MARGARET A. PALMER 《Freshwater Biology》2012,57(5):1076-1095
Summary 1. Channel complexity is an important ecological property of stream systems and is often targeted for restoration in channelised urban streams. However, channel complexity is rarely defined explicitly, and little research on channel complexity has been conducted in streams in urban catchments that have not been directly channelised by human activities. Therefore, it remains unclear whether restoration of non‐channelised urban streams has improved complexity. 2. We explicitly define channel complexity and use a multimetric approach to provide a comprehensive assessment of complexity in multiple restored, urban and forested streams on the Maryland Coastal Plain and two streams of differing land use in Colorado. We also expand on the Maryland and Colorado results with a literature survey of channel complexity from diverse geographical regions. 3. Many streams draining urban catchments in Maryland had relatively high values of some complexity metrics compared to forested reference streams in Maryland and compared to the values for pristine streams calculated from the literature. This suggests that streams in urban catchments that are not directly manipulated by human activities (e.g. channelisation or piping) may be able to maintain channel structures beneficial for aquatic organisms even when impervious surfaces are the dominant form of land use in the catchment. 4. Restored streams in Maryland had equal or lower values of many complexity metrics compared to streams draining urban catchments in Maryland. This suggests that restoration of streams draining urban catchments did not improve the overall channel complexity. 5. Our results highlight the need to explicitly define and measure the attributes of channel complexity that are targeted during restoration, to determine whether the streams in urban catchments are truly degraded with respect to channel complexity. 6. Combined with recent synthesis work suggesting that biodiversity may not be improved by increasing the channel complexity, these results indicate that targeting catchment processes may prove a more useful approach to restoration than attempting to move channel complexity in streams draining urban catchments towards conditions in forested reference streams. 相似文献
19.
Rehabilitation of aquatic habitats in warmwater streams damaged by channel incision in Mississippi 总被引：2，自引：2，他引：2
Channel incision has major impacts on stream corridor ecosystems, leading to reduced spatial habitat heterogeneity, greater temporal instability, less stream-floodplain interaction, and shifts in fish community structure. Most literature dealing with channel incision examines physical processes and erosion control. A study of incised warmwater stream rehabilitation was conducted to develop and demonstrate techniques that would be economically feasible for integration with more orthodox, extensively employed watershed stabilization techniques (e.g., structural bank protection, grade control structures, small reservoirs, and land treatment). One-km reaches of each of five northwest Mississippi streams with contributing drainage areas between 16 and 205 km2 were selected for a 5-year study. During the study two reaches were modified by adding woody vegetation and stone structure to rehabilitate habitats degraded by erosion and channelization. The other three reaches provided reference data, as two of them were degraded but not rehabilitated, and the third was only lightly degraded. Rehabilitation approaches were guided by conceptual models of incised channel evolution and fish community structure in small warmwater streams. These models indicated that rehabilitation efforts should focus on aggradational reaches in the downstream portions of incising watersheds, and that ecological status could be improved by inducing formation and maintenance of stable pool habitats. Fish and physical habitat attributes were sampled from each stream during the Spring and Fall for 5 years, and thalweg and cross-section surveys were performed twice during the same period. Rehabilitation increased pool habitat availability, and made the treated sites physically more similar to the lightly degraded reference site. Fish communities generally responded as suggested by the aforementioned conceptual model of fish community structure. Species composition shifted away from small colonists (principally cyprinids and small centrarchids) toward larger centrarchids, catostomids, and ictalurids. Fish density and species richness increased at one rehabilitated site but remained stable at the other, suggesting that the sites occupied different initial states and endpoints within the conceptual model, and differed in their accessibility to sources of colonizing organisms. These experiments suggest that major gains in stream ecosystem rehabilitation can be made through relatively modest but well-designed efforts to modify degraded physical habitats. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Habitat availability might be the most important determinant of success for a species reintroduction programme, making investigation of the quality and quantity of habitat needed to produce self‐sustaining populations a research priority for reintroduction ecologists. We used a stochastic model of population dynamics to predict whether attempts to improve existing breeding territories using artificial nest platforms improved the population growth rate and persistence of a reintroduced population of Northern Aplomado Falcons Falco femoralis septentrionalis in South Texas. We further assessed whether the creation of new territories, i.e. conversion of entire areas to suitable habitat and not simply the erection of nest platforms, would lead to a subsequent increase in the nesting population. Our model was able to reproduce several characteristics of the wild population and predicted the number of breeding pairs per year strikingly well (R2 = 0.97). Simulations revealed that the addition of nest platforms improved productivity such that the population would decline to extinction without them but is stable since their installation. Moreover, the model predicted that the increase in productivity due to nest platforms would cause the population to saturate available breeding territories, at which point the population would contain a moderate proportion of non‐territorial birds that could occupy territories if new ones become available. Population size would therefore be proportional to the increase in available territories. Our study demonstrates that artificial nest‐sites can be an effective tool for the management of reintroduced species. 相似文献