Persistence and colonisation as measures of success in bog restoration for aquatic invertebrates: a question of detection

1. van Duinen et al. (Freshwater Biol., 2006) raise an interesting point regarding Mazerolle et al.’s (Freshwater Biol., 2006, 51 , p. 333) conclusion on the ability of invertebrates, especially sedentary species, to colonise newly created bogs pools. We wish to clarify that Mazerolle et al. (2006) targeted large arthropods and the absence of smaller sedentary species was purely a result of sampling design. 2. van Duinen et al. (2006) postulate that colonisation rates by bog specialists should be higher in Canada than in the Netherlands, given the extensive amount of intact peatlands in Canada. Here, we emphasise the importance of taking the regional context into account when assessing restoration success as our study site occurs in a landscape where most bog pools have been drained. 3. An evaluation of restoration efforts should focus on both sedentary and vagile invertebrates, to resolve the importance of persistence and colonisation. Such patterns are difficult to interpret, however, when sampling designs and analyses do not account for the probability of detection: an absence may be due to non‐detection or true absence. We strongly urge investigators to directly estimate detection probability in addition to the parameters of interest (e.g. presence, abundance) to provide the best information possible regarding restoration success.     

Differential Response of Aquatic Oligochaete Species to Increased Nutrient Availability – a Comparative Study between Estonian and Dutch Raised Bogs

To assess the effects of increased nutrient availability on aquatic oligochaetes in raised bogs, species assemblages were compared within and between fairly pristine raised bogs in Estonia and raised bog remnants in The Netherlands. Within the pristine bog landscape a distinct pattern in the species assemblage is present. In the most nutrient-poor water bodies, in the ombrotrophic raised bog, only the fragmenting, almost never mature, acid-tolerant species Cognettia sphagnetorum is present. In pristine Estonian raised bogs Nais variabilis, Lumbriculus variegatus and sexually reproducing species are limited to more minerotrophic water bodies, which have a higher decomposition rate of dead organic matter and, consequently, higher nutrient availability. With ten species the lagg zone is the most species-rich part of a pristine raised bog landscape. Most of these lagg zone species are not present in Dutch bog remnants as this part of the bog landscape has long been cultivated. Nais variabilis occurs in the Dutch bog remnants much more frequently than in Estonian bogs, whereas the frequency of C. sphagnetorum and L. variegatus is similar between both countries. These three species respond differently to the increased nutrient availability in The Netherlands, which could be linked to differences in their diets. In contrast to pristine bog pools, N. variabilis in Dutch raised bog remnants is present in water bodies not influenced by minerotrophic water. In Dutch raised bog remnants the occurrence of oligochaetes is not limited anymore by nutrient availability, due to the higher atmospheric nitrogen and sulphur loads in The Netherlands. Overall, it can be concluded that the degradation of Dutch raised bogs has resulted in the loss of both the nutrient-poor parts of the landscape and the special lagg conditions.     

Drought refuges,spatial scale and recolonisation by invertebrates in non‐perennial streams

1. If resistance traits drive recolonisation after drought, then drought refuges should contribute strongly to assemblage composition within streams. If resilience traits drive recolonisation, macroinvertebrates emerging from refuges may disperse widely, colonising many streams. To determine whether the contribution of drought refuges to macroinvertebrate recolonisation in non‐perennial streams was mostly local (within stream) or broader scale (across streams), we measured the association between the composition of invertebrate assemblages in different types of in‐stream drought refuge and the assemblage composition of streams when flow resumed. 2. We sampled 16 streams of varying hydrological regime on the western side of the Victoria Range in the Grampians National Park, Victoria, Australia. Drought refuges (perennial pools, dry sediment, damp sediment, seeps, patches of leaf litter, beneath stones) were identified and sampled during autumn. Most taxa were found in perennial pools; few taxa were found aestivating beneath stones or having desiccation‐resistant stages in dry sediment. Perennial pools and perennially flowing reaches were the refuges that harboured the greatest diversity of macroinvertebrate taxa. 3. Streams were sampled again during spring. Assemblage composition of non‐perennial reaches in spring was unrelated to composition in nearby refuges in the previous autumn. In contrast, assemblage composition in perennial reaches during spring was strongly correlated with composition during autumn. Therefore, drought refuges did not directly influence assemblage composition locally within non‐perennial streams. Rather, both perennially flowing reaches and perennial pools acted as drought refuges across the broader landscape. Resilience traits are likely to drive recolonisation in these streams. 4. Monitoring of drought refuges in a particular stream will therefore not predict species composition when flow resumes. Drought refuges are likely to sustain biodiversity over larger spatial scales such as groups of streams or whole drainage networks. Consequently, stream networks will need to be managed as entities rather than as single waterways and the focus of drought refuge protection should be on perennial pools and reaches.     

Successional phases and species replacements in freshwater rock pools: towards a biological definition of ephemeral systems

1. In temporary aquatic habitats, time is probably the dominant environmental factor affecting community composition, mainly by setting constraints on colonization success and the replacement of taxa over time. The mechanism and effect of a decreasing inundation period on community development, mostly in terms of truncation, are still poorly documented. The permanent and ephemeral components of temporary communities are expected to be differently influenced by the degree of persistence of the habitat. 2. To study the effect of time on invertebrate community assembly and dynamics in a short duration type of temporary aquatic habitat, we monitored 16 ephemeral rock pools which persisted from less than a week to about 1 month at two rock pool sites in semi‐arid south‐eastern Botswana. Data were collected every 2 days during a full inundation cycle. 3. All communities were initially assembled by permanent residents recolonizing the habitat from egg banks and were later joined by actively dispersing ephemeral taxa. Species replacements only occurred in two pools. Concurrent with a decrease in the densities of Branchipodopsis wolfi, population sizes of Leberis sp. and Culicidae (Aedes sp. and Anopheles sp.) increased in these pools. Although it was possible to distinguish two successive phases at one rock pool site, community assembly was generally a gradual process determined by dispersal strategies of the inhabitants. Additional rains after initial filling triggered dispersal by ephemeral taxa, mainly Micronecta youngiana and Hydroglyphus infirmus, and positively influenced colonization success. 4. Decreasing persistence shortens community development down to a critical point below which lack of time eliminates the possibility of species replacement. Based on these findings, we define ephemeral waters as aquatic habitats lacking species replacements. Other temporary water types have a relatively longer persistence, permitting successional replacement of species.     

Animal and vegetation patterns in natural and man-made bog pools: implications for restoration

1. Peatlands have suffered great losses following drainage for agriculture, forestry, urbanisation, or peat mining, near inhabited areas. We evaluated the faunal and vegetation patterns after restoration of a peatland formerly mined for peat. We assessed whether bog pools created during restoration are similar to natural bog pools in terms of water chemistry, vegetation structure and composition, as well as amphibian and arthropod occurrence patterns. 2. Both avian species richness and peatland vegetation cover at the site increased following restoration. Within bog pools, however, the vegetation composition differed between natural and man‐made pools. The cover of low shrubs, Sphagnum moss, submerged, emergent and floating vegetation in man‐made pools was lower than in natural pools, whereas pH was higher than in typical bog pools. Dominant plant species also differed between man‐made and natural pools. 3. Amphibian tadpoles, juveniles and adults occurred more often in man‐made pools than natural bog pools. Although some arthropods, including Coleoptera bog specialists, readily colonised the pools, their abundance was two to 26 times lower than in natural bog pools. Plant introduction in bog pools, at the stocking densities we applied, had no effect on the occurrence of most groups. 4. We conclude that our restoration efforts were partially successful. Peatland‐wide vegetation patterns following restoration mimicked those of natural peatlands, but 4 years were not sufficient for man‐made pools to fully emulate the characteristics of natural bog pools.     

Are native cyprinids or introduced salmonids stronger regulators of benthic invertebrates in South African headwater streams?

The introduction of nonnative salmonids in the Southern Hemisphere generally leads to a reduction in invertebrate abundance and changes in assemblage composition. In the Cape Floristic Region of South Africa, introduced rainbow trout Oncorhynchus mykiss is the dominant predator in many headwater streams, where they have replaced small‐bodied native fishes such as Breede River redfin Pseudobarbus burchelli. To examine the consequences of this species replacement on food web structure, we used a month‐long field experiment to compare the top‐down effects of Breede River redfin and rainbow trout on benthic invertebrate assemblages (abundance and composition) and basal resources (periphyton and particulate organic matter) in 1 × 1.5 m of plastic cages. Benthic invertebrate abundance was more strongly depleted in the cages with redfin than in the cages with trout, and redfin and trout had distinct effects on invertebrate assemblage composition. On the other hand, neither redfin nor trout had a significant influence over standing stocks of periphyton or organic matter, implying that their differential effects on benthic invertebrates did not cascade down to the base of the stream food web in our experiment. Gut content analysis showed that aquatic invertebrates contributed more to the diet of redfin, while terrestrial invertebrates contributed more to the diet of trout, which may be responsible for the relatively weak effect of trout on aquatic invertebrates. This pattern contrasts with nonnative salmonid impacts elsewhere in the Southern Hemisphere. That trout can strongly alter the structure of benthic invertebrate assemblages, in addition to severely depleting native fish abundance, in Cape Floristic Region headwater streams should be weighed into management decisions, and our findings highlight the need for a detailed understanding of species‐specific top‐down effects where native predators are replaced by invasive predators.     

Invertebrate community dynamics and insect emergence in response to pool drying in a temporary river

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Long-term Developments in Ecological Rehabilitation of the Main Distributaries in the Rhine Delta: Fish and Macroinvertebrates

Significant anthropogenic pressure in the Dutch part of the River Rhine is present from the 12th century. River engineering and water pollution were the main stress factors for flora and fauna. From the middle of the 20th century measures were taken to reduce water pollution. Recently, from 1987 onwards, these activities were put into a wider context of ecological river rehabilitation. Effects of improvements on fish and macroinvertebrates in the main distributaries in the Rhine delta are reviewed. The conclusions are that (a) most of the alterations in the Rhine delta are irreversible due to hard socio-economic boundary conditions (e.g. safety, navigation); (b) chances for the development of riverine biotopes have therefore to be found in the forelands and not in the main channels of the Rhine delta; (c) further reduction of pollutants, especially thermal pollution, is needed to help original species to colonise the Rhine delta again; (d) non-indigenous species clearly leave a mark on recolonisation possibilities of original species.     

Moorland pools as refugia for endangered species characteristic of raised bog gradients

In intact raised bog landscapes transitions from ombrotrophic into minerotrophic conditions occur. These gradients are lost from many bogs due to peat harvesting and drainage, and are difficult to restore. To determine which endangered species are characteristic of pristine raised bog gradients and their current status in degraded bogs, plants and macroinvertebrates were surveyed in Estonian intact raised bogs and Dutch degraded bog remnants. Dutch national distribution data were used to determine whether communities with these species occurred outside bog habitats. Water chemistry data were used to describe associated environmental conditions. Intact bog gradients were the preferred habitat for six plant species and fifteen macroinvertebrate species, all of which are endangered. In degraded bogs these species were scarce or not recorded. In intact bogs these species lived at sites where runoff from the bog massif came into contact with regional ground water resulting in a gradient in pH, alkalinity, Ca, Fe and ionic ratio. Analysis of Dutch national distribution data revealed aggregations of these endangered species in moorland pools. These pools contained water chemistry gradients similar to those found in pristine bogs, which occurred at sites were groundwater seepage and stream water came in contact. In the past, stream water has been used to increase pH and trophic status of moorland pools facilitating fisheries. Today, this practice offers a conservation strategy for the protection of endangered species for which no short-term alternatives are available.     

Influence of fishes on macroinvertebrate communities and insect emergence production in intermittent stream refuges

1. Drying intermittent stream networks often have permanent water refuges that are important for recolonisation. These habitats may be hotspots for interactions between fishes and invertebrates as they become isolated, but densities and diversity of fishes in these refuges can be highly variable across time and space.
2. Insect emergence from streams provides energy and nutrient subsidies to riparian habitats. The magnitude of such subsidies may be influenced by in-stream predators such as fishes.
3. We examined whether benthic macroinvertebrate communities, emerging adult insects, and algal biomass in permanent grassland stream pools differed among sites with naturally varying densities of fishes. We also manipulated fish densities in a mesocosm experiment to address how fishes might affect colonisation during recovery from hydrologic disturbance.
4. Fish biomass had a negative impact on invertebrate abundance, but not biomass or taxa richness, in natural pools. Total fish biomass was not correlated with total insect emergence in natural pools, but orangethroat darter (Etheostoma spectabile) biomass was inversely correlated with emerging Chironomidae biomass and individual midge body size. The interaction in our models between predatory fish biomass and date suggested that fishes may also delay insect emergence from natural pools, altering the timing of aquatic–terrestrial subsidies.
5. There was an increase over time in algal biomass (chlorophyll-a) in mesocosms, but this did not differ among fish density treatments. Regardless, fish presence in mesocosms reduced the abundance of colonising insects and total invertebrate biomass. Mesocosm invertebrate communities in treatments without fishes were characterised by more Chironomidae, Culicidae, and Corduliidae.
6. Results suggest that fishes influence invertebrates in habitats that represent important refuges during hydrologic disturbance, hot spots for subsidy exports to riparian food webs, and source areas for colonists during recovery from hydrologic disturbance. Fish effects in these systems include decreasing invertebrate abundance, shifting community structure, and altering patterns of invertebrate emergence and colonisation.

     

The rescue effect and inference from isolation–extinction relationships

The rescue effect in metapopulations hypothesises that less isolated patches are unlikely to go extinct because recolonisation may occur between breeding seasons (‘recolonisation rescue’), or immigrants may sufficiently bolster population size to prevent extinction altogether (‘demographic rescue’). These mechanisms have rarely been demonstrated directly, and most evidence of the rescue effect is from relationships between isolation and extinction. We determined the frequency of recolonisation rescue for metapopulations of black rails (Laterallus jamaicensis) and Virginia rails (Rallus limicola) from occupancy surveys conducted during and between breeding seasons, and assessed the reliability of inferences about the occurrence of rescue drawn from isolation–extinction relationships, including autologistic isolation measures that corrected for unsurveyed patches and imperfect detection. Recolonisation rescue occurred at expected rates, but was elevated during periods of disturbance that resulted in non‐equilibrium metapopulation dynamics. Inferences from extinction–isolation relationships were unreliable, particularly for autologistic measures and for the more vagile Virginia rail.     

It is about time: genetic variation in the timing of leaf‐litter inputs influences aquatic ecosystems

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Diverse invertebrate fauna using dry sediment as a refuge in semi-arid and temperate Australian rivers

Dormant aquatic invertebrates can remain viable in riverbed sediment during dry phases, forming a source for recolonisation during wet periods. Regional differences in capacity for invertebrates to survive drying in this way are poorly understood, but may indicate regional differences in vulnerability to altered flow regimes. We compared diversity of invertebrates in dry sediment from intermittent rivers in temperate and semi-arid Australia after 4–8 weeks of drying. We predicted adaptations of semi-arid biota to severe and unpredictable drying would make dry sediment a more significant recolonisation source, with higher relative diversity when compared with temperate rivers. Emerging aquatic invertebrate assemblages were compared to those sampled in nearby pools, as a common drying refuge. Relative taxa richness in rehydrated sediments was higher in the semi-arid region (83 ± 16% of pool taxa) than the temperate (47 ± 6% of pool taxa), despite lower overall richness (24 taxa in semi-arid, 32 taxa in temperate). Semi-arid rivers had greater potential for dry riverbeds to act as a source for recolonisation, given high relative diversity and abundance in dry sediment, combined with the frequent absence of alternative refuges. However, dry riverbeds in both regions provided a significant short-term refuge for aquatic invertebrates.     

Distribution of aquatic macroinvertebrates within peatland pool complexes in the Flow Country, Scotland

Stationary water traps were used to sample the aquatic invertebrates from both shallow, drought-sensitive pools and deeper, more permanent pools on blanket bog in the Flow Country, northern Scotland during 1994–1995, an area important for nature conservation. The differences in numbers of invertebrates trapped, and the differences in species composition and abundance of adult aquatic Coleoptera and Hemiptera (the two most abundant groups caught) between these two pool types, and spatially within the deeper pools, were investigated. Using the same trapping effort, seven times more invertebrates and five times more adult Coleoptera were taken in the deep (A4) pools compared to the shallow (A3) pools, and Hemiptera were almost exclusively trapped in the A4 pools (only 2% of the catch was from A3 pools). DECORANA showed that the Coleoptera species composition of the two pool types was different, although a small overlap existed, presumably because of the proximity of the pool types and of the continuous nature of the variation between them. There was little difference in the numbers taken or species composition of Coleoptera or Hemiptera from the edges or centre of the A4 pools. Smaller Coleoptera species were found in both pool types, although one species was more common in the centre of the larger pools. Larger Coleoptera with a body length of more than 11.6 mm were not found in the A3 pools, only in the deeper A4 type. The A4 pools were found to be more stable seasonally than the shallow pools with respect to invertebrate numbers trapped, and this may be linked to the chance of drying out of the latter in dry periods. The influence of pool stability (through water level) on invertebrate abundance, development and individual species size is discussed, as is the sampling method used, the significance of the peatland fauna and its importance to breeding bird life associated with peatland pool complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detecting impacts of non‐native species on associated invertebrate assemblages depends on microhabitat

Invasive plants that displace native floral communities can cause changes to associated invertebrate species assemblages. Using a mini‐review of the literature and our own data we add to the still considerable debate about the most effective methods for testing community‐level impacts by invasive species. In endangered saltmarshes of southeast Australia, the non‐native rush Juncus acutus L. is displacing its native congener J. kraussii Hochst., with concurrent changes to floral and faunal assemblages. In two coastal saltmarshes, we tested the hypothesis that the ability to detect differences in the invertebrate assemblage associated with these congeneric rushes depends on the microhabitat of the plant sampled. We used three sampling methods, each targeting specific microhabitats: sweep netting of the plant stems, vacuum sampling of the plant tussock, and vacuum sampling of the ground directly below the plants. Over 3800 individuals and 92 morphospecies were collected across four main taxa: gastropods, crustaceans, hexapods and arachnids. Detection of differences in invertebrate density, richness and composition associated with native compared with non‐native rushes was dependent on the microhabitat sampled and these differences were spatially variable. For example, at one saltmarsh the stems and tussock of J. acutus had a lower density and richness of total invertebrates and hexapods than those of the native J. kraussii. In contrast, crustaceans on the ground were in greater abundance below J. acutus than J. kraussii. This study demonstrates that on occasions where overall differences in the assemblage are not detected between species, differences may become apparent when targeting different microhabitats of the plant. In addition, separately targeting multiple microhabitats likely leads to a greater probability of detecting impacts of invasion. Comparing the invertebrate assemblage without differentiating between or sampling an array of microhabitats can fail to determine the impact of invasive species. These results highlight that a combination of methods targeting different microhabitats is important for detecting differences within the invertebrate community, even for phylogenetically related species.     

Experimental whole‐stream warming alters community size structure

How ecological communities respond to predicted increases in temperature will determine the extent to which Earth's biodiversity and ecosystem functioning can be maintained into a warmer future. Warming is predicted to alter the structure of natural communities, but robust tests of such predictions require appropriate large‐scale manipulations of intact, natural habitat that is open to dispersal processes via exchange with regional species pools. Here, we report results of a two‐year whole‐stream warming experiment that shifted invertebrate assemblage structure via unanticipated mechanisms, while still conforming to community‐level metabolic theory. While warming by 3.8 °C decreased invertebrate abundance in the experimental stream by 60% relative to a reference stream, total invertebrate biomass was unchanged. Associated shifts in invertebrate assemblage structure were driven by the arrival of new taxa and a higher proportion of large, warm‐adapted species (i.e., snails and predatory dipterans) relative to small‐bodied, cold‐adapted taxa (e.g., chironomids and oligochaetes). Experimental warming consequently shifted assemblage size spectra in ways that were unexpected, but consistent with thermal optima of taxa in the regional species pool. Higher temperatures increased community‐level energy demand, which was presumably satisfied by higher primary production after warming. Our experiment demonstrates how warming reassembles communities within the constraints of energy supply via regional exchange of species that differ in thermal physiological traits. Similar responses will likely mediate impacts of anthropogenic warming on biodiversity and ecosystem function across all ecological communities.     

Colonization of abandoned swimming pools by larval mosquitoes and their predators following Hurricane Katrina

Thousands of flooded swimming pools were abandoned in New Orleans following Hurricane Katrina and provided a natural experiment to examine colonization of a novel aquatic habitat by mosquito larvae and their aquatic predators. We conducted a randomized survey of flooded swimming pools in two neighborhoods in January 2006 and found that 64% contained mosquito larvae, 92% contained predatory invertebrates, and 47% contained fishes. We collected 12,379 immature mosquitoes representing five species, primarily Culiseta inornata, and secondarily, the arboviral vector Culex quinquefasciatus. Dragonfly nymphs in the families Aeshnidae and Libellulidae were the most common predatory invertebrates collected among a total of 32 non-mosquito invertebrate species. Eleven species of fishes were collected, with Gambusia affinis accounting for 76% of the catch. Diversity of fishes in swimming pools was positively correlated with proximity to a levee breach and the fish assemblage found in swimming pools was similar to that found along shorelines of Lake Pontchartrain and drainage canals that flooded the study area. Mosquito larvae were rare or absent from pools containing fishes; however, path analysis indicated that the presence of top predators or abundant competitors may somewhat mitigate the effect of Gambusia affinis on mosquito presence.     

The relative contributions of refugium types to the persistence of benthic invertebrates in a seasonal snowmelt flood

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An Early Devonian arthropod fauna from the Windyfield cherts, Aberdeenshire, Scotland

New terrestrial and freshwater arthropods are described from the Windyfield cherts, a suite of silicified sinters deposited 700m north‐east of the Rhynie cherts and part of the same Early Devonian hot‐spring complex. The diverse assemblage consists of Heterocrania rhyniensis (Hirst and Maulik, 1926a), here recognized as a euthycarcinoid; scutigeromorph centipede material assigned to Crussolum sp.; the crustacean Lepidocaris; trigonotarbid arachnids; a new arthropod of myriapod affinities named Leverhulmia mariae gen. et sp. nov.; and the distinctively ornamented arthropod cuticle of Rhynimonstrum dunlopi gen. et sp. nov. The Leverhulmia animal preserves gut content identifying it as an early terrestrial detritivore. Abundant coprolites of similar composition and morphology to the gut contents of the euthycarcinoid crowd the matrix. Chert texture, faunal associations, and study of modern analogues strongly suggest that the terrestrial arthropods were ubiquitous Early Devonian forms with no particular special adaptation to localized conditions around the terrestrial hot‐spring vents. The aquatic arthropods represent biota from ephemeral cool‐water pools in the vicinity of the hot‐spring vents.     

Recolonisation patterns of benthic invertebrates: a field investigation of restored former sewage channels

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