Effects of fine sediment inputs from a logging road on stream insect communities:a large-scale experimental approach in a Canadian headwater stream

A forest headwater stream was manipulated (logging road-crossing amended) to induce fine sediment inputs. Benthic inorganic sediment concentrations .particles 1.5–250 μm increased from a 2-year pre-disturbance average of about 800 g m^–2 to over 5000 g m^–2 that persisted for 3 years. Aquatic insect communities were examined over the 5-year study period in the manipulated and nearby reference streams. Overall, the effects of the fine sediment increases on aquatic insect communities were minimal. There were no significant effects of sedimentation on total aquatic insect abundance or biomass. An index of multivariate dispersion gave no evidence of community stress at the manipulated site. Multivariate ordination plots and time trends among univariate community metrics indicated only subtle changes in community structure. Among the univariate metrics (16 time series analyses in total), six gave evidence of a sediment impact on aquatic insect communities. Of those, the clearest indications of an effect were small reductions in diversity and richness of spring communities. These resulted from a significant decline in the proportion of spring shredders, accompanied by a significant increase in the percent Chironomidae. This large-scale experimental approach integrated the realism of a whole-stream study with the control of a manipulative study by including pre-manipulation measurements and excluding other confounding catchment disturbances. In this regard, it may provide a more realistic measure of benthic community level responses to sedimentation in streams at a magnitude associated with logging activity than many previous studies.     

Effects of fish predation on larval chironomid (Diptera: Chironomidae) communities in an arctic ecosystem

Chironomid communities were analyzed in systems with three types of predator regimes to determine hierarchical effects of predation; ponds without fish present, lakes with slimy sculpin (Cottus cognatus) present, and lakes with slimy sculpin present along with burbot (Lota Iota) and lake trout (Salvelinus namaycush). Samples were collected by coring bare sediment habitats in 4 systems of each type near the Toolik Lake field station in northern Alaska. Lakes with burbot and lake trout present in addition to slimy sculpin displayed significantly higher (P<0.05) biomass, density, richness, and diversity. This is likely due to the increased complexity of the predator regime. Ponds without fish had a significantly greater percentage of predacious chironomids present.     

The effects of mixotrophy on the stability and dynamics of a simple planktonic food web model

Recognition of the microbial loop as an important part of aquatic ecosystems disrupted the notion of simple linear food chains. However, current research suggests that even the microbial loop paradigm is a gross simplification of microbial interactions due to the presence of mixotrophs-organisms that both photosynthesize and graze. We present a simple food web model with four trophic species, three of them arranged in a food chain (nutrients-autotrophs-herbivores) and the fourth as a mixotroph with links to both the nutrients and the autotrophs. This model is used to study the general implications of inclusion of the mixotrophic link in microbial food webs and the specific predictions for a parameterization that describes open ocean mixed layer plankton dynamics. The analysis indicates that the system parameters reside in a region of the parameter space where the dynamics converge to a stable equilibrium rather than displaying periodic or chaotic solutions. However, convergence requires weeks to months, suggesting that the system would never reach equilibrium in the ocean due to alteration of the physical forcing regime. Most importantly, the mixotrophic grazing link seems to stabilize the system in this region of the parameter space, particularly when nutrient recycling feedback loops are included.     

Effects of stream restoration and wastewater treatment plant effluent on fish communities in urban streams

1. Fish community characteristics, resource availability and resource use were assessed in three headwater urban streams in Piedmont North Carolina, U.S.A. Three site types were examined on each stream; two urban (restored and unrestored) and a forested site downstream of urbanisation, which was impacted by effluent from a wastewater treatment plant (WWTP). Stream basal resources, aquatic macroinvertebrates, terrestrial macroinvertebrates and fish were collected at each site. 2. The WWTPs affected isotope signatures in the biota. Basal resource, aquatic macroinvertebrate and fish δ¹⁵N showed significant enrichments in the downstream sites, although δ¹³C signatures were not greatly influenced by the WWTP. Fish were clearly deriving a significant part of their nutrition from sewage effluent‐derived sources. There was a trend towards lower richness and abundance of fish at sewage‐influenced sites compared with urban restored sites, although the difference was not significant. 3. Restored stream sites had significantly higher fish richness and a trend towards greater abundance compared with unrestored sites. Although significant differences did not exist between urban restored and unrestored areas for aquatic and terrestrial macroinvertebrate abundances and biotic indices of stream health, there appeared to be a trend towards improvements in restored sites for these parameters. Additional surveys of these sites on a regular basis, along with maintenance of restored features are vital to understanding and maximising restoration effectiveness. 4. A pattern of enriched δ¹³C in fish in restored and unrestored streams in conjunction with enriched δ¹³C of terrestrial invertebrates at these sites suggests that these terrestrial subsidies are important to the fish, a conclusion also supported by isotope cross plots. Furthermore, enriched δ¹³C observed for terrestrial invertebrates is consistent with some utilisation of the invasive C4 plants that occur in the urban riparian areas.     

Structuring of the cyanobacterial community by pelagic fish in subtropical reservoirs: experimental evidence from Australia

1. Subtropical reservoirs of Australia are commonly subject to summer blooms of cyanobacteria. The potential for food web manipulation to control cyanobacterial blooms was investigated in Lake Maroon, south east Queensland using enclosures in which the density of the Australian gudgeon Hypseleotris spp. was manipulated. 2. Zooplankton biomass and community structure were strongly affected by fish density. A size dependent predation effect of Hypseleotris on zooplankton was observed at ambient fish densities, and the community shifted towards a dominance of copepod juveniles and nauplii. Substantial increases in the populations of Ceriodaphnia and calanoid copepods were observed at low fish densities and in the absence of fish. 3. At ambient fish densities total phytoplankton and the proportion of cyanobacteria were maintained at levels similar to those prevailing at day 0. Total phytoplankton and the proportion of cyanobacteria decreased substantially at low fish densities and in the absence of fish. Chlorophytes became dominant in the ‘no fish’ treatment and the grazing‐resistant species Oocystis and Dictyosphaerium were significantly higher than at ambient fish densities. 4. The experiment demonstrated a strong positive relationship between Hypseleotris density and cyanobacteria, and the results suggest that subtropical reservoirs may be suited to food web manipulation as a means of controlling summer cyanobacterial blooms.     

Latitudinal differences in fish community trophic structure,and the role of fish herbivory in a Costa Rican stream

Synopsis We experimentally manipulated fish grazing pressure to determine whether fish herbivory played an important role in the structure of a Costa Rican stream. Non-planktonic plant matter represented a significant percentage ( 25%) of the diet of 77% of the 17 fish species in the community. We prevented fish grazing on macrophytes, tree leaves, and periphyton using fish exclusion cages. Fish grazedPanicum sp., used as a generalized aquatic macrophyte, to the stems after 6 days in control areas, and consumed all or much ofFicus insipida andMonstera sp. leaves when placed in the stream after 48 hours. Plants and leaves experimentally protected by cages remained intact. In periphyton studies, fifty percent more ash free dry weight occurred on 25 × 25 cm floor tiles protected from fish grazing by cages than on tiles in roofless controls exposed to fish grazing for 19 days, suggesting a reduction in periphyton biomass. These results demonstrate that fish herbivory affects macrophyte abundance, and impacts the amount of leaf litter in the stream. Fish herbivory may also have an important effect on overall periphyton biomass. Herbivorous fish species generally represent a larger proportion of the total fish community in tropical compared to temperate streams; thus fish grazing is more likely to have an important influence on plant and animal abundances and distributions in tropical streams.     

Benthic macroinvertebrate communities of intermittent streams in the middle reaches of the Guadiana Basin (Portugal)

The Guadiana River has an irregular hydrological regime, with severe droughts and floods, but little is known about how aquatic fauna respond to these natural events. Macroinvertebrate data and environmental information were collected at seven sites from three tributaries in the middle reaches of the Guadiana River, approximately every 3 months from April 1995 to April 1997. Despite considerable annual variation in discharge (related to duration of flood and drought periods), the number of macroinvertebrates found was consistently high. Diptera represented the major proportion of the benthic fauna (73.2%) followed by Ephemeroptera (10.3%), Coleoptera (4.1%) and Trichoptera (3.1%). Canonical correspondence analysis (CCA) was used to evaluate the relationships between taxa density and habitat variables. Generally, Plecoptera and Ephemeroptera were found in the upstream sampling sites. Wider and deeper sites were associated with the presence of Diptera and were least diverse. High values for both the Shannon-Wiener diversity index and the average score per taxon were usually found at upstream sites where Ephemeroptera and Plecoptera predominated. The data suggest that macroinvertebrates have a great capacity to recover rapidly from severe drought periods, both in terms of taxonomic diversity and number of individuals.     

Effects of natural disturbance on stream communities: a habitat template analysis of arctic headwater streams

1. We used the habitat template approach to test the hypothesis that substratum stability, freezing and nutrient supply were determinants of community structure in 19 headwater streams of arctic Alaska. Streams were selected from five categories: glacier (n = 3), mountain (4), mountain spring (4), tundra spring (4) and tundra (4). 2. Bed movement among streams ranged from 0 to 97% during a ～2‐month summer season. Glacier and mountain streams had significantly higher bed movement than tundra and spring streams (P < 0.001). 3. All glacier and tundra streams froze solid during winter; all mountain spring streams remained unfrozen. Freezing among mountain and tundra spring streams was variable, with a subset of streams flowing throughout winter. 4. With the exception of glacier streams, which showed high concentrations of NH₄⁺ and NO₃^? (P < 0.001), differences in nutrient concentrations among stream types were not significant. 5. Algal taxon richness was greatest in tundra springs (13 taxa) and lowest in glacier streams (five taxa, P < 0.001), as was algal biovolume (7350 versus 687 mm³ m^?2, P < 0.001). Macroinvertebrate taxon richness was lower in glacier streams (4.7 ± 1.7, P < 0.005) than the other stream types (20.5–25.0 taxa), and biomass was greater in mountain springs (4837 mg m^?2) and tundra springs (3367 mg m^?2, P < 0.001). 6. Multidimensional scaling and multiple regression analyses of macroinvertebrate (biomass) and periphyton (biovolume) indicated that a 2‐dimensional habitat template with bed movement and freezing as axes provides an accurate model of major factors controlling the community structure of headwater streams in arctic Alaska.     

Effects of hydrological variation and planktivorous competition on macroinvertebrate community structure in experimental billabongs

1. To study two factors which are predicted as causing changes to community structure in cut-off meanders (colloquially known in Australia as billabongs, a term of aboriginal origin), 16 experimental billabongs were constructed. These were designed to test two hypotheses: (a) that the structure of macrophyte and invertebrate communities within billabongs is altered by changing the pattern of flooding; and (b) that the presence of small planktivorous fish alters invertebrate community structure and diversity within billabongs.
2. An increase in the duration of flooding seems to favour animals better adapted to a greater availability of macrophyte habitat. Changing the seasonality of flooding resulted in prolonging of the time water was available over the summer months.
3. The presence of a planktivorous fish appears to affect macroinvertebrate communities through competition with other planktivores. Variable top-down pressure may create differing successional patterns and ultimately different communities at lower trophic levels.     

Effects of predatory ants on lower trophic levels across a gradient of coffee management complexity

1. Ants are important predators in agricultural systems, and have complex and often strong effects on lower trophic levels. Agricultural intensification reduces habitat complexity, food web diversity and structure, and affects predator communities. Theory predicts that strong top-down cascades are less likely to occur as habitat and food web complexity decrease. 2. To examine relationships between habitat complexity and predator effects, we excluded ants from coffee plants in coffee agroecosystems varying in vegetation complexity. Specifically, we studied the effects of eliminating ants on arthropod assemblages, herbivory, damage by the coffee berry borer and coffee yields in four sites differing in management intensification. We also sampled ant assemblages in each management type to see whether changes in ant assemblages relate to any observed changes in top-down effects. 3. Removing ants did not change total arthropod densities, herbivory, coffee berry borer damage or coffee yields. Ants did affect densities of some arthropod orders, but did not affect densities of different feeding groups. The effects of ants on lower trophic levels did not change with coffee management intensity. 4. Diversity and activity of ants on experimental plants did not change with coffee intensification, but the ant species composition differed. 5. Although variation in habitat complexity may affect trophic cascades, manipulating predatory ants across a range of coffee agroecosystems varying in management intensity did not result in differing effects on arthropod assemblages, herbivory, coffee berry borer attack or coffee yields. Thus, there is no clear pattern that top-down effects of ants in coffee agroecosystems intensify or dampen with decreased habitat complexity.     

A comparison of the trophic ecology of the crayfishes (Orconectes nais (Faxon) and Orconectes neglectus (Faxon)) and the central stoneroller minnow ( Campostoma anomalum (Rafinesque)): omnivory in a tallgrass prairie stream

Omnivorous fish, such as the central stoneroller minnow (Campostoma anomalum(Rafinesque)), and crayfish often play important roles in the trophic dynamics of streams. The trophic role of these two omnivores has not been compared within a system even though they both consume algae, detritus and invertebrates and often co-occur in streams in the Midwestern United States. Natural abundance of ¹⁵N and ¹³C isotopes and a whole stream ¹⁵N-labeled ammonium chloride release were used to compare the trophic ecology of the central stoneroller minnow (Campostoma anomalum (Rafinesque)) and two species of crayfish (Orconectes neglectus (Faxon) and Orconectes nais (Faxon)) in a tallgrass prairie stream. The ¹⁵N and ¹³C values of Orconectes spp. were more similar to coarse benthic organic matter (CBOM) and filamentous green algae than to invertebrates, fine benthic organic matter (FBOM), and periphyton. Values for ¹⁵N and ¹³C in C. anomalum were more similar to grazer and collector invertebrates and filamentous green algae than to FBOM and periphyton. Results from a ¹⁵N tracer release also indicated a portion of algae and/or invertebrates were a component of nitrogen assimilated in Orconectes spp. and C. anomalum diets. Gut contents of C. anomalum were also analyzed. In contrast to stable isotope data, amorphous detritus was a significant component of C. anomalum guts, followed by diatoms and filamentous green algae. A significant percentage of invertebrate material was found in C. anomalum guts sampled in the spring. Experiments were conducted in artificial streams to determine if Orconectes spp. and C. anomalum could reduce epilithic algal biomass in small streams. Algal biomass on clay tile substrata was decreased relative to controls in artificial stream channels containing O. neglectus (3.4 fold, p=0.0002), C. anomalum (2.1 fold, p=0.0012), and both species combined (3.0 fold, p=0.0003). Results indicate that Orconectes spp. are functioning more as algal and detrital processors than as predators in Kings Creek. Isotope and gut content data show that C. anomalum includes invertebrates as well as algae and detritus in its diet. Both species have the potential to affect algal biomass and are important omnivores in the stream food web.     

Effects of fish density on planktonic communities and water quality in a manipulated forest pond

We examined the effects of fish on lower trophic levels in a small pond in eastern Finland. The pond was divided into four sections with plastic curtains and stocked with crucian carp (Carassius carassius); two sections had low (4.4–5.5 g m^–3) and two high (10.4–13.7 g m^–3) densities of fish. In the summer of 1987, the pond was sampled weekly for phyto- and zooplankton until the fish were removed by rotenone in September after a three month experiment. Fish density as well as the extent of macrophyte cover had a considerable impact on planktonic communities and water quality. Mean zooplankton biomass was significantly lower and phytoplankton biomass higher, at high fish density. Water transparency was correlated negatively with chlorophyll-a at low fish density but turbidity appeared to reduce transparency at high fish density. The composition and dynamics of the plankton also differed at different fish densities. The mechanisms behind these effects, and the influences of habitat and fish behaviour on the results, are discussed.     

Influence of fish on the breeding of the red-necked grebe Podiceps grisegena (Boddaert, 1783)

I determined whether selection of breeding sites by thered-neckedgrebe Podiceps grisegena (Boddaert, 1783) was affectedbycompetition for food with fish. During 1987–89, ten ponds inScania, southern Sweden were investigated, five with(breedingsites) and five without breeding red-necked grebe(non-breedingsites). I quantified the biomass of fish and macrozoans(here:larger invertebrates and small vertebrates) and measured thephysical and chemical conditions of the ponds.Breeding sites had significantly lower relative fish abundancethannon-breeding sites. They were either devoid of fish or hadonly nine-spined sticklebackPungitius pungitius. The biomass (dry weight) ofmacrozoans,many of which represent a food resource for grebes, was 16timesgreater at breeding than at non-breeding sites. The physicalandchemical conditions of the ponds did not differsignificantly.These results are consistent with the hypothesis thatcompetitionfor macrozoans occurs between red-necked grebe and fish andthat adense population of many fish species caused red-necked grebestoavoid otherwise acceptable breeding sites.     

Effects of logging on macroinvertebrate production in a sand-bottomed, low-gradient stream

1. Macroinvertebrate production and macrophyte growth were studied in logged and unlogged sections of a sand‐bottomed, low‐gradient, blackwater stream on the Coastal Plain of Virginia, U.S.A. A section of the catchment had been clear‐cut 3 years prior to sampling. No logging occurred in the upstream area of the catchment, which had experienced almost no land disturbance by humans for over 100 years. 2. A primary difference among the logged and unlogged sections of the stream was in the abundance of macrophytes. The combined biomass of Sparganium americanum and of Chara sp. was over 300‐times greater in the logged than the unlogged section. 3. Annual macroinvertebrate production in the sediment was higher in the unlogged section (41 g dry mass m^–2) than in the logged section (25 g m^–2). 4. Annual macroinvertebrate production on Sparganium was higher in the logged section (10 g m^–2 of plant surface area) than in the unlogged section (6 g m^–2). Annual production associated with Chara, which occurred only in the logged section, was 196 g m^–2 of stream bottom covered by this plant. 5. Whole‐stream annual macroinvertebrate production, calculated by summing habitat‐specific production that was weighted by habitat availability, was greater in the logged section (103 g m^–2) than in the unlogged section (41 g m^–2). Sediments supported 99% of the annual production in the unlogged section, whereas macrophytes supported 76% in the logged section. 6. Much of the additional macroinvertebrate production in the logged section was by collector‐filterers living on macrophytes. Production by collector‐gatherers was also greater in the logged section, whereas production by other functional feeding groups changed little with logging. 7. Although logging along high‐gradient, rocky streams also results in increased macroinvertebrate production, that increase often is stimulated by greater periphyton growth rather than the macrophyte growth observed in this low‐gradient stream.     

Trophic cascading effects of predatory fish on leaf litter processing in a Japanese stream

A manipulative field experiment to test for trophic cascading effects of predatory fish on detritus processing by benthic invertebrates was performed in stream channels running through a wetland forest in northern Japan. To control for fish effects on benthic invertebrates, two simple treatments (fish-present and fish-absent) were established for 4 weeks, with two common predatory fish, rainbow trout (Oncorhynchus mykiss) and freshwater sculpin (Cottus nozawae), being introduced into and excluded from stream cages. At the end of experiment, the biomass of the dominant detritivore, an amphipod (Jesogammarus jezoensis), was significantly less in the fish-present treatment (0.56 g m^–2 in dry mass on average) than that in the fish-absent treatment (1.32 g m^–2), there being no significant treatment effect evident for the second-dominant detritivore, coleopteran larvae (Optioservus kubotai). The loss of oak leaves (Quercus crispla) from litter bags in the fish-present treatment (0.31 g week^–1 in dry mass on average) was significantly less than in the fish-absent treatment (0.54 g week^–1). Predator-induced lower biomass and likely lowered foraging activities of the J. jezoensis were responsible for the suppression of litter processing efficiency. In contrast, the standing crop of fine particulate organic matter did not differ significantly between the treatments. The experimental results revealed that the predatory fish had an indirect but significant effect on leaf litter processing in the stream.     

Influences of predatory polychaetes and epibenthic predators on the structure of a soft-bottom community in a maine estuary

Field manipulations were used to determine the importance of two predatory polychaetes, Nereis virens Sars and Glycera dibranchiata Ehlers, and epibenthic predators in structuring an intertidal soft-bottom community in Maine. Epibenthic predators were excluded from portions of the soft bottom using cages which also enclosed elevated densities of the predatory polychaetes. The experiments ran 10 wk and 20 wk beginning in June 1979. Exclusion of epibenthic predators had no effect on infaunal densities after 10 wk but produced ≈ 1.5-fold increase in total density after 20 wk. Since gulls (Larus spp.) avoided all cages, including those not designed to exclude epibenthic predators, the effect of gull predation on infaunal abundances was not tested using exclusion cages. Crabs, Carcinus maenas (Linnaeus) and Cancer irroratus Say were observed in cages not designed to exclude predators.Densities of Nephtys incisa Malmgren, Polydora ligni Webster, Streblospio benedicti Webster, Scoloplos robustus Verrill, phyllodocids, and bivalves were highest in cages containing elevated Glycera dibranchiata density and lowest in cages containing elevated Nereis virens density. N. virens was the only taxon whose abundance was reduced in the presence of Glycera dibranchiata which may account for high infaunal densities in the G. dibranchiata treatment. Laboratory experiments demonstrated that G. dibranchiata are capable of preying on Nereis virens. Additional field experiments revealed that the presence of N. Virens reduced the abundance of some taxa within the first 10 days of colonization. N. virens may have reduced infaunal densities by predation and/or disturbance at the sediment surface. These results suggest that complex interactions within the infauna are important in structuring marine soft-bottom communities.     

Direct and indirect effects of a predatory backswimmer (Notonecta maculata) on community structure of desert temporary pools

Abstract.

• 1 We assessed experimentally the effects of the predatory backswimmer, Notonecta maculata, on naturally colonizing mosquito populations in artificial outdoor pools in the Negev Desert, Israel. A single Notonecta adult per pool (8–15 litres water) had a very large negative impact on populations of Culiseta longiareolata, the most common species found in natural local pools. Notonecta caused large reductions of Culiseta egg rafts and early-instar larvae (instars I and II) and virtually 100% reductions of late-instar Culiseta larvae (instars III and IV) and pupae.
• 2 Notonecta also caused a trophic cascade in the experimental pools; by preying on periphyton-feeding Culiseta larvae, Notonecta indirectly caused significantly higher densities of diatoms, the major component of the periphyton.
• 3 Surveys of nearby natural pools taken between March and May supported the experimental results: a strong negative association between Notonecta and Culiseta among pools occurred as Notonecta increased in numbers and became more widely distributed. Anopheles (occurring only in May) and Culex mosquito immatures were not negatively associated with Notonecta. Culiseta was not associated with surface vegetation whereas both Culex and Anopheles showed strong positive associations with surface vegetation both among and within pools. We attribute the negative association between the predator and Culiseta to local prey extinctions caused by Notonecta in individual pools. Culiseta, being an open water species, is apparently more prone to predation by Notonecta than the vegetation-dwelling Culex and Anopheles.

     

Effects of food availability on predator-induced morphological defence in the ciliate Euplotes octocarinatus (Protista)

The effect of a prey's food resources on predator-induced morphological transformation was studied in two ciliate species: Euplotes octocarinatus (prey) and Stylonychia mytilus (predator). The ability to produce defence in Euplotes was much reduced by prolonged starvation. The extent of prey morphological transformation and therefore the effectiveness of the defence was inversely related to the length of time without food. The results suggest that the defence involves an energetic cost which may be a significant part of the whole cell budget, at least when food is in short supply. Not only the morphological transformation but also the maintenance of the anti-predator phenotype were energetically costly for Euplotes, the cost being proportional to the defence level. The morphological transformation was affected by the kind of food (algae) provided to the prey. Ciliates fed Chlorogonium elongatum attained their maximum width sooner than those fed Chlamydomonas. Thus, both the quantity and the quality of the food available may significantly affect the magnitude of response and therefore the potential success of an induced defence.     

Alien herbivores and native parasitoids: rapid developments and structure of the parasitoid and inquiline complex in an invading gall wasp Andricus quercuscalicis (Hymenoptera: Cynipidae)

Abstract.

• 1 Rapid and substantial changes have occurred in the parasitoid and inquiline community associated with the agamic galls of Andricus quercuscalicis since it invaded Britain in the late 1950s. The number of parasitoid and inquiline species has risen from one to thirteen over a 15-year period. Although the number of species has been relatively consistent over the last 8 years, the species composition has changed considerably and in a highly characteristic way during this period.
• 2 The parasitoid complex can be divided into two broadly distinct sets of parasitoid species; one set attacks only the gall former whereas the other set concentrates on the inquilines living in the wall of the gall.
• 3 The most dramatic change, however, is in the abundance of inquilines which were reported to be virtually absent in earlier studies on this community in Britain. Over a period of only 5 years, between 1988 and 1993, inquiline attack rose from less than 0.01 to an average of 0.26 inquilines per gall. The intensity of inquiline attack is geographically heterogenous, with high inquiline numbers restricted to south-east England. Because of the relatively high specificity of the parasitoids, high inquiline abundance is positively correlated with parasitoid species richness in knopper galls.
• 4 Parasitism rates, particularly on the gall former, were generally low (<10%). Over the last 5 years, however, seven parasitoid species have been consistently recorded and the mortality caused by these species has increased continuously. The species composition of the community associated with this alien gall wasp in Britain has quickly converged to the community known from its native range in continental Europe. Parasitoid species known to attack the galls of A.quercuscalisis on the continent have been recorded from it in Britain for the first time mainly in areas where inquilines have recently become abundant.
• 5 Since rates of parasitism of the gall former are still low, parasitoids are unlikely to play a major role in the population dynamics of this invading gall wasp at present, but the rapidly increasing inquiline and parasitoid attack could be a source of increased mortality for native cynipid species which are the alternative hosts of those parasitoid species.