Hydroptilidae (Trichoptera) of Costa Rica: the Genus Hydroptila Dalman

Seven new species of Hydroptila (Trichoptera: Hydroptilidae) from Costa Rica are described: H. carara, H. maritza, H. osa, H. paradenza, H. maza, H. rastrilla, H. singri, and one from Panama, H. nusagandia. Ten additional species occurring in Costa Rica are recorded: H. brailovskyi Bueno-Soria, H. constricta Bueno-Soria, H. curvata Bueno-Soria, H. flinti Bueno-Soria, H. icona Mosely, H. meralda Mosely, H. mexicana Mosely, H. misolha Bueno-Soria, H. paschia Mosely, and H. veracruzensis Flint. In addition, illustrations of H. denza Ross and H. grenadensis Flint are included to help clarify the taxonomy of the denza species group. Finally, an illustrated key is provided for males of all species occurring in lower Central America.     

Foraging conditions of planktotrophic larvae of echinoderms in the southwestern part of Peter the Great Bay of the Sea of Japan

Foraging of planktotrophic larvae of echinoderm common species in the Peter the Great Bay (Sea of Japan) was estimated on the basis of distribution of phyto- and meroplankton. The diversity and abundance of phytoplankton in the studied area in summer months were shown (141 algae species; abundance—up to 743000 cells/m³; biomass—more than 2.7 g/m³ of fresh weight). It was found that in Peter the Great Bay the diet of echinoderm larvae depended on their feeding behavior, duration of their pelagic stage, and abundance and size composition of phytoplankton, included up to several micrograms of fresh algae per larva.     

Ontogenetic shifts in the functional response and interference interactions of Rhyacophila dorsalis larvae (Trichoptera)

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Therefore, it is important to establish if the functional response and interference interactions differ between life‐stages. These hypotheses were tested by (i) comparing the functional response of second, third, fourth and fifth larval instars of Rhyacophila dorsalis, using three stream tanks with one Rhyacophila larva per tank and one of 10 prey densities between 20 and 200 larvae of Chironomus sp.; (ii) using other experiments to assess interference within instars (two to five larvae of the same instar per tank), and between pairs of different instars (one, two or three larvae per instar; total predator densities of two, four or six larvae per tank). 2. The first hypothesis was supported. The number of prey eaten by each instar increased with prey density, the relationship being described by a type II model. The curvilinear response was stronger for fourth and fifth instars than for second and third instars. Mean handling time did not change significantly with prey density, and increased with decreasing instar number from 169 s for fifth instars to 200 s for second instars. Attack rate decreased progressively with decreasing instar number. Handling time varied considerably for each predator–prey encounter, but was normally distributed for each predator instar. Variations in attack rate and handling time were related to differences in activity between instars, fourth and fifth instars being more active and aggressive than second and third instars, and having a higher food intake. 3. The second hypothesis was partially supported. In the interference experiments between larvae of the same instar or different instars, mean handling time did not change significantly with increasing predator density, and attack rate did not change for second and third instars but decreased curvilinearly for fourth and fifth instars. Interference between some instars could not be studied because insufficient second instars were available at the same time as fourth and fifth instars, and most third instars were eaten by fourth and fifth instars in the experiments. Prey capture always decreased with decreasing attack rate. Therefore, interference reduced prey consumption in fourth and fifth instars, but not in second and third instars. The varying feeding responses of different instars should be taken into account when assessing their role in predator–prey relationships in the field.     

Food consumption by the larvae of Sericostoma vittatum (Trichoptera), an endemic species from the Iberian Peninsula

The caddisfly Sericostoma vittatum Rambur (Trichoptera: Sericostomatidae) is an endemic species of the Iberian Peninsula. Under laboratory conditions, larvae of S. vittatum had a higher activity and metabolism during the night. Besides consuming particulate allochthonous organic matter, young stages are also able to feed and grow on faecal pellets from adults. Daily growth rates varied from 0.02 mg (0.8–3.7 mg size class animals) to 0.31 mg dry mass (10.6–22.8 mg size class animals). Due to the high densities of this species (annual mean of 25 individuals m^–2; maximum of 96 individuals m^–2) and high consumption rates (0.47 mg leaf dry mass mg animal^–1 d^–1for small larvae), this species has a potential key role on the fragmentation of allochthonous organic matter of streams in central Portugal.     

Adaptive significance of facultative paedomorphosis in Triturus alpestris (Amphibia, Caudata): resource partitioning in an alpine lake

1. Facultative paedomorphosis is a polymorphism that has important evolutionary implications in promoting morphological differentiation and variation in habitat use. It occurs in several urodele species throughout the world. Several hypotheses based on life-history theory have been proposed to explain the wide range of habitats in which facultative paedomorphosis occurs, suggesting multifactorial causes.
2. In harsh habitats, such as mountain lakes, paedomorphosis might promote niche partitioning between morphs. This hypothesis was tested by comparing micro-habitat use and diet of two coexisting morphs in an alpine lake.
3. Paedomorphs occupied all microhabitats in the lake while metamorphs occurred only along the shoreline or at the water surface. Paedomorphic newts were frequent in deep water, where they foraged mainly on plankton. Plankton was poorly exploited by metamorphic newts, which fed mainly on terrestrial insects. Difference between morphs in microhabitat use, and consequently in the diet, were consistent in both sexes and in juveniles.
4. In adults, the mass and energy value of stomach contents did not differ between morphs, suggesting a similar food availability in the habitats occupied.
5. This study indicates habitat partitioning between morphs involving dietary differences. Specific benefits and costs of each ontogenetic pathway may allow their coexistence in this deep and fishless lake. Paedomorphosis benefits individual newts by making new food resources available and presumably reducing competition at the shore of the lake. However, the proximate causes of such an ontogenetic switch remain unclear.     

Feeding habits and trophic levels of Mediterranean fish

The estimation of fractional trophic levels(TROPHs) is essential for the management offisheries resources as well as for quantifyingthe ecosystem effects of fishing. We gatheredall available information concerning thefeeding habits of 332 fish stocks, belonging to146 species, 59 families and 21 orders,throughout the Mediterranean Sea, and estimatedtheir TROPH values. The latter ranged from 2.0to 4.5 and the following functional trophicgroups were identified: (a) pure herbivores (TROPH = 2.0–2.1, mean = 2.02, SD = 0.03),which were very rare and represented by Siganus luridus, Siganus rivulatus andSarpa salpa, all of which feed on red,brown, green and blue-green algae; (b)omnivores with a preference for vegetablematerial (2.1 < TROPH < 2.9, mean = 2.5,SD = 0.12), but feeding on other prey, such assponges, hydrozoans, anthozoans, polychaetes,ostracods, isopods, amphipods and copepods. This type of omnivore was very rare among thecases reviewed; (c) omnivores with a preferencefor animal material (2.9 < TROPH < 3.7,mean = 3.4, SD = 0.19) feeding on a wide variety ofprey (e.g., algae, foraminifera, brachyurans,balanoids, ascidians, amphipods,appendicularians, annelids, isopods,gastropods, cnidarians, ophiurids, polychaetes,cladocerans, mysids, euphausids, fish larvae,cephalopods). They were the most numerous andwere mainly represented by species of thefamilies Blenniidae, Bothidae, Centracanthidae,Gobiidae, Labridae, Lotidae, Macrouridae,Mullidae, Ophidiidae, Soleidae, Triglidaeand Engraulidae; and (d) carnivores witha preference for large decapods, cephalopodsand fish (3.7 < TROPH < 4.5). They werethe next most abundant group among the casesreviewed. They were mainly represented byspecies of the families Dalatiidae, Lophiidae,Scombridae, Scyliorhinidae, Synodontidae,Torpedinidae, Merlucciidae, Xiphiidae andZeidae. This group was divided into twosubgroups: one exhibiting a preference fordecapods and fish (3.7 < TROPH < 4.0,mean = 3.85, SD = 0.09) and another one exhibitinga preference for fish and cephalopods (4.0 相似文献   

A study of the mechanism of algal uptake in yolk-sac larvae of Atlantic halibut (Hippoglossus hippoglossus)

The drinking rate of water, and the ingestion- and assimilation rates of algae in yolk-sac larvae of Atlantic halibut were examined by use of³H-dextran and¹⁴C-labelled algae. The drinking rate throughout the yolk-sac stage was in the range of 7–160 nl per larva h⁻¹, with a slight increase towards the end of the period. The ingestion rate of algae ( Tetraselmis sp.) was very low before day 30 and showed a peak between day 43 and 48 at 5° C. The assimilation efficiency of the algae was in the range of 1-5%. The clearance rate of algae was 100–1000 times higher than the drinking rate, and was correlated to the distance between the gill arches. Bigger cells were more effectively retained than smaller ones. The results suggested that the larvae acted as filter feeders from day 30 up to the point when they are expected to start feeding on bigger prey.     

Division of labor in post-emergence colonies of the primitively eusocial waspPolistes instabilis de Saussure (Hymenoptera: Vespidae)

Polyethism was quantified in post-emergence colonies of the primitively eusocial wasp,Polistes instabilis, and compared to polyethism in a sympatric advanced eusocial wasp,Polybia occidentalis. Like P.occidentalis, P. instabilis foragers collected food (nectar and prey) and nest materials (wood pulp and water).P. instabilis foragers showed some evidence of specialization with respect to which materials they gathered, but most foragers, divided their effort among food and nest materials, a pattern that is rarely seen inP. occidentalis. In colonies of both species, more foragers collected nectar than any other material; in contrast, most water foraging was performed by one or two workers. Upon returning to the nest,P. instabilis foragers gave up part or all of most nectar, prey, and pulp loads to nestmates, while water was rarely partitioned. Prey loads were most likely to be given up entirely.P. instabilis workers show evidence of conflict over the handling of materials at the nest. The frequency with which workers took portions of nectar loads from forgers was positively correlated with their frequency of aggressive dominant behavior, and with their frequency of taking other foraged materials. Compared to polyethism inP. occidentalis P. instabilis showed less individual specialization on foraging tasks and less partitioning of foraged materials with nestmates, suggesting that these characteristics of polyethism have been modified during the evolution of advanced insect societies.     

Aggregation,interference and foraging by larvae of Plectrocnemia conspersa (Trichoptera: Polycentropodidae)

The predatory net-spinning caddis larva Plectrocnemia conspersa aggregates in patches of high density during most of the year. The behavioural basis of the aggregation depends on (a) the initial tendency to spin a net where prey have been captured and (b) the abandonment of sites where prey are not captured within a threshold time after a previous meal. There is a powerful behavioural mutual interference effect in laboratory experiments between larvae at densities similar to those in the field. Larvae contest ownership of nets and the outcome is determined mainly by body size, usually without injury to either contestant. The lack of an aggressive response in August may be due to this mutual interference or to aspects of environmental instability which make an optimal allocation of foraging effort between patches difficult to attain.     

Food utilization of aphidophagous hoverfly larvae (Diptera: Syrphidae, Chamaemyiidae) on herbaceous plants in an urban habitat

We examined food utilization in a community of aphidophagous hoverfly larvae (Diptera: Syrphidae and Chamaemyiidae) in open lands in an urban habitat in central Japan for 3 years. The community consisted of 17 hoverfly species feeding on 20 aphid species occurring on 14 species of dominant herbaceous plants. In terms of larval prey preference, the dominant eight species of hoverfly were categorized into three groups: a polyphagous ‘generalist’ group consisting of four species,Episyrphus balteatus, Betasyrphus serarius, Syrphus vitripennis andSphaerophoria sp.; an oligophagous ‘specialist’ group consisting of three species,Metasyrphus hakiensis, Dideoides latus andParagus hemorrhous; andLeucopis puncticornis, which showed a preference for two aphid species on the plantTorilis scabra. The prey aphids of the second group have behavioral or morphological defense mechanisms that are effective for preventing attacks by generalist hoverflies; two prey aphids are aggressive toward generalist predators and the others are protected by ant-attendance. The specialist hoverflies seem to be adapted to overcome these defense mechanisms. The prey ranges overlapped little between the generalist and the specialist groups, while those within the generalist group overlapped greatly.     

Distribution of filter-feeding caddisflies (Trichoptera) and plankton drift in a Swedish lake-outlet stream

The objectives of this investigation were to relate the longitudinal distribution of filter-feeding caddisflies to quality and quantity of seston, and to document factors facilitating coexistence among filter-feeding species, in a 4th-order lake-outlet stream in central Sweden. A sharp decline in abundance and biomass of filtering caddisflies was evident within 1 km from the lake outlet following negative power functions. In contrast to particulate organic carbon, significant reductions of both phytoplankton and zooplankton biomass, especially some large species, were recorded between the lake-outlet and 1.9 km downstream. Differences in longitudinal and temporal distribution provide evidence of resource partitioning between filtering species included.     

Habitat exploitation by larvae of Amphipsyche meridiana (Trichoptera: Hydropsychidae) in a Javanese lake outlet

SUMMARY. 1. Trichopteran populations below a dam on the River Tuntang (Central Java) and on intake screens above the dam consisted almost exclusively of Amphipsyche meridiana. Larvae on dam screens were in tightly packed aggregations, with greater densities in deeper water, and were predominantly fourth or fifth instars during the period of observation. Below the dam, 40% of larvae were in the first three instars. Larvae at the dam screens were heavier and yielded larger emerging adults which contained more eggs per female.
2. Mean net mesh sizes of fifth instar larvae varied greatly from 34×26 μm to 125×106 μm with larger meshes having progressively thicker strands. It is suggested that larger mesh size may be positively correlated with faster flow rates. The dinoflagellate Peridinium , commonly found in the guts of larvae below the dam, was virtually absent in dam screen larvae, possibly due to mesh size differences.
3. The behaviour of larvae in aggregations was observed in a laboratory flow channel. After experimental destruction of feeding nets, larvae immediately ingested silk prior to the construction of a new net. Nets were spun in a'figure 8'fashion, and took between 11 and 30 min to complete. Stridulation between larvae occurred frequently and may be related to the defence of silk reserves within territories.     

Suspension feeding of anuran larvae at low concentrations of Chlorella algae (Amphibia,Anura)

Summary Ingestion and filtering rates in larval Xenopus laevis, Bufo calamita, Rana temporia and Bufo bufo fed suspensions of Chlorella fusca were investigated. Concentrations were measured with a Coulter Counter. (1) For all species, filtration occurred at concentrations far below those reported by other authors for Rana sylvatica feeding on Chlorella pyrenoidosa. For Bufo bufo, only larvae near metamorphosis showed ingestion at low particle concentrations. Since buccopharyngeal ventilation continues even in the absence of food particles, this threshold feeding behaviour in the younger larvae must be due to different mechanisms to those found in Daphnia and Calanus studied by other authors: probably reduction of the buccal pumping rate and the mucus production of the filter apparatus. (2) For B. calamita, R. temporaria and X. laevis the highest suspension feeding efficiency was at early tadpole stages, corresponding with the high growth rate of these stages. (3) The life histories of the species provide the basis for understanding their different retention efficiencies and functional responses.Supported by the Deutsche Forschungsgemeinschaft-DFG     

The identification of British limnephilid larvae (Trichoptera: Limnephilidae) which have single-filament gills

SUMMARY. Keys are provided to identify those British limnephilid larvae which are characterized by having gill sites occupied solely by single filaments at the final instar. Most species can be identified at the final instar but many species can also be identified at the earlier instars. A key is also supplied to distinguish the early instar larvae as a group from other limnephilid larvae. Brief notes on distribution and habitat are given. The species identified at least at the final instar are:- Apatania wallengreni, A. auricula, A. muliebris, Drusus annulatus, Ecclisopteryx guttulata, Potamophylax latipennis, P. cingulatus, P. rotundipennis, Melampophylax mucoreus, Allogamus auricollis, Hydatophylax infumatus, Chaetopteryx villosa . It was not possible to segregate Halesus radiatus from H. digitatus, Stenophylax permistus from S. vibex , or S. lateralis from S. sequax .     

Effects of partitioning allochthonous and autochthonous resources on food web stability

The flux of energetic and nutrient resources across habitat boundaries can exert major impacts on the dynamics of the recipient food web. Competition for these resources can be a key factor structuring many ecological communities. Competition theory suggests that competing species should exhibit some partitioning to minimize competitive interactions. Species should partition both in situ (autochthonous) resources and (allochthonous) resources that enter the food web from outside sources. Allochthonous resources are important sources of energy and nutrients in many low productivity systems and can significantly influence community structure. The focus of this paper is on: (i) the influence of resource partitioning on food web stability, but concurrently we examine the compound effects of; (ii) the trophic level(s) that has access to allochthonous resources; (iii) the amount of allochthonous resource input; and (iv) the strength of the consumer–resource interactions. We start with a three trophic level food chain model (resource–consumer–predator) and separate the higher two trophic levels into two trophospecies. In the model, allochthonous resources are either one type available to both consumers and predators or two distinct types, one for consumers and one for predators. The feeding preferences of the consumer and predator trophospecies were varied so that they could either be generalists or specialists on allochthonous and/or autochthonous resources. The degree of specialization influenced system persistence by altering the structure and, therefore, the indirect effects of the food web. With regard to the trophic level(s) that has access to allochthonous resources, we found that a single allochthonous resource available to both consumers and predators is more unstable than two allochthonous resources. The results demonstrate that species populating food webs that experience low to moderate allochthonous resources are more persistent. The results also support the notion that strong links destabilize food web dynamics, but that weak to moderate strength links stabilize food web dynamics. These results are consistent with the idea that the particular structure, resource availability, and relative strength of links of food webs (such as degree of specialization) can influence the stability of communities. Given that allochthonous resources are important resources in many ecosystems, we argue that the influence of such resources on species and community persistence needs to be examined more thoroughly to provide a clearer understanding of food web dynamics.     

Larval and adult seed consumption affected by the degree of food specialization in Amara (Coleoptera: Carabidae)

Many carabid beetles (Coleoptera: Carabidae) are known to feed on plant seeds, but the level of specialization on this food differs. This is the first study in which seed consumption is assessed for all larval instars and adults of ground beetles. Three species of Amara with syntopic occurrence, Amara aenea (DeGeer), Amara familiaris (Duftschmid) and Amara similata (Gyllenhal), were examined. Larvae of all three instars and adults were fed seeds of Stellaria media (L.) Vill., Capsella bursa‐pastoris (L.) Med. and Taraxacum officinale Wick. ex Wigg. in a laboratory no‐choice experiment. In general, larvae, particularly the first instar, showed greater differences in seed consumption than the adults, although the latter showed similar but less marked pattern. Amara aenea consumed all offered seed diets in all life stages. All three larval instars of granivorous A. familiaris almost exclusively fed on seeds of S. media and the adults also ate significantly more of this than other seeds. Amara similata consumed mostly seeds of C. bursa‐pastoris in the first instar and adult stages, whereas the larvae of the later instars seemed to be unspecialized on particular seed diet. Differences in seed‐specific consumption between larval instars in granivorous carabids are reported for the first time. The results provide further support for the parallel evolution of various degrees of granivory in the genus Amara, which may ultimately facilitate species coexistence. The daily seed consumption by the larvae was comparable or (in case of the third instar) even higher than that by the adults. Hence, we suggest that larvae may be the important consumers of seed in the field and should not be forgotten when seed predation is assessed.