Diet composition of two larval headwater stream salamanders and spatial distribution of prey

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Prey use of the fishing spider Dolomedes triton (Pisauridae,Araneae): an important predator of the neuston community

Summary Prey of feeding juvenile and adult Dolomedes triton (Walckenaer 1837) were sampled over two seasons on three small ponds in central Alberta, Canada. Prey were mainly insects active at the water surface with truly aquatic species making up about 14% of the diet. Throughout the season aquatic and semi-aquatic Heteroptera represented about 30% of the prey. Diptera and adult Odonata were also important prey items but their abundance in the diet was more variable seasonally. Of the 625 prey items recorded nearly 50% were represented by taxa taken no more than once by spiders in one of the five size classes (adult females, adult males, large, intermediate and small juveniles). Large spiders did not take the smallest prey available, although small and intermediate-sized spiders fed on nearly the full size range taken by larger spiders. Cannibalism was common, accounting for 5% of the observations, with females and large juveniles as the most frequently observed cannibals. We hypothesize that intraguild predation (including cannibalism) could be an important coevolutionary force structuring phenology, population dynamics and microhabitat use of the predatory guild of the neuston community.     

Feeding guild structure of beetles on Australian tropical rainforest trees reflects microhabitat resource availability

1.?We tested the hypotheses that feeding guild structure of beetle assemblages changed with different arboreal microhabitats and that these differences were consistent across rainforest tree species. 2.?Hand collection and beating techniques were used from the gondola of the Australian Canopy Crane to collect beetles from five microhabitats (mature leaves, flush leaves, flowers, fruit and suspended dead wood) within the rainforest canopy. A simple randomization procedure was implemented to test whether the abundances of each feeding guild on each microhabitat were different from that expected based on a null hypothesis of random distribution of individuals across microhabitats. 3.?Beetles from different feeding guilds were not randomly distributed, but congregated on those microhabitats that are likely to provide the highest concentrations of their preferred food sources. Herbivorous beetles, in particular, were over-represented on flowers and flush foliage and under-represented on mature leaves and dead wood. Proportional numbers of species within each feeding guild were remarkably uniform across tree species for each microhabitat, but proportional abundances of feeding guilds were all significantly non-uniformly distributed between host tree species, regardless of microhabitat, confirming patterns previously found for arthropods in trees in temperate and tropical forests. 4.?These results show that the canopy beetle community is partitioned into discrete assemblages between microhabitats and that this partitioning arises because of differences in feeding guild structure as a function of the diversity and the temporal and spatial availability of resources found on each microhabitat.     

Coexistence in a guild of filter feeding caddis larvae: do different instars act as different species?

Summary Guild structure and coexistence of filter feeding caddis larvae was studied in three lake-outlet streams in northern Finland. Natural stones were used as sampling units, and for each stone measurements of six microhabitat variables were taken. Species and species instar relationships in the multivariate microhabitat space were analyzed by a method based on Principal Components Analysis. Seven species of filtering caddis larvae were found at the study sites, but detailed analysis was restricted to the four most abundant ones (Polycentropus flavomaculatus, Hydropsyche angustipennis, H. pellucidula, H. saxonica). P. flavomaculatus was the microhabitat generalist of the guild, whereas all the hydropsychids were narrowly specialized in at least one larval instar. In all species, different instars utilized the microhabitat somewhat differentially. Moss content and Froude number were significantly different between instar microhabitats in all comparisons. Ontogenetic niche changes not only separated species instars from each other, but also profoundly changed the biotic as well as abiotic environment of the species at different phases of larval development. This may have important effects on the dynamics of interacting species and, consequently, on the guild structure. While some of the more classical models of coexistence may also be relevant for understanding coexistence in this guild of sessile stream insects, ontogenetic niche changes clearly need to be taken into consideration in future studies of guild structure and species interactions of filter feeding caddisfly larvae.     

Predation on meiobenthic assemblages: resource use of a tanypod guild (Chironomidae, Diptera) in a gravel stream

1. Three predatory chironomid species constituted numerically 8.8% (± 95% CL 2.2) of the macro- and meiobenthic community at the sediment surface and in the hyporheic zone of Oberer Seebach, a gravel stream in Lower Austria. Larvae of Thienemannimyia geijskesi (Goetghebuer) and Nilotanypus dubius (Meigen) occurred in higher densities in sediment depths between 10 and 40 cm, whereas Conchapelopia pallidula (Meigen) achieved higher densities at the sediment surface. The three species completed one generation in a year. 2. A total of ninety-seven prey species and instars were identified by gut analyses, of which forty-one benthic rotifer species constituted 69.5% of individuals and twenty-three chironomid species and their instars, 22.9%. The three tanypod species showed shifts from mainly rotifer species in early instars to chironomids and diverse other meio- and macrofaunal taxa in later instars. Rather than shifting towards larger prey sizes, growing predators expanded their upper size thresholds and continued to include smaller prey species in their diet. The extent to which tanypod instars fed on similar prey size classes declined with increasing larval size. Predation by tanypods amounted to 2.2% (± 95% CL 0.1) of the combined prey densities and prey consumption averaged 1.32 (bootstrap 95% CL 1.26–1.39) individuals per predator individual. 3. Preferences for microhabitat flow differed between predator species and in the prey assemblage. Prey densities and densities of T. geijskesi and C. pallidula were highest in pool areas, whereas N. dubius achieved high densities in riffle sites. 4. Tanypod larvae fed non-selectively among prey types. To test the significance of observed size(instar)-specific spatial and dietary overlap values amongst tanypod species, simulations were generated from random models for pairs of intra- and interspecific associations of individuals and groups of prey and predator species. Groups and individuals of tanypod instars fed near randomly on groups of prey types and a high proportion (P > 0.60) of prey individuals are quasi-randomly chosen by tanypods in those patches. Tanypod instar-pairs did not show a sustained trophic resource partitioning in time, thus reducing the degree of competitive interactions for food in this predator guild. Spatially segregated and non-segregated tanypod instars formed random aggregations independent of each other at different flow microhabitats. 5. Species-rich prey assemblages such as benthic rotifers and larval chironomids increased the probability of non-selective feeding upon a wide spectrum of prey species by tanypods. Prey choice was governed by prey availability and tanypod individuals fed on many species at rather even proportions independent of each other.     

Microhabitat use in a mediterranean riverine fish assemblage

Summary We examined microhabitat use in Barbus graellsii, Barbus haasi, Chondrostoma toxostoma, Rutilus arcasii, and Salmo gairdneri over a 19 month period in the upper Rio Matarraña, Spain. B. graellsii and Ch. toxostoma exhibited non-random microhabitat use during all seasons and preferentially occupied deep microhabitats with heterogeneous substrates. During the majority of seasons in which they were present, B. haasi and R. arcasii occurred in microhabitats similar to those occupied by B. graellsii and Ch. toxostoma. S. gairdneri was over-represented in high velocity microhabitats with erosional substrates. We did not observe any evidence of interspecific interference competition or avoidance. Substrate composition did not appear to affect microhabitat use outside of its covariation with depth and velocity. Seaonal variation in microhabitat use by B. graellsii, B. haasi and Ch. toxostoma was strongly correlated with seasonal changes in microhabitat availability. S. gairdneri, however, occurred closer to the substrate when average velocities were high. Larger B. graellsii and B. haasi sometimes occupied deeper, higher velocity microhabitats than did smaller specimens. Larger B. graellsii also occasionally occurred farther from shelter than did smaller specimens; the reverse was true for B. haasi. Larger Ch. toxostoma sometimes were found farther from both the substrate and shelter than smaller individuals, whereas smaller specimens occasionally inhabited deeper areas with more depositional substrates than did larger Ch. toxostoma. During Late Summer 1985, smaller Ch. toxostoma also occupied microhabitats with higher velocities than did larger specimens. A comparison of microhabitat use for two species present in both upper and lower portions of the Matarraña indicated that most differences in microhabitat use could be attributed to inter-site differences in microhabitat availability. The data suggest, hovever, that both species shifted to more protected microhabitats in the higher velocity site. Assemblage members generally occupied statistically distinguishable microhabitats and could be classified as: 1) high-velocity upper water column (S. gairdneri), 2) low velocity lower water column (B. graellsii, Ch. toxostoma and R. arcasii), and 3) shelter-oriented benthic (B. haasi). The introduction of S. gairdneri during Winter 1984 did not produce microhabitat shifts in any of the native species. Whether or not the native species affected microhabitat use in S. gairdneri is unknown. Interspecific competition for space, however, did not appear to strongly influence microhabitat use among the native species.     

Coexistence of two termite-eating specialists (Araneae)

1. Competition among closely-related specialist predators has rarely been studied, and thus the mechanism of their coexistence remains enigmatic. Interspecific competition among specialised co-occurring predators capturing termites should be high.
2. Here we investigated various niche dimensions, namely temporal, spatial and trophic, of a couple of jumping spider species of the genus Stenaelurillus (Stenaelurillus guttiger and S. modestus) from South Africa, to find whether these two species co-exist and along which niche dimension(s) they differentiate.
3. The two species co-occurred in two out of five study sites. Body size was not significantly different between the species. The phenology was shifted so that one species matured earlier. Circadian activity was not different, as both species were diurnal and active at similar times. Both species preyed almost exclusively on termites. The fundamental trophic niche was very similar and rather narrow. The realised trophic niche at the prey order level of both species was similar, but at the genus level it was different. In S. modestus it was narrower, as it captured mainly Odontotermes, while S. guttiger exploited a few termite species. The size of prey captured was also similar between the two species. The frequency of intraguild predation was negligible.
4. We conclude that both Stenaelurillus species are specialised termitophagous predators. The two species can coexist across broad spatial scales due to spatial segregation on the landscape. At the sites where they co-occur, the two species specialise on different termite prey, promoting local coexistence.

     

Microhabitat use in a stream fish assemblage

We examined microhabitat use among fishes in a 37-m section of Coweeta Creek, North Carolina. Numerical abundances of species changed substantially during the 17-month study period. Microhabitat availability, however, did not change markedly during our investigation. Seasonal principal component analyses of microhabitat availability and fish microhabitat use data extracted two main patterns of non-random microhabitat use. Clinostomus funduloides, Notropis eoccogenis and Semotilus atromaculatm were significantly over-represented in deep areas with low to intermediate velocities and depositional substrata. Campostoma oligolepis, Coitus bairdi, Etheostoma blennioides, Rhinichthys cataractae and Salmo gairdneri all occurred in intermediate to deep microhabitats with moderate to high velocities and erosional substrata. Five of seven species exhibited seasonal variation in microhabitat utilization, whereas six species displayed size-related variation in use. Size-related variation was probably ontogenetic. We attributed most seasonal changes in microhabitat use to variations in microhabitat availability.
We used canonical analysis of discriminants to identify factors maximizing interspecific differences in microhabitat use. This analysis indicated that species could be assigned to either a benthic or a water column guild. Species within a guild generally could not be differentiated statistically, whereas members of different guilds were readily separable. These patterns persisted throughout the study, despite changes in numerical abundances of assemblage members. There was no evidence of either exploitation or interference competition for microhabitat, consequently it is unlikely that spatial resources were limiting during our study.     

Microhabitat use by Blennius fluviatilis in the Río Matarraña, Spain

SUMMARY.

• 1 Microhabitat use by Blennius fluviatilis in the Río Matarraña, Spain, varied significantly among dates during a 19-month study. Most temporal variation, however, was attributable to changes in microhabitat availability.
• 2 B. fluviatilis demonstrated non-random use of available microhabitats during each sampling period, and generally occupied deeper microhabitats with higher average current velocities dominated by rubblegravel substrates.
• 3 B. fluviatilis also demonstrated non-random use of available nest sites; males generally nested under the largest available pieces of rubble, in areas with less gravel or sand. Water column depth influenced nest site use in two of four study areas.
• 4 We found few microhabitat differences between spawning and nonspawning periods, or between males and females. In addition, microhabitat use was similar among B. fluviatilis size-groups.
• 5 Although B. fluviatilis often were over-represented in deeper, erosional areas, blennies necessarily inhabited a wide range of microhabitats because average current velocities and water depths fluctuated greatly during the study. Tolerance of a broad range of environmental conditions may contribute to the species' persistence in habitats that exhibit extreme seasonal changes in discharge such as the Matarraña.

     

Microhabitat differentiation among serotinous plants in the Namib Desert

Abstract. Four coexisting serotinous desert plants in the central Namib were investigated with respect to microhabitat preferences. The annual Blepharis grossa preferred the microhabitat on the plains, while the perennial Petalidium setosum dominated in channels. The remaining two species, the common Geigeria alata and the rare Geigeria ornativa, were evenly distributed in all microhabitats. Interspecific competition, seed dispersal mode and ecophysiological niches might be responsible for this pattern.     

Competitive release in microhabitat use among coexisting desert rodents: a natural experiment

Summary Competitive release among desert rodents on sand dunes of differing species richness was examined in the Great Basin and Mohave Deserts, USA. Expansions in microhabitat use were exhibited by the kangaroo rats Dipodomys ordii and D. merriami (granivorous heteromyid rodents, weighing 49 and 42 g, respectively) as the number of coexisting heteromyid species decreased geographically. Perognathus longimembris, the only common small heteromyid species (7 g) exhibited no competitive release. This may be due either to the absence of competitive interactions that affect the use of space by P. longimembris or to an unacceptable increase in risk of predation that precludes the use of more open microhabitats even in the absence of kangaroo rats. The breadth of microhabitat use of an omnivorous cricetid, Peromyscus maniculatus, decreased as the density of Perognathus longimembris increased, and increased as the density of conspecifics increased. The evidence for competitive release in Dipodomys and not in Perognathus is consistent with the hypothesis that species in the same guild and of similar size compete more intensely than species of disparate size.     

Do Predators Condition the Distribution of Prey within Micro Habitats? An Experiment with Stoneflies (Plecoptera)

The selection of habitat by macroinvertebrates living in running waters may be influenced by the physical characteristics of the substratum, as well as by the presence of other species. In this study, an artificial river with three different substrata (pebbles, detritus, and leaves) was utilized to analyze the microhabitat preference of two Plecoptera prey species (Amphinemura sulcicollis and Brachyptera risi), both in absence and in presence of a Plecoptera predator species (Perla marginata). In the absence of predators, both prey species showed a clear preference for the leaf microhabitat. When the predators were present, only Brachyptera risi showed a change of microhabitat selection, with a decrease of leaves and an increase of pebbles and detritus utilization. Amphinemura sulcicollis did not change their substratum utilization. This study demonstrates that the presence of a predator may affect microhabitat selection through a switch from the preferred to the less preferred substrata, although not all species change their habitat utilization in response to predator presence. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Niche segregation among sympatric Amazonian teiid lizards

We examined standard niche axes (time, place, and food) for three sympatric teiid lizards in the Amazon rain forest. Activity times during the day were similar among species. Ameiva ameiva were in more open microhabitats and had higher body temperatures compared with the two species of Kentropyx. Microhabitat overlaps were low and not significantly different from simulations based on Monte Carlo analysis. Grasshoppers, crickets, and spiders were important in the diets of all three species and many relatively abundant prey were infrequently eaten (e.g., ants). Dietary overlaps were most similar between the two species of Kentropyx even though microhabitat overlaps were relatively low. A Monte Carlo analysis on prey types revealed that dietary overlaps were higher at all ranks than simulated overlaps indicating that use of prey is not random. Although prey size was correlated with lizard body size, there were no species differences in adjusted prey size. A. ameiva ate more prey items at a given body size than either species of Kentropyx. Body size varies among species, with A. ameiva being the largest and K. altamazonica the smallest. The two species of Kentropyx are most distant morphologically, with A. ameiva intermediate. The most distant species morphologically are the most similar in terms of prey types. A morphological analysis including 15 species from four genera revealed patterns of covariation that reflected phylogenetic affinities (i.e., taxonomic patterns are evident). A cluster analysis revealed that A. ameiva, K. pelviceps, and K. altamazonica were in the same morphological group and that within that group, A. ameiva differed from the rest of the species. In addition, K. pelviceps and K. altamazonica were distinguishable from other species of Kentropyx based on morphology. Received: 26 December 1998 / Accepted: 15 September 1999     

Ontogenetic Shifts in Patterns of Microhabitat Utilization in the Small-headed Clingfish, Apletodon Dentatus (Gobiesocidae)

The patterns of microhabitat utilization by the clingfish Apletodon dentatus were investigated, based on SCUBA diving surveys at the Arrábida Marine Park (Portugal). In all inspected microhabitats, this species was only found in algal turfs, sea urchins and boulders. The association of A. dentatus with sea urchins is here analysed for the first time. There was a differential utilization of the microhabitats, with small juveniles recruiting to algal turfs, intermediate individuals found in association with the sea urchins Paracentrotus lividus and Sphaerechinus granularis and larger fish occurring mainly in boulders. The depth distribution patterns are also analysed.     

Identifying inter‐ and intra‐guild feeding activity of an arthropod predator assemblage

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Species composition of dabbling duck assemblages: ecomorphological patterns compared with null models

Ecomorphological patterns of breeding dabbling duck (Anas spp.) assemblages were studied in six regions in northern Europe. Observed spacings among species in terms of bill lamellar density and body length were compared with expected spacings based on null models incorporating different levels of constraints (regional species pools, species relative abundances, lake size and habitat requirements of species). Deviations of observed spacings from expected ones were compared with prey abundance and prey size diversity in the lakes. Observed spacings in terms of body length, but not in terms of bill lamellar density, were greater than expected on the basis of null models. The most abundant species were generally relatively more different than less abundant species in terms of body length but not in terms of bill lamellar density. Deviations between observed and expected spacings in terms of body length were more like those predicted by the competition hypothesis in lakes with low food abundance than in lakes with high food abundance. Patterns in bill lamellar spacings were not related to food abundance nor to food size diversity. In general, patterns in body length spacings were consistent with the competition hypothesis whether the null model used in comparisons was constrained or not.     

Predator avoidance,microhabitat shift,and risk-sensitive foraging in larval dragonflies

Summary Dragonfly larvae (Odonata: Anisoptera) are often abundant in shallow freshwater habitats and frequently co-occur with predatory fish, but there is evidence that they are underutilized as prey. This suggests that species which successfully coexist with fish may exhibit behaviors that minimize their risk of predation. I conducted field and laboratory experiments to determine whether: 1) dragonfly larvae actively avoid fish, 2) microhabitat use and foraging success of larvae are sensitive to predation risk, and 3) vulnerability of larvae is correlated with microhabitat use. I experimentally manipulated the presence of adult bluegills (Lepomis macrochirus) in defaunated patches of littoral substrate in a small pond to test whether colonizing dragonfly larvae would avoid patches containing fish. The two dominant anisopteran species, Tetragoneuria cynosura and Ladona deplanata (Odonata: Libellulidae), both strongly avoided colonizing patches where adult bluegills were present. Laboratory experiments examined the effects of diel period and bluegills on microhabitat use and foraging success, using Tetragoneuria, Ladona and confamilial Sympetrum semicictum, found in a nearby fishless pond. Tetragoneuria and Ladona generally occupied microhabitats offering cover, whereas Sympetrum usually occupied exposed locations. Bluegills induced increased use of cover in all three species, and use of cover also tended to be higher during the day than at night. Bluegills depressed foraging in Tetragoneuria and to a lesser extent in Ladona, but foraging in Sympetrum appeared unaffected. Other laboratory experiments indicated that Sympetrum were generally more vulnerable than Tetragoneuria or Ladona to bluegill predation, and that vulnerability was positively correlated with use of exposed microhabitats. Both fixed (generally low use of exposed microhabitats, diel microhabitat shifts) and reactive (predator avoidance, predator-sensitive microhabitat shifts) behavioral responses appear to reduce risk of predation in dragonfly larvae. Evidence indicates that vulnerability probably varies widely among species and even among instars within species, and suggests that spatial distributions of relatively vulnerable species may be limited by their inability to avoid predation.