Microhabitat associations of three species of Dryopoidea (Coleoptera) in an Ozark stream: a comparison of substrate, and simple and complex hydraulic characters

Microhabitat associations of adults and larvae of Stenelmis lateralis Sanderson, Optioservus sandersoni Collier (Coleoptera: Elmidae) and larvae of Psephenus herricki (DeKay) (Coleoptera: Psephenidae) were examined within riffles of an Ozark stream in Missouri. The invertebrate fauna was sampled from 150 quadrats, and each quadrat was characterized by a suite of substrate, simple hydraulic, and complex hydraulic variables. Larvae were assigned to size classes for analyses. MANOVAs were performed to determine if differences existed between sites of presence and absence for each of the three species separately. Subsequently, ANOVAs and Bonferroni sequential adjustments were performed to determine differences in each habitat variable that are related to presence or absence of each group. Multiple regression was performed to determine which habitat variables were important determinants of density for each taxon. Finally, discriminant function analyses were performed to determine the degree of overlap in microhabitat associations of each group. A clear distinction was seen between sites of occurrence and absence for P. herricki, and for larvae of each elmid species (MANOVAs). For P. herricki, current velocity and the complex hydraulic characteristics of Reynolds number and boundary Reynolds number were important in determining beetle presence. In contrast, substrate characteristics were major determinants of presence for larvae of O. sandersoni and S. lateralis. In general, the density of each of the three species was related to a different subset of abiotic variables. For each species, the most definitive microhabitat associations were seen in the early instars. Microhabitat associations for larvae of each elmid species were size class-specific. Inclusion of complex hydraulic characteristics along with substrate and simple hydraulic characteristics provided greater resolution of microhabitat associations.     

Habitat selection as a source of inter‐specific differences in recruitment of two diadromous fish species

• 1 For aquatic species with highly dispersive offspring, the addition of new individuals into an area (recruitment) is a key process in determining local population size so understanding the causes of recruitment variability is critical. While three general causative mechanisms have been identified (the supply of individuals, habitat selection and mortality), we have a limited understanding of how variation in each is generated, and the consequences this may have for the spatial and temporal distribution of recruits.
• 2 We examined whether active habitat selection during settlement could be the cause of variability in populations of two diadromous fish species using a field survey and laboratory‐based choice experiments. If larval behaviour is important, we predicted there would be inter‐specific differences in abundance between sites during the survey, and that larvae would prefer water collected from sites with higher conspecific abundances during the experiments.
• 3 During the field survey, significant differences were detected between two rivers (the Cumberland and Grey), with one species (Galaxias maculatus) found in higher abundances at one site (the Cumberland River) while comparable numbers of a closely related species (Galaxias brevipinnis) were caught at both sites. Laboratory choice experiments were conducted to determine whether larval preferences during settlement could be the cause of these differences. G. maculatus larvae showed a preference for freshwater over saltwater, indicating that the fish may be responding to reduced salinities around river mouths during settlement. The results of a second experiment were consistent with the notion that larval preferences could be the mechanism driving differences in the populations of the two rivers, with G. maculatus preferring water collected from the Cumberland River while G. brevipinnis did not prefer water from either river.
• 4 These results demonstrate that active habitat selection may be important in establishing spatial patterns of larvae at settlement, and that multiple cues are likely to be involved. This study also demonstrates that the behaviours exhibited by individuals can strongly influence the structure and dynamics of populations of aquatic species with complex life cycles.

     

Space: A non-limiting resource in the niches of some abundant coral reef gastropods

Given the importance attributed to the occupation of space in benthic coral reef communities, this study asks the question: are any particular microhabitat types limiting resources for an assemblage of worm-eating gastropods on Heron reef (Great Barrier Reef). Microhabitat resource use was measured on three occasions, separated by 12 and 20-month periods. The gastropod populations were typical of those of other Indo-Pacific sites with respect to mean shell size and density. Fluctuations in species' size and density are assumed to have not significantly influenced availability of microhabitat resources. Gastropods occurred mainly in the structurally complex “refuge” microhabitats during the day and showed an increased abundance in smooth, exposed, “foraging” microhabitat nocturnally. Nassarius gaudiosus is the most extreme microhabitat specialist diurnally and the most extreme microhabitat generalist nocturnally. A similar, although less pronounced trend was exhibited by other gastropod species. Microhabitat niche overlap was high for Conus coronatus, C. miliaris, C. flavidus, Vasum turbinellus and N. gaudiosus at night and was also high during the day for all these species except N. gaudiosus, which showed little overlap with other gastropod species diurnally. Using gastropod abundance data from all samples, and independently derived microhabitat abundance data, multiple regression analysis demonstrated:

1. A significant relationship between the abundances of N. gaudiosus, C. coronatus, and C. flavidus and the abundance of microhabitat 2 (sand under rocks=“refuge”).
2. No positive association between gastropod abundance and the abundance of microhabitat 7a (thin layer of algal-bound sand on reef limestone).

Only N. gaudiosus is abundant in microhabitat 2. Therefore it is concluded that, with some exceptions, microhabitat abundance does not have a significant influence, directly or indirectly, on gastropod abundance. It is possible that density-independent mortality is maintaining gastropod densities below that at which competitive interactions, with respect to microhabitats, have significant effects on the gastropods' use of those resources.     

Stream microhabitat selectivity,resource partitioning,and niche shifts in grazing caddisfly larvae

Microhabitat selectivity, resource partitioning, and niche shifts in five species of grazing caddisfly larvae (Glossosoma califica, G. penitum, Dicosmoecus gilvipes, Neophylax rickeri, and N. splendens) were quantified by underwater measurement of microhabitat availability and utilization in three northern California streams. The microhabitat parameters water depth and velocity and rock size, roughness, and slope were measured. Comparisons of habitat available to habitat used revealed significant selection for at least two microhabitat parameters by each population, with depth and velocity being the most important. Comparisons of habitat used by different species showed significant partitioning of at least two microhabitat parameters at each site, with depth being partitioned at all sites. Non-parametric discriminant analysis revealed significant microhabitat partitioning on a multivariate level at two sites. Comparisons of habitat used at different sites quantified a major niche shift by D. gilvipes in its preference for riffles versus pools. Size-selective predation by dippers (Cinclus mexicanus) and steelhead (Salmo gairdneri gairdneri) is proposed as a hypothesis to explain the observed resource partitioning and niche shift.     

The upstream/downstream movement paradox of lotic invertebrates: quantitative evidence from a Welsh mountain stream

• 1 This study attempts to determine the mechanisms by which the downstream displacement of lotic invertebrates is compensated by the upstream movements of immatures and adults. To this end, submerged and aerial traps were set up at three sites, each 100 m apart on a small mountain stream (Yr Ogof) in North Wales and operated for 12 months.
• 2 At Site 1 (the source), 19.3% of the benthic invertebrates lost as drift were replaced by the upstream movement of aquatic stages. At Site 2, the average upstream compensation was 51.1% (although there was a marked difference between the two traps at the site). At downstream Site 3 the average compensation was 55.4%. The net loss of benthos downstream over 1 year was estimated to be 261920 individuals from Site 1, 41891 from Site 2, and 40470 from Site 3.
• 3 At Sites 1 and 2, the numbers of invertebrates drifting were positively correlated with both current speed and water depth. At Sites 2 and 3, the numbers moving upstream were positively correlated with water temperature. At all three sites, the numbers of animals drifting were positively correlated with the numbers moving upstream, under water.
• 4 In none of the eight common species of stoneffy did females show a strong overall upstream flight preference—however, two species, Leuctra nigra and Nemoura erratica, showed a significant downstream preference.
• 5 As with the stonefly nymphs, most of the caddisfly larvae showed a longitudinal distribution. Agapetus fuscipes larvae were most abundant at Site 1, yet females showed no preferred flight direction—this would seem to be inappropriate for maintaining this larval distribution pattern. However, females caught moving upstream at Site 2 were bigger and contained twice as many eggs, which were also larger, than females moving upstream at Site 1. The flight patterns of the other Trichoptera also seemed inappropriate for maintaining their respective larval distributions. Immature insects moved upstream at certain sites and times, but trends were not consistent. There was no correlation between female flight direction and local wind speed and direction.
• 6 Downstream displacement of the most abundant non-insect species, Gammarus pulex, was quite considerable at all three sites. However, at several times during the year the numbers moving upstream approached or exceeded those drifting. Maintenance of benthic population densities in this species is thought to be through a combination of upstream movement (which was highly correlated with benthic density at Sites 1 and 3) and production of young over a long (10 month) reproductive period. Maintenance of the benthic populations of the immature stages of the majority of insect species in Yr Ogof is thought to be through oviposition by females in the vicinity of their emergence sites.

     

Micro-habitat use within a guild of newt larvae (Trituridae) in an Alpine lake

Population and ecological parameters such as numbers of larvae, microhabitat use, niche breadth and niche overlap of three species of syntopic larval newts (Alpine newt Triturus alpestris, Italian crested newt T. carnifex, and common newt T. vulgaris) were studied for two years in a small pond at 1160 m a.s.l. in NE Slovenia. Differences in microhabitat partitioning among larval newts were small. The largest niche breadth was estimated for larval T. alpestris, and the narrowest estimate was for larval T. carnifex in both years. Ecological differences seem to be very small and quite variable among sites and years. It appears that the developmental stage and size of newt larvae are more important in explaining resource partitioning than the characteristics of each species. Because of the absence of potential invertebrate predators and adult newts in the second half of the breeding season, the injuries could only be caused by intra-and interspecific predation attempts.     

Differences in ecomorphology and microhabitat use of four saproxylic larvae (Diptera,Syrphidae) in Scots pine stump rot holes

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Decline of unionid mussels enhances hybridisation of native and introduced bitterling fish species through competition for breeding substrate

1. Bitterling fishes (Subfamily: Acheilognathinae) spawn in the gills of living freshwater mussels and obligately depend on the mussels for reproduction. On the Matsuyama Plain, Japan, populations of unionid mussels—Pronodularia japanensis, Nodularia douglasiae, and Sinanodonta lauta—have decreased rapidly over the past 30 years. Simultaneously, the population of a native bitterling fish, Tanakia lanceolata, which depends on the three unionids as a breeding substrate, has decreased. Furthermore, a congeneric bitterling, Tanakia limbata, has been artificially introduced, and hybridisation and genetic introgression occur between them. Here, we hypothesised that decline of the unionids has enhanced this invasive hybridisation through competition for the breeding substrate.
2. Three study sites were set in three streams on the Matsuyama Plain. We collected adult bitterling fishes (native T. lanceolata, introduced T. limbata, and foreign Rhodeus ocellatus ocellatus) once a week from April to October 2013 to measure their densities in streams and to examine seasonal differences in female ovipositor length, which elongates in the breeding season. Simultaneously, we set quadrats and captured unionids and measured environmental conditions. Each unionid individual was kept separately in its own aquarium to collect ejected bitterling eggs/larvae. Tanakia eggs and larvae were genotyped using six microsatellite markers and the mitochondrial cytochrome b gene.
3. Introduced T. limbata was more abundant, had a longer breeding period, and produced more juveniles than native T. lanceolata. Hybrids between the two species occurred at all sites, and in total 101 of the 837 juveniles genotyped were hybrids. The density of P. japanensis was low, at most 0.42 individuals/m². Nodularia douglasiae and S. lauta have nearly or totally disappeared from these sites. Hybrid clutches of Tanakia species occurred more frequently where the local density of P. japanensis was low. Mussels were apparently overused and used simultaneously by three species of bitterlings.
4. Decline of freshwater unionid populations has enhanced hybridisation of native and invasive bitterling fishes through increasing competition for breeding substrate. We showed that rapid decline of host mussel species and introduction of an invasive congener have interacted to cause a rapid decline of native bitterling fish.
5. Degradation of habitat and the introduction of invasive species interact to cause a cascade of extinctions in native species. In our study, obligate parasite species are threatened because the host species are disappearing, which means there is a serious threat of coextinction.

     

Maternal behaviours may explain riffle‐scale variations in some stream insect populations

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Habitat characteristics of grassland Pterostichus species (Coleoptera, Carabidae)

Abstract.

• 1 Pterostichus species were sampled on ninety-two sites distributed throughout north-east England using pitfall trapping.
• 2 The incidence of each species was related to measured site environmental variables using logistic regression.
• 3 Four species groups were identified on the basis of size. The extent of overlap in habitat types between species in each group varied. Two large species overlapped considerably whilst the smaller species showed different responses to one or more environmental variable.
• 4 Possible causes of the differences in habitat overlap between Pterostichus species are discussed.

     

The slow—fast life style characteristics in a suite of six species of odonate larvae

• 1 The validity of the slow—fast lifestyle dichotomy proposed by Sih (1987) was tested in a suite of six odonate species from a restricted geographical area. Data on activity and microhabitat use were obtained in a laboratory study. Further necessary information on life history, macrohabitat (ephemeral‐permanent) use and vulnerability to fish predation was provided by a literature survey.
• 2 Activity was estimated as number of moves and distance moved for the six odonate larvae. Aeschna juncea, Lestes sponsa and Sympetrum danae were categorised as high‐active species, whereas Coenagrion hastulatum, Cordulia aenea and Leucorhinia dubia were categorised as low‐active species.
• 3 C. hastulatum and L. sponsa exploited microhabitats close to the water surface, C. aenea and L. dubia close to the bottom, and A. juncea and S. danae were intermediate in their water depth utilisation.
• 4 A principal component analysis of the data from the laboratory experiment and the literature survey supported the slow—fast life style dichotomy since the variables activity, macrohabitat use, life cycle length and sensitivity to fish predators were highly correlated.

     

Microhabitat use in coexisting desert rodents—The role of population density

Summary Among some species of Sonoran Desert rodents microhabitat differences are density dependent. I studied the differences in microhabitat use among four species of heteromyid rodents (Dipodomys merriami, Perognathus amplus, P. baileyi, and P. penicillatus) at low and at high population densities. Microhabitats are defined by the abundance and size distribution of desert shrubs. During a period of low population density the rodent species showed substantial microhabitat differentiation. Following a large increase in pocket mouse (Perognathus spp.) numbers differences in microhabitat use between species disappeared. The lack of microhabitat differentiation at high density is due to microhabitat shifts rather than an expansion in the number of microhabitats used. The shifts lead to increased similarity among species in microhabitat use. Microhabitat overlap is not constant but it is highly variable and sensitive to changes in rodent abundance.     

Density-dependent regulation of Aedes cantans (Diptera: Culicidae) in natural and artificial populations

Abstract.

• 1 Mortality and size variation (siphon length) in Aedes cantans larvae were examined in natural populations in northern England in 1989 and 1990.
• 2 Under crowded conditions, density-dependent competition led to reduction in the size of both larvae and adults and increased larval mortality.
• 3 Larvae were also maintained in cages in the field at different densities. Results paralleled those for the natural populations in the ponds; larvae maintained at high densities showed increased mortality and reduced size.
• 4 Possible density-dependent factors leading to mortality and size reduction include cannibalism and contact inhibition leading to food shortages.
• 5 The main density-independent factor contributing to larval mortality was habitat desiccation.

     

Geographic isolation and climatic heterogeneity drive population differentiation of Rosa chinensis var. spontanea complex

• Global biodiversity is contracting rapidly due to potent anthropogenic activities and severe climate change. Wild populations of Rosa chinensis var. spontanea and Rosa lucidissima are rare species endemic to China, as well as important germplasm resources for rose breeding. However, these populations are at acute risk of extinction and require urgent action to ensure their preservation.
• We harnessed 16 microsatellite loci to 44 populations of these species and analysed population structure and differentiation, demographic history, gene flow and barrier effect. In addition, a niche overlap test and potential distribution modelling in different time periods were also carried out.
• The data indicate that: (1) R. lucidissima cannot be regarded as a separate species from R. chinensis var. spontanea; (2) the Yangtze River and the Wujiang River function as barriers in population structure and differentiation, and precipitation in the coldest quarter may be the key factor for niche divergence of R. chinensis var. spontanea complex; (3) historical gene flow showed a converse tendency to current gene flow, indicating that alternate migration events of R. chinensis var. spontanea complex between south and north were a response to climate oscillations; and (4) extreme climate change will decrease the distribution range of R. chinensis var. spontanea complex, whereas the opposite will occur under a moderate scenario for the future.
• Our results resolve the relationship between R. chinensis var. spontanea and R. lucidissima, highlight the pivotal roles of geographic isolation and climate heterogeneity in their population differentiation, and provide an important reference for comparable conservation studies on other endangered species.

     

Variation in the ability of larvae of phytophagous insects to develop on evolutionarily unfamiliar plants: a study with gypsy moth Lymantria dispar and Eucalyptus

• 1 By examining variation in the abilities of polyphagous insects to develop on host plants with secondary metabolites that they have never encountered previously, we may be able to gain some insights into the nature of evolution of biochemical mechanisms to process plant secondary metabolites by phytophagous insects.
• 2 The present study aimed to examine variation in the ability of gypsy moth larvae Lymantria dispar (Lymantriidae) to complete development on different species of the plant genus Eucalyptus (Myrtaceae). Leaves of at least some Eucalyptus species contain formylated phloroglucinol derivatives. These are secondary metabolites that are evolutionarily unfamiliar to the gypsy moth.
• 3 Larvae of gypsy moth showed extremely variable responses in larval performance between Eucalyptus species, between individual trees within host plant species, between moth populations, and between individuals within moth populations.
• 4 Larval survivorship was in the range 0–94%, depending on the host. Failure of at least some larvae to complete development on some Eucalyptus species indicates that gypsy moth larvae have a limited ability to process secondary metabolites in eucalypt leaves.
• 5 At least some individuals, however, appear to already possess biochemical mechanisms that process the secondary metabolites in leaves of Eucalyptus species, and therefore the abilities of larvae to complete development on phylogenetically and chemically unfamiliar hosts are already present before the gypsy moth encounters these potential hosts.

     

Instar sizes,life cycles,and food habits of five Rhyacophila (Trichoptera: Rhyacophilidae) species from the Appalachian Mountains of South Carolina,U.S.A.

The larval head widths at each instar, life cycles, and food habits of late instars were determined for five species of Rhyacophila from two Appalachian mountain streams in South Carolina, U.S.A. Rhyacophila acutiloba Morse & Ross was univoltine with two cohorts, one emerging in the spring and another presumably emerging in early autumn. Rhyacophila fuscula (Walker), R. nigrita Banks, and R. carolina Banks were apparently multicohort, univoltine species with extended flight periods. Rhyacophila minor Banks was univoltine with a spring emergence. All species were predaceous and consumed mainly Plecoptera nymphs and Trichoptera larvae.     

Peculiar hyporheic habitat of some <Emphasis Type="Italic">Rhyacophila</Emphasis> species (Trichoptera; Rhyacophilidae) in Japanese mountain streams

We investigated the distribution patterns of Rhyacophila larvae at 2 habitat scales in mountain streams in central Honshu. One was at a rapid glide within a stream reach and the other was in microvertical layers within each rapid and glide. Cobbles were predominant in rapids, whereas sand and gravels were predominant in glides. Mean sediment particle size was smaller in glides, but evenness of sediment size and porosity were greater. A total of 9 species of Rhyacophila larvae were collected from rapids. On the other hand, in glides, only 4 species, R. nipponica, R. shikotsuensis, R. kawamurae, and R. transquilla, were collected, but they were more abundant than in rapids. The larvae of R. transquilla were found mainly in upper layers of the stream bed, whereas the other 3 species, R. nipponica, R. shikotsuensis, and R. kawamurae, occurred both in upper and lower layers. The latter 3 species belong to R. nigrocephala species group, the larvae of which share several common morphological and behavioral characters adapted to hyporheic habitat, such as slender body shape and vermicular movement. It is suggested that higher porosity in glides provides more microhabitat for them, and small-sized sediment particles are appropriate for their burrowing and creeping movement in hyporheic habitat.     

Divergent echolocation call frequencies in insular rhinolophids (Chiroptera): a case of character displacement?

Aims Because rhinolophids have been hypothesized to use echolocation call frequency to recognize conspecifics, sympatric species calling at similar frequencies should be subject to acoustic character displacement, i.e. a drift in frequency values to minimize the risk of misidentification of conspecifics. However, it has been proposed that insufficient geographical separation between populations in sympatry and allopatry may counter the establishment of frequency differences by character displacement. Here we tested the hypothesis that insular populations should exhibit acoustic divergence, and this should be revealed by comparing call frequencies with those observed in mainland, allopatric populations of conspecifics. We also tested whether the evolutionary pressure towards acoustic divergence should be especially strong at sites where rhinolophid species emitting similar call frequencies roost together in order to minimize interspecific frequency overlap. Location Sardinia and southern Italy (Campania, Lazio, Abruzzo). Methods Time‐expanded echolocation calls and body size were recorded from Sardinian populations of Rhinolophus mehelyi Matschie, Rhinolophus hipposideros (Bechstein) and Rhinolophus euryale Blasius. Both call frequencies and forearm length of insular R. hipposideros and R. euryale were compared with those of populations from mainland areas of Italy where R. mehelyi is absent, to explore the hypothesis that the presence of the latter species (which calls at frequency values intermediate between the other two) may determine acoustic divergence in the other species. For Sardinian R. mehelyi and R. euryale, we also carried out intraspecific comparisons of call frequencies between bats from monospecific colonies and those from mixed colonies. Results As hypothesized, Sardinian R. hipposideros and R. euryale called at frequencies higher and lower, respectively, than in the peninsula. In this way, overlap with R. mehelyi is avoided. Body size showed no difference between insular and peninsular populations, i.e. frequency differences are not a by‐product of difference in body size determined by insularity. Frequency values in Sardinian R. euryale from monospecific colonies did not differ from those of bats roosting together with R. mehelyi. However, R. mehelyi showed frequency values significantly higher when associated with R. euryale, possibly to minimize the risk of species misrecognition. Main conclusions At least under geographical isolation, character displacement may be a causal mechanism for shifts in call frequency of sympatric rhinolophids. Species recognition and facilitation of intraspecific communication (with possible implications for mate recognition) constitute the best candidate factors for the phenomenon we observed.     

Microhabitat use by larvae and females of a rare barrens butterfly,frosted elfin (<Emphasis Type="Italic">Callophrys irus</Emphasis>)

The frosted elfin (Callophrys irus) is a localized and declining butterfly found in xeric open habitats maintained by disturbance. We described the effects of woody plant canopy cover, topography and host plant size and density on the quality of microhabitat of wild indigo (Baptisia tinctoria) host plants containing late instar frosted elfin larvae at four study sites in southeastern Massachusetts, United States. We also assessed whether females preferentially depositing eggs on host plants within specific microhabitats, therefore conferring greater survivorship to the larvae through the late-instar stage. We found that moderate amounts of canopy cover and large plant size characterized larvae-occupied host plants. In the absence of tree canopy cover, late instar larvae density remained low even when host plant density was high. However, females oviposited on wild indigo plants without regard to any of the vegetative or environmental variables we measured. These results indicate that canopy cover was an important characteristic of microhabitats containing late instar larvae, and late instar larvae occupancy was determined by suitable microhabitat conditions, and not female oviposition selection. Managing for canopy cover and microhabitat heterogeneity within relatively open habitats is recommended for the maintenance of frosted elfin populations.     

Latitudinal variation in body size of Agrilus planipennis and relationship with fecundity

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