Altitudinal differentiation in the diapause response of two species of dung flies

1. Seasonality is a prime selective factor promoting genetic differentiation of populations. Local adaptation in diapause response was investigated in the two geographically and altitudinally widespread dung flies Scathophaga stercoraria (Diptera: Scathophagidae) and Sepsis cynipsea (Diptera: Sepsidae).
2. Replicate sibships from three sites in Switzerland with low and high altitude dung fly populations were raised in a common laboratory environment simulating the natural decreasing photoperiod and temperature regimen before winter. From field phenologies, the critical photoperiod inducing diapause was predicted to be longer for high than for low altitude populations (12 vs. 10 h for Sc. stercoraria , and 12.25 vs. 11 h for Se. cynipsea ) if they are locally adapted.
3. Contrary to expectation and to Sc. stercoraria , which diapauses in the pupal stage, Se. cynipsea diapauses in the adult stage.
4. Low but significant levels of genetic differentiation in pre-winter adult emergence were evident between low and high altitude populations of both species, but they were far from the differences predicted. Scathophaga stercoraria also showed geographical differentiation independent of altitude.
5. Sepsis cynipsea females stopped reproducing at some point before winter, but altitude did not affect the timing of adult diapause. High altitude females and females that did not initiate reproduction before winter survived the simulated winter better.
6. Both species largely used temperature rather than photoperiod as a cue inducing winter diapause, an untypical case of phenotypic plasticity. The hypothesis that Sc. stercoraria , whose generation times are much longer than those of Se. cynipsea , responds to a greater extent to temperature rather than photoperiod only was rejected.     

Geographical and altitudinal population genetic structure of two dung fly species with contrasting mobility and temperature preference

Local adaptation of populations requires some degree of spatio-temporal isolation. Previous studies of the two dung fly species Scathophaga stercoraria and Sepsis cynipsea have revealed low levels of geographic and altitudinal genetic differentiation in quantitative life history and morphological traits, but instead high degrees of phenotypic plasticity. These patterns suggest that gene flow is extensive despite considerable geographic barriers and large spatio-temporal variation in selection on body size and related traits. In this study we addressed this hypothesis by investigating genetic differentiation of dung fly populations throughout Switzerland based on the same 10 electrophoretic loci in each species. Overall, we found no significant geographic differentiation of populations for either species. This is inconsistent with the higher rates of gene flow expected due to better flying capacity of the larger S. stercoraria. However, heterozygote deficiencies within populations indicated structuring on a finer scale, seen for several loci in S. cynipsea, and for the locus PGM (Phosphoglucomutase) in S. stercoraria. Additionally, S. cynipsea showed a tendency towards a greater gene diversity at higher altitudes, mediated primarily by the locus MDH (malate dehydrogenase), at which a second allele was only present in populations above 1000 m. This may be caused by increased environmental stress at higher altitudes in this warm-adapted species. MDH might thus be a candidate locus subject to thermal selection in this species, but this remains to be corroborated by direct evidence. In S. stercoraria, no altitudinal variation was found.     

Population variation in sexual selection and its effect on size allometry in two dung fly species with contrasting sexual size dimorphism

Body size is one of the most important quantitative traits under evolutionary scrutiny. Sexual size dimorphism (SSD) in a given species is expected to result if opposing selection forces equilibrate differently in both sexes. We document variation in the intensity of sexual and fecundity selection, male and female body size, and thus SSD among 31 and 27 populations of the two dung fly species, Scathophaga stercoraria and Sepsis cynipsea, across Switzerland. Whereas in S. cynipsea females are larger, the SSD is reversed in S. stercoraria. We comprehensively evaluated Fairbairn and Preziosi's (1994) general, three-tiered scenario, hypothesizing that sexual selection for large male size is the major driving force of SSD allometry within these two species. Sexual selection intensity on male size in the yellow dung fly, S. stercoraria, was overall positive, greater, and more variable among populations than fecundity selection on females. Also, sexual selection intensity in a given population correlated positively with mean male body size of that population for both the field-caught fathers and their laboratory-reared sons, indicating a response to selection. In S. cvnipsea, sexual selection intensity on males was lower overall and significantly positive, about equal in magnitude, but more variable than fecundity selection on females. However, there was no correlation between the intensity of sexual selection and mean male body size among populations. In both species, the laboratory-reared offspring indicate genetic differentiation among populations in body size. Despite fulfillment of all key prerequisites, at least in S. stercoraria, we did not find hypoallometry for SSD (Rensch's rule, i.e., greater evolutionary divergence in male size than female size) for the field-caught parents or the laboratory-reared offspring: Female size was isometric to male size in both species. We conclude that S. cynipsea does not fit some major requirements of Fairbairn and Preziosi's (1994) scenario, whereas for S. stercoraria we found partial support for it. Failure to support Rensch's rule within the latter species may be due to phylogenetic or other constraints, power limitations, erroneous estimates of sexual selection, insufficient genetic isolation of populations, or sex differences in viability selection against large size.     

Development of polymorphic microsatellite markers for the dung fly (Sepsis cynipsea)

The polyandrous fly Sepsis cynipsea has been used extensively in studies of sexual selection and local adaptation. We isolated and characterized 11 novel microsatellite markers for S. cynipsea from a genomic library and screened 32 flies for polymorphism. All microsatellite markers show high allelic diversity with an average of 9.64 alleles per locus. Two microsatellites were found likely to be X-linked. These novel markers will significantly advance studies of sexual selection and evolutionary genetics of S. cynipsea and related species, especially given the low numbers of markers currently available in this family.     

Oviposition of the dung beetle Aphodius ater in relation to the abundance of yellow dungfly larvae (Scatophaga stercoraria)

1. The dung beetle Aphodius ater and the yellow dungfly Scatophaga stercoraria are temporally co-occurring species in sheep dung, which they use for reproduction and nutrition ( A. ater ) or for reproduction only ( S. stercoraria ) during the spring in northern Germany. Scatophaga stercoraria uses fresh sheep dung pellets a few hours old for oviposition, whereas A. ater lays eggs into 2–10-day-old pellets. In the present study, the egg laying behaviour of A. ater in sheep dung in relation to the presence of larvae of S. stercoraria was investigated experimentally.
2. Choice experiments, based on examining the egg laying behaviour of beetles in 2- and 4-day-old pellets with and without high and low densities of fly larvae, showed the following. In 2-day-old pellets, the beetles did not distinguish between pellets without fly larvae or with fly larvae at low larval density but avoided laying eggs into pellets with a high larval density. In 4-day-old pellets, the beetles always preferred to lay their eggs into pellets without fly larvae, regardless of larval density.
3. The influence of different densities of larvae of S. stercoraria on dung depletion was examined by measuring the dry weight, organic matter content and organic nitrogen content of the remaining dung after larval development. The presence of the larvae led to a reduction in all three parameters.
4. The beetles' behaviour of laying eggs into older pellets, and their awareness of the presence of high densities of fly larvae, enables them to avoid egg laying into pellets that will have been depleted by fly larvae before the beetle larvae have finished their development.     

Effect of landscape structure on the spatial distribution of Mediterranean dung beetle diversity

Aim  Landscape structure influences the distribution of animals, altering their movements and their ability to reach habitat patches. We analysed the spatial patterns of dung beetle species diversity in three differently structured natural landscapes in a Mediterranean protected area in the centre of the Iberian Peninsula.
Location  Cabañeros National Park, Central Spain.
Methods  Diversity components within (α) and among (β) the three main vegetation types in the reserve were compared by using a hierarchical nested design. These were forests, scrublands and grasslands embedded in three different landscapes, where each was the most dominant and structurally connected habitat.
Results  Species richness of grassland habitat did not vary across landscapes, but forest habitat showed lower species richness in the grassland-dominated landscape. Scrubland was the least species-rich habitat, but here again there was no significant variation across landscapes. However, in all cases, there was a significant influence of habitat context (configuration of habitat patches within landscape matrix) on similarity of species composition. These tended to be more similar to the dominant landscape matrix where they were embedded, rather than to the same habitat type in other landscapes. Additive partitioning of diversity showed higher than expected values of β in all landscapes, which indicated a structured response. Highest values of β in the grassland-dominated landscape suggest that this was the least connected landscape for dung beetles.
Main conclusions  Our results suggest that in homogeneous conditions of climate and trophic resources, landscape structure may well be more important than habitat type as a determinant of dung beetle distribution in the Mediterranean.     

The distribution and biology of Lonchopteridae (Diptera) in upland regions of northern England

Abstract. 1. A survey was made of the distribution of Lonchopteridae over 2 years at forty sites in northern England. Material was collected by pitfall trapping.
2. Two species, Lonchoptera lutea and L.furcata , were taken in approximately similar numbers. No other species were recorded.
3. Considerable separation of the two species was found, with both species occurring at ten sites, whilst one species only was taken at twenty-five sites. L.furcata occurred coinrnonly on upland mineral sods, shallow peat soils and on lowland bogs whilst L.lutea was numerically most abundant on upland blanket bog.
4. Almost 39% of the L.lutea specimens and 14% of the L.furcata captures were males.
5. The capture of numbers of males of L.furcata is unusual, since the species is regarded as being parthenogenetic and males occur only in a very small part of the species' range. Confirmation of the association between the males and females of L.furcata is given, whilst there is close agreement between the cliaetotaxy of British males and females, and British and continental European females. The suggestion that the males belong to an undescribed species is rejected.
6. The seasonal capture of L.lutea adults is similar at all altitudes. Captures of males of L.furcata show an abrupt seasonal change above and below about 420 m; captures being in mid-summer in the higher altitude zone and between October and December at lower altitudes. The captures of females of L.furcata show the same trend, but this is partially obscured by the longer life-span of the females. It is suggested that this difference represents a change in the lifecycle, possibly from an annual to a biannual one at the higher altitudes.
7. The biology and distribution of the Lonchopteridae at low altitudes requires investigation.     

Exaggerated male forelegs are not more differentiated than wing morphology in two widespread sister species of black scavenger flies

Sexual selection represents a potent force that can drive rapid population differentiation in traits related to reproductive success. Hence, sexual traits are expected to show greater population divergence than non-sexual traits. We test this prediction by exploring patterns of morphological differentiation of the exaggerated fore femur (a male-specific sexual trait) and the wing (a non-sexual trait) among allopatric and sympatric populations of the widespread sister dung fly species Sepsis neocynipsea and Sepsis cynipsea (Diptera: Sepsidae). While both species occur in Eurasia, S. neocynipsea also abounds in North America, albeit previous studies suggest strong differentiation in morphology, behavior, and mating systems. To evaluate the degree of differentiation expected under neutrality between S. cynipsea, European S. neocynipsea, and North American S. neocynipsea, we genotyped 30 populations at nine microsatellite markers, revealing almost equal differentiation between and minor differentiation among geographic populations within the three lineages. Landmark-based analysis of 18 populations reared at constant 18 and 24°C in a laboratory common garden revealed moderate temperature-dependent phenotypic plasticity and significant heritable differentiation in size and shape of male forelegs and wings among iso-female lines of the three lineages. Following the biological species concept, there was weaker differentiation between cross-continental populations of S. neocynipsea relative to S. cynipsea, and more fore femur differentiation between the two species in sympatry versus allopatry (presumably due to character displacement). Contrary to expectation, wing morphology showed as much shape differentiation between evolutionary independent lineages as fore femora, providing no evidence for faster diversification of traits primarily engaged in mating.     

Effects of dung-pad conditions and density on coprophagous beetle assemblages in a Mediterranean rangeland

Dung beetles highly depend on the ephemeral microhabitat dung which is food resource and larval habitat at the same time. Environmental conditions surrounding a dung pad, such as vegetation structure, have an impact on dung beetle assemblages. We investigated the influence of dung conditions and surrounding habitat characteristics on Mediterranean dung beetle assemblages in a permanently grazed landscape in northern Sardinia. We sampled the dung beetle assemblages of donkey and horse dung in three different vegetation types and assessed species richness and abundance of dung beetles. Species richness was determined by dung and surrounding habitat conditions, whereas abundance was solely affected by dung conditions. However, species richness and abundance decreased with increasing dung density. The effect of dung density on species richness varied depending on vegetation type, with dry grassland exhibiting the highest number of dung beetles species at high dung density. Species composition in dung pads was influenced by abiotic factors with dwellers being negatively affected by increasing dung-pad temperature. Our results underline the importance of diverse vegetation, particularly with respect to the complexity of vegetation which interrelates with the microclimate. Furthermore, our findings illustrate the negative effect of high dung densities on dung beetle assemblages, suggesting that the degree of the intensity of use by grazing animals is important when considering measures for the conservation of dung beetles.     

Spatial and temporal variation in species composition of dung beetle assemblages in southern Ireland

Abstract. 1. This study attempts to identify the main community characteristics that contribute to variability in dung beetle assemblage composition and structure across a range of spatial and temporal scales.
2. Dung beetle assemblages ( Aphodius , Sphaeridium, and Geotrupes species) were monitored by dung-baited pitfall trapping at 10-day intervals during the seasonally active period at eleven sites in southern Ireland. Three of the sites were monitored over at least 2 years between 1991 and 1996.
3. Although the species composition of the above taxonomic groups was comparable among sites and years, relative abundances of component species varied considerably. Detrended correspondence analysis ordinations indicated a similar level of variability in dung beetle assemblage structure among years, and among sites ≈1–180 km apart.
4. Processes that may contribute to spatio-temporal variability in dung beetle assemblages are discussed, and strategies for future research are suggested.     

Opposing effects of spring defoliation on late season oak caterpillars

ABSTRACT. 1. The pedunculate oak, Quercus rohur L., suffers high annual levels of spring defoliation in Wytham Woods. near Oxford.
2. This spring defoliation affects late season caterpillars through a variety of damage-induced changes in the leaves.
3. Diurnea fagella (D. & S.), one of the commonest late season caterpillars, shows reduced larval survival and pupal weight on regrowth foliage when compared to undamaged primary foliage.
4. D. fagella also suffer higher larval mortality on naturally damaged primary foliage than they do on undamaged foliage.
5. Despite this, the three commonest late season caterpillar species are more abundant on damaged trees than undamaged ones. and their distributions are biased towards damaged leaves within the canopy.
6. Other factors that may be more important than leaf damage in determining the distribution and abundance of late season caterpillars are discussed. D.fagella larvae spin their larval refuges more rapidly on damaged than undamaged foliage, and this may reduce mortality by natural enemies, or ameliorate adverse effects of weather.     

The micro-distribution of aquatic macroinvertebrates in the Wye river system: the result of abiotic or biotic factors?

SUMMARY. 1. Macroinvertebrates were sampled from three habitats at each of forty-five sites in the catchment of the Welsh River Wye. Micro-distribution patterns between three habitat types were assessed for those species which occurred most commonly.
2. Of the fifty-three taxa for which analysis was possible, twenty showed a significant association with habitat type. Eleven occur mostly in margins, eight mostly in riffles, and one in flats (depositing reaches).
3. Twenty-one taxa, including eleven additional to those show significant associations, showed. significant differences between habitats in their relative abundance. Ten were most abundant in margins, eight in riffles and three in flats.
4. Factors possibly responsible for these habitat preferences are discussed.     

The growth and survival of Panolis flammea larvae in the absence of predators on Scots pine and lodgepole pine

Abstract. 1. The survival, growth and development of larvae of the pine beauty moth, Panolis flammea (D & S) (Lepidoptera: Noctuidae) were examined as part of a study to determine (i) why damaging outbreaks of this insect in Scotland are frequent on lodgepole pine but do not occur on Scots pine, and (ii) why outbreaks are associated with areas of deep un-flushed peat.
2. Larvae were studied inside predator exclusion cages on mature pine trees in Elchies forest where a major infestation occurred in 1978–79.
3. Surprisingly, larval survival was generally greatest on Scots pine and lowest on lodgepole growing in deep peat. Also, larval growth and development were greater on Scots than lodgepole pine and were unaffected by the type of soil in which the lodgepole pine was growing.
4. Larval performance was generally better on lodgepole pine that had been thinned and received fertilizer.
5. Larval survival was affected by pine shoot stage during egg hatch in one of the two years in which this was examined.
6. Observations on P.flammea pupae were confused by disease, parasitism and probably by differences in weight loss caused by differences in larval development. Parasitism by ichneumonid parasitoids was recorded on Scots pine but not on lodgepole pine.
7. It was concluded that (i) the absence of pine beauty moth outbreaks on Scots pine, and (ii) the occurrence of outbreaks on lodgepole pine growing in deep unflushed peat were not the result of lodgepole pine growing in deep peat being a more suitable host plant than lodgepole pine and Scots pine growing elsewhere. It seems more likely that the observed outbreak behaviour of P.flammea in Scotland is associated with differences in predation and parasitism in plantations of difference host plants and in plantations of lodgepole pine growing in different soils.     

Abundance and distribution within a guild of benthic stream fishes: local processes and regional patterns

1. Spatial patterns at regional and local scales were examined for evidence that species interactions can influence distribution and abundance within a guild of benthic fishes in upland streams of Oklahoma, U.S.A. Three groups of community patterns were examined: the species–area relationship, species–habitat associations, and interspecific associations.
2. The species–area relationship for riffle habitats was compared to a null species–area model based on random placement. The observed species–area curve was steeper resulting in less species per unit area in small streams than predicted by the null model.
3. Small, species-poor streams had summed fish densities at least as high as larger, species-rich streams, suggesting density compensation.
4. Several significant patterns of negative covariation were found among species at the regional scale, before and after statistically accounting for effects due to measured habitat variables.
5. For two of these negatively covarying taxa ( Cottus carolinae and Etheostoma spectabile ), the influence of each species on the distribution of the other was evaluated experimentally in field enclosures varying in depth and current velocity. The sculpin C . carolinae caused a shift in habitat use by the darter E . spectabile , but no reciprocal shift was found.
6. These results indicate an agreement between local and regional patterns of distribution for C . carolinae and E . spectabile and suggest that biotic interactions can influence regional patterns of distribution for species within this guild.     

Abundance and distribution within a guild of benthic stream fishes: local processes and regional patterns

1. Spatial patterns at regional and local scales were examined for evidence that species interactions can influence distribution and abundance within a guild of benthic fishes in upland streams of Oklahoma, U.S.A. Three groups of community patterns were examined: the species–area relationship, species–habitat associations, and interspecific associations.
2. The species–area relationship for riffle habitats was compared to a null species–area model based on random placement. The observed species–area curve was steeper resulting in less species per unit area in small streams than predicted by the null model.
3. Small, species-poor streams had summed fish densities at least as high as larger, species-rich streams, suggesting density compensation.
4. Several significant patterns of negative covariation were found among species at the regional scale, before and after statistically accounting for effects due to measured habitat variables.
5. For two of these negatively covarying taxa ( Cottus carolinae and Etheostoma spectabile ), the influence of each species on the distribution of the other was evaluated experimentally in field enclosures varying in depth and current velocity. The sculpin C . carolinae caused a shift in habitat use by the darter E . spectabile , but no reciprocal shift was found.
6. These results indicate an agreement between local and regional patterns of distribution for C . carolinae and E . spectabile and suggest that biotic interactions can influence regional patterns of distribution for species within this guild.     

Habitat suitability modelling of an invasive plant with advanced remote sensing data

Aim  Lepidium latifolium (Brassicaceae; perennial pepperweed) is a noxious Eurasian weed invading riparian and wetland areas of the western USA. Understanding which sites are most susceptible to invasion by L. latifolium will allow more efficient management of this weed. We assessed the ability of advanced remote sensing techniques to develop habitat suitability models for L. latifolium .
Location  San Francisco Bay/Sacramento-San Joaquin River Delta, California, USA.
Methods  Lepidium latifolium distribution was mapped with hyperspectral image data of Rush Ranch Open Space Preserve, providing presence/absence data to train and validate habitat models. A high-resolution light detection and ranging digital elevation model was used to derive predictor environmental variables (distance to channel, distance to upland, elevation, slope, aspect and convexity). Aggregate decision tree models were used to predict the potential distribution of this species.
Results  Lepidium latifolium infested two zones: near the marshland–upland margin and along channels within the marsh. Topographical data, which are typically strongly correlated with wetland species distributions, were relatively unimportant to L. latifolium occurrence, although relevant microtopography information, particularly relative elevation, was subsumed in the distance to channel variable. The map of potential L. latifolium distribution reveals that Rush Ranch contains considerable habitat that it is susceptible to continued invasion.
Main conclusions  Lepidium latifolium invades relatively less stressful sites along the inundation and salinity gradients. Advanced remote sensing datasets were shown to be sufficient for species distribution modelling. Remote sensing offers powerful tools that deserve wider use in ecological research and management.     

The carabid communities on peat and upland grasslands in northern England

During a two year period 13498 individuals of 66 species of carabids were taken from 44 sites on peat and upland grasslands over an altitude range of 11-847 m in the north of England. The similarities between the carabid faunas of each site have been assessed using a modified form of the Sørensen's Index and the sites clustered according to their similarities. Five carabid communities on peat and three on mineral soils have been identified and the more abundant species have been used to characterise them. Peat Community I occurs on dry heath and is characterised by peat associated species such as Trichocellus cognatus and Bradycellus ruficollis together with widespread open habitat species such as Pterostichus madidus, Notiophilus aquaticus, Calathus melanocephalus and Nebria salina. Peat Community II is found on areas where dry heath and deep wet peat are adjacent and is characterised by the species already mentioned together with typical wet habitat species such as Pterostichus diligens, P. nigrita, Patrobus assimilis. Agonum fuliginosum. Peat Community III is found on blanket bog and is characterised by the wet habitat species in the absence of the species present on the dry heath. Peat Community IV found on the lowland oligotrophic mires is characterised by the small number of species present and the addition of Pterostichus niger and Agonum ericeti to the few wet habitat species present. Peat Community V, on the scarp slope of Dun Fell, consists of the wet habitat species of Peat Community III together with Pterostichus madidus. Nebria salina, Notiophilus aquaticus and Calathus melanocephalus. Grassland Community I, on the fell tops, is characterised by the presence of Nebria gyllenhali, Notiophilus germinyi and Patrobus assimitis. Grassland Community II and III are less clearly defined but Grassland Community II may be present on wetter sites than III and is characterised by the presence of Pterostichus nigrita, P. diligens and P. strennus together with Notiophilus biguttatus. N. aquaticus, Pterosfichus madidus and Patrobus afrorufus. Grassland Community III consists of the latter group of species together with Nebria salina, Calathus melanocephalus and Notiophilus aestuans. The number of grassland sites studied was small and there may be further communities on the upland grasslands.     

Selective Defecation and Selective Foraging: Antiparasite Behavior in Wild Ungulates?

Selective defecation and selective foraging are two potential antiparasite behaviors used by grazing ungulates to reduce infection by fecal–oral transmitted parasites. While there is some evidence that domestic species use these strategies, less is known about the occurrence and efficacy of these behaviors in wild ungulates. In this study, I examined whether wild antelope use selective defecation and selective foraging strategies to reduce exposure to gastrointestinal nematode parasites. By quantifying parasite levels in the environment in relation to the defecation patterns of three species, dik‐dik (Madoqua kirkii), Grant's gazelle (Gazella granti), and impala (Aepyceros melampus), I found that nematode larval concentrations in pasture were higher in the vicinity of clusters of feces (dung middens) compared to single fecal pellet groups or dung‐free areas. In addition, experimental feeding trials in free‐ranging dik‐dik showed that individuals selectively avoided feeding near concentrations of feces. Given that increased parasite contamination was found in the immediate vicinity of fecal clusters, fecal avoidance could help reduce host consumption of parasites and may therefore be an effective antiparasite behavior for certain species. On the other hand, while the concentration of parasite larvae in the vicinity of middens coupled with host avoidance of these areas during grazing could reduce host contact with parasites, results showing a positive correlation between the number of middens in a habitat and larval abundance at control sites suggest that dung middens might increase and not decrease overall host exposure to parasites. If this is the case, dung midden formation may not be a viable antiparasite strategy.     

The influence of chemistry and habitat features on the microcrustacea of some upland Welsh streams

SUMMARY. 1. Microcrustaceans were sampled during September 1990 from three microhabitats (margins, stony riffles and gravel) at thirteen stream sites in mid-Wales.
2. Patterns in the distribution, abundance and community structure of microcrustacean taxa were related to stream chemistry, physiography, substratum composition and marginal habitat structure. Patterns of distribution between microhabitats were also assessed.
3. Chemical variables were the strongest correlates with microcrustacean parameters. Total numbers of microcrustaceans and harpacticoid copepods were reduced at sites with high aluminium concentrations, and ostracods were scarce or absent at the most acidic sites. In contrast, cyclopoid copepods were more abundant and species rich at low pH.
4. Microcrustacean communities were most species rich at sites with a high percentage cover of macrophytes on the substratum. Cladoceran species richness and abundance, and the abundance of several microcrustacean species, were also positively correlated with percentage macrophyte cover.
5. Three site groupings produced by TWINSPAN classification were primarily related to percentage macrophyte cover and marginal habitat structure, with chemistry and land use also of importance.
6. Total microcrustacean abundance was highest in margins, but of all the species, only the harpacticoid Bryocamptus cuspidatus showed a strong microhabitat preference.     

Different growth responses to temperature and resource limitation in three fly species with similar life histories

Growth responses to temperature and resource limitation in three dipteran species with similar life histories were compared. With respect to current life history theory, two points are raised. First, growth rate in real time increased steeply with temperature in all species, following the standard pattern. However, when expressed in physiological time growth rate increased as temperature decreased in the yellow dung fly Scathophaga stercoraria, remained approximately constant in Sepsis cynipsea, and increased in Drosophila melanogaster. These responses can be understood as adaptations to climate and seasonality. It is concluded that some patterns of adaptation may be more easily interpreted if, and some may even go undetected unless, they are analysed in physiological time. Second, a decrease in body size, development rate and growth rate when resources are limited is believed to be nearly universal and generally predicted by life history models. Despite their similar life histories, the three species investigated showed qualitatively different growth responses to larval food shortage. At unlimited resources, yellow dung flies showed the fastest initial larval body mass gain per unit time, while those of S. cynipsea and D. melanogaster were lower and about equal. The period of no body mass gain at the end of larval development was longest in S. stercoraria and shortest in S. cynipsea. When facing resource limitation, S. stercoraria emerged smaller but earlier (thus nearly maintaining their growth rate), S. cynipsea smaller after the same development period, and D. melanogaster smaller and later (showing reduced and much reduced growth, respectively). It is concluded that whether growth really slows when resources are limited depends on the precise ecological circumstances of the species in question. More refined models, particularly those where mortality costs are independent of time, and more experiments are necessary to account for the variation in growth and size and age at maturity present in nature. This revised version was published online in July 2006 with corrections to the Cover Date.