EFFECTS OF CHIRONOMID (INSECTA: DIPTERA) TUBE-BUILDING ACTIVITIES ON STREAM DIATOM COMMUNITIES1,2

Chironomid retreats, constructed out of sand grains upon submerged wood debris, increase the surface area available for diatom colonization. The three dimensional substratum afforded by chironomid tubes supports up to twelve times the diatom biavolume found upon adjacent, unmodified substratum in a northern Michigan stream. Diatom enumeration within scrapings from small defined areas on artificial substrata, combined with examination of intact natural substrata through scanning electron microscopy (SEM), reveals distinct, microdistribution patterns. The larval retreats of two major taxa of tube-dwelling chironomid's (Micropsectra sp. and Pseudodiamesa cf. pertinax Garrett) display significantly different diatom communities relative to adjacent masonite substratum. Substratum without chironomid tubes is primarily colonized by Achnanthes minutissima Kütz. and Cocconeis placentula Ehr., exhibiting the lowest species diversity of microhabitats examined. The diatom flora upon sand tubes of Micropsectra sp. is dominated by Opephora martyi Herib., as is the flora of sand grains collected from the stream sediment load. These two micro-habitats exhibit a high community similarity (SIMI). The SIMI index also suggests that the flora of P. pertinax tubes is highly similar to that of sand grains. Diversity, however, is almost three times greater on P. pertinax tubes and SEM observations reveal that this microhabitat is characterized by a more spatially complex flora; Nitzschia and Navicula spp. dominate the upperstory, and O. martyi is located on underlying sand grains. Results indicate that tube-building chironomids in Carp Creek affect diatom microdistribution by: (1) stabilizing sand grains and associated flora within their retreats, (2) providing a ‘refugium’ for upperstory diatom taxa from the mayfly grazer, Baetis vagans McDunnough (Insecta: Ephemeroptera), and (3) through local nutrient enrichment.     

Tube-building in two epifaunal amphipod species,Corophium insidiosum andJassa falcata

Jassa falcata andCorophium insidiosum are epifaunal tube-building marine amphipods, whose niches overlap in habitat and food requirements. Laboratory experiments were conducted to study the influence of the quality of different available particulate substrates on settlement and tube-building behaviour of these two amphipod species. Our experiments suggest thatC. insidiosum is less specialized in this respect thanJ. falcata. C. insidiosum is able to use organic materials for tube-building such as artificial (Ulva spec. powder) or mixed natural detritus as well as inorganic material (coarse sand); whereasJ. falcata utilizes organic materials, but sand only to a very limited extent.     

Sediment destabilizing and stabilizing bio-engineers on tidal flats: cascading effects of experimental exclusion

Bioturbating lugworms (Arenicola marina) were excluded from 400 m2 plots of intertidal sand which initiated sequences of direct and indirect changes in the structure of the benthic community. The sessile, tube-building species Polydora cornuta and Lanice conchilega took advantage of the absence of lugworms and settled preferentially on lugworm exclusion plots. The protruding tubes provided attachment for an ephemeral development of algal tufts (Berkeleya colonies and Enteromorpha thalli) which in turn enhanced settlement of the juvenile drifting clams Mya arenaria and Macoma balthica. This causal chain of enhanced bivalve settlement in the presence of above-ground structures, like animal tubes and algae, on lugworm exclusion plots occurred in 2 years at different tidal zones with different tube builders, algae and juvenile clams. A significant response of L. conchilega in a year with relatively low lugworm abundances at the entire site suggests that not only the actual absence of large bioturbators was responsible for the establishment of tube-dwelling species, but also a cumulative change of the sediment in exclusion plots since the onset of the experiment. While the sediment on lugworm plots remained permeable, fine particles and organic matter accumulated at exclusion plots. It is suggested that these differences in sediment characteristics were the product of divergent benthic engineering by sediment destabilizing lugworms on control plots and sediment stabilizing species on exclusion plots. Cumulative changes of the sedimentary habitat and cascading effects in the benthic community may explain the persistence of patches that are dominated by either sediment stabilizing or destabilizing species in the assemblage mosaic of intertidal sediments.     

Marine tube-dwelling diatoms and their occurrence in the Netherlands

Attached to solid substrate species of the tube-forming diatoms are found th entire Dutch coast. Probably because of the increased eutrophication over the last decades there is an indication that the abundance of certain tube-dwelling species such aParlibellus delognei andParlibellus berkeleya shows also a strong increase. At some favourable sites it is estimated that at there peak of their seasonal development more than 10¹⁰ diatomcells per square metre can be found. The taxonomy of the tube-dwelling species has a long history started in 1803 when the first species were described by the wellknown phycologist Dillwyn. In short this taxonomic history is described. In addition the process of formation and development of the muco-polysaccharide tubes is documented and illustrated. In conclusion the occurance of endo and epitubular symbionts or associates is overviewed. Especially diatoms of the generaNitzschia are found inside the tubes of some species while species from the generaLicmophora, Synedra, Amphora andCocconeis have a preference to become attached to the outer surface of tubes.     

Exceptionally well‐preserved isolated eyes from Cambrian ‘Orsten’ fossil assemblages of Sweden

Abstract: Eyes other than those of trilobites are rarely preserved in the fossil record. We describe here a set of six tiny, isolated, three‐dimensionally preserved compound eyes. These secondarily phosphatized eyes were etched from ‘Orsten’ limestone nodules dated to the Agnostus pisiformis Biozone from the Cambrian Alum Shale Formation of Sweden. The ovoid eyes arise from an elongated stalk, their surface being covered by a mosaic of regular and hexagonal‐shaped facets representing the surface of ommatidia. Facet size and pattern change within the same specimen from the posterior to the anterior end. With regard to some morphological criteria, we grouped the material in two different morphotypes, type A and B, the first being represented by specimens of two different developmental stages. From stage to stage, mostly growth in overall size and addition of new ommatidia was noticed. Among the meiobenthic ‘Orsten’ arthropods, only the crustacean Henningsmoenicaris scutula has been described as possessing stalked eyes, but the eyes of the largest specimen with preserved eyes of this species are much smaller than the new eyes and do not display any kind of ommatidia on their visual surface. However, fragments of larger specimens of H. scutula and the co‐occurrence of this species with the new isolated eyes in the sieving residues make it likely that the latter belong to this species but belong to more advanced stages than those described previously of H. scutula. Ontogenetically, the eye stalks of this fossil crustacean elongate progressively, while the regular hexagonal facets, lacking in early stages, appear later on.     

Lip morphology and ultrastructure of osmophores in Cyclopogon (Orchidaceae) reveal a degree of morphological differentiation among species

Floral fragrances play an important role in pollinator attraction; they serve as signals for primary rewards such as nectar. The presence of osmophores (a specialized glandular tissue that produces fragrance) in the terrestrial orchid Cyclopogon has only been described in a single species. There are fragrant and odorless species within this genus, but no data on the similarities or differences between them has been published. Here, we present new data on the lip morphology and ultrastructure from eight Cyclopogon species to better understand the mechanisms of pollinator attraction of this group. To achieve this goal, we used light, scanning, and transmission electron microscopy. Five out of eight species presented globular trichomes associated with fragrance production on the abaxial side of the labellum. Together with subepidermal cells, they compose the secretory tissue. Despite the absence of globular trichomes, C. apricus also presented cells associated with fragrance production. Lipid droplets, plastids containing plastoglobuli, and starch were indicators of secretory activity present in these species. This same pattern of fragrance production and release, associated with flower morphology, may result in the restriction of pollination by halictid bees.

     

Selective predation by a sculpin and a stonefly on two chironomids in laboratory feeding trials

Sculpin and stonefly predators fed selectively on the larvae of the chironomids Paratendipes over Cricotopus in laboratory stream microcosms. In these experiments, Cricotopus were usually tube-dwelling, whereas Paratendipes were usually free-living. Paratendipes were also bright red, which may have influenced selectivity by visual feeding sculpin, but tactile feeding stoneflies were most likely influenced only by the difference in tube-dwelling behavior of the two prey types. Both chironomids were abundant in the field, but exhibited discrete microhabitat distributions. Field collected sculpin ate mostly Cricotopus, probably because Cricotopus occurred in a more accessible microhabitat.     

The uncommon cavitated secretory trichomes in Bauhinia s.s. (Fabaceae): the same roles in different organs

Cavitated secretory trichomes are characterized by a short or absent stalk that is connected to a secretory hollow head. They are rare structures in angiosperms; in Fabaceae, they have been recorded in only seven genera, including Bauhinia s.s. Because B. curvula and B. rufa exhibit glands that are responsible for attracting pollinators to flowers, this study aimed to test whether the cavitated secretory trichomes present in the flowers of these species have an attraction function. As leaf trichomes are commonly related to plant defence, comparative analyses of the morphology, ontogeny, ultrastructure and chemical profile of the secretory trichomes present in flowers and leaves were conducted. It was found that cavitated secretory trichomes are similar in their external morphology and development, regardless of the organ or species analysed. However, interspecific differences were found in the secretion process and chemical profile of the exudate. The differences found in the cavitated secretory trichomes between species indicate that they secrete distinct compounds, whereas the similarities found in these structures between vegetative and reproductive organs indicate that the cavitated trichomes have equivalent ecological functions within a species, probably in plant defence during organ development. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2016, 180 , 104–122.     

Mangrove forests may serve as stable environments for the meiobenthic Echinoderes komatsui (Kinorhyncha: Cyclorhagida): distribution patterns and population dynamics in a subtropical estuary

Echinoderes komatsui (Kinorhyncha: Cyclorhagida) is a meiobenthic animal inhabiting the interstitial spaces of the sediment on a subtropical tidal flat along the Oura River, Japan. This species mostly occurred within 0–10?mm from the surface of the sediment, and the dispersion pattern was significantly patchy. The population dynamics of E. komatsui were investigated by monthly surveys from January 2014 to May 2016 at four sites along the river, and from April 2015 to May 2016 at one site in the mangrove forest. Echinoderes komatsui occurred all year round; however, the population density showed different patterns among the sampling sites in response to seasonal changes. On the tidal flat, the population density was high in winter, but very low in summer. In the mangrove forest, the density was high (or not low) throughout the year. As was shown in laboratory experiments, E. komatsui survived in 1–44 salinity seawater but died at 0 (salinity experiments), and died within 4.5 days at 40°C (temperature experiments). Therefore, the low population density recorded in summer on the tidal flat was likely caused by high temperature and fresh water. The shade offered by the mangrove forest suppressed the increase in temperature of the sediment in the summer, probably resulting in the higher population density at this site relative to the tidal flat population. Mangrove forests may also mitigate the disturbance of the sediment by summer typhoons and serve as stable environments that are fundamental in the sustainability of estuarine meiobenthic fauna.     

Diel and seasonal vertical distribution of meiobenthic copepods in muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay)

The vertical distribution of meiobenthic copepods was investigated within muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay, France). The aim of the study was to determine if in muddy sediments, as previously established in sandy sediments, meiobenthic copepods migrate vertically according to the seasons or diel periods. Two experimental approaches were used, viz: a three-season comparison was made of the diel vertical distribution of the harpacticoid Canuella perplexa T. & A. Scott (1893) and secondly the depth distribution of a meiobenthic copepod assemblage was followed for a 24 h period, in shallow water subtidal locations. The harpacticoid C. perplexa vertically migrated through the top three centimeters of the sediment, showing diel and seasonal variations in depth distribution. The differential vertical distributions shown by the dominant meiobenthic populations suggest that emergence into the water column may mainly concern surface dwelling copepods. The physical and biological factors affecting seasonal and diel changes in the copepod assemblage of the fish ponds are discussed.     

Epipelic diatoms blooming in Isahaya Tidal Flat in the Ariake Sea, Japan, before the drainage following the Isahaya-Bay Reclamation Project

A blooming diatom sample from Isahaya Tidal Flat in the Ariake Sea, south‐west Japan, before the bay was closed and drained following the Isahaya‐Bay Reclamation Project, is taxonomically examined. When the sample was collected on 25 May 1996, the area was a muddy tidal flat. Altogether, 103 diatom species were observed within 1000 counts of frustules. Both the dominant and subdominant diatom species were large raphid species. Light microscopy and scanning electron microscopy observation revealed that the dominant species was Haslea nipkowii (F.Meister) Poulin et G. Masse, which was originally described as a species of Gymsigma. So far, a report of correctly identified H. nipkowii has been presented only from China, because H. nipkowii sensu Poulin et al. from USA and France probably belongs to the other taxon, Gymsigma pallidum Riznyk. The subdominant species is described as a new species, Nitzschia gyrosigmasp. nov. This new species is similar to Nitzschia sigmoidea under light microscopy, but scanning electron microscopy observation reveals that their fine structures are quite different. Nitzschia granulata var. hyalina is transferred to the genus of Tryblionella and raised to an independent species, Tryblionella hyalina (Amosse) comb. nov.     

Non-volatile components of the essential oil secretory cavities of Eucalyptus leaves: Discovery of two glucose monoterpene esters, cuniloside B and froggattiside A

The essential oils extracted from the embedded foliar secretory cavities of many Eucalyptus species are of economic value as pharmaceuticals and fragrance additives. Recent studies have indicated that Eucalyptus secretory cavities may not be exclusively involved in the biosynthesis and storage of essential oils. Therefore, we selected three species upon which to perform an examination of the contents of foliar secretory cavities: Eucalyptus froggattii, E. polybractea and E. globulus. This paper describes the isolation and structural characterization of two non-volatile glucose monoterpene esters, which we have named cuniloside B and froggattiside A, from within the secretory cavities of these species, and shows the presence of these compounds in solvent extracts of the leaves from two other species of Eucalyptus. Both compounds were found in high proportions relative to the essential oils extracted from the leaves. We propose that many other carbohydrate monoterpene esters previously isolated from bulk leaf extracts of various Eucalyptus species may also be localized within the non-volatile fraction of foliar secretory cavities.     

Seasonal dynamics and spatial distribution of chydorid cladocerans in relation to chironomid larvae in the sandy littoral zone of an oligo-mesotrophic lake

The seasonal variation of the principal macro- and meiobenthic taxa in the sandy littoral zone of the oligomesotrophic Dutch Lake Maarsseveen I was studied during two years. Population peaks of the different taxa were clearly separated in time. In early spring there were chironomid density peaks of Stictochironomus sticticus, in one year followed by a Polypedilum maximum. From June–July chydorid cladocerans dominated, with a peak of Monospilus dispar followed by a peak of Rhynchotalona falcata. In autumn the chironomid Cladotanytarsus mancus became dominant, remaining so throughout the winter.To study the spatial heterogeneity of the major macro- and meiofaunal taxa, samples were taken in a grid of 2.5 × 10 m. Distributions of all but one taxon were significantly different from random, with Morisita indices varying from 1.23 (chironomids) to 2.10 (the chydorid Monospilus dispar). Wind-induced disturbance presumably had strong and species-specific effects on littoral macro- and meiobenthic taxa. Chydorid heterogeneity increased immediately following the first autumn storm of the season; this may be explained by the tendency of these organisms to remain attached to detritus particles.Temporal and spatial correlation coefficients between macro- and meiobenthic taxa were generally low, suggesting that interactions between these groups are weak, with distribution patterns that are independent of each other. Among the meiofaunal taxa, positive spatial and temporal correlation coefficients were found; apparently, the similarity in both seasonal dynamics and spatial distribution is larger among the meiofaunal taxa than between macro- and meiofaunal taxa. Also among most of the chironomid species significant positive temporal correlations were found, except for Stictochironomus sticticus and Polypedilum sp.; these species have similar life-cycles, but were during one year temporally separated by several alternating settlement peaks. In the next year, Polypedilum disappeared completely following an extremely strong Stictochironomus settlement peak.     

Species Concepts in the Cylindrocladium floridanum and Cy. spathiphylli Complexes (Hypocreaceae) Based on Multi-allelic Sequence Data, Sexual Compatibility and Morphology

Much attention has recently been devoted to the delimitation of species units in Cylindrocladium(Cy.). In this regard the present study focuses on the taxa within the unresolved Cy. floridanum and Cy. spathiphylli species complexes. Maximum parsimony analyses of DNA sequences of ITS, β-tubulin and histone regions of rRNA genes, and mating experiments revealed a geographically isolated species of Cylindrocladium in the Cy. spathiphylli(teleomorph:Calonectria spathiphylli) species complex.Cy. pseudospathiphylli sp. nov. (teleomorph:Ca. pseudospathiphylli sp. nov.) is described as a new phylogenetic, biological and morphological species. It is distinguished from Cy. spathiphylli by being homothallic, having smaller macroconidia, and distinct DNA sequences of β-tubulin and histone genes. Similarly, parsimony analysis of a combined data set also indicated several phylogenetic species to exist within Cy. floridanum(teleomorph:Ca. kyotensis). Based on differences in vesicle morphology and conidium dimensions, the Canadian population of Cy. floridanum, formerly known as Cy. floridanum Group 2, is described as Cy. canadense sp. nov., while a further collection from Hawaii is described as Cy. pacificum sp. nov.     

Breeding bird communities on Scottish farms

The Common Birds Census, begun by the British Trust for Ornithology has now been monitoring bird population levels on a nationwide basis since 1962. Separate indices were constructed for Scotland and the rest of Great Britain for 12 of the commonest species. Of the species examined blue tit (Parus caeruleus), wren (Troglodytes troglodytes), song thrush (Turdus philomelos), lapwing (Vanellus vanellus), chaffinch (Fringilla coelebs) and skylark (Alauda arvensis) have increased since 1963 and show very similar population trends to the rest of Great Britain. Whitethroat (Sylvia communis), willow warbler (Phylloscopus trochilus) and swallow (Hirundo rustica) have all declined nationally, the decline in the swallow appears to have begun earlier in Scotland. The blackbird (Turdus merula) and dunnock (Prunella modularis) showed similar upward trends until 1972 when the Scottish population started to decline; a much more noticeable decline in the Scottish robin (Erithacus rubecula) population began in 1966. The total density of territory-holding males has not increased but the biomass has and this is due to more, bigger birds but fewer passerines. The species diversity measured by the Shannon Wiener index (H.) has improved a little since 1971 and it is concluded that during the study period the farmland plots censused in Scotland have on average not shown evidence of deterioration as habitats for territory-holding birds.     

Mussel beds — amensalism or amelioration for intertidal fauna?

The faunal assemblages of a mussel bed (Mytilus edulis L.) and ambient sandflat were compared to study how a bioherm of suspension feeding organisms affects benthic communities in a tidal flat. During a survey of mussel beds in the Wadden Sea at the island of Sylt (North Sea), a total of 52 macrofaunal species and 44 meiobenthic plathelminth species were detected. They occupied different microhabitats in the mussel bed. 56% of the macrofauna species were dwelling in the sediment beneath the mussels and 42% were epibenthic or epiphytic. The latter were restricted in their occurrence to the mussel bed. Along a transect from the sandflat to the mussel bed the mean species densities of macrofauna did not differ significantly, while abundances were significantly lower in the mussel bed than in the sandflat. The composition of the assemblages shifted from a dominance of Polychaeta in the sandflat to Oligochaeta in the mussel bed. Surface filter-feeding polychaetes of the sandflat (Tharyx marioni) were displaced by deposit feeding polychaetes under the mussel cover (Capitella capitata, Heteromastus filiformis). The total meiobenthic density was lower and single taxa (Ostracoda, Plathelminthes, Nematoda) were significantly less abundant in the mud of the mussel bed. The plathelminth assemblage was dominated by grazing species (Archaphanostoma agile), and differed in community structure from a sandflat aseemblage. An amensalistic relationship was found between the suspension-feeding mussels and suspension-feeding infauna, while deposit-feeders were enhanced. The presence of epibenthic microhabitats results in a variety of trophic groups co-occurring in a mussel bed. This is hypothesized as trophic group amelioration and described as an attribute of heterotrophic reefs.     

The sperm of Hylodinae species (Anura, Leptodactylidae): Ultrastructural characteristics and their relevance to interspecific taxonomic relationships

Aaabstract Hylodinae leptodactylids(sensu Lynch 1971) form a group of diurnal frogs, which is hypothesized on the basis of morphological traits to be the closest relatives of the dendrobatid frogs. Our study describes ultrastructural characteristics of sperm from three hylodine species(Hylodes phyllodes, Crossodactylus sp. n. andMegaelosia massarti) to reassess the intergeneric relationships within the Hylodinae, as well as the supposed relationship between the Hylodinae and Dendrobatidae. The ultrastructure of the sperm is very similar among the three species and is indicative of its conserved nature within the Hylodinae. The structure of the acrosomal complex was very similar to that of other leptodactylid species, to most of the remaining species included in the Bufonoidea lineage, and also to that observed in the dendrobatid species examined so far. Since such a structure has been considered a plesiomorphic trait, it contributes little to our understanding of the relationships between the Hylodinae and Dendrobatidae. The flagellar apparatus ofCrossodactylus sp. n. is very similar to that of most leptodactylids. The sperm ofMegaelosia massarti andHylodes phyllodes display a distinctive condition in their axial and juxtaxonemal fibers. This distinctive flagellar condition expands the already known variability in sperm structure within the Leptodactylidae.     

中国膨果豆属(豆科)一新组合

原簇毛黄耆亚属的部分种类从黄耆属中分出,在此基础上恢复了膨果豆属,由此也产生了许多新组合。其中,新组合蒺藜叶膨果豆包含了原蒺藜叶黄耆和甘青黄耆。为验证该分类处理的合理性,该文统计分析了蒺藜叶黄耆和甘青黄耆在果实形态上的差异,同时比较了二者的地理分布式样。结果表明:甘青黄耆和蒺藜叶黄耆之间存在着明显区别,甘青黄耆种级的分类学地位应予以保留,新组合为甘青膨果豆[Phyllolobium tangutica(Batalin)Y.Kang M.L.Zhang]。     

The ecological effects of the decline in Rabbits (Oryctolagus cuniculus L.) due to myxomatosis

The Rabbit (Oryctolagus cuniculus) population in the British Isles increased rapidly from the 1800s to 1950 due to climatic amelioration, predator reduction and agricultural changes. It became the major vertebrate pest of agriculture, causing an estimated £50 million in damage and lost production each year. Myxomatosis reached Britain in 1954-55 causing 99-9% mortality in some Rabbit populations and, carried by the mosquito and flea vectors, the disease spread rapidly. The consequent decline in the Rabbit population caused dramatic changes in agriculture and the native fauna and flora. It promoted woodland regeneration and increased grassland and cereal production; herb and grass height increased, flowering was noticeable and plant successions ensued. Some small legumes and annual plants became extinct locally and much floristically rich vegetation became dominated by a few grass species or shrubs. The increased grass growth probably promoted an increase in the number of many invertebrate species as well as in the vole (Microrus agrestis). Some species of insect became reduced in number and the Large Blue Butterfly (Maculinea arion) has become extinct (1979) since the decline of the ant (Myrmica spp.) fauna necessary to rear the butterfly larvae. Breeding sites for the Sand Lizard (Lacerta ugilis), Stone Curlew (Burhinus oedicnemus) and Wheatear (Oenanrhe oenanthe) have been reduced by habitat change. Immediately after myxomatosis many predator populations suffered from a lack of Rabbit prey with consequent poor breeding success, but those able to switch to voles, and other predators which are no longer taken in Rabbit trapping, have increased in numbers, e.g. Fox (Vulpes vulpes), Polecat (Mustela putorius), Short-eared Owl (Asio Barnmeus) and Kestrel (Falco tinnunculus). Others such as the Stoat (Mustela ermineu) and the Buzzard (Buteo buteo) declined immediately after myxomatosis through lack of prey and have recovered in nubers only slowly; the Peregrine falcon population has declined partly as a result of lack of open habitat. The breeding success of many predators was also reduced. Parasites of the Rabbit also declined; the flea (Spilopsyllus cuniculi), roundworms and tapeworms, as well as coccidiosis carried by Rabbits and particularly affecting young hares (Lepus europaeus) were all considered to be affected. Species such as the Pheasant Phasianus spp., the hare and the Roe Deer (Capreolus capreolus) increased their use of woodland habitat and/or benefited from the increased food available. Rats (Rartus nomegicus) appeared to decline following increased predation and loss of habitat. In Australia similar vegetational changes occurred in many areas after the introduction of myxomatosis and predators such as the Fox and Wedge-tailed Eagle (Aquila audax) were reduced by control measures following increased predation on sheep. Many bird and marsupial species were reduced in number after the loss of Rabbit prey or on becoming an alternative prey item. In Britain the loss of the fur industry has been outweighed economically by the increased agricultural production and reduced control and maintenance costs following myxomatosis. Since myxomatosis appeared Rabbit numbers have increased only slowly, probably because of increased predator pressure on low density populations and the periodic recurrence of the disease. Rabbit behaviour may have changed so that burrows are not used as much as in the past, Rabbit trapping has ceased and many habitats have been lost. Rabbit numbers could still reach moderate densities but a reversal of many of the ecological effects of my xomatosis is unlikely.