Core and occasional species: A new way forward

1. Various methods have been used to divide communities into core species and occasional or satellite species. Some methods are somewhat arbitrary, and there is evidence that many communities are more multimodal than bimodal. They also tend to rely on having multiple years of data.
2. A completely novel method is presented that not only has no requirement for long‐term datasets but can divide communities into multiple groups. It is based on probability a species is present, calculated using Simpson''s index and the sequential removal of species from the data.
3. The sequential Simpson''s index method was applied to species data from a grassland insect community. It was also applied to eleven other datasets that had been divided into core and occasional species in previously published studies.
4. The new method was found not only to be consistent with previous core–occasional assessments but also able to identify multimodality in species abundance distributions.
5. Although ideally used with a measure of persistence (frequency of occurrence) to rank species, community structure is consistently described even with only species abundance data.
6. The method can be applied to short or long‐term datasets and can help identify multimodality and provide valuable insight into how communities change in time or space.

     

Alien herbivores and native parasitoids: rapid developments and structure of the parasitoid and inquiline complex in an invading gall wasp Andricus quercuscalicis (Hymenoptera: Cynipidae)

Abstract.

• 1 Rapid and substantial changes have occurred in the parasitoid and inquiline community associated with the agamic galls of Andricus quercuscalicis since it invaded Britain in the late 1950s. The number of parasitoid and inquiline species has risen from one to thirteen over a 15-year period. Although the number of species has been relatively consistent over the last 8 years, the species composition has changed considerably and in a highly characteristic way during this period.
• 2 The parasitoid complex can be divided into two broadly distinct sets of parasitoid species; one set attacks only the gall former whereas the other set concentrates on the inquilines living in the wall of the gall.
• 3 The most dramatic change, however, is in the abundance of inquilines which were reported to be virtually absent in earlier studies on this community in Britain. Over a period of only 5 years, between 1988 and 1993, inquiline attack rose from less than 0.01 to an average of 0.26 inquilines per gall. The intensity of inquiline attack is geographically heterogenous, with high inquiline numbers restricted to south-east England. Because of the relatively high specificity of the parasitoids, high inquiline abundance is positively correlated with parasitoid species richness in knopper galls.
• 4 Parasitism rates, particularly on the gall former, were generally low (<10%). Over the last 5 years, however, seven parasitoid species have been consistently recorded and the mortality caused by these species has increased continuously. The species composition of the community associated with this alien gall wasp in Britain has quickly converged to the community known from its native range in continental Europe. Parasitoid species known to attack the galls of A.quercuscalisis on the continent have been recorded from it in Britain for the first time mainly in areas where inquilines have recently become abundant.
• 5 Since rates of parasitism of the gall former are still low, parasitoids are unlikely to play a major role in the population dynamics of this invading gall wasp at present, but the rapidly increasing inquiline and parasitoid attack could be a source of increased mortality for native cynipid species which are the alternative hosts of those parasitoid species.

     

REGULARLY ARRANGED PROTEIN ON THE SURFACES OF GRAM-NEGATIVE BACTERIA

• 1 Many species of Gram-negative bacteria carry a layer of regularly arranged sub-units on the outer surface of their outer membrane. The subunits are arranged tetra-gonally or hexagonally and have centre-to-centre spacings ranging from 4 to 35 nm, depending on the bacterial species.
• 2 The regularly arranged layer has been detected by electron microscopy in whole cells, cell walls, outer membranes and assemblies of isolated subunits. The regular arrays can be seen in intact cells by shadowing or freeze-etching and, occasionally, in thin sections or after negative-staining. Freeze-etching and negative-staining have been used to show the regular arrays in isolated cell walls and outer membranes. Negative-staining is used in the examination of assembled isolated subunits.
• 3 Optical diffraction of electron micrographs provides more detailed information of the fine structure of the subunits in the regular array.
• 4 The regularly arranged surface layer can be removed by protein perturbants, by chelation of divalent cations with EDTA and EGTA, by cation substitution or by acidification.
• 5 The two surface subunits which have so far been purified have been found to be acidic proteins with molecular weights of 67000 (Acimtobacter 199A) and 140000 (Spirillum serpens).
• 6 In Acinetobacter 199A the surface protein is attached to the protein of the outer membrane through a salt bridge involving Ca²⁺ or Mg²⁺. Evidence exists that there may be a similar mode of attachment in other species.
• 7 Isolated surface proteins from Acinetobacter 199A and from Spirillum spp. have the ability to reassemble into the same pattern as that seen on the bacterial surface, either in isolation or in the presence of cell-wall fragments to act as nucleating agents. Self-assembly of Acinetobacter 199A a-protein requires chloride ions.
• 8 Acinetobacter 199A a-protein can only be incorporated onto the bacterial surface if an intact lipopolysaccharide membrane is formed first to receive the intrinsic membrane proteins to which the a-protein attaches. Impairment of lipopolysaccharide synthesis by bacitracin prevents incorporation of a-protein and other membrane proteins into the outer membrane.
• 9 Continuing incorporation of pre-formed radioactive a-protein into the outer membrane in Acimtobacter 199A can be detected for 10 min after transference from radioactive to non-radioactive growth medium.
• 10 Spirillum metamorphum, Flexibacter sp. and Acinetobacter 199A synthesize more surface protein than is required to cover the cell surface. The excess is secreted into the growth medium.
• 11 The regularly arranged surface protein of Acinetobacter 199A provides partial protection against isolated lysosomal proteinases from polymorphonuclear leucocytes. Spirillum spp. is protected from Bdellovibrio invasion by the surface protein.
• 12 Secreted a-protein from Acimtobacter 199A has phospholipase A, activity. No phospholipase activity can be detected when the a-protein is bound to the bacterial surface.

     

Apparent competition leaves no detectable imprint on patterns of community composition: observations from a natural experiment

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Genetic structure and demographic history of the melon fly Zeugodacus cucurbitae (Coquillet) (Diptera: Tephritidae) in Thailand

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Productivity influences trophic structure in a temporally forced aquatic ecosystem

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The successful introduction of the alpine marmot Marmota marmota in the Pyrenees,Iberian Peninsula,Western Europe

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Alternative seed defence mechanisms in a palo verde (Fabaceae) hybrid zone: effects on bruchid beetle abundance

Abstract.

• 1 We asked three questions about the patterns of relative abundance of insect herbivores across host plant taxa at a palo verde hybrid zone. (1) What is the morphological structure of the hybrid zone and does this suggest a certain pattern of introgression? (2) How are putative parental seed defence mechanisms expressed in hybrid plants? (3) Do ovipositing females prefer host plant taxa on which their offspring have best survivorship?
• 2 Morphologically, hybrids were either intermediate or tended to resemble one parental species. Previous studies have suggested that unidirectional introgression results in loss of parental defence mechanisms against herbivores. Hybrid plants in general lacked seed coat resistance and early pod abscission which are known to act as plant defence mechanisms against bruchid beetles in the parental palo verde trees.
• 3 All other sources of bruchid mortality that we examined did not vary across parental and hybrid taxa, with the possible exception of egg parasitism which occurred at a lower frequency on one parental palo verde species.
• 4 Thus, survivorship of bruchid offspring should be greater on hybrid palo verdes.
• 5 Patterns of egg densities suggested that females may prefer hybrid hosts in some years but not others. An oviposition choice experiment conducted in the field, however, showed bruchids have no preference for hybrids over one of the parental species.
• 6 These results suggest that some insect herbivores may have higher densities on hybrid host plants because they are less resistant.

     

Seventy years of changes in the abundance of Danish charophytes

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Andean bear Tremarctos ornatus natural history and conservation

• 1 A wealth of information has been generated for the Andean bear Tremarctos ornatus during the past four decades, and a thorough review of the species' natural history, ecology and conservation is provided here.
• 2 The Andean bear is the only remaining bear species in South America. Evolutionarily, it is the youngest of all ursids and the only remnant taxon within the subfamily Tremarctinae. The species is distributed throughout the Andes mountain range from Venezuela to Bolivia, but the limits of its current and past range are uncertain.
• 3 The species is polyestrous, capable of delayed implantation and a facultative seasonal breeder. Genetic information is scarce, and species‐specific markers need to be developed for a more appropriate assessment of the genetic structure of wild populations.
• 4 Andean bears inhabit a wide variety of habitats across the Andes including different forest types and high‐elevation grasslands. They are omnivorous with a frugivorous/folivorous emphasis that is reflected by adaptations of the typical tremarctine mandible.
• 5 Andean bears are vulnerable to extinction due to land conversion and poaching. Efforts have been made to protect them, but threats have not been reduced significantly. Therefore, the species is expected to move faster towards extinction than any other carnivore in the region.

     

NUTRIENTS IN AFRICAN LAKE ECOSYSTEMS: DO WE KNOW ALL?

SUMMARY

It is nearly sixty years since the first studies were undertaken on the nutrient chemistry of African lakes. There have been numerous studies on the chemical composition of African waters in the intervening years. Yet as recently as five years ago it was stated that little was known about nutrient cycling in lakes. Nutrient ‘species’ simply formed an additional list compiled along with lists of species of algae, zooplankton, aquatic plants and fish. A spate of monographs, papers and reports in recent years, however, has begun to fill some of the gaps in our knowledge of nutrient cycling in African lake ecosystems. This paper reviews the recent literature of nutrients in African lakes from the point of view of nutrient sources, in-lake nutrient kinetics and nutrient sinks, with particular reference to nitrogen and phosphorus, and their cycling rates into and out of various biotic and abiotic compartments. The principle conclusions that can be drawn from the review are as follows:

1. Allochthonous inputs, particularly in terms of external nutrient loading, have been relatively well-studied in recent years, but little is known of autochthonous nutrient inputs, despite numerous observations that nutrient regeneration is likely to be substantial in African lakes.

2. The rôle of microbial processes in nutrient cycling in African lakes is almost totally unknown, except in relation to nitrification and denitrification.

3. Recent studies have begun to examine the kinetics of the uptake of phosphorus by algae in African lakes; nitrogen uptake, other than nitrification, and nutrient release have only rarely been examined.

4. Nutrient uptake and release by aquatic macrophytes is reasonably well known, especially in the ‘nuisance’ weed species.

5. The role of zooplankton, zoobenthos and fish in nutrient cycling in African lakes has largely been ignored.

6. A great deal of study has been devoted to the rôle of abiotic process, particularly at the sediment-water interface, in the nutrient dynamics of African lakes.

As yet, little emphasis has been placed on inter-compartmental exchanges in studies on nutrient cycles but it would appear that these processes are now beginning to receive attention and, as nutrient cycling in African lake ecosystems becomes better known, research will tend toward a more numerical approach.     

Aquatic food‐web structure along a salinized dryland river

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Differential survival of two minnow species under experimental sunfish predation: implications for re‐invasion of a species into its native range

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The biology of Chrysopidae and Hemerobiidae (Neuroptera), with reference to their usage as biocontrol agents: a review

• 1 Many regions have well-developed faunas of Chrysopidae and Hemerobiidae, many of which are potential control agents, but only a few widely distributed species have been seriously considered as such.
• 2 Most of the biological information available concerns Chrysopa species in north temperate areas. C.carnea Stephens, in particular, has been utilised in many pest control programmes. Prepupal or adult diapause constitutes a well-defined stage in the life cycles of many temperate species.
• 3 Larval searching behaviour is efficient, and larvae of most species studied can utilise a wide range of prey organisms or sugar-based foods. The quality of the larval food can affect reproduction of the ensuing adults. Cannibalism is frequent, and may serve as the main food supply when other sources are scarce. Artificial diets for mass rearing are outlined.
• 4 Adult Hemerobiidae are predators. Adult Chrysopidae are either predators or honey-dew feeders, the latter possessing symbiotic yeasts which aid amino acid synthesis. Sprays based on sugar and yeast hydrolysates can be applied in the field as (i) attractants and (ii) alternative or additional food.
• 5 A wide range of predators and hymenopterous parasites attack all stages. Many widespread and non-specific parasites may attack lacewings introduced from other areas.
• 6 Potential use of Chrysopidae and Hemerobiidae in integrated control is enhanced by their tolerance to some insecticides.
• 7 Lacewings are potential control agents of pests in greenhouse, field crops, and orchards. Native species should be augmented rather than others introduced. It would probably be wise to encourage only one or few lacewing species against any given pest.

     

Why is one of the periodical cicadas (Magicicada septendecula) a comparatively rare species?

ABSTRACT.

• 1 The same woodland rarely supports two different broods of 17-year cicadas, and never two that appear in successive years. Theoretically, this is because a build-up of predators, generated by the leading brood, would eliminate the lagging one, or because nymphs of the lagging brood would suffer a competitive disadvantage, or both.
• 2 Nevertheless, substantial numbers of 17-year cicadas of all three species (Magicicada septendecim, M.cassini and M.septendecula) did appear in Grant County, Kentucky, in 1974 (Brood XIV, expected) and 1975 (not expected). This is interpreted to mean that many individuals delayed their emergence until the eighteenth year.
• 3 Dissected eggnests show that the expected build-up of hymenopterous egg parasitoids failed to occur, although there may have been a build-up of dipteran parasitoids, which may leave no trace in the eggnest.
• 4 Excavated young nymphs show that establishment rate was poorer in 1975 than in 1974, which is attributed to nymphal competition.
• 5 Identification of eggnests from the two years shows that one of the species (M.septendecula, which is usually the rarest in mixed-species populations) is much more susceptible to delaying its development by a year than are the other two species.
• 6 It is predicted that the 1975 emergence will produce no adult progeny, i.e. that there will be no emergence in 1992.
• 7 The sporadic occurrence of this phenomenon, other factors being equal, would be sufficient to explain the comparative rarity of M. septendecula, or even its local extinction.
• 8 Historical records from northern Illinois show frequent emergences one year behind schedule. These delayed individuals never produce progeny that survive to the next generation. M.septendecula is absent from northern Illinois and indeed absent from the northern areas of all periodical cicada broods in the northern part of the range.

     

Conservation genetics of South American aquatic mammals: an overview of gene diversity,population structure,phylogeography, non‐invasive methods and forensics

• 1 Most aquatic mammals have high dispersal potential, and there are often severe conservation concerns related to their legal or illegal harvesting. Therefore, economic, social and forensic factors often arise in decisions relating to their population management. Molecular markers are essential tools in modern conservation genetics, revealing previously unknown aspects of aquatic mammal behaviour, natural history, population structure and demography. Molecular markers also have been used to define management units, to recognize taxonomic units, to conduct forensic analyses and to control illegal wildlife trade, providing valuable information for decision‐making in wildlife conservation and management.
• 2 We review studies published in peer‐reviewed journals between 1993 and 2010, in which genetic approaches have been applied to conservation‐related issues involving natural populations of 25 species of aquatic mammals in South America. These studies cover just 34% of the 70 aquatic mammal species recorded in South America.
• 3 Most of the studies are related to population structure, phylogeography, gene flow and dispersal movements. In addition, recent findings relate to evolutionarily significant units, management units, forensics and conservation policy.
• 4 Finally, we look to the future and, based on numbers of studies and conservation concerns, suggest which species, geographic areas and genetic studies should be prioritized. Moreover, we discuss constraints on research and suggest collaborative works that would provide critical information towards the effective conservation and management of aquatic mammals in South America.

     

Litter‐dwelling beetles (Insecta: Coleoptera) can survive in clear‐cutting during subsequent soil ploughing

1. A 2‐year study of litter dwelling beetles was conducted in different mature pine stands and clear‐cuts in Lithuania using the litter sifting method. We hypothesized that clear‐cutting and subsequent ploughing would increase species diversity and the abundance of beetles, and also would encourage the immediate appearance of early‐successional beetle species replacing late successional species in the clear‐cuts.
2. We did not confirm a hypothesis regarding increase in the number of species and abundance of beetles in clear‐cuts.
3. Our hypothesis regarding the immediate appearance of early successional species and disappearance of late‐successional species in clear‐cuts was confirmed.
4. We also revealed that subsequent soil ploughing in clear‐cuts did not accelerate this process, which was linked to the possibility of late successional species surviving in the undisturbed spaces between the strips of ploughed soil.
5. The present study shows that late‐successional forest litter‐dwelling coleopteran species of old pine forests have a better chance of survival in a ploughed clear‐cut, at least in northern Europe, than has been reported in other studies.

     

Avian ecological succession in the Amazon: A long‐term case study following experimental deforestation

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Changes in vegetation structure and composition of a lowland mire over a sixty‐five‐year interval

1. Mires are characterized by plant communities of high conservation and societal value, which have experienced a major decline in area in many parts of the world, particularly Europe. Evidence suggests that they may be particularly vulnerable to changes in climate and nutrient addition. Although they have been the focus of extensive paleoecological research, few attempts have been made to examine the dynamics of mire vegetation during the current era of anthropogenic environmental change.
2. To assess long‐term change in the spatial structure and composition of a lowland mire community, in 2016 we resurveyed plots first surveyed in 1951. Measures of species richness and composition were compared between the two surveys, and changes in community composition were related to plant traits.
3. Overall, mean species richness declined by 26%. The area of occupancy declined in 37% of species, which were primarily oligotrophic species typical of nutrient‐poor bog communities. Conversely, occupancy increased in 21% of species, especially those that were more tolerant of higher nutrient availability. These changes were associated with variation in plant functional traits, as indicated by an increase mean Ellenberg trait values for nitrogen and mean temperature, and a decline in values for precipitation. These results suggest that eutrophication and climate change have been key drivers of floristic change on this site.
4. Synthesis. This investigation provides a rare assessment of the dynamics of a mire community over a multi‐decadal interval. Results indicate that substantial change has occurred in the composition of the community, and the distribution of species within it. The investigation provides evidence of the impact of environmental change on the composition and structure of a lowland mire community, and highlights challenges for its future conservation.