CADMIUM, LEAD AND COPPER IN FRESHWATER MUSSELS FROM THE ASSINIBOINE RIVER, MANITOBA, CANADA

Cadmium, lead and copper levels were examined in adductor muscle,foot, gonad, mantle, gill, and heart of 9 species of freshwatermussels from the Assini-boine River, using anodic strippingvoltametry. Metal levels in most organs were lower than in bottomsediments. The metals generally showed significantly higherconcentrations in heart and hemolymph samples than in the othertissues examined. However in four species, gill tissues showedthe highest values forcopper, and Quadrula quadnda and Ligumiarecta accumulated the greatest amounts of copper overall. Cadmiumconcentrations were particularly high in heart and hemolymphof Lampsilis radiata sili-quoidea, L. vcntricosa, and Ligumiarecta. Metal concentrations in tissues of a given species showedvarious relationships to weight of soft parts, shell length,and shell weight, but inverse correlations predominated, indicatingthat metals in many organs were less concentrated in older individuals.In L. radiatasiliquoidea and L. vcntricosa, copper concentrationswere higher in males than in females. Lead levels were alsohigher in L. vcntricosamales. (Received 24 June 1994; accepted 8 September 1994)     

Sex ratio and maturity indicate the local dispersal and mortality of adult stoneflies

1. Despite a recent upsurge in interest, there remains remarkably little information about the dispersal and survival of the adults of most stream‐dwelling insects, although this is a basic requirement for understanding their long‐term population dynamics. 2. Using Malaise traps for a whole annual flight period, we captured adult stoneflies (Leuctra nigra) along transects perpendicular to three upland Welsh streams. We assessed spatial and temporal patterns in sex ratio to infer local dispersal and, using maturity as an age marker, estimated the mortality of adult females. 3. Nearly all adult stoneflies (99%) were taken in the period 26 April–23 July, and the onset of the male and female flight periods was the same. Most males (90%) had been caught by late June. Females were classified as immature (without ripe eggs) or mature, and 90% of immature females had been caught by mid‐late June (depending on catchment). As immature females declined in the catch, mature females increased, 10% having been caught by late‐May to early June and 90% by early to mid‐July. The median catches of immature and mature females were separated by 32 days in all three catchments. 4. There was a female bias in the sex ratio overall, which increased as time passed and was attributable partially to the greater longevity of females. Late in the flight period, however, female bias was also greater near the stream channel implying a return of mature females (but not males) from the riparian vegetation, presumably to oviposit. 5. The number of mature females was less than the number of immatures in two of the three channels. Over all three catchments, the overall mortality of females over the 32 days taken to mature was estimated at 29%, equivalent to an exponential daily rate of 1.1% day^?1. The apparently negative mortality rate in one catchment (i.e. more matures than immatures being caught) could be due to an influx of adult females from elsewhere along the channel to oviposit. 6. Natural markers of age and population structure, such as sex ratio and female maturity, thus enabled us to detect a return of females to the stream to oviposit, after prior limited dispersal into the riparian zone, and to infer longitudinal movements in search of suitable sites. We were also able to estimate mortality in the field. Such natural markers seem to have been underexploited in the study of adult aquatic insects.     

SPECIES RICHNESS OF FRESHWATER GASTROPOD COMMUNITIES IN CENTRAL NORTH AMERICA

Species richness of freshwater gastropod communities (SR) wasexamined at 429 sites in central North America. Lakes and riversshowed the highest SR values, as did habitats with organic substrates,shale and clay. SR was significantly correlated with speciesrichness of aquatic macrophytes, particularly in lotic habitats.Of the 8 water chemistry variables examined, SR in the studyarea as a whole was significantly positively correlated withinorganic phosphorus, chloride, total alkalinity, total dissolvedsolids and pH, and inversely correlated with dissolved organicmatter. Stepwise multiple regression analyses showed that contributionsof the respective chemical variables varied in different typesof water bodies. Different variables interacted in their effectson SR. In all cases more than half of the variability in SRremained unexplained by the chemical variables examined. Manyfactors apparently influence SR, their relative importance varyingwith situation. (Received 24 October 1986;     

Availability of and access to critical habitats in regulated rivers: effects of low-head barriers on threatened lampreys

1.  Conservation of freshwater animal populations requires their access to, as well as sufficient availability of, critical habitats, such as those for reproduction. Abundant small-scale barriers may cause extensive fragmentation of freshwater habitat but, by comparison to larger structures their effects are rarely considered by catchment managers. The relationship between the distribution of, and access to, spawning habitat in a regulated river, characterized by abundant small barriers, was examined for river lamprey Lampetra fluviatilis , a threatened migratory fish.
2.  Telemetry of adult lamprey in the River Derwent, North East England was used to quantify upriver migration and access to spawning habitat, together with surveys of spawning habitat availability and spawning activity between 2002 and 2007.
3.  Access in to the Derwent appeared severely restricted by a tidal barrage, beyond which lamprey migrated rapidly in unobstructed reaches. Of all lamprey tagged in the lower 4 km of river, or ascending the barrage, 64% and 17% passed the first and second weirs respectively, with high flows crucial for this. Although over 98% of lamprey spawning habitat occurred more than 51 km upstream, on average just 1.8% of river lamprey spawners were recorded there.
4.  In order to protect or rehabilitate species or species assemblages, greater attention needs to be paid to the relative spatial distribution of low-head barriers and the resultant availability of key habitats within individual catchments. This is particularly important given the renewed emphasis internationally on low-head hydropower solutions as a source of renewable energy, and the rapid growth in numbers of low-head barriers in many catchments.     

Linking climate change and species invasion: an illustration using insect herbivores

Climate change and invasive species are two of the most important ecological issues facing the world today. Yet, to date these two factors have largely been viewed independently. In order to prevent large-scale economic and environmental damage and as a first step towards predicting and preventing invasions, it is important to understand the factors affecting invasions. Here, we focus on insect herbivores and link the climate change and invasive research fields. We illustrate using existing published research that life history traits can be useful indicators of future invasive potential. However, climate change will also affect propagule pressure and the communities into which invaders will arrive. With the aid of a meta-analysis we show that climate-induced community changes are likely to increase niche-availability in the future, further exacerbating the problem of invasive species. It is timely and important that further research linking these two important ecological threats is undertaken.     

Speciation in the greater galagos (Prosimii: Galaginae): review and synthesis*

A marked morphological and genetical discontinuity among the greater galagos points to the existence of two genetical species within the taxon, Galago crassicaudatus E. Geofl'roy 1812. This contribution investigates the conditions surrounding this speciation event, and places it within a phylogenetic context. Information pertaining to body size, litter size, sexual dimorphism, locomotor mode and karyotypic structure is assessed. It is hypothesized that G. crassicaudatus diverged from its more gracile sibling, G. garnettii, approximately 2 million years ago, in respotise lo the increasing aridification of Africa that accompanied the Northern Hemisphere Pleistocene glaciations.     

Competition and macroevolution: the ghost of competition yet to come?

Competition theory is the focus of much debate among both neontologists and palaeontologists. This paper explores the expansion of competition theory into macroevolution, since this is the relevant context for palaeobiologists, and challenges the contention that microevolutionary processes are generally inappropriate to the interpretation of macroevolutionary pattern. We show that the term 'interspecific competition' is imprecise, since it conflates processes operating at various hierarchical levels, and recommend a terminological change in accordance with hierarchy theory. Finally, we reassess the role of competition and its absence in radiations. Since evolutionary novelties must be fixed at speciation, and speciation occurs in response to habitat destruction rather than the freeing of ecological space, we believe the role of competition to be minimal in both radiation and the generation of novelty.