SHAPE DIFFERENCES AMONG BOREHOLES DRILLED BY THREE SPECIES OF NATICID GASTROPODS

Naticid gastropods leave a record of predation in the form ofcharacteristic countersunk circular boreholes. We fed bivalveprey to naticids to test whether the ratio between the innerand outer borehole diameter differed among three Recent naticidspecies: Euspira heros, E. lewisii and Neverita duplicata. Fossilshells from a Miocene-aged assemblage, containing naticids previouslyidentified as E. heros and N. duplicata, were also includedin our analyses. Ratios of the inner to outer diameters of naticidboreholes in bivalve shells showed that there were significantdifferences in borehole shape between E. heros and the two otherRecent species. We found no significant differences betweenthe ratios of E. lewisii and N. duplicata; however, a principalcomponent analysis showed that boreholes distinctly clusteraccording to species. The Miocene boreholes were also distinctfrom the Recent, indicating that the Miocene naticids may bea separate species from E. heros and N. duplicata. We have shownthat there is a species-specific component to borehole geometry.This may have important implications for palaeobiological studies,because the index of borehole functionality, previously describedas an inner to outer borehole ratio of 0.5 for all naticids,may differ between species. (Received 23 March 2004; accepted 10 January 2005)     

Predicting small‐mammal responses to climatic warming: autecology,geographic range,and the Holocene fossil record

Forecasting how species will respond to climatic change requires knowledge of past community dynamics. Here we use time‐series data from the small‐mammal fossil records of two caves in the Great Basin of the American West to evaluate how contrasting and variable local paleoclimates have shaped small‐mammal abundance dynamics over the last ～7500 years of climatic change. We then predict how species and communities will respond to future scenarios of increased warming and aridity coupled with continued spread of an invasive annual grass (Bromus tectorum). We find that most community‐level responses to climatic change occur in the mammalian abundance structure at both sites; the dominance of the community by individuals from species with a southern geographic affinity increases with climatic warming. This suggests that responses occurred in situ rather than by the immigration of new taxa over this time interval. Despite predictability at the community‐scale, species‐level relationships between abundance and climate are variable and are not necessarily explained by a species' geographic affinity. Species present at both sites, however, exhibit remarkably similar responses to climate at each site, indicating that species autecology (specifically dietary functional group) is important in determining response to climatic warming. Regression‐tree analyses show remarkable concordance between the two cave faunas and highlight the importance of a granivorous dietary strategy in this desert ecosystem. Under projections of increased temperature and decreased precipitation over the next 50 years, our results indicate that granivores should thrive as communities become more dominated by individuals with a southern geographic affinity. Granivores, however, are negatively impacted by the invasion of cheatgrass. The last century of anthropogenic impacts has thus placed granivores at a greater risk of extinction than predicted under climate‐only scenarios.     

Effects of fishing and acidification‐related benthic mortality on the southeast Australian marine ecosystem

Oceanic uptake of anthropogenic carbon dioxide (CO₂) is altering the carbonate chemistry of seawater, with potentially negative consequences for many calcifying marine organisms. At the same time, increasing fisheries exploitation is impacting on marine ecosystems. Here, using increased benthic‐invertebrate mortality as a proxy for effects of ocean acidification, the potential impact of the two stressors of fishing and acidification on the southeast Australian marine ecosystem to year 2050 was explored. The individual and interaction effects of the two stressors on biomass and diversity were examined for the entire ecosystem and for regional assemblages. For 61 functional groups or species, the cumulative effects of moderate ocean acidification and fishing were additive (30%), synergistic (33%), and antagonistic (37%). Strong ocean acidification resulted in additive (22%), synergistic (40%), and antagonistic (38%) effects. The greatest impact was on the demersal food web, with fishing impacting predation and acidification affecting benthic production. Areas that have been subject to intensive fishing were the most susceptible to acidification effect, although fishing also mitigated some of the decline in biodiversity observed with moderate acidification. The model suggested that ocean acidification and long‐term fisheries exploitation could act synergistically with the increasing sensitivity to change from long‐term (decades) fisheries exploitation potentially causing unexpected restructuring of the pelagic and demersal food webs. Major regime shifts occur around year 2040. Greater focus is needed on how differential fisheries exploitation of marine resources may exacerbate or accelerate effects of environmental changes such as ocean acidification.     

Conservation of Britain's biodiversity: the case of Hieracium cyathis (Asteraceae) and its relation to other apomictic taxa

Hieracium cyathis (Ley) W. R. Linton (Asteraceae), Chalice Hawkweed, is a rare species endemic to Britain. It is a distinct member of Hieracium Section Oreadea , characterized by a short acladium and out-curved tips to the phyllaries. Historic records and current field survey indicate it has occurred in two localities in SW England and seven in South Wales. It is still present in all sites except for one Welsh locality, is significantly threatened at Cheddar Gorge, and two Welsh sites have only three plants each. Comparative morphology, cultivation experiments and amplified fragment length polymorphism (AFLP) analysis do not support the reported differences between material from SW England and Wales. AFLP analysis showed that every plant in the field was genetically similar but different, and minor genetic variation was found in one progeny array. It is a triploid (2 n  = 27) with apomictic seed production, and 26% potentially viable pollen. It qualifies as 'Near Threatened' under the 2001 IUCN threat criteria. General guidelines for conservation of microspecies of Hieracium are discussed.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 669–680.     

Effects of shoreline development on the nearshore environment in large deep oligotrophic lakes

1. In large deep oligotrophic lakes, the shallow nearshore waters may provide the most important habitat for animals to feed and breed, and it is this area of the lake where humans are most likely to have initial impacts as the shoreline is developed. Nutrients in fertilizers, sediments and sewage effluents are likely to be rapidly intercepted by nearshore algae at the lake edge, having heterogeneous effects nearshore before offshore effects are noted. 2. Here we examined the spatially explicit effects of residential development on nearshore periphyton communities in three large deep oligotrophic lakes that have all experienced modest residential development in the Pacific Northwest of the United States. We demonstrate that substantial nearshore changes in the basal food web are detectable even with low levels of shoreline development. These changes can potentially affect whole‐lake food web dynamics. 3. For our primary study site (Lake Crescent, Washington, USA), we found that algal biomass and accumulation of detritus were higher at developed sites. In addition, both macroinvertebrate and periphyton communities exhibited a shift in composition with more detritivores and filamentous green algae at developed sites. These differences were more pronounced during the spring than at other times of year. 4. A complementary investigation of field patterns in Priest Lake and Lake Pend Oreille (Idaho, USA) suggested that, although spatial and temporal patterns were idiosyncratic, indicators of productivity and the presence of filamentous green algae were generally higher at developed sites across lakes. 5. Stable isotope signatures and water column nutrients were not useful in distinguishing developed and undeveloped sites, increasing the potential usefulness of periphyton monitoring during early stages of lake development. 6. A laboratory investigation suggested that common macroinvertebrate grazers assimilated a much greater proportion of diatoms than the filamentous green algae that are associated with fertilization at developed sites. 7. These findings have at least two clear implications: (i) periphyton may be used to detect human impacts before disturbance is evident in offshore monitoring programmes and (ii) nearshore impacts in response to modest residential development have the potential to disrupt lake food web dynamics.     

Genetic variability in Irish populations of the invasive zebra mussel, Dreissena polymorpha: discordant estimates of population differentiation from allozymes and microsatellites

1. The recent arrival and explosive spread of the zebra mussel, Dreissena polymorpha (Pallas), in Ireland provided a rare opportunity to study the population genetics of an invasive species.
2. Eight polymorphic allozyme loci ( ACO-1, ACO-2 , EST-D, GPI, IDH-2, MDH, OPDH and PGM ) were used to investigate genetic diversity and population structure in five Irish populations, and the results were compared with those from a previous microsatellite study on the same samples.
3. The mean number of alleles per locus (2.7 ± 0.1) was similar to the mean for the same loci in European populations, suggesting that Irish founder populations were large and/or multiple colonization events took place after foundation. A deficiency of heterozygotes was observed in all populations, but was uneven across loci.
4. Pairwise comparisons, using Fisher's exact tests and F _ST values, revealed significant genetic differentiation among populations. The overall multilocus F _ST estimate was 0.118 ± 0.045, which contrasted with an estimate of 0.015 ± 0.007 from five microsatellite loci on the same samples in a previous study.
5. Assuming that microsatellites can be used as a neutral baseline, the discordant results from allozymes and microsatellites suggest that selection may be acting on some allozyme loci, specifically ACO-1, ACO-2 , IDH-2 and MDH, which contributed most to the significant differentiation between samples.