Recovery of three arctic stream reaches from experimental nutrient enrichment

1. Nutrient enrichment and resulting eutrophication is a widespread anthropogenic influence on freshwater ecosystems, but recovery from nutrient enrichment is poorly understood, especially in stream environments. We examined multi‐year patterns in community recovery from experimental low‐concentration nutrient enrichment (N + P or P only) in three reaches of two Arctic tundra streams (Kuparuk River and Oksrukuyik Creek) on the North Slope of Alaska (U.S.A.). 2. Rates of recovery varied among community components and depended on duration of enrichment (2–13 consecutive growing seasons). Biomass of epilithic algae returned to reference levels rapidly (within 2 years), regardless of nutrients added or enrichment duration. Aquatic bryophyte cover, which increased greatly in the Kuparuk River only after long‐term enrichment (8 years), took 8 years of recovery to approach reference levels, after storms had scoured most remnant moss in the recovering reach. 3. Multi‐year persistence of bryophytes in the Kuparuk River appeared to prevent recovery of insect populations that had either been positively (e.g. the mayfly Ephemerella, most chironomid midge taxa) or negatively (e.g. the tube‐building chironomid Orthocladius rivulorum) affected by this shift in dominant primary producer. These lags in recovery (of >3 years) were probably driven by the persistent effect of bryophytes on physical benthic habitat. 4. Summer growth rates of Arctic grayling (both adults and young‐of‐year) in Oksrukuyik Creek (fertilised for 6 years with no bryophyte colonisation), which were consistently increased by nutrient addition, returned to reference rates within 1–2 years. 5. Rates of recovery of these virtually pristine Arctic stream ecosystems from low‐level nutrient enrichment appeared to be controlled largely by duration of enrichment, mediated through physical habitat shifts caused by eventual bryophyte colonisation, and subsequent physical disturbance that removed bryophytes. Nutrient enrichment of oligotrophic Arctic stream ecosystems caused by climate change or local anthropogenic activity may have dramatic and persistent consequences if it results in the colonisation of long‐lived primary producers that alter physical habitat.     

Cryptic speciation at organic‐rich marine habitats: a new bacteriovore annelid from whale‐fall and fish farms in the North‐East Atlantic

Vigtorniella ardabilia sp. nov. , a new chrysopetalid annelid, is described from a whale‐fall in Sweden and from sediment samples collected beneath fish farms in Norway. The new Vigtorniella species is morphologically almost identical to Vigtorniella flokati from whale‐falls in the Pacific Ocean, although molecular evidence from four genes shows that they are different species. Population genetic structure and phylogenetic relationships of V. ardabilia sp. nov. were assessed using molecular data from the nuclear genes 18S and 28S, and the mitochondrial 16S and cytochrome c oxidase subunit I (COI). High levels of gene flow are reported between contrasting organic‐rich environments in the North Atlantic (fish farms and whale‐fall). Observations of feeding biology and habitat suggest that V. ardabilia specializes on bacterial mats, rather than on whale‐falls, although the two species of Vigtorniella for which data were available show very different feeding behaviours. Our results further showed an unexpectedly low divergence rate in Vigtorniella for the mitochondrial markers, suggesting stabilizing selection. Analyses carried out with parsimony, maximum likelihood, and MrBayes all placed the genus Vigtorniella as sister group to Dysponetus, suggesting a close evolutionary link to sediment‐dwelling fauna. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 774–785.     

Preen waxes do not protect carotenoid plumage from bleaching by sunlight

The plumage coloration of wild birds often changes during the breeding season. One of the possible reasons for this is that sunlight, and particularly ultraviolet (UV) wavelengths, degrades the pigments responsible for plumage coloration. It has been suggested that birds may apply preen wax to feathers to protect feathers from bleaching. This hypothesis is tested by exposing carotenoid-based breast feathers of Great Tits to ambient light, light filtered to exclude UV and darkness. Preen waxes were experimentally removed from feather samples and the effect of light on coloration of treatment and control feathers compared. Ambient light had an effect on feather colour but preen wax did not. Feathers exposed to sun gradually became less saturated and hues shifted towards shorter wavelengths. This was not apparent in control feathers kept in darkness. Feathers exposed to full-spectra sunlight faded more than those that were kept in light with UV wavelengths removed. There was a decrease in brightness of feathers in both experimental and control groups, which was assumed to be an effect of dirt accumulation. This experiment confirmed earlier suspicions regarding the detrimental effects of UV irradiation on carotenoid-based coloration of avian feathers but failed to show any protective function of preen waxes. The possible consequences of these mechanisms of colour change for birds with regard to mating strategies are discussed.     

At what spatial scales does resource selection vary? A case study of koalas in a semi‐arid region

The conservation of any species requires understanding and predicting the distribution of its habitat and resource use, including the effects of scale‐dependent variation in habitat and resource quality. Consequently, testing for resource selection at the appropriate scales is critical. We investigated how the resource selection process varies across scales, using koalas in a semi‐arid landscape of eastern Australia as a case study. We asked: at what scales does tree selection by koalas vary across regions? We tested the importance of the variation of our ecological predictors at the following scales: (i) the site‐scale (a stand of trees representing an individual koala's perception of local habitat); (ii) the landscape‐scale (10 × 10 km area representing a space within which a population of koalas exists); and (iii) a combination of these scales. We used a mixed‐modelling approach to quantify variation in selection of individual trees by koalas among sites and landscapes within a 1600 km² study area. We found that tree species, and tree height, were the most important factors influencing tree selection, and that their effect did not vary across scales. In contrast, preferences for trees of different condition, which is the state of tree canopy health, did vary across landscapes, indicating spatial variation in the selection of trees with respect to tree condition at the landscape‐scale, but not at the site‐scale. We conclude that resource selection processes can depend on the quality of those resources at different scales and their heterogeneous nature across landscapes, highlighting the consequence of scale‐dependent ecological processes. Designing studies that capture the heterogeneity in habitat and resources used by species that have an extensive distribution is an important prerequisite for effective conservation planning and management.     

Testing the resource‐matching hypothesis in the mast seeding tree Nothofagus truncata (Fagaceae)

Abstract: The genus Nothofagus in New Zealand and Australia exhibits strong mast seeding (i.e. highly variable seed crops between years). Seed crop variation is synchronized within and between species over large spatial scales, and results in greatly increased wind pollination efficiency which could provide a selective benefit favouring the maintenance of mast seeding. However, the null hypothesis (that plants simply match their reproductive effort to the variable resources available each year) has not been tested in Nothofagus. Here we use a 33‐year dataset on seedfall and wood ring increments for 19 individual Nothofagus truncata trees at Orongorongo, New Zealand, to test for the presence of switching (exaggeration of seedfall variability by diverting resources into, then out of, reproduction). A generalized least squares model explained 40.7% of the variance in standardized ring widths, using six weather variables (absolute minimum temperatures in March (lag 0) April (lag 0 and lag 1), May (lag 0) and rainfall in November and February (lag 0) ) and seedfall. Seedfall had a negative relationship with the current year's ring widths even after controlling for all significant weather variables. This shows that switching is occurring in N. truncata within individuals among years, and therefore that masting in this species is the result of selective forces such as increased wind pollination efficiency. As this result has been demonstrated for very few masting species, we call for this test to be applied more widely.     

Bats, flowers and fruit: evolutionary relationships in the Old World

Old World phytophagous bats (Megachiroptera: Pteropodidae) number 173 species of which 79% are Asian and 21% African. Bats arose, presumably monophyletically, in the early Tertiary, the Megachiroptera soon diverging from the Microchiroptera. By the Cretaceous-Tertiary boundary the major groups of modern angiosperms were present, some of these probably being pollinated nocturnally by large insects and non-flying mammals and others with seeds dispersed by terrestrial vertebrates. Early bats were perhaps initially attracted to such flowers and fruit by the insects found around them, later finding the plants themselves nutritious. Megabats today feed upon floral resources, fruit and leaves from a total of at least 188 plant genera in 64 families. They may effect both pollination and seed-dispersal, and both bat-flower and bat-fruit syndromes are commonly recognized. Individual species are generally catholic in their feeding, favoured food varying with locality and season. Depending upon roosting habits and season, megabats may travel considerable distances each night to feed and may undertake seasonal migrations. Their feeding in orchards may sometimes require their control, but the future of certain species is more seriously threatened by slaughter for food and particularly by habitat destruction.     

Calanoid–cyclopoid interactions: evidence from an 11-year field study in a eutrophic lake

1. The interactions between calanoid and cyclopoid copepods were examined in an 11-year field study of a eutrophic lake (Heiligensee, Berlin, Germany).
2. A diminishing ratio of calanoids to cyclopoids was observed. The responses, however, were species specific. While two cyclopoid species responded with increased populations ( Cyclops vicinus, Thermocyclops oithonoides ), one species exhibited marked declines ( C. kolensis ). Other species extended the duration of their pelagic phase ( Mesocyclops leuckarti, Diacyclops bicuspidatus, T. oithonoides, C. vicinus ), leading to higher population overlaps. Eudiaptomus graciloides and E. gracilis, which used to be present throughout the year, were more frequently absent.
3. These changes coincided with a series of mild winters during which prey availability (algae and rotifers) was high.
4. Enhanced prey availability, in conjunction with a flexible diapausing strategy, are hypothesized to underly the increased success of C. vicinus . Predatory losses due to early occurrence and enhanced abundances of C. vicinus, rather than competition for the same food resources, are hypothesized to be responsible for the declines of C. kolensis and Eudiaptomus .
5. Summer species tended to develop higher abundances early in the season, which led to enhanced seasonal means during spring. These changes cannot be explained by the interaction between calanoids and cyclopoids alone, but were probably a result of changes in fish predation.