Does lemming winter grazing impact vegetation in the Canadian Arctic?

In low-productivity environments such as the tundra, it has been proposed that regular, multi-annual population cycles of lemmings could be driven by winter food depletion in years of peak abundance. If lemming population dynamics is controlled by food resources, we predict that (1) winter grazing should negatively impact the abundance of food plants, (2) this impact should be proportional to lemming density and (3) high lemming winter grazing pressure should result in reduced plant growth during the following summer. We tested these predictions on Bylot Island, Nunavut, Canada, where two species of lemmings are present: the brown (Lemmus trimucronatus) and collared lemming (Dicrostonyx groenlandicus). We installed 16 exclosures in their preferred wintering habitat (snowbeds) and annually sampled plant biomass inside and outside exclosures at snow melt and at peak growth during the summers of 2009–2012, covering a full population cycle. Winter grazing had no impact on total vascular plant or moss biomass at snow melt in all years. Among plant families, only Caryophyllaceae, which was uncommon, showed a decline. In moss taxa, a negative effect was found on Polytrichum in only 1 year out of three. Overall, plant regrowth during the subsequent summer showed annual variation and tended to be reduced in the 2 years of high lemming abundance. However, this could be a consequence of summer grazing. Overall, the impact of lemming winter grazing on plants was weak and short-lived, even in years of high lemming abundance. Therefore, our results are not consistent with the hypothesis that food depletion during winter was the cause of the lemming decline following peak abundance at our study site. Other factors may limit lemming populations and prevent them from reaching densities high enough to exhaust their food resources.     

Songbirds using crops planted on farmland as cover for game birds

We counted songbirds in crops planted on shooting estates specifically for game management purposes on farmland in Britain and elsewhere in Europe. Winter game crops provide cover and feed areas for pheasants Phasianus colchicus and red-legged partridge Alectoris rufa, while summer game crops are designed to provide brood-rearing cover for these species. In central and southern England, 30 plots of winter game crops, either kale, quinoa or cereal up to 2 ha in area, and 30 adjacent arable-field plots, were surveyed for birds up to six times at monthly intervals during the winter 1997–1998. In the Scottish lowlands, six plots of summer game crops up to 4 ha in area, and adjacent arable fields were surveyed in summer 1999 or 2000. The winter game plots contained more than ten songbirds per hectare in most months, while the adjacent arable-field plots contained less than one. In all three winter game crop types, songbird numbers declined significantly in the second half of the winter while numbers in the arable fields did not. Of the 26 species recorded in the winter game crops, 10 have undergone rapid decline over the last 30 years. Considering these declining species alone, the winter game crops still contained more individuals than the adjacent arable fields throughout the winter. Densities in both the kale and quinoa were higher than in the cereal game crop. The six summer game crops sampled in mid-summer contained on average 2.9 songbirds per hectare, while the adjacent arable fields contained 0.4. Of the 14 species recorded in these summer game crops, eight have undergone rapid or moderate declines over the last 30 years. Although winter and summer game crops are planted in relatively small plots and hence concentrate birds, these plots are widely planted and our results suggest that they benefit birds on farmland.     

Effect of Length of Time before Incorporation on Survival of Pathogenic Bacteria Present in Livestock Wastes Applied to Agricultural Soil

In response to reports that the contamination of food can occur during the on-farm primary phase of food production, we report data that describes a possible cost-effective intervention measure. The effect of time before soil incorporation of livestock wastes spread to land on the rate of decline of zoonotic agents present in the waste was investigated. Fresh livestock wastes were inoculated with laboratory-cultured Salmonella, Listeria, and Campylobacter spp. and Escherichia coli O157 before they were spead onto soil. Incorporation of the spread wastes was either immediate, delayed for 1 week, or did not occur at all. Bacterial decline was monitored over time and found to be significantly more rapid for all waste types when they were left on the soil surface. There were no significant differences in initial bacterial decline rates when wastes were spread in summer or winter. Our results indicate that not incorporating contaminated livestock wastes into soil is a potential intervention measure that may help to limit the spread of zoonotic agents further up the food chain. The implications of these findings are discussed in relation to current advice for livestock waste disposal.     

A Whole-Lake Experiment to Determine the Effects of Winter Droughts on Shallow Lakes

Lake-level fluctuations are common in the North American Great Plains region, where large-scale climate systems (El Niño, the Pacific Decadal Oscillation) and periodic droughts cause substantial hydrologic variability in both summer and winter. To date, most such research has focused on the effects of summer droughts on prairie lake ecosystems; therefore, we studied the impact of water-level decline during winter on ecosystem structure and function. Specifically, we hypothesized that lower lake levels during winter would increase anoxia, freezing and scouring of benthos, fish kills, herbivory by zooplankton, and nutrient release from sediments. In addition, we tested the hypothesis that winter droughts may initiate a switch between alternative stable states (turbid, clear). Physical, chemical, and biological variables were monitored from 1996 to 2001 in both Wascana Lake, which experienced a 50% decline in lake level, and Buffalo Pound Lake, where water levels were constant. A combination of before-after-control-impact (BACI) and multivariate analyses showed that drawdown resulted in elevated NH₄-N concentrations following reinundation; otherwise there were few detectable effects on lake water chemistry (PO₄-P, NO₃-N, total dissolved nitrogen, total dissolved carbon) or pelagic food web structure (phytoplankton, zooplankton), and the experimental lake remained in a macrophyte-rich state. There was, however, a 2.5-fold increase in macrophyte abundance and a shift from a community dominated by Ceratophyllum demersum before drawdown to one composed of Potamogeton pectinatus after manipulation. Overall, the lack of substantial dewatering effects suggests that lakes of the northern Great Plains may be resilient to severe winter conditions, possibly because of the recruitment of fish from regional metapopulations during summer. Further, our results indicate that lower water levels during winter likely promote the buffer mechanisms that reinforce a macrophyte-rich, clear-water state in shallow prairie lakes.     

Seasonal changes in inhibin activity in seminal plasma and serum concentrations of FSH, LH and testosterone in the male goat (Capra hircus)

Inhibin activity in goat seminal plasma was measured by in vitro assay throughout successive 9 months and its relationship with the serum FSH, LH and testosterone concentrations was investigated. Total inhibin activity (TIA) in seminal plasma gradually increased from spring to summer, reduced in autumn (P<0.05) and recovered toward winter (P<0.05). Serum FSH and LH reached a peak in mid-summer (P<0.01) and returned to the low levels in autumn. Serum testosterone also increased in mid-summer and kept the high levels until the early winter (P<0.05). Some positive correlation was found in monthly levels between seminal TIA and serum FSH (r=0.305; P<0.05). Results suggest that the summer increase of inhibin activity in seminal plasma relates with the mid-summer rise of serum FSH levels in the male goat.     

Invasive alien species under attack: natural enemies of Harmonia axyridis in the Netherlands

The aphid predator Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is an invasive alien species in Europe and North America with negative effects on non-target species (including a decline of native ladybird populations), as well as fruit production, and human health. It is, therefore, important to find out which natural enemies could be used to reduce their numbers. Knowledge of H. axyridis’ natural enemies is summarised and data collected from the Netherlands over the past ten years are presented. Beetles were sampled from winter aggregations and from spring through to autumn with illuminated screens at night. Natural enemies were not found in samples of H. axyridis from 2003–2007. From 2008 onward H. axyridis adults were infested by: Hesperomyces virescens Thaxt. fungi (summer and winter), Parasitylenchus bifurcatus Poinar and Steenberg nematodes (winter), Coccipolipus hippodamiae (McDaniel and Morrill) mites (winter), and Dinocampus coccinellae (Schrank) parasitoids (summer and winter). Our results indicate that these natural enemies are starting to use H. axyridis as a host, but are as yet not sufficiently abundant to control the population.     

The endocrine basis of reproductive inactivity in Monarch butterflies overwintering in central California

Monarch butterflies (Danaus plexippus) collected during winter in central California are reproductively inactive. Oögenesis is stimulated in such animals by environments simulating summer conditions. Allatectomized or neck-ligatured winter animals do not normally undergo oögenesis when placed in summer conditions, but apparently normal oögenesis occurs if they are injected with juvenile hormone isomers. Injections of such isomers into winter animals held in environments simulating winter also promote oögenesis, even though winter conditions typically inhibit ovarian development. Reproductive dormany in winter Monarchs of central California therefore appears to be due (at least partially) to environmentally induced inactivity of the corpora allata.     

Diving through the thermal window: implications for a warming world

Population decline and a shift in the geographical distribution of some ectothermic animals have been attributed to climatic warming. Here, we show that rises in water temperature of a few degrees, while within the thermal window for locomotor performance, may be detrimental to diving behaviour in air-breathing ectotherms (turtles, crocodilians, marine iguanas, amphibians, snakes and lizards). Submergence times and internal and external body temperature were remotely recorded from freshwater crocodiles (Crocodylus johnstoni) while they free-ranged throughout their natural habitat in summer and winter. During summer, the crocodiles'' mean body temperature was 5.2 ± 0.1°C higher than in winter and the largest proportion of total dive time was composed of dive durations approximately 15 min less than in winter. Diving beyond 40 min during summer required the crocodiles to exponentially increase the time they spent on the surface after the dive, presumably to clear anaerobic debt. The relationship was not as significant in winter, even though a greater proportion of dives were of a longer duration, suggesting that diving lactate threshold (DLT) was reduced in summer compared with winter. Additional evidence for a reduced DLT in summer was derived from the stronger influence body mass exerted upon dive duration, compared to winter. The results demonstrate that the higher summer body temperature increased oxygen demand during the dive, implying that thermal acclimatization of the diving metabolic rate was inadequate. If the study findings are common among air-breathing diving ectotherms, then long-term warming of the aquatic environment may be detrimental to behavioural function and survivorship.     

Latitudinal trends in reproduction,recruitment and population characteristics of some rocky littoral molluscs and cirripedes

This paper reviews progress in the COST 647 rocky littoral programme involving three patellids, two trochids and two cirripedes on European Atlantic coasts. Northern geographical limits are set primarily by repopulation failure, and northern populations are characterised by short, mid-summer breeding periods, high frequency of failed or poor recruitments and low density of large, long-lived individuals. Towards the south molluscan breeding periods lengthen and become later, extending in some cases throughout much of the year but with least or no activity in mid-summer. There are probably fewer recruitment failures and thus higher densities, but individuals are of smaller maximum size and shorter life-span.The cirripedes show similar latitudinal trends in recruitment timing but Semibalanus is restricted to a single annual brood throughout its range.The two species reaching their southern limits show progressive restriction to the lowest tidal levels.Recruitment failures do not result from inadequate gonad activity. They arise in cirripedes during the planktonic phase and in the molluscs during settlement and early shore life. The temperature sensitivity of molluscan spat is primarily responsible for the north/south gradient in recruitment times from summer towards winter.Formerly University of Leeds, England     

Seasonal variation in numbers of eggs laid byCulex quinquefasciatus Say (Diptera: Culicidae) at Khartoum

Regular counts of the eggs ofCulex quinquefasciatus Say were recorded during the period April 1979 – March 1981. The results indicate that the lowest numbers of eggs laid were during summer months (May and June) and the highest ones were during winter months (November and January). The decline of numbers during summer was mainly due to small size of adults (0.57 mg, average wt of female). Populations flourished during the rainy season (July – October) and reached their peak in August. Bigger batches of eggs were then obtained. In winter prolongation of larval life gave rise to large-sized adults and hence bigger batches of eggs.     

Seasonal and diurnal changes in photosynthetic limitation of young sweet orange trees

This study tests the hypothesis that potted sweet orange plants show a significant variation in photosynthesis over seasonal and diurnal cycles, even in well-hydrated conditions. This hypothesis was tested by measuring diurnal variations in leaf gas exchange, chlorophyll fluorescence, leaf water potential, and the responses of CO₂ assimilation to increasing air CO₂ concentrations in 1-year-old ‘Valência’ sweet orange scions grafted onto ‘Cleopatra’ mandarin rootstocks during the winter and summer seasons in a subtropical climate. In addition, diurnal leaf gas exchange was evaluated under controlled conditions, with constant environmental conditions during both winter and summer. In relation to our hypothesis, a greater rate of photosynthesis is found during the summer compared to the winter. Reduced photosynthesis during winter was induced by cool night conditions, as the diurnal fluctuation of environmental conditions was not limiting. Low air and soil temperatures caused decreases in the stomatal conductance and in the rates of the biochemical reactions underlying photosynthesis (ribulose-1,5-bisphosphate (RuBP) carboxylation and RuBP regeneration) during the winter compared to the values obtained for those markers in the summer. Citrus photosynthesis during the summer was not impaired by biochemical or photochemical reactions, as CO₂ assimilation was only limited by stomatal conductance due to high leaf-to-air vapor pressure difference (VPD) during the afternoon. During the winter, the reduction in photosynthesis during the afternoon was caused by decreases in RuBP regeneration and stomatal conductance, which are both precipitated by low night temperature.     

Presence and behavior of bowhead whales (Balaena mysticetus) in the Alaskan Beaufort Sea in July 2011

The Western Arctic bowhead whale (Balaena mysticetus) is highly adapted to sea ice and annually migrates through the Bering, Chukchi, and Beaufort seas. While the overall distribution and seasonal movements of bowhead whales are mostly understood, information about their distribution in the Alaskan Beaufort Sea in early to mid-summer has not been well documented. In July 2011, we conducted an exploratory flight in the Alaskan Beaufort Sea, north of Camden Bay (71°N 144°W), near the location of a single satellite-tagged bowhead whale. Eighteen bowhead whales were observed, and behavior consistent with feeding was documented. To our knowledge, this is the first documentation of behavior consistent with feeding north of Camden Bay in mid-July. Few studies have focused on bowhead whale distribution in the Alaskan Beaufort Sea in early to mid-summer, and no long-term, region-wide surveys have been conducted during summer. Bowhead whales are already exposed to anthropogenic disturbance in the Canadian Beaufort Sea in summer, the Alaskan Beaufort Sea in fall, and the Chukchi and Bering seas from fall through spring. The presence of bowhead whale aggregations in the Alaskan Beaufort Sea in summer should be considered when assessing the cumulative effects of human-related activities.     

Migration patterns of pronghorn in southwestern North Dakota

Wildlife managers need empirical data about pronghorn (Antilocapra americana) movements in North Dakota to assess whether mid-summer surveys represent occupancy of pronghorn in hunting units during the fall hunting season. Using data from 121 radiocollared pronghorn we evaluated patterns of pronghorn migrations in southwestern North Dakota from 2004 to 2007. Pronghorn exhibited 2 primary movement patterns between summer and winter ranges: migrations >15 km (45%) and movement <15 km (55%). Most migratory pronghorn moved northeast or east in the spring and southwest or west in the fall. Average distance moved for migratory pronghorn was 70.6 km (range = 17.4–253 km). Mean date of pronghorn migration in spring was 20 March (SD = 20 days) and in fall was 22 October (SD = 17 days). Nearly all migratory pronghorn (97%) returned to within 15 km of their previous summer range, whereas only 61% of pronghorn returned to within 15 km of their previous winter range. Most pronghorn moved across hunting and survey unit boundaries; however, only 7 fall migrations occurred between the aerial survey and the hunting season. During years of our study, the mid-summer survey provided representative information about hunting unit occupancy of radiocollared pronghorn for the fall hunting season. © 2011 The Wildlife Society     

Population structure change of Salpa thompsoni from austral mid-summer to autumn

Changes in the population structure of Salpa thompsoni from austral mid-summer to autumn off the Adelie Coast, Antarctica, were examined using cluster analysis based on reproductive states. S. thompsoni was the dominant macrozooplankton species through the research periods although the abundance decreased markedly in autumn. In both summer and autumn we identified three geographically coherent subpopulations, which were considered to be either a mating swarm or physical aggregation. Many aggregate forms with an empty (dead) embryo were observed, and the ratio of newborn solitary forms decreased in autumn, indicating sexual reproduction of the salps was deactivated. The significant reduction in size of mature solitaries suggested that the capacity of asexual reproduction was also reduced in autumn. In addition to water temperature decline, the phytoplankton shortage (which was partly caused by high grazing pressure of S. thompsoni during summer) might be the factor causing decline in their own population size in autumn. Accepted: 25 May 1999     

Seasonal biochemical plasticity of a flight muscle in a bat, Murina leucogaster

Cellular and biochemical responses of the pectoral muscle to variation in seasonal activity were studied in the bat, Murina leucogaster ognevi. We collected bats in mid-hibernation (February), end-hibernation (April), and mid-summer (August) to track major activity periods in their annual cycle. Our findings indicated that myofiber cross-sectional area decreased to 68% between mid- and end-hibernation, but returned to the winter level in mid-summer. Total soluble protein and total RNA concentrations were not altered over these sampling periods. Oxidative potential gauged by citrate synthase activity increased 1.47-fold from mid- to end-hibernation and then remained at the similar level in mid-summer. Glycolytic potential gauged by lactate dehydrogenase activity changed little between mid- and end-hibernation but increased 1.42-fold in summer, compared with the winter level. Thus, the myofibers underwent disuse atrophy during hibernation, while enzymatic catalytic function recovered towards the level of mid-summer.     

Urea Uptake and Carbon Fixation by Marine Pelagic Bacteria and Archaea during the Arctic Summer and Winter Seasons

How Arctic climate change might translate into alterations of biogeochemical cycles of carbon (C) and nitrogen (N) with respect to inorganic and organic N utilization is not well understood. This study combined ¹⁵N uptake rate measurements for ammonium, nitrate, and urea with ¹⁵N- and ¹³C-based DNA stable-isotope probing (SIP). The objective was to identify active bacterial and archeal plankton and their role in N and C uptake during the Arctic summer and winter seasons. We hypothesized that bacteria and archaea would successfully compete for nitrate and urea during the Arctic winter but not during the summer, when phytoplankton dominate the uptake of these nitrogen sources. Samples were collected at a coastal station near Barrow, AK, during August and January. During both seasons, ammonium uptake rates were greater than those for nitrate or urea, and nitrate uptake rates remained lower than those for ammonium or urea. SIP experiments indicated a strong seasonal shift of bacterial and archaeal N utilization from ammonium during the summer to urea during the winter but did not support a similar seasonal pattern of nitrate utilization. Analysis of 16S rRNA gene sequences obtained from each SIP fraction implicated marine group I Crenarchaeota (MGIC) as well as Betaproteobacteria, Firmicutes, SAR11, and SAR324 in N uptake from urea during the winter. Similarly, ¹³C SIP data suggested dark carbon fixation for MGIC, as well as for several proteobacterial lineages and the Firmicutes. These data are consistent with urea-fueled nitrification by polar archaea and bacteria, which may be advantageous under dark conditions.     

Effects of Temperature and Salinity on Vibrio vulnificus Population Dynamics as Assessed by Quantitative PCR

The abundance of Vibrio vulnificus in coastal environments has been linked to water temperature, while its relationship to salinity is less clear. We have developed a culture-independent, most-probable-number quantitative PCR approach to examine V. vulnificus population dynamics in Barnegat Bay, N.J. Based on the combined analysis of our results from Barnegat Bay and from the literature, the present data show that (i) V. vulnificus population dynamics are strongly correlated to water temperature and (ii) although the general trend is for V. vulnificus abundance to be inversely correlated with salinity, this relationship depends on salinity levels. Irrespective of temperature, high abundances of V. vulnificus are observed at 5 to 10 ppt, which thus appears to be the optimal salinity regime for their survival. At 20 to 25 ppt, V. vulnificus abundances show a positive correlation to salinity. Unsuccessful attempts to resuscitate V. vulnificus, combined with our inability to detect cells during the winter despite an assay adapted to detect viable but nonculturable (VBNC) cells, suggest that the decline and eventual disappearance of V. vulnificus from the water column during the winter months is due primarily to a significant reduction in population size and is not only the consequence of cells entering the VBNC state. These findings are in line with the hypothesis that the sediment serves as a refuge for a subpopulation of V. vulnificus over the winter and weather-driven mixing events during the spring initiate a summer bloom in the water column.     

Seasonal variation in body composition and morphology of adult muskrats in central Saskatchewan, Canada

We quantified seasonal variation in body composition and morphology of adult muskrats ( Ondatra zibethicus ) inhabiting freshwater marsh environments in central Saskatchewan, Canada. The study areas were characterized by long and cold winters extending over six months during which muskrats were restricted to foraging under ice. A total of 162 adult muskrats were collected during nine sampling periods across the year. The large accumulation of fat reserves (16% of body mass) during winter and the concurrent decline in protein mass suggested a reduced maintenance requirement associated with the presence of energy-rich food resources. Dietary fibre content increased significantly during mid-summer and was manifested by changes in gut morphology. Mobilization of fat reserves during summer months by both sexes reflected high energetic demands for reproduction. Males depleted fat reserves soon after spring break-up, while near-exhaustion of fat reserves in females occurred 4–6 weeks later, during lactation. Pregnant females contained significantly greater fat and protein reserves compared to non-pregnant and lactating females. The dynamics of body reserves in muskrats should be viewed as an integral part of the sex-specific life-history traits of this important herbivore species of marsh environments.     

Seasonal polyphenism and leaf mimicry in the comma butterfly

The comma butterfly, Polygonia c-album, exhibits seasonal polyphenism with a darkish winter morph and a lighter summer one. Phylogenetic analysis suggests that the winter morph represents the ancestral condition. We suggest two hypotheses for the evolution of the summer morph and the maintenance of seasonal polyphenism in the comma: (1) that the summer morph is better protected against predation on summer roost sites, whereas the winter morph is better protected on hibernation sites, and (2) that the summer morph is energetically less expensive and results from deallocation of resources from soma (e.g. dark wing pigmentation) to reproduction. We tested the antipredation hypothesis in experiments using great tits, Parus major, as predators on winter and summer morph commas presented simultaneously on tree trunks or on nettles. However, this hypothesis was not supported as the winter morph was better protected than the summer morph on both backgrounds. Predation when both morphs were present was lower on nettles, and summer morphs placed in exposed positions on tree trunks outdoors disappeared sooner than winter morphs placed on the same background. In addition, in a final experiment, 18 summer morphs released in their natural habitat in the evening exclusively chose leaves for roost sites, whereas 12 of 19 winter morphs chose a tree trunk, branch or twig. We conclude that evolution of the summer morph is consistent with the life history hypothesis and that its choice of summer roost sites is associated with a low predation pressure.     

Scavenging in Antarctica: Intense variation between sites and seasons in shallow benthic necrophagy

The response of scavengers to a feeding cue at Adelaide Island, West Antarctic Peninsula was investigated using a baited video camera system. Fourteen experimental deployments, each lasting 72 h were conducted at two contrasting sites during the winter and summer of 2005. The rate of bait consumption varied between sites but not between seasons, and was low in comparison with studies at lower latitudes and greater depths. At the Hangar Cove site, the nemertean Parborlasia corrugatus was out-competed at the bait and displaced by the lysianassid amphipod Cheirmedon femoratus during winter. However, C. femoratus did not feed on the bait during summer, allowing P. corrugatus to monopolise the feeding opportunity. At the South Cove site the asteroid Odontaster validus dominated the bait in both seasons but sporadic feeding by the nototheniid fish Notothenia coriiceps considerably affected consumption rates during two of the six deployments. Scavengers were attracted to the bait in very high numbers and opportunistic necrophagy seems to be a successful strategy in an environment that is intensely disturbed by ice.