Ecological Archives E093-148-A1

P. Legagneux, G. Gauthier, D. Berteaux, J. Bêty, M-C. Cadieux, F. Bilodeau, E. Bolduc, L. McKinnon, A. Tarroux, J-F. Therrien, L. Morissette, and C.J. Krebs. 2012. Disentangling trophic relationships in a High Arctic tundra ecosystem through food web modeling. Ecology 93:1707–1716. http://dx.doi.org/10.1890/11-1973.1

Appendix A. Biomass, diet, production and consumption data used in the ECOPATH modeling for each functional group and details of the methods used to collect the data.

For each functional group (Table 1), we present the biomass (B), diet (d), production (P) and consumption (Q) estimates that we used in ECOPATH with ECOSIM (EwE) modeling. Table A1 provides annual biomass estimates. In arctic ecosystems, annual lemming biomass fluctuates considerably depending on the phase of the population cycle. The phase of the cycle (peak, intermediate or crash, Table A1) was assigned based on lemming abundance (see below) following Bêty et al. (2002). Determining peak years was obvious and was confirmed by the presence of Snowy Owls, which nest only in peak lemming years at our study site (Gauthier et al. 2004). The low phase (crash) of the lemming cycle was characterized by a very low (~0 lemmings trapped) lemming density (both species pooled). Remaining years were considered as intermediate years. Table A2 provides the diet matrix used in the models for lemming peak and crash years (for intermediate lemming years, the diet matrix is close to the one of lemming crash years). Table A3 presents the values of P and Q used in the models. For migratory species, we corrected Q for the proportion of time spent on Bylot Island. Table A4 presents the confidence intervals of the different parameters that were used in the sensitivity analyses based on Monte Carlo simulations. We present below the methods used to derive the values presented in Tables A1 to A4.

Plants

Aboveground biomass

We sampled aboveground live biomass annually in wetlands (polygon fens) between 1993 and 2009. Because geese but not lemmings (Bilodeau and Gauthier, unpublished data) used lemming exclosures during three consecutive years and found that lemmings had very limited impact on vascular plants and mosses) could remove a significant proportion of the biomass through grazing in this habitat (Gauthier et al. 2004), we sampled the vegetation in areas protected from geese (i.e., exclosures). Every year, 12 new exclosures were set up at just after snow melt in June. Exclosures were 1 × 1 m and were made of chicken wire 30 cm high (2.5 cm mesh). Plant biomass was sampled inside the exclosures at the end of the growing season in mid-August by removing, sorting, drying and weighing all vascular plants in a 20 × 20 cm plot (see Gauthier et al. 1995 for details). We also sampled aboveground live biomass in mesic tundra in 2007–2009 using the same general method as in wetlands. However, because both lemmings and geese could potentially remove biomass in this habitat, we excluded both groups by using exclosures made of welded wire (1.25 cm mesh) dug into the ground. Because plant communities are more diversified in this habitat and included many evergreen plants, we used larger plots (20 × 50 cm) and we sampled twice during the season, soon after snow-melt in June and at the end of the growing season in mid-August.

We extrapolated the annual plant production in mesic tundra for the whole period 1993–2009 based on the annual plant production measured in wetlands. We assumed that annual variations were similar in wetland and mesic tundra because abiotic factors such as temperature and precipitation are major determinants of plant production in the Arctic (Shaver and Chapin 1995, Gauthier et al. in press). The validity of this assumption was supported by the positive relationship found between NDVI (Normalized Difference Vegetation Index) measures at our study site and annual standing crop in wetlands (see below). During 2007–2009, average biomass in August was 50.5 g·m-2 ± 2.8 SE in wetlands and 44.2 g·m-2 ± 6.8 SE in mesic tundra. We back-calculated the biomass of vascular plants in mesic tundra from 1993 to 2006 using the average ratio in standing crop between mesic and wetland habitats measured in 2007–2009 and assuming that the proportion of the major groups (forbs, shrubs, and sedges/grasses) remained the same. Mosses cover 39% of the mesic tundra (average value calculated from Duclos (2002) who measured moss plant cover in 8 mesic plant communities on Bylot Island). Because relatively few vascular plants grow in mesic moss carpet (unlike in wetlands), the vascular plant biomass in mesic tundra was corrected (multiplied by 61%). We used the NDVI derived from Advanced Very High Resolution Radiometer (AVHRR) from the National Oceanic and Atmospheric Administration (NOAA) satellites (Brown et al. 2006). NDVI is considered a reliable, large scale index of vegetation production (Myneni et al. 1997). We used pre-processed 10-day maximum value composites from 1989 to 2009, at 1-km2 spatial resolution, made available by the Canada Centre for Remote Sensing (Pouliot et al. 2009a; http://ccrs.nrcan.gc.ca/index_e.php). From 5 selected areas of 8 km2 on the south plain of Bylot Island, we retained the annual maximum NDVI value at the end of July. We found a positive and significant relationship between annual standing crop measured in wetlands and maximum NDVI values (F1,17 = 5.72 ; P = 0.03 ; R2 = 0.22). With the exception of the high values measured in wetlands in 2000 and 2001, NDVI tracked fairly well standing crop of vascular plants measured on Bylot Island (Fig. A1).

For mosses, standing crop and primary production were estimated in only one year: in 2004 (Pouliot et al. 2009b) in wetlands and in 2009 in mesic tundra (Bilodeau and Gauthier, unpublished data). In wetlands, standing crop was measured by cutting, drying and weighing the green, live moss portion of 22.5 cm2 cores sampled in exclosures in mid-August. In mesic tundra, live moss portion was sampled on six 10 cm2 random plots in mid-August. The standing crop was 1881 g·m-2 ± 3 SE in wetlands and 292 ± 33 in mesic tundra. In wetlands, mosses cover about ~ 55 % of the ground (Massé 2002) and only 39% in mesic tundra (see above). Taking into account the proportion of the different habitats, moss biomass = 253.8 g·m-2 ± 1.20 at the landscape level.

Production/Biomass (P/B) ratio

For herbaceous plants (grasses and sedges), the P/B ratio was assumed to be equal to 1 because standing crop at the end of the growing season is a good measure of annual net primary production (Gauthier et al. 1995). For evergreen plants in mesic tundra, plant production was estimated by the difference in dry biomass between the end and the beginning of the season. P/B ratios were obtained by dividing primary production to the standing crop at the end of the season. P/B ratio = 0.68 ± 0.07 SE for shrubs and 0.82 ± 0.08 SE for forbs, respectively. These values are close to those reported by (Krebs et al. 2003). Pouliot et al. (2009b, 2010) estimated annual moss production in wetlands at 96.9 g·m-2 ± 10.0 by measuring elongation on individual moss shots using natural markers, which yielded a P/B ratio of 0.052. We used this value for mosses growing in both wetlands and mesic tundra.

Snow goose

Biomass

The reproduction of Greater Snow Geese has been monitored annually from 1993 to 2008 (Dickey et al. 2008). Nest density was based on the number of nests found in a small area (30 ha) located in the centre of the colony and thoroughly searched each year. In order to validate this nest density index at a broader scale, we compared the nest density to the number of snow geese estimated during an aerial survey of the whole south plain of Bylot Island conducted every five years (Reed et al. 2002). We found a strong positive relationship between density of adult geese during the survey and nest density (y = 0.0165x + 0.1114, R2 = 0.92, Fig. A2). Based on this relationship, we used our annual nest density index to assess annual goose density in the study area for adults. We transformed density in biomass using body mass measurements of geese taken annually in mid August (2752 g for adult males and 2405 g for adult females from Dickey et al. 2008).

Diet

Diet in wetland habitats is known from oesophagus analysis of adult geese collected during laying and incubation on Bylot Island (Gauthier 1993). For mesic tundra, we used the data from Audet et al. (2007) who determined the diet of goslings using direct observations. A study based on radio-marked geese estimated that geese spent 75% of their time in wetlands and 25% in mesic tundra at our study site (Hughes et al. 1994). We thus weighted the diet for time spent in each habitat. The diet used in the models is presented in Table A2.

P/B ratio

We calculated a P/B ratio empirically using reproduction, growth and recruitment data for each year. Production was calculated from hatching to fledging using the following equation:

P = (r·(1 - sc·b) + r ·s·c·(b + Σ(g·emt))(A.1)

where r is the proportion of females in the breeding population (0.5), s the nesting success (mean = 0.63 ± 0.06 SE, Gauthier et al. unpublished data), c the clutch size (mean = 3.7 ± 0.07 SE, Gauthier et al. unpublished data), b is egg mass (mean = 116.2 ± 0.2 g, Gauthier et al. unpublished data), g is daily growth rate of young (47.5 g·d-1, Lesage and Gauthier 1997), m is the daily exponential mortality rate (pre-fledging survival = 50% over the season; m = -0.017·d-1 Lepage et al. 2000), and t is the time needed to reach fledging mass (40 days, Lesage and Gauthier 1997). This production was divided by adult biomass. P/B ratio was calculated for each year (1993 to 2009, mean P/B = 0.93 ± 0.03 SE). Using the equation of Maurer (1998), the allometric P/B ratio was estimated at 0.29 for an adult with a body mass of 2571 g.

Consumption/Biomass (Q/B) ratio

We calculated a separate Q/B ratio for young and adults. Data on food intake and energy requirement were available at our study site for young only. Considering 18 hours of feeding per day (Gauthier and Tardif 1991), the mean Q/B ratio of young was estimated at 21.7 ± 10.9 SE based on the data of Piedboeuf and Gauthier (1999). The daily energy expenditure of adult geese has been estimated by Bedard and Gauthier (1989) at the spring staging areas. Considering a mean body mass of 2571 g and assuming that birds spend 100 days on Bylot Island annually, the Q/B of adults was estimated at 15.2. We thus used a mean empirical Q/B value of 18.5. Using the equation (Nagy 1987) to estimate intake rates in birds, we calculated the allometric Q/B ratio at 12.9 for an adult goose with an average body mass of 2571 g over 100 days.

Lemmings

Biomass

Lemming abundance was estimated annually on Bylot Island with snap traps from 1994 to 2009 and with live traps from 2004 to 2009 (see Gruyer et al. 2008, 2010 for methods). Snap-trap data only provide an index of abundance while live trapping allows calculation of an estimate of true densities using mark recapture analyses. We examined the relationships between abundance indices obtained from snap-traps and real abundance estimates obtained with live traps using data from 2004 to 2009 for each species and trapping grid (N = 24). We removed one outlier in the brown lemming for which snap-traps abundance estimates provided aberrant values (i.e., no lemmings in snap traps during a peak year due to record rainfall during the trapping period). We obtained a positive relationship for brown lemmings (F1,9 = 16.8, P = 0.003, R2 = 0.61; see Fig. A3) but not for the collared (F1,9 = 4.15, P = 0.07). Using this relationship, we reconstructed brown lemming density for the period 1994–2004. Although no lemmings were trapped in 1993, an estimate was derived based on a winter nest survey (see Gruyer 2007). The collared lemming is much less abundant than the brown on Bylot Island and it shows weak cycle of abundance (Gruyer et al. 2008), which may explain the lack of relationship between the two methods. However, using the snap-trap data, we found a significant relationship between collared and brown lemming indices (F1,14 = 8.92, P = 0.01, R2 = 0.39) suggesting that both species fluctuates in synchrony (see also Gruyer et al. 2008). We thus used the cycle of abundance of brown lemming cycle to set collared lemming abundance at 1, 0.5 and 0.1 lemmings·ha-1 during peak, intermediate and crash years respectively. Body mass was assessed from all animals trapped over the years (mean = 36.0g and 43.2g for brown and collared lemming, respectively).

Diet

We used data available from the literature to characterize the diet of each lemming species in the Canadian arctic (Batzli and Pitelka 1983, Rodgers and Lewis 1986, reviewed in Batzli 1993). Both references give similar diets and thus we averaged these estimates (Table A2).

P/B ratio

We calculated the percentage change in density from our live trapping grids in early June (shortly after snow-melt, thus before summer predation mortality) between 2007 (a year of intermediate abundance) and 2008 (a year of peak abundance). Mean empirical P/B = 8.45 and 7.33 for brown and collared lemming respectively. These values are close to those reported for small mammals by Ruesink et al. (2002) and for lemmings by Krebs et al. (2003). Using the equation of Banse and Mosher (1980) for mammals and our body mass values, the allometric P/B ratios were 3.4 and 3.1 for brown and collared lemmings respectively.

Q/B ratio

Although Klaassen et al. (2002) measured the basal metabolic rate (BMR) of lemmings in the Canadian Arctic for the brown and collared lemming, no field estimate of daily energy expenditure was available. Using the intake rate equation of Nagy (1987) for mammals, the allometric Q/B was 147.6 and 131.9 for the brown and collared lemming, respectively. Because Klaassen et al. (2002) found that the BMR was higher in brown than in collared lemming, we also modeled the Q/B ratio by increasing the Q/B of brown lemmings by 20% . While not directly measured on Bylot Island, we considered that an empirical value compared to the allometric one.

Arthropods

Biomass

Arthropods were sampled on Bylot Island throughout the summer from 2005 to 2009. Modified malaise/pitfall traps were used to capture surface-active and low-flying arthropods in both mesic and wetland habitats (5 traps per habitats; Picotin 2008 for details). All arthropods were identified at the family level, counted, measured, and converted to dry mass from known regressions between body mass and length (Rogers et al. 1977, Sage 1982, Sample et al. 1993, Hodar 1996). Arthropod standing crop was measured only in 2009 from 0.8 × 0.8 m emergence traps (Ryan 1977) deployed throughout the summer in both mesic and aquatic habitats. Traps were emptied every 6 to 10 days and individuals were treated as previously described. We compared density estimates from our emergence traps with the only known data for the Canadian Arctic, the study of Ryan (1977) on the north coast of Devon Island, 300 km to the north-west of Bylot Island. A significant, positive relationship was found between the abundance of individual family insects trapped on Bylot and Devon (Spearman rank correlation: R = 0.73; P = 0.011, see Fig. A4). Using the biomass of insects trapped in pitfall traps, we also found that the relative abundance of each family were correlated among years from 2005 to 2009 (Spearman rank correlations, all Rs > 0.54; all P < 0.001), indicating a similar community structure every year. Chironomidae and Muscidae dominated the arthropod community and Staphylinidae contributed marginally to the arthropod biomass.

While all the dominant families in pitfall traps (>8% of the total insect sampled) were also present in the emergence traps, we failed to obtain a significant relationship for biomass between our two sampling methods (F1,19 = 2.09; P = 0.17). Emergence and pitfall traps may not sample the same arthropods as larval stages are not monitored in emergence traps and more mobile species may be over-estimated in the pitfall traps. The two methods may thus capture different portions of the arthropod community. However, we are confident that pitfall traps were efficient to assess the peak of arthropod abundance and their phenology (Picotin 2008). Moreover, arthropod families known for being eaten by shorebirds were present in the pitfall traps (see below). We thus used the total biomass value (341.0 mg·m-2) found in emergence traps in 2009 as an overall minimum biomass available and used the average proportion of families sampled in pitfall traps each year (2005–2009) to calculate the biomass of each above ground arthropod family. We used the same value every year. In comparison, the arthropod biomass sampled also using emergence traps was 300 mg·m-2 in Alaska and 54.1 mg·m-2 in Devon Island (Bliss et al. 1973, Ryan 1977). However, emergence traps do not sample soil fauna (mainly detritivorous species such as Collembolla and nematods; Danks 1981). Ryan (1977) estimated a soil fauna of arthropods at 852 mg·m-2 for Devon Island. We summed this estimate of soil fauna to the above ground fauna biomass (see above) to obtain a total annual density of 1.193 mg·m-2.

Diet

We reviewed the literature available for the diet of arctic arthropods (Addison 1977, Ryan 1977, Whitfield 1977, Danks 1981, Gill and Peterson 1987, Wirth et al. 1987, Borror et al. 1989). Diet can radically change between the developmental stages (e.g., larvae can be carnivorous and imago herbivorous). We arbitrarily weighed equally (50/50) the time spent in either larvae or imago forms for each family. Based on the available information in the literature, we attributed the most likely diet for each arthropod family. Diet was constituted either of detritus (detritivorous arthropods), plants (for most herbivorous families, the proportion of mosses, sedges/grasses, shrubs or forbs was usually provided) or other arthropods (carnivorous arthropods) in various proportion. We weighed each family according to their proportion measured in pitfall traps from 2005–2009 to estimate an overall diet for arthropods. For families sampled in traps, this leads to an overall diet of 12% of plants (mainly shrubs, Danks 1981), 31% of detrititus and 57% of arthropods. However, when taking into account the soil fauna (mainly detritivorous species), the diet matrix was composed of 80% of detritus, 16% of arthropods, and 4% of plants.

P/B ratio

No empirical data of annual arthropod production was available on Bylot Island. We did not use allometric relationships to infer the P/B ratio of arthropods (mainly insects) because these are not accurate (Banse and Mosher 1980). In their review, Banse and Mosher (1980) provided a mean value of P/B value = 2.45 ± 0.31 SE for non aquatic insects. We thus used this value as a constant in our models.

Q/B ratio

Respiration of insects has been experimentally measured on Devon Island (Procter 1977) and regressions relating O2 consumption and dried body mass of insects were available. Relations changed with temperature and Procter (1977) provided three different regression for 2, 7, and 12 °C. The mean summer temperature on Bylot Island from 2005 to 2007 was 5.7 °C. We thus used the 7 °C regression to infer the Q/B based on the dry biomass. The equation was: logR = log(-0.1143) + 0.9343 logW where R is the respiration expressed in µl O2 mg-1 hr-1 and W the dry mass expressed in mg. Following this equation, we calculated the Q/B for each family for which we had a mean biomass per individual in 2008. The number of days without frost on Bylot Island is 100 days ± 2.5 SE (mean from average air temperature recorded at automated weather stations from 1994 to 2007). We assumed that arthropods consumption occurred during 100 days, yielding a mean Q/B of 9.8 ± 0.2 SE (N = 32).

Shorebirds and Passerines

Biomass

From 2005 to 2009, an intensive nest survey of all shorebirds and of the Lapland Longspur (by far the most abundant passerine) has been carried out over an 800-ha area. The number of nests·km-2 found within the search area was considered an index of density. The mean nest density of shorebirds was 4.0 nests·km-2 ± 1.3 SE (2005–2008). Although highly variable between years, these densities were comparable to a previous survey carried out on Bylot Island in 1977 (Kempf et al. 1978). We used our mean nest density estimate for all years of our model. Densities were transformed in biomass by using mean body mass of individual species weighed for their relative abundance. Body mass came from the literature (Parmelee et al. 1967, Paulson 1995, Johnson and Connors 1996, Moskoff and Montgomerie 2002, Tracy et al. 2002).

The annual nest density of Lapland Longspur ranged from 10.1 to 13.4 nests per km2 and we thus assumed a constant nest density across years (12.3 nests per km2). Because a few other passerine species also occur on Bylot Island (Table 1), we inflated by 10% the Lapland Longspur density. Densities were transformed in biomass by using body mass measurements of individual longspurs captured on Bylot Island (mean body mass = 29.2g).

Diet

We reviewed the literature to assess the summer diet of shorebirds and Lapland Longspurs from several arctic sites across North America (Parmelee et al. 1967, Holmes and Pitelka 1968, Baker 1977, Parmelee 1992, Paulson 1995, Johnson and Connors 1996, Tracy et al. 2002). Shorebirds feed exclusively on arthropods whereas longspurs feed predominantly on them but also consume a small proportion of seeds from shrubs and grasses (estimated at 20% of their diet; Table A2).

P/B ratio

Production of shorebirds was calculated using the same procedure as in Snow Geese (Eq A.1) because both are precocial birds. Parameters for the equation came from White-rumped and Baird Sandpipers, the most abundant shorebird species on Bylot Island, which were studied from 2005 to 2009. Values were: r = 0.5, s = 0.48 ± 0.11, n = 4, b = 9.1 ± 0.04 (mean for the two species), g = 1.27 g·d-1 ± 0.11 and 1.41 g·d-1 ± 0.10, m = -0.033 and -0.043, and t = 30 and 24 days for White-rumped and Baird Sandpipers, respectively (McKinnon 2011, unpublished data). This production was divided by adult biomass. Overall, empirical P/B = 0.59 but this value varied according to years and was greater in lemming peak years (2008, P/B = 0.78) than in other years (P/B = 0.53 ± 0.08). We thus applied these two values for lemming peak years and all other years, respectively.

For Lapland Longspur, an altricial species, we calculated production by modifying Eq. A.1 as follows:

P = (r·(1 - sc·b) + (r·s·c·h·M)(A.2)

Parameters were the same as in Eq. A.1 except for h, the survival of chicks from hatching to fledging, and M, body mass at fledging. Parameter values were estimated from a long-term monitoring of Lapland Longspur on Bylot Island, except for h. Values were: r = 0.5, c = 5.4 ± 0.09 SE, and s = 0.49 ± 0.05 (Gauthier et al. unpublished data). Cluster and Pitelka (1977) provided similar demographic estimates for this species in Alaska including for h. Their raw estimate of s was comparable to Bylot (0.52 ± 0.07) but they were able to correct it for renesting (corrected s = 0.62 ± 0.06), and they estimated h = 0.71 ± 0.06. We thus used the latter two parameter values in Eq. A.2. Breeding monitoring of Lapland Longspurs was carried out from 1995 to 2009. We used year specific values of P/B except for 1993 and 1994 where mean P/B was used (mean empirical P/B = 1.42 ± 0.09). Using the equation of Maurer (1998), the allometric P/B was estimated at 0.66 for shorebirds (average body mass of 95 g) and 0.90 for Lapland Longspurs (average body mass of 29 g).

Q/B ratio

Using the daily energy expenditure equation of Piersma et al. (2003) determined in the field, we obtained an empirical Q/B of 53.7 for shorebirds assuming a 70 days stay on the island. Daily energy expenditure of Lapland Longspurs was also measured empirically in the field by Custer et al. (1986). Again assuming a 100-day stay on Bylot Island, we estimated Q/B at 103.1. Using the equation of Nagy (1987) to estimate intake rate in birds, we estimated the allometric Q/B at 20.5 for shorebirds and 72.8 for passerines.

Weasel

Biomass

Estimates of weasel density are difficult to obtain, especially in the Arctic, and we used those given in the literature because none were available for Bylot Island. Estimated densities ranged from 0.02–2 individuals·km-2 in the literature (Hanski et al. 1991, Oksanen et al. 1999). Based on observations made on Bylot Island (F. Bilodeau et al. unpublished data) and elsewhere (Gilg et al. 2003), weasels respond to lemming density and are more abundant in a lemming peak year than in a low lemming year. Radio-tracking of a weasel family in a lemming peak year revealed a home range of 5 km2 on Bylot (Bilodeau and Gauthier unpublished data). We therefore used densities of 0.4 ind.·km-2 during peak years, intermediate densities after a peak year (0.1 ind.·km2) and low densities (0.02 ind.·km-2) in other years.

Diet

King and Powell (2007) reviewed the diet of weasels worldwide. Only three studies investigated their diet in the tundra (Canada: Simms 1978 and Greenland:, Sittler 1995, Gilg et al. 2003). The diet reported by Simms (1978) was determined during a low lemming year and was composed at 75% of collared lemmings and only 6% of brown even though the latter species was reported to be more abundant than the former one at the study site. Birds (18%) and insects (1%) completed the diet. In Greenland (Sittler 1995), collared lemmings are the only lemming species present and they constituted the exclusive prey (100%) during high lemming years and the predominant prey (90%) during other years, with birds accounting for the remaining 10%.

In a year of peak in lemming abundance, we considered the weasel diet to be composed exclusively of lemmings and, because the brown is much more abundant than the collared in those years on Bylot Island, we set the proportion of each species in the diet equal to the proportion measured during trapping sessions (i.e., no selection). We used the diet provided by Simms (1978) for all the other years.

P/B ratio

No empirical data of annual weasel production was available on Bylot Island. We thus solely derived the P/B value allometrically from the equation of Banse and Mosher (1980) for mammals. In 2009 and 2010, 6 males (mean mass = 170 g) and 2 females (mean mass = 98.5 g) were trapped on Bylot Island. Considering an average mass of 134 g, P/B = 2.15.

Q/B ratio

We used the equation of Nagy et al. (1987) for mammals to estimate intake rate of a 134 g weasel (40 g·day-1), which yielded an allometric Q/B of 108.7. However, we corrected this value to account for the additional energy expanded by females raising young during 10–12 weeks (King and Powell 2007). This was done by adding to Q/B the term. The corrected allometric Q/B (131.7) was used only during lemming peak years because no young were seen outside those years (Gauthier and Bilodeau unpublished data).

Arctic Fox

Density

Since 1996, arctic fox dens have been mapped during intensive ground surveys and are monitored annually for reproductive activity. The area monitored increased from about 100 km2 initially to 520 km2 in 2006 (Szor et al. 2008). The number of breeding dens per km2 provides an estimate of the number of breeding adults. However, non-breeding adults are also present. Because a large number of individuals have been marked since 2003, the proportion of reproductive individuals among marked adults can be estimated from subsequent re-sightings and behavioural observations (Tarroux 2011). Trapping and re-sighting efforts were fairly constant from 2006 to 2009 and the number of adults trapped annually was similar during these years (mean = 22.5 ± 2.3 SE) and not affected by the lemming phase. However, the proportion of reproductive individuals among marked adults varied among years and was related to the phase of the lemming cycle (Tarroux 2011). We found a strong negative relationship (F1,6 = 26.5, P = 0.004, R2 = 0.81) between the proportion of dens used and the proportion of non reproductive foxes among marked individuals (Fig. A5). This indicates that a large number of individuals remain in the study area as non-breeders during years of low lemming abundance. We thus assumed that 100% of the local fox population bred during lemming peak years and used the density of breeding adults recorded at dens in those years (mean from 2004 and 2008 = 0.08 individuals per km2) as the density of foxes in the study area. This value is comparable to other studies as Angerbjörn et al. (1999) reported densities of breeding foxes ranging from 0.02 to 0.29 foxes per km2 along the Siberian arctic coast (mean = 0.12 breeding foxes per km2). Densities were converted in biomass assuming a mean body mass of 3.3 kg. The red fox (Vulpes vulpes) is rare and only accidentally sighted on Bylot Island, and was thus not considered.

Diet

Diet of arctic foxes on Bylot Island was assessed using carbon and nitrogen stable isotope analysis of blood samples from 2003 to 2009 (Tarroux et al. 2010). Main potential food sources are lemmings, seals (along the coast or on the sea ice), geese and bird eggs (goose, passerines, and shorebirds). The estimated proportions of seal and bird eggs in the diet were not affected by the lemming phase and thus we used values averaged across years. We assumed that eggs of different bird species were consumed according to their availability (see density estimates above). Thus goose eggs accounted for 18.5% of the fox diet, passerines 1% and shorebirds 0.5%. Consumption of geese and lemmings varied according to lemming phase (see Table A2a and b). Because we could not separate lemming species with the isotopic analysis, we assumed no selection on lemming species and thus proportion of each species in the diet varied according to the proportion measured during trapping sessions. Our diet was established from samples collected in spring and summer but in winter marine resources may be very important as foxes move to the sea ice (Roth 2002). Based on radio-tracking data (Tarroux et al. 2010a, unpublished data) we estimated that foxes were present on the island 8 months per year. We thus did not consider the 4-month period in winter when foxes were away from the island, feeding predominantly on seals.

P/B ratio

Production (in terms of biomass of weaned cubs per year) was calculated using the following equation:

P = r·f·n·M(A.3)

where f is the proportion of females breeding, n is the litter size of weaned cubs, M is body mass of weaned cubs and r as in Eq. A.1. The average minimum litter size was available from 1996 to 2009 and the proportion of females breeding from 2003 to 2009. We estimated that f = 0.39, 0.67, and 1.0 and n = 2, 4.9, and 5.9 depending on the lemming phase (crash, intermediate or peak, respectively) and r = 0.5 (which corresponds to the actual sex ratios based on trapping data from 2003 to 2009). P/B varied annually with a mean empirical P/B = 1.50 ± 0.25 (range: 0.10–3.50). Using the equation of Banse and Mosher (1980) for mammals, we estimated the allometric P/B ratio at 0.76 based on a body mass of 3.3 kg.

Q/B ratio

Daily food intake values from arctic foxes maintained in outdoor captivity were available from Fuglei and Øritsland (1999). Food intake varied depending of the period of the year (larger in summer than in winter; Fuglei and Øritsland 1999). We used a mean value of food intake to calculate an empirical Q/B assuming that animals were on the island for 8 months (mean Q/B = 46.4; winter Q/B = 37.6; summer Q/B = 56.4). Considering that weaning occurs at ~8 weeks after birth (Tannerfeldt and Angerbjörn 1998), we corrected Q/B according to the young produced annually to account for this extra cost. We thus added to Q/B the term Q/B·(8/35)·P/B. Mean corrected Q/B was 62.3 ± 2.7 year-1 (range: 47.4–83.4). We used the equation of Nagy et al. (1987) for mammals to estimate intake rate of a 3.3 kg fox (555 g·day-1), which yielded an allometric Q/B of 42.1.

Avian predators

Density

Nests of avian predators were systematically searched annually. Snowy Owl nests were recorded from 1993 to 2009, Long-tailed Jaeger and Glaucous Gull from 2004 to 2009, Rough-legged Hawk from 2007 to 2009 and Peregrine Falcon and Parasitic Jaeger in 2008 and 2009. Because nest detection rate is typically high for avian predators in the tundra, we assumed that the number of nests found was a reliable index of abundance and thus 2 times the number of nests divided by the size of the area searched (100 km2) every year yielded avian predator density.

The density of Snowy Owl, Long-tailed Jaeger and Rough-legged Hawk varied considerably with the phase of the lemming cycle (J. F. Therrien et al. unpublished data; Gilg et al. 2006). In years where data was lacking, we used the 2008 nest density as the reference value for lemming peak years, 2005 and 2007 for intermediate years and 2006 and 2009 for crash years. Nest density per km2 ranged from 0 to 0.11 in Snowy Owls, 0 to 0.92 in Long-tailed Jaeger, and 0.01 to 0.06 in Rough-legged Hawk. This contrast with glaucous gull nest density, which remained fairly constant across years (mean = 0.16 nests·km-2 ± 0.004 SE). Parasitic Jaeger and Peregrine Falcon nests densities were low but identical in 2008 and 2009 (0.02 and 0.01 nests per km2 respectively) and we thus considered them constant in all years.

Densities were converted in biomass using body mass data obtained during capture of individuals on Bylot Island for Snowy Owls, Long-tailed Jaegers, and Glaucous Gulls (mean mass = 2169, 298, and 1110 g, respectively) and completed from the literature (Court et al. 1988, Kerlinger and Lein 1988, Haven and Lee 1999, Bechard and Swem 2002).

Diet

The diet of avian predators was intensively studied primarily through the systematic collection and analysis of regurgitation pellets during the period of 2007–2009 (since 2004 for owls) following the method of Lewis (2004). For several species (especially owls and gulls), we complemented diet information with prey delivery data of adults feeding young obtained from direct observations or automated cameras deployed at nests. We averaged the diet based on data collected across years. We converted the occurrence of prey items found in pellets to biomass from known mean mass (for different size classes) of the prey. When the distinction between brown and collared lemming was not possible (unidentified lemming proportion was 37% and 75% in the Long-tailed and Parasitic Jaegers, respectively; 0% for the other birds of prey), proportions of lemming species in the diet followed the densities of each lemming species estimated during trapping sessions. Long-tailed Jaegers are known to consume arthropods (Haven and Lee 1999; Therrien personal observation) but these soft-bodied animals are rarely encountered in pellets. We thus used carbon and nitrogen stable isotope analyses of blood samples to assess the proportion of arthropod in the diet (J. F. Therrien et al. in preparation). We used the same method as for foxes and we assessed the diet for each individual using five sources (marine fishes, birds, arthropods, brown and collared lemmings). Mean contribution of arthropods in the diet of Long-tailed Jaegers was 26.3% ± 1.4 (SE) in 2008 (a lemming peak year). We therefore adjusted our diet matrix for this proportion of arthropods assuming no annual variation (see Table A2). For the Peregrine Falcon and Parasitic Jaeger, the two species of avian predators with the lowest abundance, diet was extracted from the literature (Court et al. 1988, Haven and Lee 1999).

P/B ratio

Production (in terms of biomass of fledged year-1) was estimated using the following equation:

P = r·n·s·M(A.4)

where n is here the mean number of fledglings in successful nests, M the body mass of fledglings and s and r are as in Eq. A.1. We estimated allometric P/B values from the equation of Maurer (1998) for birds using mean body mass data measured from adults captured on Bylot Island or from the literature (see above). Table A3 provides both empirical and allometric P/B values used for each species.

Q/B ratio

Based on behavioral observations of prey delivery rate at nests (see above), we were able to calculate food requirements of nesting Snowy Owls, Rough-legged Hawks, Glaucous Gulls, and Long-tailed Jaegers. When converting the number of prey consumed in biomass, we took into account that each predator species selects lemmings of different body mass (J. F. Therrien et al. in preparation). When calculating empirical Q/B values, we also accounted for the time spent by each species on Bylot Island, which was determined by field observations or satellite-tracking for Snowy Owls (time spent was 70 days for parasitic and Long-tailed Jaegers and 100 days for the other avian predator species). We used the equation of Nagy (1987) for birds to estimate intake rates of adults of average body mass for each species (see above). Empirical values could not be derived for Parasitic Jaegers and Peregrine Falcons, hence allometric values were used. Table A3 provides both empirical and allometric Q/B values used for each species. The empirical value for Long-tailed Jaegers is considerably higher than the one predicted by allometric equations. We believe that this is caused by a much higher killing rate for lemmings that expected based solely on energetic requirements. Unlike raptors, their small body size does not allow them to swallow lemmings whole most of the time. Thus, they have to eviscerate them, which often results in considerable amount of wasted food (Andersson 1971). This could explain why our observations revealed a higher prey capture rate in Long-tailed Jaegers than in other avian predators.

Table A1. Annual biomass (in dry kg·km-2) recorded on Bylot Island and used in the EwE models for the different functional groups (detailed in Table 1). Each year is also categorized based on lemming abundance (i.e., peak, intermediate, or crash).

Functional
group
1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Peak Int. Crash Peak Int. Int. Crash Peak Int. Crash Crash Peak Int. Crash Int. Peak Crash
Mosses 253788 253788 253788 253788 253788 253788 253788 253788 253788 253788 253788 253788 253788 253788 253788 253788 253788
Forbs 599 392 478 496 686 945 1324 1566 1348 914 1077 788 1148 1468 968 986 360
Shrubs 10252 6446 8175 8492 11743 15286 14923 21683 20382 15629 13441 12929 17089 17955 13281 15457 16405
Sedges/
Grasses
10216 6408 8146 8462 11702 15181 14420 21308 20154 15574 13103 12851 16880 17473 17791 14229 12597
Snow
Goose
27.4 10.8 13.1 10.7 14.5 17.9 11.1 13.5 12.9 16.0 22.0 10.6 14.0 12.4 13.5 14.4 14.7
Brown
lemming
10.40 0.36 0.10 2.22 0.71 1.09 0.12 3.64 1.35 0.29 0.10 8.67 0.10 0.10 0.15 1.95 0.10
Collared
lemming
1.32 0.15 0.17 1.28 0.19 0.52 0.16 1.30 0.18 0.17 0.17 0.82 0.57 0.28 0.97 0.58 0.25
Arthropods 1193 1193 1193 1193 1193 1193 1193 1193 1193 1193 1193 1193 1193 1193 1193 1193 1193
Shorebirds 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.21 0.23 0.09 0.07 0.15
Passerines 0.23 0.23 0.24 0.23 0.23 0.22 0.23 0.23 0.23 0.25 0.23 0.23 0.22 0.24 0.23 0.23 0.23
Weasel 0.09 0.01 0.001 0.09 0.01 0.001 0.001 0.09 0.01 0.001 0.001 0.09 0.01 0.001 0.01 0.09 0.001
Arctic
fox
0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08
Snowy
Owl
0.38 0.00 0.00 0.08 0.00 0.000 0.000 0.13 0.00 0.00 0.00 0.14 0.00 0.00 0.013 0.089 0.00
Rough-
legged
Hawk
0.04 0.01 0.006 0.04 0.002 0.01 0.006 0.04 0.01 0.006 0.006 0.04 0.01 0.006 0.02 0.04 0.006
Glaucous
Gull
0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.10 0.11 0.12 0.11
Long-
tailed
Jaeger
0.17 0.11 0.03 0.17 0.03 0.11 0.03 0.17 0.11 0.03 0.03 0.17 0.10 0.05 0.11 0.18 0.00
Parasitic Jaeger 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007
Peregrine
falcon
0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005


Table A2. Diet matrix (proportion of the diet based on biomass) of each functional group used in the EwE models for lemming peak (A) and crash (B) years. For intermediate lemming years, the diet matrix is close to the one of lemming crash years. Values are from local data and the literature (see text for details).

(A) Group 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1 Mosses 0.01 0.11 0.03
2 Forbs 0.08 0.02 0.01 0.10
3 Shrubs 0.18 0.01 0.86 0.04 0.10
4 Sedges/Grasses 0.73 0.87 0.10
5 Snow Goose 0.19 0.15 0.59 0.08 0.49 0.10
6 Brown lemming 0.80 0.47 0.38 0.54 0.10 0.43 0.20 0.20
7 Collared lemming 0.20 0.10 0.45 0.31 0.20 0.22 0.20 0.10
8 Arthropods 0.16 1.00 0.80 0.008 0.26
9 Shorebirds 0.01 0.001 0.001 0.03 0.30
10 Passerines 0.01 0.002 0.06 0.001 0.01 0.07 0.30
11 Weasel 0.003 0.09
12 Arctic fox 0.004
13 Snowy Owl
14 Rough-legged Hawk
15 Glaucous Gull 0.01 0.005
16 Long-tailed Jaeger
17 Parasitic Jaeger
18 Peregrine Falcon
19 Detritus 0.80 0.22 0.100

(B) Group 5 6 7 8 9 10 11 12 13 14 15 16 17
1 Mosses 0.01 0.11 0.03
2 Forbs 0.08 0.02 0.01 0.10
3 Shrubs 0.18 0.01 0.86 0.04 0.10
4 Sedges/Grasses 0.73 0.87 0.10
5 Snow Goose 0.36 0.88 0.08 0.49 0.10
6 Brown lemming 0.07 0.15 0.57 0.02 0.42 0.20 0.20
7 Collared lemming 0.87 0.22 0.34 0.09 0.22 0.20 0.10
8 Arthropods 0.16 1.00 0.80 0.003 0.26
9 Shorebirds 0.003 0.03 0.30
10 Passerines 0.06 0.007 0.09 0.02 0.08 0.30
11 Weasel
12 Arctic fox
13 Rough-legged Hawk
14 Glaucous Gull
15 Long-tailed Jaeger
16 Parasitic Jaeger
17 Peregrine Falcon
18 Detritus 0.80 0.260 0.003


Table A3. Values of P/B and Q/B parameters used in the EwE models (P = annual production, B = standing biomass, Q = annual consumption). Unless mentioned otherwise, empirical values were derived from studies conducted on Bylot Island. Empirical P/B calculations incorporated the production of growing offspring, some of which will eventually die after fledging or weaning. This explains why empirical P/B ratios are often larger than allometric ones, which calculated production over a full year. Several empirical Q/B ratios are also larger than allometric ones because we took into account the extra consumption due to food provisioned to young.

# Functional
group
Allometric
P/B
Empirical
P/B
Allometric
Q/B
Empirical
Q/B
1 Mosses 0.02 a 0.05
2 Forbs 0.74 a 0.82
3 Shrubs 0.63 a 0.68
4 Sedges/Grasses 0.81 a 1.00
5 Snow Goose 0.29 b 0.93 12.8 d 18.5
6 Brown lemming 3.40 c 8.45 147.6 d 177.1 f
7 Collared lemming 3.10 c 7.33 131.9 d --
8 Arthropods 2.45 c -- 9.8 e --
9 Shorebirds 0.66 b 0.59 20.5 d 53.7 g
10 Passerines 0.90 b 1.42 72.8 d 103.1h
11 Weasels 2.15 c -- 108.6 d --
12 Arctic Fox 0.76 c 1.50 42.1 d 62.3 i
13 Snowy Owl 0.31 b 1.38 13.8 d 15.6
14 Rough-legged Hawk 0.37 b 2.60 16.5 d 24.5
15 Glaucous Gull 0.36 b 0.58 15.9 d 15.2
16 Long-tailed Jaeger 0.50 b 1.39 15.5 d 63.8
17 Parasitic Jaeger 0.45 b 1.00 19.8 d --
18 Peregrine Falcon 0.40 b 2.00 17.5 d --

aKrebs et al. 2003 bMaurer 1998 cBanse and Mosher 1980 d Nagy 1987 eProcter 1977 fKlaassen et al. 2003 gPiersma et al. 2003 hCuster et al. 1986 iFuglei and Øritsland 1999.


Table A4. One side 95% confidence interval (expressed in percentage of the mean value) of the different parameters used in the sensitivity analysis of the models. Confidence interval was calculated from the variance associated with field data. When no error was estimable, the 20% default value recommended by Ecoranger was used. This was the case for birds of prey as the census for the number of nests within the study area is exhaustive, without any estimate of detection probability.

# Functional
group
B
(%)
P/B
(%)
Q/B
(%)
1 Mosses 10 20 b
2 Forbs 69 19
3 Shrubs 22 20
4 Sedges/Grasses 28 20 b
5 Snow Goose 9 6 b 58
6 Brown lemming 69 31 20 b
7 Collared lemming 101 36 20 b
8 Arthropods 100 a 26 4
9 Shorebirds 52 17 20 b
10 Passerines 62 17 20 b
11 Weasel 100 a 17 20 b
12 Arctic Fox 100 a 33 20 b
13 Snowy Owl 20 b 20 b 20 b
14 Rough-legged Hawk 20 b 20 b 20 b
15 Glaucous Gull 20 b 20 b 20 b
16 Long-tailed Jaeger 20 b 20 b 20 b
17 Parasitic Jaeger 20 b 20 b 20 b
18 Peregrine Falcon 20 b 20 b 20 b

aSet arbitrarly brecommended by the software


Fig. A1. Vascular plant standing crop measured in mid-August in wetland plots protected from goose grazing and maximum NDVI values (open dots) from 1990 to 2007 in the south plain of Bylot Island. The positive relationship between standing crop and NDVI is also provided.


Fig. A2. Relationship between adult density recorded in the study area (520 km2) from aerial survey performed every five years (from Reed et al. 2002, and J. Lefebvre and A. Reed, unpublished data) and snow goose nest density recorded at the main colony (data from Dickey et al. 2008).


Fig. A3. Relationship between lemming density estimated by mark–recapture from live trapping and lemming abundance index measured with snap traps on Bylot Island from 2004 to 2009 in mesic and wet habitats. The solid line represents the significant relationship in the brown lemming only.


Fig. A4. Relationship between arthropod density (g·m-2) measured on Bylot Island (present study, see details in text; E. Bolduc et al. unpublished data) and on Devon Island (Ryan 1977) for common arthropod families (N = 11). Some family names are indicated.


Fig. A5. Relationship between the annual proportion of dens used by arctic foxes and the proportion of non-reproductive arctic foxes among a sample of marked individuals on Bylot Island.


Literature Cited

Addison, J. A. 1977. Population dynamics and biology of Collembola on Truelove Lowland. Pages 363–3382 in L. C. Bliss, editor. Truelove Lowland, Devan Island, Canada. The University of Alberta Press, Edmonton, Alberta, Canada.

Andersson, M. 1971. Breeding behaviour of the Long-tailed Skua Stercorarius longicaudus (Vieillot). Ornis Scandinavica 2:35–54.

Angerbjörn, A., M. Tannerfeldt, and S. Erlinge. 1999. Predator-prey relationships: arctic foxes and lemmings. Journal of Animal Ecology 68:34–49.

Audet, B., G. Gauthier, and E. Levesque. 2007. Feeding ecology of greater snow goose goslings in mesic tundra on Bylot Island, Nunavut, Canada. Condor 109:361–376.

Baker, M. C. 1977. Shorebird food habits in the eastern Canadian Arctic. Condor 79:56–62.

Banse, K. and S. Mosher. 1980. Adult body mass and annual production/biomass relationships of field populations. Ecological Monographs 50:355–379.

Batzli, G. O. 1993. Food selection by lemmings. Pages 281–301 in N. C. Stenseth and R. A. Ims, editors. The biology of lemmings. Academic Press, San Diego, California, USA.

Batzli, G. O. and F. A. Pitelka. 1983. Nutritional ecology of microtine rodents - Food-habits of lemmings near Barrow, Alaska. Journal of Mammalogy 64:648–655.

Bechard, M. J. and T. R. Swem. 2002. Rough-legged Hawk (Buteo lagopus). In A. Poole, editor. The Birds of North America Online. Cornell Lab of Ornithology, Ithaca, New York, USA.

Bedard, J. and G. Gauthier. 1989. Comparative energy budgets of Greater Snow Geese Chen caerulescens atlantica staging in 2 habitats in spring. Ardea 77:3–20.

Bêty, J., G. Gauthier, E. Korpimaki, and J. F. Giroux. 2002. Shared predators and indirect trophic interactions: lemming cycles and arctic-nesting geese. Journal of Animal Ecology 71:88–98.

Bliss, L. C., G. M. Courtin, D. L. Pattie, R. R. Riewe, D. W. A. Whitfield, and P. Widden. 1973. Arctic tundra ecosystems. Annual Review of Ecology and Systematics 4:359–399.

Borror, D. J., C. A. Triplehorn, and N. F. Johnson. 1989. An introduction to the study of Insects. Saunders College Publishing, Philadelphia, Pennsylvania, USA.

Brown, M. E., J. E. Pinzon, K. Didan, J. T. Morisette, and C. J. Tucker. 2006. Evaluation of the consistency of long-term NDVI time series derived from AVHRR, SPOT-Vegetation, SeaWiFS, MODIS, and Landsat ETM+ sensors. Ieee Transactions on Geoscience and Remote Sensing 44:1787–1793.

Court, G. S., C. G. Gates, and D. A. Boag. 1988. Natural history of the Peregrine Falcon in the Keewatin district of the Northwest Territories. Arctic 41:17–30.

Custer, T. W., R. G. Osborn, F. A. Pitelka, and J. A. Gessaman. 1986. Energy budget and prey requirements of breeding lapland longspurs near Barrow, Alaska, U.S.A. Arctic and Alpine Research 18:415–427.

Custer, T. W. and F. A. Pitelka. 1977. Demographic features of a Lapland longspur population near Barrow, Alaska. Auk 94:505–525.

Danks, H. V. 1981. Arctic Arthropods, a review of systematics and ecology with particular reference to the North American fauna. Entomological Society of Canada, Ottawa, Canada.

Dickey, M. H., G. Gauthier, and M. C. Cadieux. 2008. Climatic effects on the breeding phenology and reproductive success of an arctic-nesting goose species. Global Change Biology 14:1973–1985.

Fuglei, E. and N. A. Øritsland. 1999. Seasonal trends in body mass, food intake and resting metabolic rate, and induction of metabolic depression in arctic foxes (Alopex lagopus) at Svalbard. Journal of Comparative Physiology B-Biochemical Systemic and Environmental Physiology 169:361–369.

Gauthier, G. 1993. Feeding Ecology of Nesting Greater Snow Geese. Journal of Wildlife Management 57:216–223.

Gauthier, G., J. Bêty, J. F. Giroux, and L. Rochefort. 2004. Trophic interactions in a high arctic snow goose colony. Integrative and Comparative Biology 44:119–129.

Gauthier, G., R. J. Hughes, A. Reed, J. Beaulieu, and L. Rochefort. 1995. Effect of grazing by greater snow geese on the production of graminoids at an Arctic site (Bylot Island, Nwt, Canada). Journal of Ecology 83:653–664.

Gauthier, G. and J. Tardif. 1991. Female feeding and male vigilance during nesting in greater snow geese. Condor 93:701–711.

Gilg, O., I. Hanski, and B. Sittler. 2003. Cyclic dynamics in a simple vertebrate predator-prey community. Science 302:866–868.

Gill, G. D. and B. V. Peterson. 1987. Heleomyzidae. Pages 973–980 in J. F. McAlpine, B. V. Peterson, G. E. Shewell, H. J. Teskey, J. R. Vockeroth, and D. M. Wood, editors. Manual of Nearctic Diptera. Agriculture Canada, Ottawa, Canada.

Gruyer, N. 2007. Étude comparative de la démographie de deux espèces de lemmings (Lemmus sibericus et Dicrostonyx groenlandicus) à l'île Bylot, Nunavut, Canada. MsC. Laval, Québec, Canada.

Gruyer, N., G. Gauthier, and D. Berteaux. 2008. Cyclic dynamics of sympatric lemming populations on Bylot Island, Nunavut, Canada. Canadian Journal of Zoology 86:910–917.

Gruyer, N., G. Gauthier, and D. Berteaux. 2010. Demography of two lemming species on Bylot Island, Nunavut, Canada. Polar Biology 33:725–736.

Hanski, I., L. Hansson, and H. Henttonen. 1991. Specialist predators, generalist predators, and the microtine rodent cycle. Journal of Animal Ecology 60:353–367.

Haven, W. R. and S. Lee. 1999. Parasitic Jaeger (Stercorarius parasiticus).in A. Poole, editor. The Birds of North America Online. Cornell Lab of Ornithology, Ithaca, New York, USA.

Hodar, J. A. 1996. The use of regression equations for estimation of arthropod biomass in ecological studies. Acta Oecologica 17:421–433.

Holmes, R. T. and F. A. Pitelka. 1968. Food overlap among coexisting sandpipers on Northern Alaskan tundra. Systematic Zoology 17:305–318.

Hughes, R. J., A. Reed, and G. Gauthier. 1994. Space and Habitat Use by Greater Snow Goose Broods on Bylot Island, Northwest-Territories. Journal of Wildlife Management 58:536–545.

Johnson, O. W. and P. G. Connors. 1996. American Golden-Plover (Pluvialis dominica). In A. Poole, editor. The Birds of North America Online. Cornell Lab of Ornithology, Ithaca, New York, USA.

Kempf, C., X. Harmel, B. Sittler, and A. Piantanida. 1978. Notes géomorphologiques, ornithologiques et mammalogiques sur l'île Bylot et la région de Pond Inlet - Canada. Rapport d'expédition. Groupe de recherche en écologie arctique, Schiltigheim.

Kerlinger, P. and M. R. Lein. 1988. Causes of mortality, fat condition, and weights of wintering Snowy Owls. Journal of Field Ornithology 59:7–12.

King, C. M. and R. A. Powell. 2007. The natural history of weasels and stoats: ecology, behavior, and management. Second edition. Oxford University Press, New York, New York, USA.

Klaassen, M., J. Agrell, and A. Lindstrom. 2002. Metabolic rate and thermal conductance of lemmings from high-arctic Canada and Siberia. Journal of Comparative Physiology B-Biochemical Systemic and Environmental Physiology 172:371–378.

Krebs, C. J., K. Danell, A. Angerbjorn, J. Agrell, D. Berteaux, K. A. Brathen, O. Danell, S. Erlinge, V. Fedorov, K. Fredga, J. Hjalten, G. Hogstedt, I. S. Jonsdottir, A. J. Kenney, N. Kjellen, T. Nordin, H. Roininen, M. Svensson, M. Tannerfeldt, and C. Wiklund. 2003. Terrestrial trophic dynamics in the Canadian Arctic. Canadian Journal of Zoology 81:827–843.

Lepage, D., G. Gauthier, and S. Menu. 2000. Reproductive consequences of egg-laying decisions in snow geese. Journal of Animal Ecology 69:414–427.

Lesage, L. and G. Gauthier. 1997. Growth and organ development in Greater Snow Goose goslings. Auk 114:229–241.

Lewis, S. B., M. R. Fuller, and K. Titus. 2004. A comparison of 3 methods for assessing raptor diet during the breeding season. Wildlife Society Bulletin 32:373–385.

Maurer, B. 1998. The evolution of body size in birds. II. The role of reproductive power. Evolutionary Ecology 12:935.

Moskoff, W. and R. Montgomerie. 2002. Baird's Sandpiper (Calidris bairdii). In A. Poole, editor. The Birds of North America Online. Cornell Lab of Ornithology, Ithaca, New York, USA.

Myneni, R. B., C. D. Keeling, C. J. Tucker, G. Asrar, and R. R. Nemani. 1997. Increased plant growth in the northern high latitudes from 1981 to 1991. Nature 386:698–702.

Nagy, K. A. 1987. Field metabolic-rate and food requirement scaling in mammals and birds. Ecological Monographs 57:111–128.

Oksanen, T., M. Schneider, U. Rammul, P. Hamback, and M. Aunapuu. 1999. Population fluctuations of voles in North Fennoscandian tundra: contrasting dynamics in adjacent areas with different habitat composition. Oikos 86:463–478.

Parmelee, D. F. 1992. White-rumped Sandpiper (Calidris fuscicollis). In A. Poole, editor. The Birds of North America Online. Cornell Lab of Ornithology, Ithaca, New York, USA.

Parmelee, D. F., H. A. Stephens, and R. H. Schmidt. 1967. The birds of southeastern Victoria Island and adjacent small islands. National Museum of Canada Bulletin 222:1–229.

Paulson, D. R. 1995. Black-bellied Plover (Pluvialis squatarola). In A. Poole, editor. The Birds of North America Online. Cornell Lab of Ornithology, Ithaca, New York, USA.

Picotin, M. 2008. Variation climatique, abondance d'arthropodes et phénologie de la reproduction chez deux espèces de limicoles nichant dans le Haut-Arctique. Université du Québec à Rimouski, Rimouski, Quebec, Canada.

Piedboeuf, N. and G. Gauthier. 1999. Nutritive quality of forage plants for greater snow goose goslings: when is it advantageous to feed on grazed plants? Canadian Journal of Zoology-Revue Canadienne De Zoologie 77:1908–1918.

Piersma, T., A. Lindstrom, R. H. Drent, I. Tulp, J. Jukema, R. I. G. Morrison, J. Reneerkens, H. Schekkerman, and G. H. Visser. 2003. High daily energy expenditure of incubating shorebirds on High Arctic tundra: a circumpolar study. Functional Ecology 17:356–362.

Pouliot, D., R. Latifovic, and I. Olthof. 2009a. Trends in vegetation NDVI from 1 km AVHRR data over Canada for the period 1985-2006. International Journal of Remote Sensing 30:149–168.

Pouliot, R., L. Rochefort, and G. Gauthier. 2009b. Moss carpets constrain the fertilizing effects of herbivores on graminoid plants in arctic polygon fens. Botany-Botanique 87:1209–1222.

Procter, D. L. C. 1977. Invertebrate respiration on Truelove Lowland. Pages 383–394 in L. C. Bliss, editor. Truelove Lowland, Devan Island, Canada. The University of Alberta Press, Edmonton, Alberta, Canada.

Reed, A., R. J. Hughes, and H. Boyd. 2002. Patterns of distribution and abundance of greater snow geese on Bylot Island, Nunavut, Canada 1983-1998 Wildfowl 53:53–65.

Rodgers, A. R. and M. C. Lewis. 1986. Diet Selection in Arctic Lemmings (Lemmus sibiricus and Dicrostonyx groenlandicus) - Forage Availability and Natural Diets. Canadian Journal of Zoology-Revue Canadienne De Zoologie 64:1684–1689.

Rogers, L. E., R. L. Buschbom, and C. R. Watson. 1977. Lenght-weight relationships of shrub-steppe invertebrates. Annals of the Entomological Society of America 70:51–53.

Roth, J. D. 2002. Temporal variability in arctic fox diet as reflected in stable-carbon isotopes; the importance of sea ice. Oecologia (Berlin) 133:70–77.

Ruesink, J. L., K. E. Hodges, and C. J. Krebs. 2002. Mass-balance analyses of boreal forest population cycles: Merging demographic and ecosystem approaches. Ecosystems 5:138–158.

Ryan, J. K. 1977. Synthesis of energy flows and population dynamics of Truelove Lowland invertebrates. Pages 325–346 in L. C. Bliss, editor. Truelove Lowland, Devan Island, Canada. The University of Alberta Press, Edmonton, Alberta, Canada.

Sage, R. D. 1982. Wet and Dry-weight Estimates of Insects and Spiders Based on Lenght. American Midland Naturalist 108:407–411.

Sample, B. E., R. J. Cooper, R. D. Greer, and R. C. Withmore. 1993. Estimation of Insect Biomass by Length and Width. American Midland Naturalist 129:234–240.

Simms, D. A. 1978. Spring and summer food habits of an ermine (Mustela erminea) in the central arctic. Canadian Field-Naturalist 92:192–193.

Sittler, B. 1995. Response of stoat (Mustela erminea) to a fluctuating lemming (Dicrostonyx groenlandicus) population in North East Greenland: preliminary results from a long term study. Annales Zoologici Fennici 32:79–92.

Szor, G., D. Berteaux, and G. Gauthier. 2008. Finding the right home: distribution of food resources and terrain characteristics influence selection of denning sites and reproductive dens in arctic foxes. Polar Biology 31:351–362.

Tannerfeldt, M. and A. Angerbjörn. 1998. Fluctuating Resources and the Evolution of Litter Size in the Arctic Fox. Oikos 83:545–559.

Tarroux, A. 2011. Patrons d'utilisation de l'espace et des ressources chez un carnivore terrestre de l'Arctique: le renard polaire. UQAR, Rimouski, Quebec, Canada.

Tarroux, A., D. Ehrich, N. Lecomte, T. D. Jardine, J. Bêty, and D. Berteaux. 2010. Sensitivity of stable isotope mixing models to variation in isotopic ratios: evaluating consequences of lipid extraction. Methods in Ecology and Evolution 1:231–241.

Tracy, D. M., D. Schamel, and J. Dale. 2002. Red phalarope (Phalaropus fulicarius). In A. Poole and F. Gill, editors. The Birds of North America. The Birds of North America, Inc., Philadelphia, Pennsylvania, USA.

Whitfield, D. W. A. 1977. Energy budgets and ecological efficiencies on truelove Lowland. Pages 607–620 in L. C. Bliss, editor. Truelove Lowland, Devan Island, Canada. The University of Alberta Press, Edmonton, Alberta, Canada.

Wirth, W. W., W. N. Mathis, and J. R. Vockeroth. 1987. Ephydridae. Pages 1027–1047 in J. F. McAlpine, B. V. Peterson, G. E. Shewell, H. J. Teskey, J. R. Vockeroth, and D. M. Wood, editors. Manual of Nearctic Diptera. Agriculture Canada, Ottawa, Canada.


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