Some individuals respond to habitat degradation by dispersing to less degraded areas while others remain but display altered behaviours, potentially compensating for the habitat change. We examined the latter possibility by evaluating foraging behaviour and size of lesser snow geese over a period during which their habitat became severely degraded. We show that in this now-degraded habitat, adults spend more of their total time in motor activities and less time in vigilance and comfort behaviours. Goslings spend less of their total time foraging and more in comfort and other behaviours. The pecking rate of both adults and goslings while foraging increases, as do motor and searching behaviours of adults. These changes have not enabled the birds to keep pace with the loss of vegetation, and the size of goslings has continued to decline, likely leading to a reduction in reproductive success. The persistent use of degraded salt marsh is probably related to philopatry and will further damage the marsh.

Co-occurrence of winter-deciduous and evergreen oaks is common in some Mediterranean-type climate areas. However, whether these species show an overlap in their regeneration niche is still poorly understood. We explored experimentally the changes in survival, growth, biomass partitioning, leaf nitrogen content, and water use efficiency (δ¹³C) in seedlings of a deciduous oak (Quercus cerrioides) and an evergreen oak (Quercus ilex) in response to co-variation in light and water availability. Quercus cerrioides exhibited higher root length, root area, leaf nitrogen content, and less negative δ¹³C, but lower leafiness than Q. ilex. The interaction between species and light in specific leaf area and root–shoot ratio indicated different mechanisms to overcome water stress in the two oaks, with Q. ilex relying on leaf hardening and Q. cerrioides relying on a high root–shoot ratio. However, the two species showed similar survival and growth in most of the light–water gradient. Ecological inference of these results indicates that seedlings of these species have a similar ability to cope with variations in light and water in spite of their contrasting leaf habit. This similar performance suggests a competition for similar micro-sites during establishment, rather than a partitioning of the regeneration niche.

The nitrogen (N) supply is limited in many peatlands, and the mineralization of organic matter represents a major source of N to plants. The goal of this paper is to establish the relationship between decomposition rates, mineralization rates, and the N concentration of peat along a peatland gradient in four peatlands in western, boreal Canada. The four peatlands differ physically, chemically, and floristically and include a bog, a poor fen, and two moderate-rich fens, one wooded and the other open. The fens are enriched by ground water inputs, which we hypothesized led to higher concentrations of N in peat, faster decomposition of litter, and higher N mineralization rates. Net N mineralization was virtually identical to net ammonification over a 2-y period, both measured using an in situ incubation technique. Net daily mineralization rates increased from the bog to the open, moderate-rich fen, with intermediate values in the poor fen and moderate-rich wooded fen. This increasing trend along the bog–open, moderate-rich fen peatland gradient was mirrored for mineralization rates on a temporal and spatial basis. Virtually no nitrification was detected in any of the sites. Estimated aboveground integrated ecosystem decomposition rates ranged from 17%·y⁻¹ in the bog to 31%·y⁻¹ in the wooded, moderate-rich fen. Decomposition rates were significantly correlated with the mean daily net N mineralization rate and with total N in the upper 20 cm of peat. The net mineralization rate also was positively correlated with the total N content of the peat in 1991. The total N content of the peat increased from 5.8 mg·g⁻¹ in the bog to 11.5 mg·g⁻¹ in the open, moderate-rich fen, with poor fen and moderate-rich wooded fen values intermediate. The total C content of the peat ranged from 370 to 400 mg·g⁻¹ and was not significantly different among the four peatlands. TC:TN quotients for the peat cores were 68 in the bog and 36–38 in the fens, correlating negatively with net ammonification rates. Based on our data, the processes of mineralization of N and decomposition are tightly linked processes, both of which were higher in the fens than in the bog in our four western continental peatlands. Moreover, both processes are more affected by the quality of the organic matter, as indicated by the TC:TN quotients of the surface peat, than by surface water chemistry variables.

Coyotes (Canis latrans) have expanded their range to the north and east in North America during the last century. It has been suggested that vegetative cover reduces hunting efficiency of forest-dwelling coyotes, which could explain their lower performance compared to rural coyotes. Also, in their northern range, coyotes must periodically cope with deep and soft snow conditions for which they are not morphologically adapted. We snow-tracked coyotes in a forested landscape of southeastern Québec to test the hypothesis that coyotes modify their hunting strategy with respect to vegetative cover, snow condition, and hare distribution (Lepus americanus), the main prey species during winter in our study area. When snow sinking depth hampered mobility, coyotes used habitats with the lowest snow sinking depth (coniferous habitats) in a greater proportion than availability (47.0 versus 29.7%), despite dense lateral cover. As a result, coyotes chased hares over short distances (17 m on average). However, when snow conditions did not hamper mobility, use of coniferous habitats decreased to 18.5% in favour of open habitats, which were used more than availability (47.7 versus 32.5%), despite low hare abundance. Use of sites with little lateral cover and low sinking depth facilitated long chases by coyotes (126 m on average). Throughout winter, coyotes used sites characterized by less lateral cover and lower snow sinking depth than random sites. Our results suggest that coyotes selectively used habitat and hunting strategy to maximize their net energy budget throughout winter. Fragmentation of forest landscapes generates abundant openings and small refuges which may benefit coyotes to the detriment of native prey populations.

In winter ungulates must compete for forage of low quality that may be energetically costly to obtain due to high locomotion costs associated with snow. We hypothesized that white-tailed deer would select plant species and plant parts to maximize their net energy budget based on snow conditions and forage availability. We predicted that as winter progress or under deep snow conditions, deer would 1) reduce selectivity, 2) enlarge bite size, and 3) increase cropping rate. For three winters, we studied white-tailed deer found in the Pohénégamook wintering area (southeastern Québec), at the northeastern periphery of the species range. Utilization rates of plant species varied in relation to fibre contents but were not related to protein, ash, or phenolic contents, suggesting that energy represented the key nutritive element during winter. Deer were less selective as winter progressed and snow depth increased. Deer consumed all available plant species, but their foraging strategy was centred around deciduous twigs; deer were reluctant to increase the amount of coniferous twigs in their diet. However, snow conditions affected diet composition. During a very mild winter, deer reduced their intake of balsam fir and consumed some species that were likely unavailable when snow was deep. Bite size increased over the winter, whereas cropping rate increased with snow sinking depth. To cope with changing locomotion costs in snow, white-tailed deer adjusted three variables: travelling distance, forage intake, and cropping rate.

In Los Tuxtlas, Mexico, there are numerous deep crater lakes in varying trophic states. In a warm eutrophic monomictic lake of the region we analyzed changes in the phytoplankton community and how they relate to water quality. During the periods of circulation, early and late stratification, there was an increase in species diversity marked by an increase in the abundance of many species of diatoms and chlorophytes. These periods were characterized by low transparency, high specific conductance, and high concentrations of ammonium and dissolved silica. Microcystis aeruginosa dominated during the entire stratification period, when both diversity and succession rates were low. Stratification was characterized by high temperatures (> 30 °C), low transparency, high pH, and high concentrations of soluble reactive phosphorus and nitrate. Thus, in Lake Chalchoapan, physical changes associated with stratification, circulation, and tropical seasonality determine the succession dynamics of the phytoplankton community.

Rankings of species-specific juvenile tree growth and survivorship define competitive hierarchies that play a central role in forest dynamics and may also vary in response to herbivory. We conducted an experiment to examine species-specific rankings of sapling growth and survival for six common tree species in temperate forests of the northeastern US as a function of both resource availability and herbivory by white-tailed deer (Odocoileus virginianus). Juveniles of six tree species were planted in the presence and absence of deer, in high and low light neighbourhoods dominated by each of two different tree species known to both reflect and alter soil resource availability. Under closed canopy conditions, survival and radial growth of most species was low. Under high light conditions, red oak and eastern hemlock saplings inside exclosures grew significantly faster when protected from deer, and eastern hemlock saplings grew faster in red oak- than red maple-dominated neighbourhoods. Browsing significantly decreased survival under high light for all species except beech. Rank order of species-specific growth and survival within treatment combinations changed dramatically. For example, beech saplings had the second highest survivorship under high light / deer neighbourhoods, but fell to the lowest rank when deer were excluded. These rank-order changes in growth and survivorship indicate that both light availability and herbivory act in concert with gap-phase dynamics to regulate tree population dynamics in eastern deciduous forests.

Invaders can have negative impacts on native flora, fauna, and ecosystems, especially on remote islands where they compete with indigenous plants and animals. Since their introduction on Anticosti Island (Québec) in the late 1890s, white-tailed deer (Odocoileus virginianus) have had detrimental effects on preferred forage species. To determine the impact of deer browsing on tree growth and forest structure, we compared stem density, age, and size of conifer species across a range of open, semi-forested, and forest stands, where browsing severity on balsam fir (Abies balsamea), a preferred species, was variable. Most balsam fir saplings showed signs of browsing, with maximum impact at low sapling density. At most stands, balsam fir saplings were smaller than white spruce (Picea glauca) and black spruce (Picea mariana) saplings and developed bonsai-like growth forms. Browsing was light on white spruce; no browsing was recorded on black spruce. Tree-ring analysis was used to differentiate the influence of deer browsing from the possible effects of past insect activity on conifer species. Periods of radial growth reduction coincided with documented spruce budworm (Choristoneura fumiferana) and hemlock looper (Lambdina fiscellaria) infestations during the 20^th century. The combined influence of insect defoliation and deer browsing on fir was evidenced by contrasted patterns in stem growth above and below browsing height. Balsam fir sapling mortality in the 1980s and early 1990s was likely due to severe deer browsing rather than insect defoliation. Reduced sapling growth and recruitment of balsam fir to the canopy will likely modify the forest composition from balsam fir- to white spruce-dominated stands.

Interactions within populations at the periphery of a species' range may depart from those in populations more centrally located. Throughout its core range, limber pine (Pinus flexilis, Pinaceae) depends on Clark's nutcrackers (Nucifraga columbiana, Corvidae) for seed dispersal. Nutcrackers, however, rarely visit the Pawnee National Grassland peripheral population of limber pine on the eastern Colorado plains. Using live mammal trapping, fluorescent pigment tracking of disseminated seeds, and limber pine seed germination experiments in the field, we tested the hypothesis that limber pine seeds in this peripheral isolate are dispersed by nocturnal rodents. Live trapping and tracking indicated that deer mice (Peromyscus maniculatus, Muridae) and Ord's kangaroo rats (Dipodomys ordii, Heteromyidae) are the likely seed dispersers in this population. Rodents cached seeds in surface caches on tree leaf litter, rock, or soil substrate or buried them under soil, tree litter, or plants. Seeds cached under soil and plants, as opposed to surface caches, accounted for the greater number of stored seeds. Numbers of seeds per cache for buried caches was significantly higher than numbers of seeds for surface caches. The largest caches on average were those buried under plants. Also, we found that some rodent caches contained one or more seeds up to 27 d after the caches were made. In experiments simulating observed cache types, we determined that most cache types, but especially buried caches, had some germination potential. Rodents disseminated seeds over shorter distances than do nutcrackers, possibly explaining previously observed genetic substructuring in the Pawnee population. Seed dispersal by rodents also precludes the metapopulation dynamics typical of limber pine in its core range, and may lead to the loss of peripheral populations over time.

This study aims at determining the dendrochronological indicators of a changing snow accumulation regime on an island of a recently created reservoir in northern Québec. Reservoir Robert-Bourassa (LG-2) is a vast lake (2,835 km²) covered by ice from mid-December to mid-May. Snow drifts across the frozen lake until it is trapped by obstacles on islands and at reservoir margins. Pre-established trees on the islands are negatively affected by the local augmentation of snow accumulation. Changes in tree growth forms of a severely exposed forested island indicate that damage occurred soon after reservoir filling. At the island edges, the decay of trees increases the wind exposure of border trees, causing massive foliage loss, thus reducing tree growth. Beyond the edge, in the island interior, drifted snow accumulates due to the wind breaking effect of the shoreline trees. Since reservoir filling, incidents of stem breakage, shoot bending and tilting, and branch tearing have increased due to snow packing. Such anomalous growth features appeared during the first 3 y after reservoir filling. Tree rings also indicate the trauma of wind and cold exposure stress. Such stress results in the incomplete formation of annual rings and the development of a series of resin ducts. The amount of snow packing damage to trees depends on the abundance of snowfall and on winter levels of the reservoir. The combination of these two factors controls the amount of snow reaching the island forests when drifted by the wind.

A range of stands was sampled in the southern boreal forest of eastern Canada to determine the impact of forest development stages and light availability on the dynamics of an abundant understory shrub: mountain maple (Acer spicatum). Mountain maple was studied at both the population and individual stem levels. At the population level, a total of 190 1-m² quadrats were sampled in five forest types representing a successional gradient (young aspen, mature aspen, mixedwood, shade-tolerant conifer, and old spruce budworm-affected conifer forests). At the individual stem level, a total of 100 stems of different sizes were harvested in a sub-sample of the quadrats. Mountain maple stem biomass, density, and population structure were found to be affected by forest composition, the coniferous forest being the least favourable. At the individual stem level, light availability and stem size were found to have an important impact on stem morphology and growth, suggesting a high level of plasticity in relation to canopy opening. From these results, four developmental phases of mountain maple population dynamics were identified: 1) following a drastic disturbance, a first phase of rapid growth, and potentially intense competition with aspen suckers, when present, takes place; 2) following the development of a closed aspen canopy, the overall density, biomass, and presence of mountain maple in the understory increase; 3) following recruitment of conifer trees into the overstory canopy, mountain maple enters a suppression phase associated with a decrease in light; and 4) following the occurrence of small scale disturbances, mountain maple quickly responds to rapidly dominate the openings, which further ensures its maintenance in the understory.

Ectoparasites dwelling in bird nests regularly reduce reproductive success and condition of breeding birds. Thus, establishing the factors that determine the abundance of ectoparasites is important for better understanding of reproductive trade-offs and life history evolution in birds. A recent hypothesis states that interspecific differences in the abundance of ectoparasites may be caused by nest composition. For example, great tits (Parus major) have nests made of mosses and fur, whereas Ficedula flycatchers have nests made of grasses, bast, and bark, and tits are more infested by nest-dwelling ectoparasites than flycatchers. We swapped nests between pairs of great tits and collared flycatchers (F. albicollis) during egg-laying or early incubation and counted parasitic Protocalliphora blow flies at the end of breeding to test this hypothesis experimentally. We controlled statistically for habitat (oak versus spruce forest), brood size, season, year, and mean nestling weight before fledging. We found a significant effect of bird species (tit > flycatcher), habitat (oak > spruce), and year. There was no effect of nest type. Consequently, the hypothesis ascribing the different abundance of ectoparasites in great tits and collared flycatchers to different nest composition was not supported by our study.

Leaf-cutting ant nests represent a potential source of disturbance within Neotropical forests that might favour selective establishment of some plant species. To test this hypothesis, I counted the number and determined the composition of plant species and individuals established in 10 abandoned Atta cephalotes nests and adjacent understory plots in an old-growth forest of Costa Rica. Specifically, I evaluated whether abandoned leaf-cutting ant nests differentially affect plant assemblages according to their 1) regeneration status, 2) seed size, and 3) dispersal mode. No differences were found in the relative abundance of species (and individuals) with different regeneration status, seed size, and dispersal mode between understory plots and abandoned Atta nests. Moreover, entire sites (abandoned ant nests and their nearby understory plots) were frequently grouped together according to those characteristics, suggesting that local effects were stronger than the effect of nests. Four non-mutually exclusive factors are discussed to explain the lack of a consistent effect of abandoned ant nests on plant assemblage composition: refuse dump location, spatial heterogeneity, dispersal limitation, and the local species pool. Chance events in the dynamics of both ant and plant species populations apparently restrict the effect of abandoned nests to an ecological time. Abandoned ant nests, however, might favour selective establishment of some plant assemblages if their refuse piles are located on the soil surface and if the potentially favoured plant species are locally available.

In light of declining populations of many North American songbirds, there is a need to understand the value of habitats used by species throughout the annual cycle, including the post-breeding and migratory periods. Here, we identified the songbird community and examined habitat use and degree of habitat specialization of species using high-elevation habitats in southern British Columbia in fall. Surveys were conducted along transects in habitats that included alpine grassland, subalpine shrub meadows, and montane coniferous forest. We detected a total of 6,608 individuals representing 70 species. Twelve species dominated the community and represented more than 85% of the observations. Horned lark (Eremophila alpestris) and American pipit (Anthus rubescens) were most abundant in alpine grasslands; yellow-rumped warbler (Dendroica coronata), dark-eyed junco (Junco hyemalis), and white-crowned sparrow (Zonotrichia leucophrys) were most common in semi-open subalpine habitats; and golden-crowned kinglet (Regulus satrapa) and mountain chickadee (Poecile gambeli) were most abundant in continuous coniferous forest. Nearly all species commonly observed in this study also breed at high elevations, while species that breed only at lower elevations were rarely or never observed. This suggests that high elevations are preferred in fall by species that use habitats with similar structure at other times of the year. Species showed considerable variation in habitat specialization. Some, such as horned lark and Lincoln's sparrow (Melospiza lincolnii) primarily used a single high-elevation habitat type, while others such as chipping sparrow (Spizella passerina) and yellow-rumped warbler were common in multiple high-elevation habitats.

Species invasions have several stages: 1) immigration of propagules, 2) establishment, and 3) spread and replacement of native species. The unconstrained growth of a species contributes to competitive ability during establishment and spread in bare soil conditions such as exist in newly restored wetlands. Phalaris arundinacea, an invasive perennial grass, is problematic in wetlands across temperate North America. Studies have shown that other wetland species have slower growth than P. arundinacea during the first 2 y following germination, implying that P. arundinacea invasiveness may be related to high rates of biomass production during establishment. We conducted a uniform planting study to observe P. arundinacea growth over two growing seasons. Phalaris arundinacea grew rapidly during establishment, producing a total biomass of 124 g·plant⁻¹ in four months and 525 g·plant⁻¹ at the end of two growing seasons. Root:shoot ratios were < 1 during the first four months of establishment, but were > 2 for the rest of the study. The shift in root:shoot ratio suggests P. arundinacea may pre-empt other species during establishment by first securing above ground space and then spreading rapidly belowground. Phalaris arundinacea vegetative growth likely facilitates dominance of this species when growth is unconstrained. Species-specific information about unconstrained growth is important to developing a predictive understanding of early establishment of wetland plant communities in bare ground conditions, i.e., in newly created, restored, and disturbed wetlands.

Processes that structure bird communities can be divided into two general categories: niche-based and dispersal-based. By examining the proportion of coniferous specialist individuals and the species composition in two forest bird communities, we tested the relative importance of habitat preference and availability (niche-based process) versus random settlement of individuals (dispersal-based process) in determining community composition. We examined two sites on Cape Breton Island, Nova Scotia, Canada: one undisturbed, the other with a history of human disturbance. To test for random settlement, for each forest type we generated model communities based on a random selection of individuals, weighted by the relative proportions of individuals and species in the observed community. In both communities, the proportion of individuals that were coniferous specialists deviated from random. In the disturbed forest, the proportion of coniferous specialist species increased as coniferous habitat increased, consistent with an effect of habitat preference and availability on community structure. This effect was not evident in the undisturbed forest. The proportion of coniferous specialist species, especially at the disturbed site, was similar to the proportion produced by our random model, a different result than for individuals. Examining results only at the species level may mask the processes operating at the level of individuals. Total species richness at both sites was accurately predicted by our random model, suggesting that species richness may be independent of the processes that determine community composition.