Disturbances are expected to increase variability and/or decrease predictability in ecosystems, while dispersal (or immigration) may have positive or negative effects on ecosystem stability. We conducted a mesocosm experiment with pelagic zooplankton to examine the independent and interactive effects of a nutrient pulse and immigration from neighbouring lakes on (a) temporal variation in the mesocosm communities and (b) variation among spatial replicates. Surprisingly, nutrient enrichment had no significant effect on among-replicate variability in algal or zooplankton biomass, and it decreased both among-replicate variability in zooplankton community composition and temporal variability of algal biomass (measured as the coefficient of variation). The nutrient pulse increased temporal variation in zooplankton biomass but decreased temporal change in relative species abundances. However, both these effects depended on dispersal, suggesting a context-dependent role of dispersal in community stability. We discuss the importance of considering multiple measures and aspects of community variability.

We examined the determinants of zooplankton and phytoplankton metacommunity structure across 25 boreal wetland ponds. Our objective was to determine whether plankton metacommunities exhibit spatial structuring, thus suggesting neutrality, or are merely structured by local environmental features, suggesting that they are under niche-based control. According to Redundancy Analysis (RDA), zooplankton community structure was primarily controlled by concentration of major ions and geographical location of the pond, while phytoplankton community structure was primarily controlled by major ion concentration, nitrogen concentration, and geographical location. According to variance partitioning in RDA, zooplankton community structure was attributed more to pure spatial position of the pond (16.7% of variance) than to pure environmental factors (4.7% of variance). For phytoplankton, community composition was controlled by both spatial and environmental factors, although the effect of pure spatial position (11.1% of variance) on phytoplankton community structure was somewhat weaker than for zooplankton. For zooplankton, community similarity was negatively (P < 0.01) related to both geographical and environmental distance. For phytoplankton, community similarity was negatively (P < 0.05) related only to geographical distance. Finally, cluster analyses showed that zooplankton and phytoplankton communities formed highly dissimilar groupings, thus implying low community concordance. Our results suggest that both zooplankton and phytoplankton comply with both neutral and niche-based models. Our results further imply that even across small spatial scales and even for small organisms such as plankton, communities might be strongly spatially structured. The finding that spatial configuration was even more important than local environmental factors in controlling zooplankton community composition suggests that zooplankton may be dispersal-limited within relatively small spatial scales or that zooplankton metacommunities might be related to mass effects.

It is not uncommon for different species within a guild to be non-randomly segregated within a landscape through the occupation of different preferred macrohabitats. The explanation most amenable with ecological theory is that different guild members are adapted for exploiting the different opportunities offered by such macrohabitats. Morphological characters are possible adaptations reflecting habitat preferences. We investigated morphological traits in a guild of small foliage-gleaning, insectivorous birds breeding in central Ontario, Canada (4 families; 23 species). We measured 27 skeletal features and compared 2 types of differences: those between conspecific sexes (that by necessity occupy the same macrohabitat) and those between different guild members (that tend to occupy different macrohabitats). We predicted that if macrohabitat differences are reflected in different morphologies, the differences between conspecific sexes would be less than the differences between species, at least after correcting for size. We used (a) principal components analysis (PCA), (b) distance matrices derived from PCA scores, and (c) Mantel tests. Although conspecific male and female morphologies were correlated, nearest neighbours in morphological space were frequently non-conspecifics. Accordingly, because morphological differences between similar species that tend to occupy different macrohabitats are often smaller than morphological differences between conspecific sexes, our findings indicate that skeletal morphology provides no basis for explaining patterns of within-guild macrohabitat segregation.

Squirrels, especially those in temperate regions, hoard seeds in terrestrial scatterhoards or larders. Arboreal seed storage is rare. Here we show for the first time that the tropical Indian giant squirrel (Ratufa indica) larder hoards seeds in arboreal nests, a behaviour not previously described. Seeds of 6 tree and liana species in an Indian cloud forest were hoarded during the fruiting season. Seeds of 2 species were hoarded but never consumed when fresh probably because of secondary metabolites. Common species with hard seed coats were most frequently hoarded. Squirrels exhibited variation in hoarding behaviour in different areas of the study site. Squirrels that were at risk of nest robbing resulting from competition for nesting sites did not hoard seeds.

This paper reports large variations in stable carbon and nitrogen isotope ratios of lake anchovy (Coilia ectenes taihuensis) from Lake Chaohu, China. The lake anchovy exhibited a significant ¹³C- and ¹⁵N- enrichment in relation to increasing fish length, and the isotopic compositions of small lake anchovy (≤ 130 mm) were significantly more enriched than those of large lake anchovy (>130 mm). The significant differences in the isotopic compositions of small and large lake anchovy suggested that their assimilated diets differed over a period of time and reflected the size-related diet shift of this fish. Bellamya aeruginosa and Corbicula fluminea were used to establish the baseline carbon signal of benthic and pelagic food webs, and these data were used to parameterize a 2-source mixing model to estimate in consumers the contribution of carbon derived from benthic versus pelagic food webs. Mixing models showed that small lake anchovy derived only 37% of their carbon from benthic food web, indicating increased reliance on pelagic prey, whereas benthic prey contributed 71% of large lake anchovy diet, suggesting greater use of benthic sources. These data indicate that there was a change in lake anchovy feeding strategy related to their size, suggesting a role in dynamic coupling between pelagic and benthic food chains. The trophic position of small lake anchovy averaged 3.0, indicating a zooplankton-based diet, compared with 3.6 in large lake anchovy, indicative of an increase in piscivorous diet. Overlap in the isotopic compositions of small and large lake anchovy probably indicated that these fish occasionally shared common diets, as suggested by stomach content studies, and/or resulted from the differences in the rate of isotopic turnover depending on differences in growth rate and metabolic turnover between small and large anchovy during diet shift from pelagic to benthic food webs. This study presents the contributions of benthic and pelagic food webs supporting lake anchovy and indicates that the intraspecific isotopic dynamic should be considered when applying stable isotope analyses to infer trophic interactions in aquatic ecosystems.

Large herbivores directly affect plant communities in alpine ecosystems. In addition, they may compete with, or facilitate foraging by, small herbivores and also cause strong indirect effects on plants. We used an exclosure experiment to examine short-term (5-y) effects of cessation of sheep grazing on rodent grazing and plant communities in an oceanic alpine environment of low productivity with a long history of heavy sheep grazing. Exclusion of sheep significantly impacted plant communities. Vascular plant height increased, but Deschampsia flexuosa was the only vascular plant species that increased in sheep exclosures. Changes in the frequency of graminoids, herbs, and dwarf shrubs in exclosed plots were not related to cessation of grazing, but 6 bryophyte species significantly increased or decreased in response to exclusion of sheep. The absence of large grazers thus brought about a change in the species composition in favour of successional bryophytes and the preferred fodder plant. Neither vascular plant nor bryophyte species richness, nor the total cover of bryophytes and lichens, were affected. Cessation of sheep grazing reduced the level of rodent grazing. Rodent grazing correlated with changes in plant communities that led to reduced height and cover of vascular plants, reduced cryptogam cover, and reduced frequencies of 3 bryophyte species. A strong correlation between sheep fodder value index and rodent grazing indirectly indicated additive herbivory. In addition, some of the rodent effects were compensatory; e.g., Nardus stricta, which is not grazed by sheep, was significantly reduced by rodents. Our study points to a more central role of facilitation in structuring herbivore assemblages in the short term, with direct implications for the joint effects of large and small herbivores on the cover and frequency of graminoids and bryophytes.

The only 3 published studies relating vertebrate herbivores to plant fluctuating asymmetry (FA) found significant correlations between grazing intensity and plant FA. The general value of these early findings is unclear, however, because FA studies are sensitive to selective reporting, the tendency to publish only a subset of studies that were undertaken. From 2000 to 2003 we quantified the correlations between past herbivory and plant FA in 3 plant–herbivore systems centred on a single mammal species, the North American porcupine (Erethizon dorsatum). We measured leaf FA in pairs of paper birch (Betula papyriferae; n = 24 pairs), quaking aspen ( Populus tremuloides; n = 25 pairs), and jack pine ( Pinus banksiana; n = 15 pairs) trees each containing a control (uneaten) and test (eaten) tree. Although damage incurred by trees from porcupine browsing was severe, we found no statistical association between plant FA and herbivory. We obtained this finding even though our study design did capture subtle variations in plant FA associated to plant genotype or year of sampling. Our study contrasts with earlier findings that plant FA is related to herbivory pressure. There may have been a publication bias as a result of selective reporting in this field of research. Therefore, replication (same hypothesis, same study system) and quasireplication (same hypothesis, different study system) are particularly important.

Invasive species are a growing international conservation concern. In Canada, the federal agency responsible for national parks, Parks Canada, has recently identified non-native species as important threats to the integrity and richness of Canadian national parks. To test for potential effects of non-native species on native richness, we examined the relationship between native and non-native/invasive species for 3 taxa – plants, mammals, and birds – in 42 Canadian national parks. We found positive relationships between native and non-native/invasive species richness for plants and birds and a negative relationship between native and non-native/invasive mammal species richness. Consistent with most large-scale studies, our results suggest that for birds and plants, regions that are good for native species are also good for non-native species. However, we provide one of the few examples of a negative relationship between native and non-native/invasive species. In mammals we show that there are more non-natives present in species-poor communities. This may indicate that non-native mammal species are having a negative impact on native species, that non-native mammal species are more able to invade richness-poor communities, or that a third factor such as fire, habitat degradation, or climate change has a negative effect on native species while having a positive effect on non-native species. In any case, it is evident that the pattern present between native and non-native mammals differs from those in plants and birds and could be representative of a negative effect associated with non-native introductions.

Flowering phenology can strongly affect reproductive success. In mass-flowering species, synchronous individuals may have a reproductive advantage because of the increased number of pollinators and decreased probability of predispersal seed predation. We investigated flowering phenology in relation to female reproductive success, and the responses of pollinators and predispersal seed predators to flowering variation, in 4 populations of Sorbus aucuparia in the northwest Iberian Peninsula, 2 of them over a 3-y period. Flowering lasted about 2 weeks at the end of spring, during which most individuals in the populations flowered synchronously (i.e., exhibited mass-flowering). Variation among individuals and populations in flowering dates and flowering duration was significant, and the differences remained consistent between years, especially between those with greater production of flowers and fruits. Pollinator visit frequency was independent of flowering phenology. The relationship between flowering phenology and predispersal seed predation was not significant as well. Contrary to the general hypothesis for mass-flowering, plants flowering earlier showed lower seed predation rates and higher female reproductive success (i.e., greater total dispersed fruits). The selective pressure exerted on flowering phenology by predispersal seed predators may be limited by the effect of plant size on flowering phenology. Plant size and local conditions are important factors affecting phenology and female reproductive success, and they may explain the observed variation in flowering phenology.

Large carnivore populations are recovering in many protected areas in North America, but the effect of increasing carnivore numbers on existing predator–prey and predator–predator interactions is poorly understood. We studied diet and spatial overlap among cougars (Puma concolor) and gray wolves (Canis lupus) in Banff National Park, Alberta (1993–2004) to evaluate how wolf recovery in the park influenced diet choice and space use patterns of resident cougars. Cougars (n =13) and wolves (n= 8 in 2 packs) were monitored intensively over 3 winters (2000–2001 to 2002–2003) via radio telemetry and snowtracking. We documented a 65% decline in the local elk population following the arrival of wolves, with cougars concurrently switching from a winter diet primarily constituted of elk to one consisting mainly of deer and other alternative prey. Elk also became less important in wolf diet, but this latter diet switch lagged 1 y behind that of cougars. Wolves were responsible for cougar mortality and usurping prey carcasses from cougars, but cougars failed to exhibit reciprocal behaviour. Cougar and wolf home ranges overlapped, but cougars showed temporal avoidance of areas recently occupied by wolves. We conclude that wolves can alter the diet and space use patterns of sympatric large carnivores through interference and exploitative interactions. Understanding these relationships is important for the effective conservation and management of large mammals in protected areas where carnivore populations are recovering.

The decrease in community similarity was examined in corticolous oribatid mites (Acari: Oribatida) sampled along a 36-m vertical profile of 5 western redcedar trees in a temperate rainforest on Vancouver Island, Canada. Samples were collected every 2 m, and all adult oribatid mites were identified to species. When compared to species recorded from previous ground/canopy sampling efforts in the same trees, the 62 corticolous species unequivocally support the separation of these 2 communities at 4m. All sampling heights contained canopy oribatid species, but only 0–4 m communities contained ground-dwelling oribatids. There was significant overall spatial autocorrelation and decay in community similarity with distance originating from species turnover at 4 m, suggesting limited range expansion of ground species into corticolous habitats. Community similarity, richness, and abundance of corticolous oribatid mite assemblages were not autocorrelated after 4 m above ground. Observed patterns at 4 m likely represent an environmental transition zone for ground-dwelling species, such as changes in moisture availability, rather than a physical dispersal barrier for individuals. We conclude that the trunk is not a dispersal corridor for ground species to colonize tree crowns and suggest that low similarity between nearest neighbouring sampling points, combined with the presence of immature and gravid oribatids, supports the assumption that corticolous oribatid mite assemblages are likely dispersal-limited residents.

Fallopia japonica is one of the most troublesome alien invasive plants across temperate regions, with large negative impacts on plant species diversity. We examined its impacts on topsoil chemistry and nutrient stocks in standing biomass at 6 sites with contrasting resident plant communities in Belgium. Topsoil and biomass were sampled in invaded and closely adjacent uninvaded plots. Standing biomass and mineral nutrient concentrations in soil (ammonium acetate exchangeable cations and P, total C, and N) and plants were determined. Soil under F. japonica generally had higher exchangeable nutrient concentrations (Cu: 45%, K: 34%, Mg: 49%, Mn: 61%, P: 44%, Zn: 75%). Standing biomass was 3- to 13-fold higher depending on site. Despite lower nutrient concentrations in aboveground biomass, invaded stands had 3.2- to 5.4-fold larger nutrient stocks in aboveground biomass compared to the resident vegetation. We conclude that F. japonica enhances nutrient cycling rates and topsoil fertility, probably due to nutrient uplift. The impacts were greatest in sites with low nutrient concentrations in uninvaded plots, suggesting that F. japonica may contribute to soil homogenization in invaded landscapes.

Abiotic factors have been reported to cause variation in parasite pressure among host populations, but such relationships have not been studied in detail, and conflicting evidence exists about the nature of these relationships. Here we study within- and between-population variation in chewing lice parasitization in an arid bird species, the Trumpeter finch (Bucanetes githagineus), and the influence of ambient humidity on parasite load. We found a high prevalence of 2 chewing lice even in particularly dry years and a positive effect of humidity on prevalence at a monthly scale. Nonetheless, our results clearly reveal that lice can become abundant at low ambient humidity conditions and that birds in arid environments are not necessarily under lower ectoparasitic pressure than birds in humid regions. We suggest that lice may adapt their life cycle to overcome the most critical period by synchronizing the more resistant phase (eggs) to the period when relative humidity is lowest (i.e., summertime). We stress that studies on the effect of ecological factors on host–parasite relationships should consider detailed aspects of the life cycle of the latter and the main biological traits of the different stages of the parasites.

In many plant species, population persistence at the limit of their distribution relies on clonal growth, but little is known about the consequences for genetic diversity, spatial patterns, and growth of the offspring. The rare European tree Sorbus torminalis (Rosaceae) was chosen to explore the patterns and limitations of clonal growth. Offspring were mapped in 7 small populations at the northern limit of the species' distribution, their size was recorded in 2 consecutive years, and the degree of shading (diffuse site factor, DSF) was measured at the forest floor. A subsample of offspring and adults was genotyped with microsatellites to determine the frequency of vegetative reproduction, and another group of offspring was protected against browsing. Clonal origin was observed in 98% of the offspring, and thus they were classified as root sprouts. The fine-scale distribution of the root sprouts was mainly clumped, and variation of DSF explained some of this pattern. Mixed linear modeling of root sprout size, with DSF, sprout density, and distance to the nearest adult tree as explanatory variables, suggested inter-offspring competition, but there were significant interactions among the explanatory variables, In addition, browsing by deer reduced growth of the root sprouts. Root sprout mortality was 17% after 1 y, and highest for young, small, and isolated offspring growing in high-light microhabitats. Root sprout growth and mortality were not directly affected by distance to adult trees. We conclude that clonal growth is common in the northern populations of the study species, and that root sprout distribution and growth are controlled by complex interactions between light, browsing, distance to the parent tree, and sprout density.

Evaluating forest ecological integrity remains a major challenge for ecologists. We analyzed understory vegetation using an approach that combined plant functional types and vertical stratification to evaluate the effects of human disturbances on the ecological integrity of sugar maple-dominated stands in southern Québec. Ecological integrity was evaluated by analyzing the divergence of understory species assemblages from those observed in comparable unmanaged forest. Multivariate analyses of biological traits revealed 13 emergent groups that share common traits associated with a similar life history strategy. Responses of these groups, of specific traits, and of understory structure to different human disturbances were tested. Nine of the 13 emergent groups varied in occurrence or diversity among disturbance types. Analyses also revealed a set of traits specifically associated with unmanaged old growth forest, indicating that species possessing these traits may be sensitive to human disturbance. Overall, the understory vegetation assemblage was found to be relatively stable among all human disturbances investigated. However, our results suggest some issues of possible long-term conservation concern given a continuation of human disturbances: (i) an increase of species associated with open environment, including exotic species; (ii) a decrease of spring geophytes; (iii) a decrease of certain shade-tolerant forbs; and (iv) a modification of understory structure by the development of a dense sapling stratum.