Natural geographic barriers and escarpments inhibited the post-glacial colonization of many lakes by fish on the eastern Canadian Boreal Shield. Hence, fishless lakes containing freshwater communities that evolved without fish predation are commonly found on the Boreal Shield next to fish-present lakes. The aim of this study was thus to assess how different top-down control from fish or invertebrate predation structure zooplankton communities in eastern Canadian Boreal Shield lakes throughout the ice-free season. We examined zooplankton community characteristics using univariate indices such as abundance, richness (S), evenness (J') diversity (H'), and multivariate species assemblages (Bray—Curtis dissimilarity) in 5 lakes with a single fish population, brook trout, Salvelinus fontinalis, and in 5 naturally fishless lakes throughout the ice-free season. The total abundance of zooplanktonic organisms was significantly higher in fishless lakes over the whole sampling period; this was related to the presence of small herbivorous species such as rotifers. Species assemblages of zooplankton were also significantly different between the 2 types of lakes throughout the season, principally due to the high abundance of rotifers and the scarcity of immature and mature daphnids in fishless lakes. Our results suggest that the low intensity of selective predation by brook trout on large herbivores and the heavy predation by Chaoborus americanus larvae on daphnids in fishless lakes appear to be the key factors for structuring the zooplankton community. Multivariate indicators identified patterns that were not revealed with the usual univariate indices, showing the importance of selecting appropriate indicators for the assessment of community structure.

Nomenclature: Edmondson, 1959; Pennak, 1978; Bernatchez & Giroux, 2000.

We investigated the stand history of whitebark pine forests on 3 mountains in the Lolo National Forest, Montana, USA to characterize the fire regimes and other disturbance agents that historically operated at these sites and to explore the potential influences of modern fire suppression on these forests. We used hLarsonistorical fire atlas data and dendroecological data to reconstruct the distinct stand. The fire regimes of each site fit within the general definition of mixed-severity fire regimes, but distinct differences in fire frequency anween them. All 3 stands contained at least 1 post-disturbance cohort and had experienced at least 1 widespread fire over their histories. We found no consistent fire—climate relationship at these sites. Mountain pine beetles were the primary mortality agent in the current stands at all 3 sites. Subalpine fir began establishing at each site within 2 decades of the most recent widespread fire and well before fire suppression was effective in this region. Fire suppression may have reduced the occurrence of fire during the late 20^th century at all 3 sites, but only the forest on Point Six has exceeded the mean interval between widespread fires. The differences in fire activity and effects of fire suppression that we observed at these sites are likely the result of different biophysical site characteristics and disturbance legacies and hold important implications for the development of site-specific management strategies for whitebark pine restoration.

Nomenclature: ITIS, 2008.

We assessed the seasonal climatic response of 2 Pinus and 2 Quercus tree species in a littoral island in northwest Spain, analyzing earlywood, latewood, and total ring widths. We used bootstrapped response functions to identify the variables controlling growth, and we estimated the pure and shared effects of local climate components (temperature and water balance) and a large-scale atmospheric pattern (North Atlantic Oscillation, NAO) on tree growth using a variance partitioning approach. For all species, the response functions showed stronger climatic signals in latewood and total ring than in earlywood. The pure effects of temperature, water balance, and NAO on tree growth were significant. However, a null shared effect between local climate and NAO was evidenced due to the absence of a direct link between NAO in the previous autumn and the other significant climatic variables. Pinus pinaster was the species most sensitive to local climate, mainly to water availability during its active period as a consequence of higher water use efficiency. Quercus growth was negatively influenced by winter temperature, and growth of P. pinea and both Quercus species was inversely related to NAO in the previous autumn. The obtained results suggest that Q. robur and Q. pyrenaica have similar growth behaviour and climatic sensitivity. However, both P. pinea and P. pinaster showed contrasting growth dynamics and sensitivity in this Atlantic littoral island, despite their common Mediterranean origin.

Nomenclature : Castroviejo et al., 1986–1989.

Seed dispersal by animals is a key interaction, with effects on the population ecology and evolution of many plant lineages. Despite the fact that infrequent seed dispersers can potentially provide important services to plant populations, little attention has been paid so far to scarce mutualists. We assessed different aspects of quantity and quality of seed dispersal from fruit removal to seed germination in the Iberian pear, Pyrus bourgaeana, finding that fruit consumers markedly differed in the nature of their interaction with the tree. Whereas the abundant rodents, rabbits, and deer damaged all seeds eaten, the uncommon carnivores badger and fox and the abundant boars dispersed a large fraction of ingested seeds as viable propagules, acting as legitimate seed dispersers. Despite low rates of visitation by badgers to fruiting trees, they transported more viable seeds than the abundant boars, due to better seed treatment and a higher feeding rate on pears. Seed dispersal by all 3 legitimate dispersers, especially the badger, enhanced post-dispersal P. bourgaeana seed survival, supporting the “escape” predation hypothesis. Pyrus bourgaeana showed relatively high frequencies of visits by a myriad of frugivores; however, it relied on the dispersal service provided by an infrequent carnivore, the badger, rather than on those provided by the abundant mammalian herbivores. Therefore, under some circumstances, uncommon animal counterparts play major roles in their mutualistic interactions with flowering plants.

Nomenclature: Váldes et al., 2007.

This paper reports on the capability of the long-lived conifer Pilgerodendron uviferum in southwestern South America to record fire scars, making it the southernmost tree-ring fire recording species on Earth. We present detailed descriptions of the fire-scar morphology of this species and compare tree-ring fire-scar dates to independent sources of fire dates. The fire scars found on Pilgerodendron uviferum are morphologically similar to those found on conifers in western North America. All fire scars were crossdated on 80 out of 96 sampled cross-sections collected at 8 dispersed sites. Groups of micro-rings were the most common anatomical feature that impeded crossdating of fire-scar dates. A total of 597 fire-scar tips were successfully crossdated on these 80 cross-sections. The average number of fire scars per cross-section was 7.4, and the full collection of crossdated fire scars spanned from 1570 to 2004 AD. The crossdated fire-scar dates were highly synchronous within stands, and years of abundant scars matched years of widespread fire in documentary fire records from nearby areas. The high terpene content and mechanical properties of the wood of Pilgerodendron uviferum contribute to its resistance to decay and therefore long-term preservation of scars on both live and dead standing trees. The suitability of Pilgerodendron uviferum as a tree-ring fire recording species creates a significant opportunity to extend research on multi-century fire activity in relation to climate variability at mid to high latitudes (i.e., 43–55° s) in southwestern South America.

Nomenclature: Marticorena & Rodriguez, 1995.

Forest harvesting is a major cause of habitat alteration negatively affecting forest-dwelling caribou (Rangifer tarandus caribou) in the boreal forest. In order to identify female caribou habitat requirements, we conducted a fine-scale habitat selection analysis in a managed forest of eastern Canada. Five land-cover types used by 8 female caribou during 2 periods (winter and snow-free) were considered to characterize structural attributes, ground cover, and lichen abundance at 320 GPS locations and at 200 random points within home ranges. Because caribou rely on a limited food supply in winter, we predicted that they would select sites of higher biomass of terrestrial and/or arboreal lichens. Since female caribou (especially those with calves) are more vulnerable to predation during the snow-free period, we predicted that they would select sites where predation would be reduced by a denser hiding cover (i.e., high basal area, shrub height, and/or lateral cover) or by a lower forage availability for alternative prey (i.e., low shrub density). Within each land-cover type, comparisons between used and random sites were conducted using an exploratory PCA analysis followed by conditional logistic regressions. Our results demonstrated that, in winter, female caribou selected sites with higher terrestrial lichen biomass or ericaceous shrub cover in old spruce stands and old cutovers. During the snow-free period, female caribou did not select sites of denser hiding cover. However, well-regenerated shrub layer was avoided during both periods, suggesting that caribou avoided sites containing abundant forage attractive to moose and, consequently, wolf. At a fine scale, forest management should focus on protecting sites or stands with a high biomass of terrestrial lichens. Silvicultural practices that prevent cutovers from regenerating into areas with abundant moose forage should also be favoured.

Nomenclature: Marie-Victorin, 1995; Farrar, 1996; Brodo et al., 2001, Feldhamer et al., 2003.

Patterns of and controls over N₂ fixation by green alder were studied in post-fire, mid-succession, and white spruce upland forests in interior Alaska, focusing on the hypothesis that ecosystem-level nitrogen (N) inputs decrease with successional development. N₂-fixation rates tracked plant phenology during the 1997 (drought) and 1998 (normal precipitation) growing seasons. The best model for predicting acetylene reductase activity (ARA, µmol C₂H₄·g nodule_DWT^-1·h^-1) across all stands and sampling periods included a linear response to soil temperature and a quadratic response to Julian day (r² = 0.23, P < 0.0001). There were few significant relationships between seasonal maximum values for ARA and measured leaf traits; however, we did detect an inverse correlation between foliar N to P ratio and seasonal maximum ARA. During 1998, stands with higher maximum ARA had higher soil %N, and maximum ARA was positively correlated with subcanopy %P in O and A soil horizons. During 1997, leaf %P and N resorption were lower and leaves were thinner compared to 1998. Drought effects were most pronounced in mid-succession, where alder exhibited reduced ARA, leaf %P, leaf thickness, and lower leaf resorption of P and N. Although ARA and nodule biomass did not differ among stand types, increases in alder densities with successional time translated to increasing ecosystem-level N inputs across the chronosequence. These results contradict established theory predicting a decline in N₂-fixation rates and N₂-fixer abundance during successional stand development.

Nomenclature: Viereck & Little, 2007.

Les patrons et les facteurs régissant la fixation du N₂ par l'aulne crispé ont été étudiés dans des peuplements après feu, de milieu de succession et de pessières blanches dans des forêts des hautes terres de l'intérieur l'Alaska, en se concentrant sur l'hypothèse que les niveaux d'apport d'azote (N) dans l'écosystème diminuent au cours de la succession. Les taux de fixation de N₂ suivaient la phénologie des plantes au cours des saisons de croissance de 1997 (sécheresse) et 1998 (précipitations normales). Le meilleur modèle pour prédire l'activité de la réductase de l'acétylène (ARA, µmol C₂H₄·g nodule_{poid sec}^-1·h^-1) parmi tous les peuplements et les périodes d'échantillonnage incluait une réponse linéaire à la température du sol et une réponse quadratique au jour julien (r² = 0,23, P < 0,0001). Il y avait peu de relations significatives entre les valeurs saisonnières maximales de l'ARA et les traits mesurés des feuilles; cependant, nous avons détecté une corrélation inverse entre le ratio foliaire N:P et le maximum saisonnier de l'ARA. En 1998, les peuplements ayant un ARA maximal plus élevé avaient un % N du sol plus grand; l'ARA maximal était corrélé positivement avec le % P des horizons O et A du sol en sous-canopée. En 1997, le % P des feuilles et la résorption foliaire de N étaient inférieurs et les feuilles plus minces qu'en 1998. Les effets de la sécheresse étaient les plus prononcés en milieu de succession là où les aulnes avaient des niveaux plus faibles d'ARA, de % P foliaire, d'épaisseur des feuilles et de résorption foliaire de P et N. Bien que l'ARA et la biomasse des nodules ne variaient pas entre les types de peuplements, l'augmentation de la densité des aulnes au cours de la succession s'est traduit par des apports accrus de N dans l'écosystème le long de la chronoséquence. Ces résultats contredisent la théorie reconnue prédisant un déclin des taux de fixation de N₂ et de l'abondance de fixateurs de N₂ au cours du développement successionnel des peuplements.

The coexistence mechanism of Abies sachalinensis and Picea jezoensis, which usually regenerate on fallen logs, was examined with respect to differences in suitable conditions for germination and shade tolerance in Hokkaido, northern Japan. Germination conditions were evaluated through the effect of log hardness, moss height, light condition, and shading by taller seedlings on fallen logs, and shade tolerance was evaluated by physiological and morphological traits and survival dynamics in a natural coniferous forest. In contrast to P. jezoensis, the number of germinated seedlings of A. sachalinensis increased with moss height. The number of germinated seedlings decreased with shading only in P. jezoensis. Consequently, it is suggested that germination of P. jezoensis is limited to fresh, recently fallen logs. The survival rate of A. sachalinensis under low-light conditions (< 5% of relative photosynthetic photon flux density) was higher than that of P. jezoensis. Abies sachalinensis had a higher leaf mass ratio (total leaf mass/total mass) and leaf area ratio (total leaf area/total mass) than P. jezoensis. In conclusion, earlier establishment of P. jezoensis on fallen logs and higher shade tolerance of A. sachalinensis are suggested to contribute to the coexistence of these 2 species.

Nomenclature: Ohwi & Kitagawa, 1992.

Major forest disturbance such as clearcutting may increase nitrification rates in the forest floor, but the magnitude of this NO₃^- flush varies among different forest ecosystems. Here, we tested the hypothesis that this variation could partly be due to differences in deer-browsing intensity. More specifically, we hypothesized that nitrification rates would decrease as deer browsing increased and that this effect would be higher in clearcuts than in forests. Our experimental design consisted of 3 replicated blocks, each consisting of 3 plots (10–40 ha) in which white-tailed deer densities were kept at 0, 7.5, and 15 individuals.km^-2 for 6 y and a fourth plot in which natural deer densities varied between 27 and 56 deer.km^-2. In the first year, 70% of mature balsam fir (Abies balsamea) forests in each plot were clearcut harvested. Average potential nitrification in forest floor samples was higher in clearcut than in forest plots. In clearcut plots, potential nitrification at the high deer density was about 2.5 times higher than at lower deer densities, thereby contradicting our first hypothesis. In forest plots, potential nitrification was negatively related to indices of soil available C but was unrelated to deer density. The shrub and herb vegetation in clearcut plots was dissimilar to, and more altered by, deer browsing than the understory vegetation in forest plots. In clearcut plots, increasing deer density reduced the percent cover of nitrophilous herbaceous species and increased the percent cover of graminoid plants. Possible mechanisms that could explain the interaction between forest disturbance and deer browsing intensity in controlling the magnitude of the NO₃^- flush are (1) soil N inputs via feces and urine, (2) loss of soil NO₃^- sinks due to the disappearance of nitrophilous plant species, and (3) browser-induced succession towards rangeland plant communities that stimulate rhizodeposition and soil N dynamics.

Nomenclature: Gleason & Cronquist, 1991.

Seedling emergence and establishment was monitored in 3 microhabitats during growing seasons in a Mediterranean coastal sand dune community in Poleg Stream Nature Reserve, Israel. Seedling emergence varied temporally among the 3 microhabitats, with a delay in the timing of seedling emergence in shrub understoreys due to lower soil average temperatures and lower irradiance. In contrast, seedling emergence on trails was advanced because of more intense irradiance and higher soil temperatures on their more exposed soil surfaces. Microhabitats showed significant differences in individual densities, species diversity, and species richness of total seedlings (P < 0.0001). Open areas generally possessed significantly greater total seedling densities, species diversity, and species richness compared to shrub understoreys and trails. Twelve key species and 5 functional groups showed significant microhabitat preferences. Seedling patterns indicated that emergence responses could account for observed patterns of variation in the 5 functional groups and dominant species populations. In this semi-arid ecosystem, negative interactions between the shrub canopy species (white weeping broom) and its understorey occurred for seedling establishment because of lower seed densities in the seed bank, a larger amount of litter on the soil surface, and the dense woody canopy. On the trails, trampling decreased plant diversity and discouraged the establishment of most functional groups and key species except annual grasses and Polycarpon succulentum and Cutandia philistaea. The variability in seedling response patterns for the different microhabitats will assist in understanding the patchy regeneration strategies of this coastal sand dune community and provide a basis for vegetation management.

Nomenclature: Fragman et al., 1999.

Animals subject to environmental stress often exhibit higher levels of developmental instability, frequently measured as Fluctuating Asymmetry (FA), small, random deviations from perfect left-right symmetry in bilaterally symmetrical animals. We used FA measurement as a means of determining the impact of a catastrophic ecosystem disturbance (a major Class F3 tornado) on populations of Schizocosa ocreata, a common forest-dwelling wolf spider. As FA in sexually selected ornamental traits in males has been shown in some (but not all) species studied to be a sensitive indicator of environmental stress, we measured FA of foreleg tufts in male S. ocreata. Spiders from the first post-disturbance generation were collected by pitfall trapping in the spring of 2000, and preserved specimens were photographed and measured using digital imaging. Spiders from disturbed and undisturbed areas within the forest did not differ significantly in body size parameters, although body condition varied significantly between sites. Signed (R-L) FA of male tuft area was normally distributed with a mean of zero, indicating “ideal” or “true” FA, a reflection of Developmental Instability (DI). Although tuft area was not significantly different between sites, tuft area FA in male S. ocreata was significantly higher in the disturbed site, suggesting that ecosystem-level stress may produce higher levels of developmental instability in arthropod populations. Results of our study indicate that FA in this secondary sexual character (male leg tufts) is a more sensitive indicator of putative environmental stress than a non-sexual trait (femur length). To our knowledge, this is the first study of FA in invertebrates associated with environmental stress from a catastrophic natural disturbance.

Nomenclature: Dondale & Redner, 1990.

Eastern North America contains the greatest diversity of freshwater mussels in the world. Additional information on threats and on habitat requirements and distributions of freshwater mussels is necessary to preserve diverse freshwater mussel communities, as many species are in decline. Models of freshwater mussels can predict species distributions by determining natural and anthropogenic environmental factors within the watershed, riparian area, or upstream that may influence occurrences. Subwatershed-based models developed for Elliptio complanata and E. dilatata in the Mid-Atlantic and Ohio drainage regions of the United States using existing survey data performed well on training datasets but did not accurately predict independent species occurrences. Additional studies are necessary to evaluate the quality of existing data, the utility of subwatershed-based models, and the feasibility of modelling freshwater mussel distributions across large extents.

Nomenclature: Turgeon et al., 1998.

Theory suggests that host—parasite interaction should lead to local adaptation of parasites to their host. In mistletoe— host tree interactions the foraging patterns of fruit-eating birds can play an important role in host local adaptation, depending on the tree species on which the mistletoe fruits were consumed (host provenance) and the tree species on which the mistletoe seeds were deposited (host fate). Yet this interaction has not been previously documented. To determine the effects of host provenance, bird gut processing, and host fate on mistletoe seed germination and seedling establishment of Psittacanthus calyculatus, we conducted a seed inoculation experiment in Tlaxcala, Mexico. Mistletoe fruits were collected from Crataegus pubescens (Cp), Prunus serotina (Ps), and Salix bonplandiana (Sb) and measured. We then manually removed the exocarp and pulp of half the fruits, and the other half were given to grey silky-flycatchers (Ptilogonys cinereus) for gut processing. Obtained seeds of both groups of fruits were measured and deposited on branches of other trees of the same 3 host species in a full factorial design. Mistletoe fruit size varied significantly among host tree species, but differences did not coincide with those in gut retention time. Bird gut processing and the host provenance × host fate interaction were the best predictors for the occurrence of germination and establishment of seedlings. Seed germination and seedling establishment were more likely when seeds were gut processed by birds, but gut retention time had no significant effects. The significant host provenance × host fate interaction was largely due to higher success of mistletoe seeds from Sb to Sb and lower success from Sb to Ps. Our results suggest that to understand the efficiency of infection of P. calyculatus and possibly other mistletoe species, the linked effects of the digestive processes undergone by mistletoe seeds and the species of host trees where the seeds were consumed and ultimately deposited should be considered.

Nomenclature: Kuijt, 2009.

During 1998–1999 a severe drought occurred in northwestern Patagonia that provoked an extensive wildfire. We monitored vegetation cover and the soil seed bank to study the diversity and functional group gap dynamics in burned and unburned sites. Species were grouped into 3 functional groups: forbs, fugitive species, and annual grasses. Post-drought vegetation recovered quickly due to a rainy spring in the second year but decreased after a dry and warm spring in the third year. These patterns underline the close relationship that exists between phenological phases and meteorological variables. Drought decreased richness but did not affect the presence of stress-tolerant species, whereas fire increased richness by allowing the establishment of fugitive species. Species in the fugitive functional group may be fire adapted and depend on seed accumulation in the seed bank (storage effect) to coexist with other gap species. Forbs exhibited their highest vegetation cover and seed bank density in the unburned site. Global climate change suggests an increase in the frequency and amplitude of El Niño/Southern Oscillation phenomena that, in northwestern Patagonia, are related to the occurrence of drought, fire, and changes in vegetation dynamics.

Nomenclature: Correa, 1969–1999.

There are often marked differences in the incidence of nest-dwelling ectoparasite species on different coexisting and similar avian host species. This has been shown especially for fleas (Siphonaptera), larvae of flies (Diptera), and mites (Acarina) in nests of tits and flycatchers breeding in nest-boxes in close proximity to each other. One of the possible reasons for these differences is the marked differences in nest composition between avian species. We show here differences in ectoparasite presence and nest composition for blue tits (Cyanistes caeruleus) and pied flycatchers (Ficedula hypoleuca) coexisting in oak forests in central Spain. There also may be intraspecific differences in local preferences for nest-building materials according to availability of plant materials, which could be due to arthropod repellent properties of different potential nest components. We show here a local difference in nest composition between 2 pied flycatcher populations in relation to availability of a preferred material associated with higher ectoparasite presence in the locality without the preferred nest material. We test the hypotheses that differential incidence of ectoparasites at the interspecific and intraspecific levels may depend on nest composition. We conducted a nest exchange experiment in one study locality in 2007 placing in nest-boxes occupied by flycatchers 1) nests constructed by blue tits in 2006 in another locality and removed before use and stored frozen, 2) nests constructed by flycatchers in 2006 in another locality with different nest composition and removed before use and stored frozen, and 3) nests constructed by other flycatcher pairs in the same study locality in 2007. Another group of flycatcher nests was kept as pure control, while a few blue tit nests constructed in 2007 and taken over by flycatchers were used for comparison with nests of treatment 1. No effect on presence of mites and blowflies of either nest-constructing species or locality of construction was observed for pied flycatcher nests, and for fleas only an effect of locality but not of nest constructing species was detected. On the other hand, presence of mites and blowflies differed between nests constructed by blue tits and occupied by either blue tits or pied flycatchers. Nest composition does not explain the differential incidence of nest-dwelling ectoparasites on coexisting avian host species.

Nomenclature: Moss, 1978; Cramp, Perrins & Brooks, 1993.