Nestedness is a widely studied pattern in ecology and biogeography. Nestedness has been termed perfect when sites harbouring low-diversity assemblages contain subsets of species in progressively more diverse assemblages. Nestedness has been studied in various regional and environmental contexts, but few studies have rigorously examined environmental factors underlying this pattern. We studied the degree and determinants of nestedness in insect assemblages of headwater streams. We hypothesized that nested habitat characteristics and nested niche structure generate nestedness in these organisms and tested this hypothesis in 8 boreal drainage basins (63–70° N, 23–29° E). Stream insect assemblages were significantly nested in all 8 regions based on the nestedness temperature calculator and in 5 regions based on discrepancy analysis. Nestedness was weak, however, as suggested by high matrix temperature values. Site ranks in the maximally packed nestedness matrix were significantly correlated to stream size in 2 of the regions and to environmental gradients in 5 of the regions. Nestedness was primarily governed by stream size and local environmental gradients. The relationships of nestedness to environmental gradients suggest that, at least in some regions, stream insects show nested niche structure with regard to their responses to environmental gradients. These environmental relationships are highly region-specific, however, suggesting strong context-dependency in nested subset patterns.

Biodiversity (species richness and species diversity) of chydorid Cladocera were examined by weekly sweep net sampling during the ice-free period and through surface sediment assemblages in 9 limnologically different lakes in southern Finland. Species richness in the sweep net samples was low in 2 lakes with recent ecological perturbations and the highest in one oligotrophic lake. Species diversity was the lowest in 2 eutrophicated lakes and generally higher in the oligotrophic lakes. The biodiversity values in sediment assemblages showed trends similar to those in the sweep net samples; the lowest values were observed in one of the eutrophic lakes and the highest in the oligotrophic lakes. It is likely that the observed differences were due to the impact of nutrients on the development of littoral vegetation and consequently chydorid habitats and resources. The role of nutrients as a forcing mechanism on chydorid biodiversity was indicated by high and significant negative correlations between species diversity in both total phosphorus and sweep net and sediment samples. The comparison between biodiversity in the 2 sample types showed that the biodiversity values were almost consistently higher in the surface sediment assemblages than in the sweep net samples, suggesting that surface sediment analysis provides an effective alternative method to living material examination for biodiversity evaluations.

Land-use history can have large effects on the different life stages and demography of forest plant species. Here we studied how the legacies of former land use in post-agricultural forests, and increased phosphorus (P) availability in particular, may alter the germinability and seed quantity in populations of the forest herbs Primula elatior and Geum urbanum. We collected seeds in experimental populations of P. elatior and G. urbanum established in post-agricultural and ancient forest stands 10 y ago and determined the number of seeds per fruit and germination percentage. The effect of P availability on the production of germinable seeds was tested in a pot experiment with 3 P levels. Former land use had an impact on the mean germination percentage: seed germinability tended to be higher in post-agricultural compared to ancient forest sites. For G. urbanum, the number of seeds per fruit was also higher in post-agricultural forest. Whereas P availability had no effect on G. urbanum seed quantity and germinability, the germination percentage of P. elatior seeds increased significantly with P supply. Whereas previous studies showed that former agricultural land use can have detrimental effects on particular life stages of forest herbs (e.g., reduced juvenile or adult survival), the production of germinable seeds might rather benefit from it. The environmental legacies of former land use thus affect the various life stages of a plant differently, which results in complex effects of land-use history on the demography of forest plants.

An apparently disjunct population of tricolored bats (Perimyotis subflavus) exists in southwest Nova Scotia. During the summers of 2003–2004 and 2007–2008 we trapped bats in mist nets set at a bridge over the Mersey River in Kejimkujik National Park. In total we captured 42 tricolored bats (41 female and 1 male) and fitted 32 females and the single male with radio transmitters and tracked them to their roost sites daily. Characteristics of roost sites were compared to those of randomly selected, potentially available roost sites using an a priori—selected candidate set of models and ranked using AIC_C for model selection. In total we found 99 unique roost trees in 9 spatially distinct (8 female, 1 male) roosting areas. On average, bats spent 2.5 d in a roost tree. While conspecifics from other parts of the species' range typically roost in tree foliage, maternity colonies of tricolored bats in Nova Scotia roosted exclusively in Usnea trichodea lichen, typically in conifers (of which 91% were spruce; Picea spp.) that were on average 212 m from water. Only 4% of the 300 random trees from the landscape contained Usnea trichodea. These trees were a mixture of softwood and hardwood (58% and 42%, respectively) and were, on average, 550 m from water. These findings represent an apparently unique relationship between lichens and bats that likely impacts many aspects of the species biology, including distribution, social structure, and parasite prevalence.

To investigate the indirect effects of browsing by sika deer on a gall midge (Procystiphora uedai) on dwarf bamboo, we tested the hypothesis that by changing the quality of plant modules, deer browsing indirectly affects multiple life history traits of P. uedai both before and after colonization. A previous study in the same system reported that following gall induction, larval survival was lower in galls on previously browsed shoots, due to higher levels of parasitism. We elucidated the indirect effects of deer browsing by examining the oviposition preference, neonate survival, and potential fecundity (i.e., weight of survivors) of P. uedai on browsed versus non-browsed dwarf bamboos using exclosures. Browsing caused opposite indirect effects on different parameters. Ovipositing females preferred large, non-browsed more than small, browsed dwarf bamboo shoots. Browsing increased neonate survival, presumably by producing relatively soft, small dwarf bamboo shoots. However, deer browsing decreased the weight of survivors, due presumably to the relatively smaller galls that produced smaller shoots. Thus, the present study suggests that deer browsing has lower impact on the total survival rate of larvae than the previous study as a result of increased neonate survival, which will offset the lower survival rate of successfully colonized larvae on browsed dwarf bamboo. Therefore, our study illustrates that the indirect effects of mammal browsing on insect herbivores are not as simple as previously reported. Our study emphasizes the need for evaluating both the colonization process and post-gall-induction survival and fecundity if we are to fully understand the indirect effects of mammal browsing on insect herbivores.

Basking is a common thermoregulatory behaviour in many ectotherms, including reptiles. Because the key physiological processes affecting net energy retention (NER) are temperature dependent, ectotherms have the potential to modulate their energy budget by using basking behaviour. Many aquatic chelonians bask extensively. The energetic significance of basking is, however, largely unknown. We used biologging to measure the body temperature of free-ranging juvenile northern map turtles in Ontario, Canada. We measured the contribution of basking behaviour to the ability of turtles to reach their optimal body temperature for NER. We also used the predicted standard metabolic rate as a proxy to estimate the effects of basking on NER. Our results show that basking is essential for turtles to reach the optimal temperature for NER and suggest that basking behaviour allows turtles to increase their metabolic rate by 17.2 to 30.1%, which should translate into an even greater increase in NER. In addition, our results show that basking behaviour allows turtles to buffer the effects of climatic variations on their T_b and thus potentially on their energy budget. Collectively, our results suggest that basking behaviour has important ramifications for the energy budget, and by extension the fitness, of temperate-zone turtles.

Recent experiments suggest that introduced, non-migratory Canada geese (Branta canadensis) may be facilitating the spread of exotic grasses and decline of native plant species abundance on small islets in the Georgia Basin, British Columbia, which otherwise harbour outstanding examples of threatened maritime meadow ecosystems. We examined this idea by testing if the presence of geese predicted the abundance of exotic grasses and native competitors at 2 spatial scales on 39 islands distributed throughout the Southern Gulf and San Juan Islands of Canada and the United States, respectively. At the plot level, we found significant positive relationships between the percent cover of goose feces and exotic annual grasses. However, this trend was absent at the scale of whole islands. Because rapid population expansion of introduced geese in the region only began in the 1980s, our results are consistent with the hypothesis that the deleterious effects of geese on the cover of exotic annual grasses have yet to proceed beyond the local scale, and that a window of opportunity now exists in which to implement management strategies to curtail this emerging threat to native ecosystems. Research is now needed to test if the removal of geese results in the decline of exotic annual grasses.

We explored the multiple-spatial-scale diversity patterns of canopy and understorey north-temperate mature tree trunk spiders following a hierarchically nested design. We investigated local dynamics and dispersal limitations of canopy and understorey spider assemblages by using a combination of additive partitioning of richness and changes in species composition through spatially nested multivariate ANOVA. Community composition differed significantly between canopy and understorey assemblages and also at stand and site spatial scales, while beta richness was higher than expected from random at the site spatial scale only. Alpha richness did not differ from random at any spatial scale considered in the regional context of our study (tree, stand, and site) and was similar in the canopy and the understorey when rarefied. There was a shift in the contribution of alpha and beta richness as the spatial resolution increased because beta diversity contributed more to tree spider richness and alpha diversity to our site-level spider richness. Our study demonstrates that diversity patterns of mature tree trunk spiders in north-temperate hardwood forests are scale dependent in vertical and horizontal space: at our tree and stand spatial scales, local dynamics such as niche availability and species interactions may drive bark spider assemblage diversity since mean richness did not change significantly whereas species composition did.

Although temperature is recognized as an important barrier to reptile distribution, the mechanisms of this limitation are poorly understood. We investigated the association between temperature, habitat selection, and thermoregulation in a population of massasauga rattlesnakes (Sistrurus catenatus) near their northern range limit, where low temperatures are likely an important constraint. Movement data indicated that the lower limit of the massasauga's performance range (i.e., ≥ 50% of optimal) was 19.9 °C. Operative environmental temperatures were almost always below the massasauga's preferred range (30.0–33.6 °C) and frequently below its performance range in spring and fall. Massasaugas differed from other northern snakes by thermoregulating primarily by microhabitat selection and not by macrohabitat selection. Massasaugas thermoregulated more effectively as their visibility increased and forest cover decreased. Gravid females increased thermoregulatory behaviour in response to low temperatures in spring and summer. Male and nongravid female massasaugas did not take full advantage of thermoregulatory opportunities in the spring and fall, and as a consequence were often too cool to perform essential functions such as prey capture. Our results are consistent with the hypothesis that temperature limits massasauga distribution primarily via effects on gestation and hence juvenile recruitment.

Most experiments on effects of anti-predator behaviours use small enclosures and study behaviour and development of prey in the constant and immediate presence of predators. While useful, such studies are difficult to relate to natural situations where prey and predators are unrestricted. We describe a system designed specifically to estimate the impact of fish on foraging of larval Chironomus tentans under field levels of encounters with fish. The system involves raceways designed to control movement of fish over patches of chironomids so the impact of realistic, short-term encounters between predators and prey could be measured. Fish passes significantly reduced foraging activity, but the reduction was small (median of 1.16 min·fish event^-1·larvae^-1, or 6.5% of the time normally spent active) and did not depend on larval hunger nor fish size or species. Other laboratory experiments using large wading pools indicated 15 cm was the best estimate of the distance over which larvae respond to fish. We estimated foraging time lost in the field as frequency of encounter with fish (estimated from video recordings of fish traffic in 2 lakes) multiplied by time lost per encounter (estimated from laboratory studies). The most realistic estimates suggest larvae in the lakes would reduce their foraging time by 4–16% as a result of interactions with fish. Results suggest traditional techniques might overestimate the effects of predators on behaviour of prey.