Aim We examined the relative influence of geographical location, habitat structure (physiognomy), and dominant plant species composition (floristics) on avian habitat relationships over a large spatial extent. Although it has been predicted that avian distributions are more likely to covary with physiognomy than with floristics at coarse scales, we sought to determine, more specifically, whether there remained a significant association between gradients in assemblages of bird species and dominant plant species within a general biome type, after statistically controlling for structural variation and geographical location of sampling sites.Location Our sample consisted of a subset of North American Breeding Bird Census survey sites that covered most of the range of eastern forests, from Florida to Nova Scotia, and west to Minnesota and North Dakota (up to c. 2500 km between sites).Methods We restricted our analyses to the single year (1981) that provided the largest sample of sites (47) for which vegetation data were available within ± 2 years of the avian surveys. We examined the relationship between avian community composition and tree species composition over this series of forested plots. Data were divided into four sets: (1) bird species abundances, (2) tree species abundances, (3) physiognomic or structural variables and (4) geographical location (latitude and longitude). We performed separate detrended correspondence analysis ordinations of birds and trees, before and after statistically partialling out covariation associated with structural variables and geographical location. To gauge the relationship between the two sets of species we correlated site scores resulting from separate ordinations. We also compared continental-scale patterns of variation in bird and tree assemblages to understand possible mechanisms controlling species distribution at that scale.Results Both bird and tree communities yielded strong gradients, with first-axis eigenvalues from 0.75 to 0.97. All gradients were relatively long (> 4.0), implying complete turnover in species composition. However, geographical location accounted for < 10% of the total variation associated with any ordination. Prior to partialling out covariation resulting from location and physiognomy, bird species ordinations were strongly correlated with tree species ordinations. The strength of association was reduced after partialling, but one bird and one tree axis remained significantly correlated. There was a significant species-area effect for birds, but not for trees.Main conclusions There was a significant relationship between bird species assemblages and tree species assemblages in the eastern forests of North America. Even after partialling out covariation associated with spatial location and forest physiognomy, there remained a significant correlation between major axes from
Microhabitat usage by different species of fish was studied to examine the potential for niche partitioning in riffle areas of a mountain river characterised by frequent natural disturbances. We randomly sampled 96 riffle-area plots (mostly 1 m · 1 m) in a stream in south-western Taiwan for fish abundance and microhabitat characteristics during the dry season from November 2008 to March 2009. Density and electivity values associated with microhabitat usage indicate the presence of niche partitioning among four major species of fish based largely on flow velocity and water depth. Hemimyzon formosanum, a herbivore, prefers higher velocity and shallower water but avoids sandy substrate. Onychostoma alticorpus, a herbivore, prefers lower velocity and deeper water. Rhinogobius nantaiensis, an omnivore, prefers higher velocity, shallower water and gravel-sized substrate but avoids boulder substrate. Acrossocheilus paradoxus, an omnivore, prefers lower velocity and deeper water but avoids pebble-sized substrate. The existence of differentiation of microhabitat preference and overlap of microhabitat usage suggests that interspecific competition is a factor affecting the structure of this fish assemblage, which may remain at early successional stages because of frequent disturbances in the stream. Study results also show that density and electivity detect preference differently. Density detects microhabitat preference for two herbivores while electivity detects microhabitat preference for two omnivores.
These findings demonstrate that directly applying western cognitive norms to a Mandarin-speaking population can cause biased interpretations. The results of this study can be an important reference for clinical settings and research related to cognitive assessments in Mandarin-speaking Chinese populations.
Our study indicates that totally implantable port systems yield a higher risk of complications in terminally ill patients. Further investigation should be carefully conducted to compare outcomes of various central venous access devices in patients with advanced cancer and to develop preventive strategies against catheter failure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.