Aim Urban macroecology studies can provide important insights into the impacts of climate change and human intervention in ecosystems. Current theory predicts that urban trees are constrained by temperature in very cold climates but not in other climates. Here we predict the climatic niche variables of planted urban tree populations from the realized climatic niche of native populations and explore whether niches are constrained across all temperatures. Location Global (182 cities across six continents). Time period Urban tree data: 1980–2016. Native tree data: 1950–2017. Major taxa studied Two hundred and three tree species. Methods We used urban tree inventory data and Global Biodiversity Information Facility occurrence data to compare the realized climatic niches of native and urban tree populations. Realized climatic niches are calculated by combining bioclimatic data with native tree and urban tree occurrence data. Regression is used to predict the climatic niche of urban tree populations from the climatic niche of native populations. Results The realized climatic niche of native tree populations was a good predictor of the realized climatic niche of urban tree populations, although climatic niches are attenuated in urban populations. Urban tree niches were 38–90% wider than native tree niches, with the mean annual temperature niche breath of urban tree populations 3.3 °C (52%) wider than native tree populations. Main conclusions Urban trees are planted in climates that are outside the realized climatic niche of native populations. Temperature remains a strong filter on urban tree populations across the full temperature range. Temperature increases attributable to the combined effect of the urban heat island and global climate change are likely to have a substantial impact on urban tree populations around the globe. This is particularly true for temperate cities, where cold climate trees are planted near the upper limits of their realized temperature niches.

The flathead catfish Pylodictis olivaris is a large piscivore that is native to the Mississippi and Rio Grande river drainages but that has been widely introduced across the United States. River ecologists and fisheries managers are concerned about introduced flathead catfish populations because of the negative impacts on native fish communities or imperiled species associated with direct predation and indirect competition from this apex predator. We studied the trophic relations of introduced flathead catfish in an Atlantic river to further understand the effects on native fish communities. Crayfish (Astacidea) occurred most frequently in the flathead catfish diet, while sunfish Lepomis spp. comprised the greatest percentage by weight. Neither of two sympatric imperiled fish species (the federally endangered Cape Fear shiner Notropis mekistocholas and the Carolina redhorse Moxostoma sp., a federal species of concern) was found in any diet sample. An ontogenetic shift in diet was evident when flathead catfish reached about 300 mm, and length significantly explained the variation in the percent composition by weight of sunfish and darters Etheostoma and Percina spp. Flathead catfish showed positive prey selectivity for taxa that occupied similar benthic microhabitat, highlighting the importance of opportunistic feeding and prey encounter rates. Flathead catfish displayed a highly variable diel feeding chronology during July, when they had a mean stomach fullness of 0.32%, but then showed a single midday feeding peak during August (mean fullness = 0.52%). The gastric evacuation rate increased between July (0.40/h) and August (0.59/h), as did daily ration, which more than doubled between the 2 months (3.06% versus 7.37%). Our findings increase the understanding of introduced flathead catfish trophic relations and the degree of vulnerability among prey taxa, which resource managers may consider in fisheries management and conservation of native fish populations and imperiled species.

Artificial fish habitats have been widely deployed by fisheries managers to increase the concentration of fish at known locations, often without any validation of how well they meet management goals. This study used an innovative sampling method, sonar imagery, to visually evaluate artificial fish habitat designs and their effectiveness in concentrating fish in two turbid North Carolina Piedmont reservoirs. Habitats encompassed equal volumes, but materials and general designs varied; cube habitats were constructed from PVC pipes, plastic barrels, and corrugated plastic pipes, a commercially available product called Porcupine, or evergreen trees. We found that all habitats held significantly more fish than the control sites that were lacking vertical structure. Among artificial habitats, the cubed, corrugated pipe design concentrated significantly more fish than the other designs, and the biodegradability of habitat provided by bundled evergreen trees was reflected in reduced concentrations of fish over time. Received January 28, 2016; accepted August 10, 2016 Published online November 10, 2016

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