Habitat use of introduced pumpkinseed Lepomis gibbosus in small European streams has received little study despite the species’ potential associations to native fauna of conservation and angling amenity, e.g. brook lamprey Lampetra planeri, European bullhead Cottus gobio, brown trout Salmo trutta. We examined body size, relative body condition, habitat use and species-species associations of pumpkinseed with accompanying fishes in two small streams in southern England during August 2001. Pumpkinseed body condition decreased with pumpkinseed density; the latter correlated with % clay and % riparian grasses in fish 92 mm FL. Most pumpkinseed size classes occurred more often than expected in stretches with conspecifics and with brown trout >300 mm FL; densities of the latter did not correlate with any habitat variables. Indeed, correlations between trout densities and habitat variables were observed mainly in smaller size classes. Habitat associations in other species corresponded to known levels of rheophily; substratum, channel slope, channel width and riparian trees were also important habitat variables. Pumpkinseed dispersal and establishment under conditions of climatic change, which could have ecological and management ramifications, are discussed.
The global-scale natural experiment created by the widespread dissemination of most of the 111 species of pines (genus Pinus, family Pinaceae) has shed light on many aspects of plant invasion ecology. Introductions and the fate of alien pines have been well documented worldwide, facilitating the accurate labelling of species as “naturalized”, “invasive”, or “non-invasive” using objective criteria. Thirty species are naturalized and 21 are invasive. Three life-history traits that clearly separate invasive from non-invasive taxa define the inherent ability of species to disperse over long distances, win in competition against other plants, and to survive or proliferate under a range of disturbance regimes. The realization of colonization opportunities for potentially invasive pines is determined by extrinsic factors, especially those that mediate seedling establishment. Meta-analysis of many introduction/invasion events revealed the interplay of factors. Detailed studies of pine invasions have elucidated the roles of long-distance seed dispersal and propagule pressure in driving invasions. Enhanced understanding of the ecology of pine invasions has improved our ability to manage these invasions. No other speciose genus of plants has yielded important insights on so many facets of invasion ecology.