title: Average niche breadths of species in lake macrophyte communities respond to ecological gradients variably in four regions on two continents.
abstract: Different species' niche breadths in relation to ecological gradients are infrequently examined within the same study and, moreover, species niche breadths have rarely been averaged to account for variation in entire ecological communities. We investigated how average environmental niche breadths (climate, water quality and climate-water quality niches) in aquatic macrophyte communities are related to ecological gradients (latitude, longitude, altitude, species richness and lake area) among four distinct regions (Finland, Sweden and US states of Minnesota and Wisconsin) on two continents. We found that correlations between the three different measures of average niche breadths and ecological gradients varied considerably among the study regions, with average climate and average water quality niche breadth models often showing opposite trends. However, consistent patterns were also found, such as widening of average climate niche breadths and narrowing of average water quality niche breadths of aquatic macrophytes along increasing latitudinal and altitudinal gradients. This result suggests that macrophyte species are generalists in relation to temperature variations at higher latitudes and altitudes, whereas species in southern, lowland lakes are more specialised. In contrast, aquatic macrophytes growing in more southern nutrient-rich lakes were generalists in relation to water quality, while specialist species are adapted to low-productivity conditions and are found in highland lakes. Our results emphasise that species niche breadths should not be studied using only coarse-scale data of species distributions and corresponding environmental conditions, but that investigations on different kinds of niche breadths (e.g., climate vs. local niches) also require finer resolution data at broad spatial extents.
authors.affiliation: Geography Research Unit, University of Oulu, P.O. Box 3000, 90014, Oulu, Finland. janne.alahuhta@oulu.fi.|Freshwater Centre, Finnish Environment Institute, P.O. Box 413, 90014, Oulu, Finland. janne.alahuhta@oulu.fi.
authors.forename: Janne
authors.initials: J
authors.lastname: Alahuhta
authors.affiliation: Geography Research Unit, University of Oulu, P.O. Box 3000, 90014, Oulu, Finland.
authors.forename: Antti
authors.initials: A
authors.lastname: Virtala
authors.affiliation: Geography Research Unit, University of Oulu, P.O. Box 3000, 90014, Oulu, Finland.
authors.forename: Jan
authors.initials: J
authors.lastname: Hjort
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences (SLU), P.O. Box 7050, 750 07, Uppsala, Sweden.|Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences (SLU), 901 83, Umeå, Sweden.
authors.forename: Frauke
authors.initials: F
authors.lastname: Ecke
authors.affiliation: Natural Resources Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Duluth, MN, 55811, USA.
authors.forename: Lucinda B
authors.initials: LB
authors.lastname: Johnson
authors.affiliation: Illinois Natural History Survey, Prairie Research Institute, University of Illinois, 1816 South Oak Street, Champaign, IL, 61820, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: Sass
authors.affiliation: Natural Environment Centre, Biodiversity, Finnish Environment Institute, Paavo Havaksen Tie 3, 90570, Oulu, Finland.
authors.forename: Jani
authors.initials: J
authors.lastname: Heino
mesh_terms: D000531:Altitude; D002980:Climate; D004463:Ecology; D060106:Lakes; D013696:Temperature
keywords: Aquatic plants; Climate; Lakes; Latitude; Niche width; Water quality