Theoretical habitat templets, species traits, and species richness: floodplain vegetation in the Upper Rhône River

Abstract

SUMMARY The floodplain vegetation at approximately 100 sites located in nine different habitat types of the Upper Rhône River, France, was surveyed three times over the past 27 years. Information on species traits of the higher plants comprising the Rhône floodplain vegetation was based on studies conducted between Geneva, Switzerland, and Lyon, France. These data were structured using a ‘fuzzy coding’ technique and then examined using ordination analyses to investigate: (i) relationships among species traits; (ii) habitat utilization; (iii) the relationship between species traits and habitat utilization; and (iv) trends of species traits and species richness in the framework of spatial–temporal habitat variability to test predictions of the river habitat templet and the patch dynamics concept. Size, number of descendants per reproductive cycle, number of reproductive cycles per individual, and the regeneration potential of an individual were positively related with each other, whereas the degree of attachment to the soil decreased, and the reproductive period shifted from autumn/late summer towards early summer/spring, as size increased. The habitat utilization by the higher plants of the floodplain revealed a double lateral gradient: the first was from the banks of the temporary waters to terrestrial flats; the second from aggrading pebble to aggrading silt habitats. These gradients were related to gradients in water saturation, oxygen conditions, nutrient loading, and nutrient retention of the soils. A significant relationship between species traits and habitat utilization was observed for the floodplain vegetation, i.e. plant communities used particular habitat types with a particular set of species trait modalities (= categories). Patterns of species trait modalities were significantly related to temporal and spatial habitat variability but only modalities of the trait ‘parental care’ conformed to trends predicted from theory. No trends were observed when species richness of different habitat types was considered in the framework of spatial–temporal habitat variability. Although the habitats of the Upper Rhône clearly act as a templet for the species traits of the floodplain vegetation, the lack of agreement between observations and predictions on trends in species traits and richness in terms of habitat variability suggest that important elements of theory should be rejected. However, human‐induced changes in these habitats are too recent when compared with the longer time periods required for floodplain vegetation to respond to such changes.