Biological characteristics of an invasive south African species

Abstract

Senecio inaequidens, a south African species that has recently invaded parts of Europe, especially human disturbed habitats, was examined under laboratory and glasshouse conditions to assess the germination of achenes, soil seed banks, growth of seedlings and its breeding system. These observations allowed identification of ecological characteristics that may contribute to the invasiveness of the species. Achenes derived from three populations of S. inaequidens were germinated over a wide temperature range (from 14/6°C day/night temperatures to a constant temperature of 30°C). They exhibited a rapid achene germination especially when temperatures reached 20°C. Germination of seeds from soil samples also exhibited a prolonged germination over time suggesting therefore different types of dormancy. Growth response was studied along a nitrogen gradient from 0.33 to 16.0 mmol l À1 and data were interpreted using growth analysis. Seedlings of S. inaequidens exhibited a slow growth in low nutrient availability and a rapid growth rate when exposed to high nutrient availability, which contributed to producing a large leaf area and biomass. Four types of pollination were studied in S. inaequidens. Hand-pollinations showed that S. inaequidens was mostly self-incompatible. Self-pollinated capitula only showed 7.6% viable achenes, significantly lower than insect-pollinated and cross-pollinated capitula. Some individuals were more self-fertile than others ensuring the production of some offspring in a situation of colonisation. Natural pollination occurred with generalist insects. Most of these results confirm the invasive ability of S. inaequidens.

Rapid Plant Invasion in Distinct Climates Involves Different Sources of Phenotypic Variation

“…Sexual reproduction is mainly allogamous and is initiated in late spring (May–June), approximately two months after massive germination, and continues through late autumn (November–December). Ex situ germination tests have indicated that germination is absent at temperatures below 2°C [37]. Entomophilous pollination with generalist pollinators is most common.…”

Clinal differentiation during invasion: Senecio inaequidens (Asteraceae) along altitudinal gradients in Europe

“…inaequidens extends to 1 m tall with numerous stems bearing yellow capitulae. Individuals can produce up to 1,500 capitulae over a flowering period, each capitulum bearing roughly 100 achenes (hereafter referred to as "seeds") (Lopez-Garcia and Maillet 2005). Sexual reproduction initiates in late spring (May-June), approximately 2 months after germination, and continues through late autumn (November-December).…”

“…Sexual reproduction initiates in late spring (May-June), approximately 2 months after germination, and continues through late autumn (November-December). The species is considered self-incompatible, but some individuals were observed exhibiting partial self-fertility in France (Lopez-Garcia and Maillet 2005). Entomophilous pollination with generalist pollinators is most common.…”

Ecological Roles of Railway Verges in Anthropogenic Landscapes: A Synthesis of Five Case Studies in Northern France

“…This perennial herb presents a self-incompatible reproductive system and is pollinated by insects; the effective fruit production is high, with 75% viable achenes, which are well dispersed by wind and animals (Lopez-Garcia and Maillet 2005). This species was introduced in the south of France (Mazamet) in 1936 and then observed in Gare d'Austerlitz (a Parisian railway station) in 1990 (Henry and Maurin 1999).…”