Competitive effect versus competitive response of invasive and native wetland plant species

Abstract

Non-native plants can have adverse effects on ecosystem structure and processes by invading and out-competing native plants. I examined the hypothesis that mature plants of non-native and native species exert differential effects on the growth of conspecific and heterospecific seedlings by testing predictions that (1) invasive vegetation has a stronger suppressive effect on seedlings than does native vegetation, (2) seedlings of invasive species are better able to grow in established vegetation than are native seedlings, and (3) invasive species facilitate conspecific and inhibit heterospecific seedling growth. I measured growth rates and interaction intensities for seedlings of four species that were transplanted into five wetland monoculture types: invasive Lythrum salicaria; native L. alatum, Typha angustifolia, T. latifolia; unvegetated control. Invasive L. salicaria had the strongest suppressive effect on actual and per-individual bases, but not on a per-gram basis. Seedlings of T. latifolia were better able to grow in established vegetation than were those of L. salicaria and T. angustifolia. These results suggest that L. salicaria is not a good invader of established vegetation, but once established, it is fairly resistant to invasion. Thus, it is likely that disturbance of established vegetation facilitates invasion by L. salicaria, allowing it to compete with other species in even-aged stands where its high growth rate and consequent production of aboveground biomass confer a competitive advantage.

Inducible defences as key adaptations for the successful invasion ofDaphnia lumholtziin North America?

“…Superior competing native species will probably prevent the establishment of the alien species, whereas competitive superiority by the invader is more likely to favour its establishment in the novel community (Orians 1986). Previous studies found that high competitive ability permitted the invasions of introduced plant and animal species (Byers 2000;Hager 2004;Vilà & Weiner 2004). For example, Baker & Levinton (2003) reported that the invasive zebra mussel Dreissena polymorpha has a higher filtration efficiency than the native North American mussels and attributed the observed decline of native species to this competitive difference.…”

“…Several studies evaluated competitive effects between introduced and native plant species (e.g. Hager 2004; for a review, see Vilà & Weiner 2004), as well as between alien and indigenous animal species (e.g. Byers 2000;Baker & Levinton 2003).…”

Disturbance governs dominance of an invasive forb in a temporary wetland

“…Disturbance can facilitate invasion by reducing competition and changing resource conditions in favor of one species over another (Burke and Grime 1996;Domènech and Vilà 2008;Hager 2004;Hobbs and Huenneke 1992). For disturbance-dependent ecosystems, the 'disturbance' is often the elimination, or alteration, of historical disturbance regimes that causes shifts in composition, structure and function, and can facilitate invader dominance (MacDougall and Turkington 2007;Sher et al 2000).…”

Biomass explains the intensity of facilitative – not competitive – interactions: three intraspecific tests with annuals

“…The positive effect weakened and turned neutral during the last three weeks of life of B. didyma. This could be considered an indication of a threshold neighbour biomass constraining size-dependent positive interactions, and is intriguing because such a threshold has been proposed previously (Hager, 2004;Navas and Moreau-Richard, 2005) in studies that focused on competition, not facilitation. However, in our study, age-dependent interactions in B. didyma became neutral during the period of seed set and thus the change could be related to the physiological changes brought on by reproduction, when resources are invested in reproductive organs at the expense of vegetative growth, as is typical in annuals (Bazzaz et al, 1987) compared to a simple threshold biomass.…”

“…early life-history stages) but weakens as allocation strategies gain importance with increasing yield and/or age. Other studies (Bonser and Reader, 1995;Hager, 2004;Navas and Moreau-Richard, 2005) suggest that biomass effects on competitive interactions become insignificant after the neighbour biomass reaches a certain threshold (at later life-history stages). Such a threshold yield could partly explain the inconsistent detection of sizedependent interactions in previous studies (i.e.…”