Ecological resistance, seed density and their interactions determine patterns of invasion in a California coastal grassland

Authors: Thomsen, Meredith A.¹; D'Antonio, Carla M.²; Suttle, Kenwyn B.¹; Sousa, Wayne P.¹

Source: Ecology Letters, Volume 9, Number 2, 1 February 2006 , pp. 160-170(11)

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Abstract:

<title type="main">Abstract</title>

Relatively little experimental evidence is available regarding how ecological resistance and propagule density interact in their effects on the establishment of invasive exotic species. We examined the independent and interactive effects of neighbour cover (biotic resistance), winter vs. spring water addition (abiotic resistance) and seed density on the invasion of the European perennial grass Holcus lanatus into a California coastal grassland dominated by exotic annual grasses. We found that decreased competition from resident exotic grasses had no effect. In contrast, increased late-season water availability eroded the abiotic resistance offered by naturally dry conditions, facilitating invasion. Finally, watering treatment and seed density interacted strongly in determining seedling survival: while seedling mortality was close to 100% in ambient and winter water addition plots, survivor numbers increased with seed density in spring-watered plots. Thus, decreased abiotic resistance can amplify the effect of increased propagule density on seedling establishment, thereby increasing the likelihood of invasion.

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1461-0248.2005.00857.x

Affiliations: 1: Department of Integrative Biology, University of California-Berkeley, Berkeley, CA 94720-3140, USA 2: Department of Ecology, Evolution and Marine Biology, University of California-Santa Barbara, Santa Barbara, CA 93106-9610, USA

Publication date: 2006-02-01