Abstract
The relative contribution of long-distance dispersal and local diffusion in the spread of invasive species has been a subject of much debate. Invasion of the intertidal mudflats by Spartina alterniflora is an ideal example of stratified diffusion, involving both long-distance dispersal of seeds and local diffusion due to clonal growth. In conjunction with experimental data on range radius-versus-time curve, a traveling wave equation-based model is used to investigate the sensitivity of the spread rate of exotic S. alterniflora to parameters of long distance dispersal (c, maximum colonial establishment rate) and local colony diffusion (r, intrinsic growth rate) at two tidal marshes, the Eastern Chongming and the Jiuduansha Islands, at the Yangtze River estuary. Both Eastern Chong ming and Jiuduansha Islands are now national natural reserves in China, which were established in 2005. However, the mudflats and salt marshes in the two reserves are now heavily infested with introduced S. alterniflora, which may threaten the estuarine ecosystems and their biodiversity. S. alterniflora was first found in 1995 on Chongming. For rapid sediment accretion in mudflats in the estuary, S. alterniflora was also intentionally introduced to Jiuduansha in 1997 and Chongming in 2001, which has led to a rapid range expansion in the estuary. Our results show that range expansion of species with stratified diffusion is affected by both long-distance dispersal and local colony diffusion, and that there is a critical c*, below which the spread rate is more influenced by long-distance dispersal than by local diffusion. After applying this model to the invasion of S. alterniflora in the Yangtze River estuary, we derive that c = 1.7 × 10-3, c* = 0.126 and c = 4.8 × 10-3 km-2·yr-1, c* = 0.140 km-2·yr-1 at Chongming and Jiuduansha (Shanghai), respectively. Our results suggest that the range spread of S. alterniflora in the Yangtze River estuary is more influenced by long-distance dispersal than local colony diffusion, and that S. alterniflora generates about 1.7 × 10-3 to 4.8 × 10-3 colonies per square kilometers per year. This study provides important information about dispersal dynamics of S. alterniflora that may be useful for finding optimal control strategies. ·
Highlights
Like other complex biological processes, the expanding process of invasive species is often numerically intractable [1]-[5]
Our results show that range expansion of species with stratified diffusion is affected by both long-distance dispersal and local colony diffusion, and that there is a critical c*, below which the spread rate is more influenced by longdistance dispersal than by local diffusion
Our results suggest that the range spread of S. alterniflora in the Yangtze River estuary is more influenced by longdistance dispersal than local colony diffusion, and that S. alterniflora generates about 1.7 × 10−3 to 4.8 × 10−3 colonies per square kilometers per year
Summary
Like other complex biological processes, the expanding process of invasive species is often numerically intractable [1]-[5]. Models of the spread of animal and plant populations were based on the process of diffusion and predicted a simple linear rate of spread [2] [6] [7]. In a review of 14 invasive plants, seven showed linear spread and seven exponential spread [8]. Invasive species have both a long-distance dispersal (i.e., leads to establishment of offspring far from parents) and a local reproduction (by which colonies increase in local density) [9]. A combination of different dispersal scales is called stratified diffusion [9]. Various types of range expansion (i.e., different range-time curves) depends substantially on how and where short and long-distance dispersers are produced and what distances they move [9]
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