Modeling the interactive effects of competition and landscape patterns on exotic species spread

Although invasion by exotic species is recognized as a major ecological problem, little is known about the interactive effects of competition and landscape patterns. In this paper, neutral landscape model and spatially explicit model are employed to numerically analyze the interactive effects of key demographic traits, competition abilities and landscape patterns on the spread dynamics of exotic species. The results showed that: (1) Competition is critically important for the spread of exotic species, which mediates the effects of landscape structure. The spread of competitively superior exotic species is much easier in large and highly clumped habitat while spread of inferior ones does well in small and scattered landscape patterns. Strong competitors can efficiently exploit the massive clumping resources, and poor competitors tend to escape from competition of native species in disrupted niches; (2) The spread of invasive exotic species is positively related to the seed production and negatively related to the reproduction age. The fitting curve varies with landscape patterns and competition abilities. For strong exotic competitors, spread dynamics mostly grows logarithmically with the seed production, but quadratic polynomial equation can better fit their relationship in some scenarios. For inferior ones, quadratic polynomial fitting appears in all landscape scenes but H = 0.5, h = 0.75; (3) The mean dispersal distance is vital to the spread of exotic species. Comparing to convex increase of superior exotic species, inferior exotic competitor shows a fast concave growth with the increasing mean dispersal distance; (4) It will not be an effective method to control invasion of inferior exotic species by increasing landscape fragmentation. According to our simulation results, habitat conservation needs to be distinctively treated for particular case. For example, the abundance of poor exotic species increases when landscape aggregation, seed production and mean dispersal distance decrease. So different management strategies should be taken according to different targets, landscape scenarios, competition and demography characteristics.