Naturalization of plant populations: the role of cultivation and population size and density

Abstract

Field experimentation is required to assess the effects of environmental stochasticity on small immigrant plant populations-a widely understood but largely unexplored aspect of predicting any species' likelihood of naturalization and potential invasion. Cultivation can mitigate this stochasticity, although the outcome for a population under cultivation nevertheless varies enormously from extinction to persistence. Using factorial experiments, we investigated the effects of population size, density, and cultivation (irrigation) on the fate of founder populations for four alien species with different life history characteristics (Echinochloa frumentacea, Fagopyrum esculentum, Helianthus annuus, and Trifolium incarnatum) in eastern Washington, USA. The fate of founder populations was highly variable within and among the 3 years of experimentation and illustrates the often precarious environment encountered by plant immigrants. Larger founder populations produced more seeds (P < 0.001); the role of founder population size, however, differed among years. Irrigation resulted in higher percent survival (P < 0.001) and correspondingly larger net reproductive rate (R(0); P < 0.001). But the minimum level of irrigation for establishment, R(0) > 1, differed among years and species. Sowing density did not affect the likelihood of establishment for any species. Our results underscore the importance of environmental stochasticity in determining the fate of founder populations and the potential of cultivation and large population size in countering the long odds against naturalization. Any implementation of often proposed post-immigration field trials to assess the risk of an alien species becoming naturalized, a requisite step toward invasion, will need to assess different sizes of founder populations and the extent and character of cultivation (intentional or unintentional) that the immigrants might receive.

Testing weed risk assessment paradigms: Intraspecific differences in performance and naturalisation risk outweigh interspecific differences in alienBrassica

“…Seed sowing studies, such as ours, tend to show substantial variation in performance among sites, even at fine spatial scales (e.g. Minton & Mack, ). Furthermore, all three species are naturalised in the study region, yet there were few quadrats with λ > 1 in this study, and this was not due to the climate being especially inclement during the experiment.…”

Native and exotic plants of fragments of sagebrush steppe produced by geomorphic processes versus land use

“…Both the total species pool of exotics and the local species richness of fragments were greater for the AG Islands. The greater prevalence of exotic species on the AG Islands than the kipukas was expected if agriculture is a strong source of propagules supporting establishment and naturalization of exotics (e.g., Lonsdale 1999;Mack 1981Mack , 1988Mack , 2000Mack et al 2000;Minton and Mack 2010;Salo 2005).…”

“…Many studies now implicate transportation corridors as pathways of exotic species introduction that can result in invasion and degradation of adjacent and nearby areas (e.g., Bangert and Huntly 2010;D'Antonio and Vitousek 1992;Gelbard and Harrison 2003;Harrison et al 2002;Larson et al 2001;Sutton et al 2007;Yensen 1981). Mack and others have argued that agriculture has played a particularly significant role in introduction of many exotic, sometimes invasive, species, through both the repeated introduction of species associated with crops (e.g., as contaminants of seed stocks or as common crop weeds) and the tendency of agriculture to support local adaptation and naturalization of species associated with crops through various cultivation practices (e.g., Lonsdale 1999;Mack et al 2000;Minton and Mack 2010;Yensen 1981). The increased occurrence of non-native species that often is associated with humans and their actions may play a stronger role in the contemporary diversity and species composition of the native communities of fragmented habitat than does their insularity.…”

Refinement of weed risk assessments for biofuels using Camelina sativa as a model species

“…2006; Barney & DiTomaso 2008). Additionally, biofuel feedstocks possess a high likelihood of becoming invasive because of sustained propagule pressure associated with large‐scale cultivation (Mack 2000; Buddenhagen, Chimera & Clifford 2009; Davis 2009; Minton & Mack 2010). Unfortunately, identifying potential invaders and estimating the damage that may be incurred if a plant is introduced remains a challenge to invasion biologists.…”

“…(2010). Minton & Mack (2010) have recently contributed methods to assess the effects of cultivation and population size and density, on the persistence of founder populations. To our knowledge, their study is the first attempt at employing field‐based empirical approaches to assess invasion potential.…”