Dispersal limitation inferred from an experimental translocation ofLomatium(Apiaceae) species outside their geographic ranges

Abstract

Determining limitations on poleward range expansion is important for predicting how climate change will alter the distribution of species. For most species, it is not known what factors set their distributional limits and the role dispersal limitation might play if range-limiting factors were altered. We conducted a transplant study of three related and cooccurring Lomatium species at their northern range limits to test competing hypotheses of range limitation. We added seeds to experimental plots inside and outside the species' geographic range (a regional treatment) in a replicated design with vegetation intact and vegetation reduced (a disturbance treatment) and with herbivore access and herbivore exclusion (an herbivory treatment). Germination and reemergence were measured through two growing seasons, along with community-level variables. A fully-crossed linear mixed model revealed that Lomatium survivorship outside the current range was as good or better than survivorship within the range, at least when the vegetative community remained intact. This suggests that the species are dispersal limited. Germination often was improved in the presence of an intact vegetative community, but this potentially facilitative effect was absent in second-year reemergence. Plots exposed to herbivory had slightly, but significantly, reduced germination, though reemergence did not differ between herbivore treatments. Lomatium dissectum, a rare species, had significantly lower survivorship than its congeners, suggesting that range shifts in rare taxa may be particularly difficult. Seed additions beyond species' range limits may be a strategy for overcoming dispersal limitation and assisting species in poleward migrations.

Testing appropriate habitat outside of historic range: The case of Amorpha herbacea var. crenulata (Fabaceae)

“…Because the species is long-lived, it may take years before the population can be judged as sustainable, but the preliminary indications are that the populations are doing well. In a comparative outside-of-range northward introduction trial of one rare species, Lomatium dissectum with two co-occurring common congeners, Marsico and Hellmann (2009) found that the species survived well or better outside of range than within range, at least when the vegetative community remained intact. Examples of south Florida endangered species translocations in novel habitat with at least first generation recruits are Jacquemontia reclinata House (Maschinski & Wright 2006) and Lantana canescens (Possley, Maschinski, Rodriguez, & Dozier 2008).…”

“…As this study demonstrates, microhabitats that were not historically known may prove to be optimal for species' survival and growth. Dispersal limitation has been demonstrated to limit species ranges (e.g., Marsico & Hellmann 2009) and can occur at fine scales of a few metres (Primack & Miao 1992;Eriksson 1998). Because the pine rockland/transverse glade ecosystem of A. herbacea var.…”

Phylogeography of postglacial range expansion in Juglans mandshurica (Juglandaceae) reveals no evidence of bottleneck, loss of genetic diversity, or isolation by distance in the leading-edge populations

“…A latitudinal decline in genetic diversity, especially in terms of allelic richness, has been commonly found in high-latitude Northern Hemisphere tree lineages (e.g. Comps et al, 2001;Marsico and Hellmann, 2009;Ohsawa and Ide, 2011). Yet there are exceptions to this general pattern.…”

Experimental assessment of dispersal and habitat limitation in an oligotrophic wet meadow

“…Small gaps created by raking provide more light, nutrients and lower competition from the surrounding vegetation (Morgan 1997), whereas individuals are more exposed to harsh conditions (more desiccation, herbivory; Foster 2001, Kolb et al 2007, Kotorová and Lepš 1999, Morgan 1997. Germination and initial establishment are, therefore, positively affected, while survival is reduced by disturbance (Foster and Gross 1997, Foster et al 2004, Jakobsson and Eriksson 2000, Janeček and Lepš 2005, Křenová and Lepš 1996, Marsico and Hellmann 2009. At the end of the experiment, ca, 1.5 times more surviving individuals were still found in disturbed plots; of those, 16 individuals reached reproductive stage in undisturbed plots against 17 in disturbed ones.…”