Evolutionary history and intraspecific competition mediate ballistic seed dispersal

Abstract

Dispersal plays an important role in the survival and spread of plant populations. However, when grown under stress, a plants' architecture and fecundity may be modified, which can compromise seed dispersal. While populations within a species exhibit trait variation in response to their environment, a mechanistic understanding of how trade-offs between dispersal ability and competitive ability vary across species' ranges is currently lacking. Using a common garden design, populations of a widespread weedy species (Cardamine hirsuta) were grown to (1) characterize how traits that influence dispersal differ between populations and (2) identify whether a trade-off between dispersal ability and competitive ability varies among populations in response to intraspecific competition. We measured trait differences between populations and characterized dispersal kernels through exhaustively capturing seeds. In the absence of competition, populations exhibited differences in fecundity and height. Of these traits, fecundity varied more strongly between populations and had a stronger influence on dispersal capacity. The experimental data were then used to parameterize cellular automaton models to explore the consequences of these trait-mediated dispersal responses for long-term population dynamics. These simulations identified intraspecific competitive effects on fecundity as the primary driver of variation in spread and patch density among populations. Within-species variation of dispersal traits occurs among populations across the range of C. hirsuta. In response to conspecific competition, populations also have unequal fecundity and long-distance dispersal (LDD). Model simulations suggest predictions of species spread are highly modified by characterization of metapopulation life-history traits such as high fecundity and maintenance of LDD. These mechanisms creating within-species variation would be important to incorporate in population models of species range expansion and stability. Read the free Plain Language Summary for this article on the Journal blog.