Dispersal, dormancy and life‐history tradeoffs at the individual, population and species levels in southern African Asteraceae

Abstract

SummaryDispersal and dormancy are important risk-reducing strategies in unpredictable environments. Negative covariation between these strategies is theoretically expected, but empirical evidence is limited and inconsistent. Moreover, covariation may be affected by other lifehistory traits and may vary across levels of biological organization.We assessed dispersal (vertical fall time of fruits, a proxy for wind dispersal ability) and dormancy (germination fractions measured during germination trials) in populations of 15 annual and 12 perennial wind-dispersed species in six Asteraceae genera from South Africa.Dormancy was higher in annuals than in perennials, whereas fall time was largely determined by evolutionary history. Controlling for phylogeny, dispersal and dormancy was negatively associated across species and life-history categories. Negative covariation between dispersal and dormancy was not evident at either the individual level (except for seed heteromorphic species) or the population level.Our study provides rare empirical support for the theoretical expectation of tradeoffs between dormancy and the alternative risk-reducing strategies, perenniality and dispersal, but refutes the expectation of increased dispersability in perennials. Although negative covariation between dispersal and dormancy at the species level appears not to be a simple consequence of upscaling individual-level mechanistic tradeoffs, our findings suggest that selection for one strategy may constrain evolution of the other.

A research agenda for seed‐trait functional ecology

“…First, we need to deepen our understanding of the interaction between seed persistence in soil and dispersal within communities. The hypothetical trade-off between dispersal and local persistence (Venable & Brown, 1988;Ehrl en & van Groenendal, 1998) does not always show up in data from natural communities (Waal et al, 2015;Metzner et al, 2017), yet it has important consequences for whether community composition changes via migration or seed bank dynamics. Second, although we have a detailed understanding of dormancy breaking and germination cueing (Batlla & Benech-Arnold, 2010;, we struggle to predict germination dynamics in communities (Larson & Funk, 2016).…”

Variation in morphological traits affects dispersal and seedling emergence in dispersive diaspores of Geropogon hybridus

“…The correlation between diaspore terminal velocity, as a proxy for dispersal capability, and seedling emergence can also be, with some restrictive assumptions, viewed in light of an expected trade‐off between two risk‐reducing mechanisms: dispersal and dormancy (Venable and Brown, ; Rees, ). Relying implicitly or explicitly on the assumption that long‐term dormancy is either low or independent of short‐term seedling emergence, many previous studies have used fraction of seedling emergence as a continuous measure of seed dormancy that further represents an important axis of temporal dispersal (Rees, ; De Waal et al., ). Using similar variables to those that we used (diaspore terminal velocity and germination fraction), De Waal et al.…”

“…Beyond seed mass, however, little is known about how diaspore traits affect performance at early life stages. Although a trade‐off between dispersal and dormancy has been widely proposed, interspecific and intraspecific findings are not consistent in this aspect (De Waal et al., ). Relatively little is known about how intraspecific variation in diaspore traits other than dispersal rate and seed mass can be used to predict plant establishment at early life stages, such as seedling emergence (Skarpaas et al., ).…”

“…Last, we used univariate and multivariate analyses to test the effects of diaspore morphological traits on dispersal potential (approximated by diaspore terminal velocity, V t −1 ) and on seedling emergence. We focused the analyses on dispersive diaspores and predicted that (1) dispersal potential will be more tightly associated with traits that shape diaspore geometry, and will be less tightly associated with diaspore mass or within‐diaspore mass allocation (to achene and pappus), as the latter are also associated with diaspore functions other than dispersal; (2) seedling emergence will be positively affected by seed mass; and (3) seedling emergence will be positively associated with dispersal capabilities, mirroring the pattern observed in an interspecific case where a trade‐off between dispersal and dormancy is hypothesized (De Waal et al., ).…”

Roles of the Environment in Plant Life-History Trade-offs

“…Dormancy is significantly higher in annuals than in perennials (note that perenniality is an alternative risk-reducing strategy; [68]) and dormant seed banks are thus better associated with annuals than perennials [13,25,69]. Dormancy is an important adaptive trait that links plant life-history to seasonal change.…”