Background/Question/Methods Climate change may alter how organisms disperse; this may in turn affect how species spread across a landscape, making management more challenging or requiring changes in current management practices. Wind dispersed plants have emerged as a useful study system for investigating the effects of climate change on dispersal; while many previous studies in this system have successfully quantified wind dispersal through a variety of different models, they often assume that propagules are released from only a single point on an individual. This simplifying assumption, while useful, has the potential to over- or under-estimate dispersal. Here, we investigate the effects of climate change on dispersal and examine how projected dispersal patterns change when accounting for all sources of seed release on a plant. Using the wind-dispersed invasive thistles Carduus nutans and Carduus acanthoides, we quantify temperature-driven shifts in the entire distribution of flower heights using a passive warming experiment, and then model the effects of these flower height shifts on dispersal using the Wald analytical long distance (WALD) dispersal model. We also use the WALD model to compare dispersal distances considering the entire distribution of flower heights to those under the common practice of using only maximum seed release height.
Results/Conclusions An approximately 0.6 °C increase in ambient temperature increased C. nutans mean and maximum flower heights by 11.88 cm (12.46%) and 12.82 cm (12.12%), respectively; larger mean and maximum flower height increases of 21.30 cm (26.44%) and 31.90 cm (36.84%) were observed in C. acanthoides. Seeds from warmed individuals were more likely to exceed a given dispersal distance than those from unwarmed counterparts; warmed C. nutans and C. acanthoides seeds were on average 1.83 and 2.70 times as likely, respectively, to travel 50 m or more, with this disparity becoming stronger at longer dispersal distances. Long-distance dispersal events were less likely when kernels considered the entire flower height distribution rather than assuming seed release exclusively from the maximum height, as is commonly assumed. Our study demonstrates that a) higher growing temperature increases flower heights and thus the expected frequency of long-distance dispersal events, and b) using maximum seed release heights rather than actual distributions of seed release heights may slightly overestimate likelihood of long-distance dispersal events. The latter has especially important implications in models of population spread, as such models are often sensitive to long-distance dispersal events so that overestimating the frequency of these events may overestimate spread rates.
