Parameters of life-history and size were measured for 120
randomly selected plants (60 originating from each population).
Date of senescence was recorded to assess phenology. Capitula
number was counted on the date of senescence to estimate fitness.
The number of leaves (>2 cm length) and the diameter of the
rosette, measured in two perpendicular measurements to the
nearest 0.5 cm, were recorded on the day the first capitula opened.
Then, the most recent, fully expanded leaf was collected and a
digital photograph was taken, including a ruler for scale. Leaf area
was determined using ImageJ v. 1.6 (Schneider et al., 2012). These
leaves were dried in an oven at 60 C for 72 h. Dry weights were
measured and specific leaf area (SLA) was calculated as the ratio of
leaf area to leaf mass. Dried leaves were ground and used for analyses
of d13C and leaf nitrogen content (see section on “Physio