3.1 Life history responses to heat
The life history traits survival, fecundity and the resulting population growth rate of both species were strongly affected by temperature. For both species, survival was significantly reduced from control to mild and from mild to high heat (Figure 1A, all p-values available in Table S1). Cross-species survival comparisons revealed significant differences at 20 oC (p<0.001) and 23oC (p=0.08), with B. fernandoi surviving longer than B. calyciflorus s.s (Figure 1A, Table S1). Fecundity analysis with the K-W test revealed that both B. calycifloruss.s. and B. fernandoi had a significant lower fecundity at the highest imposed heat (B. calyciflorus s.s.: 20oC vs. 32 oC, p<0.001; 23 oC vs. 32oC, p=0.001; 26 oC vs. 32oC, p=0.002; B. fernandoi : 20oC vs. 26 oC, p<0.001; 23 oC vs. 26oC, p=0.004, Figure S1A, Table S1). Across the two species, significant differences were observed at 26oC, in which the heat-tolerant B. calycifloruss.s. had higher fecundity than the heat-sensitive B. fernandoi(Bcal26 vs. Bfer26, p<0.001, Figure S1A, Table S2). Generalized linear models revealed that both survival and fecundity were significantly dependent on temperature (GLM: survival, p<0.001; fecundity, p<0.001), species (GLM: survival, p<0.001; fecundity, p=0.006), and their interaction (GLM: survival, p< 0.001; fecundity, p=0.001) (Figure S1B, S1C).
The intrinsic rate of population increase (r ) was above zero for both species, indicating a positive growth rate at all tested temperatures. However, r was always higher for the heat-tolerantB. calyciflorus s.s. than for the heat-sensitive B. fernandoi (Figure 2B). For B. calycifloryus s.s, rincreased with the increase of temperature until its maximum at 26oC. In contrast, r remained constant inB. fernandoi from 20 oC to 23oC, and decreased at 26 oC.