4. Offspring survival
In 1980-2000, viviparous species can produce surviving offspring (survived from embryonic development) at much larger range of latitudes and elevations than can oviparous species (Fig. 6a, c), with a higher offspring survival (during both embryonic development and post-hatching/after-birth growth) at lower latitudes and elevations. The offspring survival of oviparous species is also higher at lower latitudes and elevations. After climate warming, the offspring survival increases in both oviparous (by 135.7% in average) and viviparous (by 74.1% in average) species in regions where they can produce viable offspring in 1980-2000 (Fig. 6b, d). However, in oviparous species, the increments at mid-latitudes (>33 oN) are less than those at low latitudes (there are no surviving of oviparous offspring at high latitudes).
In response to climate warming, oviparous females at warm sites can produce additional clutches (relative to the past) over the year because they will start earlier in the year (around April). However, oviparous females at cold sites (where air temperatures are low) can produce additional clutches (relative to the past) over the year because they will keep producing new clutches late in the year (around July) (Fig. 6e, f). Additional clutches early in the year contribute to offspring survival more than do those late in the year, because early clutches have longer time for growth before hibernation. Similarly, these patterns hold for viviparous species (Fig. 6g, h).