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).